A Sedimentary Record of Marine Flooding Events from Coastal Salt Ponds, Southwest Puerto Rico UPR Sea Grant Project# R-94-2-10 Final Project Report Submitted to University of Puerto Rico Sea Grant College Program 27 April 2015 Clark E. Sherman Department of Marine Sciences University of Puerto Rico – Mayagüez Project period: 1 February 2010 to 31 December 2014 (including no-cost extensions)
Executive Summary Summary of Impacts and Contributions Objectives Objective 1 – Document the Chronology and Frequency of Marine Flooding Events The documented stratigraphy reveals a dramatic change along this coastline involving an abrupt transition from normal marine conditions to restricted hypersaline lagoons. Radiometric data indicate that this transition first occurred ~1400-1700 yr BP, with a second transition occurring ~400-500 yr BP. The sharpness of each of these shifts suggests that they may have been event driven. A shell-hash layer dated at ~600 yr BP indicates an overwash event that may have been responsible for the second transition documented in the core stratigraphy. Current salt pond settings are geologically quite young and seem to have been established only ~400 yr BP. Within the salt pond sediments, thin carbonate sand layers in some cores suggest overwash events. However, because they are so recent, their precise age cannot be established by radiocarbon methods. It appears that there may been 2-3 overwash (marine-flooding) events over the last ~400 yr. Objective 2 – Document the Physical Character and Composition of Marine Flood Deposits The character and composition of all primary facies have been documented to determine deposition setting and environmental changes over time as well as differentiate potential washover deposits. Three primary facies have been described, the Halimeda facies, peat facies, and organic-rich mud facies. Potential washover deposits occur as thin (~1 cm) layers of coarser marine grains consisting primarily of mollusk fragments (i.e., shell hash) within the organic-rich muds of Unit I. Objective 3 – Correlate Marine Flood Records with Historical and Other Geologic Records The most striking feature of the documented stratigraphy is the abrupt transition from normal marine conditions to mangrove swamp and isolated hypersaline pond. Radiocarbon ages [1]