Continental weathering products: Clay mineral surfaces as sinks for organic carbon in marine environments; chemistry and petrography of bed sediments from large rivers---Provenance and chemical weathering

Continental weathering and organic carbon (OC) burial in marine sediments are important processes because they act as sinks for atmospheric carbon dioxide. Continental weathering products provide information about provenance, marine sediment quality/quantity, denudation and continental crust composition. In this study I explore two topics that impact some of these issues directly or indirectly.; Abundant clay inter-layer surface area/spaces are proposed as sites for excess OC storage/preservation in clay-rich rocks (Kennedy et al. 2002). I tested this hypothesis by: (1) measuring mineral surface area (MSA) of representative clays to assess the Ethylene Glycol Monoethyl Ether (EGME) MSA method, (2) studying field samples to investigate the characteristic relationship between MSA and total organic carbon, and (3) experimentally evaluating the adsorption potential of clays for dissolved natural organic materials. The EGME-MSA method informs us about the availability of interlayer spaces. But, its application to ancient sediments seems impractical as clays undergo changes during burial daigenesis. Testing the EGME-MSA hypothesis in such sediments is also complicated by observations that they contain particulate OM. However, results from the adsorption experiments suggest that surface sorbed DOC is <1wt% of clays. These results suggest MSA plays a relatively small role compared to other mechanisms.; The second study is an investigation of the petrography and chemistry of bed sediment from rivers draining collisional tectonic zones to understand the factors that affect their composition. I compare basin lithology, physiographic and GIS parameters with weathering and maturity indices --- Chemical Index of Alteration, weathering index of Parker, and the Q/(Q+Rf). Detailed study on the Red River in Asia reveals statistically meaningful correlations between the weathering indices and sedimentary to metamorphic rock ratio and sedimentary rock cover. Otherwise, correlations are poor. Lithology, related to the tectonic setting, appears to have the greatest affect on bed sediment composition in such rivers. There are apparent differences in the river sediment composition from tropical to temperate rivers. However, these differences can be attributed to tectonic provenance. In such high flow velocity and large-sediment yield streams the effects of weathering in the bed sediment are subdued and their composition reflects their provenance.