OSTRACODES FROM THE RIO DA BATATEIRA FORMATION (LOWER CRETACEOUS, ARARIPE BASIN): PRELIMINARY RESULTS ON SYSTEMATICS, BIOSTRATIGRAPHY AND PALEOECOLOGY

VANESSA N. SYRIO ¹ AND ARISTÓTELES M. RIOS-NETTO ²

¹ Laboratório de Micropaleontologia (LabMicro) / Depto. de Geologia / IGEO / UFRJ.
² Laboratório de Micropaleontologia / Instituto de Geociências / UnB.

Presented by DIOGENES DE ALMEIDA CAMPOS

The Araripe Basin occupies an area of about 8,000 km², in the northeastern part of Brazil (Ceará, Pernambuco and Piauí states). Besides being worldwide famous for its paleontological content, the study of the Araripe Basin is especially significant since its geological history can be partially correlated with the geologic development of some Brazilian marginal basins. The present study is focused on the Rio da Batateira Formation, since there are some unsolved questions regarding this unit such as stratigraphic boundaries, depositional environment and correlation with other lithostratigraphic units. The sample studied in the first phase of the research was collected in an outcrop of the Batateira River, locality of Lameiro, Crato City, Ceará State (S 7º14'57.8''; W 39º27'11.6''). At this locality, the Rio da Batateira Formation is formed by dark grayish shales and carbonates, rich in microfossils (mainly ostracodes and conchostraceans). The following taxa were found: Candona sp., Harbinia micropapillosa, Theriosynoecum silvai, Darwinula martinsi, Brasacypris sp.1 and Zonocypris sp.1. Among these taxa, Candona sp. and Harbinia are characteristic from the Biozone 011 (Do Carmo 1998, D.Sc. Thesis, Curso de Pós-graduação e Geociências/UFRGS; Paulo Milhomem, personal communication), generally associated with the Alagoas stage (Late Aptian/ Early Albian). Furthermore, Theriosynoecum silvai and Darwinula martinsi, present in the sample, are also associated with this biozone. All ostracodes found in the sample are non-marine. Most of them can tolerate salinity variations from 0% to 10%, and Darwinula martinsi up to 15% (Do Carmo 1998, op. cit.). These preliminary analysis indicate fresh to mixohaline depositional environment. — ( December 20, 2001 ).