Cenomanian algae and microencrusters from the El Abra Formation, W Valles–San Luis Potosí, Mexico

This work deals with calcareous algae and microencrusters (incertae sedis) from the upper part of the El Abra Formation, which crops out at the W Valles–San Luis Potosí Platform. Two assemblages of calcareous algae are recognized: one composed of rivulariacean-type cyanobacteria such as Cayeuxia kurdistanensis Elliott and Garwoodia sp. as well as the dasycladalean species Clypeina sp., Neomeris cretacea Steinmann, Salpingoporella hasi Conrad, Radoičić and Rey, Trinocladus cf. T. divnae Radoičić; the bryopsidales Boueina pygmaea Pia, Halimeda cf. H. elliotti Conard and Rioult, and the microencrusters Lithocodium aggregatum Elliot and Thaumatoporella parvovesiculifera (Raineri), and the other assemblage consisting of the gymnocodacean algae Permocalculus irenae Elliott and P. budaensis Johnson. The first assemblage is associated with the benthic foraminifera Pseudolituonella reicheli Marie, Hemicyclammina sigali Maync, Daxia cenomana Cuvillier and Szakall, Merlingina cretacea Hamoui and Saint Marc, is dated as mid-late Cenomanian on the basis of the stratigraphic distribution of the foraminifera, and suggests an oligotropic environment within the euphotic zone on the open marine platform. Over this is documented a succession consisting of a community with abundant gymnocodacean algae and a decrease in the benthic foraminifera which could be related to increased nutrient availability in mesotrophic conditions. The shallowwater association composed of the studied microfossils is typical of the Tethys Realm.