Roveacrinoidal assemblages (Crinoidea, Roveacrinida, Saccocomidae) from the Albian carbonate microfacies of Sierra Azul (Sabinas Basin, Coahuila, Mexico)

Abstract

Plate sections of saccocomid crinoids spotted in the Albian carbonate deposits of the Georgetown Formation from Sierra Azul (Coahuila, NE, Mexico) are reported and described. These microfossil remains consist of discarded proximal plates and partial thecae, i.e. primibrachial plates and radial pieces of a partial cup. These roveacrinoids are associated with calcisphere blooms and an abundant diversified planktic foraminiferal assemblage, mostly consisting of favusellids. All these features are evidence of a high primary productivity within an unstable deepening environment. Such pelagic crinoids have been so far regarded as opportunistic organisms that thrived during transgressive eustatic levels and phyto-planktic blooms, in abundance/accumulation events all indicative of hypoxic conditions. The overall microfossil assemblage assigns to this finding an Albian-Early Cenomanian age. Such an event might be well correlated and/or contemporaneous to the bundle of hypoxic events known as OAE1. Such saccocomid plates in Albian deposits revive the debate on the transition between the late Jurassic genera (Saccocoma Agassiz and Crassicoma Sieverts-Doreck & Hess, in Hess) and the late Cretaceous ones (mainly Applinocrinus Peck).