Alexander P. Gubanov

Two Palaeozoic Hydrothermal Vent Communities from the Southern Ural Mountains, Russia

The Sibay and Yaman Kasy massive sulphide deposits contain macrofossil assemblages that represent some of the oldest known hydrothermal vent communities. The deposits are hosted respectively by Middle Devonian and Silurian arc-related volcanic rocks in the Ural Mountains of Russia, and formed under the same environmental constraints as modern vent sulphides. The Sibay palaeocommunity comprises, in order of decreasing abundance, tubes of an indeterminate ?annelid and the vestimentiferan Tevidestus serrriformis Shpanskaya, Maslennikov and Little and articulated specimens of the modiomorphid bivalve Sibaya ivanovi gen. et sp. nov. The Yaman Kasy palaeocommunity comprises, in order of decreasing abundance, tubes of the ?polychaete Eoalvinellodes annulatus gen. et sp. nov. and the vestimentiferan Yamankasia rifeia Shpanskaya, Maslennikov and Little, and specimens of the ?kirengellid tergomyan Themoconus shadlunae gen. et sp. nov., the lingulate brachiopod Pyrodiscus lorrainae gen. et sp. nov., an indeterminate vetigastropod, and the ambonychiid bivalve Mytilarca sp. Some of these taxa have affinities to endemic taxa at modern hydrothermal vent sites and some belong to taxa that are typical of Palaeozoic non-vent marine palaeocommunities. Therefore, there has been movement of taxonomic groups in and out of the vent ecosystem through the Phanerozoic.

Age constraints from small shelly fossils on the early Cambrian terminal Cadomian Phase in Iberia

Abstract The records of biotic and biogeochemical events around the Proterozoic-Cambrian transition are well preserved in sedimentary rock successions in Iberia. Until recently, sparsely fossiliferous siliciclastic and carbonate successions in central Spain were believed to be largely Proterozoic in age and to have suffered late Cadomian deformation. Small shelly fossils identified as Anabarella sp. cf. A. plana are here reported from south-central Spain and are consistent with broadly Ne-makit-Daldynian to Tommotian, early Cambrian age. At a location in southwestern Spain, siliciclastics that yield Platysolenites antiquissimus in association with an unidentified trilobite are interpreted to be coeval with the upper stratigraphic record of P. antiquissimus in Baltica. Both fossil occurrences are nearly time-equivalent to Tommotian-age rocks in North Iberia that yield ichnofossils and acritarchs. These beds unconformably overlie Neoproterozoic turbidites deformed by late Cadomian folding. Small shelly foss...

Early Cambrian palaeogeography and the probable Iberia–Siberia connection

Abstract The end of the Proterozoic–beginning of the Cambrian is marked by some of the most dramatic events in the history of Earth. The fall of the Ediacaran biota, followed by the Cambrian Explosion of skeletonised bilaterians, a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from ‘snowball earth’ to ‘greenhouse’ conditions all happened within a rather geologically short period of time. These events took place against a background of the rearrangement of the prevailing supercontinent; some authors view this as a sequence of individual supercontinents such as Mesoproterozoic Midgardia, Neoproterozoic Rodinia and Early Cambrian Pannotia. Assembled in the Mesoproterozoic, this supercontinent appears to have existed through the Neoproterozoic into the Early Cambrian with periodic changes in configuration. The final rearrangement took place during the Precambrian–Cambrian transition with the Cadomian and related phases of the Pan-African orogeny. The distribution of Early Cambrian molluscs and other small shelly fossils (SSF) across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time. Subsequently, Rodinia experienced breakup that led to the amalgamation of Gondwana, separation of Laurentia, Baltica, Siberia and some small terranes and the emergence of oceanic basins between them. Spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the Vendian–Early Cambrian.

A middle Cambrian fauna of skeletal fossils from the Kuonamka Formation, northern Siberia

An assemblage of mineralized skeletal fossils containing molluscs, hyoliths, chancelloriids, protoconodonts, lobopods, paleoscolecids, bradoriids, echinoderms and hexactinellid sponges is described from the middle Cambrian part of the Kuonamka Formation, exposed along the Malaya Kuonamka and Bolshaya Kuonamka rivers, northern Siberian Platform. The sampled succession is attributed to the Kuonamkites and lower Tomagnostus fissus–Paradoxides sacheri biozones of the Amgan Stage of Siberia, correlated with Series 3, Stage 5—lower Drumian Stage of the IUGS chronostratigraphical scheme for the Cambrian. This work complements descriptions of molluscs from the same samples published by Gubanov et al. (2004) with additional material. It contains forms in common with coeval faunas from Australia, China, Western Gondwana, Avalonia, Laurentia and Baltica, increasing potential for global biostratigraphic correlation and understanding of palaeogeographic connections.

