The Triassic period started more than 250 million years ago and spanned over 50 million years. We spoke to Professor Rossana Martini about her work in studying marine shallow-water (reefal) limestone from this period, and the importance of this research to understanding the biological and ecological changes that occurred during the Triassic.
Delving deep into the Panthalassa Ocean The Panthalassa Ocean covered around 70 percent of the Earth’s surface during the latter part of the Triassic period, an area much larger than the modern Pacific Ocean. The sediments deposited in this immense ocean are therefore the best record of the environmental and biological conditions during the Triassic. As the Principal Investigator of the REEFCADE project, Prof. Rossana Martini has deep expertise in the analysis of rocks and sediments dating from the Upper Triassic, from which new insights can be drawn about the environment and climate during this period. “The idea in the project has been to check the composition of limestone rocks originating in different parts of the world. We have found organisms that allow us to date rocks precisely as from the Upper Triassic,” she says. Much of the previous research on the sedimentary rocks and biodiversity of this period has focused on limestone deposited in the much smaller Tethys Ocean; now researchers aim to gather more information about the Panthalassa, then draw comparisons between deposits of reefal limestone in the two oceans. “This means the most accessible and well preserved limestone deposits that were deposited in the continental plateau during the Upper Triassic,” explains Prof. Martini.
REEFCADE project A large number of samples have been gathered from all over the world during the project, including Japan, the Far East of Russia, as well as North and South Americas, which have then been subjected to rigorous analysis. These limestone rock samples were originally deposited in a fairly shallow waters, typically at a depth of less than 150 metres, with Prof. Martini and her PhD students looking for the presence of certain organisms that would allow them to date the rocks as precisely as possible. “I am a specialist in Permian and Triassic small Foraminifera, which are very valuable unicellular organisms to date rocks and specify rock depositional environments. We also use Conodonts, which are small pieces of very old vertebrates resembling eels, which lived in the sea from the Palaeozoic period to the end of the Triassic. Conodonts are also very useful for dating rocks, as they became extinct at the boundary between the Triassic and Jurassic
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Global reconstruction at 220 Ma (Norian) after the Panalesis model (Verard, 2019b); Robinson projection.
periods,” she outlines. By analysing these rocks, and looking at their isotopic composition, researchers hope to identify the different factors that affect how they are distributed and controlled within the oceans. “We have applied the same workflow in all the studied localities in the frame of REEFCADE,” says Prof, Martini. Researchers have conducted in-depth analysis of these rocks, looking for example at their diagenetic features and their chemical
studies also allow us to be more precise about the reservoirs of natural resources, of gas or oil for example,” she continues. The aim now is to bring various different strands of research in the project together and establish a clearer picture of what happened in the huge Panthalassa Ocean during the Upper Triassic period. One of the main goals is to understand how organisms were distributed around the Panthalassa Ocean at this time, a
The idea in the project has been to check the composition of rocks found in different parts of the world. We have found some organisms that allow us to date these rocks precisely as from the Upper Triassic. composition, and trying to gain deeper insights. Along with analysis, Prof. Martini and her research group have spent time out in the field. “We go out into the field, often exploring localities and outcrops for the first time, we collect samples and then we go back to the lab. We proceed to the preparation of the samples, which are very thin slices of rocks, and we look at them in the microscope, to see the components of the rocks and to date their deposition,” she says. This evidence provides a basis for Prof. Martini and her students to then effectively reconstruct the depositional systems during the Upper Triassic period. “We can reconstruct the environment in the past, the ecology at this time. There are also some applications to industry, since these
topic on which views have shifted over recent years. “Until around 15 years ago it was considered that the Tethys Ocean was the niche of biodiversity. It was assumed that marine life during the Triassic developed first in the Tethyan ocean,” says Prof. Martini. This was because the Tethys Ocean at that time was very shallow, in comparison to the Panthalassa, with a large zone on the continental shelf that was ideal for the development of life. “We know that more than 75 percent of life in the sea is nowadays developed on the continental shelf, and not in the deep. Nutrients and oxygenation are much more abundant in such environments, and the temperature is more conducive,” explains Prof. Martini. “This is one of the reasons why it was
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