Origin and diagenesis of calcretes in Upper Miocene limestones, Southern Madrid Basin, Spain

Abstract

Different calcrete profiles are associated with lacustrine limestones in Upper Miocene formations on the south of the Madrid Basin. The limestones overlie mudstones which interfinger thin limestones beds and are also interbeded with sandy-filled channels. This set of underlying deposits represent a fluvial lacustrine complex which evolved to a large shallow lake system. Two calcrete profiles, referred as ATS and MIR profiles, have been studied in detail. The profiles exhibit a typical zonation of diagenetic facies as follows: microsparite mosaics, massive calcrete with floating texture, horizons containing pisoliths with gravitational coatings and laminar crusts. These features have different development and vertical distribution in the studied pro files. Moreover, each pro file shows particular features. Hollows and cavities filled by terrigenous and/or carbonate particles cemented by calcite are relevant in the ATS profile whereas in the MIR substrate platy cavities were developed. These variations would be indicative of the different paleomorphological position of the areas where the calcretes were developed.