Sequence Development of the Late Miocene Mixed Carbonate-Siliciclastic Cercado Formation, NW Dominican Republic

Preserved paleotopography and exceptional exposure of the Late Miocene Cercado Formation in the Dominican Republic allows for the evaluation of controls in a mixed carbonate-siliciclastic system exposed along a selected ~1.4 km transect of the Arroyo Bellaco River. Three sequences (DS1, DS2, DS3) were deposited over a gently northward dipping (<1°) substrate. Our initial results indicate that the three sequences developed a basinward progradational pattern during an overall relative sea-level fall interrupted by two relative sea-level fluctuations, with each successive rise resulting in a sea-level position that was further basinward than the previous sequence. DS1 (1-6.5 m thick) is composed of two stages. Proximally, stage 1 and stage 2 are characterized by shallow marine siliciclastics that grade basinward into isolated corals and coral reef mounds (<1-2 m thick; stage 1), a mix of in-situ and transported mainly branching Porites and Agaricia-type platy corals (stage 2), and Montastrea-type coral mounds (stage 2) that developed further basinward compared to stage 1. DS1 is capped by a laterally extensive sharp to gradational contact that is interpreted as a sequence boundary (SB1), evidencing possible subaerial exposure and marine wave planation that indicates a minimum sea-level fall of 2m. DS2 (2-7.5m thick) is composed of a distinct ~1 meter-thick laterally traceable marginal marine to marine bioturbated siliciclastic sandstone deposited during low and rising relative sea level. Proximally, cross bedded grainy heterozoan-dominated facies overlie the sandstone and transition basinward to fine branching and head corals. Further basinward coral mound zones are abundant. DS2 is overlain by a laterally extensive sharp, erosional surface that is interpreted as a sequence boundary (SB2) evidencing local subaerial exposure and marine wave planation that indicates a minimum sea-level fall of 2m. DS3 (1.5-12 m thick) consists of a basal shallow marine siliciclastic sandstone that grades basinward into Pocillopora-type reefs, then mixed small head corals and finally coral stringers in fine-grained siliciclastic facies. The upper portion of DS3 is composed of marine to marginal marine siliciclastic sandstones and conglomerates that migrated basinward over DS3 carbonate facies. This initial work provides the basis for further analyses and quantification of the controls on this mixed system and comparison to other Caribbean project study sites.

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California