Early Diagenetic Aluminosilicate Formation and Burial of Biogenic Silica in Tropical Deltas

The rapid diagenetic conversion of biogenic SiO2 to authigenic clay and subsequent burial in deltas has potentially major implications for the marine Si cycle, ocean alkalinity balances, and the cycle of multiple elements that are incorporated into clays (for example, K+, Li+, Ge, and F-). In this project, a research team at Stony Brook University will conduct an integrated study using a novel application of the natural cosmogenic radionuclide 32Si, diagenetic modeling of del7Li and Ge in pore water and sediment, and laboratory incubation experiments to constrain the quantity, compositions, and mechanisms of formation of authigenic clay. They will focus on the clinoform delta complex in the Gulf of Papua, for which they have archived samples available for pore water and sediment analysis, and initiate new sampling of a representative coastal mudbank of French Guiana, deposits that represent a functional diagenetic extension of the Amazon delta. The latter site will provide a basis for optimization of analytical techniques, laboratory experiments, and generalization. Broader impacts: The Si cycle is a central component of biogeochemical processes controlling ocean and Earth surface composition. Knowledge of Si sources and sinks and their response to anthropogenic perturbations are critical to predictive models of future ocean conditions. Authigenic aluminosilicate formation and burial in tropical deltaic systems appears to be a significant component of the marine Si cycle but is relatively poorly constrained. Elements such as Li and Ge that are closely coupled to the Si cycle and extracted into authigenic aluminosilicates are also used in reconstruction of ancient Earth surface processes and provide perspective on modern ocean biogeochemical balances. The integrated study proposed here, including novel application of the cosmogenic radionuclide 32Si with potentially major implications, will provide important new quantitative constraints on the role of tropical deltaic systems in the Si cycle and on processes controlling the flux of minor elements such as Li and Ge at the continental boundary. Graduate and undergraduate education and technical training will be integrated into laboratory and field research.