Abstract

Dolomite can (1) selectively replace certain components of a rock such as coralline algae and (2) mimically replace certain fossils such as echinoid fragments. We dolomitized coralline alga, echinoid, foram, pelecypod, Halimeda, gastropod and coral fragments at 250 °C in two-molar CaCl2/MgCl2 solutions and found that coralline algae, echinoids, Halimedae, and forams dolomitized faster than the other fossils.

Echinoids and forams were mimically replaced, whereas pelecypods, gastropods, and corals were replaced by dolomite, which destroyed the original skeletal architecture. Artificial conversion of high-Mg calcite coralline algae and echinoid fragments to low-Mg calcite prior to dolomitization had no discernible effect on the rate of dolomitization or the fabric of the dolomitized fossils.

On the basis of these results and petrographic analyses of natural, low-temperature dolomites, we conclude that mimic replacement and fossil selective replacement is more likely to be affected by the crystal size than by mineralogy.

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