Stratigraphic/sedimentological analysis of a Lower Cretaceous carbonate succession in the Actopan Platform, Hidalgo State, Mexico: documentation on an Early Albian deepening event

The Actopan Platform, exposed near the town of Actopan, in the State of Hidalgo, is part of the system of carbonate platforms developed extensively in Mexico during the Early Cretaceous. However, despite the excellent outcrops and easy access this platform is still poorly studied. A sedimentologic and biostratigraphic analyisis of a 345 m-thick stratigraphic section located in the southwestern region of this platform was conducted. The collected information allowed, for the first time, to document the presence of deep-water calcareous facies of Lower Albian age. The results of the analysis of depositional textures, sedimentary structures, fossil content, and diagenetic attributes were used to identify facies and their depositional environments, and to define facies associations. The lower part of the section consists of the following facies: skeletal-peloidal mudstone/wackestone, peloidal-skeletal packstone/grainstone, oncoid packstone, boundstone of Chondrodonta sp. and requinids, and cryptalgal laminites. The depositional environments of the facies vary from shallow subtidal (lagoonal) to supratidal. These facies stack forming subtidal and peritidal cycles. The Choffatella decipiens benthic foraminifer is common in this facies and indicates an Aptian age. This shallow-water sedimentary package is normally overlain by a succession of pelagic facies with intercalations of gravity-induced, coarse-grained carbonate deposits including turbidites and debris flows. Colomiella recta, Favusella sp. and Microcalamoides diversus are typical planktic microfossils in this calcareous unit indicating a Lower Albian age. The large-scale trend of this Lower Cretaceous facies succession allowed documenting a deepening event that took place in the Early Albian and that had not been previously reported in this platform.