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Geological Society of Australia

ABSTRACTS Number 55

13th Victorian Universities Earth Sciences Conference The University of Melbourne September 1999

THE UNIVERSITY OF MELBOURNE

THE COMMITTEE FOR THIS YEARS 13™ VICTORIAN UNIVERSITIES EARTH SCIENCES CONFERENCE WOULD LIKE TO THANK THE FOLLOWING SPONSORS

CSIRO Atmospheric Research

Geological Society of Australia Geological Survey of Victoria La Trobe University School of Earth Sciences Monash University School of Earth Sciences North Limited

School of Graduate Studies, Academic Activity Grants The University of Melbourne School of Earth Sciences

ISSN 0729-1IX © Geological Society of Australia Incorporated 1999 Copies of this publication may be obtained from the Geological Society of Australia Incorporated, 706 Thakral House, 301 George St, Sydney, NSW, Australia, 2000. Example citation for papers in this volume: Ahearne, D., 1999. Chemical hydrogeology of the mineral waters of the Central Highlands, Victoria. Geological Society of Australia, Abstracts No. 55, pp 42.

VICTORIAN UNIVERSITIES EARTH SCIENCES CONFERENCE

The University of Melbourne September 1999

THE UNIVERSITY OF MELBOURNE

Geological Society of Australia Abstract Volume Number 55

INDEX: 1. TECTONICS AND PETROLEUM GEOLOGY

2. SEDIMENTOLOGY AND PALAEONTOLOGY

3. ATMOSPHERIC AND OCEANIC SCIENCES

4. ENVIRONMENTAL SCIENCES

5. ECONOMIC GEOLOGY AND GEOCHEMISTRY

6. IGNEOUS GEOLOGY AND VOLCANOLOGY

Organising Committee: Chris Reed, Maurizio Tonelli & Sarah Tweed

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

1. TECTONICS AND PETROLEUM GEOLOGY Talks: pp 2-4 Posters: pp 5-16

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 IT Victotmian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

THE MIO-PLIOCENE BOUNDARY IN THE OTWAY BASIN, SE AUSTRALIA: EUSTATIC OR TECTONIC EVENT? Julie Dickinson School of Earth Sciences, The University of Melbourne, Parkville, Vic.

The boundary between Miocene and Pliocene aged sediments in the Otway Basin is characterised by three features: 1) a large time gap in the stratigraphic record, 2) a change f r o m carbonate dominated sedimentation in the Miocene to mixed clastic/carbonate during the Pliocene, and 3) the occurrence of phosphate nodules on or close to the boundary. The Otway Basin is comprised of a number of depositional embayments separated by structural highs, which has resulted in different outcrop stratigraphy of the MioPliocene boundary across the basin. To the west, in the Gambier Embayment the Werrikoo Limestone, a late Pliocene unit of calcarenite and sandstone, overlies early Miocene carbonate of the Glenelg Group. In the region of Portland, it is the early Pliocene Whalers Bluff Formation which overlies late Miocene Port Campbell Limestone. Around Geelong, early Miocene sedimentation is represented by the Fyansford Clay, which is overlain by the Moorabool Viaduct Formation of mid Pliocene age. Foraminiferal paleoecology of outcrop samples shows a change from outer shelf (100-150m) deposition in the Miocene to inner shelf (<30m) in the Pliocene. The correlation of outcrop sections across the Otway Basin constrains the timing of the unconformity to the late Miocene (6-5 my) as a result of significant regression. Although global sea level curves indicate regression at this time due to glacio-eustatic changes, in this region there is also strong evidence for a tectonic control. Interpretation of seismic lines offshore and the construction of cross sections onshore show an angular unconformity at the Mio-Pliocene boundary, inferring uplift and deformation during the late Miocene prior to erosion of stratigraphic section and subsequent deposition of Pliocene sediment. The Miocene record is dominated by carbonate deposition and clastics do not become prevalent until the onset of the Pliocene. The lack of clastic input during the Miocene is inferred as evidence, in conjunction with seismic interpretation, for the initial uplift of Mesozoic highs such as the Otway Ranges, Mornington High and Strzelecki Ranges in the late Miocene.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne. September 1999

AMPLITUDE VARIATION WITH OFFSET ANALYSIS IN THE MOOMBA FIELD OF THE COOPER BASIN Leanne Frederiksen Department of Earth Sciences, Monash University, Clayton, Vic.

Amplitude Variation with Offset (AVO) commonly refers to the anomalous amplitude response, as a function of the incident ray that tends to characterise gas sands from other background reflectors on a seismic section. The anomalous response of the gas sand essentially comes about because of a significant change in the bulk modulus of a gas sand compared with that of the adjacent lithology. Bulk modulus is a function of the rock matrix, the grains and the fluid contained in the rock. This difference in bulk moduli is manifest as a contrast in the P-wave to S-wave velocity ratio of a gas sand compared with that of the adjacent lithology. There is no significant AVO response in a wet sand under the same circumstances. The Moomba field of the Cooper Basin is at a mature phase in exploration, with less than fifty percent of recoverable gas reserves remaining. AVO may help delineate these gas sands which are often contained in seismically 'subtle' stratigraphic and subunconformity traps. The AVO response of gas sands may, however, be concealed by the presence of coals. To test the validity of forward modelling for an AVO response in three Moomba gas wells, crossplotting of acoustic velocities versus porosity/water saturation should reveal a separation of the (Vp/Vs) ratio of a gas sand from that of a wet sand. This separation was observed in two wells but failed in a third. This failure may have been due to a decrease in the pore pressure which occurs in depleted reservoirs and which can nullify the AVO response. However the available pore pressure data was insufficient to substantiate this hypothesis. A model, using actual field data, was devised to test the AVO effect of coal and gas sands. Variables such as thickness, impedance contrast, porosity and fluid content were perturbed to examine the effects on amplitude versus offset behaviour. Both coals and gas sands in the Moomba field were found to exhibit a decrease in amplitude with offset, the degree of which depends on the surrounding lithology. Resolution of gas sands within coals depends on both the thickness of the coals and the thickness of the gas sand. Forward modelling of one of the wells has shown some moderate AVO effects where gas sands are resolvable, however considerably greater AVO effects, including phase changes, are observed on the relevant prestack seismic section.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

RAYLEIGH WAVE PHASE VELOCITIES IN WESTERN VICTORIA Miranda Mayle Department of Earth Science, Monash University, Clayton, Vic.

An array of 40 portable, short period seismometers was located over a 270km by 150km area of western Victoria, for just over four months, mid 1998. Station spacing was approximately 30km by 50km with four almost east west lines of 10 recorders. This array covered most of the exposed Lachlan Fold Belt in Western Victoria with the north line (D) between Nhill and Bendigo and the south line (A) between Casterton and Geelong on the south line (A). A large Papua-New Guinea earthquake of July 17th, produced strong surface wave records with a dominant period of about 10 seconds from 39 stations. Vertical ground movement was sampled at 20 samples per second. Phase velocities were 144* 141' 142* 145' 143* -35* calculated from Fourier phases -35* extracted f r o m windowed portions of the signal about the NSW LF98 first coherent Rayleigh wave Different widow -36* package. -36' s\ SA Nhill lengths were investigated and a • • VIC d1 Welch window with a length • • 4.5 times the dominant 10 Bendigo D 1 0 # C1 -37* second period was used. Two • • -37* • • independent methods were C10 let • • • Casterton j oasierton * # used to measure phase. Signal Melbourne! amplitudes over the periods of interest were less than 16% of y \ * " * # |!A1 * Hamilton * Baiter* 6 r1 ?0 J # # original amplitudes. The signal • Kf • . a. ..i o ^ ; peaked in the power spectrum km J at 0.9Hz and 0.12 Hz and noise I 0 100 200 present. The [-39* w a s -39 141* 142* 143* 144* 145* contamination of the signal, through the arrival of higher modes, scattering, multipathing and noise meant that window position had to be interpolated for some stations. Phase velocities ranged from 3 km/s to 4.2 km/s for periods between 8.9 and 20.48 seconds calculated along almost north-south paths between stations on adjacent lines. Mean group velocity was 2.69 km/s. Phase velocity varies with both path location and with the period of the wave. In general phase velocity decreased with decreasing period and higher velocities were seen in the west. The phase velocities between lines A and B showed the greatest frequency dependence while those between the C and D lines showed the least. Average phase velocities (across the whole array from line A to line D) showed smoother variation ranging between 3.3 km/s and 3.6 km/s.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13'" Victor"km Universities Earth Sciences Conferences, The University of Melbourne, September 1999

GEOLOGIC EVOLUTION OF THE YILANLI FORMATION (WESTERN BLACK SEA-TURKEY) Alan A. Bayrak School ofEarth Sciences, The University of Melbourne, Parkville, Vic.

The aim of this study is to examine the geologic evolution of Yilanli Formation (Western Black Sea, Turkey) which is composed of hard microcrystalline limestones and dolomitic limestones. Yilanli Formation deposited in a large area as platform type carbonate in Western Black Sea. Yilanli Formation is underlain by mixed clastics and carbonates of Devonian and overlain by detritic Carboniferous series which are the main source of hardcoals in that area. Yilanli Formation in some district has significant amount of organic matter that can produce oil or gas. Thus the geologic evolution of this formation has been important for geoscientists in terms of source rock possibility. Considering the burial history of the region and rock stratigraphic units, deposition of the Yilanli Formation started 340mybp. Bottom temperature of the formation varied only gently till the Lower Cretaceous and was not too high enough to generate oil until the 75mybp. Since the formation was buried deeply after 90mybp as a result of supporting volcanic material into the region from island-arc volcanism, temperature increased and reached maximum value of about 140 °C at 70mybp. Not only high sedimentation rate, but also high heat flow values of 55mW/m2 from the volcanic activity increased the temperature. At 70mybp, the cracking of oil into gas commenced and continued slightly increasing until the 30mybp. Later, as the erosion and cooling took place in the region temperature remained almost constant value of 111 °C, and cracking reaction ceased when the temperature is below a critical threshold value of about 110 °C. The Yilanli Formation in terms of vitrinite reflectance reached the value of about 1.2% at present conditions at bottom of the formation. Porosity and thermal conductivity evolution of the Yilanli formation also proved that basin was deeply buried during Cretaceous times and later. While the porosity decreased abruptly during the deposition of the Yilanli formation thermal conductivity increased. Both were constant till the sedimentation time of the Caglayan Formation. Particularly during the deposition of thick Yemislicay Formation (in Filyos area) Yilanli formation was compacted at a maximum rate and the porosity reached the value of lower than 4%. Maximum hydrocarbon generation took place from the source rock between 80 and 65mybp. By using burial history analysis of the region, important knowledge about the geologic evolution of the Yilanli Formation has been obtained. Present day geologic observations have proved these results.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victor'ian Universities Earth Sciences Conferences, The University of Melbourne, September 1999 w

PETROPHYSICAL CHARACTERISATION OF HIGH PORE PRESSURE IN FAULT ZONES Kevin C. Chang Department ofEarth Sciences, Monash University, Clayton, Vic.

In addition to mineral constituents, physical properties of rocks can also depend on the nature of contained pore fluids. The presence of a pore pressure can have a significant effect on the rock's elastic properties, as an increase in pore pressure lowers the speed of elastic waves. Studies of this fluid-rock interaction has become very important in recent times, as variation of pore pressure in the earth's crust is of major economic and ecological interest. Detection and monitoring of pore pressure by petrophysical methods can have major applications in many fields of geoscience, including waste deposit site selection, gas and mineral exploration and earthquake prediction. The shear strength of a fault is dependent on its effective normal stress. The effective stress is the difference between stress normal to the fault plane (a ) and the pore pressure (Pp). An increase in pore pressure decreases the effective stress on a fault, hence decreasing its shear strength (x) as shown by the Coulomb-Mohr failure criterion: T = To + ^(C -Pp) where x is the cohesive strength and £ is the coefficient of static friction. This decrease of shear strength destabilises the fault and can cause seismic slip. This means it is possible to implicitly monitor the stability of a fault zone, by monitoring how elastic wave velocity varies with change in pore pressure. The motivation for this study is provided by a lack of experimental data relating high pore pressure and the elastic properties of deformed crystalline rocks. Laboratory experiments were carried out involving ultrasonic wave propagation through water-saturated leucogranite specimens. The specimens were collected from a ductile fault zone in the French Massif Central, at constant intervals from the undeformed protolith to the mylonite. These granite specimens were jacketed in order to achieve a high pore pressure when subjected under a hydrostatic confining pressure. For an unsaturated sample without pore pressure, the P-wave velocity increases as the pores and microcracks are progressively closed with increasing confining pressure. The complete closure is observed at ~ 200 MPa indicated by the commencement of linear behaviour (Rey et al, 1994). P-wave velocities are observed to decrease by about 1 km/s, when the pore pressure is increased to the value of the confining pressure (Figure 1). This finding is consistent with observations made by Nur and Figure 1. P-wave velocity as a function of confining and pore pressure. Simmons (1969). The reduction in P-wave velocity is attributed to the lower density of the pore fluid compared to the non-porous solid matrix at high confining pressures. n

P - W a v e Velocity (km/s)

Confining Pressure (MPa)

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne. September 1999

These results manifest the potential that exists for prediction of seismic ruptures. When P-wave velocity appears anomalously low for a given depth (analogous to confining pressure), it indicates the presence of a high pore pressure, hence lowering the shear strength for a possible seismic event. From the nine specimens obtained from the protolith to the mylonite, a shear zone profile is displayed in Figure 2, showing the variation of isobaric P-wave velocity. All these samples contain a pore pressure equalling to the confining pressure. A general trend of decreasing Pwave velocity toward the shear plane is '•A observed. However when we consider the •x "X' complexity of the experimental process, Increasing Strai Protoith Mybnite we realise that many crude factors could k. contribute to the uncertainty of the results. Rey et al (1994) also observed a F i g u r e 2. Shear Zone P-Wave Velocity systematic decrease of P-wave velocity Profile toward the mylonite, for the same specimens without the pore pressure. Each specimen was extracted in three orthogonal directions. Preliminary results also show presence of a P-wave velocity anisotropy, resulting from the strong fabric of the strained specimens. This was also observed by Rey et al (1994) with dry samples, though anisotropy seems to be attenuated with high pore pressure. Further investigation can be conducted on the anisotropic nature of the specimens. This includes investigating the effect of shear wave velocity and shear wave splitting in a fabricated medium. Another approach is to investigate the fluid flow signature using electrical conductivity measurements in orthogonal directions. The acoustic impedance contrast of the shear plane also allows measurement of reflectivity to investigate the existence of a transition zone between the protolith and the mylonite. REFERENCES: Nur, A. & Simmons, G. (1969), The effect of saturation on velocity in low porosity rocks, Earth Planetary Science Letters, 7, pp. 183-193.

and

Rey, P.F., Fountain, D.M. and Clement, W.P. (1994), P-wave velocity across a non-coaxial ductile shear zone and its associated strain gradient: consequences for upper crustal reflectivity, Journal of Geophysical Research, 99, pp. 4533-4548.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13,h Victorian Universities Earth Sciences Conferences, The University of Melbourne. September 1999

POLYMETAMORPHISM AND THE TECTONIC EVOLUTION OF THE DANBA DOMAL TERRAIN, SICHUAN PROVINCE, WESTERN CHINA l M. H. Huang, lI. 5. Buick, 21. S. Williams and lR. Maas department of Earth Sciences, La Trobe University, Bundoora, Vic. "Research School of Earth Sciences, The Australian National University, Canberra, ACT 0200, Australia

The Danba Domal Metamorphic Terrain (DDMT), within the eastern portion of the Songpan-Garze Orogenic Belt (western China; SGOB), is a major belt of polymetamorphosed and deformed Mesoproterozoic to Mesozoic sedimentary and volcanic rocks between the North China Craton, the Yangtze Block and the Tibetan Block. Although the SGOB is generally characterised by regionally extensive, low-grade Triassic flysch sediments, the DDMT consists of: Mesoproterozoic migmatized orthogneiss basement; Neoproterozoic-Triassic covering metasediments; and syntectonic granites, and reached much higher metamorphic grades. Isograds have been defined within the DDMT based on the distribution of index minerals in metapelites, namely biotite, garnet, staurolite, kyanite, and sillimanite. At the highest grades a zone of migmatization can also be delineated in the central northern portion of the DDMT. These isograds are locally concentric around the basement orthogneiss domes and grade generally increases towards the north. The higher-grade sillimanite zone locally truncates the trend of lower grade zones, suggesting that it might reflect a separate metamorphic event. Three metamorphic events have been distinguished in the metapelites: (1) an earliest (Ml) Barrovian-style prograde metamorphism up to mid-amphibolite facies grade (Grt+St+ Ilm+Ky+Mu+Qtz) that probably developed during Indosinian-Yanshanian (Triassic-Jurassic) southwards-directed shortening (Dl); (2) a subsequent (M2) hightemperature SilkfcKfs overprint associated with E-W compression, and possibly the emplacement of syntectonic (-110 Ma) dioritic-syenitic intrusions and the migmatization of the gneiss domes (D2), and (3) late stage, retrograde (M3) growth of Qtz+Ser+Chl in variably developed SE-NW oriented crenulation cleavages, and in Miocene NW trending fault and shear zones that developed during the Himalayan Orogeny (D3-D4). Garnet porphyroblasts from all grades have been examined by electron microprobe to determine their element partitioning. Normal growth zoning has been found in the garnet through kyanite zones, indicating prograde growth during the M l . In contrast, garnet grains in the sillimanite zone are generally compositionally homogeneous, or record complex zoning patterns that most probably reflect a metamorphic overprint during M2. P-T conditions estimated from metapelites and amphibolites from the different zones using conventional thermobarometry and the THERMOCALC computer program are as follows: biotite zone (~475°C, -4.2 kbar), garnet zone (-530-580° C, -5-7 kbar); staurolite zone (-570-590° C, -6-7.7 kbar ); kyanite zone (-580-610° C, -6.6-8 kbar); and sillimanite zone (600-690° C, 5-6 kbar for non-Kfs assemblages). Temperatures within the sillimanite zone increase northwards within the DDMT. Pressure calculations on metapelites containing kyanite and sillimanite suggest a slight decrease in pressure from M1 (8-6 kbar) to M2 ( - 6 to 5 kbar), however it is unclear whether this difference is significant statistically. No garnet was found associated with the muscovite-poor, migmatitic Sil+Kfs assemblages, rendering them less useful for thermobarometry.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13,h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

However, it is inferred that these assemblages record temperatures in excess of -700°C and formed through muscovite dehydration partial melting. This partial melting might have been responsible for the generation of voluminous pegmatites that occur throughout the high-grade portion of the terrain. The age of high-grade metamorphism in the DDMT has been investigated by U/Pb dating of monazite from metapelites using SHRIMP II. Monazite intergrown with foliation-defining muscovite and biotite from a kyanite zone sample yielded a main population age of - 1 8 0 Ma. This compares well with K/Ar ages of 154-180 Ma determined from illite for regionally extensive low-grade metamorphism in the SGOB outside of the DDMT. In contrast, monazite included in foliation-forming biotite from two samples in the supposedly younger sillimanite zone yielded slightly older main population ages of -185 and -195 Ma respectively. These ages are generally consistent with the emplacement ages of voluminous Indosinian S-type granitoids throughout the SGOB (210-190 Ma), but the oldest age (-195 Ma) is significantly older than monazite from the kyanite zone sample. These data suggest that Ml occurred at or before - 1 8 0 Ma. However, the significance of-185-195 Ma monazite in the sillimanite-zone samples remains unclear. Either the M2 event that formed the sillimanite zone was progressive with Ml Barrovian metamorphism, or M2 occurred later, but was not associated with new monazite growth. In the northern DDMT, structures in sillimanite zone rocks appear to be synchronous with those developed in - 1 1 0 Ma syenite intrusions (Rb/Sr WR isochron). If this is the case, then the -185-195 Ma monazite ages have been preserved through a younger M2 overprint that reached at least -700°C. Unlike most metamorphic monazite, in which Pb/U is relatively uniform, the Pb/U apparent ages of monazite from one sillimanite zone sample and the kyanite zone sample (taken close to the sillimanite-in isograd) range down to 170 and 140 Ma respectively. Backscattered electron images of selected monazite grains show no evidence of growth zoning, but lower Pb/U tends to occur close to the grain margins. This might reflect partial (diffusional?) radiogenic Pb loss from the monazite during a post-crystallization, high-temperature thermal event, possibly the inferred younger sillimanite zone overprint. Post-Mi, coarse grained pegmatites emplaced throughout the high grade portions of the DDMT yield Rb-Sr mineral isochrons at - 1 8 0 Ma and -100-120 Ma, consistent with the Ml and M2 events reflecting two separate events rather than a continuous evolution. Further investigations are under way to constrain the timing of M2. Throughout the DDMT, Rb-Sr studies of biotite and muscovite in metapelites record significantly younger ages. WR-biotite model Rb-Sr ages throughout the DDMT consistently yield ages of -26-33 Ma regardless of regional grade, whereas WRmuscovite model Rb-Sr ages show a considerably larger spread (33-130 Ma). These data may be consistent with either: a) a thermal event that was hot enough to reset biotite (Tc - 3 0 0 °C) but not muscovite Rb-Sr (Tc -500°C) isotope systems; or b) initially slow differential cooling during the Mesozoic, followed by rapid cooling and exhumation in the Oligo-Miocene. The isotopic resetting does not appear to be related to pervasive deformation. However, major strike slip fault zones associated with granite emplacement to the south west of the DDMT developed in the interval 10-20 Ma during the later stages of the Himalayan Orogeny.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victoi •ian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

The DDMT is regarded as a product of poly metamorphism combined with early crustal thickening and top-to-the-south decollement caused by the subduction of the South China block under Laurasia during the Indosinian Orogeny (Ml in the DDMT), followed by uplift induced by granitoid intrusion due to the E-W collision between the Tibet and South China Blocks, possibly during the Yanshanian Orogeny (M2). Further uplift or exhumation and cooling might have occurred during the Himalayan movement when convergence between the India Plate and Eurasia took place.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

3D STRUCTURAL MODELING AND RESTORATION OF DETACHMENT FOLDS AND FORELIMB THRUSTS FROM CAPE LIPTRAP, AUSTRALIA AND THE PNG FOLD BELT Jeffrey Keetley, Kevin Hill & Cue Nguyen Australian Geodynamics Cooperative Research Centre, Earth Sciences Department, La Trobe University, Bundoora, Vic.

