Effects of Sea Level and Upwelling on Development of a Miocene Shallow-Water Tropical Carbonate Ramp System, Ponce, Puerto Rico
Diana Ortega-Ariza, Evan K. Franseen, "Effects of Sea Level and Upwelling on Development of a Miocene Shallow-Water Tropical Carbonate Ramp System, Ponce, Puerto Rico", Sequence Stratigraphy: The Future Defined, Bruce Hart, Norman C. Rosen, Dorene West, Anthony D’Agostino, Carlo Messina, Michael Hoffman, Richard Wild
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Middle-late Miocene (ca. 13-10 Ma) Ponce Limestone exposures in southern Puerto Rico provide an opportunity to evaluate development of a tropical carbonate ramp system during a time of known regional upwelling in the Caribbean. Three sequences (DS1, DS2, and DS3) developed in response to relative sealevel fluctuations. Each sequence is characterized by basal heterozoan-larger benthic foraminifera (LBF) facies that grades upward to a photozoan facies composed of corals tolerant of cool and turbid water at the top. DS1 transgressive deposits include Kuphus (?incrassatus), Amphistegina-Archaias packstone interbedded with Amphistegina packstone, and Archaias angulatus and gastropod-rich packstone. Maximum flooding is indicated by a Globigerinid planktonic foraminiferal facies. Upper DS1 strata consist of Montastraea imperatoris, Goniopora imperatoris, and several species of Porites coral rud-floatstone and framestone, which were deposited during highstand and sea-level fall. DS1 is capped by a surface of subaerial exposure (SB1).
DS2 transgressive deposits consist of Amphistegina-coralline red algae packstone-grainstone that grade upward to coralgal-Amphistegina packstone deposited during highstand and sea-level fall. DS2 is capped by a surface of subaerial exposure (SB2).
A rapid sea-level rise for DS3 is interpreted due to the apparent lack of transgressive deposits.
Preserved strata consist of prograding coralgal clinoforms developed during highstand. SB1 (~13-12 Ma) and SB2 (~11-10 Ma) may correlate with unconformities in other Caribbean areas, which could indicate regional tectonic or eustatic control on sequence development. The dominance of heterozoans and larger benthic foraminifera tolerant of mesotrophic and temperate water conditions and the presence only of those photozoan corals tolerant to turbidity and cooler water are consistent with a system affected by upwelling. The presence of photozoan corals only in the highstand and regressive portions of sequences suggests highest upwelling intensity and/or transport of upwelled water and nutrients to shallowest water ramp environments during transgressions. Our results have direct implications for other similar age-equivalent systems developed in the Caribbean, including those forming important reservoirs, and other tropical systems in the rock record affected by adverse photic zone conditions.