Lithologic and geochemic features of the Upper Emsian (Lower Devonian) carbonate-clayey deposits at the Ilych river (the Northern Urals)

The Upper Emsian deposits in the northern part of the Urals are mainly composed of normal-marine clayey limestones with abundant organic remains. However, there are rare, predominantly clayey sections, which conditions of sedimentation remain unclear. The object of the study is one of such atypical Upper Emsian deposits, exposed at the Ilych River near the mouth of the Shezhim-Yu River. These rocks were studied by petrographic (optical microscopy) and geochemical (silicate and X-ray diffraction) methods. The argillites include kaolinite, ferruginous chlorite and muscovite. The interpretation of the chemical analysis data showed that the clayey material of the argillites correspond to the continental clays of the tropical climate with a high degree of chemical decomposition of the original rocks (weathering crusts), probably formed before the Late Emsian time. During the Late Emsian transgression, this clay material was eroded, transported and accumulated in the coastal shallow-water conditions of the passive continental margin. Fragments of the Upper Emsian sections containing similar kaolinite-bearing argillites form a strip along the western slope of the Urals from the Ilych River middle course to the Shchuger River. We concluded about the location of the removal source in the Verkhnepechorskaya depression southern part, where the Upper Emsian rocks with stratigraphic unconformity overlaid the Upper Silurian strata.