Diagenetic analysis of tetrapod from the Upper Triassic, Puesto Viejo Group, Argentina

ADRIANA C. MANCUSO; ELENA PREVITERA; ELOY S. SÁNCHEZ; MARCELO S. DE LA FUENTE; ADRIANA C. MANCUSO; ELENA PREVITERA; ELOY S. SÁNCHEZ; MARCELO S. DE LA FUENTE

ANDEAN GEOLOGY

SERVICIO NACIONAL GEOLOGIA MINERVA

Año: 2016 vol. 43 p. 197 - 214

0718-7092

The Puesto Viejo Group crops out in the San Rafael Block, southwest Mendoza, Argentina. This groupis an important unit for the knowledge theTriassic faunas. It is composed of basal Quebrada de los Fósiles Formation(QF) overlying by the Río Seco de la Quebrada Formation (RSQ). In this study, we report tetrapod remains from theRSQ Formation that includes, until now, exclusively therapsids. Non-mammalian therapsids predominated in terrestrialecosystems during the Late Paleozoic and Early Mesozoic. Although cynodonts and dicynodonts have been studied fromseveral perspectives, the relation between taxa and sedimentary context has been scarcely documented. This study isaimed to elucidate the diagenesis of tetrapods from the Puesto Viejo Group and its relation to depositional environment.Diagenetic features of therapsid bones from the RSQ Formation were analyzed through thin sections to interpret thedegree of taphonomic alteration. Diagenetic processes inferred include substitution; fracturing; brittle deformation anddifferent permineralization events. Combined analyses through scanning electron microscopy; energy-dispersive X-rayspectrometry (SEM-EDX); X-ray diffractometry (XRD) and petrographic studies reveals the substitution of hydroxyapatiteby francolite. The presence of fluorine in some samples suggests a link between the elemental composition and depositionalenvironments: floodplain and crevasse splay. Permineralization stages include infilling of vascular canals, trabeculae andfractures with iron oxides and iron carbonate minerals during the burial history. This contribution represents a relevantapproach to elucidate the relation between diagenesis on tetrapods and their paleoenvironments, as exemplified in thiscase study from the Puesto Viejo Group during the Upper Triassic.