Taphonomic analysis of an autochthonous fossil concentration in Jurassic lacustrine deposits of Patagonia, Argentina

ZACARÍAS, IRACEMA A.; MONFERRAN, MATEO D.; MARTÍNEZ, SERGIO; GALLEGO, OSCAR F.; CABALERI, NORA G.; ARMELLA, CLAUDIA; SILVA NIETO, DIEGO

PALAEOGEOGRAPHY PALAEOCLIMATOLOGY PALAEOECOLOGY

ELSEVIER SCIENCE BV

Año: 2019 vol. 514 p. 265 - 281

0031-0182

A new fossiliferous level from the Las Chacritas Member(Bajocian-Callovian) of the Cañadón Asfalto Formation, which crops out in theCañadón Asfalto Basin (Extraandean-Chubut) Argentina was analyzed. The study ofthis assemblage was made on the basis of paleoecological, sedimentological andtaphonomic criteria. This polytypic assemblage is composed mainly of bivalves,spinicaudatans, gastropods, and ostracods, associated with plant remains (such asBrachyphyllum sp., Charophytes,conifers, seeds, and indeterminate remains). The tabular bed of oncoliticpackstone facies corresponds to a shallow marginal lacustrine environment ofintense organic productivity. Taphonomic and paleoecological features, such asclosed articulated valves, random orientation, and size-frequency histogramsindicate an autochthonous fauna. The short life cycle with a quick turnover ofthe population, suggests that the time-averaging would only comprise a fewyears. On the other hand, the analysis of Energy dispersive X-ray spectrometrysupports that early diagenesis affected the remains and favoring the dissolutionof aragonite/calcite, as well as the silicification of shells. Therefore, thisfossil assemblage can be classified as a sedimentological concentration, whichcould have been originated by seasonal cyclicity in an environment subject towater level fluctuations.