Trilobites, Biostratigraphy, and Geochemistry of the Middle Cambrian Kuonamka Formation (Northeastern Siberian Platform, Kyulenke River)

—We studied the middle Cambrian unit of the Kuonamka Formation section on the Kyulenke River (Siberian Platform) and performed its biostratigraphic subdivision based on trilobites. The middle Cambrian section has intervals corresponding to the regional zones of the Amginian Stage. Six levels with mass accumulation of fauna remains have been identified: Two levels are located within the Ovatoryctocara Zone; the third level is at the boundary between the Ovatoryctocara and Kounamkites zones; the fourth layer is confined to the roof of the Triplagnostus gibbus Zone; and the fifth and sixth levels are located within the Tomagnostus fissus–Paradoxides sacheri Zone. The composition of rocks and bitumens of their organic matter (OM) has been studied, including the geochemical specifics of the mineral components of rocks (iron, sulfur, and CO2) and of saturated hydrocarbons of bitumens as well as noncarbonate carbon isotopes in the OM. It has been established that the OM sedimentation took place under normal aeration of the sea basin waters, without hydrogen sulfide contamination of the bottom waters. The intensity of chemical and biochemical transformations of mineral and organic components during diagenesis was controlled by the contents of organic carbon and sulfate ion, the activity of the anaerobic prokaryote community, and the rate of sediment mineralization. We have also established relationships between the content of organic carbon in potentially oil source rocks and the contents of iron oxide, total sulfur, and sulfide and sulfate sulfur as well as the ratios of saturated hydrocarbons. The alternation of highly carbonaceous black shales and carbonaceous rocks is apparently due to a change in the composition of biologic communities of microorganisms (sources of hydrocarbon biomarkers) and in the intensity of OM transformation during diagenesis. We assume that the OM transformation included sulfate reduction and dealkylation of high-molecular steroids in the unconsolidated OM-enriched marine sediments with the participation of bacteria. The intensity of these processes depended on the mass of the primary OM, the amount of sulfate ion, and, hence, the pH and Eh of the medium.

Palinostratigraphy and Paleoenvironments in the Gorodishchi Section (Middle Volga River Region, Kimmeridgian–Hauterivian)

—Eight dinocyst-based and three spore- and pollen-based biostratigraphic units are defined in the Kimmeridgian, Volgian, and Hauterivian of the Gorodishchi section, based on a biostratigraphic analysis of the successions of marine and terrestrial palynomorphs. Algological assemblages are described in more detail, and additional criteria for the definition of dinocyst zones established by previous researches are given. A more detailed biostratigraphic subdivision of the middle part of the Volgian is proposed. A local dinocyst zone in the Hauterivian and a biostratigraphic succession of spore–pollen units in the entire section are described for the first time. The research results demonstrate that the boundaries of many palynostratigraphic units exhibit a considerable correlation potential. Based on a biofacies analysis of the microphytoplankton, the dynamics of transgressive–regressive events is studied in relation to the accompanying oxygen and trophic conditions. Possible relationships between marine paleoenvironments and climatic changes reconstructed on the basis of spore–pol­len data are discussed.

CORRELATION OF THE SILURIAN SEQUENCE OF THE 25-KOTYUZHINY STRUCTURAL WELL WITH THE DNIESTER REFERENCE SECTION OF THE SILURIAN IN THE VOLYN-PODILLYA PLATE

The paper is devoted to lithostratigraphic and biostratigraphic subdivision of the Silurian deposits of 358 m total thickness in the 25-Kotyuzhiny structural well and its comparison with the stratotypic Dniester section of the Silurian system in accordance with Legend to the geological map of Ukraine, the Volyn-Podolsky series of 1: 200 000 scale, consistent with the latest modernization of Silurian stratigraphic charts. The described section is a parastratotype for Silurian litho-stratons of the Kovel-Khotyn structural and facies zone and a reference one for Silurian deposits in the central part of this zone. The Silurian in the 25-Kotyuzhiny well is represented by the lower (Llandoverian and Wenlockian stages) and upper (Ludlovian and Przhidolian stages) series. According to the lithological-facies composition and sedimetantaion conditions during Silurian times, there are 3 major completed stages of sedimentation as transgressive-regressive cycles, corresponding to the the Yarugian, Malinovetsian and Rukshinian series, which are quite clearly subdivided into 10 suites and 12 sub-suites. In correlation with the Dniester reference section, litho-stratons of the Silurian are characterized mainly by carbonate and clay-carbonate composition, relative stable thickness and facies pattren, diversity of fauna with a predominance of shallow benthic forms. The well is characterized by bituninous manifestations indicating hydrocarbon potential of the area and its prospectivity for shale gas accumualtions in the formations of the upper Silurian in particular.

STRATIFICATION OF CRETACEOUS DEPOSITS OF THE SECTION ¹ 29 – ZAKHIDNOÎKTYABRSKA (KARKINITSKO-NORTH CRIMEAN TROUGH) BY PALYNOLOGICAL DATA

The Karkinitsko-North Crimean trough is a promising region of Ukraine for the search for hydrocarbons, and one of the main oil and gas complexes is the Cretaceous.Therefore, a detailed biostratigraphic subdivision of the Cretaceous sediments is important and necessary, which are the basis for further prospecting work and for the correlation of North Crimean trough with the similar age deposits of the adjacent regions. The Neocomian strata are especially problematic for subdivision and correlation. According to the results of the study of microphytofossils, the stratification of Cretaceous deposits of the Karkinitsko-North Crimean trough was carried out on the example of the supporting well ¹ 29 – Zakhidnoîktyabrska. There are four spore-pollen complexes: Barremian, Aptian, Albian and Cenomanian. For the first time, the Cretaceous deposits were dissected according to the systematic composition of dinocysts, as well as the paleontological characteristics of sediments by other groups of microfossils – spores and pollen of higher plants, remnants of green algae, acritarchsand miñroforaminifers.