The Lower Devonian turbidite sequences exposed at Cape Liptrap, 150 km SE of Melbourne Australia, were deposited in front of growing mountains to the east and were deformed as part of the Middle Devonian orogeny throughout Eastern Australia. The deformation immediately followed rapid deposition of several kms of homogeneous turbidites and it commenced whist they were in a soft sediment state giving rise to a number of unusual structural styles. Key observations are: 1. Individual sandstone layers were thrust to form ramp anticlines, duplexes, fault propagation folds and detachment folds whilst the intervening shales were commonly deformed by pure shear. A consequence of this is that whilst thrust shortening is balanced across all sandstone beds, no thrust propagates through the shales to the next sandstone (Hill et al., 1996). This is similar to results from the centrifuge experiments of Dixon and Liu (1992) and has important consequences for the interpretation of surface folds at depth in areas with thin competent beds separated by thick shales, as in Papua New Guinea. 2. Folding and thrusting occur equally downwards as well as upwards, such that ramp anticlines are often symmetrical in cross section, given a 180° rotation about a pole parallel to the fold axis. This is interpreted to be due to the relatively soft nature of the thick pile of sediments at the initial time of deformation, such that the effect of gravity was minimal. The shales/muds may be best modeled as a fluid. 3. Both sandstones and shales were subsequently open to tightly folded locally and regionally in association with the development of near vertical, N-S axial planar cleavage in the shales. 4. The folds commonly involve thickening of the mudstones in the forelimb and then thrusts breaking through the competent sandstones in the forelimb. This is similar to processes inferred in the oil-bearing anticlines of Papua New Guinea. 5 . Fault propagation folds and rounded open folds developed where sandstonershale ratios are 1:2 and 1:4. Chevron folds developed where sandstone:shale ratios are 1:1. Within the chevron fold sequence, the folds only persist vertically for 1.5 - 2 x the wavelength of the fold and horizontally for 3 - 4 x the wavelength. 6. Overall the measurable shortening is approximately 50%. The hydrocarbon-bearing structures in the Pliocene Fold Belt of Papua New Guinea have previously been compared to structures in the Canadian Rockies and the Appalachians (eg, Hobson 1986; Hill 1991). This has recently been shown to be inappropriate as the PNG structures are cored by a shale dominated clastic section,

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3'h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

like Cape Liptrap, rather than the thick limestones and quartzites in the Rockies and the Appalachians. Scant seismic lines and - 4 0 wells in the Iagifu-Hedinia area of PNG suggest that detachment folding developed in the clastics in the core of the Iagifu-Hedinia anticline followed by break-through thrusts in the forelimb. The aim of this study is to apply 3D geometrical and mechanical modeling to similar structures from PNG and from Cape Liptrap in order to understand the development of the structures and to better predict the subsurface structure of undrilled anticlines in PNG. Currently, a three-dimensional structural model of Iagifu-Hedinia has been built using 3DMove using five balanced sections and SAR images supplied by Chevron Niugini (eg. Franklin & Livingston 1996). In a 400 square metre area at Cape Liptrap with 100% exposure, 3000 dip and strike readings are being used to build a 3D model as well as detailed models of individual structures. Using 3Dmove, the structures in both areas are currently being restored to reveal their kinematic evolution and intermediate morphologies. ACKNOWLEDGEMENTS: This paper was published with the permission of the Director of the Australian Geodynamics Cooperative Research Centre. The authors thank Midland Valley and Paradigm for making available balanced cross section software and the Chevron and Esso Joint Ventures in PNG for access to data and sponsorship. REFERENCES: Hill, K.C., Simpson, R.J., Kendrick, R.D., Crowhurst, P.V., O'Sullivan P.B. & Saefudin 1. (1996), Hydrocarbons in New Guinea, controlled by basement fabric, Mesozoic extension and Tertiary Convergent margin tectonics. In Buchanan P.G. (ed) Petroleum Exploration, Development and Production in Papua New Guinea, Proceedings of the third PNG Petroleum Convention, Port Moresby Sep 1996, pp. 63-76. Hill, K.C. (1991), Structure of the Papuan Fold Belt, Papua New Guinea. Bulletin American Association of Petroleum Geologists, 75, pp. 857-872. Hobson, D.M. (1986), A thin skinned model for the Papuan thrust belt and some implications for hydrocarbon exploration. The APEA Journal, 26 (1), pp. 214-224. Franklin, S. & Livingston, J. (1996), Development of an Infill Well Program to Maximize Economic Return from the Iagifu-Hedinia Field: Parti. Integrated Structural, Stratigraphic, and Reservoir Attribute Modeling as input to Reservoir Simulation and Well Targeting. Petroleum Exploration, Development and Production in Papua New Guinea, Edited by P.G. Buchanan. Dixon, J. & Liu, S. (1992), Centrifuge modeling of the propagation of thrust faults. Thrust Tectonics 1992, Edited by K.R. McClay

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University»of Melbourne, September 1999

INVERSION OF WIDE-ANGLE SEISMIC DATA FOR 3-D CRUSTAL STRUCTURE OF NW TASMANIA N. Rawlinsonu, G.A. Houseman2 & C.D.N. Collins13 Australian Geodynamics Cooperative Research Centre Department of Earth Sciences, Monash University, Clayton, Vic. 2 Australian Geological Survey Organisation, Symonston, ACT, 2609 2

Geophysics has played an important role in helping to reveal the structure and composition of Tasmaniafs crust, but it has been principally used in the context of mineral exploration, so potential field surveys have been prevalent and seismic surveys limited. Consequently, the deep crustal structure of Tasmania is not well understood. In 1995, 144' 145* 146* a 3-D wide-angle seismic dataset was recorded throughout Tasmania as part of the TASGO project. AGSO's research vessel Rig Seismic performed a circumnavigation of Tasmania during which -36,000 shots were fired from its airguns with an average shot spacing of 50m. A network of 44 recorders distributed throughout Tasmania recorded seismic energy from the shots. The map of NW Tasmania on the right shows the portion of the survey 146' 144' 145* relevant to this paper. The primary goal of this study is to map the crustal structure of Tasmania down to at least Moho depth. Below, we briefly describe the inversion method we employ and some results of 2-D and 3-D reconstructions of NW Tasmania using the TASGO wide-angle seismic dataset. The models used in our reconstructions are composed of smooth interfaces that separate layers in which velocity varies linearly with depth. In 2-D, each interface is described by a set of piecewise cubic B-spline curve segments, while in 3-D, each interface is defined by a mosaic of bicubic B-spline surface patches. Crustal structure is mapped by tracing rays through a given initial model, comparing these model traveltimes with observed traveltimes picked from a refraction section, and then adjusting the model parameters to improve the traveltime fit. The process of tracing rays between sources and receivers is accomplished using a shooting method which is capable of finding the first arrivals of refracted and reflected phases. A subspace inversion method is used to solve the inverse problem, which is formulated as a non-linear optimization problem in which we seek to minimize an objective function that consists of a data residual term and a regularization term. A 2-D crustal model of the western north coast of Tasmania has been constructed using both refraction and wide-angle reflection traveltimes from shot line 5 to receivers 7,10 and 31. The starting model for the inversion consists of 4 13

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13" Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

crustal layers overlying a mantle half-space, with each of the four interfaces described by 22 nodes. A 12-D subspace method is used to invert 882 traveltimes for interface node depth and layer velocity parameters. After 10 iterations, the RMS data misfit was reduced from 263 ms to below 100 ms. The major lateral feature of the model is the pinchout below Three Hummock Island of a low velocity crustal layer that lies immediately above the mantle. This structure may represent a crustal detachment caused by mid-crustal material underthrusting more mafic lower-crustal material during a compressional event. In addition, an upward deflection of the Moho of nearly 50 km lateral extent and maximum amplitude of ~5 km, replicated in the overlying interface but offset to the SE, may indicate the presence of a high velocity wedge of crustal material beneath the Arthur Lineament. Recently, a 3-D crustal model of the region encompassed by lines 5, 8 and 9 was constructed. The model used in the inversion consists of three crustal layers overlying a mantle half-space. Each interface is described by 120 nodes. A 15-D subspace method is used to invert 1304 refraction and reflection traveltimes for depth and velocity parameters. After 5 iterations, the RMS data misfit is reduced from 309 ms to 120 ms. The final model is consistent with the 2-D model described above; in particular, the upward deflection of the lower crustal layer in the vicinity of the Arthur Lineament is well matched. The robustness of the 3-D model varies with depth, with the top interface being the least well resolved and the Moho the best resolved interface. This is due to the prevalence of rays that refract or reflect from the Moho and the poor spatial coverage of rays near the surface. The 3-D model shows a general thickening of the crust from -26 km in the region of the King-Island sub-basin to -36 km near the centre of Tasmania. Previous estimates of crustal thickness have suggested that the crust is between 27.5 km (Leaman 1989) and 32 km thick (Richardson 1989) beneath central Tasmania. Our inversion results also indicate that NW Tasmania has an average crustal P-wave velocity of 6.2 km/s and an average mantle P-wave velocity immediately below the Moho of 8.0 km/s. The crustal structure of northern Tasmania obtained from the inversion of seismic traveltimes is consistent with independent interpretations (Barton 1999) of marine deep reflection profiles that were collected concurrently with the wideangle data. The most notable similarities are the basic three-layer character of the crust, the Moho geometry and the crustal detachment feature. REFERENCES: Barton, T.J. (1999), Crustal structure of northern Tasmania based upon a deep seismic transect.The Last Conference of the Millennium, Halls Gap. Geological Society of Australia, Abstracts 53, pp.83-84. Leaman, D.E. (1989), The gravity field. In: Burrett, C.F. & Martin, E.L. eds. Geology and Mineral resources of Tasmania, Geological Society of Australia, Special publication 15, pp. 451-455. Richardson, R.G. (1989), Crustal structure. In: Burrett, C.F. & Martin, E.L. eds. Geology and Mineral resources of Tasmania, Geological Society of Australia, Special publication 15, pp. 465467.

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FLUID FLOW IN A MAJOR CRUSTAL THRUST ZONE, REDBANK HIGH STRAIN ZONE, CENTRAL AUSTRALIA Caroline M. Read & Ian Cartwright Department of Earth Sciences, Monash University and VIEPS, Clayton, Vic.

Crustal-scale fault zones world wide are associated with the juxtaposition and exhumation of rocks of different crustal levels. During exhumation events the infiltration of fluids is a common phenomenon as shown by the hydrous assemblages found within shear zones that cut high-grade anhydrous metamorphic rocks. The sources of these fluids is often not apparent from the surrounding rocks. Substantial devolatilisation of high-grade rocks is unlikely to accompany later low grade shearing and igneous activity does not always occur during shearing. The Redbank High Strain Zone (RHSZ) forms a major crustal boundary separating the Central and Southern Provinces of the Arunta Inlier in central Australia. The RHSZ is a 400km long north-dipping zone of faults and shears that juxtaposes amphibolite facies Southern Province gneisses with Central Province granulites. Exhumation along the RHSZ is thought to have occurred in two major episodes. According to Shaw and Black (1991), Rb-Sr ages indicate that shearing occurred initially around 1500-1400 Ma forming amphibolite facies (Type 1) mylonites. This was followed llOOm.y. later by the formation of low-grade (greenschist facies) mylonites (Type 2) during the Alice Springs Orogeny (at 300-350 Ma). The sheared rocks of the RHSZ are dominated by protomylonites and have locally-developed mylonite to ultramylonite fabrics. RHSZ rock compositions vary, but are dominated by granitic and mafic amphibole-bearing assemblages. The unsheared rocks to the south of the RHSZ are coarse-grained granitic gneisses and to the north of the RHSZ the rocks are dominantly mafic granulites. The rocks show varying degrees of rehydration from the precursor gneisses surrounding them. Lenses of bimineralic quartz-epidote rocks (5 to 15m wide) occur parallel to the main shear fabric. They preserve macroscopic textural features which indicate that they are metasomatic equivalents to the gneisses that host them. These altered sheared mylonites suggest substantial amounts of fluid infiltrated the RHSZ, channelled along narrow zones of greater permeability. The variation in the degree of strain, evident in thin section, along these zones is possibly a feature of the different rates of recovery within bi- and polymineralic lithologies, where quartz and epidote recovery is rapid. However the differing apparent amounts of fluid infiltration across the shear zone indicates fluid flow was highly focussed and not solely dependant on the degree of strain. Oxygen isotope values in several across strike traverses along the RHSZ indicate a complex history of fluid-rock interaction. 8 , 8 0 values range from 3.3 to ll%o with most values between 6-9%o. Lowering of the 5 18 0 values locally within larger shears occurs in conjunction with major silicification and epidotisation. Owing to the large volumes of fluids that have infiltrated these areas, the isotope signature of the fluids is likely to be preserved over large distances, and therefore be recorded in 15

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the rock values. However there are zones of silicification and epidotisation which have 5 0 values in the 6-9%o range. The lower 5 0 values are indicative of the infiltration of meteoric fluids into the shear zones. Within the other metasomatic zones it is possible that fluids that effected these rocks were also meteoric but their isotopic signatures were changed by fluid-rock interaction prior to the fluids reaching them. Alternatively other crustal sources may also have contributed to the fluid budget. There is a lack of evidence of magmatic activity during the Alice Springs Orogeny implying hydrothermal circulation of meteoric fluids did not occur at this time. The anhydrous nature of the basement granulites precludes them from being a source of fluids during shearing. Therefore it is likely that much of the fluids came directly from the surface or from within the Amadeus Basin which covered the Arunta Inlier prior to exhumation. The lack of Alice Spring ages from the host lithologies surrounding the shear zones implies that isotopic resetting is generally not occurring out of the shear zones. This implies that fluid transfer throughout the unsheared rocks of the southern province was limited during the Alice Springs Orogeny. The evidence of fluid infiltration within the shear zones of the RHSZ is indicative of channelling of meteoric fluids through narrow pathways during the active exhumation of the terrain. Reequilibration of the meteoric fluids increases their 5 O values, which suggests the fluids have enjoyed major fluid-rock interaction and are possibly further along the flow path than meteoric fluids seen elsewhere in the Arunta Inlier. In summary the isotopic and petrologic evidence indicates the Redbank High Strain Zone has acted as a major fluid conduit during exhumation of the Arunta Inlier. Shearing is complex and has occurred during different uplift events, however the oxygen isotope analyses suggest there was infiltration of meteoric fluids into the zone during at least one of the shearing events. As with many major crustal structures world wide the juxtaposing of different tectonic and metamorphic terrains is coupled with fluid infiltration, and we suggest the earths surface could represent a major reservoir for the fluids present during exhumation. IX

REFERENCES: Shaw, R. D. & Black, L. P. (1991), The history and tectonic implications of the Redbank Thrust Zone, central Australia, based on structural, metamorphic and Rb-Sr isotopic evidence. Australian Journal of Earth Sciences, 38, pp. 307-332.

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2. SEDIMENTOLOGY AND PALAEONTOLOGY Talks: pp 18-22 Posters: pp 23-28

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STRATIGRAPHY, SEDIMENTOLOGY, AND ICHNOLOGY OF PART OF THE EARLY CARBONIFEROUS MANSFIELD BASIN, CENTRAL EASTERN VICTORIA Heather AnselI School of Ecology and Environment (Earth Science), Rusden Campus, Deakin University, Clayton, Vic.

The Devil's Plain Formation of the Mansfield Group (Late Devonian to Early Carboniferous) is located in the Mansfield Basin, Central Eastern Victoria and comprises a fluvial sequence of interbedded red pigmented sandstones, siltstones, and mudstones. The Mansfield Basin is the northern-most structural sub-basin of the four remnant structural basins ('synclinoria'), which constitute the north-northwesterly trending Mount Howitt Province as part of the Palaeozoic Lachlan Fold Belt. Both small and large scale sedimentary structures have been observed within the Devil's Plain Formation. Near the junction of Broken River, within Bridge Creek; a complete stratigraphical section contains sedimentological features such as small scale planar and cross lamination, flaser and lenticular bedding, tool marks and current ripples of progressively differing directions, and evidence of hydroplastic and quasi-solid mechanical deformation such as raindrop impact marks and desiccation cracks, and load structures respectively. Trace fossils recognized include Scalarituba, Palaeophycus, Skolithos, and Cruziana. Thin beds, overlap of floodplain deposits with upper pointbar deposits, close proximity of tracefossils with pointbar deposits, and thin trough beds which are poorly represented suggest a shallow meandering river channel. Rapid changes in paleocurrent direction and facies type indicate frequent changes in sediment transport direction, and therefore deposition was on a low topography. Adjacent to the Bridge Creek Section, differential erosion of sandstone channel beds and siltstone have produced benched undulating hill profiles. Large scale planar and cross lamination and bedding is also present at Tolmie Road cuttings and Blue Range State Park stratigraphical sections on the northern border of the Mansfield Basin and the Barjarg Granite. The large scale sedimentary structures deposited in deeper fluvial channels contrasts with the Bridge Creek section. Overall the entire Devil's Plain Formation is regarded as representing a freshwater fluviatile basin.

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FIRST RECORD OF PERMIANELLA HE & ZHU, 1979 (PERMIANELLIDAE; BRACHIOPODA) FROM PENINSULAR MALAYSIA M. J. Campi1,Shuzhong Shen1, Mohd Shafeea Leman2 & G. R. Shi1 School of Ecology and Environment, Deakin University, Rusden Campus, Clayton, Vic. "Jabatan Geologi, Universiti Kebangsaan Malaysia, Bangi 43600, Selangor, Malaysia.

