9307168 Popp A detailed study of isotopic biogeochemistry of the Jurassic marine Oxford Clay is proposed. The goal is to further understand sedimentary microbial processes and how they affect preservation of carbon and sulfur in organic and inorganic phases. The relationship between those microbial processes and depositional environments will be elucidated. Effects of specific microbial processes and the environments in which they are prevalent will be identified. Results of analyses of organic-sulfur compounds in these rocks should provide new information on the role of these compounds in the carbon-sulfur-iron system. Samples of the initial phase of this study were collected from active quarries and a core taken in central England. The quarry exposures allowed acquisition of large, fresh samples of this immature, organic-carbon-rich mudrock. The samples, representing all stratigraphic horizons and biofacies, were obtained in collaboration with experts on the vertebrate and invertebrate paleoecology of the Lower Oxford Clay. Preliminary measurements include (i) carbon and oxygen isotopic compositions of the extensive and well preserved biominerals in this unit; (ii) carbon isotopic compositions of bulk organic materials; (iii) relative abundances and carbon-isotopic compositions of organic sulfur compounds and pyrite. These results have provided unique geochemical information which we will build upon in our continued study. Further goals in the continuation of this project include (i) confirming a phytoplanktonic origin for pristane and phytane; (ii)reconstructing the structure of the community of consumer organisms using compound-specific isotopic analyses; (iii) expanding the scope of the study stratigraphically to include the Middle and Upper Oxford Clay; (iv) elucidating the timing of organic sulfur formation in the widely varying paleoenvironments of the Oxford Clay. The work proposed will test hypotheses developed during our prel iminary study and should provide new insights on the coupling of the carbon and sulfur biogeochemical cycles in organic- rich marine sediments. ***
