Modelo sedimentario y paleogeográfico de un lago salino con presencia de bacterias endoevaporíticas. Mioceno de la Cuenca de Madrid

Abstract

This work focuses on the Christmas tree gypsum formation, a Lower Miocene unit cropping out in the eastern part of the Madrid basin. This formation is typically composed by large primary twinned gypsum crystals showing habits which differ from the commonly accepted Mottura's rule. The gypsum occurs interbedded with dolomite facies that have been interpreted to precipitate in relation with microbial mats and endoevaporitic bacteria communities. Thus, elucidating the precise sedimentary, paleogeographic and lithostratigraphic conditions has implications to explain the concurrence of all those peculiarities in the unit. The deposition of the sedimentary sequence took place in mudflat-saline lake complexes controlled by NW-SE strike-slip faults in the basement of the basin. Location of the faults has been determined according to different criteria (e.g. isopach maps and tectonic structures affecting the basin margin). The petrogenetic model of the sedimentary sequence has been integrated in the tectonic and climatic regimes.