Tafonomía y Paleoecología de las ostras de la Formación San Juan Raya, Aptiense del sureste de Puebla, México

Abstract

The San Juan Raya Formation outcrops southwest of Tehuacán, Puebla State. It is made up of highly fossiliferous marine and marginal marine rocks of Early Cretaceous (Aptian) age. The taphonomical record of studied oysters consists of: a) shell debris, b) reworked oysters in calcareous sandstone, and c) oyster aggregates of different sizes in muddy deposits, from ostreoliths to bioherms formed by Ostrea alicula Hamlin, 1884 and Amphidonte (Ceratostreon) acuticosta (Nyst y Galeotti, 1840) oysters. The latter represent banks or natural reefs where oysters allowed the coexistence of diverse invertebrates such as corals, gastropods, sea urchins and many bivalve species, since their shells served as substrate or shelter from predators. In some cases there are encrusting bryozoans and serpulids, bioerosion produced by sponges and by bivalves, and associations that represent ecological successions and competition amongst oysters and other species. Described oyster taphofacies suggest changes in the dynamics of sedimentary deposits, the origin of assemblages formed by the gregarious habit of oysters as well as by environmental processes, and time-averaging involved in their formation.