Ostracoda and foraminifera biostratigraphy and palaeoenvironmental evolution of the Aptian Santana Group, post-rift of the Araripe Basin, Brazil

Abstract

The Santana Group, consisting of the Barbalha, Crato, Ipubi and Romualdo formations, records the post-rift sequence of the Gondwana break-up in the Araripe Basin. The post-rift phase of the South Atlantic rifting is dated as the Alagoas Stage, which corresponds to the ostracod biozone 011. A detailed ostracod stratigraphical distribution along the Santana Group, allowed to standardise a common ostracod for the biozone name and a code, the Pattersoncypris micropapillosa Biozone (OST-011). Four different ostracod associations were recognized establishing the subzones: Pattersoncypris cucurves (OST-011.1), Pattersoncypris cucurves-Neuquenocypris berthoui (OST-011.2), Damonella grandiensis (OST-011.3) and Pattersoncypris crepata (OST-011.4). Planktic foraminifera were also recovered in different associations, leading to identify two international biostratigraphic intervals and calibrate the ostracod subzones, the Early Aptian Leupoldina cabri Zone includes the OST-011.1 and OST-011.2 subzones, and the upper Late Aptian Hedbergella infracretacea–Microhedbergella miniglobularis composite zone correlated to the OST-011.4 subzone. Between these zones there is an interval without foraminiferal biostratigraphy resolution, the OST-011.3 subzone which is assigned to the lower Late Aptian. The palaeoenvironmental evolution of the Santana Group was reconstituted from the integrated study of ostracods, planktic and benthic foraminifera. Through the Aptian, the Araripe Basin evolved from a transitional to a marine environment, recording estuarine, fluvial to bayhead deltas, a bay coastal watershed that reached better-marine conditions under extreme aridity and the full installation of an epeiric sea flooding the area.