FOSSILDIAGENESIS OF LESTODON ARMATUS REMAINS FROM PLEISTOCENE PLAYA DEL BARCO SITE (BUENOS AIRES PROVINCE, ARGENTINA)

MARIN-MONFORT, MARÍA DOLORES; SANTISTEBAN, CARLES; GARRONE, MARIANA CAROLINA; MONTALVO, CLAUDIA INÉS; FERNANDEZ-JALVO, YOLANDA; F. J. FERNÁNDEZ; TOMASSINI, RODRIGO LEANDRO

VIRTUAL

Congreso; 4th Virtual Palaeontological Congress; 2023

Fossil diagenetic approach including mineralogical, geochemical, and paleohistological features present in the fossils of the extinct megamammal Lestodon armatus (Xenarthra, Mylodontidae) have been performed. Thin section of 15 ribs and vertebrae fragments were recovered from Late Pleistocene fluvial deposits at Playa del Barco (southwestern Buenos Aires Province, Argentina). They were examined under light microscope, polarizing petrographic microscope, and scanning electron microscope (SEM), combining with chemical analysis using energy dispersive spectroscopy (EDS) and micro-X-ray diffraction (µXRD). Original bone histology is well preserved without microbial attack signs, although numerous radial microcracks were identified in the secondary osteons of all specimens evidencing wet depositional environment. Presence of hydroxyapatite, as the main mineral component of the bone matrix, suggests that there were no significant compositional changes in the internal crystalline structure. The chemical composition of infilling and crusts indicates that the enrichment with new elements was due to direct exchange with the host deposits. Mineral precipitation infilling fissures, cracks, and cavities of the bone microstructure (i.e., osteocyte lacunae, canaliculi, vascular canals, trabecular structure) allows us to identify different diagenetic pathways. Some samples were buried in a continental vadose zone (fillings of iron oxides, micrite with quartz grains and dogtooth calcite cements) while other were buried in freshwater phreatic zone (blocky mosaic calcite). The interpretation of the microstructural and mineralogical analysis is consistent with the environmental context of the Playa del Barco and can be used to reconstruct the post-burial history of the specimens.