Mineralogy and chemistry of the lower Pennsylvanian Kendrick fauna, eastern Kentucky: 1. Trace elements

Abstract

The original calcite and aragonite mineralogy is preserved for the fauna of the lower Pennsylvanian Kendrick shale of eastern Kentucky. The brachiopods secreted low-Mg calcite shells with ∼2 mole% MgCO 3, the crinoids and rugose corals secreted intermediate-Mg calcite endoskeletons and exoskeletons with ∼5–8 mole% MgCO 3. The average Sr content of 1140 ppm for the brachiopods, 2140 ppm for the crinoids and 1770 ppm for the rugose corals is in accord with their respective mineralogy. The mineralogy of the Kendrick crinoids is at variance with that of their Holocene counterparts, which secrete high-Mg calcite endoskeletons. On the other hand, the low- to intermediate-Mg calcite mineralogy for the Kendrick rugose corals is in accord with observations for other Paleozoic rugose corals, but is significantly different from the aragonite and/or high-Mg calcite mineralogy of Holocene scleractinians and octocorals. The Kendrick molluscs (cephalopods, gastropods and pelecypods) secreted aragonite skeletons and shells with Mg contents of less than 1000 ppm, which is analogous to the Mg content of the aragonite skeletons and shells of their Holocene counterparts. However, the average Sr content of 4040 ppm for the cephalopods, 5210 ppm for the gastropods and 4840 ppm for the pelecypods of the Kendrick shale is higher by a factor of ∼2 over the average Sr content of their Holocene counterparts. Intermediate-Mg calcite with ∼4–8 mole% MgCO 3 is the dominant carbonate phase of the calcareous shale matrix material of the Kendrick shale. Other carbonates constituting the matrix are sedimentary aragonite and low-Mg calcite. This varied carbonate mixture of the matrix material is not corroborated by elemental analysis, which by its very nature cannot define the different carbonate phases of bulk-rock samples.