This paper presents a first record of a permianellid species from the Leptodus shales of the Gua Musang Formation, northwest Pahang, Peninsular Malaysia. The specimen is assigned to Permianella typica He & Zhu, 1979 and is most likely to be of late Guadalupian (Middle Permian) in age based on its association with Vediproductus Sarytcheva (in Ruzhentsev & Sarytcheva, 1965). This new record of Permianella from Peninsular Malaysia becomes the most southerly record for this genus, both during the Permian and for the modern geographical distribution of reported fossils. Permianellids are an unusual brachiopod group, characterised by an elongate bilobate outline, anterior incision and posterior attachment ring for anchoring to crinoid stems during life. The palaeogeographic distribution of this group extended from the Cathaysian Province of the Palaeoequatorial Realm to the adjacent transitional zones between this realm and the Gondwana and Boreal Realms to the south and north respectively. This group is restricted to the Permian, with records from the Kungurian to the Changhsingian (Shen & Shi, 1998). The Malaysian specimen is assigned to Permianella typica He & Zhu, 1979 on the basis of an elongate bilobate outline, deep anterior incision and the presence of a marginal brim along the lateral commissure, and it was collected from a fossiliferous horizon in the Leptodus shales from the Merapoh-Sungai Yu area, Pahang State. The Leptodus shales are characterised by pyroclastic sediments, particularly tuffaceous siltstones and shales. Previous work has interpreted this area as an island arc or seamount setting during the later Permian, and the Leptodus shale faunas were suggested to be early Changhsingian (Lopingian) in age (Mohd Shafeea Leman; 1993). However, it appears that a reassessment of the suggested age for this locality is required, as several specimens belonging to the genus Vediproductus Sarytcheva (in Ruzhentsev & Sarytcheva, 1965) have been found in association with the specimen of Permianella typica. Vediproductus is a characteristic genus of late Guadalupian brachiopod faunas and has not been found above the Guadalupian-Lopingian boundary. It is also a typical Palaeoequatorial genus and has been found in Transcaucasia (Ruzhentsev & Sarytcheva, 1965) and from the Lengwu substage of the Maokouan (late Guadalupian) of South China (Chao, 1927; Liang, 1982, 1990). The discovery of Vediproductus (along with several other typical Middle Permian brachiopod genera) suggests that the fauna at this Malaysian locality may be older than previously thought. REFERENCES: Chao, Y. T., (1927), Productidae of China, Part 1: Producti. Palaeontologia Sinica, Series B 5(2), pp. 1-244 Grunt, T. A. & Shi, G. R., (1997), 'A hierarchical framework of Permian global marine biogeography', in Y. G. Jin & D. Dineley, (eds) Palaeontology and Historical Geology, Proceedings of the 30th International Geological Congress 12, VSP, Utrecht, pp. 2-17.

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He, X. L. & Zhu, M. L. (1979), A new form of brachiopods and its systematic classification. Journal of China Institute of Mining and Technology 4, pp. 131 -140, (in Chinese). Liang, W. P. (1982), 'Brachiopoda', in G. P. Wang et al. (eds) Palaeontological Atlas of East China, 2, Geological Publishing House, Beijing, pp. 228-230. (in Chinese). Liang, W. P. (1990), Lengwu Formation of Permian and its brachiopod fauna in Zhejiang Geological Publishing House, Beijing, pp. 1-522. (in Chinese).

Province.

Mohd Shafeea Leman. (1993), 'Upper Permian brachiopods from northwest Pahang, Malaysia', in T. Thanasuthipitate (ed.) Proceedings of the International Symposium on Biostratigraphy of Mainland Southeast Asia: Fades & Paleontology 1, pp. 203-218. Ruzhentsev, V. E. & Sarytcheva, T. G. (1965), Razvitie i smena morskikh organizmov na rubezhe Paleozoia i Mezozoia. (The development and change of marine organisms at the Palaeozoic-Mesozoic boundary.) Akademia Nauk SSSR, Paleontologicheskii Istitut, Trudy 108, pp. 1-232. (in Russian). Shen, S. Z. & Shi, G. R.. (1998), Taxonomy, stratigraphy and palaeobiogeography of Permianellids (Brachiopoda). Proceedings of the Royal Society of Victoria 110(1/2), pp. 267-279.

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THE USE OF SONIC VELOCITY IN UPLIFT STUDIES OF THE BROWSE BASIN, NORTH WEST SHELF AUSTRALIA Christine Dawe School of Earth Sciences, The University of Melbourne, Parkville, Vic.

The purpose of this study of a succession of Mesozoic to Cainozoic carbonates in the Browse Basin, Western Australia, is to determine the controls on sonic velocity and to constrain the uplift history of the region. Composite well logs and petrological data from eight wells in the area were analysed and the relationship between sonic velocity, lithologic composition and depth identified. The sonic velocity of the carbonates was found to be controlled by mineralogy, porosity and diagenetic processes. The sonic velocity through sediments is highly dependent on carbonate content. Sediments with a high carbonate content display higher velocities than those with low carbonate contents. For a given carbonate content, sonic velocity increases linearly with depth. This is a result of porosity loss with depth. Porosity loss is facilitated by the mechanical and chemical processes of compaction and cementation. Sonic velocity is also controlled by diagenetic processes. Where mechanical compaction is the dominant diagenetic process, the sonic velocity gradient of the sediments is shallow. As chemical compaction is initiated in the carbonates the sonic velocity gradient becomes steep. The point at which this gradient change occurs is 500-600m below the top of the succession. Anomalously high sonic velocities in part of the sequence correspond to uplifted sections. The Ashmore Reef-1 well, north of the Browse Basin, has been uplifted and exhibits high velocities (Hillis, 1992). Evidence for uplift in this well can be seen in thin sections, which display wellcemented pore spaces at depths too shallow for chemical diagenesis. REFERENCES: Hillis, R.R., 1992. Evidence for Pliocene Erosion at Ashmore Reef (Timor Sea) from the Sonic Velocities of Neogene Limestone Formations. Exploration 23, pp. 489-495.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

THE ECOLOGY OF FORAMINIFERA IN BASS STRAIT Andrew Smith School of Earth Sciences, University of Melbourne, Parkville, Vic.

A marine cruise was carried out in October, 1998 by the RV Franklin to offshore Gippsland. The purpose of this cruise was to acquire shallow seismic data, sea bed grab samples and piston cores to understand the evolution of the Bass Canyon and Gippsland Shelf. This research describes the modern foraminiferal distribution from the some of the 73 sea bed grab samples obtained on this cruise. The samples came from two transects from near shore, inner shelf to outer shelf in a southwesterly direction, a third running in a similar direction from mid shelf to the head of the Bass Canyon, and another from mid shelf to bathyal depths within the Bass Canyon. An assessment can be made on the distribution of various species from this study, for example, Ammonia beccarii prefers shallow inner shelf water depths, while Astrononion centroplax prefers deeper outer shelf water depths. Along with this, trends can also be followed, such as the increase in the percentage of planktonic fauna with respect to benthic fauna at depths of greater than 250m. The samples were preserved in alcohol at time of collection and rinsed in a rose Bengal solution in the laboratory, allowing the labeling of individual foraminifera as either dead, alive or relict at time of collection. This allows the assessment of production rates, which can provide information on post-mortem influences such as transport, mixing and destruction of tests. Aside from this research providing information on the ecology of modern foraminifera in Bass Strait, it also allows the construction of a modern analog, which may be used to help infer past environments, based on ancient foraminiferal assemblages from the region.

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SEDIMENTARY CYCLES AND PALAEOENVIRONMENTS OF THE EARLY MIOCENE OF GIPPSLAND Damien Keys, School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Metre scale minor cycles occur in cool water carbonates of Early Miocene age in Gippsland, Victoria. They are exposed in quarries 10 kilometres south of Sale, in eastern Victoria. These carbonates belong to the Gippsland Limestone Formation, one of five formations comprising the Seaspray Group in the Gippsland Basin. The Gippsland Limestone Formation is of Longfordian age (Lower Miocene). Reddish clayey marls comprise the bottom unit of each cycle. Relatively high planktonic ratios (around 10-12%) and high infaunal foraminiferal counts, suggest a low energy outer shelf depositional environment. The clayey marls grade upward into orange green marls that are rich in fine bryozoa, echinoids and bivalves. The planktonic count in the marl decreases to around 2%, with cibicidid content increasing. The marls are interpreted to have been deposited in inner to mid shelf environments. Fossiliferous cemented horizons occur at the top of the cycles. These calcarenite units are often discontinuous and are rich in brachiopods and bivalves. Paleaoenvironmental reconstruction from foraminiferal studies suggest an inner shelf environment of deposition. The presence of the large foraminifera Amphistegina in some calcarenites would also suggest periods of warm marine conditions. The cycles observed in Gippsland are similar to Miocene cycles observed by Shubber et al (1997) in the St Vincent Basin of South Australia. Shubber et al (1997) observed bryozoan miliolid-echinoid rudstone basal units, through bryozoan grainstone units capped by bryozoan-Amphistegina hardgrounds at the top. The origin of third and fourth order sedimentary cycles is a point of contention among many researchers. Currently three theories are proposed for third order cyclicity. The commonly accepted theory proposed by Haq et al (1987) is of glacial eustacy. This holds for certain periods of Earth history, but cannot explain cyclicity in "warmer" non glacial phases in Earth history. Stress release at plate boundaries at third order intervals is a theory proposed by Cloetingh (1992). The driving force behind this mechanism comes from mid ocean ridge spreading. This results in local and regional marine transgressions. The final theory relies on variations in sediment supply driven by isostatic uplift and subsequent erosion of the continental interior. This seems the most feasible explanation for Gippsland given the large sedimentation rates occurring within the basin at the time. REFERENCES: Cloetingh, S.P. (1992), Lithospheric Dynamics and the Tectonics of Sedimentary Basins, reprinted from Proceedings ofKoninklijke Nederlanse Akademie van Wetenschappen, Amsterdam, 95 (3), pp. 349-369. Haq, B., Hardenbol, J., Vail, P.R. (1987), Chronology of Fluctuating Sea Levels Since the Triassic (250 million years to present), Science, No. 235, pp. 1156-1167.

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Shubber, B., Bone, Y., McGowran, B. and James, N.P. (1997), Cementation in Cool-water Subtidal Carbonate Cycles: The Tertiary Port Vincent Limestone, St Vincent Basin, South Australia, In Cool Water Carbonates - SEPMSpecial Publication No.56, Society for Sedimentary Geology, Tulsa.

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THE SEDIMENTOLOGY OF THE DAAHL SANDSTONE, NORTH-WEST BLACK RANGE, WESTERN VICTORIA Matthew Keppich-Arnold School of Ecology and Environment, Deakin University, Rusden Campus, Clayton, Vic

The Daahl Sandstone (Member) is located within the Mount Difficult Subgroup in the Late Silurian Grampians Group, of the Black Range, Western Victoria. The Daahl Sandstone is a medium grained and quartz rich sandstone. The unit ranges between an approximate 10 to 20 metres in thickness and stretches for about 9 km in a north-south direction. At the southern boundary the unit is faulted out by the Marathon Fault, whereas the northern boundary comes into contact with overlying alluvium. The average dip within the Daahl Sandstone is between 5 and 20 degrees, to the west-north-west. There are limited sedimentary structures within the Daahl Sandstone, at the base of the unit there is extensive trough cross bedding, however, towards the middle of the unit large scale cross beds become dominant. The boundary at the base of the unit is marked by a flat surface, marking a possible break in deposition, whereas, the boundary at the top of the unit is dominated by skolithos burrows. The large scale cross beds suggest that the depositional environment of the unit is aeolian in nature, and would have occurred on the shoreface, most likely as a series of beach dunes. The fact that the overlying unit contains high numbers of skolithos burrows indicates a change in depositional environment, to a shallow marine environment.

REFERENCES: Cay ley, R.A. & Taylor, D.H. (1997), Grampians special map area geological report. Geological Survey of Victoria Report, 107.

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THE CRETACEOUS/TERTIARY BOUNDARY IN VICTORIA Alan D. Partridge Department of Earth Sciences, La Trobe University, Bundoora, Vic.

The extinction of the dinosaurs, possibly as the consequence of a meteor impact, has given the Cretaceous/Tertiary boundary a comparatively high public profile, but it has been little studied in Victoria, even though each of the three basins along the southern margin of Victoria contain thick sedimentary sequences extending from the Late Cretaceous into the Early Tertiary. In the Otway Basin all traditional stratigraphic tables show an unconformity centred on the boundary, whereas in the Gippsland and Bass Basins the boundary is known to lie within the non-marine to paralic Latrobe Group and the non-marine Eastern View Group respectively. Identification of the position of the boundary depends on palynology, as unfortunately calcareous planktonic foraminifera and nannofossils have not been recorded at this stratigraphic level in any of these three basins. Correlation using both spore-pollen and dinoflagellate cysts has been established with marine sections in New Zealand, where the boundary can be precisely located based on calcareous microfossils and the presence of the iridium anomaly. In the Gippsland Basin the boundary is identified in the lower part of the marine Kate Shale (new name), which occurs as a boomerang-shaped wedge 150 km long by 25 km wide, that approximately underlies the modern 80 to 100 metres bathymetric contours on the modern Gippsland Shelf. The formation varies from 5 metre thick at its northern and southern extremities to over 120 metres thick in the middle of the Central Deep. In a seaward direction the formation pinches out due to a combination of starvation and erosion by younger submarine canyons. Landward, the shale splits and interfingers with the sand, shale and coal facies on the coastal plain, with the approximate position of the Cretaceous/Tertiary boundary located by a major change in the spore-pollen assemblages. The Kate Shale represents the maximum Cretaceous marine transgression in the Gippsland Basin, and is also the seal for the principal reservoirs of the Flounder Field. Following the mapping of the Kate Shale in the Gippsland Basin, a similar unit was predicted to occur in the Otway Basin, and was subsequently located using palynology. This is the Massacre Shale (new name), identified on electric logs as a prominent shale below the sandstones of the Pebble Point Formation. It occurs in a broad arc extending from the Whelk-1 well, offshore from King Island, through numerous wells in the Port Campbell and Tyrendarra Embayments, to Caroline-1 in the eastern portion of the Gambier Embayment, and varies from about 5 to 26 metres thick. Similar to the Kate Shale, the Massacre Shale pinches out seaward due to sediment starvation and erosion, and also represents the maximum Cretaceous marine transgression in the Otway Basin. Equivalent shoreline and continental facies have been identified only in the northeastern portion of the Port Campbell Embayment, where the Massacre Shale is interpreted to be replaced by the Moomowroong Sand. As the latter unit is found in outcrop along creeks and rivers flowing from the western side of the Otway Ranges, it is likely that the Cretaceous/Tertiary boundary does occur in outcrop in Victoria. Successfully proving this hypothesis will depend on finding unweathered exposures suitable for palynological and other analyses. 26

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

occur in outcrop in Victoria. Successfully proving this hypothesis will depend on finding unweathered exposures suitable for palynological and other analyses. In the Bass Basin palynological data suggest that the Cretaceous/Tertiary boundary has been penetrated in only a few wells in the coal measure facies of the Eastern View Group, but it is not associated with any identified lithological change. These continental facies are interpreted to have been in connection with the Otway Basin via a river system extending through the Torquay Sub-basin and around the northern margin of the Otway Ranges into the Colac Trough. Now that the Cretaceous/Tertiary boundary has been demonstrated to occur widely in the stratigraphic record in Victoria, the next step is to identify suitable stratigraphic sections, with conventional core coverage or in outcrop, that could be investigated in more detail to locate the global iridium anomaly event. Conventional cores taken in exploration wells within the Gippsland Basin have potentially sampled the stratigraphic interval that should contain the iridium anomaly. As the latter is widely distributed in New Zealand, there should be no reason it cannot similarly be found in Victoria.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

GUADALUPIAN (MIDDLE PERMIAN) ARCTIC-TYPE BRACHIOPODS FROM THE MEADE PEAK MEMBER OF THE PHOSPHORIA FORMATION SOUTHEASTERN IDAHO, U.S.A: PALAEOGEOGRAPHICAL AND PALAEOBIOGEOGRAPHICAL IMPLICATIONS Weldon Elizabeth,A., School of Ecology and Environment, DeaJcin University, Rusden Campus, Clayton, Vic.

This study focuses on a collection of brachiopods from the Meade Peak Member of the Phosphoria Formation, Montpelier Canyon, Idaho, U.S.A. The Meade Peak Member is a cool-water deeper ramp facies, which transgressed over the carbonate bank in the Phosphoria Basin. The cool-water upwelling current in the region created conditions capable of phosphatic deposition. Investigation into the brachiopods' global and temporal distribution may reveal migration patterns, and the origins of the cool-water currents. The brachiopods currently identified include: the Arctic-type fauna IRhynoleichus sp. and Yakovlevia sp., and the bipolar genera ISvalbardia sp. and Costatumulus sp. The genus Yakovlevia has a short stratigraphical range, and is limited in occurrence. Plotting this data aids in the reconstruction of the palaeogeography and palaeobiogeography for the Middle Permian. Previous studies by Wardlaw into the biostratigraphical zonation of the Meade Peak Member using the ranges of important conodonts and brachiopods indicate that it is Roadian to Wordian in age. The brachiopod fauna in this collection can be correlated to some Permian Siberian faunas. In this way biostratigraphical data will assist in the determination of the relative age of the Siberian faunas for which there are no conodont elements to act as indicators. The most abundant brachiopod in the collection is IRhynoleichus sp. which shows morphological differences between the juvenile and adult specimens. Further study and a statistical analysis of these differences may assist in describing the ontogeny of the species. Each brachiopod species illustrates adaptations to individual niches through their morphological differences. This information enables the reconstruction of the palaeoecological environment. Key Words: Brachiopoda, Permian, Phosphoria Formation, Palaeogeography, Palaeoecology.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

3. ATMOSPHERIC AND OCEANIC SCIENCES Talks: pp 30-36 Posters: pp 37-40

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13'" Victo? 'ian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

MODELLING NORTH AUSTRALIAN PALEO CLIMATE Pandora Hope School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Has the climate of North Australia always been as it is today? Proxy data and external parameters such as changes in insolation can give clues to the past climates of Northern Australia, but may not give us the whole picture. One way to fill in the gaps is with a global atmospheric circulation model. In the climate of North Australia today most of the rain falls during summer, and the majority of the winds in January and August blow from opposing directions. In the mean, moisture arriving in North Australia arises from three sources - deriving in regions of high pressure - the Siberian high, a high in the southern Indian ocean, and a region of high pressure in the eastern Pacific. Were these source regions different in the past? Was the amount of precipitation different? Taking the last glacial maximum as an example, aspects of the modern climate system are modified to conditions implied from proxy evidence and external parameters. One aspect of the climate during the last glacial maximum that may have caused a large change in the climate of Northern Australia is the lowering of the sea level in the tropics. This change is implemented into the Melbourne University General Circulation Model, and it is seen that the mean circulation patterns remain similar, but the amount of available moisture and precipitation is reduced.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

A CLIMATOLOGY OF 500 hPA EXTRATROPICAL CYCLONES S. Murray Keable School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Forty years of 500 hPa geopotential height data have been used to compile seasonal climatologies of extratropical cyclones for both hemispheres. The 'finding' and 'tracking' of these systems was performed using an objective automated scheme (Murray and Simmonds 1991). Maps of the positions of formation (cyclogenesis) and decay (cyclolysis), together with other cyclone statistics are presented. In the Southern Hemisphere the distribution of 500 hPa cyclones was found to be fairly similar to that of surface level systems. System density was maximised in the circumpolar trough region and over the Antarctic continent. Velocities of cyclone centres were found to peak in the latitude band 50-55° S but notably 500 hPa systems appeared to move on average in a much more zonal (easterly) direction than their sea level counterparts. Highest rates of intensification, indicating developing cyclones, were found in the baroclinic zone near 50° S in the Indian Ocean. The deepest systems, on average, were found in this region along with north of the Ross Sea in winter. Much more regionality was exhibited in the results for the Northern Hemisphere than for the Southern Hemisphere. Certain preferred 500 hPa cyclone paths were evident but these varied considerably in geographical location with the seasons. The major orographic barriers appeared to play a large part in determining the behaviour of these systems. The average velocity of centres was maximised in two broad bands, over the western Pacific Ocean and in the northwestern Atlantic Ocean/eastern Canada region. Considerable agreement was found with previous Northern Hemisphere studies of 500 hPa extratropical cyclones (Parker et al. 1989, Bell and Bosart 1989).

Figure 1. Chart of 500 hPa geopotential height field for January 1, 1996 at 00Z with cyclone centres identified by the automatic scheme. 31

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

Figure 2. Map of all 500 hPa cyclone tracks for the summer (Dec./Jan./Feb.) of 1995-6.

