Carbonate Sedimentology of the Upper Riphean (Neoproterozoic) Uk Formation, Southern Urals

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Abstract

Lithological characteristics and results of the lithofacies analysis of carbonate deposits in the most complete section of the Upper Uk Subformation of the Riphean stratotype (northern part of the Bashkir Anticlinorium, southern Urals) are presented. The subformation is divided into the following members or sequences (from the bottom to top): Yuryuzan, Medved I, Manaysu, and Medved II. The subformation bottom occurs at the base of a huge stromatolite buildup. The Yuryuzan member is characterized by the thin-columnar branching stromatolites Patomella. The Medved I and Medved II members are represented mainly by bioherms consisting of the columnar-branching stromatolites Linella, interbiohermal rocks, and local packets of layered granular limestones found only in the lower member). The Manaysu member comprises layered (mainly cyclic) deposits with abundant molar tooth (MT) structures. The growth of the Yuryuzan member stromatolites occurred most likely in the upper subtidal-peritidal zone within the inner carbonate ramp under the influence of siliciclastic-bearing currents. Stromatolite buildups in Medved I and Medved II members were formed as a part of wide facies belts below the normal wave base (inner/middle ramp boundary) but within the photic zone. Layered limestones in the Medved I member are periodic storm current deposits. Environments of the inner ramp and upper middle ramp dominated during the deposition of Manaysu sediments with signatures of the influence of normal and storm waves. The sequence including the upper part of the Lower Uk Subformation, as well as the Yuryuzan and Medved I members of the Upper Uk Subformation, reflects a progressive deepening of the basin. The later slowdown in the rate of sea level rise (or fall) fostered the change in facies and the formation of the shallow-water Manaysu member. Subsequently, the transgressive trend appeared again, resulting in the formation of Medved II member. The upper boundary of the Uk Formation corresponds to a major break in the geological record associated with global glaciation.

Translated title of the contributionЛитология и обстановки осадконакопления карбонатных отложений укской свиты верхнего рифея (неопротерозой) Южного Урала
Original languageEnglish
Article number2
Pages (from-to)487-508
Number of pages22
JournalLithology and Mineral Resources
Volume56
Issue number6
DOIs
Publication statusPublished - Nov 2021

Keywords

  • Bashkir Anticlinorium
  • carbonate ramp
  • facies
  • MT structures
  • stromatolites
  • tempestites
  • Upper Riphean

OECD FOS+WOS

  • 1.05 EARTH AND RELATED ENVIRONMENTAL SCIENCES
  • 1.05.GC GEOCHEMISTRY & GEOPHYSICS
  • 1.05.KY GEOLOGY
  • 1.05.RE MINERALOGY

State classification of scientific and technological information

  • 38 GEOLOGY

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