CRYOGENIAN-EDIACARAN EARTH HISTORY WITH INTERCONTINENTAL DRILLING

The Cryogenian-Ediacaran (717-538 Ma) is one of the most dramatic intervals in Earth history: the Earth was entombed in Snowball Earth glaciations, ocean sulfate concentrations crashed and rebounded, the global carbon cycle underwent high-amplitude fluctuations, algae emerged as the dominant primary producer in the oceans, and metazoans first appeared and diversified. However, the discontinuous and fragmented nature of outcrop-based studies has hindered developing quantitative models of the Earth system during this critical period. The Geological Research through Integrated Neoproterozoic Drilling (GRIND) project begins to rectify this scientific shortcoming by obtaining cores through the archetype successions that record this environmental and biogeochemical change.

To date, GRIND has focused on the Ediacaran-Cambrian transition (ECT; c. 560-530 Ma) in south Namibia (Nama Group), strata of west Brazil (Corumbá Group), and South China (Doushantuo, Dengying and equivalent formations). Drilling in Namibia and Brazil is complete, and drilling in China will commence this year. The characterized split cores from Namibia and Brazil will be permanently archived at in-country repositories as well as the Federal Institute for Geosciences and Natural Resources in Berlin-Spandau, Germany. These cores will be available for future research, education and national capacity building activities and mark the first step towards creating an onshore core archive like that of the IODP.

We are now starting phase 2 of GRIND in which we will drill Cryogenian successions (GRIND-CRY). These cores will focus on retrieving low-grade sedimentary core for biomarkers to better assess the relationships between Snowball Earth, geochemical change, the emergence of algae, and to document the first appearance of demosponge biomarkers. Proposed targets are Oman, Brazil, and Namibia. Although Namibia strata are overmature, the shelf-slope transect on the western margin of Namibia spans glacial deposits with iron formation and a mixed carbonate-siliciclastic sequence with the Trezona carbon isotope anomaly and microfossils, which will complement data from other sites.