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

A new fossiliferous level from the Las Chacritas Member (Bajocian-Callovian) of the Cañadón Asfalto Formation, which crops out in the Cañadón Asfalto Basin (Extraandean-Chubut) Argentina was analyzed. The study of this assemblage was made on the basis of paleoecological, sedimentological and taphono...

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Published in:Palaeogeography, palaeoclimatology, palaeoecology palaeoclimatology, palaeoecology, 2019-01, Vol.514, p.265-281
Main Authors: Zacarías, Iracema A., Monferran, Mateo D., Martínez, Sergio, Gallego, Oscar F., Cabaleri, Nora G., Armella, Claudia, Silva Nieto, Diego
Format: Article
Language:English
Subjects:
Argentina
Cañadón Asfalto Formation
Fossil concentration
Marginal lacustrine facies
Middle Jurassic
Taphonomy
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Summary:A new fossiliferous level from the Las Chacritas Member (Bajocian-Callovian) of the Cañadón Asfalto Formation, which crops out in the Cañadón Asfalto Basin (Extraandean-Chubut) Argentina was analyzed. The study of this assemblage was made on the basis of paleoecological, sedimentological and taphonomic criteria. This polytypic assemblage is composed mainly of bivalves, spinicaudatans, gastropods, and ostracods, associated with plant remains (such as Brachyphyllum sp., Charophytes, conifers, seeds, and indeterminate remains). The tabular bed of oncolitic packstone facies corresponds to a shallow marginal lacustrine environment of intense organic productivity. Taphonomic and paleoecological features, such as closed articulated valves, random orientation, and size-frequency histograms indicate that the fauna is autochthonous. The short life cycle with a quick turnover of the population, suggests that the time averaging would only comprise a few years. In addition, the analysis of Energy dispersive X-ray spectrometry supports early diagenesis affecting the remains and favoring the dissolution of aragonite/calcite, as well as the silicification of shells. Therefore, this fossil assemblage can be classified as a sedimentological concentration, which could have been originated by seasonal cyclicity in an environment subject to water level fluctuations. •Continental invertebrate concentration from the Middle Jurassic of Patagonia•Polytypic benthic assemblage from lacustrine facies Cañadón Asfalto Formation•Early diagenesis in the vadose zone induced the silicification of the fossil remains.•Autochthonous concentration classified as a sedimentological origin
ISSN:0031-0182
1872-616X
DOI:10.1016/j.palaeo.2018.10.020