Paleosalinity history of middle Holocene lagoonal and lacustrine deposits in the Enriquillo Valley, Dominican Republic based on pore morphometrics and isotope geochemistry of ostracoda

Abstract

The southwestern region of the Dominican Republic (Enriquillo Valley) contains exceptionally well-preserved, relict marine and saline lake deposits of mid-Holocne age. Abundant euryhaline ostracodes found in this deposit include Cyprideis salebrosa, C. mexicana, C. similis ,a ndC. edentata. Morphometric and geochemical analyses performed on Cyprideis spp. provide high 18 Oa nd 13 C values that are coincident with relative abundances of irregularly shaped pores that permeate the ostracode carapace. We recognize three stratigraphic intervals with distinct ostracode pore shape and stable isotope trends: (I) a 4.5-5.0m interval that contains ostracodes with highly irregular shaped pores (multiradiate) and high amplitude variability in 18 Oa nd 13 C values; (II) a 5.0-5.6m interval com- prised of ostracodes with circular pores and an overall trend towards low 18 Oa nd 13 C values; and (III) a 5.6-6.5m interval containing ostracodes with an upward increasing abundance of circular pore shapes coincident with a decreasing trend in 18 Oa nd 13 Cv alues. When the Enriquillo lagoon was first separated from the Caribbean Sea approximately 4.3 ka, an arid and evaporative climate led to hypersaline water in a restricted lagoon environment. By the middle to late-Holocene, increased precipitation in the valley resulted in a coastal lake system that became progressively oligohaline. Moderate to small amplitude variability in the salinity proxy data ( 18 O) sug- gest short-term oscillations in the precipitation-evaporation budgets at that time. At least two marine incursions likely contributed to the observed variability in ostracode 18 Oa nd 13 C values. Evidence for abrupt changes in base level indicate that climatic factors or also tec- tonic activity may have contributed to the observed paleoenvironmental trends recorded in these deposits.