Figure 3. The average system density for the Southern Hemisphere for winter (June/July/August). The contour interval is 0.5 cyclones/1000 degree latitude square.

REFERENCES: Bell, G.D. & Bosart, L.F. (1989), A 15-year climatology of Northern Hemisphere 500 mb closed cyclone and anticyclone centres. Mon. Wea. Rev., 117, pp. 2142-2163. Murray, R.J. & SimmondsJ. (1991), A numerical scheme for tracking cyclone centres from digital data. Part I: Development and operation of the scheme. Aust. Met. Mag., 39, pp. 155-166. 32

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3' Victor ian Universities Earth Sciences Conferences, The University ofMelbourne, September 1999 h

Parker, S.S., J.T. Hawes, S. J. Colucci and Hayden, B.P. (1989), Climatology of 500 mb cyclones and anticyclones. Mon. Wea. Rev., 117, pp. 558-570.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

A GLOBAL MODEL OF ISOTOPES IN ATMOSPHERIC WATER David Noone School of Earth Sciences, The University of Melbourne, Parkville, Vic.

It has been recognised for many decades that isotopic ratios reflect the environmental conditions under which they were deposited. The stable isotopic content of water (HDO and H2 1 8 0) trapped in the polar ice caps captures a unique climate history over many glacial/interglacial cycles. While isotopic data obtained from deep ice core drilling gives a broad understanding of shifts in the quaternary climate, the details of the complex behaviour of the atmosphere remains unknown. The use of numerical Global Circulation Models (GCM) in climate analysis has enabled diagnosis of many important atmospheric processes. As these models describe all aspects of the atmospheric flow they are an ideal basis for examining the behaviour of stable water isotopes on timescales from daily to millennial. While it has been demonstrated that even simple isotopic models can reveal much of the behaviour of isotopes in atmospheric water. Modeling the global cycle of isotopes can be achieved by applying these simple models at each phase change that occurs to individual air masses as they move from its source to the precipitation site. Slight differences in the molecular weight of the isotopic species leads to different saturation vapour pressures for each isotope. This results in a fractional change in isotopic ratios as the moisture changes state. Such a scheme has been fitted to the hydrologic cycle within the Melbourne University GCM. Figure 1 shows the annual mean distribution of H2 18 0 in precipitation from a 10-year climate simulation. As the efficiency of fractionation is dependent on temperature isotopic depletion is greatest in the high latitudes. Indeed the lowest isotopic values of around -45%o are seen over Eastern Antarctica in agreement with ice core data of - 5 2 % o . At the Antarctic coast, values are higher in agreement with measurements at Halley Station of - 2 0 % o . In the tropics the temperature dependence is less pronounced. Water

D J F - J J A v a r i a t i o n o f 2-8%o a n d g r e a t e r t h a n 8%o. 34

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999 th

temperature dependance for all model points.

relationship for all model points,

continually recycling inside convective cells, typical of the Western Equatorial Pacific, leads to a continued depletion of the isotopic species. This is revealed in the Figure as values of over -10%o near the highlands of Indonesia and the Amazon Basin. Similarly as an air mass moves inland over continental areas the heavy isotopes are successively removed preferentially producing the strong zonal gradients over landmasses. This is again consistent with the observations and other model studies although our model systematically underestimated the depletion aver the arid regions of southern Africa and Australia. Seasonal variations are also well represented. Summer (DJF) to- Winter (JJA) differences are greatest high latitudes where the temperature range is most largest (14%o in Antarctica, 12%o Greenland and Siberia). Oceanic regions show less variability reflecting the thermal inertial of the sea surface temperatures. The Figure shows variability over Northern Australia and Eastern Asia associated with the monsoon with isotopic values related with changes in the frequency of occurrence and strength of convective activity. In reconstructing past climate, isotopic content is used as a proxy for temperature. Figure 2 shows the H2 0 values as a function of modelled air temperature. The high correlation reflects the temperature dependence of fractionation efficiency. The slope is 0 . 5 2 % o / ° C compared to the observed 0 . 5 3 % o / ° C . This is reduced at higher temperatures and is consistent with theoretical estimates of isotopic values in tropical and oceanic region. The HD0/H2 0 ratio is considered to be almost constant for any condensation process that occurs at equilibrium. The model predicts this relationship (Figure 3) with a high degree of accuracy giving a slope of 8.1 compared to 8.0 for the Meteoric Water Line. Non-equilibrium effects are also well represented in the model with the global deuterium excess of 7.2%o compared to the expected 10%o. These results allow confidence that the model captures the basic features of both the spatial distribution and temporal variability of isotopes on annual timescales. Observational measurements of daily isotopic content are unavailable so it is not possible to directly assess the possibility that while the averaged results are reliable that smaller transient features may be unresolved by the isotopic scheme. Nonetheless the model is thought to be of great use for investigation of paleoclimate though linking the isotopic signals to the atmospheric flow characteristics. 18

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

THE SEMIANNUAL OSCILLATION IN A 40 YEAR NCEP REANNALYSIS Claire Yeo School ofEarth Sciences, The University of Melbourne, Parkville, Vic.

The Semiannual oscillation (SAO) in the Southern Hemisphere transpires throughout the depth of the troposphere and is distinguished at the surface by an expansion and weakening of the circumploar trough of low pressure surrounding Antarctica from March to June and from September to December and an contraction and intensification from June to September and December to March. The sea level pressure in the mid to high latitudes of the Southern Hemisphere shows a marked half yearly cycle with minima found in March and September. This SAO is understood to have its origins in the annual march of the tropospheric temperature differents between the southern oceans and Antarctic continent. Recent research has shown that the oscillation has undergone considerable variability over the last century. However the quality of the data upon the analysis of this phenomenon has been performed raises questions as to the real extent of the variabilty. The aim of this project is to document the SAO of mean sea lenel pressure and surface pressure in the National Centres for Environmental prediction/ National Centre for Atmospheric research (NCEP/NCAR) reanalysis set covering the 40 year period 1958-1997. These analyses represent our best understanding of the global atmosphere over this period. With these quality data the project compares the structure of the SAO with that revealed in earlier studies.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999 lh

SPATIAL AND TEMPORAL VARIABILITY AS REVEALED IN A 20-YEAR RECORD OF GLOBAL PRECIPITATION Mark Anolak School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Dr. P. Xie of the U.S. National Oceanic and Atmospheric administration (NOAA) has constructed a 20 year precipitation data set for the period 1979 to 1998. This project investigates the general trends and modes of variability as revealed in this data set. The large spatial and temporal variability of global precipitation makes it extremely difficult to produce an exact global precipitation climatology. More recently, Legates (1987) and Sharma (1997) have provided their own interpretation of the climatology of global precipitation, however, through the use of satellite and rain gauge measurements, along with numerical model predictions, Xie has constructed the best estimates of the averaged monthly precipitation over regions separated by 2.5° latitude and 2.5° longitude modern technology can provide. The data set has shown that about 63% of the global precipitation occurs within 30° of the Equator illustrating the dominance the ITCZ has over global precipitation. It also reveals that the global annual average is 2.6871 mm/day, which is somewhat less than Legates (1987) and Sharma (1997) previously thought (3.0767 mm/day and 3.0384 mm/day respectively). A strong seasonal variation over certain locations are obvious in the precipitation data with the annual migration of the ITCZ dominating. Figures calculated suggest a significantly decreasing trend in the annually averaged global precipitation records for the 20-year period. The annually averaged precipitation measurements have also strongly suggested an 11-year oscillation. Out of all the months, November displays the most significant drying trend of greater than 9% over this period. Through the use of the Principal Component Analysis (PCA), the main modes of temporal variability in the precipitation records have yielded that several regions are dominated by the annual cycle, whereas other regions are dominated by the semiannual oscillations along with temporal scales of less than half a year. REFERENCES: Legates, D.R. (1987), A Climatology of Global Precipitation. Publ. Climatology, 40 (1), 86 pp. Sharma, S.K. (1997), A New Digitised Global Precipitation Climatology and Comparison with Satellite and GCM Estimates. Ph.D. Thesis, School of Earth Sciences, The University of Melbourne, Parkville, 3052, Australia.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

APPLICATION OF AN AIR QUALITY FORECASTING SYSTEM TO THE MELBOURNE REGION Vaughan J. I. Barras School of Earth Sciences, The University of Melbourne, Parkville, Vic.

In preparation for the Sydney 2000 Olympic games, an urban air quality forecasting model is being developed and tested in Melbourne and Sydney. Know as the Australian Air Quality Forecasting System, it is currently running as a pilot system combining the LAPS (Limited Area Prediction System) forecasts with the CIT (California Institute of Technology) chemical model. Over the course of this year, an online version of this system is being established via a program of modification and refinement of the LAPS forecast model. As this progresses, model performance and forecast accuracy is being measured against observation collected for specific Melbourne and Sydney photochemical smog events. One of these events that occurred in Melbourne last summer will be presented with specific reference to the circulation patterns around Port Phillip Bay. Evaluation of the various forecast model representations of this episode will also be discussed with respect to ongoing refinements to the LAPS representation and the incorporation of a more complex chemical mechanism.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Unix>ersities Earth Sciences Conferences, The University of Melbourne, September 1999

FORECASTING RAINFALL FOR FIJI Lynette Gilbert School ofEarth Sciences, The University of Melbourne, Parkville, Vic.

Recently with funding from AusAID the National Climate Centre, in conjunction with the Fiji Meteorological Service produced a stand alone, PC-based, prediction scheme for Fiji seasonal rainfall. The FMS is currently making use of the new prediction scheme in the monthly weather summary. The scheme was proved to be well-suited for Fiji with higher skill levels than those presently obtained in Australia. Examined is the relationship between Fiji rainfall and the SOI focusing particularly on the resultant skill when the lead time for the forecast is increased. Presently the forecast is provided whilst already into the current predicted season. An increase in the lead time , if enough skill is retained would be a way of overcoming this. The results from extending the predictors from just SOI to an inclusion of Sea Surface Temperature from the NIN04 region will also be discussed. It is hoped that this additional predictor may provide an increase in the skill of the forecast.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3'h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

WAVES PRODUCED VIA CALDERA COLLAPSE James Gray Department of Mathematics and Statistics, Monash University, Clayton, Vic.

This poster will attempt to explain the generation of waves that occur during caldera collapse of a volcano. Numerical simulations and wave tank experiments will be shown for the case of a simplified model of caldera collapse, with extensions to a more realistic case also being presented. The production of tsunamis in this context have long been thought to occur, but the difficulties encountered due to a lack of evidence mean that it can is hard to pin down the precise generative mechanism of the waves. Hopefully accurate computations of the waves produced in a caldera collapse will enable us to gain a better understanding of volcanically initiated tsunamis.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

4. ENVIRONMENTAL SCIENCES Talks: pp 42-48 Posters: pp 49-53

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999 ,h

CHEMICAL HYDROGEOLOGY OF THE MINERAL WATERS OF THE CENTRAL HIGHLANDS, VICTORIA Douglas Ahearne School ofEarth Sciences, The University of Melbourne, Parkville, Vic.

This study investigates the mineral waters found in the Daylesford region of the Central Highlands, Victoria. The major ion composition, field parameters, stable isotope values, radium concentrations, and flow rates have been used to investigate the hydrogeological system. The five mineral springs included in this study are Ballan (Northern and Southern springs), Hendersons, Jubilee Lake, Vaughan (Jim Paull), and Korweinguboora. Three of the springs are north and two of the springs south of the Great Dividing Range, which is the recharge area for the mineral springs region. The springs included in this study occur on an approximately north - south line. For the springs included in this study, it is approximately 50 kilometres from the northernmost spring in this to the southernmost spring. The mineral waters are slightly acidic, with pH values ranging from approximately 6.1 to 6.7. Electrical conductivities range from approximately 1.6 to 2.8 mS/cm. Water temperatures are low, ranging from 10 to 16°C. Eh values range from approximately 20 to 90 mV. Bicarbonate and carbon dioxide gas levels are greater than lOOOmg/L for all of the minerals springs except Vaughan, which has anomalously low values. For Vaughan, carbon dioxide gas levels are approximately 650 mg/L and bicarbonate concentrations are approximately 570 mg/L. Major ion analysis of the mineral waters shows that they are predominantly Na - HCO3 type waters. The waters also have high concentrations of Ca. In some cases the concentration of Ca approaches the concentration of Na. Comparisons with historical data shows a general consistency in chemical composition of the springs over a twenty year period. However, comparison with historical data shows some minor fluctuations in element ratios and concentration of elements at some of the springs. The major ion composition of the springs shows some regional variation. Whilst retaining the characteristics of a mineral water, each of the springs has a unique chemical composition. This suggests that each spring has a discreet flowpath through the fractures of the Ordovician aquifer. Springs to the north and south of the Great Dividing Range show some differences in major ion composition. The springs south of the Great Dividing Range have higher Na concentrations relative to Ca and Mg. To the north of the Great Dividing Range the springs have higher Ca concentrations relative to Na and Mg. The spring and surface waters have been analysed for several stable isotope ratios. These include 5 0 , 8 H, and 8 CC0 as. These isotopic ratios can be used to indicate the source of the water, the processes affecting the water after infiltration, and the source of CO2 gas in the water. The 8 13 CC0 gas values for the spring waters range from -8.1%o to -9.9%o. These values indicate an igneous source for the CO2 gas. All except one of the mineral springs have 5 0 and 8 H values that lie to the left of the global and local meteoric water lines. It is unusual for waters to plot in this position. Given the high carbon dioxide content of the spring waters it is likely that CO2 exsolution has lowered the 5 0 values of the mineral water. The mineral spring I8

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

that has 5 1 8 0 and § 2 H values that plot on or very near to the global and local meteoric water lines has much lower CO2 levels than the other springs. The waters from this spring are either too low in C 0 2 to lower the 5 1 8 0 values or have been mixed with surface water or shallow groundwater. Samples for radium analysis were collected for Vaughan, Hendersons, Ballan (southern spring), and Jubilee Lake. The Radium - 226 values range from 0.19 to 1.20 Bq/L. The Radium - 228 values range from 0.22 to 1.42 Bq/L. It has been possible to measure the flow rates for two of the spring outlets. By comparing this with local rainfall data a correlation between flow rate and rainfall has been observed. An increase in rainfall is accompanied by an increase in flow rate. This can be explained by an increase in pressure on the flow system from the increasing infiltration.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3'h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

ARSENIC CONTAMINATION OF GOLD-MINE WASTEWATER, CENTRAL VICTORIA Susanna Finger, Department of Earth Sciences, La Trobe University, Bundoora, Vic.

At a central Victorian gold mine, water pumped from underground workings has been found to contain concentrations of iron (Fe) and arsenic (As) above EPA recommended levels. The water is treated by passing it through an aeration tower; oxidizing ferrous iron to ferric iron, which precipitates as poorly crystalline ferric oxy-hydroxide. The precipitate is trapped in three settling ponds, before delivery to a large siltation dam from which it travels to a wetland. Arsenic in the mine water is removed by adsorption onto the Fe-oxyhydroxide, and this process has worked consistently for much of the mine's history. In recent years, however, elevated arsenic levels have been detected at the siltation dam outlet, necessitating additional water treatment (mainly through dosing with ferrous sulfate to increase the Fe:As ratio). The main aim of this study was to identify how and why arsenic remobilization was occurring, and suggest ways of overcoming the problem. Water samples were collected from eight sites within the water treatment system at the mine, from well head to discharge from the site, at monthly intervals from February to July. In this study arsenic was analyzed as As(III) and total arsenic [As(Total)]. Concentrations of As(Total) vary from 0.20 to 2.12ppm; As(III) generally represents 10-20% of this (0.02 to 1.02ppm). In general, As(Total) decreased through the system, and this observation is consistent over time. However, there was an increase in As(Total) between sites 5 and 6 (i.e. in the siltation dam), with the magnitude of this increase decreasing from February to May, so that it was absent in June and July. (Figure 1.0) 2.5

II p, | I

2.0

!S19 I 00

1o „.s O.O

The concentration of As(III) mirrors that of total As, showing a consistent decrease through the system and increase in concentration in the siltation dam over summer. From the results obtained the main area of arsenic remobilization has been determined as the Siltation Dam. This dam has a maximum depth of 9-10m in the centre, and over summer the dam water becomes stratified, with a reducing layer 44

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13'h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

From the results obtained the main area of arsenic remobilization has been determined as the Siltation Dam. This dam has a maximum depth of 9-10m in the centre, and over summer the dam water becomes stratified, with a reducing layer developed below 7m over a relatively limited area in the dam centre (Table 1). The development of this stratification in the dam matches the increase in As levels in the dam water, and the two factors are probably related. Table 1.0: Dissolved Oxygen Content of Water at Depths in Dam, representative of Stratified Reduced Layer: Dissolved Oxygen (April) 8.03mg/L 0.85mg/L

Depth (in centre of dam) 6m 9m

Dissolved Oxygen (July) 10.84mg/L 9.96mg/L

The main mechanism for As remobilization in the dam would appear to be the release of As from Fe-oxyhydroxides among the sediments on the floor of the dam, due to dissolution of these minerals in the reducing bottom water when the dam is stratified over summer. It is known that Fe-oxyhydroxides dissolve in reducing conditions and particularly at the sediment-water interface. Any adsorbed As would be released as a result of this dissolution. Despite the reducing conditions, both As(III) and As(V) are remobilized by this process, accounting for the fact that the As in the siltation dam water contains only - 2 0 % As(III). Presumably, the As diffuses upwards from the bottom reducing water in to the main body of the dam. The seasonal nature of the increase in As can be readily explained by the fact that stratification is seasonally controlled, the colder month's cause mixing of the dam waters, effectively ending the presence of the reducing bottom water. A high magnitude rise in As at the time of mixing was not identified, either because the short-lived peaks occurred between sampling dates, or because the oxidizing potential of the water was sufficient to cause the immediate re-precipitation of Feoxyhydroxides (and hence adsorption of As) when mixing occurred. A simple, inexpensive remedy to the problem of As remobilization in the siltation dam would be the positioning of an air bubbler on the floor of the deepest part of the dam. This would then be used to oxygenate the bottom waters, preventing water stratification. REFERENCES: Pierce M. L. & Moore C. B. (1982), Adsorption of Arsenite and Arsenate on Amorphous Iron Hydroxide; Water Research 16, 1247-1253

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

LATE QUATERNARY/HOLOCENE DUNE BUILDING AND PALAEOSOL FORMATION - KING ISLAND V SOUTH EASTERN AUSTRALIA Sanja Van Huet Earth Science Department, Monash University, Clayton, Vic.

Depositional sequences in dune deposits on King Island (Bass Strait) have preserved evidence for climate related changes since the last glacial period (approx. 26,000 ybp. oxygen isotope Stage 2). The changes appear to correlate with climatic fluctuations during the late Quaternary/Holocene. In particular, a superpositional sequence of five palaeosol horizons, exposed in a dune blow out at Pass River on the northwest coast, may prove to be significant in the assessment of environmental "twitches" over the last 6,500 years. Results from C 14 dating (ANSTO #OZD 567-571) suggests that the formation of the palaeosol horizons was not related to seasonality, but to larger scale climatic changes linked to climatic oscillations during the Holocene. The average interval between each horizon is approximately 500 years. At other sites, where C14 dating was not as informative, sediment analysis has revealed significant differences in grain size and sorting, suggesting differing depositional regimes - again related to climate. Dune horizons that reveal a higher content of shelly/calcareous material and larger overall grainsize are inferred to have been formed during episodes of warmer climate, when the air/surface temperature inversion would have been more pronounced, generating stronger and more intense winds. These winds would, in turn, generate larger and more powerful waves which would 'dredge' large quantities of shell material from a greater area of the ocean floor and transport them to shore to be accumulated within the dune horizons (Jim Bowler, pers. comm.). Dune horizons that had a higher percentage of silicious material were inferred to have formed during periods of more moderate temperature inversion (and therefore wind and waves of less intensity) where the reworking of older sediments, especially those closer to shore, would result in a concentration of silicious material and the destruction of calcareous material. This alternation in the character of the dune building material prima facie correlates with Holocene fluctuations observed in south-eastern Australia and in precipitation levels recorded for Lake Keilembeite. The consequences of alternation of climate is currently being assessed.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3' Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999 h

THE TRUCK'S BOGGED AGAIN: CATCHMENT SEDIMENT STORAGE AND ARID-ZONE FLUVIAL INSTABILITY Gresley Wakelin-King Department ofEarth Sciences, La Trobe University, Bundoora, Vic.

