Evolution of Stratal Geometry and Carbonate-Siliciclastic Mixing in a Transpressional Basin of a Mature Volcanic Arc: Cibao Basin, Northern Dominican Republic
An integrated stratigraphic model for the Cibao Basin in the northern Dominican Republic characterizes three stacked depositional sequences. The three sequences, each bounded by distinct subaerial exposure surfaces, contain a succession of changes that are reflected in geometry of the stacked sigmoids, the bedding style, and the type of carbonate deposition. Together, these successive changes dictate how potential reservoir-scale characteristics vary through the sequence bundle. The basal sequence (Cercado Formation) is dominated by siliciclastic sands with scattered patch reefs across the inner to middle shelf. These inner shelf deposits prograde as low-angle clinothems. The patch reefs, although locally well developed, form isolated carbonate bodies encased in fine sand and mud. Topset deposits are mostly shallow-water siliciclastic sands. The middle sequence is a series of clinothems dominated by middle shelf skeletal carbonates in a silt-sized siliciclastic matrix (Gurabo Formation). In-situ branching-coral thickets dominate the carbonates, with distinctive coral debris beds. These clinothems have well-developed carbonate topsets that infilled inner shelf accommodation space as they prograded seaward. These topset beds are composed of shallow-water corals, red algae, molluscs, and abundant benthic foraminifers. The uppermost sequence (Mao Formation) is series of steeply inclined clinothems, and deposits are significantly more carbonate dominated. Progradation occurred as rhythmic siliciclastic mud-skeletal slope carbonate cycles, capped by coral-rich topset beds. The evolution of the sequence bundle is marked by a striking increase in carbonate with each succeeding sequence. This change is likely related to a combination of both intrinsic and extrinsic controls. Intrinsically, progressive progradation of the shelf margin into the basin seaway helped improve marine circulation for carbonate growth and increased distance from bedload (fluvial?) siliciclastics (suspended load mud was still prevalent). Regionally, the progressive closure of the Central American Seaway began to reduce upwelling intensity and associated surface water productivity, this decline favored conditions for skeletal carbonate precipitation. That regional paleoceanographic conditions factored into the long-term evolution of the sequence composition demonstrates the importance of extrinsic influences on stratal geometry and composition in mixed systems.
AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California