Journal of Conference Abstracts

Depositional Architecture of the Pliocene Pedro Castle Formation, Grand Cayman: A Paleoenvironment and Sea Level Record

Astrid Arts (astrid.arts@crestar-energy.com)¹ & Brian Jones (Brian.Jones@UAlberta.ca)²

¹ Crestar Energy, 333-7th Ave SW, Calgary, Alberta T2P 4M8, Canada

² Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

Facies analysis provides insight to the paleoenvironment of a given horizon and can be a useful way of comparing local sea level history to established eusatic sea level curves.

This study of the Pliocene Pedro Castle Formation on the southwestern corner of Grand Cayman is part of continuing research in understanding the development and evolution of the Cayman Islands. Shallow core and accessible outcrops examined from 11 localities displayed seven facies assemblages with a faunal and floral distribution that records a changing environment throughout deposition. These assemblages in an ascending order include: 1) rhodolith Amphistegina Trachyphyllia facies, 2) Amphistegina rhodolith facies, 3) foram Halimeda rhodolith facies, 4) rhodolith, free living and branching coral Amphistegina facies, 5) Stylophora Halimeda Amphistegina facies, 6) Halimeda Amphistegina facies, and 7) rhodolith coralline red algae facies. These facies in a vertical sequence are indicative of a trangressive succession. Numerous autogenic and allogenic processes controlled the development of this succession. Antecedent topography, substrate and water energy were the dominant autogenic controls and sea level was the dominant allogenic control. The identification and interpretation of the impact of these individual processes on both facies composition and architecture revealed information vital to the accurate reconstruction of Tertiary paleoenvironments and sea levels.

There are inherent problems when utilizing plants and animals such as rhodoliths, Trachyphyllid and Stylophorid corals, foraminifera, red and green algae, echinoids, gastropods and bivalves to determine paleoenvironments and paleo-sea levels. Identifying biota indicative of any one environment is difficult due to the adaptive nature of these marine plants and animals. Further, when examining outcrop or core, the fossil assemblage and abundance rather than presence of a particular biota are the more important indicators of paleoenvironment.

Results from this research demonstrate a transgressive succession during the deposition of the Pedro Castle Formation. A gradual increase in bathymetry is seen as a quieter more restricted faunal assemblage is preserved. Sea level, of 30-40 m asl, interpreted from this area is in accordance with estimates of Pliocene sea level determined from other localities in the Caribbean and globally.

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