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

Abstract

The Puesto Viejo Group crops out in the San Rafael Block, southwest Mendoza, Argentina. This group is 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 the RSQ Formation that includes, until now, exclusively therapsids. Non-mammalian therapsids predominated in terrestrial ecosystems during the Late Paleozoic and Early Mesozoic. Although cynodonts and dicynodonts have been studied from several perspectives, the relation between taxa and sedimentary context has been scarcely documented. This study is aimed 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 the degree of taphonomic alteration. Diagenetic processes inferred include substitution; fracturing; brittle deformation and different permineralization events. Combined analyses through scanning electron microscopy; energy-dispersive X-ray spectrometry (SEM-EDX); X-ray diffractometry (XRD) and petrographic studies reveals the substitution of hydroxyapatite by francolite. The presence of fluorine in some samples suggests a link between the elemental composition and depositional environments: floodplain and crevasse splay. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and iron carbonate minerals during the burial history. This contribution represents a relevant approach to elucidate the relation between diagenesis on tetrapods and their paleoenvironments, as exemplified in this case study from the Puesto Viejo Group during the Upper Triassic.

Bone microstructure and diagenesis of saurischian dinosaurs from the Upper Cretaceous (Neuquén Group), Argentina

“…These processes are the result of differences in burial depth, temperature and geostatic pressure suffered by the fossils in each burial environment. Similar diagenetic features have been identified in other vertebrate remains (Holz and Schultz, 1998;Wings, 2004;Reichel et al, 2005;González Riga and Astini, 2007;González Riga et al, 2009;Casal et al, 2013;Previtera, 2011Previtera, , 2013Previtera et al, 2013;Previtera et al, 2016).…”

“…Calcite appears to have been precipitated during the later stages of diagenesis, as suggested by Flügel (1982). This main cement occurs in both spongy and compact bone and it is represented by at least two generations: fibrous calcite cementation and blocky calcite generation (Previtera et al, 2016). The siderite often found in bedded sedimentary deposits with a biological component suggests a biogenic origin under low-oxygen and low-Ph conditions (Lim et al, 2004).…”

Fosildiagénesis en restos de dinosaurios preservados en depósitos fluviales de la Formación Lago Colhué Huapi (Cretácico Superior), Cuenca del Golfo San Jorge, Argentina

“…Esta sustitución iónica del hidroxilo (OH -) por fluoruro (F -) ha sido documentada anteriormente por Lucas y Prévôt (1991), Elorza et al (1999), Paik et al (2001), Tuba et al (2006) y Rogers et al (2010). También fue mencionada en estudios realizados en tetrápodos triásicos de Argentina por Previtera et al (2013Previtera et al ( , 2016, y particularmente en restos de dinosaurios cretácicos por González Riga y Astini (2007) y Previtera (2013,2017).…”

Permineralización en restos de dinosaurios preservados en depósitos de desbordamiento de la Formación Bajo Barreal (Cretácico Superior), Patagonia central, Argentina.

“…Por el contrario los trabajos vinculados a la etapa fosildiagenética son menos frecuentes y más complejos. Sin embargo, los recientes trabajos han demostrado la importancia de abordar estos estudios en detalle, en parte el estudio de la composición química de los restos fósiles con el fin de reconstruir la historia diagenética (Denys et al, 1996;Elorza et al, 1999;Lécuyer et al, 2003;Berreteaga et al, 2004;Cladera et al, 2004;Merino y Morales;González Riga y Astini, 2007;Castaños et al, 2010;Previtera et al, 2013Previtera et al, , 2016Tomassini et al, 2014Tomassini et al, , 2015.…”

“…Como consecuencia, los errores estadísticos en las concentraciones elementales, expresadas en % peso, pueden diferir hasta en un 20% de los valores. Según Previtera et al (2016) los elementos con porcentajes mayores de 10% presentan un error de 4%; en otros elementos con porcentajes que oscilan entre el 10% y el 1%, la estadística de error es del 15% y por último, los elementos con porcentajes menores del 1% presentan un error del 20%.…”