New finds of Jurassic plants from the Abalak formation deposits of Uvat District (West Siberia)

Plant remains from the middle Jurassic deposits of Frolov-Tampey structure-facies zone of West Siberia recognized and monograph-ically described in the article. Most frequent finds of flora in Jurassic terrestrial deposits of West Siberia are poorly preserved and plant remains generally represented as meroleims. Considering this, even poorly preserved vegetable detritus could have significant scientific implication in many cases. The object of study in this work is a number of core samples with different preservation stages of plant remains. All the samples were collected from a drilling well of 2690.08 m - 2780.65 m depth interval. Only two samples contained relatively well preserved finds of flora, which are marked as № 116/1350 and №1351 and deposited in the Paleontological Museum of National Research Tomsk State University. The sample № 116/1350 was taken from 2690.08 m and consists of massive dark-grey claystone enriched with plant remains of putative plant bed. The sample № 116/1351 was taken from 2780.65 m and consists of grey middle-grain sandstone with abundant of poorly preserved fragments of rhizome. Description of plant remains examined with use of Comparative morphology method with assignment to higher categories S.V. Meyen's systematics. According to the Structure-Facial zonation of West Siberia, the understudied area is located in Frolov-Tampey structure-facies zone [Reshenie..., 2004]. As reported by palynology data the core sample № 116/1350 is dated Middle Jurassic (Callovian age). These deposits are included into Lower Abalak SubFormation (U₂ sand productive bed termed by Tyumen Geological classification). The second sample № 116/1351 was dated as Bajoci-an and confined to Middle Subformation of Tyumen Formation (U₅ sand productive bed). Plant assemblage in the sample № 116/1350 consist of typical Jurassic fern genera as Coniopteris Brongniart with dissected on 3-5 lobes pinnules. Furthermore, fragments of Czekanowskia sp. and Phoenicopsis sp. leaves identified. However, the exceptional find is a singular foliage of Doratophyllum sp. which is which is a genera of Cycadopsida. In the result, the phototable was made by author where shown the major finds. On this basis, phytostratigraphical significance of studied fossil plants considered and described plant assemblage compared with known plant complexes from abutting areas as well. Co-occurrence of described plants in the sample confirm position of a fossiliferous bed within the Malyshevsky phytohoryzont.

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