New data on the Jurassic deposits biostratigraphy within the Mura-Kova interfluve

Age of the Murskaya suite is determined bypalinological data in the very wide range - from the Early to Middle Jurassic period. In the opinion of M.M. Odintsova, the upperpart of the section can be composed of the Upper Jurassic sediments. Until the present time the rare fossil plant remains from theMurskaya suite where the age determination of sediments is difficult were known. The present paper gives a detailed description ofeight new Jurassic quarries stripping the Murskaya suite sediments along the Bratsk-Kodinsk road. Sediments of the studied quarriescontain the fossil plant remains, which substantially supplement our knowledge of the Jurassic flora of the Murskaya suite. Duringthe present study 11 genera and 10 species of fossil plants have been recognized. The given complex of the studied plants is a newone for the Murskaya suite and it is distinguished for the first time. The comparison of the macrofloristic complex recognized by theauthors with the complexes of A.I. Kirichkova revealed in the Jurassic sediments of Western Siberia allows us in some measure toconsider the rocks of the middle part of the suite as Middle Jurassic ones. Associations and complexes of the plant remains are described.Various phytooryctocoenoses are revealed. This is, presumably, the existence of the oxbow lakes series (fine-grained, aleuriticsandstones and aleurolites), the water regime of which was changed. Shallowing and waterlogging of water bodies led to formationof turf swamps (coal horizons occurred in all sections). Abundance of the fossil horsetail remnants and roots proves the plentyof moisture. Paleoecological description of communities with predominance of Czekanowskia, Phoenicopsis and Ginkgo genera isgiven. Communities with predominance of Czekanowskia genus were developed on low, superhumid, periodically waterlogged riversides.On the contrary, communities with Ginkgo genus preferred to take up their residence within mesophilous ecotopes. Processesof waterlogging on the alluvial plain existed in the Mura-Kova interfluve; they were of the local character. Rare frequency ofphytooryctocoenosis with the prevalence of Phoenicopsis genus supports this fact. The discussed material proposes the growingginkgo-coniferous forest where the evergreen representatives of Pinus and Picea genera known by pollen and deciduous species ofGinkgo genus formed the arbour layer. Near-shore brushwood was composed of deciduous representatives of Czekanowskia genusand herbaceous representatives of Coniopteris genus. Equisetums grew near the lake and, probably, partially in the water. The examinedcomplex of macrofloristic remains fits well into the general development pattern of Jurassic flora within the Siberian paleogeographicalarea. The climatic conditions of the Middle Jurassic period after the Toarcian warming become moderately warm andhumid again. The floristic complex studied by the authors and the presence of coalinised rocks formed under warm and humid conditionssupport this point of view. The paper contains 6 pages of typescript, 2 figures and 1 text table. References include 9 titles ofresearch works of domestic authors.

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