Diagenesis of Late Miocene micritic lacustrine carbonates,udMadrid Basin, Spain

摘要

Mud-grade lacustrine limestones of Miocene age from the Madrid Basin, Spain, reveal varied and complex diageneticudhistories. Microporous micrites occur as well as micrites with anhedral mosaics. The micrites have recrystallized fromuda metastable precursor, in part under sub-oxic meteoric diagenetic conditions probably before extensive karstification inudthe Pliocene. The absence of aragonite relics, their mainly micritic microfabric, low Sr content and covariant trend of Srudand Mg suggest that the micrites formed from mainly high-magnesian calcite muds. Lacustrine micrites can be comparedudto marine forms and criteria used to assess the composition of the marine precursor muds can be applied to lacustrineudlimestones to complement other techniques to identify original lake water compositions.