DETECTION OF DIAGENESIS IN PALEOSOL CARBONATE NODULES USING OPTICAL AND CATHODOLUMINESCENCE MICROSCOPY

The Meade Basin, Kansas preserves a record of changes in paleoenvironment, paleovegetation and small-mammal fauna during the Miocene-Pleistocene. Stable isotope values of paleosol carbonates from Meade Basin paleosols can be used to track some of the changes, including the relative abundance of plants that used the C3 photosynthetic pathway versus C4; changes in soil temperature; and paleohydrology. However, diagenesis may alter the isotopic signature of the carbonates. To investigate this, we used cathodoluminescence (CL) and optical microscopy to determine the extent of diagenetic alteration in paleosol carbonate nodules collected from the Meade Basin. The CL and petrographic images reveal a range in the extent of preservation and diagenesis throughout the samples, and the observed fabrics suggest some recrystallization and/or dissolution and precipitation from secondary fluids. Given the limited burial of these rocks, the secondary fluids are probably groundwaters. We placed each sample in one of three categories based on the abundance of diagenetic fabrics present, with category 1 samples being the best preserved. In addition, ostracods and charophytes present in one sample that was previously interpreted as a calcrete suggest that this particular sample formed in a shallow lacustrine environment, rather than in an ancient soil. These data may explain some of the variability present in the stable isotope values and estimated carbonate clumped isotope temperatures from the samples, and we will use discuss the role of diagenesis on existing stable isotope records from these paleosol carbonate nodules.