Caracterización de depósitos carbonáticos ligados a paleosurgencias en el sector de BataIlones-Macovadeso (Neógeno de la Cuenca de Madrid)

Abstract

Carbonate deposits showing domic shape and columnar internal structure have been recognized in the Valdeinfierno quarries (Batallones-Malcovadeso area, central-southern Madrid Basin). Two lithological units (U2 and U3) are differentiated in the carbonates. Unit U2 is mainly brecciated dolomite that consists of dolomicrite with calcite cements. Unit U3 is made up of both calcite and dolomite and is characterized by columnar shapes resembling travertine. Under the microscope, the carbonates consist of limestones with alveolar and biogenic textural features. Abundant clayey masses have been observed within and between the columns. The carbonate units are underlain by a detrital unit (U1) composed of feldspar-rich sandstones. The upper part of the section shows a mudstone unit with local dolomitic carbonate inserts (U4) which is in turn covered by a package of limestone beds (U5). Clays occurring in unit U3 show a different composition (sepiolite > trioctahedral smectite ± illite) than those forming unit U4 (dioctahedral smectite > illite ± kaolinite). Stable isotopic composition of carbonates from units U2, U3 and carbonate inserts of U4 is very similar for dolomite, with δ13C values ranging from -6,21 to -7,78%o, and from -3,23 to -4,05%= for δ18O. Calcite carbonates from units U5 and U2 show δ13C values ranging from -8,07 to -11,75%0, and δ18O values from -5,27 to -7,35%o. Calcite occurring in dolomite beds shows intermediate values between the two groups above mentioned. Both sedimentary features of the carbonate deposits in the studied section and compositional results indicate that the lake environment in which carbonates were deposited underwent changes in the water chemistry that were related to input of groundwater through springs, this resulting in spread-out of the lake water body.