Geologicheskii Vestnik

A review of the existing ideas about the prevalence, morphology and genesis of neptunian dikes cutting through carbonate reef Lower Permian massifs showed ambiguity in the interpretation of their genesis — they were considered as consedimentary interbiohermic cavities, interlayers associated with periodic flooding of reefs, as well as filling tectonic cracks. New data obtained during field observations on the Toratau, Yuraktau massifs and in the Shakhtau quarry allowed us to establish a large morphological diversity of neptunian dikes and conclude that in the formation of some bodies it is possible to distinguish in their gevelopment the stages of calm and active (catastrophic) sedimentation. The latter was accompanied by the formation of underwater landslide folds, crushing breccias and collapse structures of large blocks of reef rocks. Deep parts of tectonic clefts on the Yuraktau, where the material of the overlapping deposits could not reach, was «healed» by radially radiant aggregates of calcite crystals. Neptunic dikes are indicators of seismic impact on the reef zone in the western side of the Pre-Uralian foredeep and reflect the influence of the Early Permian collision and the growth of the Ural Mountains on the adjacent part of the East European Platform. Outcrops of tubifite biogerms of Asselian age were found in the southern part of the Pre-Uralian foredeep. A modern analogue of this process can be the landslide of large blocks of rocks in the area of the Great Barrier Reef of Australia, discovered by underwater multibeam equipment.

neptunian dikes, paleoseismic indicators, limestones, reef massifs, Pre-Uralian foredeep

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