Organización del relleno sedimentario en los yacimientos de mamíferos del Cerro de los Batallones, Cuenca de Madrid

Abstract

Nine fossil mammal sites of late Miocene age (~ 9 Ma) have been found so far in Cerro de los Batallones. The mammal sites occur as up to 15 m deep, irregular cavities hosted in clays (mostly sepiolite), chert and carbonate bedrock. Initial development of cavities resulted from solution of underlying evaporite formations. Piping and subsequent chambering accounted for further enlargement and stability of the cave system. The sedimentary infill of the cavities consists mainly of poorly-sorted clastic deposits and calcareous marlstone. Six main lithofacies are recognized. The detrital components derived directly from the host bedrock. Calcareous marlstone occurs either as basal underground pond deposits or top layers sealing the cavities, usually off-lapping the adjacent bedrock. δ18O and δ13C compositions of the carbonate range from -3.71 to -7.48‰ and from -6.84 to -12.05‰, respectively. Marlstone deposits in the lowermost part of the cavities display patent similarity to isotopic signatures from bedrock. Deposition of calcareous marlstone took place in short-lived lakes (i.e. ponds) fed by rain and groundwater that developed in a pseudo-karst landscape acting as natural traps for the large variety of fossil mammals recorded in Cerro de los Batallones.