PALEOECOLOGICAL SUCCESSION OF REEF AND LAGOONAL DEPOSITS IN THE DOMINICAN REPUBLIC DURING THE EARLY-TO MIDDLE HOLOCENE

The southwestern region of the Dominican Republic contains well-preserved reef and lagoon deposits that have been the focus of numerous paleoclimatic studies. During the Early-to Middle Holocene, the Enriquillo Valley was an extension of the Caribbean Sea where a fringing coral reef thrived until alluvium deposits separated the lagoon from the sea creating the modern saline lake. Our objective herein is to use ostracodes and stable isotopes (d¹⁸O, d¹³C) to document the paleoecological succession of a stenohaline reef to oligohaline lagoon that was potentially forced by the northern migration of the Intertropical Convergence Zone (ITCZ) with increased northern hemispheric warmth during the Early-to Middle Holocene time interval.

The stratigraphic section at Las Clavellinas comprises an upward fining sequence of alternating calcarenite and micrite that grades up-section into a thick grey mudstone. We observe three microfossil associations. Biofacies A is characterized by the stenohaline marine ostracode Bairdia victrix associated with a relatively rich foraminiferal assemblage. This facies is associated with Acropora cervicornis and Montastraea annularis corals accordingly. Biofacies B is characterized by the mesohaline ostracoda Loxoconcha fisheri in association with Loxoconcha levis(?) and the coral Acropora cervicornis. Biofacies C contains mesohaline Loxoconcha sp. and brackish Cyprideis salebrosa. The Acropora cervicornis coral bed pinches out laterally up-section into a clastic shell bed.

The paleoecological succession indicates a transition from dry/cool conditions in a marine lagoon that gave way to warm/wet conditions and increased freshening in the lagoon. These past climate reconstructions in the Dominican Republic provide another perspective into tropical climate evolution during development of the Middle Holocene Thermal Maximum and the impact on reef ecosystems.