Fowlers Creek rises from the Barrier Ranges in western NSW, and flows NE for 55km. It terminates amongst the dunefields and dry swamps bordering Lake Bancannia. The climate is arid, with potential evaporation fully 13 times the annual rainfall. Vegetation is sparse and low except for the clusters of red gums along the creek banks. The aim of my thesis is to describe the geomorphology and sedimentology of the creek in order to understand what processes operate within it; and focussing especially on those processes that make arid-zone creeks different from "normal" (ie temperate-zone) creeks. Techniques used include surveying (EDM, stadia, and GPS geodetic), sediment granulometry, OSL dating, and lots of oldfashioned boots-&-hammer field observations. The idea behind geomorphology as an indicator of fluvial process is that the shape of each river will be formed in response to its flow conditions: slope, sediment load, volume and speed of water, and so on. Any river's slope, channel cross-section (shape and size), channel planform and floodplain character result from a complex web of feedback systems. If a river is in dynamic equilibrium, the inter-relatedness of these systems can be demonstrated by the mathematical relationships measured within a system: for example, along a river's length, cross-sectional area A will be found to be proportional to discharge Q (A= xQ , where x and y are empiricallyderived constants). So investigations in a river system can be quantitative (surveying) as well as qualitative (observed geomorphology). What would we expect to find, in an equilibrium "normal" (temperate-zone) creek? We would expect to find that discharge would systematically increase downstream, with concomitant regular increases in channel width and depth. Slope would be concave, steeper at the top & more gentle towards base level; on a reach scale the river would slope downhill towards base level. Sediments would be coarser at the top and become finer downstream. The river's planform would be braided, straight or meandering according to the coarseness and abundance of its sediment load (among other things). And, naturally, water would flow from the top of the system, and keep flowing until base level, with little change in density along the way. Arid zone rivers are not merely dry versions of "normal" rivers: there are profound differences. • Rainfall is strongly variable in time and quantity, so that long periods of drought may be broken by anything from a sprinkle of rain to a mighty downpour. • Rainfall is variable spatially. Part of the catchment may receive no rain, while other areas receive major rain. • Landscapes may be changing slowly, since the onset of aridity has decreased tha availability of the major agent of geomorphic change (water). • Compared to temperate areas, vegetation is sparse on the slopes and floodplains but more common within the channel. As a result, arid-zone rivers are characterised by extreme variability of discharge, and sometimes exceptional channel roughness. Flow does not necessarily start at the top, y

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3' Victorian Universities Earth Sciences Conferences, The University> of Melbourne, September 1999 h

nor does it often go to base level. Discharge increases as you go downstream, up to a point; then it deceases again until flow ceases. The points of major discharge and flow cessation may be anywhere in the creek; grainsize varies accordingly. Water density may increase dramatically as sediment-rich flows lose water; this has implications for turbulence and bed shear stress. Arid-zone rivers are likely to be in disequilibrium on a reach and a landscape scale (due to rainfall variability, and slower geomorphic process respectively). Data analysis of this study is continuing, and results of the surveying are incomplete. However I expect that figures for slope, cross-sectional area and so forth to compliment the following deductions derived from field observations: • Fowlers Ck is divided into 3 sections, the upstream catchment, the middle trunk which is confined by outcrop, and the downstream distributary fan. • The trunk and fan sections display regular relationships appropriate for arid-zone creeks - as distance downstream increases, cross-sectional area and width to depth ratio decreases (the reverse of "normal" creeks), as does grainsize; the planform becomes increasingly sinuous. • Catchment, trunk and proximal (less sinuous).fan are anabranching in planform (multiple channels divided by stable vegetated bankfull-height islands). • In the catchment, upstream of the bottleneck formed by the trunk section, large amounts of sediment are held in disequilibrium catchment storage. • In the catchment, relationships between downstream distance, slope, channel planform and channel cross-section size and shape are extremely irregular. In particular, where floodplains are storing particularly large amounts of sediment (a "bulge") the channel becomes more and more shallow, with increasingly poor bank definition, until it vanishes entirely, leaving only floodplain. The channel reestablishes itself further downstream. • The floodplain of the creek acts as the channel during very high flows. However floodplain "bulges" may be above flood levels, giving them stability at the crest; but the up- and downstream edges of the bulges are areas of increased and unpredictable geomorphic activity. The volume of sediment in catchment storage suggests that the creek is in the process of seeking a new equilibrium in response to new conditions. This is supported by observations of bank stratigraphy which indicate a previous more high-energy regime. Possible causes for this change are: • gradual transition from a wetter climate; • a sudden change in hydrological conditions after European settlement; or • recovery and floodplain construction after a megaflood. Optically-Stimulated Luminescence dating will address this question. So who cares? Continental Australia is 70% arid. "Normal" creeks are not normal here. Understanding current arid-zone fluvial processes is a crucial first step in effective land use planning and infrastructure design. Knowledge of the historical causes of landscape change is equally important in understanding and fixing land degradation. Finally, if future climate change brings increased climatic variability to the inland, it will be very desirable to be more familiar with megaflood paths and processes. 48

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13*h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

CHARACTERISATION OF VEGETATION AND PHYSIOCHEMICAL CONDITIONS OF TAILINGS AT ABANDONED TIN MINE SITES IN NORTHEAST TASMANIA Rachael Bennett Department of Earth Sciences, Monash University, Clayrton, Vic.

Monarch, Star Hill and Endurance are three of the abandoned tin mines in the Gladstone region of northeast Tasmania. The mine wastes (mainly tailings), which cover their surfaces, provide a source of contaminants to ground and surface waters. These wastes are also the substrate available to plants and not surprisingly many areas are only sparsely vegetated. In order to remediate the sites by revegetation it is important to understand the existing plant life and the geochemical conditions under which they exist. More specifically we aim to understand: the existing vegetation on the mine sites and their surrounding areas; the physical and chemical properties of sediments on and around the mine sites; the physical and chemical conditions that prevent or enhance plant growth on the mine sites; what rehabilitation (revegetation) strategies may be most effective. The Gladstone region supports a mosaic of sclerophyll, scrub and heath communities. The dominant eucalypts are E.amydalina and E.viminalis. Other common species include, Leptospermum scoparium, Kunzia ambigua, Banksia tnarginata and many grass-like plants of the Cyperaceae family. The plant cover ranges from 1-2% in some areas of the mine sites up to >90% at some established sites. An established site being one that shows no obvious signs of recent disturbance. Species richness (the number of different species present) does not differ between established and mine sites. Species diversity (Calculated) was found to be slightly higher at established sites than at most mine sites. Preliminary results of a number of physical and chemical characteristics of the waters and sediments have been obtained. The results indicate pH values ranging between 2.62 and 6.87 in surface and ground waters; the lowest of these are at the Endurance mine site. Soil pH ranges from 4.47 to 5.41 at both mine and established sites demonstrating that soils in the Gladstone region are naturally acidic. Preliminary results for soil nutrients have shown that total nitrogen levels are below detection limits at mine sites (<0.01%) and range from 0.06 to 0.924% at established sites. Available phosphorous ranges from 0.15 to 0.4mg/100g, with lower concentrations present at the mine sites than established sites. Most of these phosphorous concentrations are lower than typical ones in non-impacted areas. Water erosion, including sheet and gully erosion, is evident especially at exposed sites. Other physical soil characteristics including soil impedance and infiltration rates vary both within and between sites, although variation is greater at the mine sites than at established sites. Both visual and chemical differences are present between the different mine sites and established sites. With results obtained from chemical analysis of waters and sediments it is hoped that any characteristics affecting vegetative growth will be identified so that suitable remediation techniques can be recommended.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victor'ian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

3D COMPUTER MODELLING OF GROUNDWATER FLOW SYSTEMS IN THE LAKE CORANGAMITE-BARWON RIVER REGION Michael J. Blackam University of Ballarat, Vic.

Located in the Western District Volcanic Plains of Victoria, the 240 square km. study area contains wetlands of national and international significance. The numerous shallow saline and hypersaline lakes (typically ephemeral, and 'windows' to the water table) have developed in response to recent geomorphic processes. These include Lakes Beeac, Cundare, Weering, Martin, and Lough Calvert. Permanent saline lakes with larger catchments include Lake Corangamite (Australia's largest permanent water body- 23,000 ha) which lies within a basin of internal drainage, fed by the Woady Yaloak River. Lake Murdeduke (1,500 ha) further to the east and within the Barwon River Basin, may be a remnant of a formerly much greater Lake Corangamite as hypothesised by Currey (1964). Lake Colac (2,700 ha) is the only significant freshwater body in the study area. Artificial controls on the wetlands include the Woady Yaloak River Diversion Scheme, implemented following flooding in the 1950s, which aims to regulate water level in Lake Corangamite to a 'normal' value of 114.7 metres AHD. During operation of the scheme river water, together with it's salt load, is diverted overland to the Barwon River Basin via a channel and discharged into a tributary of the Barwon River. The nearby Lough Calvert Drainage Scheme reduces flooding of pastoral land by controlling water levels in the Lough Calvert system of ephemeral lakes and swamp. Lake Colac levels (when high) are also controlled by discharge through Lough Calvert. The Woady Yaloak Diversion Scheme, though effective for its intended purpose (minimising lake surface area fluctuation due to level changes), has caused a progressive increase in the salinity of Lake Corangamite by evaporative concentration, to the detriment of ecology. Furthermore, the diversion of Woady Yaloak River water places additional pressure on Barwon River water quality. Allowing lake levels to increase can reduce these environmental pressures, but only at the loss of significant pastoral land. As well, high water tables accompany high lake levels, thereby aggravating the dryland salinity problem which is extant in the region. A three layer unconfined groundwater model was constructed using Groundwater Vistas software as a pre-processor for Modflow (a modular 3D finite-difference groundwater model). Layer distinction within the model is based on geology, which has been explicitly modelled from topographic and geological maps, as well as bore logs for subsurface geology. Contoured grid files of elevation created using Surfer software were input to define the tops and bottoms of the 500 metre square discrete cells. Lake Corangamite is modelled as a constant head boundary (to the west) as are the Leigh and Barwon Rivers which form the eastern boundary. A general-head boundary to the north allows for groundwater inflow due to the regional gradient. No-flow cells define model boundaries at the limits of the aquifers, which includes much of the southern boundary. Zone defined parameters such as hydraulic

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 jjth Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

conductivity (k x , ky? k z ) and storage (Sy) are assigned according to relevant geology. Data for recharge and evapotranspiration zones were derived from contoured meteorological data to satisfactorily reflect variation across the region. Irrigation pumping is modelled as a system stress during transient simulations. The model contains 28,800 cells, of which 20,179 are active, the remainder representing no-flow zones. Both steady-state and transient conditions were simulated, during which Modflow achieves convergence (i.e. solves the equations for heads in cells) using iterative processes. Transient simulations (which predict head distributions over time) are divided into 'stress periods' during which varying conditions such as recharge and evapotranspiration remain constant. The stress periods in turn are subdivided into discrete time steps. Starting heads for the transient simulation are derived from a steady-state simulation. Modflow saves both head and cell-by-cell flow data to files. Contour plots (fig. 1) and colour flood plots can be created from the saved head files, whilst cell-by-cell data can be used to compute a mass balance, and to plot velocity vectors of groundwater flow. Preliminary results appear to confirm an eastward flow of groundwater from Lake Corangamite toward Lake Murdeduke, as well as substantial [saline] flows from the south-east into the Barwon River. The latter supports previous studies (e.g. Sinclair Knight Merz, 1997) that the increase in salinity of the Barwon River between Winchelsea and Shelford is due to a large influx of highly saline groundwater from the Murdeduke region. It is unclear at this stage whether hypothesised groundwater flows from the Lake Corangamite Basin to the Barwon River Basin actually occur.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

REFERENCES: Currey, D. T. (1964), The Former Extent of Lake Corangamite. In Proceedings of the Royal Society of Victoria, vol. 77. Royal Society of Victoria, Melbourne, pp. 377-387. SINCLAIR, KNIGHT & MERZ Pty Ltd, (1997), Groundwater Processes in the Lake Murdeduke Bcirwon River Area. Corangamite Salinity Implementation Group. ACKNOWLEDGMENT: The Corangamite Catchment Management Authority have provided funding assistance for this project.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13*h Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

GEOLOGICAL CONTROLS ON THE MORPHOLOGY OF THE BELLS BEACH TO POINT ADDIS REGION Juliana Roadly School of Ecology7 and Environment (Earth Sciences), Rusden Campus, Deakin University, Clayton, Vic.

Point Addis and Bells Headland (South Side) is a 5 kilometre coastal fringe within the Northwestern onshore section of the Torquay Basin. The location is well known for its heavily slumped and vegetated coastal cliffs, its well-exposed headlands fronted by shore platforms and poorly developed sand dunes. Outcropping strata are composed of Upper Oligocene to Miocene marine sediments formed in varying palaeoenvironments. Between the two exposed Upper Oligocene Limestone headlands and shore platforms of Point Addis and Bells South Side, lies a broad intermediate beach named Addiscott. Shear coastal cliffs and slump zones made up of soft silty carbonaceous and heavily burrowed quartz sands, of the Upper Eocene to Lower Oligocene Anglesea Sand, back the beach. This formation underlies the mottled red to yellow ferruginous sandy clays and occasional conglomerate beds of the Lower Oligocene Angahook Formation. Jarosite Headland, a well-exposed resistant point along the coastline, divides Addiscott Beach in two sections. The shear cliff face at Jarosite Headland is made up of Angahook Formation sediments above heavily jointed Anglesea Sand. At the base of the Headland, the near shore rock platform material is mainly derived from the sands and clays of the Angahook Formation. The Limestone Headlands, such as Point Addis, predominantly consist of hard cemented and soft uncemented calcareous sediments of the Point Addis Limestone. Wave action undercutting the cliff faces is evident at various levels reflecting seasonal variations in tides and storm activity. Complex jointing structures made up of parallel sets in three directions are found within the limestone formations, create planer zones of weaknesses with in the rock faces. Joints within the Anglesea and Angahook formations show toppling failure along these joint planes leads to extensive erosion via block falls, creating shear cliff faces. The secondary minerals jarosite and gypsum fill the joint planes within the Anglesea Sand areas. Within the Angahook Formation, secondary mineralization of jarosite, gypsum and limonite also occurs along the joint planes as well as concentrated along some beds within the formation. Major landslides occur in-between the headlands and show evidence of being predominantly caused by instability within some beds of the Angahook Formation. Failure is on a much larger scale than at the headlands and is partly along relatively low angle slide planes. The rupture surface is along unconsolidated sand and conglomerate beds above which sits laminated clay beds.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 th

5. ECONOMIC GEOLOGY AND GEOCHEMISTRY Talks: pp 55-60 Posters: pp 61-69

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13lh Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

HIGH DEFINITION GRAVITY SURVEYS FOR KIMBERLITE EXPLORATION T. I. .Allen Department of Earth Sciences, Monash University, Clayton, Vic.

Gravity data obtained at Hiles Lagoon, near Terowie, indicates the presence of a subtle gravity low, within a strong north-westerly trend of decreasing gravity. The small gravity low over the lagoon possesses roughly circular dimensions with a diameter of approximately 200 m and is the likely response of a concealed kimberlite pipe. These results are of particular interest since previous aeromagnetic, radiometric and geochemical exploration have had little success in detecting a kimberlite pipe at Hiles Lagoon. Density determinations typical of kimberlites and shales from the region, were employed to create a structural model of a kimberlite pipe and the surrounding country rock. Resulting gravity raster images from the kimberlitic model allow us to confidently interpret the field response as a kimberlite pipe and justify the application of the gravimetric technique for exploration in the region.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

THE ORIGIN AND CHARACTERISTICS OF THE DUGALD RIVER ZN - PB - AG DEPOSIT, NW QLD. Lorna Campbell, School of Earth Sciences, The University of Melbourne, Parkville, Vic.

The Dugald River Zn-Pb-Ag deposit is located within the Eastern Fold Belt of the Mount Isa Inlier, north-west Queensland. It has been extensively drilled and delineated by several mining companies since it was first recorded in 1881, although has yet to be mined due to a high manganese impurity occurring within the sphalerite. Current resource estimates are 50Mt at 12.1% Zn, 1.9 %Pb, 41g/t Ag. The tabular deposit is hosted by a graphitic slate unit within a thicker package of laminated and massive slates that have been strongly sheared and metamorphosed to upper greenschist facies. It is expressed at the surface as a gossanous horizon with a strike length of 2.5km and a width of approximately 8m. It also displays a distinct vegetation anomaly due to increased zinc levels in the soil. The close association of faulting to the deposit has led to years of intense debate as to whether the deposit is a stratiform, sedex type, or essentially just a mineralized fault zone. Field work and 3D computer modeling has established the stratabound nature of the deposit, confined to the same stratigraphic horizon of the black slate package along its strike length. However, it also emphasizes the strong influence of faulting and shearing on the remobilization and distribution and of metals within the lode horizon. Petrographic analysis of the ore types indicates a primary pyrite phase and possibly a primary sphalerite phase within the graphitic shale, with strong evidence for remobilization and recrystallization during deformation. Late coarse grained sphalerite, pyrrhotite and galena are also associated with quartz and/or calcite veining, brecciating and contorting laminated slate clasts, with all phases overprinted by coarse pyrite clusters. In areas of intense shearing, extensive clast rotation has occurred, resulting in rounded quartz and slate clasts in a fine - grained annealed sulfide matrix. The bulk of the evidence appears to support a sedex type origin for the Dugald River deposit, with strong remobilization during deformation leading to the ore textures, metal distribution and lode shape observed.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

THE USE OF PARTIAL LEACH TECHNIQUES IN EXPLORATION GEOCHEMISTRY: MIITEL MINE AREA, WIDGIEMOOLTHA DOME, WESTERN AUSTRALIA Leigh McDonald Department of Earth Sciences, Monash University, Clayton, Vic. Victorian Institute of Earth and Planetary Sciences (VIEPS)

Partial leach geochemical techniques may be to able detect mineralisation at depths greater than 1000 m through most types of barren overburden, transported or otherwise. This is useful in trying to find ore deposits in areas such as the Kambalda region where significant mining over the last thirty years has depleted the shallow nickel sulphide ore bodies and exploration is now focussing on targets at significantly greater depths. The basis of the partial leach techniques is to measure the concentrations of trace elements that have migrated from depth (i.e., the ore body) and have become bound to material near the surface. Partial leach techniques can be designed to target organic material and iron and manganese oxyhydroxides. Only a specific part of the sample is dissolved, the nature of which is dependent on the type of leaching solution that is used. Enzyme leach solutions attack material attached to amorphous manganese oxides and is the most specific of the partial leach. This technique has provided the most promising results from surveys in the Kambalda region. The aims of this project are to understand how effective partial leaches, particularly enzyme leach, are in detecting geochemical anomalies in the regolith, to provide comparisons of the anomalies observed between different leaching techniques and determine an optimal sampling strategy. Optimising the sampling strategy involves determining the optimum sample spacing, line length, sample material and the importance of sample depths, relative to the regolith profile, determine whether sulphidic sediments produce an anomaly and whether it is distinguishable from the ore anomalies. The site selected for this study is the Miitel mine area, on the eastern flanks of the Widgiemooltha Dome. This area was selected on the basis of a strong enzyme leach response in previous studies, the geological and geochemical characteristics of the ore shoot, and the very high exploration potential of that area of the Widgiemooltha Dome. Soil and sediment samples were collected every 20m and 40m along 800m transects across the ore body. Samples were also collected at different depths in relation to regolith horizons. Partial leach geochemistry techniques that have been applied during the project include the patented Enzyme Leach technique and a number of non-commercial analytical techniques designed to extract elements from specific fractions of the solid materials. The other techniques included adsorbed and exchangeable elements (0.1m nitric acid), amorphous Fe and Mn oxide solids (0.1m hydroxylamine hydrochloride) and carbonate minerals (sodium acetate), in addition to a simple extraction using deionised water. All extracted solutions were analysed using conventional ICP-MS or ICP-OES techniques. 60 elements were analysed in the Enzyme Leach extractions with ranges in concentration from below detection limit to approximately 10,000ppb. Based on preliminary interpretation of graphs of concentrations versus distance, there are distinctive anomalies evident across the ore body. The preliminary results indicate that partial leach techniques are an effective exploration tool. Continuing work on 57

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

this study will include examining the effectiveness of alternative and simpler partial leach techniques, statistical analysis of the geochemical data and increasing our understanding of element mobility in sediments and groundwater.

