Implicações tafonômicas e diagenéticas de ensifera, formação Crato, Bacia do Araripe, cretáceo inferior

Abstract

The Crato Formation from Araripe Basin, northeast Brazil, is one of most significant Cretaceous Lagerstätte since it records well-preserved fossil invertebrates, vertebrates, plants and icnofossils deposited in lacustrine carbonate beds. In this dissertation we seek to understand the preservational processes responsible for fossilization of Ensifera, insect, through SEM-EDS and Raman spectroscopy. Using these non-destructive techniques we have got to characterizemorphology, chemical and mineral compositions in micrometre scale. We compared soft-tissue preservation in different layers of Crato limestone. Our results reveal that anaerobic bacterial respiration processes played a key role in the preservation of labile-tissues. Ensifera fossils display preservational stages ranging from kerogenization to pyritization. Kerogenization seems to be product of repolymerization in situ aliphatic molecules from the cuticle of the organism itself during mesodiagenesis, whilepyritization occurs immediately following the decaying of carcass during early diagenesis. We suggest that these preservation processes are governed principally by variations in the positioning and residence time of the carcass in different microbial zones of the Araripe paleolake.