New data on Ordovician–Silurian conodonts and stratigraphy from the Severnaya Zemlya Archipelago, Russian Arctic

Thirty samples from 22 sections collected by the SWEDARCTIC international expedition to Severnaya Zemlya in 1999 contained Ordovician and Silurian conodont faunas. Several taxa, including Apsidognathus cf. milleri , Aulacognathus cf. kuehni , Nudibelodina sensitiva , Ozarkodina broenlundi and Pterospathodus eopennatus , allow precise dating of the strata in this region for the first time. The occurrence of Aphelognathus pyramidalis and Rhipidognathus aff. R. symmetricus in samples from the Strojnaya Formation fits well with the earlier dating of these strata as latest Ordovician. However, Aphelognathus sp. in sample BG-99/14-a, collected from the upper Ushakov Formation, indicates that at least in the lower reaches of the Ushakov River the top of this formation is considerably younger than considered earlier: the sampled strata are Late, not Early Ordovician in age. In the Ordovician and Silurian the present-day Severnaya Zemlya region was dominated by extensive shallow-water, mainly semi-restricted basin environments with habitat specific faunas. The occurrence of Riphidognathus aff. R. symmetricus at some levels in the Upper Ordovician suggests extreme shallowing episodes in the basin. On Severnaya Zemlya, ‘normal-marine’ faunas (including Pt. eopennatus ) invaded the distal peripheral regions of the wide shallow-water platform at times of maximum sea-level rise only. The occurrence of Oz. broenlundi and N. sensitiva indicates that in the early Silurian the Severnaya Zemlya basin was quite well connected to the basins over modern North Greenland as well as to the Baltic Palaeobasin. The lower Silurian conodont assemblages in the Vodopad to Samojlovich formations are most similar to those described from the eastern Timan–northern Ural region.

Oelandiella, the earliest Cambrian helcionelloid mollusc from Siberia

The helcionelloid molluscs Oelandiella korobkovi and O. sibirica Vostokova are redescribed on the basis of type material from the lowest Cambrian of northern Siberia. Oelandiella is reinstated as a recognizable genus separated from Latouchella Cobbold, of

The Early Cambrian helcionelloid mollusc Anabarella Vostokova.

One of the oldest known helcionelloid molluscs, Anabarella Vostokova, is redescribed on the basis of type material from the lower Cambrian of north Siberia. Published records of the type species, Anabarella plana Vostokova, show a very wide range in morphology, but studies of variation through ontogeny and in taphonomy confirm assignment to a single variable species. Other described species are reviewed.

Latest Helcionelloid Molluscs from the Lower Ordovician of Kazakhstan

The helcionelloid mollusc Chuiliella elenae gen. et sp. nov. is described from the Lower Ordovician of Kazakhstan. It represents the geologically youngest record of a group of mainly bilaterally symmetrical ancient molluscs which originated in the earlies

The Ordovician of the Severnaya Zemlya Archipelago, Russia.

The Ordovician strata belonging to the North Kara Basin are well exposed in the Severnaya Zemlya Archipelago. They are dominated by shallow marine sedimentation. Based on faunal evidence, the North Kara Terrane was located at tropical latitudes. Macro- and microfossil assemblages from Severnaya Zemlya contain elements typical of both Siberian and Baltic biotic provinces. An increasing number of taxa common to Laurentia is consistent with the closure of the Iapetus and the convergence between Baltica, Siberia, Laurentia and the North Kara Terrane positioned between them. Short descriptions of the main lithological, faunal features and ages of each stratigraphic unit are given.

Middle Cambrian molluscs of ‘Australian’ aspect from northern Siberia

An assemblage of silicified helcionelloid molluscs is described from the Kuonamka Formation (Middle Cambrian Amgan Stage) of the Bolshaya Kuonamka and Malaya Kuonamka rivers, northern Anabar Shield, northern Siberia. In addition to the new genera Kuonamkaella and Anabaroconus, the assemblage contains species of Yochelcionella, Eotebenna, Pseudomyona, and Protowenella. These latter genera were previously unknown from the Middle Cambrian of Siberia and indicate a strong affinity with coeval molluscan faunas from the Australian Middle Cambrian. The fauna provides evidence for close palaeogeographic links to East and West Gondwana, Baltica, and Laurentia during the Middle Cambrian, and facilitates biostratigraphic correlation between these crustal blocks.