GEOLOGICAL SOCIETY OF A USTRAL1A, ABSTRA CTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September J 999

GEOLOGY OF THE KUTARTA ZINC-LEAD DEPOSIT, LENNARD SHELF, WESTERN AUSTRALIA Adrian Pittari School of Earth Sciences, The University of Melbourne, Parkville, Vic.

The Kutarta Mississippi-Valley-Tvpe (MVT) deposit, located on the Lennard Shelf, Western Australia, contains 2.1 Mt at 7.5% zinc, 0.3 % lead and 30 g/t silver (Wilson 1999). A late Givetian to early Frasnian retreating carbonate platform interfingering with marginal slope and basinal facies forms the main stratigraphic sequence. The Cadjebut Fault, a major basinal structure, separates this sequence from underlying Ordovician shale (Fig. 1). Strongly dolomitized platform limestones play host to the main mineralized pods. Mineralisation is generally stratabound and occurs in the hanging wall of the Cadjebut Fault. (Fig. 2) The host rocks have been altered to silty matrix breccias, which appear to have formed, by hydrothermal karsting. Matrix and clast replacement and breccia cements are the dominant mineralisation styles. Mineralized veins, cavities and minor fault breccias are also present. The simple mineralogy consists of sphalerite, galena, marcasite, minor pyrite, calcite and dolomite. Although an MVT deposit, the style of mineralisation has many features in common with the lead-zinc deposits in Ireland.

Figure 1. Typical stratigraphic sequence and structure at Kutarta 59

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

REFERENCES: Wilson, N., 1999. A review of drilling, geology, mineralisation and structures at Kutarta.. Western Metals Ltd, unpublished.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 I3,h Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE HYDROTHERMAL GEOCHEMISTRY OF COPPER CHLORIDE SPECIES FROM 20-300 C Jay BlackJ, Joel Brugger1, D.C. "Bear " McPhail1 and Leone Spiccict2 Departments of1 Earth Sciences and Chemistry Monash University, Victorian Institute of Earth and Planetary Sciences (VIEPS).

Copper chloride speciation is important for copper transport in hydrothermal systems; however, little is known about the thermodynamics of the important complexes. Copper can exist in hydrothermal solutions as oxidised (cupric) and/or reduced (cuprous) forms. Cupric chloride spectra were measured using ultraviolet (UV) spectrophotometry at 25, 60 and 90°C. Figure 1 shows example cupric-chloride UV spectra measured at 25°C and 0.005m to 18m LiCl. The changes in the spectra indicate different copper complexes as the chlorinity changes. The spectra were fitted using principle component analysis to determine the number of complexes necessary to describe the data. Secondly the molar absorbance spectra (Fig. 2a) and the distribution of the species (Fig. 2b) were fitted to the data using a chemical speciation model and a least squares method. At least five species are required to explain the Cu(II) spectra and a clear change in coordination is seen in the spectra from the single peak of CuCl+ (-40000cm' 1 ) to three absorbance peaks of CuCl42" (-26000, 36000, 42500cm'1). In another set of experiments, cuprous chloride spectra were measured at 20, 40, 60 and 80°C and 0.3m to 17m LiCl. Oxidation of the copper was minimised by bubbling nitrogen through deionised water for 2 hours, followed by hydrogen for one minute, and preparing the copper solutions under a nitrogen atmosphere in a sealed glove box. The measured spectra still show signs of oxidation (less than approximately 10% of the total copper), making quantitative interpretation of the spectra difficult; however, the results suggest two or three Cu(I)-chloride species. The results show that copper can be transported effectively in hydrothermal chloride brines and will allow us to predict the solubilities of copper-bearing minerals in ore-forming environments. Future work will include extension of the measurements to higher temperature (up to 300°C) using a newly designed high-temperature cell, improvement of the quality of the Cu(I) spectra and application of the experimental results to ore-forming environments.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

Figure 1: Cupric chloride spectra at 25°C.

Figure 2: Deconvolution of Cu(II)-chloride spectra a) molar absorbance b) cupric species distribution.

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GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

AN EXPERIMENTAL STUDY OF CUPRITE SOLUBILITY IN AQUEOUS NACL SOLUTIONS BETWEEN 50°C AND 250°C AND SATURATED WATER VAPOR PRESSURE Weihua Liu Victorian Institute of Earth and Planetary Sciences (VIEPS) Department of Earth Sciences, Monash University,Clayton, Vic.

The geochemistry of copper in hydrothermal solutions is poorly known, despite its importance in controlling the transport and deposition of copper in the Earth's crust. Identifying the important copper aqueous species and measuring reliable thermodynamic properties of those species is very important for predicting ore transport and depositon in geological systems. Unfortunately the existing knowledge about such properties is limited and controversial. The aim of this study is to determine the speciation and dissociation constants of Cu(I) chloride complexes in NaCl solutions between 50°C and 250°C using mineral solubility experiments. Cuprite (cuprous oxide) was chosen in order to avoid redox reactions in the experiments. The pH of solution is buffered by acetic acid -sodium acetate and chloride concentrations are using NaCl (0.01m to 2m). The experiments are conducted in evacuated silica glass tubes, which are placed in a water bath (50°C) or laboratory oven (150°C and 250°C). Preliminary experiments indicated complexing of Cu(I) with acetate so the concentration of total acetate was also varied in subsequent experiments to identify the important Cu(I)-acetate species. Total copper concentration is measured using a neocuproine method. Cu(II) concentrations are negligible based on the lack of colour in the quenched experimental solutions and UV-Vis absorbance spectra of the quenched solutions.. Measured copper concentrations vary between 0.0001m and 0.2m. Copper concentration increases with increasing temperature, decreasing pH and increasing chloride concentration. Logarithms of the equilibrium constants (log K) of copper complexes were fitted by non-linear regression to the measured copper concentrations, chloride concentration and high-temperature pH (using known properties of the pH buffer). Preliminary interpretation of our results shows that CuCl(aq), CuCh' (dominant) and CuCl32' and at least CuAc(aq) were present in our experiments. The derived log K values of copper chloride complexes at 50°C agree with recently published values (Xiao et al., 1998; Geochim. Cosmochim. Acta, 62, 2949) but are at least one log unit higher than those published in Sveijensky et al. (1997; Geochim. Cosmochim. Acta, 61, 1359).

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

At higher temperature there is greater discrepancy with the published values in both previous studies, where our results lead to predicted higher copper concentrations (Fig. 1).

logCl (total,m)

Fig.l. Solubility of Cuprite in NaCl-HAc solutions at 150°C (pH calculated for 150°G. The circles represent experimental data from this study. The squares and triangles stand for calculated solubility using logKs of copper reactions from Xiao et al (1998) and Sverjensky et al (1997), separately.

^ GEOLOGICAL SOCIETY OF A USTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

USE OF HEAVY MINERALS (PARTICULARLY TOURMALINE) AS PROVENANCE INDICATORS: AN EXAMPLE FROM EARLY CRETACEOUS SEDIMENTS OF THE NW SHELF,W.A. Michael P. Martin, Department of Earth Sciences, La Trobe University, Bundoora, Vic.

In the Barrow Sub-basin, offshore northwestern Western Australia, the Neocomian Barrow Group (a petroleum reservoir) comprises a dual delta complex. The younger of the deltas, Barrow Delta 2, was mainly sampled from two petroleum wells, -3.25 km apart, namely Roller 1 and Roller 4, with additional samples from Onslow 1, Flinders Shoal 1, Pasco 1, Q23M and Flag 1. The arkosic braided channel sands of the delta are dominated by quartz and feldspar, and contain a diverse and abundant heavy mineral suite. Tourmaline was selected for a detailed provenance study because its geochemistry varies significantly according to its petrogenetic origin. The experimental procedure was to separate populations of tourmaline grains from core samples and geochemically analyse them for their major elements by microprobe. The data obtained were plotted on ternary diagrams in order to deduce the provenance. Only idiomorphic tourmaline grains were used; rounded grains were excluded as they are probably derived from a second cycle sedimentary source. Two types of ternary diagram were employed for provenance determination. The first is the Vladykin et al (1975) diagram, which is based on tourmaline Y-sites alone (typically R 2 + , r 3 + and R 4 + ) ; its three vertices are (A1(Y) + 0.5Mn); (Fe + 0.5Mn + 0.5Ti); and (Mg + Cr + 0.5Ti). The petrogenetic fields that are delineated on the Vladykin et al triplot are Na-Li pegmatites (field I), granites and their associated pegmatites (field II), muscovite pegmatites associated with metamorphic belts (field III), and metamorphic and carbonate rocks (field IV). Table 1 demonstrates that Barrow Delta 2 tourmalines from Roller 1 and Roller 4 (and all the other wells) are predominantly from muscovite pegmatites associated with metamorphic belts (field III), with subordinate amounts from metamorphic and carbonate rocks (field IV) and granites and associated pegmatites (field II). The second tourmaline diagram was developed by Henry and Guidotti (1985) and employs both the Y- and Z- site (typically r 2 + and R^ + ) cationic geochemistry; the first version has Al (Y and Z site), Fe and Mg vertices (AFM diagram), whereas the second has Ca^ + (X-site), Fe and Mg vertices (CFM diagram). The AFM triplot has 8 petrogenetic regions: 1) Li-rich granitoid pegmatites and aplites, 2) Li-poor granitoids and their associated pegmatites and aplites, 3) Fe^ + -rich quartz tourmaline rocks (hydrothermally altered granites), 4) metapelites and metapsammites coexisting with an Al saturating phase, 5) metapelites and metapsammites not coexisting with an Al saturating phase, 6) F e 3 + - r i c h quartz tourmaline rocks, Ca-silicate rocks and metapelites, 7) low-Ca metaultramafics and Cr, V-rich metasediments, and 8) metacarbonates and metapyroxenites. The CFM diagram is not discussed here because the Barrow Delta 2 tourmalines are mainly Ca-poor. The Henry and Guidotti diagrams 65

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

provide more detailed information than those of Vladykin et al; by incorporating Z-site geochemistry they can subdivide the metamorphic field to more accurately reflect provenance. The Henry and Guidotti AFM plots for Roller 1 and 4 (Table 1) confirm the Vladykin et al conclusion that the provenance is dominated by metamorphic rocks (fields 4, 5 and 6), but with a considerable contribution from granites (fields 2 and 3). The granitic percentages in both wells are similar but the metamorphic regions (4, 5 and 6) differ. Roller 4 is richer in tourmalines from an Al-depleted provenance (i.e. region 6), whereas Roller 1 has more tourmalines from metapelites and metapsammites coexisting with an Al-saturating phase (region 4). This indicates that components of the provenance can change even for two wells which are only 3.25 km apart. Barrow Delta 2 strata in Roller 1 and 4 have been divided into 2 subunits on the basis of overall lithology (Table 1). Subunit a in Roller 1 and 4 is richer in tourmalines from Al-depleted metamorphic rocks (region 5), whereas subunit b has more tourmalines in region 4 (Al-rich metamorphics). Sub population

Number of

& well

samples

3 3 4 4

73 75 79 79

Roller 1 s.u. a Roller 1 s.u. b Roller 4 s.u. a Roller 4 s.u. b

Henry and Guidotti AFM plot

Vladykin plot I

III

4.1 4.0 11.4 7.6

91.8 85.3 78.5 74.7

4.1 10.7 10.1 17.7

32.0 31.5 32.5 29.5

2.0 2.7 2.5 2.6

24.0 30.1 16.3 19.2

38.0 27.4 31.2 34.6

4.0 8.3 17.5 14.1

Table 1. - Percentages of tourmaline in different petrogenetic fields (s.u. = sub unit; n = number of analyses).

Compared to the Roller wells, Onslow 1 and Pasco 1 have more tourmalines in regions 2 and 4 and less in regions 5 and 6. This represents differences in the overall provenance of the two areas, with less granitic material in the Roller area, coupled with an increase in the proportion of sediment derived from Al undersaturated metapsammites and metapelites. The relative abundances of the stable/ultrastable heavy minerals (tourmaline, zircon, garnet and rutile) in the Barrow Delta 2 samples also show interesting trends. Flag 1, for example, has 24% more garnet than any other well, probably because Barrow Delta 2 at Flag 1 is a mass flow deposit which recycled the underlying garnet-rich Barrow Delta 1 strata. The heavy mineral suites in Q23M, Pasco 1 and Flinders Shoal 1 are very similar, implying a common provenance, except that Pasco 1 has much less garnet, most likely due to diagenetic removal. Roller 1 and Roller 4 have similar heavy mineral percentages, but the nearby Onslow 1 has more tourmaline and less zircon. Perhaps the west side of the delta (Onslow 1) had a slightly different provenance to the centre-east side (Roller wells). The Henry and Guidotti AFM idiomorphic tourmaline results also suggested subtle provenance differences across the delta (between Roller 1 and 4). Based on the seismic geometry of Barrow Delta 2, the dominant sediment source was from the palaeo-Ashburton River, with a subordinate contribution from the palaeo-Robe and Cane Rivers. At this time conglomerates were deposited onshore in the Ashburton River area whereas sands were deposited onshore in the Robe River area (Hocking et al. 1988), indicating a much higher sediment discharge from the Ashburton River.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conferences, The University of Melbourne, September 1999

This provenance is confirmed by the heavy mineral data. The Gascoyne Province, drained by the Ashburton River, consists of granites (including tourmaline-bearing adamellite), pegmatite (with tourmaline), low grade schists (with accessory tourmaline), and garnet-bearing medium and high grade metamorphics (Williams 1986). The idiomorphic tourmaline geochemistry (especially from Onslow 1 and Pasco 1) shows a high proportion of granitic and pegmatitic material (region 2, Henry and Guidotti diagram), as well as grains from low grade schists together with medium and high grade metamorphics (regions 4, 5, and 6). Garnet has been derived entirely from the medium grade schists (based on its composition), and the angular and idiomorphic zircons probably came from granites. The palaeo-Cane and Robe Rivers were sourced by Wyloo Group (quartz muscovite schist), siliciclastics, BIF, carbonate, basalt, dolerite, acid sills and tuff. A different heavy mineral suite would be expected if these rivers dominated deposition of Barrow Delta 2, with more garnet (from the Wyloo Group), more rounded tourmalines from the siliciclastics, more idiomorphic zircons from the acid sills and tuff, and very little idiomorphic tourmaline. REFERENCES: Henry, D.J. & Guidotti, C.V. (1985), Tourmaline as a petrogenetic indicator mineral: an example from the staurolite-grade metapelites of NW Maine. Am. Min., 70, 1-15. Hocking, R.M., Voon, J.W.K. and Collins, L.B. (1988), Stratigraphy and Sedimentology of the Basal WinningGroup, Northern Carnarvon Basin. In: Purcell, P.G. and R.R. (edn), The Northwest Shelf, Australia. Proceedings of the Petroleum Exploration Society of Australia Symposium, Perth 1988. Vladykin, N.V., Antipin, V.S., Kovalenko, V.I., Afonina, G.G., Lapides, I.L., Novikov, V.M., and Gormacheva, G.S. (1975), Zap. Vses. mineral. Obshck, 104, 402-412. Williams, S.J. (1986), Geology of the Gascoyne Province, Western Australia. Geological Survey of Western Australia, Report 15.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

TRACE-ELEMENT AND ISOTOPE GEOCHEMISTRY OF BAGANA VOLCANO, BOUGAINVILLE ISLAND, SOUTHWEST PACIFIC Andrew Pharoah School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Our current understanding of processes operating in subduction zones is based on many years of study into numerous oceanic island and continental arcs. From these studies, coupled with experimental work on dehydration reactions and element partitioning behaviour, broad tectonic, geophysical and geochemical models have emerged. However, in detail many parameters remain either poorly constrained or contentious. The aim of this research is to constrain some of the parameters associated with source composition and magma generation processes that produce island arc lavas on Bougainville Island. This will eventually be achieved through the interpretation of trace-element and radiogenic isotope data for a number of different volcanoes on the island, although the specific focus of this paper is on

Figure 1. Southwest Pacific Locality Map, modified from Cooper and Taylor, (1985).

Bougainville Island is located to the northeast of Australia between the Solomon Islands and New Britain, Papua New Guinea, (Fig. 1.). Although politically a part of Papua New Guinea, geologically Bougainville Island is the northwestern extension of the Solomon Islands Arc. It is broadly a northwest southeast trending island initially formed as a response to southwesterly subduction of the Pacific Plate along the now inactive Kilinailau - North Solomon Trench. Subduction along this arc-trench system ceased upon collision with the abnormally thickened oceanic lithosphere of the Ontong Java Plateau sometime during the Miocene, (Cooper and Taylor, 1985). Arc reversal occurred approximately 10 Myr BP, with subsequent subduction of the Solomon Sea Plate in a northeasterly direction along the New Britain - San Cristobal Trench, (Cooper 68

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 th

and Taylor, 1985). Subduction in this direction continues to the present day and is responsible for ongoing volcanic activity on Bougainville Island and other parts of Melanesia. Bagana is the only historically active volcano on Bougainville Island, with volcanic activity observed throughout the past decade. It is a roughly symmetrical cone composed of mainly thick, blocky, massive to moderately vesicular lava flows and minor interspersed volcanoclastic debris, (Bultitude, 1976; Bultitude et al., 1978). Lavas are typically andesitic in composition, and exhibit a porphyritic texture. Phenocryst phases are dominated by plagioclase and subordinate clinopyroxene, with minor amounts of iron-titanium oxides, although some lavas contain sparse phenocrysts of brown hornblende. Most rocks contain small amounts of orthopyroxene microphenocrysts, and some have rare olivine microphenocrysts, but very few contain both, (Bultitude et al., 1978). The major-element and some trace-element data for Bagana have been documented by Bultitude et al., (1978), and more recently by Rogerson et al., (1989). Most of the rocks analysed contain between 53 and 57 wt. % Si0 and can therefore be classified as Low-SiC^ (Basaltic) Andesites. The K 0 content of Bagana andesites are moderately high, ranging from 1.34 to 1.70 wt. %. As a consequence, these andesites can be classified into the calc-alkaline suite of rocks in the bivariate system K 0 versus Si0 of Gill, (1978). This poster will present new Sr/ Sr and Nd/ Nd isotope and HR-ICP-MS trace-element data for Bagana. These data suggest that the mantle-wedge is relatively enriched, with a signature more reminiscent of an ocean island basalts rather than of typical mid ocean ridge basalts. Initial modelling of trace-element and isotope ratios suggests that this mantle source region has subsequently become overprinted by a slabderived fluid signature. 2

143

144

REFERENCES: Bultitude, R.J. (1976), Eruptive history of Bagana volcano, Papua New Guinea, between 1882 and 1975. In Johnson, R.W., (Editor), Volcanism in Australasia, Elsevier, Amsterdam, pp. 317336. Bultitude, R.J., Johnson, R.W. and Chappell, B.W. (1978), Andesites of Bagana volcano, Papua New Guinea: chemical stratigraphy, and a reference andesite composition. BMR Journal of Australian Geology and Geophysics 3, pp. 281-295. Cooper, P.A. and Taylor, B. (1985). Polarity reversal in the Solomon Islands arc. Nature 88: pp. 428-430. Gill, J.B. (1978). Role of trace element partition coefficients in models of andesite genesis. Geochimica et Cosmochimica Acta 42, pp. 709-724. Rogerson, R.J., Hilyard, D.B., Finlayson, E.J., Johnson, R.W., McKee, C.O. with contributions from Chappell, B.W., Price, R.C., Nion, S.T.S., Joseph, L., Sumaiang, R., Duguman, J. and Patia, H. (1989). The Geology and Mineral Resources of Bougainville and Buka Islands, Papua New Guinea. Geological Survey of Papua New Guinea Memoir 16, 217 pp.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

6. IGNEOUS GEOLOGY AND VOLCANOLOGY Talks: pp 71-79 Posters: pp 80-90

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13* Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

FACIES ANALYSIS AND PALAEOVOLCANOLOGY OF A COMPOSITE SCORIA CONE - MOUNT BUNINYONG, CENTRAL VICTORIA Christie Batiste School ofEcology and Environment, Deakin University, Rusden Campus.

