Taxonomia, paleobiogeografia, paleoecologia e bioestratigrafia (Ostracoda) do Oligo-Mioceno da Formação Pirabas (Pará, Brasil).

Abstract

The limit Oligo-Miocene is marked by one of the largest marine transgressions in the world recorded in the Pirabas Formation, a predominantly carbonate sequence exposed in the littoral northern Brazil. The identification of ostracods from 35 outcrops samples and 22 from the drill core FPR-160 Primavera, collected in the Pirabas Formation, trough an extensive survey of the literature as well as the comparative study with type material from Bold´s and Howe´s collections allowed the identification of 36 new species, 12 species left in “aff.” and three in “cf.”; and 27 species common to the Caribbean Neogene; two species recognized for other areas and more one species already described for the studied unit herein, as well as 38 in open nomenclature completing a record of a total of 119 species. This broad taxonomic study provided a robust database for the accuracy of paleoenvironmental, biostratigraphic and paleogeographic studies from this unit, and also to increase the record of the paleobiodiversity of Neogene Ostracods from North of Southwestern Atlantic. The taxonomic study of ostracods yielded approximately 23 families, 64 genera and 119 species. The facies association indicate from shallow marine plataformal to lagoonal environments, and the ostracods genera as Haplocytheridea, Cytheridea, and mainly, Perissocytheridea and Cyprideis genus, as well as benthic foraminifera of Ammonia and Elphidium genera indicated the salinity variation in the environments. The 27 common species to Caribbean units showed a tiny similarity compared to the large number of new species recorded to Pirabas unit. The irradiation, restriction and extinction of the ostracofauna in these regions, due to the tectonic and eustatic process in these regions, provided a new arrangement in the distribution and consequently the paleobiogeographics provinces. However, it is considered that the ostracofauna recorded to Pirabas unit is inserted in a new subprovince correlated to the Caribbean subprovinces. In Pirabas Formation, the record of the five species indexes Glyptobairdia crumena, (N5 / N6) and Neocaudites macertus (N4 and N5) inserted in Globigerinatella insueta Zone; and Pokornyella deformis (N6 to N16), Cytherella stainforthi (N2 to N5), Quadracythere brachypygaia (N3 to N6) in Globigerinoides trilobus Zones, Catapsydrax dissimilis and Catapsydrax stainforthi allowed to determinate the Late Oligocene to Early Miocene to Pirabas sequence. The more than 100 species recorded into this interval allowed the recognition of a Cytherella stainforthi zone which is subdivided in four subzones: Jugosocythereis pannosa, Quadracythere brachypygaia, Glyptobairdia crumena and Porkonyella deformis with limits marked by first and last occurrence along the succession. This new zonation is preliminarly calibrated with the zonal planktonic foraminifers, corresponding to N3 to N7 zones of Blow, included in the Chatian to Burdigalian ages, corroborating with Neogene ostracod biostratigraphy to the Caribbean region. Thus, this ostracod zonation is of great significance for local, intrabasinal and regional correlation, particularly where foraminiferal, nannofossil or palinomorfs control is poor due to the litoral caracteristc of the Pirabas sequence.