LATE NEOGENE PLANKTONIC FORAMINIFERA OF THE CIBAO VALLEY, BIOSTRATIGRAPHY AND PALEOECOLOGY

The late Neogene history of the Caribbean region presents many questions of global geologic significance. Since the late Miocene, tectonic, volcanic, and eustatic events in Central America and the Caribbean have helped shape global climate, oceanography, and marine biogeography. This study is an examination of a ~5.1 million year time slice (8.6-3.5 Ma) during which intensified geologic activity in Central America directly influenced Atlantic paleobiology and paleoceanography. In order to assess ecologic changes in Caribbean surface waters, a dense sampling of planktonic foraminifers is described from the Cercado, Gurabo, and Mao Formations in the Cibao Valley, northern Dominican Republic. The well-exposed, fossiliferous strata located in the Cibao Valley provide vital information concerning the geologic history of the Caribbean, serving as useful tools in understanding how tectonic and eustatic events have shaped depositional environments and marine community distributions. In addition, the use of planktic foraminifers provides a biostratigraphic framework for a region whose stratigraphy has proven difficult to correlate. Predominant taxa carry distinct implications concerning the evolution of Caribbean paleoecology and paleoceanography. Increasing abundances of Gs. sacculifer and Gs. ruber along with a decrease in G. bulloides suggests increasing salinity and diminishing primary productivity throughout the study period. A sharp increase in Gs. sacculifer and Gs. ruber at ~4.7 Ma implies a sudden rise in Caribbean surface water salinity with a decline in primary productivity. The mechanism for this change is isolation of the Caribbean Ocean through enhanced closure of the Central American Seaway (CAS). The closure of this oceanic pathway cut off the Pacific and redirected warm, equatorial waters northward, giving rise to the Gulf Stream. Upwelling events are suggested in the upper Cercado Fm. (~6.1 Ma) and in the middle Mao Fm. (~4 Ma) by spikes in G. bulloides and Neogloboquadrina spp. respectively. These events suggest that specific episodes of uplift in the Isthmus of Panama blocked the flow of Atlantic deep-to-intermediate waters. The last recorded upwelling event likely represents the final closure of the CAS, a significant event in Neogene global geology.