EVALUATING CONTROLS ON MIOCENE CARBONATE-DOMINATED SEQUENCES IN PUERTO RICO AND THE DOMINICAN REPUBLIC

Exceptional exposures of the Middle-Late Miocene carbonate sequences in Puerto Rico (PR) and Late Miocene mixed carbonate-siliciclastic sequences in the Dominican Republic (DR) provide an opportunity to construct quantitative sea-level histories and compare the contributions of sea level, structure, paleogeography, and oceanographic conditions in development of these sequences. In the Ponce Limestone (PR) three depositional sequences (DS) are identified, each of which are capped by sequence boundaries indicating relative sea-level falls on the order of 10’s of meters. Basal DS1 subtidal heterozoan facies grade upward into Porites reef facies, which migrated down paleoslope during a relative sea-level fall. DS2 is dominated by heterozoan facies that are overlain by a karst breccia. DS3, dominated by abundant heterozoan facies, transitions upward to coral reef facies and red algae boundstone in downslope areas suggesting shallow water conditions after a relative sea-level fall. In the Cercado Formation (DR) three mixed carbonate-siliciclastic sequences are identified, each of which are capped by sequence boundaries indicating relative sea-level falls of at least several meters. DS1 is characterized by shallow marine siliciclastics that grade basinward into a mix of in-situ and transported corals and coral mounds. Basal DS2 and DS3 are composed of shallow marine siliciclastics deposited during low and rising relative sea level. In DS2 grainy heterozoan facies overlie the sandstone proximally and transition basinward to branching and head corals. In DS3 the sandstone grades basinward into Pocillopora reefs, then mixed small head corals and finally transported coral forming stringers in fine-grained siliciclastic facies. The succession culminates with deposition of marine siliciclastic sandstones and conglomerates at the top of DS3. The ability to constrain sea-level history provides the basis to evaluate other controls on the systems. For example, the relative absence of photozoan components in basal portions of Ponce sequences suggests a perturbed system during transgressions (e.g. nutrient excess). In contrast, photozoans occur throughout Cercado sequences in the study area, indicating conditions for their development were not greatly affected during sea-level fluctuations.