Anisian bivalves from Serra (Valencia, Iberian Ranges): taxonomy, environments and biogeographic implications

Abstract An exceptional assemblage of Middle Triassic (Anisian) bivalves from the lower part of the Muschelkalk of Serra municipality (Sierra Calderona, Valencia, Spain), in the easternmost sector of the Iberian Ranges, is systematically studied and integrated to its stratigraphic, sedimentological and biogeographical framework. The assemblage contains cosmopolitan and diverse fauna including Hoernesia socialis (Schlotheim), Myophoria vulgaris (Schlotheim), Pleuromya elongata (Schlotheim), Unionites fassaensis (Wissmann), and Neoschizodus laevigatus (Goldfuss). Additionally, the ichnofauna of the site is described and studied for the first time, including the ichnogenera Planolites , Oravaichnium , Taenidium and Thalassinoides . Sedimentary facies record a variety of environments including coastal shabkha, carbonate tidal flats, subtidal agitated areas and shallow mid-ramp settings, that define the installation of a carbonate ramp in the area in response to the first broad marine Triassic transgression. The bivalve fossils were found in facies corresponding to well-oxygenated shallow-marine (mid ramp) environments, characterized by low energy conditions excepting moderate wave action during storms. These environments probably represent for this area the conditions of maximum marine flooding during the first extensive transgressive episode that occurred during the Middle Triassic in Iberia.