Dolomitization, time boundaries and unconformities: examples from the dolostone of the Taurus mesozoic sequence, south-central Turkey

Abstract

A Mesozoic carbonate unit in the Taurus platform consists of thick dolostone sequences with both massive, thick beds and thinner beds intercalated with limestone. Dolomite preferentially replaced micrite in the original carbonate. In an initial phase of dolomitization, dolomicrite formed, which later as through dissolution and recrystallization resulted in clear dolomite crystals and dolosparites. An additional type of dolomite is dolosparite filling voids. These dolomite crystals represent either replacement of precursor calcite cement or growth into void space. Dissolution of late, coarsely crystalline dolosparite, precipitation of saddle crystals, local dedolomitization, and some late calcite cement in the voids, all indicate short-term atmospheric exposure of the sequence during or after the main dolomitization event. Dolomitization does not appear to be restricted to a specific environment. There is no evidence that the dolomite formation occurred in an evaporite, supratidal, or high intertidal setting. Our present state of knowledge does not allow an unequivocal explanation of the dolomitization event of massive platform dolomites. However, the association of dolomitization with sea-level fluctuations such as repetitive and minor transgressive and regressive periods might be a clue to the mechanism for the formation of thick dolomite beds in the Taurus Mesozoic platform, as noted by the increasing of the dolostone/limestone ratio near the time boundaries (Triassic/Jurassic and Jurassic/Cretaceous). Stable isotope data support mostly marine-derived solutions as the dolomitizing fluid. Marine solutions can be the only source of the large quantities of Mg 2+ ions needed for dolomitization of massive platform dolomite as was suggested by Land (1985) and Given and Wilkinson (1987).