Estudos taxonômicos e paleoecológicos dos foraminíferos e ostracodes do aptiano/albiano da formação romualdo da bacia do araripe, sítio canastra, NE-Brasil

Abstract

The Araripe sedimentary basin is located in northeastern Brazil between the states of Ceará, Piauí and Pernambuco, and has a stratigraphic framework made up of sediments deposited during the rifting of Gondwana. It is characterized as an important fossiliferous deposit and holds relevant paleontological and paleoenvironmental information for understanding the opening up of the Atlantic Ocean through the records of marine ingressions during the Aptian Albian period of the Cretaceous Mesozoic Era. The Romualdo Formation is one of the stratigraphic units that make up the Araripe Sedimentary Basin and has a wealth of (micro)fossils and their remains. The aim of this work was to identify the microfossils present in the Canastra outcrop and infer paleoenvironmental and paleoecological information about marine incursions during the Aptian/Albian of the Araripe Basin. Fourteen samples were collected in the southwestern part of the Araripe Basin, at the Canastra outcrop located in Araripina/PE. The material was prepared by breaking up and weighing 100 g of the samples, immersing them in 29% hydrogen peroxide (H2O2) for 24 hours, then washing them in #250, #125 and #0.062 mm sieves, placing them in an oven at 60°C for drying and finally sorting. It was possible to find 7.770 microfossils, of which 221 (2.8%) were foraminifera and 7.549 (97.2%) ostracods. The most abundant samples were: 0.5 m (819), 0.6 m (1030) and 0.8 m (959). The foraminifera species found were: Astacolus sp., Astacolus sp. 1, Agathammina sp. 1, Agathammina pusilla, Bathysiphon sp., Conorboides minutissima, Miliolinella sp. 1, Pseudonodosaria sp., Quinqueloculina sp., Rhabdammina sp., Spirosigmoilina sp. 1 and Spirosigmoilina rajkae?.and of ostracodes: Alicenula sp. 1, Alicenula sp. 2, Cyprídea sp., Damonella sp. 1, Damonella grandiensis, Damonella ultima, Dicrorygma cf. minuta, Ilyocypris sp. 1, Ilyocypris sp. 2, Mantelliana sp. 1, Mantelliana speculum, Mongolianella sp. 1, Mongolianella sp. 2, Mongolianella aptianensis, Paracypria sp., Paracypris sp., Pattersoncypris sp. 1, Pattersoncypris sp. 2, Pattersoncypris sp. 3, P. cucurves, P. salitrensis and Theriosynoecum sp. The number and diversity of foraminifera and ostracod species in the Canastra outcrop are similar to those found in the outcrops in the central-south and southeast regions of the basin, while the eastern region is less similar. No guide foraminifera were found in this unit, but it is important to highlight the ostracode Damonella grandiensis for determining the Aptian age deposits in the Araripe Basin. In addition, the association of foraminifera and ostracods found in this study indicated a paleoenvironment formed by records of sea level oscillations throughout the Aptian/Albian in the Canastra section, Araripe Basin, with periods represented by transitional to marine environments on the inner shelf with moderate to intense hydrodynamics. Finally, it is an outcrop where shallow waters predominate, with little organic matter and high oxygenation.