The genus Perissocytheridea Stephenson, 1938 (Crustacea: Ostracoda) and evidence of brackish water facies along the Oligo-Miocene, Pirabas Formation, eastern Amazonia, Brazil

摘要

Perissocytheridea Stephenson is characteristic of brackish water fades. In 57 samples from the Upper Oligocene to Lower Miocene, from five localities, Pirabas Formation, Para State, Brazil eleven species have been identified. Among these species, four are new reports: Perissocytheridea punctoreticulata n. sp., Perissocytheridea largulateralis n. sp., Perissocytheridea colini n. sp. and Perissocytheridea pirabensis n. sp.; five species in open nomenclature: Perissocytheridea sp. 1, P. sp. 2, P. sp. 3, P. sp. 4, and P. sp. 5 and two species left in "aff." abbreviation: Perissocytheridea aff. Perissocytheridea pumila and Perissocytheridea aff. Perissocytheridea brachyforma subsp. excavata. The distributional pattern of the Perissocytheridea combined with the occurrence of foraminifera Elphidium and Ammonia in the studied sections supports the presence of the brackish water facies to the respective layers. Their quantitative variation through the studied sections indicate more than one phase of salinity reduction (about >5 and <30 ppm) and/or the decrease of the sea level, forming lagoon along the Pirabas Formation. This genus has a wide paleobiogeographical occurrence and stratigraphic distribution ranging from the Cretaceous to Recent, and already been recorded in the northern of South America, especially in the Neogene of Solimoes Basin, but this is the first report of a neotropical genus to the Oligo-Miocene deposits of Pirabas Formation, northern Brazilian Coast, Para State. (C) 2015 Elsevier Ltd. All rights reserved.