Bivalves of the Crato Formation (Cretaceous), Araripe Basin and their paleoenvironmental and paleogeopgraphic implications

• Grant number: 16/14396-1
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Effective date (Start): October 01, 2016
• Effective date (End): June 30, 2017
• Field of knowledge: Physical Sciences and Mathematics - Geosciences - Geology
• Principal Investigator: Marcello Guimarães Simões
• Grantee: Victor Ribeiro da Silva
• Host Institution: Instituto de Biociências (IBB). Universidade Estadual Paulista (UNESP). Campus de Botucatu. Botucatu , SP, Brazil

Abstract

The 50 to 60-m-thick, late Aptian Crato Formation, Araripe Basin, comprises a succession of laminated limestones inter-bedded with sandstones, marls and clays, intercalated between the underlying oil-rich "Rio da Batateiras beds", Barbalha Formation, and the first evaporites of the Ipubi Formation. The 10 to 13-m-thick basal portion is composed of metric-scale well-laminated microbially-induced limestones deposited in lacustrine environment, possibly under hypersaline conditions. The unit epitomizes one of the richest Mesozoic fossil Konservat-Lagerstätten in the world, yielding an exceptionally well preserved and diverse fossil biota. Despite of that there are many controversies about the paleoenvironmental conditions in particular about the possible marine influence during the generation of limestones, sandstones and shales that were deposited immediately above the laminated carbonates. These succession is well exposed in a series of quarries in the Nova Olinda county, State of Ceará. Since the mid 2000's, mollusk bivalves are known to occur immediately above the laminated limestones. These fossil invertebrates can potentially be used as paleoenviromental indicators, particularly providing indications about the marine influence (or not) in this part of the succession. This assumption has profound implications to paleogeographic reconstructions of the Araripe Basin, following Gondwana break-up and South Atlantic Ocean opening. Notably, however, is the fact that even more than 10 years after the first reports these fossils are still not formally studied or described. During the last two years, in a series of extensive field works, conducted under the scope of CNPq, FAPESP and FUNDUNESP-Petrobras projects, our scientific team was able to collect more than a hundred of bivalve specimens, many showing good preservation quality, which are now deposited in the scientific collection of the Institute of Biosciences, UNESP, Botucatu campus. In this context, the main goal of this proposal is to (a) prepare, (b) describe and (c) systematically classify, by the first time, those bivalves in order to add evidences about the possible marine influence (or not), during the deposition of the sedimentary succession immediately above the laminated limestones of the Crato Formation. To achieve this, the collection available at the IBB/UNESP will be investigated using standard paleontological techniques. At the end, a preliminary systematic classification must be presented also including brief taphonomical and paleoecological interpretations. (AU)