Geochemical Proxy Based Reconstruction : The Trace Elemental And Isotopic Compositions Of Marine Biogenic

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Geochemical proxy-based reconstruction widely utilizes the trace elemental and isotopic compositions of marine biogenic carbonates to interpret the past climatic and oceanographic conditions. However, such proxy-based reconstructions are often challenged by marine diagenesis as carbonates are highly susceptible to diagenesis, especially partial dissolution and secondary calcite recrystallization. Thus quantifying diagenetic effect is a prerequisite for development of any carbonate-based geochemical proxy. Among the metal isotopes, Mg isotopic composition (δ26Mg) of foraminiferal carbonates is a promising proxy to reconstruct the secular seawater δ26Mg variability, which is useful in understanding long-term changes in Mg geochemical cycle. However, as the trace metals like Mg in marine carbonates show greater susceptibility to diagenetic alterations due to its low abundance as compared to that in the co-existing pore fluids, development δ26Mg of marine carbonates as a geochemical proxy critically requires a thorough understanding of the fractionation behaviors of Mg isotopes during diagenesis. Therefore, the primary goal of this dissertation is to quantify the effect of diagenesis on metal isotopes, in particularly, δ26Mg of marine carbonates from various depositional settings to evaluate the effect of advection, diffusion and lithological variation within the sedimentary column on the extent of calcite diagenesis. For this purpose, trace elemental (e.g., Mg/Ca and Sr/Ca) and
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