Palaeoceanographical events from the late Miocene to Pleistocene of the Rio Grande Rise (south-western Atlantic) as indicated by Ostracoda

摘要

The present research assesses the significance of ostracods from the Rio Grande Rise for the understanding of the palaeoceanographical evolution of this important physiographical feature of the south-western Atlantic. The core MD11-L2P3, drilled in the western portion of the Rio Grande Rise, contains sediments ranging from the late Miocene (Tortonian) to the Pleistocene, according to planktonic foraminifer biostratigraphy. Thirty-one ostracod species belonging to 19 genera and nine families were identified. Cytheropteron and Krithe are the richest genera with six and four species, respectively. Bradleya ybate sp. nov., Bradleya majorani sp. nov. and Microcythere acuminata sp. nov. are described. Some species present high abundance and long stratigraphical occurrence throughout the studied section (e.g. Bradleya majorani sp. nov., Henryhowella asperrima, Poseidonamicus miocenicus Benson and Cythereis richardbensoni Yasuhara etal.), yet most have a shorter stratigraphical distribution. Cumulative diversity enabled the characterization of three assemblage groups, herein named AG I, AG II and AG III. Changes in the assemblage compositions are ascribed to hydrological variations associated with Neogene climatic events, inasmuch as the studied interval records the cooling trend established during the late mid-Miocene Climatic Optimum.http://zoobank.org/urn:lsid:zoobank.org:pub:146FF2DE-C331-4DB0-852D-EC8BC5D658A