GEO Solid Earth Brown Bag Seminar

Oct 6, 2022, 12:30 pm1:30 pm
Guyot 220



Event Description

Abstract: Sedimentary rocks deposited during the Neoproterozoic era (1000-540 Ma) provide evidence for dramatic changes to Earth's climate and environments, including Snowball Earth glaciations, potential perturbations to the global carbon cycle (carbon isotope excursions), and the evolution of animals. Carbonate rocks, which record information about the physical and chemical properties of the environments in which they form, can serve as archives for Neoproterozoic environments, but they are also easily altered during post-depositional diagenesis. To add complication, much of the Neoproterozoic carbonate record is dolomite (CaMg(CO3)2), an incompletely-understood mineral that is typically thought to form via the diagenetic alteration of primary CaCO3. In this talk, I present two studies that demonstrate that Neoproterozoic dolomites can and do preserve primary environmental data:  First, I will show a nanometer-resolution crystal orientation map of one ca. 574 Ma dolomitic ooid that records the onset of the Shuram carbon isotope excursion. We interpret this ooid’s fabric as primary and support a primary origin for the Shuram excursion. Next, I will show carbonate clumped isotope measurements from a ca. 810-635 Ma succession of micritic dolomite in a drillcore from Western Australia. Calculated temperatures are identical to temperatures in modern sabkha-like settings where microbially-mediated dolomite precipitates today. We interpret these temperatures as representative of the primary depositional environment, again suggesting dolomite formed in depositional settings. Finally, I will preview the work I’m starting at Princeton: a facies classification project targeting carbonates that record the first Neoproterozoic carbon isotope excursion, the Bitter Springs (ca. 810 Ma).