Quimioestratigrafia da Bacia Sedimentar do Araripe (Cretáceo Inferior), Nordeste do Brasil

Abstract

Chemostratigraphy is an essential tool for the understanding of the depositional characteristics and the processes that are responsible for the paleoclimatic changes on Earth. Trace metal and stable isotopes are used to understand geologic processes during planetary evolution and how they interacted with life. Therefore, the aim of this work was to understand the behavior of geochemical indicators during the paleoenvironmental perturbations that occurred during the Lower Cretaceous (Aptian-Albian) in the Araripe Basin (Ceará, Northeast, Brazil). The Araripe Basin is characterized by a rich fossil assemblage (Konservat -Laggerstätte), in which the processes responsible for fossil preservation are linked to paleoenvironmental changes. To evaluate the paleoenvironmental variations, geochemical indicators of volcanism (Hg/TOC, Hg/Al, and Hg/Fe), paleosalinity (Sr/Ba), redox conditions (V/Cr, V/V+Ni and V /Ni), isotopic oscillations (δ13CVPDB and δ18OVPDB), paleoproductivity (CuEF, ZnEF, NiEF, and BaEF), and paleoredox anomalies (VEF, FeEF, CrEF, MnEF, and PbEF) were determined. Volcanicevents were responsible for changes in paleoproductivity and paleoredox conditions during deposition of the Barbalha, Crato, and Romualdo formations and could be associated with the volcanism of the Ontong Java (OJP) and Rajmahal-Kerguelen South (SKP) plateaus. Increased anomalies in proxies of paleoproductivity, and paleoredox conditions were observed during volcanism events. In this case, the development of productivity and anoxia in aquatic ecosystems may have been triggered by the increase in atmospheric CO2 caused by volcanism. Furthermore, the cyclic mass mortality events recorded may be related to global processes that caused local changes in the Araripe Basin.