59th Annual Report on Research 2014

PROPOSED RESEARCH SUMMARY

Smectite-illite interstratified clay minerals are ubiquitous in many sedimentary basins. Progressive transformation of smectite to illite via mixed layer illite/smectite has been correlated with petroleum generation and therefore this reaction is considered as a proxy for hydrocarbon exploration. More recently, formation of illite from smectite was found to occur in biologically catalyzed reactions in short time and bypassed high temperature, pressure and long time required for this transformation in natural environments. If the smectite-illite reaction is biologically catalyzed in natural environments, it will require a paradigm shift in our fundamental understanding of this reaction as well as its relationship with petroleum maturation. The proposed research seeks to fill in this important gap between controlled lab and natural environments by applying phosphate-oxygen isotope ratios as a tracer and recorder of biological activities during this transformation using sediment records from Mississippi Delta, LA and Fithian, IL. It will combine sequential extraction of sediment P phases with Nuclear Magnetic Resonance (NMR) and phosphate oxygen isotope ratios (d¹⁸O_P) to identify biotic/abiotic environment and temperature of illite (or mixed layer I/S) formation. The outcome of the proposed research, whether it corroborates the laboratory findings or not, will significantly advance our understanding of this reaction as well as broaden the application of d¹⁸O_P as a tracer of this reaction pathway.

ACHIEVEMENTS MADE SO FAR FROM THE FUNDED GRANT

What was accomplished under these goals?

Sediment sampling across the geochemical gradient in Mississippi Delta was completed in July 2014. Additionally sediment samples from Fithian, IL have just arrived. Sediment, pore waters alongwith mineralogical composition of sediment are being analyzed. Identification of layered smectite and illite minerals including interstratified (I/S) has provided promising results that is hoped to help us address the research question directly. We have been processing sediment from Mississippi site and extracting P pool and analyzing for phosphate oxygen isotope ratios. While the start of project took some time due to logistical challenges, but now we have all taken pace of this research and hoped to have results very soon.

What opportunities for training and professional development has the project provided?

• A PhD graduate student (Sunendra R. Joshi) has been funded by this research. Sunendra brings his expertise in isotope biogeochemistry to address research question posed in this proposal.

• A summer intern (Awet Negusse) undergraduate with Chemistry major) was trained on basic aspect of phosphorus biogeochemistry. He was involved in sampling and processing of soil and porewater samples.

How have the results been disseminated to communities of interest?

Published book chapter is available online and could be send as an electronic pdf file.