Vibrational spectroscopy and X-ray diffraction applied to the study of Cretaceous fish fossils from Araripe Basin, Northeast of Brazil

In this work, we investigate fossils of the fish coelacanth belonging to the Cretaceous Period from two different formations belonging to Araripe Basin (Brejo Santo and Romualdo Formations), in Northeast of Brazil, through Raman and infrared spectroscopy and X-ray diffraction. The coelacanth processes of fossilization have occurred of different manners as a consequence of the different environment surrounding the fossils. The results obtained by different techniques showed that the matrix found in the Romualdo Formation is composed of calcite and quartz, whereas the matrix found in the Brejo Santo Formation is comprised of calcite, quartz, and albite. On the other hand, the presence of (PO4)(-3) units in the fossils of coelacanth was proved clearly from the Raman spectroscopic analysis, supporting the results furnished by X-ray diffraction measurements. The fossil from Brejo Santo Formation is well preserved, presenting mainly the hydroxyapatite and the fossil from the Romualdo Formation that is partially substituted by calcite, indicating the occurrence of a substitution process. Copyright (c) 2014 John Wiley & Sons, Ltd.