TY - JOUR

T1 - The origin of boulders in the Neoproterozoic of Eastern Sayan Ranges, south-west Siberia: Glacial transport versus winnowed concretions

AU - Aleksandrov, Dmitrii

N1 - Funding Information: This work was undertaken as part of my PhD at Novosibirsk State University, supervised by D.V. Grazhdankin. I thank J.K. Sovetov, V.I. Rogov and K.E. Nagovitsin for generously sharing their field observations, knowledge and experience. This study was supported by the Russian Science Foundation grant 20-67-46028, and by the IAS Postgraduate Research Grant (fieldwork, SEM studies). The manuscript was prepared under the Government Contract FWZZ‐2022‐0002 (Ministry of Education and Science of the Russian Federation). I thank anonymous reviewers for their constructive comments, which helped to improve the manuscript. Publisher Copyright: © 2022 The Authors. The Depositional Record published by John Wiley & Sons Ltd on behalf of International Association of Sedimentologists.

PY - 2022/6

Y1 - 2022/6

N2 - The Cryogenian geological record of Siberia is scarce and ambiguous. Late Neoproterozoic strata of presumed glaciogenic origin of the Marnya Formation, Oselok Group cropping out along the Uda River in the Eastern Sayan Ranges, south-western Siberia has received considerable attention due to the presence of at least three distinctive diamictite units. The lower diamictite unit (Karapchetui Member) is in subvertical contact (previously interpreted as a glacial valley) with stratigraphically older strata of the Tagul and Ipsit formations of the Karagas Group, and is represented by a wedge-shaped unit of breccia that hosts numerous ellipsoidal sandstone bodies (previously thought to be boulders). The boulders are here reinterpreted as early diagenetic quartz and feldspar-cemented sandstone concretions exhumed and redeposited from the Ipsit Formation when the latter was still uncemented and easily erodible. Tectonic compression, reverse faulting and localised continuous syndepositional uplift led to exhumation of the concretions, whereas subsequent extension, reactivation of the fault and ‘negative inversion’ of the basin produced accommodation space for redeposition of the exhumed concretions. In the process of redeposition, exfoliating concretions produced abundant debris that provided clasts for the breccia deposit. The Karapchetui diamictite, therefore, can serve as a sedimentary archive of late Neoproterozoic tectonic activity at the south-western margin of the Siberian Craton.

AB - The Cryogenian geological record of Siberia is scarce and ambiguous. Late Neoproterozoic strata of presumed glaciogenic origin of the Marnya Formation, Oselok Group cropping out along the Uda River in the Eastern Sayan Ranges, south-western Siberia has received considerable attention due to the presence of at least three distinctive diamictite units. The lower diamictite unit (Karapchetui Member) is in subvertical contact (previously interpreted as a glacial valley) with stratigraphically older strata of the Tagul and Ipsit formations of the Karagas Group, and is represented by a wedge-shaped unit of breccia that hosts numerous ellipsoidal sandstone bodies (previously thought to be boulders). The boulders are here reinterpreted as early diagenetic quartz and feldspar-cemented sandstone concretions exhumed and redeposited from the Ipsit Formation when the latter was still uncemented and easily erodible. Tectonic compression, reverse faulting and localised continuous syndepositional uplift led to exhumation of the concretions, whereas subsequent extension, reactivation of the fault and ‘negative inversion’ of the basin produced accommodation space for redeposition of the exhumed concretions. In the process of redeposition, exfoliating concretions produced abundant debris that provided clasts for the breccia deposit. The Karapchetui diamictite, therefore, can serve as a sedimentary archive of late Neoproterozoic tectonic activity at the south-western margin of the Siberian Craton.

KW - basin inversion

KW - diamictite

KW - exhumed concretions

KW - Neoproterozoic

KW - Siberia

UR - http://www.scopus.com/inward/record.url?scp=85127760880&partnerID=8YFLogxK

U2 - 10.1002/dep2.188

DO - 10.1002/dep2.188

M3 - Article

AN - SCOPUS:85127760880

VL - 8

SP - 869

EP - 879

JO - Depositional Record

JF - Depositional Record

SN - 2055-4877

IS - 2

ER -