Further palynomorphs of Early Cambrian age from clastic sediments underlying the Moravian Devonian (borehole Němčičky-3)


Authors: Vavrdová M, Bek J

Published in: Bulletin of Geosciences, volume 76, issue 2; pages: 113 - 125;

Keywords: Acritarchs, Cambrian, “Basal clastics”, SE Moravia,

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Relatively well preserved, diversified assemblages of acid-resistant plant microfossils were obtained from dark grey siltstones and silty shales from core No. 10, Němčičky-3 borehole (depth 5396 m), situated in southern Moravia. Microfossils were studied in palynological residua, thin sections and in scanning electron microscope. The analysed rocks yielded numerous transparent to light yellow palynomorphs (TAI 1 to 1+), frequently filled with minute crystals of pyrite. 26 genera and 55 species of acritarchs and prasinophytes were identified, including age-significant forms. Recovered microfossils (acritarchs, cyanobacterial sheats, fragments of various resistant tissues of uncertain origin and abundant prasinophyte phycomata) indicate marine origin as well as the late Early Cambrian age of fine-grained intercalations in so-called basal clastics, corresponding to the Vergale/Rausve regional stages of the East European Platform. Characteristic is the common presence of minute ribbon-like threads, filled with pyrite crystals and entangled in dense clusters. Recovered microfossils reveal close affinities to assemblages of fossil microplankton known from the late Early Cambrian sequences of East European (Latvia, Ukraina) and Baltoscandian platforms (SW Sweden, Bornholm, Baltic depression, Bothnian sea). Coeval fossil populations of marine microplankton have been recently isolated from boreholes Němčičky-6 and Měnín-1. Some aspects of possible secondary provenance of palynomorphs are discussed. One sample of fine-grained mudstones from the Uhřice-1 borehole (depth 3600 m) contained continental assemblage of dispersed miospores and plant tissues of Middle Devonian age. Sagatum gen. nov. is defined together with a new combination of Sagatum priscum (Kirjanov and Volkova) comb. nov.