Chapter 27 The glaciogenic Bol'shoy Patom Formation, Lena River, central Siberia

The Bol9shoy Patom Formation (Fm.) is part of the Upper Precambrian Patom Supergroup, which comprises a siliciclastic and carbonate succession divided into (from base to top) the Ballaganakh, Dal9nyaya Tayga and Zhuya Groups (Gr.). The supergroup was deposited within the bay-like passive margins of the Siberian craton. The Bol9shoy Patom Fm. is the lower unit of the Dal9nyaya Tayga Gr. Massive and stratified diamictites with subordinate sandstones, mudstones, siltstones, conglomerates and conglo-breccias form the Bol9shoy Patom Fm. New biostratigraphic (microfossils of Pertatataka type, Ediacaran fossils) and chemostratigraphic data ( 87 Sr/ 86 Sr, δ 13 C) point to a Vendian (Late Cryogenian and Ediacaran) age for the Dal9nyaya Tayga and Zhuya Groups. Unsorted diamictite matrix, a very wide range of size and roundness of dispersed erratic clasts, the presence of glacial grooves on boulders, dropstones and till pellets in laminated mudstones and siltstones are all evidence for intense ice rafting and ice-shelf sedimentation in the northeastern part of the Patom basin during deposition of the Bol9shoy Patom Fm.