Chapter 28 Late Cryogenian (Vendian) glaciogenic deposits in the Marnya Formation, Oselok Group, in the foothills of the East Sayan Range, southwestern Siberian Craton

Abstract

AbstractThe glaciogenic deposits of the Ulyakha Member (Mb.) referred to as Ulyakha diamictite (tillite), and the associated Late Cryogenian (Early Vendian) glaciofluvial deposits, are the lower strata of the Marnya Formation (Fm.) of the Oselok Group (Gr.) in the southwestern Siberian craton, which rest erosionally over the Cryogenian (Late Riphean) Karagassy Group. The Oselok Group deposits fill the Peri-Sayan foredeep and their stratigraphic equivalents immediately overlie the basement of the Siberian Platform. The glaciogenic deposits, including diamictite, breccia, boulder conglomerate and sandstone, had multistage sedimentation, were widespread, and underlie a cap dolomite of the lower Ozerki Mb. The Late Cryogenian (Early Vendian) age of the Ulyakha Mb. is defined by traces of shallow-marine soft-bodied animals in the middle part of the Ozerki Mb., and by findings of Ediacaran-like Metazoa in the overlying Bolshaya Aisa Mb. of the Marnya Fm. Deposition of the Ulyakha tillites and associated rocks has been correlated with the Late Cryogenian (Marinoan) glaciation based on the δ13C patterns in carbonate deposits in the Marnya and Uda formations and their stratigraphic position much below the Pre-Manykai and Zhuya δ13C negative signatures, which have been equated to the Wonoka anomaly.