Ocorrência de fósseis de preguiças terrícolas em calcretes da base de depósitos fossilíferos do tipo tanque no estado de Alagoas

Abstract

This study analyzes fossil material of ground sloths from the Pleistocene megafauna, collected from conglomeratic deposits known as calcretes with siliciclastic and carbonate cement, associated with natural tanks in northeastern Brazil. These tanks, formed by erosion processes in fractures of the crystalline basement, accumulated water and concentrated bones of this fauna, transported during rainy periods. During droughts, with rivers and lakes dry, animals would gather near these deposits, either falling into them or being carried, after death, into these natural depressions. The study involved the removal of ground sloth fossils from calcrete blocks, their preparation, cataloging, and subsequent identification of cranial and post-cranial elements. Additionally, X-ray Diffraction and X-ray Spectrometry analyses were performed to determine the lithoclastic composition and the predominant type of cement in the formation of the calcretes. The material was identified through comparison with relevant literature and fossils from the paleovertebrate collection of the Paleontology Sector at the Natural History Museum of the Federal University of Alagoas. The classification adopted in this work was based on morphological studies proposed by Paula-Couto and Castor Cartelle, emphasizing taphonomic similarities. The presence of these fossils in calcrete deposits can be attributed to climatic changes, and the formation of the calcrete to the decomposition of bioclasts, which generated part of the carbonate cement associated with natural carbonate from rock decomposition and the precipitation of dissolved silica in an aqueous environment. The results highlight that calcretes, in addition to concentrating bioclastic material, also reveal an environmental condition of climate change - from a humid period to a semi-arid regime typical of present-day conditions in the semi-arid region of northeastern Brazil.