Lithological Features of the Uryuk Formation in the Vendian Tolparovo Section (Southern Urals)

Abstract

New results of the lithological structural–textural observations and petrographic study of rocks of the Uryuk Formation (sandstones and gravelstone-sandstones with the subordinate mudstone interlayers) exposed in the Malyi Tolpar River basin in the Bashkir meganticlinorium. For the first time, a wide development of synsedimentary underwater landslide folds (varying from the first tens of centimeters to the first meters in size) has been established in the Uryuk deposits. The sandstones demonstrate the oblique, wavy, flaser, and horizontal (with paired thin clay lamina) stratification, as well as massive layers. Signs of shallow wave ripples have been established. The rocks are characterized by mechanoglyphs and textures similar to Arumberia banksi, which presumably represent the lithified textures of bacterial mats that existed under shallow-marine environments with sandy–clayey sedimentation. Despite the absence of direct lithological signs of diamictites, the Uryuk deposits likely form a single sedimentary sequence with the underlying Tolparovo–Suirovo marine glacial deposits, in which a shallow-sea sedimentation regime was established by the end of the Uryuk time. It is shown that the presence of ferruginous minerals in the sandstone cement is secondary in nature and is associated with their epigenetic transformations. It is concluded that the red color of rocks of the Uryuk Formation cannot be used for the stratification of its sections and reconstruction of sedimentation conditions in the Uryuk time.