Located approximately 11 kilometres southeast of Ballarat in Victoria, Mount Buninyong belongs to the Newer Volcanics phase of volcanism, which was widespread throughout western-central Victoria from the late Miocene to Recent. Mount Buninyong is a scoria cone complex overlying folded Ordovician sediments and Devonian granite. Consisting of two prominent cones formed during independent volcanic eruptions, the mountain stands 740 metres above sea level and covers an area of just under four square kilometres. The height of the younger, or most recent cone varies from 180 metres above the surrounding plain on the western flank to 240 metres on the eastern flank, the latter being considerably higher and steeper suggesting a westerly palaeo-wind direction during eruption. Pyroclastic material is crudely bedded and consists predominantly of unconsolidated scoriaceous fragments. Randomly bedded within the scoria deposits are basaltic blocks and bombs. Near-vent bombs are up to one metre in diameter with several retaining their spindle or ellipsoidal shape. The cones were most likely built up rapidly during explosive Stromboliantype eruptions whereby pyroclastic tephra consisting of highly vesiculated basaltic scoria, volcanic bombs and blocks were ejected during the early stages of eruption. The more quiescent effusion of lava during later eruption stages produced extensive flows emanating from the older cone. The earliest outpouring of lava was the Clarendon flow from the eastern side of the cone, which moved to the south and southeast. This was followed by a second lava flow from the northwest flank, which moved southwest towards the township of Buninyong before continuing south along the Yarrowee River. The lava is an olivine hawaiite (ne ~ 12, an/ab + an ~ 43) (Irving & Green, 1976) and comprises olivine phenocrysts set in a fine-grained groundmass of feldspar, clinopyroxene, opaque oxides glass. Xenoliths and xenocrysts of assumed mantle origin occur both in the flows and pyroclastic fragmentals. These inclusions are predominantly Cr-diopside lherzolite nodules with pale green Crdiopside, and Cr-Al spinels. Nodules of magnesian olivine formed during early fractionation in the mantle or through disaggregation of the Cr-diopside series xenoliths (Price et al, 1988), are up to ten centimetres in diameter and often form the core of volcanic bombs. Xenocrysts of quartz displaying corona textures and fluid inclusions are of shallow crustal origin and were most likely derived from the underlying Palaeozoic sediments. The mountain represents a composite vent sequence comprising pyroclastic facies formed through fire fountaining, lava flows, and a possible lava lake developed prior to the final scoria cone formation.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

REFERENCES: Irving, A. J. & Green, D. H. (1976), Geochemistry and petrogenesis of the newer basalts of Victoria and South Australia. Jour. Geol. Soc. ofAust., 23, pp. 45-66. Price, R. C. et al (1988), Cainozoic volcanic rocks. In J. G. Ferguson & J. A. Douglas (eds.), Geology of Victoria, Victorian Division Geological Society of Australia, Melbourne.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE COMPOSITION, DISTRIBUTION, ORIGIN AND EVOLUTION OF THE COLIBAN AND CAMPASPE RIVER VALLEY BASALTS. Peter Coceani Earth Sciences Department, La Trobe University, Bendigo.

Field and laboratory work was conducted on lava flows in the Coliban River channel in order to assess the composition, distribution and likely origin of the basalt. Residual mesas remain along the course of the Coliban paleochannel from Metcalfe to Lake Eppalock. Extensive field mapping and sampling and subsequent data analysis has shown that two continuous alkali basalt lava flows once occupied the former Coliban River Valley. The two flows are distinguished by the presence of springs emerging between the flows, the lower flow being weathered to a greater extent and the presence of benches highlighting the top of the lower flow from the base of the upper flow. Dissection of the landscape as the Coliban River found a new channel cut the basalt flow and eroded the surrounding Ordovician bedrock so that the basalt residuals now sit high above the surrounding landscape. The Coliban residuals are present overlying both outcrop of the Harcourt Granodiorite and Ordovician bedrock. In places, basalt covers the contact zone, which to the south, rises abruptly above the surrounding land. Green Hill, a prominent lava dome 7km north of Kyneton has been, in the past, taken to be the source of the Campaspe River basalt. (Cherry, 1994, p.36). A prominent flow boundary exists around the basalt expelled from Green Hill suggesting that this Newer Volcanic eruption point may have formed on lava already present. Green Hill may therefore be younger than basalt dated at approximately 3.12 million years in Barfold Gorge by Wallace and Oilier (1986, p. 177). Petrological differences occur between samples taken from Green Hill and the surrounding lava field which extends into the Campaspe valley. Green Hill from its position in the landscape may be the same age as Kangaroo Hill and Pattens Hill, found west of Malmsbury and dated at 2.62 million years. (Wallace, 1990, p.70) Four flows exist in the Campaspe River, best exposed at Barfold Gorge. The lower three flows are normally polarized while the upper, dated flow is reversely polarised suggesting a time lapse between eruptions. (Wallace, 1986, p.l77).Furthermore, a basaltic paleosol varying in thickness exists between the lower two most flows suggesting that substantial time elapsed between the eruptions of these lower flows. This may indicate that none of the Campaspe flows were sourced from Green Hill and that an older eruption point exists or once existed. The Harcourt Granodiorite intrudes the Ordovician bedrock and its contact aureole stands high above the weathered granitic basin and flanking bedrock. This contact forms a topographic divide between Green Hill to the south and the Coliban residual's to the north. This boundary would have restricted the flow of basalt directly from Green Hill into the Coliban paleochannel. Basalt would have had to flow west towards Taradale before finding the Coliban River. In summary, it appears that separate eruption points may have been responsible for the separate Coliban and Campaspe River basalts and Green Hill may not be the source for any of the flows.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13* Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

REFERENCES: Cherry, D.P and Wilkinson, H.E. (1994), Bendigo, and part of Mitiamo, 1:100,000 map geological report. Geological Survey of Victoria Report, 99. Wallace, D.A and Oilier, C.D. (1986) 'The Cainozoic Lava Flows of Barfold Gorge', Victorian Naturalist, 103, no. 6, pp. 175-177 Wallace, D.A. (1990), Petrology and Geochemistry of the Newer Volcanics of the Western Highlands of Victoria, Australia, (unpublished thesis)

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

GEOLOGY OF THE GRANITIC RATHJEN GNEISS, AND IMPLICATIONS FOR THE EVOLUTION OF THE KANMANTOO GROUP, SOUTH AUSTRALIA M.J. Perkins, P. D. Fleming & C. M. Gray. School of Earth Sciences, La Trobe University, Bundoora, Vic.

The' Rathjen Gneiss forms a sheet-like granitic body within the multiply deformed migmatite zone of the southern Adelaide Fold Belt, South Australia. Its origin has remained a point of conjecture since first mapped by A.J.R. White (1966). Disagreement centres on whether the Rathjen Gneiss was formed from a slab of intruded granitic magma, or whether it represents a sheet of igneous material of volcanic origin, deposited during Kanmantoo Group sedimentation and then deformed and metamorphosed during the Delamerian Orogeny. The Rathjen Gneiss was previously mapped as a single uniform body, but remapping has identified four distinctive units. The northern end of the body shows clear intrusive relationships, characterised by numerous metasedimentary enclaves and discordant contacts with surrounding rocks. Further south this unit grades into three stratigraphically concordant units, with a series of coarse feldspathic interbeds that parallel the lower boundary suggestive of a tuffaceous origin. Both the northern and southern components of the Rathjen Gneiss are intimately related, as all four units are chemically and mineralogically similar, though texturally distinct. This is suggestive of a caldera complex where both volcanic and intrusive activities co-exist. Two of the concordant units of the Rathjen Gneiss were deposited as eruptive horizons within a caldera complex, with a later sill intruding the volcanic pile. Such an origin has dramatic implications for the evolution of the Kanmantoo Group, and the entire southern Adelaide Fold Belt. It has been argued that the Kanmantoo Group was deposited in a marginal basin along the southeastern continental margin of Early Palaeozoic Australia (Liu, 1992), but the possible presence of a caldera complex raises questions about the inferred depth of marine deposition, and the nature of the crustal substrate. The syn-depositional volcanic activity recorded in the Rathjen Gneiss also casts doubts on previous assumptions, that no volcanic detritus is recorded within the Kanmantoo Group (Preiss, 1987). REFERENCES: Liu, S. F. (1992), Mafic dykes and their geological setting in the Southern Adelaide Fol Belt, Ph.D Thesis, La Trobe University, Melbourne. Preiss, W. V. (1987), The Adelaide Geosyncline, Government Printer, South Australia, pp.268281. White, A. J. R. (1966), Petrology and structure of the Rathjen Granitic Gneiss of the Palmer region, South Australia. J. geol. Soc. Aust., 13(2), pp. 471-489.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

VOLCANOLOGY AS AN EXPLORATION TOOL: THE ARCHEAN WHIM CREEK BELT, PILBARA CRATON Geoff Pike Department of Earth Sciences, Monash University, Clayton, Vic.

The Whim Creek Belt is the preserved fragment of rocks deposited in the c.3Ga Whim Creek Basin. The Whim Creek Group lies unconformably over midArchean amphibolites and granitoid. Present day basin margins are northeastsouthwest trending strike-slip faults, previously interpreted to have been active both prior to and during basin formation (Barley, 1987). The belt contains three sub-economic, base metal sulphide deposits at Whim Creek, Mons Cupri and salt Creek. Previous models of formation of base metal deposits in the Whim Creek Belt have described VHMS-style, syn-volcanic mineralisation, (Large, 1992). Exploration has, consequently, focussed on expose rhyolite bodies, considered to be source of this mineralisation. SHRIMP and Pb-Pb dating of felsic volcaniclastic rocks and galena samples from mineralised zones, respectively, give date of c.3,010 Ma for sedimentation (Hickman et al., 1998) and 2,945 Ma for mineralisation (Huston pers. comm.). this discrepancy has been explained by a relatively long-lived (>50 Ma) basin and/or the presence of significant unconformities within the stratigraphy. New volcanological and sedimentological data is presented of a bimodal volcanic and volcaniclastic succession of 1 to 1.5 km stratigraphic thickness. Subaqueous basaltic lavas interdigitate with intrusive rhyolite cryptodomes in the west of the belt. In the east, rhyolite domes dominate and are wholly emergent. Sedimentation is demonstrably syn-volcanic to immediately post-volcanic and no significant unconformity exists within the Whim Creek Group. Previous sequence stratigraphic interpretation (Krapez & Lisenlohr, 1998) describes four component sequences. However, the reliance of sequence stratigraphy on unconformities as a sequence boundaries makes the technique unsuitable in volcanic-dominated terranes in which the emplacement of massive volcanic or high-level intrusive bodies generates topography and large volumes of sediment, resulting in the development of angular but time-conformable boundaries that are often, mistakenly, interpreted as unconformities. This study recognises a large volume, bimodal volcanic event, followed by turbidite sedimentation over a geologically instantaneous time period. Mineralisation is, therefore, >50 Ma younger than volcanism and sedimentation. This age constraint, lack of primary VHMS associated structure and the recognition of a structural control linking mineralisation, chlorite-sericite alteration and a newly discovered felsic intrusive body strongly suggest that the mineralisation results from a post-depositional, mesothermal event at c.2,945 Ma. Similar events are recognised throughout the west Pilbara (Smithies & Champion, 1999). Basic volcanological and sedimentological study, therefore, give important constraints on the timing and significance of crustal-scale events and may also be used to define prospective areas for base metal mineralisation without resorting to expensive and time-consuming geochemistry or drilling.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13* Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

REFERENCES: Barley, M.E. (1987), The Archean Whim Creek Belt, an ensialic limit-bounded basin in the Pilbara Block, Australia. Precambrian Research, 37, 199-215. Hickman, A.H., Smithies, R.H. and Huston, D.I. (1998), Excursion guide to the geology of the granite-greenstone terrane of the west Pilbara. Geological Survey of Western Australia and Australian Geological Survey Organisation. Krapez, B. & Lisenlhor, B. (1998), Tectonic setting of Archaean (3325-2775 Ma) crustalsupracrustal belts in the West Pilbara Block. Precambrian Research, 88, 173-205. Large, R.R. (1992), Australian volcanic-hosted massive sulfide deposits: features, styles and genetic models. Economic Geology, 87,471-510. Smithies, R.H. & Champion D.C. (1999), Secular compositional changes in Archaean granitoid rocks of the west Pilbara. Geological Survey of Western Australia 1997-1998 annual review.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

HYDROMAGMATIC ERUPTION AND PYROCLASTIC SURGE DEPOSITION PROCESSES AT LAKE PURRUMBETE MAAR Mireille Slots, Earth Sciences Department, Monash University, Clayton, Vic.

Lake Purxumbete is one of several young eruptive centres located along an east-west lineament near Camperdown in western Victoria. It is located in the Tertiary-Quaternary basaltic intraplate Newer Volcanics Province (NVP) of southeastern Australia. The Lake Purrumbete maar resulted from the explosive interaction between basalt magma and groundwater stored in limestone aquifers of the Otway Group. It has a diameter of approximately 2.5-3 kilometers and a well defined tuff ring up to xmetres high. Periodic variations in the eruption style and intensity are indicated by variation in the thickness, grainsize and structures of individual beds. Cross bedding of outward dipping beds indicates deposition by pyroclastic surge. Structures such as ripples and duneforms, large climbing bedforms, microtruncations and low angle cross stratification indicate deposition by base surge. Inward dipping beds around the maar are generally much steeper than outward dipping beds and are characterised by secondary slumping in addition to primary surge deposits. Commonly, outward dipping ash beds are truncated at the inner edge due to the collapse of the crater walls into the vent during and after the eruption. Fall modified surge deposits produced by continuous fall out while surges were propagating are also found in this near vent setting. Finer and coarser grained beds within the same bedsets may be explained by variation in the water to magma mass ratio during explosive eruption. The juvenile fraction of the deposit is lapilli sized and variably vesicular, from 0 to 50%. Vesicularity estimates suggest this magma would not have erupted explosively without contact with groundwater, however original volatile content of the magma is unknown so it is unknown if vesiculation reached its peak prior to water-magma interaction. The deposit contains ash sized debris which is dominated by sedimentary and calcereous grainsderived from underlying aquifers, and glassy ash fragments. Lithics from the Stony Rises lava which directly underlie the tuff ring are non vesicular and vary from lapilli to block sized clasts. Another type of lithic may have a similar composition to juvenile clasts as indicated by mineralogy and are also lapilli to block sized clasts. Related maars and tuff rings (e.g. Lake Keilambete, Lake Bullen Merri) in the NVP generally have an asymmetric distribution of ash, with high walls on the east and low walls or none at all on the west. This feature is most prominent at Lake Purrumbete. Oilier (1967) presumed this distribution to be due to prevailing westerly winds at the time of eruption affecting the usual radial transport direction from vent. New mapping and logging of the Lake Purrumbete base surge deposits suggests that the dominant control on ash distribution was directed lateral blasts. Hence, the directed lateral blasts appears to be a more important control on distribution than the prevailing wind direction during eruption.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE VILLA SENNI ERUPTION UNIT OF THE ALBAN HILLS VOLCANO, ROME, ITALY: VOLCANIC ERUPTION, TRANSPORT AND DEPOSITIONAL MECHANISMS Watkins, S.D. Department of Earth Sciences, Monash University, Clayton, Vic.

The Villa Senni Eruption Unit (VSEU) represents the final eruption of the Tuscolano-Artemisio phase of the basaltic Alban Hills Volcano, which is located approximately 20 kilometres south east of Rome. The Tuscolano-Artemisio phase was the first and largest of three main eruptive phases of the volcano, and is characterised by extensive deposits of pyroclastic density currents which stretch radially for 30 kilometres or more from the central vent area, a rare phenomenon for basaltic volcanoes. Eruption and deposition of the VSEU at approximately 320 ka immediately preceeded caldera subsidence which marked the end of the initial eruptive phase. The products of the Alban Hills Volcano, including those produced in the large pyroclastic eruptions, are predominantly K-foiditic to phono-tephritic in composition, being generally rich in potassium (5-12%) and having an SiC>2 content of between 46-52%. The VSEU is characterised internally by two distinct facies. The lower facies consists predominantly of ash and scoria clasts which has been cemented by the growth of zeolites ± clays over almost its entire extent. The upper facies is more fines depleted, contains abundant scoria and spatter clasts, a significantly higher percentage of crystals, lava and xenolith lithic clasts, and is almost entirely unconsolidated. The two facies are separated internally by a contact which varies from erosive to gradational moving radially away from the central vent area. These two facies represent two distinct phases in the eruption. The initial deposits are finer grained, suggesting more efficient explosivity within the vent. Explosions were most probably due to hydromagmatic processes caused by the addition of external water from the large carbonate hosted aquifers underlying the central vent area. This is supported by the almost uniform presence of hydrous zeolites and clays throughout these deposits, the growth of which is dependent on the availability of a significant amount of water. The transition to the upper facies is marked by the deposition of a lithic and spatter rich breccia. The higher lithic and magma chamber-derived xenolith content within the breccia and overlying facies suggests that collapse of the central vent area and/or initial caldera subsidence (due to partial magma chamber collapse) were significant in the deposition of this facies. Volcanological theories for transportation and deposition of pyroclastic density currents generally fall into two conflicting models: en masse deposition versus progressive aggradation. Internal grainsize and component changes within the VSEU strongly suggest that this unit was deposited by progressive aggradation, with internal variations and structures predominantly due to changing eruption dynamics and components at the source. Topography, local flow dynamics and interaction with the pre-existing ground surface (including erosion) have also influenced the formation of the deposit in some areas.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13,h Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

SPRING WELL, WESTERN AUSTRALIA. A SUBAQUEOUS FELSIC DOME COMPLEX Scott Crozier Department of Earth Sciences, Monash University, Clayton, Vic.

Spring Well is a 2.69 Ga. felsic volcanic complex, located 110km north of Leonora in the Eastern Goldfields province of the Archaean Yilgarn craton, Western Australia (Giles 1986). Spring Well is one of several calc-alkaline centres in the Eastern Goldfields, which are thought to have been erupted in an arc system similar to the modern marginal arc system of the Western Pacific (Myers 1997). Spring Well differs from other calc-alkaline centres in the Eastern Goldfields in containing a higher proportion of acid rocks (mainly rhyolite) and lower proportions of mafic components. Previous work in the late 1970fs interpreted the complex as a subaerial volcanic complex involving major explosive ignimbrite eruptions. More recently, staff at Great Central Mines Limited identified relatively deep water deposits of carbonaceous shale and chert together with large volumes of predominantly monomictic rhyolite breccias with clast morphologies strongly resembling hyaloclastite. The transition from coherent, flow banded rhyolite to in-situ and resedimented rhyolite hyaloclastite indicates that quench fragmentation and not pyroclastic explosion was the dominant fragmentation process. All these features indicate a predominantly subaqueous setting for both fragmentation and deposition of the Springwell Complex. The rhyolite breccia units are predominantly monomictic, composed of poorly sorted angular, juvenile blocks deposited through mass flow processes. Proximal deposits are characterised by crudely graded units with the base of the flow units having higher proportions of coarser/larger blocks. In more distal locations, medium grained breccias of angular to subangular rhyolite grade rapidly into planar to low angle cross stratified sandstones. Andesite within the complex is often observed as highly amygdaloidal, flow-contorted bodies, interpreted as either lava flows or high level intrusions. Andesitic clasts occur within breccias and fine grain, massive andesite intrusions occur throughout the complex,. The Spring Well complex represents a subaqueous lava dome complex, comprising multiple eruption points, each erupting rhyolite with a different phenocryst compositions. The dome complex produced large volumes of quench fragmented detritus that was re-sedimented down talus slopes adjacent to the lava domes. Consequently, rocks derived from ambient sedimentation, including shale and chert, are restricted to the distal parts of the complex. I Acknowledge Great Central Mines for their financial and logistical support in this project.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

REFERENCES: Giles, C.W. (1982), The geology and geochemistry of the Archaean Spring Well felsic volcanic complex'. Journal of the Geological society of Australia, 29 (1 -2), pp. 205-220 Hallberg, J.A. and Giles, C.W. (1986), 'Archaean felsic volcanism in the northeast Yilgarn Block, Western Australia'. Australian Journal of Earth Sciences, 33, pp. 413-427 Myers, J.S. (1997), 'Archaean geology of the Eastern Goldfields of Western Australia - regional overview. Precambrian Research, 83 (1-3) ,pp. 1-10

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 th

MAFIC DYKES FROM THE MT. PAINTER INLIER, SOUTH AUSTRALIA: PETROGENESIS, GEOCHEMISTRY AND TECTONIC IMPLICATIONS Daniel Halas Earth Sciences Department, Monash University, Clayton, Vic.

