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