Abstract

A quantitative approach consisting of the detection and analysis of Mg and Sr distribution patterns in low-Mg calcite cement has proven useful in providing key information concerning the fundamental diagenetic processes of recrystallization and cementation. Electron microprobe analyses of cements found rimming carbonate sediments from three localities (two surface and one subsurface) on Barbados, W. I., have been combined with petrographic observations to infer the following: 1) Cementation occurred simultaneously with the recrystallization of high-Mg calcite and aragonite sediment grains. 2) Cementation continued after the transformation of metastable sediment grains to low-Mg calcite. The mechanism which caused the last phase of cementation was probably CO 2 evolution. 3) Most of the cementation took place in the vadose diagenetic environment; although some specimens show initial cements low in Mg and St. These initial cements may have been precipitated in the marine environment as metastable carbonate phases, which later recrystallized to low Mg calcite in the freshwater phreatic environment; or they may have been precipitated in the phreatic environment. 4) The minor element (Mg and Sr) content of the fluid phase is systematically partitioned into the precipitate. In the samples under consideration this resulted in a minor element distribution characterized by a Mg maximum followed by a Sr maximum. This distribution is characteristic of freshwater cementation and can be used to determine the origin of pre-Pleistocene low-Mg calcite cement.

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