Distinguishing tsunamis shell bed deposit using sedimentologic and taphonomic features: an example from (Lower Upper Cretaceous) Southern Patagonia, Argentina

AUGUSTO N. VARELA, SEBASTIÁN RICHIANO & DANIEL G. POIRÉ

Mendoza, Argentina

Congreso; 18 International Sedimentological Congress; 2010

IAS

La Formación Mata Amarilla del Cretácico superior temprano de la Southern Patagonia, en el área de Tras Lagos presenta importantes acumulaciones bioclásticas en su parte inferior. Se presenta en este trabajo una caracterización taxonómica y sedimentológica de las misas, y se propone una modelo de las etapas temporales en su depositación, en el marco de un paleoambiente de lagoon. This work is made from detailed sedimentologic logs, facies analysis, and the study of its paleontological content and taphonomics attributes. The unit is composed of alternating white sands and mudstones, with bioclastic accumulations interbedded in the lower section. The depositional environment for the Mata Amarilla Fm. is a lagoon limited by shallow marine bars. The fine sedimentation is sporadically interrupted by storm events represented by coquines, bioclastic sands and shell pavements with an heterogeneous and allochtonous malacofauna association. Some areas of the lagoon become exposed allowing the development of vegetation on the susbstrate and the generation of pedogenetic processes. Subsequently, an advanced regression stage occurs when a fluvial system invades the lagoon area representing the beggining of the Mata Amarilla Fm. medium section deposition.