Abstract
The Crato Formation palaeoentomofauna from the Lower Cretaceous (Aptian)
of northeast Brazil is extremely well preserved. Crato insects are often
complete with abdomen, thorax, head, legs, wings articulated and fragile
cuticle details observed at the macro and micro scale. The Crato
Formation stands out for the high diversity of fossil insects with at
least 386 described species, so far. We investigate the preservation
pathways through SEM-EDS and Raman spectroscopy, which give fundamental
insights regarding the understanding of this complex theme. Our study
compared cuticle soft-tissue preservation of Ensifera in different
layers of the Crato limestone. The results of our analyses confirmed
that the anaerobic bacterial respiration processes influenced the
labile-tissues preservation. Ensifera fossils display preservational
stages ranging from kerogenization to pyritization. Kerogenization
represents the partial or complete chemical transformation of organic
material into aliphatic and cyclic hydrocarbons in situ during
mesodiagenesis, while pyritization occurs during the decaying of carcass
in the early diagenesis. Here, we followed the previous hypothesis of
fish tissue preservation that these processes are governed principally
by variations in the positioning and residence time of the carcasses in
different microbial zones within the sediment column. Besides
early/mesodiagenetic modifications, oxidation processes during recent
weathering led to some mineral transformations that played a key role in
the preservation of Ensifera.
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