GRIND-ECT: geological research through integrated Neoproterozoic drilling – Ediacaran–Cambrian transition

GRIND (Geological Research through Integrated Neoproterozoic Drilling), sponsored by the International Continental Scientific Drilling Program (ICDP), aims to create a core archive of the Neoproterozoic Era via three phases: Tonian (GRIND-TON), Cryogenian (GRIND-CRY), and Ediacaran–Cambrian Transition (GRIND-ECT). The latter is the first phase undertaken and focuses on the geological and biogeochemical context of Late Ediacaran environmental perturbations and biological turnovers that culminated in the Cambrian Explosion. Mixed siliciclastic–carbonate successions of Namibia, Brazil, and China were chosen as GRIND-ECT targets. Here we report on the completed Namibian and Brazilian components. The Namibian stratigraphy drilled consists of the Kuibis–Schwarzrand sub-groups of the late Ediacaran–early Cambrian Nama Group on the western margin of the Kalahari craton in southern Namibia. These strata contain a rich record of Ediacaran fauna, including Cloudina and related small calcifiers, and simple to complex trace fossils that inhabited environments spanning shorelines to deeper-marine ramps. In addition, cores were drilled through the Late Ediacaran Corumbá Group in Brazil, which records a marine carbonate platform developed along the southeastern margin of the Amazon craton. These units are marked by a transition from a rimmed shelf to a distally steepened ramp and host the first appearance of Cloudina in Brazil and a myriad of acritarchs and trace fossils. Collectively, six Namibian cores totalling 2379 m and two Brazilian cores totalling 306 m were drilled. All cores were split and fully characterized and are housed at the Bundesanstalt für Geowissenschaften und Rohstoffe, Berlin–Spandau, Germany, and either at the Ministry of Mines in Windhoek, Namibia, or at the Universidade de São Paulo, Brazil. Ongoing efforts are integrating stable isotope and redox-sensitive element geochemistry and U–Pb and Re–Os geochronology throughout these cores, with detailed facies analyses to reconstruct the conditions under which metazoa expanded; diversified; and, in some cases, went extinct. GRIND-ECT cores offer exceptional opportunities to create and test hypotheses about the causes and consequences of Earth system transformation during the evolution of animals.