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.

中文翻译：

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乌拉尔南部Uk组上Riphean（新元古代）碳酸盐沉积学

摘要

介绍了 Riphean 地层上 Uk 亚组最完整部分（Bashkir Anticlinorium 北部、乌拉尔南部）碳酸盐岩沉积物的岩性特征和岩相分析结果。亚组分为以下成员或序列（从下到上）：Yuryuzan、Medved I、Manaysu和Medved II。地层底部出现在巨大叠层石堆积物的底部。Yuryuzan 成员以细柱状分支叠层石Patomella为特征。Medved I 和 Medved II 成员主要以由柱状分枝叠层石Linella组成的生物礁为代表、生物间岩层和仅在下层发现的局部层状粒状石灰岩包）。Manaysu 成员包括层状（主要是环状）沉积物，具有丰富的臼齿 (MT) 结构。Yuryuzan 成员叠层石的生长最有可能发生在内部碳酸盐斜坡内的上潮下带 - 周带带，受含硅碎屑流的影响。Medved I 和 Medved II 段的叠层石堆积物是作为正常波基（内/中斜坡边界）下方但在光带内的宽相带的一部分形成的。Medved I 段的层状石灰岩是周期性风暴电流沉积物。内坡和中上坡的环境在 Manaysu 沉积物沉积过程中占主导地位，具有正常波和风暴波的影响特征。包括下 Uk 亚组上部以及上 Uk 亚组的 Yuryuzan 和 Medved I 段在内的层序反映了盆地的逐渐加深。后来海平面上升（或下降）速度的减缓促进了相的变化和浅水马奈苏段的形成。随后，海侵趋势再次出现，导致了Medved II成员的形成。Uk 组的上边界对应于与全球冰川作用相关的地质记录的重大断裂。后来海平面上升（或下降）速度的减缓促进了相的变化和浅水马奈苏段的形成。随后，海侵趋势再次出现，导致了Medved II成员的形成。Uk 组的上边界对应于与全球冰川作用相关的地质记录的重大断裂。后来海平面上升（或下降）速度的减缓促进了相的变化和浅水马奈苏段的形成。随后，海侵趋势再次出现，导致了Medved II成员的形成。Uk 组的上边界对应于与全球冰川作用相关的地质记录的重大断裂。