Fossildiagenetic history of a Pleistocene mammal assemblage from the Argentine Pampas based on histotaphonomic

MARIN-MONFORT, DORES; CARLES SANTISTEBAN; M. GARRONE; CLAUDIA MONTALVO; YOLANDA FERNÁNDEZ JALVO; FERNANDO J. FERNÁNDEZ; RODRIGO L. TOMASSINI

Valencia

Congreso; 4th Palaeontological Virtual Congress; 2023

Universitat de Valencia

Fossildiagenetic approach including mineralogical, geochemical, and paleohistological features present in the fossils of the extinct megamammal Lestodon armatus (Xenarthra, Folivora, Mylodontidae) have been performed. Thin section of 15 fragments of ribs and vertebrae were recovered from Late Pleistocene fluvial deposits at Playa del Barco (southwestern Buenos Aires Province, Argentina). They were examined under light microscope, polarization petrographic microscope and scanning electron microscope (SEM) combining with chemical analysis using energy dispersive spectroscopy (EDS), and X-ray diffraction (µXRD). Original bone histology is well preserved without microbial attack, although numerous radial microcracks were identified in the secondary osteons of all specimens evidencing wet depositional environments. Presence of hydroxyapatite, as the main mineral component of the bone matrix, suggests that there were no compositional changes in the internal crystalline structure during fossilization. The similarity in the chemical composition of the sediments inside and attached on the fossils surface shows that the enrichment with new elements was due to direct exchange with the sediments in which they were buried. Mineral precipitation infilling fissures, cracks and cavities of the bone microstructure (i.e. osteocyte lacunae, canaliculi, vascular canals, trabecular structure) shows different preservation patterns in which specific fossildiagenetic pathways can be differentiated and allows us to identify different burial stages. Some samples were buried in a continental vadose zone (with fillings of iron oxides, micrite and quartz minerals) while other were buried in phreatic zone (permineralization with mosaic calcite). The interpretation of the results of the microstructural and mineralogical analysis is consistent with the environmental context of the Playa del Barco.