NEOGENE SEDIMENTATION AND TECTONICS IN THE CIBAO BASIN AND NORTHERN HISPANIOLA - AN EXAMPLE OF BASIN EVOLUTION NEAR A STRIKE-SLIP-DOMINATEDPLATE BOUNDARY

Sedimentologic analyses, subsidence history interpretation, and a new gravity survey are synthesized to interpret basin evolution in a regio n of large strike-slip offsets and oblique crustal convergence within the northern Caribbean plate boundary zone. We investigate the mid-Mio cene to mid-Pliocene Yaque Group, which accumulated in the western Cib ao basin of northern Hispaniola. Asymmetric subsidence of the Cibao ba sin was accompanied by southward transgression and deposition of an up ward-fining succession from shallow-marine or brackish water conglomer ate through sub-wavebase siltstone to deep-water calcareous siltstone and uncommon interbedded sandstone; bioclastic Limestone is locally pr esent and in most cases accumulated in a forereef location. In early P liocene time (ca. 4 Ma), fine-grained sediment deposition was briefly interrupted by widespread conglomerate accumulation; however, basin su bsidence was uninterrupted, and water depths continued to increase. At this time, basinal subsidence accelerated as the Cordillera Septentri onal was uplifted along the Septentrional fault zone at the basin's no rthern flank. The across-strike gravity profiles require a S-vergent t hrust component along most of the Septentrional fault zone. Gravity va riations indicate that the Septentrional fault zone dips northward (si milar to 50 degrees) in the central part of the basin, adjacent to the Septentrional fault zone, where the basin is deepest, and steepens ea stward and westward. Contrasts in sedimentation patterns between the C ibao basin and elsewhere in northern Hispaniola reveal a complex histo ry of dominantly strike-slip faulting modified by varying amounts of c onvergence.