Estudo dos calcretes da coleção de paleovertebrados do setor de paleontologia do MHN-UFAL, com foco em fósseis de Toxodon sp

Abstract

The semi-arid region of Alagoas presents a significant occurrence of fossiliferous deposits, which may contain remains of the Pleistocene megafauna, as well as conglomerates at the bottom of fossiliferous tanks called calcrete. The material analyzed in this study includes four fragmented teeth, a fragmented mandible with two teeth, an incomplete calcaneus of Toxodon sp., and the cement from a calcrete block from the city of Cacimbinha – Alagoas. The calcrete blocks were collected in 2001 and are deposited in the paleovertebrate collection of the Paleontology Sector of the Natural History Museum of the Federal University of Alagoas (SPMHNUFAL). The study consisted of separating the calcrete blocks, removing and cleaning the fossils (in the case of the genus Toxodon sp.), as well as performing analyses by Xray Diffraction (XRD) and Energy Dispersive Spectroscopy (EDS). From the nine calcrete blocks analyzed, four teeth, a fragment of a mandible with two stillarticulated teeth, and a partially preserved calcaneus of Toxodon sp. were found. The remaining blocks, not yet analyzed, will be used in future studies. The analyses of the calcareous/siliciclastic cement presented results that corroborate the hypotheses suggested for the extinction of the megafauna, as they demonstrate a change from a more humid climate to a semi-arid regime in northeastern Brazil. The results of the EDS and XRD analyses support this hypothesis, as the type of cementation of the calcretes is typically formed by the precipitation of minerals from the carbonate and silicate groups, which represent environments transitioning from higher humidity to greater aridity.