Mafic dykes which intrude the Proterozoic basement of the Mt. Painter Inlier, South Australia were found to be tholeiitic in composition and showed typically strong enrichment trends in Ti0 , FeO and V. The mafic dykes exhibit a large range of Mg-numbers, 3 3 - 5 1 , which suggests they have undergone significant amounts of fractional crystallisation from their source. Variation diagrams clearly indicate that clinopyroxene fractionation was a major control during evolution of the dykes. The dykes are oriented NW-SE and NE-SW and are thought to be related to the Wooltana Volcanics, a similar basaltic unit in the region which has been calculated to have ages consistent with the Gairdner Dyke Swarm (from the Gawler Craton to the west) at ~ 827 Ma. The dykes and volcanics share many geochemical similarities that are clearly evident in variation diagrams. The dykes may be classed as metadolerites and placed into two contrasting geochemical groups: dykes with low and high Zr contents (86-147 and 206-274 ppm respectively). These groups also display contrasting Ti0 , P O and Nb contents and are believed to have evolved from parental magmas representing different degrees of mantle melting. This was highlighted by their fractionation paths that showed contrasting gradients. Although the dykes have been subjected to metamorphism and deformation which occurred in the region mostly during the Delamerian Orogeny (-500 Ma), their geochemistry seems to be largely unaffected, except in cases of extensive alteration. The most significant effect of the metamorphism was to completely replace primary clinopyroxene with actinolite, the predominant mineral formed under amphibolite facies conditions. Incompatible trace element abundance patterns suggest that the mafic dykes, Wooltana Volcanics and dykes of the Gairdner Dyke Swarm were all derived from similar source mantle that shows a relative depletion in K. These patterns also show that the two dyke groups with contrasted Zr are closely related, with the high Zr group being enriched in incompatible elements compared to the low Zr dykes. This feature aids in confirming separate mantle melting events for the two groups. The mafic dykes and associated Wooltana Volcanics are most likely the result of intraplate magmatism associated with an underlying mantle plume which is believed to be related to a period of crustal extension and weakening prior to the beginning of continental breakup. 2

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Uni versities Earth Sciences Conference, The University of Melbourne, September 1999

CHANGING ERUPTION STYLES IN A COMPLEX, INTRAPLATE VOLCANO: THE MOUNT NOORAT VOLCANIC COMPLEX, NEWER VOLCANICS PROVINCE, VICTORIA Michelle Hough Earth Sciences Department, Monash University, Clayton, Vic.

Located in the late Tertiary-Quaternary Newer Volcanics Province of Western Victoria, 6 km north of the township of Terang, the Quaternary Mount Noorat Volcanic Complex, estimated to be between 40,000 and 60,000 years in age (Stone, 1972), represents one of the most recent phases of volcanism in Australia. The Mount Noorat Volcanic Centre records two distinct styles of explosive basaltic volcanism: an early phase of phreatomagmatic activity resulting in the deposition of a tuff ring succession, followed by Strombolian, magmatic volcanism that produced the nested scoria cones that define the present day geomorphology of the complex. The Mount Noorat Volcanic Complex illustrates the fine balance between phreatomagmatic and magmatic explosive activity in continental intraplate settings. Rapid fluctuations in water/magma mass ratio are exhibited in the complex facies variations, notably the degree of fragmentation, vesicularity and shapes of the pyroclasts. Such facies changes allow interpretation of the significance of external water in the explosive fragmentation process as opposed to the influence of magmatic volatiles. Initial results suggest that variation in eruptive style is dominantly controlled by: the recharge rates of the surrounding aquifer, the rate of rise of magma through the conduit which consequently controls the amount of magma being intersected by water, and the ability of the magma conduit to develop and maintain an impermeable lining on the walls of the conduit. Detailed stratigraphic logging conducted at Mount Noorat has revealed that base surge was the predominant mode of transportation and deposition of pyroclasts in the proximal tuff ring succession during the early stages of eruption, whilst deposition due to air fall would appear to have been more significant in the later stages of the phreatomagmatic activity. Throughout most of the succession however, surge modified-fall deposits (Cas et al, 1989) are recurrent, hence it would appear that at the time of deposition both the processes of base surge and air fall were occurring simultaneously. Small-scale cross-bedding, dune forms and chute and pool structures are noted within the base surge deposits and occur most frequently lower in the stratigraphy, whilst a progressive gradation to planar lamination occurs upsequence. This is interpreted as a gradual decrease in the energy of the base surges, perhaps reflecting decreased explosive intensity. Massive cone building scoria deposits, over 100 m thick, occur proximal to the vent system and resulted from a low eruption column as typically associated with Strombolian eruption. Thinner (l-2m) crudely stratified and often graded distal deposits of scoria mantle the tuff ring succession. Normal and reverse grading are commonly exhibited in the distal deposits and reflect pulsating changes in the height of the eruption column or wind direction and strength. Strombolian volcanism was followed by a waning stage of Hawaiian activity, resulting in the welded spatter deposits and relatively small clastogenic lava flows that occur to the north and south of the complex. 83

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

INFILTRATION-DRIVEN PARTIAL MELTING OF MAFIC DYKES - A POSSIBLE MECHANISM FOR GHOST DYKE DEVELOPMENT Cameron D. Quinn School of Earth Sciences, The University of Melbourne, Parkville, Vic.

Mapping of the Archaean Sleaford Complex on the western margin of Sleaford Bay, Eyre Peninsula revealed a sequence of strongly boudinaged and fragmented mafic dykes within a homogeneous leucosome-bearing charnockite. Pegmatitic leucosome is present along dyke margins, within boudin necks and as veins within boudins. Mineralogical zonation developed within mafic dyke fragments and boudins. Boudin cores preserve the assemblage amphibole + orthopyroxene + clinopyroxene + plagioclase + quartz. Towards boudin margins and pegmatite veins, biotite formed, followed by poikiloblastic garnet and alkali feldspar. Occasionally, orthopyroxene predates garnet at dyke margins. Some dykes have been partially to completely replaced by planar bodies of pegmatitic melt, referred to as ghost dykes by Ghosh & Sengupta (1998). To assess possible effects of melt infiltration on mafic lithologies thermodynamic modelling was undertaken within the Na20-Ca0-K20-Fe0-Mg0Al 2 03-Si02-H 2 0 (NCKFMASH) system using the internally consistent dataset of Holland & Powell (1998). The infiltration of externally derived melt causes a change in the bulk composition (X) of the mafic dykes. To describe assemblage development in the dykes, the effect of this change on the stable mineral assemblage with regard to pressure (P) and temperature (T) must be constrained. A P-X pseudosection at 790°C is included (Figure 1) where X represents the addition of melt to the bulk composition preserved in the boudin cores. The solidus corresponds to the generation of new melt by partially-melting the mafic dykes — not the infiltration of externally derived melt. Phase diagram analysis (Figure 1) shows that the observed mineralogical zonation can be attributed to melt infiltration during prograde metamorphism. If melt infiltration led to partial melting of the dykes, continued production of melt within a dyke can lead to the selective removal of that dyke — hence the development of ghost dykes. Structural observations of boudinage development in the mafic dykes suggest that strain partitioned into the host charnockite. This caused a pressure gradient to develop across the two lithologies driving melt-flow from the partially-molten charnockite to the mafic dykes - initiating partial melting in the dykes. The concentration of melt flow along dyke margins and boudin necks may have caused the removal of the mafic dykes. REFERENCES: Ghosh, S.K. & Sengupta, S. (1998), Boudinage and composite boudinage in superimposed deformations and syntectonic migmatization. Journal of Structural Geology, 21; 1, pp. 97-110. Holland, T.B.J & Powell, R. (1998) An internally consistent thermodynamic dataset for phases of petrological interest. Journal of Metamorphic Geology, 16; 3, pp. 309-343

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 1

(NCKFMASH +pl + q)

P(kbar)

Percentage of externally-derived melt added

Figure 1. P-X pseudosection at 790 C where X equals the percentage of externally-derived melt added to the mafic bulk composition. Arrows show a possible prograde P-X paths.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE PALAEOENVIRONMENTAL AND PALAEOVOLCANOLOGICAL DEVELOPMENT OF THE MT. TYPO AND WHITFIELD REGIONS, MT HO WITT PROVINCE, VICTORIA, AUSTRALIA Rebecca A. Ruscoe Department of Earth Sciences Monash University, Clayton, Vic.

The easterly verging Mount Howitt Province developed in response to the middle Devonian Tabberabberan Orogeny, which produced uplift and elimination of marine conditions in Victoria. Shortly post-dating the Tabberabberan Orogeny, Upper Devonian to Lower Carboniferous subaerial sedimentary and volcanic successions where deposited within the Mt. Howitt sedimentary basin system, which is now preserved as four en echelon structural basins (synclinoria). The Mansfield Basin, is the northern most structural basin of the Province, its northern margin preserves a sedimentary succession (Blue Range Volcanic conglomerates) initially deposited contemporaneously with the Tolmie Igneous Complex volcanics, sourced from the Wabonga Caldera at the northeast margin of the Basin. Later activity in the basin is dominated by sedimentation only (Mansfield Group), evident in the upper sedimentary successions of the Mansfield Basin and at its eastern margin, marked by the Mt. Typo Syncline. The Mt. Typo Syncline consisting of volcanics, conglomerates and sandstones, may have once been part of the Mansfield Basin succession. Deformation of the Mt. Howitt basin system during the Carboniferous Orogeny has produced greater degrees of deformation along the basin margins, as represented by the Typo Syncline than in the basin interior. Previous studies have concentrated research on the western and southern regions of the Mansfield Basin, and thus this research intends to rectify this information bias through detailed mapping and petrography of the Mt. Typo syncline sediments. The aim is to determine clast provenance of the Mt. Typo sedimentary succession and determine their regional significance. The origin and setting of the volcanics in the area will be established through mapping, petrographic and geochemical analysis. The Tolmie Igneous Complex volcanics are extremely crystal-rich and were deposited in a subaerial environment as indicated by the extensive welded ignimbrites throughout the region. Fiamme, (flattened pumice) present in the deposits are rich in large quartz and feldspar phenocrysts, suggesting the magma was crystal rich upon emplacement. The lack of pyroclastic fall sequences in the study area suggests that an eruption column was not established, and that eruption possibly occurred as a 'boiling over' from the conduit. The redbed formations of the Mt. Typo Syncline indicate the palaeoenvironment of the basin was a terrestrial setting, given the presence of iron oxides. The conglomerates (Timbertop Conglomerate) within the basin suggest deposition occurred in a high-energy environment, and is consistent with successions of a braided river or fan deposit. The well-rounded and sorted nature of the clasts indicates erosion was from a source with high relief and a considerable distance from the final site of the deposit. Preliminary investigations indicated the source of the clasts was possibly an Ordovician metasediment. The sandstones (Devils Plain Formation) overlie the conglomerates and are fine-grained and extremely well sorted. The depositional structures of these sediments changes from dune to laminar and again to ripple beds with rip up clasts, indicating the flow regime varied throughout the evolution of deposition. 86

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 th

This is possibly consistent with a meandering river system indicating a reduction of relief.

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13lh Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE FACIES AND STRATIGRAPHIC ARCHITECTURE OF THE HIGHLY DEFORMED METAVOLCANIC PACKAGES ASSOCIATED WITH THE PERSEVERANCE NICKEL DEPOSIT; ARCHAEAN AGNEW-WILUNA GREENSTONE BELT, WESTERN AUSTRALIA. Mark Tail Department of Earth Science, Monash University Clayton, Vic.

The Archaean Perseverance Ultramafic Complex of the Yilgarn Craton is one of the largest ultramafic bodies in Western Australia. The core of the body reaches thicknesses up to 700m along its strike length of 2km (Sharp, 1996). It is a lens shaped body, consisting of mesocumulate and adcumulate textured ultramafic rock. The surrounding areas are dominated by packages of highly altered metavolcanics and metasedimentary rocks. Unlike the type example at Kambalda, where pillow basalt and sulphidic sediment underlie the mineralised komatiites, the Perseverance nickel deposit and nearby Rocky's Reward deposit have a close spatial affinity with felsic/mafic volcanics and minor sedimentary strata. This research focused upon the area along strike between the Perseverance Ultramafic and the 11-Mile Well prospect in the south of WMC Resource's Leinster tenement. By documenting the petrographic, textural and geochemical features of the various units in the area, and consideration of the various contact relationships, construction of the present day stratigraphy is possible. Combined with particular focus on the relationship between the mineralised ultramafic bodies and the associated felsic packages, a basis is formed for development of exploration tools in similar terrains. Due to the high levels of metamorphism and structural control prevalent in the area, finding primary textures and mineral assemblages is almost impossible. However, small pockets of primary igneous and sedimentary texture are identified and are extremely valuable in interpreting the palaeovolcanology and palaeoenvironment of the area. Metamorphic grade increases from upper greenschist facies north of the near mine environment to amphibolite facies in the south, suggesting temperatures up to 550°C. Stratigraphic interpretation is extremely complex as episodes of thrusting have stacked a number of packages, resulting in package repetition through logged sections. All periods of deformation are directly related to movement along the Perseverance Fault. This feature is part of the Keith Kilkenny Lineament, which is a regionally extensive structure that defines the eastern boundary of the Agnew-Wiluna Greenstone Belt (Sharp, 1996). Previous works in the area have failed to provide adequate understanding of the origins of facies or of the stratigraphic architecture in the area. Most work has concentrated upon the economically valuable ultramafic units with little emphasis on the other packages. Sulphidic black shales and metacherts are identified in some areas, suggesting that a very low energy, subaqueous environment existed at the time of eruption. Several of the surrounding felsic rocks have previously been described as tuffs or lapilli tuffs (Barnes et al, 1988). This implies an explosive, pyroclastic origin for the deposits, evidence for which is not apparent in any of the regions considered by this work. This research has identified a number of coherent, plagioclase phyric felsic units that represent effusive lavas or intrusive sills. Further research is needed to establish whether

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13 Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999 th

they are of an extrusive or intrusive nature, but evidence of flow banding and the presence of large euhedral feldspar phenocrysts is indicative of a non-pyroclastic emplacement mechanism. The Perseverance ultramafic complex has long been considered a type example of thermal erosion of substrate by hot, low viscosity, komatiites (Barnes, et al 1988). The thickness and shape of the body is thought to represent a large, extremely deep channel, up to 1 kilometre deep, through which komatiites flowed and were emplaced (Barnes et al, 1988). A number of contacts were observed through the base of this unit, looking for evidence of such behaviour. This research discovered little evidence for thermal erosion. All contacts appeared to be structurally controlled with extremely high strain levels and alteration observed in the contact zone. Evidence for an intrusive origin or perhaps a structural juxtaposition of the ultramafic/felsic bodies appears more obvious. The area surrounding the Perseverance nickel deposit is interpreted as a trimodal volcanic sequence, dominated by ultramafic and felsic magmatism, with minor basic activity in the southern regions. Emplacement occurred subaqueously, into a very low energy probably deep marine or lacustrine type setting. REFERENCES: Barnes, S.J., Hill, R.E.T. & Gole, M.J. (1998), The Perseverance ultramafic complex, Western Australia: product of a Komatiite lava river. Journal of Petrology . 29, Part 2, pp. 305-331 Sharp, D. (1996), The stratigraphy and structure of the southern portion of the Agnew-Wiluna greenstone belt. WMC resources internal report, K/3700

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

THE FACIES ARCHITECTURE OF THE TRI-MODAL VOLCANIC SUCCESSIONS OF THE SOUTHERN PORTION OF THE ARCHAEAN AGNEW-WILUNA GREENSTONE BELT, LEINSTER, WESTERN AUSTRALIA Jessica Trofimovs Department of Earth Science, Monash University, Clayton, Vic.

The Perseverance Mine is located within the Agnew-Wiluna Greenstone Belt, which in turn is located in the northern third of the Norseman-Wiluna Greenstone Belt of the Archaean Yilgarn Craton, Western Australia. The discovery of nickel mineralisation in 1971, has resulted in intense exploration and mining activity currently owned by Western Mining Corporation (WMC) (Sharp, 1996). Detailed study of the facies architecture centering around the felsic volcanics, and their relationship to mafic-ultramafic rocks is presented and suggests important constraints on further mineralisation in the area. Lower greenschist to amphibolite facies metamorphism destroys much of the primary texture however low strain/metamorphic grade sections preserve original textural and structural features. Recognition of primary mineralisation (Perriam, 1996) suggests that detailed examination of facies architecture will provide important constraints on the distribution of mineralisation. Although the majority of primary textures have been destroyed, distinct metamorphic packages are observed and may be interpreted to give the units origin. Feldspar and quartz phyric units dominate with overprinting metamorphic assemblages and varying degrees of strain masking original texture. Previously described as lapilli tuff deposits (Sharp, 1996) the dominant felsic lithologies show evidence of features observed within coherent bodies. The presence of porphyritic textures, flow banding and amygdaloidal structures aids in the identification. High strain, intensely metamorphosed schists and gneisses surround the phyric units, whether these are indicative of a higher grade of strain/metamorphism in the same phyric unit or a unique lithology will be established by trace element geochemical analysis. The association of tri-modal volcanic products with deep water, subaqueous sedimentary sequences of chert and black shales, along with the vast quantities of volcanics present, is suggestive of a rifting, extensional system perhaps a backarc basin associated with subduction. REFERENCES Sharp. D.R. (1996), The Stratigraphy and Structure of the Southern Portion of the Agnew-Wiluna Greenstone Belt" Internal Report (WMC). Perriam.R.P.A. (1996), The Geology and Mineralisation of the Agnew-Wiluna Greenstone Belt: 1. The Perseverance Leases of Leinster Nickel Operation" (WMC).

GEOLOGICAL SOCIETY OF AUSTRALIA, ABSTRACTS No. 55 13th Victorian Universities Earth Sciences Conference, The University of Melbourne, September 1999

AUTHOR INDEX Ahearne, D. Allen, T.I... Anolak, M Ansell, H Barras, V.J.1 Batiste, C Bayrak, A.A Bennett, R Black, J Blackam, M.J Brugger, J Buick, I.S Campbell, L Campi, M.J Cartwright, 1 Chang, K.C Coceani, P Collins, C.D.N Crozier, S Dawe, C Dickinson, J Finger, S Fleming, P.D Frederiksen, L Gilbert, L Gray, C.M Gray, J Halas, D Hill, K Hope, P Hough, M Houseman, G.A Huang, M.H Keable, S.M Keetley, J

Keppich-Arnold, M Keys, D Leman, M.S Liu, W Maas, R Martin, M.P Mayle, M McDonald, L McPhail, D.C.B Nguyen, C Noone, D Partridge, A.D Perkins, M.J Pharoah, A Pike, G Pittari, A Quinn, C.D Rawlinson, N Read, C.M Roadly, J Ruscoe, R.A Shen, S Shi, G.R Slots, M Smith, A Spiccia, L Tait, M Trofimovs, J Van Huet, S Wakelin-King, G Watkins, S.D Weldon, E.A Williams, I.S Yeo, C

42 55 37 18 38 71 5 49 61 50 61 8 56 19 15 6 73 13 80 21 2 44 75 3 39 75 40 82 9 30 83 13 8 31 9

25 23 19 63 8 65 4 57 61 9 34 26 75 68 76 59 84 13 15 53 86 19 19 78 22 61 88 90 45 46 79 28 8 36