Vol 32, No 5 (2024)

Based on data on the geochemical characteristics ((La/Yb)_N, Eu/Eu* and content of Th) of clay rocks of Podolian Transnistria, South-Eastern Poland, Belarus and Volyn, Lithuania, the vicinity of St. Petersburg, South-Eastern White Sea region and Arctic Norway, categories of rivers that transported fine-grained aluminosiliconclastics to sinks that existed during the Vendian and Early Cambrian were reconstructed in the west of the East European Platform. The distribution of data points of clay rocks of the Volynian time on the (La/Yb)_N–Eu/Eu* diagram with the fields of the composition of pelitic fraction of bottom sediments in the estuary of modern rivers of various categories allows us to assume that for Lithuania and Podolian Transnistria the feeding provinces were, among other things, paleowatersheds composed of volcanic formations. For Eastern Belarus and the South-Eastern White Sea region, the influence of erosion products supplied by rivers flowing through igneous/metamorphic terranes (crystalline basement) is noticeable. A significant part of the clastic material was carried by rivers that drained sedimentary formations, as well as large rivers, i.e. rivers whose length exceeded 1000 km and whose drainage area was more than 100,000 km². The existence of the latter is confirmed by the presence of detrital zircon in the rocks of the Zhukov Formation of South-Eastern Poland, borrowed possibly from the rocks of Fennoscandia. In the Redkinian time, along with large rivers (rivers category 1) and rivers fed by the products of erosion of sedimentary formations (rivers category 2), transport of fine-grained clastics was also carried out by rivers that drained rocks of the crystalline basement ((rivers category 3; this is typical of Belarus and Volyn, the South-Eastern White Sea and Arctic Norway) and by rivers flowing through areas of distribution of volcanic associations (rivers category 4). The distribution of data points of the clay rocks of the Kotlin stage on the (La/Yb)_N–Eu/Eu* diagram suggests that the main agents of transport of fine-grained aluminosiliconclastics to sinks at that time were large rivers and rivers fed by fine particulate matter due to the erosion of predominantly sedimentary rocks. The Early Cambrian paleowatersheds were apparently composed not only of crystalline rocks, but also of sedimentary formations. All of the above is in fairly good agreement with the previously established fact of a gradual increase in the contribution of erosion products of sedimentary rocks to the formation of Vendian–Early Cambrian sedimentary sequences from Podolian Transnistria to Arctic Norway.

The geological features of the Mansurovo unique locality of the remains of tetrapods and ichnofossils, Orenburg Region (Gostevskaya Formation, Lower Olenekian Substage, Ustmylian Horizon) are considered. A layer-by-layer description cross-section of 16 ditchs and their correlation with the section construction along the line of ditchs are provided. The Mansurovo section, based on biostratigraphic (Wetlugasaurus malachovi grouping of the Wetlugasaurus Fauna) and lithologic-facies data, correlates with the middle part of the stratotype section of the Gostevskaya Formation (Buzuluk Depression of the East European Platform). The geological features of the locality indicate a heterogeneous structure of the identified four geological units of channel-floodplain genesis within the study area, which correspond to alternating sedimentation cycles. The genesis of deposits was clarified using structural-textural analysis and microlithological analysis of rocks in thin sections. The faunistic complex of tetrapods and macroflora, as well as unique complex of ichnofossils were also characterized. Based on the data of lithological-facial analysis, a sedimentation model of the genesis of the locality is presented, showing the uneven nature of sedimentation pattern due to the wandering of river branches and their periodic drying out in a hot and arid climate during the Early Olenekian. Taking into account paleontological data, taphonomy was analyzed, indicating the burial process in the river setting in strong current condition and the possible death of Temnospondyli in subaquatic conditions.