ABSTRACT

Calcite rim-cement in the Blackjack Creek Formation (Pennsylvanian, Missouri) differs from the remaining pore-fill calcite chemically as well as morphologically. Staining with alizarian red-S and potassium ferricyanide shows that nonferroan calcite characterizes the subordinate dogtooth ("first-generation") rimcement, whereas ferroan calcite characterizes the dominant mosaic ("second-generation") cement. This compositional difference most likely records contrasting cementing environments, and it is suggested that the nonferroan first-generation cement is the product of conversion from aragonite that precipitated in the marine environment. The ferroan second-generation calcite was precipitated as such from circulating ground water in primary pores lined with the earlier calcite and in ores resulting from solution of aragonitic bioclasts after partial lithification of the carbonate sediment.

The relative susceptability of components to dolomitization was lime-mud matrix > ferroan-calcite spar (cement and calcite-replaced aragonite bioclasts) > nonferroan-calcite sparry cement > nonferroan-calcite bioclasts. The ferrous iron content of ferroan dolomite was apparently inherited from replaced ferroan calcite.

Silica preferentially replaced nonferroan-calcite bioclasts, and recent weathering altered ferroan calcite and ferroan dolomite to produce pores and limonite.