Early Jurassic shell beds from marginal marine environments in southern Mendoza, Argentina

摘要: Abstract External estuarine facies in Late Sinemurian beds from the base of Puesto Araya Formation Atuel river region, Mendoza Province, Argentina, contain concentrations a new species Cardinioides (a shallow burrowing suspension-feeding Pachycardiidae bivalve) and low diversity benthic fauna. These bivalves appear tidal inlet wave-dominated estuary (environment similar to lagoon-barrier island systems), forming bioclastic lags at channel bases. The taphonomic attributes (such as shell articulation, degree fragmentation abrasion, bioclast size, orientation) change North South, monospecific nearly complete large shells with through smaller associated few marine environments, only isolated fragmented specimens fully biota including not other but also brachiopods ammonoids. This, together different palaeoecologic, sedimentologic stratigraphic studied localities are evidence southwards changing environmental conditions marginal (brackish) on eastern margin Neuquen basin that time. From detailed analysis features, size distribution shells, fauna localities, is regarded brackish water endemic, possibly salinity euryhaline species, which inhabited well oxygenated waters. Salinity, turbulence levels food supply were main limiting factors species.