Microscopia eletrônica de varredura de campo amplo e mapeamento elementar de raios-X de fósseis do período cretáceo

Abstract

In this work it is presented a scanning electron microscopy approach applied to a shrimp fossil from the Cretaceous period (with an area of approximately 280 mm²), collected inthe Ipubi Formation, in the Araripe Sedimentary Basin, Brazil. This approach relies on the detection of signals of backscattered electrons (BSE) and X-rays (emitted from the ionization process) generated in a large-field. scanning. High-definition large-field images from BSE and X-raysare obtained from the coherent overlapping of thousand of adjacent images obtained during the scan of the whole area of the fossil. Through the interpretation of those images it was possible to unveil details of the morphology of the fossil that are imperceptible by light microscopy, as well as compositional features of the fossilized material along length scales that varied from micrometers to centimeters. Morphological details of pleopods, pereopods, antennas, antennules and somites of the shrimp were better visualized in th large-field images from BSEs, and also in the large-field elemental maps for calcium (Ca) and phosphorus (p) (mineralized as Hydroxyapatite [Ca5(PO4)3(OH]). Furthermore, the large-field elemental maps of phosphorus (P) and fluorine (F) presented a correlation, indicating the mineralization of the fluorapatite [Ca5(PO4)3(OH]), a fossilization process that is responsible for the preservation of the fossil. Other important information, obtained by correlating the elemental maps of zinc (Zn) and sulphur (S) indicated a very rare fossilization process, the mineralization of the zinc sulphide (ZnS), observed for the first time in the Araripe Sedimentary Basin.