Olga K. Bogolepova

Early Palaeozoic unconformity across the Timanides, NW Russia.

Abstract The Lower Palaeozoic sequences, unconformably overlying the Timanides of Timan, Pechora, Pai-Khoi, Vaigach, Novaya Zemlya and the Polar, Northern, Middle and Southern Urals are described and interpreted with regard to their stratigraphy, sedimentation, structure and biogeography. These mainly shallow marine sedimentary successions, with associated igneous rocks (largely alkaline), are Ordovician in age, reaching back into the Late Cambrian in some areas, particularly in the east, along the front of the Urals. They were deposited during rifting of Baltica’s northeastern margin and subsequent development of a passive continental margin. The underlying, mainly Neoproterozoic basement of turbidites in the west and calc-alkaline volcanites and ophiolites further east are briefly referred to, with particular emphasis on the age of the youngest rocks. Based on these data, a Timanian orogenic belt can be traced along the northeastern and eastern margin of the East European Craton. The timing of orogeny can be constrained to the Vendian, perhaps extending into the Early Cambrian.

New data on the Silurian of Severnaya Zemlya, Russian Arctic

Abstract Recent stratigraphic investigations on October Revolution Island (Severnaya Zemlya) have revealed the presence of Silurian terrigenous-carbonate deposits with rich faunas of graptolites, cephalopods, ostracodes, brachiopods, gastropods, and bivalves. The graptolites indicate a mid Telychian (late crispus-griestoniensis Zone) age for the strata bearing them.

Bohemian-type Silurian (Telychian) bivalves from Arctic Russia

Abstract The Bivalvia genera Ctenodonta, Dualina? and Sibirinka have been identified from the Silurian Telychian Stage, Llandovery Series of Severnaya Zemlya, Arctic Russia. This is the second record of the earliest epibyssate pteriomorphs previously reported from Siberia; they flourished later in the basins of central and southern Europe. Their distribution is consistent with surface ocean currents carrying abundant cephalopods, whose accumulation on the bottom surface together with ocean current activity represented a favourable environment for epibyssate bivalves.

Silurian Cephalopod Limestone Biofacies From Eastern Siberia

The cephalopod facies in the East-Siberian Basin was deposited during the interval represented by the Parakidograptus acuminatus - Coronograptus cyphus graptolite Biozones of early Silurian (Rhuddanian) age. They consist either of black bituminous limestones with numerous cephalopods or lenses of cephalopod limestones in black graptolitic shales. Mass accumulations of cephalopods occur along narrow belts in the depositional basin. Our model suggests that these deposits developed on the outer margins of marine shelves during episodes of upwelling, when the circulation of oceanic gyres was weak.

Two bryozoan assemblages from the Ordovician of the Russian Arctic

Abstract Two assemblages from the Ordovician rocks of the Arctic region contain exclusively trepostome bryozoans. The first assemblage from the Yunoyaga Formation (Middle Ordovician) of Maly Oleniy Island, Novaya Zemlya, contains Monticulipora mammulata d’Orbigny, 1850 and Nicholsonella vaupeliformis Modzalevskaya, 1955. Both species possess thick-branched ramose colonies characteristic for rather high energy environments. The second assemblage comes from two localities of the Stroinaya Formation (Upper Ordovician) of the October Revolution Island containing the single species Amplexopora angusta Astrova, 1965. The monospecific bryozoan fauna of branched, rarely encrusting growth forms and sedimentological characteristics of embedding rocks (floatstone) suggest low energy conditions in deeper environments, apparently accompanied by high salinity conditions.