A COUPLED CLUMPED ISOTOPE AND MULTISPECTRAL IMAGING APPROACH REVEALS COOL TEMPERATURES IN PRE-SNOWBALL DOLOMITES (Invited Presentation)

Our collective understanding of Earth’s climate and environments through geologic time is limited by our ability to interpret the carbonate rock record — an archive that often is obscured or overprinted by poorly-understood depositional and diagenetic processes including dolomite precipitation and recrystallization. In order to access the archive preserved in ancient carbonates, we require geochemical and petrographic tools to “see through” diagenesis and reconstruct primary depositional environmental conditions. Here I will present a novel method of combining petrography and geochemistry to more completely understand fabric-preserving dolomites by coupling clumped isotope (Δ₄₇) measurements and high-resolution multispectral images of polished slabs. Clumped isotopes have the power to reveal the depositional temperatures of carbonate rocks — if primary signals can be disentangled from diagenetic resetting and overprinting. I apply these methods to a suite of dolomites deposited in very shallow, evaporative environments during the climatically unique and poorly-understood late Tonian period: the ca. 80 million years before the first Neoproterozoic snowball glaciation (~800-717 Ma). Together, images of polished slabs and micro-drilled Δ₄₇ measurements reveal multiple generations of dolomite formation and associated clumped isotope “resetting”, including what appear to be primary, syndepositional phases of dolomite that preserve clumped temperatures as low as 17±8°C. These cool, primary dolomites are distinguishable from later, hotter phases of diagenetic dolomite on the basis of visible light response to UV irradiation (365 nm). Applying the resolving power of high-resolution, narrow-band imaging and the sensitivity of the clumped isotope system to this suite of Tonian dolomites, we are able to distinguish cooling depositional temperatures before the first Neoproterozoic snowball Earth from co-hosted diagenetic signals held by later dolomite phases.