in Jurassic and Cretaceous Stratigraphy

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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Plasencia P. Bioestratigrafía y Paleobiología de Cono- dontos del Triásico Medio del Sector Oriental de la Península Ibérica. Valencia: Servei de Publica- cions de la Universitat de Valencia, 2009: 408. Plasencia P., Márquez-Aliaga A. Aportaciones al estu- dio de la recuperación y extinción de los cono- dontos durante el Triásico. Geotemas, 8: 229-232. 172 Rigo M., Preto N., Roghi G., et al. Upper Triassic cono- dont extinction events. Geophysical Research Abstracts, 2005, 7: 1-2. Tanner L.H., Lucas S.G., Chapman M.G. Assessing the record and causes of Late Triassic extinctions. Earth-Science Reviews, 2004, 65: 103-139.
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 The Palynofloras at the Jurassic-Cretaceous Boundary (Russian Far East) V.S. Markevich, E.V. Bugdaeva * Laboratory of Palaeobotany, Institute of Biology and Soil Science, Far East Branch of Russian Academy of Sciences, Vladivostok 690022, Russia (E-mail: markevich@ibss.dvo.ru) The palynofloras were studied from the Upper Jurassic to Lower Cretaceous terrestrial deposits of the Bureya Basin and terrestrial and marine beds of Pri- morye region. In Bureya Basin the Upper Jurassic is represented by Talyndzhan Formation, the Lower Cretaceous - by Urgal Formation. Talyndzhan Fm. is composed of gravels, sandstones, shales, mudstones, tuffs, tuffites and coals (more than 20 seams). The thickness of this stratigraphic unit is 500 m. The Urgal Formation over- lies the Talyndzhan Formation conformably or with local unconformity and consists of conglomerates, gravels, sandstones, shales, mudstones and coals (about 50 seams). Thickness is about 600 m. The Urgal For- mation is divided into Dublikan and Soloni Sub- formations, some geologists range these stratigraphic units into Formations (Vachrameev and Doludenko, 1961; Krassilov, 1972, 1973). The deposits of these formations were sampled in detail with special emphasis on coals. Abundant and well-preserved palynomorphs were obtained. The Upper Jurassic strata were deposited in brackish coastal environments. Horsetails, bryophytes, ferns, ginkgoaleans, czekanowskialeans and conifers made up plant communities of this age (Vachrameev and Doludenko, 1961; Krassilov, 1972, 1973). The burials are dominated by ginkgoaleans and czekanowskialeans, the role of ferns and cycadophytes is high. The Late Jurassic palynoflora is characterized by predominance of fern spores, mainly have been as- signed to osmundaceous and cyatheaceous ferns (up to 90%). The participation of diverse mosses is consi- derable. Gymnosperms are dominated by pollen close to Pinaceae and Ginkgocycadophytus. Palynological assemblages from middle and upper parts of Talyndzhan Formation are similar to assemblages of Chonok Formation containing the Volgian Buchias (Vilyui syneclise), Sytogin Formation (Priver- khoyansky depression), the upper Volgian deposits of Kheta River basin and Paks Peninsula (Eastern Si- beria). In the Cretaceous the sea retreats from this area and the accumulation of sediments took place on swam- py seaside plains. The Berriasian palynoflora is dominated by ferns, mainly belonging to Cyatheaceae, Dicksoniaceae, Du- plexisporites (up to 84%). The palynomorphs Sterei- sporites bujargiensis, Neoraistrickia rotundiformis, Contignisporites dorsostriatus, Appendicisporites tri- costatus, Concavissimisporites asper appeared. Among gymnosperms Classopollis and Pinaceae prevail (Markevich, 1995). The Valanginian palynoflora is dominated by conifers (up to 60%) and Ginkgocycadophytus. Ferns reduce up to 50%. The osmundaceous ferns lost their significance, gleicheniaceous and schizaeaceous re- placed them. The cyatheaceous ferns, ginkgoaleans, cycadophytes, cheirolepidiaceous plants and conifers provided a basis for the Early Cretaceous plant communities. Essential features of these plant communities are inherited from the Jurassic vegetation. Their conserva- tism is related to similar environments. The Berriasian palynoflora in Primorye region is known from Tauhe Formation of marine origin and from Ustinovka Formation with the Berriasian fossil plants (Primorye region, Coastal Uplift). Tauhe For- mation contains ammonites Neocomites ex gr. neo- comiensis (Orb.), Dalmasiceras sp. and bivalves Buchia cf. volgensis (Lah.), Nucula sp., Myophorella (Myophorella) nottica Konov., Stolmorhynchia sp., Cyclothyris acuticostalis Smirn. (Markevich et al., 2000). This palynoflora is dominated by gymnosperms, mainly by Classopollis. Among spores Cyathidites predominates. The peculiarity of palynological assem- blage is the appearance of costate spores Appendici- sporites (Markevich, 1980, 1995). The Berriasian palynoflora from marine Tauhe Formation has a similarity with palynoflora from Dublikan Formation. The Berriasian flora from localities of Tauhe Formation comprises ferns, cycadophytes, and conifers (Krassilov, 1967). Acknowledgements: Our research was supported by Presidium FEBRAS (grants 09-1-P15-02). Key words: Jurassic-Cretaceous non-marine stratigraphy; Palynology; Russian Far East References: Krassilov V.A. The Mesozoic flora of Bureya River (Ginkgoales и Czekanowskiales). Moscow: Nauka, 1972: 150 (in Russian). Krassilov V.A. Materials on stratigraphy and palaeo- floristics of coal-bearing beds of Bureya basin. In: Krassilov V.A. (ed). Fossil floras and phytostrati- graphy of the Far East. DVNC AN SSSR, Vladi- vostok, 1973: 28-51 (in Russian). 173
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