Paper No. 175-1
Presentation Time: 8:00 AM
WHAT DRIVES CARBONATE PRECIPITATION AND DISSOLUTION IN MARINE SEDIMENTS?
Marine sediments are teeming with microbes. These microbes degrade organic matter, fueling a complex interplay of biogeochemical processes and strongly influencing porewater geochemistry. Microbes, therefore, can drive diagenetic loss or modification of primary signals or introduce new, secondary features into the geological record. Carbonate minerals are particularly sensitive to microbial (diagenetic) processes because many of these processes drive major swings in porewater pH and total inorganic carbon content, fostering carbonate dissolution, carbonate precipitation, or both. Here, we use reaction transport modelling to disentangle the effects of various microbially-mediated primary and secondary redox processes and equilibrium processes on porewater carbonate geochemistry. We also explore the environmental conditions that can promote carbonate growth at or just below the sediment-water interface. Together, these analyses allow us to tease apart which porewater reactions are the most effective drivers of carbonate saturation state under various environmental conditions. Lastly, we investigate the sensitivity of porewater saturation state to secular variability in paleoenvironment (seawater chemistry, ocean redox conditions, bioturbation, organic matter content and quality, and weathering rates) to identify which intervals in the geologic past would have been most conducive to early diagenetic carbonate dissolution or precipitation. Our results indicate a tight coupling between diagenetic dynamics and paleoenvironmental conditions and emphasize the importance of diagenesis in the interpretation of the geological record.