Combination of analytic techniques to chemical characterization and preservation of Jurassic clam shrimp carapaces from La Matilde formation, Patagonia

Abstract

Chemical studies of fossil clam shrimps have taken relevance in the possibility of inferring about fossilization processes. Laser–induced Breakdown Spectroscopy (LIBS) is an attractive technique for geological analyses because the laser can ablate a few micrograms directly from a small area on the solid sample. On the other hand, RAMAN spectroscopy is a technique that allows rapid and non-destructive in situ detection of the components of the samples and has been used in micropalaeontology to identify carbonaceous materials. In this study, the aim was an analysis of the preservation of the clam shrimp Eosolimnadiopsis? Santacrucensis Gallego, 1994 from La Matilde Formation (Jurassic) using diverse methods including LIBS, RAMAN and X–ray fluorescence (XRF) techniques as well as surrounding rock. Afterwards LIBS results were evaluated using principal component analysis (PCA). According to XRF data, Si was the main element, indicating that the rock sample consists primarily of silicate minerals. Our results of LIBS and PCA analysis indicate chemical changes between the points from carapaces and rock matrix. Some areas of the carapace showed high peaks of Ca, Na, Mg and it was variable for Si, while in other parts of the carapace and rock matrix the Si remained at high intensity. Also, RAMAN spectroscopic analysis revealed the presence of amorphous carbon. This is the first report and evaluation on the LIBS and RAMAN techniques applied to fossil clam shrimps and contributes to obtaining a range of additional information to subsequently establish the different mechanisms involved in the taphonomic history of these organisms.