EPS Colloquium: Sasha Turchyn

Can a Record of Ocean Chemistry by preserved in Oceanic Crust?

Reconstructing the chemistry of the ocean over Earth history is largely done through the chemical analysis of various low temperature sedimentary minerals and rocks that formed in past oceans. However, low-temperature sedimentary minerals and rocks can suffer from small spatial chemical differences due to the chemical heterogeneity in sedimentary environments, and furthermore can undergo chemical alteration post-deposition, broadly termed diagenesis. Thus trusting the sedimentary record can be challenging. Minerals form in oceanic crust during hydrothermal circulation, and these minerals also record the chemistry of the fluid from which they precipitate. In this talk I will tell two stories, the first using epidote and quartz veins to understand how the oxygen isotopic composition of hydrothermal vent fluid, and thus the ocean, may have changed over time. The second story is using the calcium isotopic composition of carbonate vein minerals to understand fluid-rock interaction and how the calcium isotopic composition of the ocean may evolve over time.