Vibrational spectroscopy, X-ray diffraction and EDS applied to reveal the fossilization pathways of fossil shells from the Jandaíra Formation, Upper Cretaceous Northeast Brazil

Abstract

The Jandaíra Formation, Potiguar Basin, is well known for hosting a rich marine fauna from the Late Cretaceous of Brazil. Among the organisms that compose this diverse fossiliferous assemblage, the gastropods stand out for their abundance of individuals. In this study, four samples of Tylostoma sp (LP/UFC CRT 2868, LP/UFC CRT 2869, LP/UFC CRT 2870 and LP/UFC CRT 2871) were analyzed in order to understand the different diagenetic processes involved in their preservation. The fossil specimens were collected near Mossoró, state of Rio Grande do Norte. In this work, we have combined a set of high-resolution techniques such as Raman spectroscopy, X-ray diffraction (XRD), Fourier-transform infrared (FTIR) and Scanning Electron Microscopy (SEM) and energy dispersive spectroscopy (EDS) to characterize the fossil specimens mineralogically. All fossil shells are preserved as internal molds, meaning they have lost their original organic matter. After the decomposition of organic debris, the inner part of the shell is filled with surrounding sediment. Our results revealed dolomite as the dominant phase in host rock. On the contrary, the fossil samples LP/UFC CRT 2868, LP/UFC CRT 2869, LP/UFC CRT 2870 and LP/UFC CRT 2871 showed calcite as the dominant phase. These data indicate that a similar diagenetic process was involved in the preservation of these fossil shells. Here, we document discoveries and new perspectives for looking at the abundance of fossil shells in the Jandaíra Formation.