Miocene-Pliocene Heterozoan-Dominated Systems in the Dominican Republic: Analogs for Neogene Reservoirs in the Caribbean

Abstract

Shallow-water heterozoan carbonate systems form important hydrocarbon reservoirs in the rock record, yet models for these systems are lacking. Well exposed Miocene to Pliocene mixed carbonate-siliciclastic ramp strata in NE Dominican Republic provide an excellent opportunity to evaluate controls on heterozoan-dominated systems. Outcrop study and strontium isotope age dates indicate five 3rd-order sequences (DS) developed in response to relative sea-level fluctuations. DS1a (ca. 15.75-12.93 Ma) basal facies are dominated by echinoid and bivalve packstones deposited during transgression, and patches of in-place Montastraea and Porites corals at the top, deposited during highstand and falling sea level. DS1b (ca. 12.93-11.34 Ma) consists of three internal sequences. Each sequence consists of basal rhodolith, benthic foraminifera, mollusk, and echinoid packstones, and bioturbated wackestones capped by paleosols. DS2 (ca. 11.34-7.14 Ma) basal mollusk, echinoid, and benthic foraminifera packstones, deposited during transgression, grade upward to in-place Montastraea and Porites coral patches deposited during highstand and falling sea level. DS3 (ca. 7.14-4.57 Ma) basal marine claystones with whole vertebrates, and mollusk and benthic foraminifera fragments were deposited during transgression. They grade upward to mollusk, echinoid, and benthic foraminifera packstone, followed by in-place Montastraea and Porites coral patches at the top, deposited during highstand and falling sea level. DS4 (ca. 4.57-? Ma) basal mollusk, echinoid, and benthic foraminifera packstones, deposited during transgression, grade upward to abundant in-place Montastraea and Porites coral buildups. Upwelling was an important process in the Caribbean during the Middle and Late Miocene. The pattern of heterozoans deposited during transgressions, and photozoans (cool- and turbid- water corals) only occurring during highstands and regressions in our study is similar to patterns identified in other Caribbean Miocene ramp sequences. This regional pattern supports a relationship of upwelling to relative sea level, with highest upwelling intensities during transgressions. The abundance of photozoan corals in DS4 coincides with decreased upwelling and dominance of photozoan systems throughout the Caribbean. Our results provide predictive models for heterozoan reservoirs, and have direct application to important Neogene heterozoan reservoirs in the Caribbean, such as offshore Venezuela.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016