Newly Discovered Exposures of Neoproterozoic Diamictite within the Samre Fold-Thrust Belt of Northern Ethiopia

Abstract:

Life and climate evolved dramatically during the early Neoproterozoic - sedimentary rocks from this period record both the diversification of eukaryotic life as well as large scale fluctuations of the carbon cycle and paleogeography during the lead up to Cryogenian glaciation. Understanding global change leading up to this glaciation is critical for interpreting the conditions that initiated dramatic climate and geochemical oscillations. The Tonian-Cryogenian Tambien Group (Tigray region, northern Ethiopia) is a mixed carbonate-siliciclastic sedimentary succession deposited in an arc proximal basin that culminates in the Negash diamictite interpreted to represent the ca. 717-662 Ma Sturtian Glaciation. The presence of intercalated tuffs suitable for high precision U-Pb geochronology makes these sedimentary rocks an ideal target to temporally constrain physical and isotopic stratigraphic data sets of the early Neoproterozoic. The lower Tambien Group has been temporally constrained and used to establish global synchroneity of large scale carbon isotopic change ca. 800 Ma (Swanson-Hysell et al., 2015). We report the discovery of extensive exposures of upper Tambien Group successions southeast of the town of Samre within a newly mapped fold-thrust belt. Stratigraphic study across these exposures opens an opportunity to document environmental change across the basin during the apparently conformable transition from a mixed carbonate-siliciclastic platform into the Negash diamictite of the Sturtian Glaciation. The presence of ashes within the sediments holds the promise of combining high-precision dates with chemostratigraphic data to constrain global change before and during the onset of Snowball Earth glaciation.