A COMPREHENSIVE DATASET OF HYDROGEN AND OXYGEN ISOTOPE VALUES FROM PENNSYLVANIAN-AGED PALEOSOLS, ILLINOIS BASIN, USA

Isotopic studies of hydrous phyllosilicates from paleosols provide information on the ancient environment that influenced episodes of soil formation and/or diagenetic overprinting during subsequent burial. Four cores from the middle-upper Pennsylvanian Illinois Basin were sampled, with emphasis on paleosol B-horizons, that include mineral mixtures of kaolinite, illite, and smectite. The stable oxygen and hydrogen-isotope compositions are presented here from eleven phyllosilicate samples. Results were combined with data collected from three additional paleosol-bearing cores (n=20) to assess isotopic trends from paleosols within the Tradewater through the Mattoon Formations, with emphasis on the Desmoinesian and Missourian Series, across the Illinois Basin. Phyllosilicate δD and δ¹⁸O values range from -66‰ to -27‰ ±4.0‰ and 17‰ to 23‰ ±0.2‰, respectively. Samples near the basin interior tend to have more positive δD values, ranging from -36‰ to -27‰, and less positive δ¹⁸O values, ranging from 18.2‰ to 19.2‰, with the exception of samples from the Charleston Core which trend in the opposite sense (ranging from -66‰ to -54‰ for δD). The samples collected from the shallowly buried, <130m depth, LaSalle Core on the northern margin of the Illinois Basin exhibit more negative δD values and more positive δ¹⁸O values, ranging from -51‰ to -38‰ and 18.9‰ to 22.4‰ respectively. These results suggest that the shallowly buried samples on the northern margin of the Illinois Basin retain signatures of a pedogenic origin, whereas samples from the deeper, basin interior have a more complex history with signatures of pedogenic and diagenetic origin. Calculation of phyllosilicate crystallization temperatures using these data along with elemental data and phyllosilicate abundances will help address this variability and provide an unprecedented context from which to assess basin-scale modification of original environmental geochemical signatures.