Génesis y significado de los niveles de crinoides y bivalvos acumulados a techo de las plataformas someras del Jurásico Medio (Subbético, Sur de España)

Laburpena

The stratigraphic record of the External Zones of the Betic Cordillera allows to distinguish three sections where bioclastic accumulations mark the demise of the Middle Jurassic shallow-water carbonate platforms. The westwards opening of the Tethys triggered the formation of fault blocks in the Southern Iberian Palaeomargin. On the shallowest areas of the fault block, shallow platforms were developed. Nowadays, these platforms appear represented by the Jabalcuz Fm. (Intermediate Units) and Camarena Fm. (External Subbetic). In the uppermost part of the Jabalcuz Fm., a lumachelle of filaments –interpreted as hurricane-related deposits– is overlain by marls and radiolarian-rich interbeds of the Era de la Mesa Fm. In contrast, in the uppermost part of the Camarena Fm., subtidal encrinites and crinoids and bivalves tempestites occur, changing vertically to Ammonitico Rosso facies (Upper Ammonitico Rosso Fm.). The three sections studied suggest a genetic model where, after the crisis in the oolite production, crinoidal accumulations appeared in the shallower areas of the blocks, while bivalves dominated the deeper areas. The scarcity of crinoids over the platform represented by the Jabalcuz Fm. is a sign of the differential subsidence of the studied platforms.