Mineral species and formation processes: Raman spectroscopic and microscopic analysis of stains from a late pleistocene continental drowned faunal bone assemblage, Central Chile

In this study we address the analysis of bone staining and its sedimentary deposits to obtain a better understanding of the taphonomic trajectories of faunal assemblages in dynamic site formation processes. The fossil remains belong to continental fauna recovered at GNL Quintero 1, a Late Pleistocene drowned terrestrial site located nearshore at Quintero bay in the central coast of Chile (32 degrees S). By conducting Raman spectroscopic and microscopic analyses we aim to identify the mineral compounds of bone staining and their sedimentary matrix, perform a first geochemical characterization of the depositional environments and carry out paleoenvironmental inferences. Stains are present on most remains and recur in a variety of colors, indicating the presence of minerals, such as hematite, goethite, pyrolusite, pyrite or marcasite, mackinawite, and greigite. Mineral species identified are associated with oxic and anoxic environments, suggesting that the bones and sediments underwent both sulfuricization and sulfidization processes. Spectroscopic data obtained suggest that the trajectory of the remains was much more dynamic than previously assumed. These geochemical scenarios of alternating oxidation and reduction reflects the diverse environments involved during the terrestrial phase, the transitional phase of rising sea level, and subsequently the marine phase.