Early Neogene palaeoenvironmental variability along the margins of the eastern Caribbean plate

摘要

This paper is the first review of Early Neogene palaeoenvironmental variability along the eastern Caribbean plate margins. We present new benthic foraminiferal data from (1) a single Spring Garden Member sample, Montpelier Formation, Jamaica at the Pots and Pans exposure, and (2) an offshore Dominican Republic gravity core (LDEO Eastward EA46-67 005D). Regional comparisons are made between our new data, the Cipero-Brasso-Nariva facies-belt complex of Trinidad, and coeval formations with suitable benthic foraminiferal data in Jamaica, the Dominican Republic, and Venezuela. We call these sites 'marginal regions' with respect to the Caribbean tectonic plate.Planktonic Foraminifera were used for biostratigraphic control and benthic foraminifera for palaeoenvironmental inferences. Shannon's Diversity Function H, the Benthic Foraminiferal Oxygenation Index (BFOI), and a Nutrient Flux Index (NFI) are used to explore and quantify palaeoenvironmental variability. We also present an Open Sea Nutrient Flux Index (OSNFI), calculated from the summed log-transformed plus unity proportional abundances of Globocassidulina subglobosa, Pullenia bulloides, Oridorsalis umbonatus and Spheroidina bulloides, to quantify nutrient flux to the deep-sea.Planktonic Foraminifera placed our Spring Garden sample at the Middle Miocene (Zone M6), and Core EA46-67 005D in the Pliocene/Pleistocene. Dominant benthic foraminifera differed for each marginal regional exposure. The Spring Garden Member was dominated by Loxostomum applinae and Core EA46-67 005D by Siphonodosaria hispidula. Other Dominican Republic sections were dominated by Bolivina spp. Siphonodosaria insecta dominated many Cipero Formation exposures.The marginal regions experienced varying nutrient fluxes to the sea floor. The lower bathyal Sombrerito and middle bathyal Trinchera Formations, Dominican Republic, experienced an enhanced nutrient flux to the sea floor. This may have been due to local upwelling, or delivery of nutrient-rich water from an upwelling cell along the northern South American shelf by a northerly-flowing filament. The neritic to bathyal Brasso Formation also experienced upwelling, indicated by the development of a pronounced oxygen minimum zone (OMZ). The extent of the oxygen depletion differed between the Brasso and the Sombrerito and Trinchera Formations, Uvigerina spp. being abundant in the Brasso but rare in the Dominican Republic. In contrast, the deep-water Cipero and Jamaican Basins were nutrient deficient.Oxygen concentrations based on BFOI varied between the marginal regions. The Cipero and Jamaican Basins were generally well oxygenated. The Sombrerito Formation, within the Azua Basin, was also well oxygenated. The Azua Basin, however, became low oxic during deposition of the Trinchera Formation, and this persisted to the Pliocene/Pleistocene Core EA46-67 005D.