ASSESSING THE IMPACT OF DIAGENESIS ON ISOTOPIC COMPOSITION OF PALEOSOL CARBONATES FROM THE CHU BASIN, KYRGYZSTAN

The Chu Basin lies in the northern foreland of the Tian Shan range of Central Asia. Neogene sedimentary rocks provide a temporal record of Tian Shan evolution and climate in this unique continental environment. Basin fill is composed of siliciclastic sedimentary rocks with interbedded paleosol horizons throughout. Gypsum and carbonate are abundant, suggesting seasonally arid conditions have existed throughout the basin’s history. Paleosol carbonate samples were analyzed for δ¹⁸O with numerous samples showing anomalously negative values. These paleosol samples were investigated using petrographic techniques to better understand why anomalously negative δ¹⁸O values are present in some pedogenic carbonates. The majority of the samples were predominantly micritic to microsparitic with siliciclastic angular grains dispersed throughout. Samples were evaluated and categorized based on grain size, composition, microstructure and morphology. Our goal was to determine whether anomalous variance through time is due to changes in water composition at the time of deposition or related to post-burial diagenesis. We hypothesize that post-burial groundwater interaction led to calcite cementation from fluids that do not reflect the environment at the time of deposition. This research highlights the importance of distinguishing between primary cements closely associated with environmental conditions and later diagenetic products from other fluid sources in studies of paleoclimate and paleoaltimetry.