First record of the Early Carboniferous ammonoid genus Goniatites from the Greater Karatau (Kazakhstan palaeocontinent)

The Late Viséan ammonoid genus Goniatites had a near-global distribution within the tropical seas but was rarely reported from Central Asia. New investigations of the Early Carboniferous sedimentary succession in the Greater Karatau of Kazakhstan revealed a species-poor new assemblage with Goniatites and assists in the biostratigraphic subdivision of the section. The new species Goniatites zhankurganensis and G. abaiensis are described; these species have a morphological position at both ends of the morphological spectrum of the genus.

Ammonoids of the Genus Yakutosirenites from the Carnian Stage of Northeast Asia

A revision of ammonoids of the genus Yakutosirenites (Sirenitidae) from the Carnian deposits of Northeast Asia have been carried out. Based on the study of the morphogenesis of the most important structures of the shell, a division of the genus Yakutosirenites into two subgenus is proposed: Yakutosirenites with the type species Sirenites pentastichus Vozin, 1964 and Vozinites with the type species Sirenites armiger Vozin, 1965. A description of the genus and its subgenera and species is given. The significance of the species of these subgenera for the biostratigraphic subdivision and correlation of the Lower/Upper Carnian boundary interval is substantiated. The boreal-thethyan correlation of the Yakutosirenites pentastichus zone have been refined. For the first time, taking into account the data of the revision of the genus Yakutosirenites, the upper part of the pentastichus Zone is compared only to the Arctosirenites canadensis Beds of the Arctic Canada and to the lower Subzone of the Tropites welleri Zone of British Columbia, wich are an equivalent to the lower part of the Tropites subbullatus Zone of the Alpine standard.

Diatoms and their application in stratigraphic and paleogeographic studies

Modern data on diatom algae – unicellular microorganisms with siliceous frustule composing Class Bacillariophyceae, are reviewed. Brief characteristic of biology, morphology, frustule structure and its elements, principles of diatom systematics, and also biogeography and ecology are given. A role of diatoms in sedimentation and peculiarities of preservation of their remains in bottom sediments are discussed. Special attention is paid to issues of effective application of data on fossil diatoms for detailed biostratigraphic subdivision, dating and correlation of sedimentary successions (first of all, marine deposits) as well as for paleoenvironmental reconstructions. General characteristic of diatom zonations proposed for marine Cretaceous and Cenozoic sediments is given. Main features of diatom evolution are discussed.

Ediacaran Acanthomorphic Acritarchs and Other Microfossils from Chert Nodules of the Upper Doushantuo Formation in the Yangtze Gorges Area, South China

Silicified microfossils preserved in chert nodules of the Doushantuo Formation in the Yangtze Gorges area of South China have great potential to improve the biostratigraphic subdivision and correlation of the Ediacaran System. This potential can be realized only if solid taxonomy is available. However, a systematic treatment of these microfossils (particularly acanthomorphic acritarchs) is lacking, greatly limiting their biostratigraphic potential. This paper presents the systematic paleontology of silicified microfossils from upper Doushantuo Formation (Member III) chert nodules at three sections in the Yangtze Gorges area. More than 90 species of microfossils are described, including 66 named taxa of acanthomorphs, seven named taxa of sphaeromorphs, 12 taxa of cyanobacterial filaments and coccoids, four taxa of algal thalli, and two species of tubular microfossils. Several acritarch species, includingAppendisphaera clavan. sp.,Mengeosphaera grandispinan. sp.,M. stegosauriformisn. sp.,Leiosphaeridia, and possiblySinosphaera rupina, are shown to be multicellular organisms, consistent with the proposition that some Ediacaran acritarchs may be diapause eggs of early animals. This study supports the view that theTianzhushania spinosaacanthomorph biozone is unique to the lower Doushantuo Formation in South China (and perhaps its equivalent in northern India) and that Ediacaran acanthomorph assemblages from Australia, Siberia, and East European Platform are younger than theTianzhushania spinosabiozone. It is proposed that the first occurrence ofHocosphaeridium anozos, a species with easily recognizable morphology and wide taphonomic and geographic distributions, be used to define the second Doushantuo acanthomorph biozone succeeding theTianzhushania spinosabiozone. New taxa described in this paper include three new genera (Bispinosphaeran. gen.;Yushengian. gen.; andGranitunican. gen.) and 40 new species:Appendisphaera?brevispinan. sp.,A. clavan. sp.,A.?hemisphaerican. sp.,A. longispinan. sp.,A. setosan. sp.,Bispinosphaera peregrinan. gen. n. sp.,Crinita paucispinosan. sp.,Ericiasphaera densispinan. sp.,Hocosphaeridium dilatatumn. sp.,Knollisphaeridium denticulatumn. sp.,K. longilatumn. sp.,K. obtusumn. sp.,K. parvumn. sp.,Mengeosphaera angustan. sp.,M. bellulan. sp.,M.cf.bellulan. sp.,M. constrictan. sp.,M.?cuspidatan. sp.,M.?gracilisn. sp.,M. grandispinan. sp.,M. latibasisn. sp.,M. miniman. sp.,M. spicatan. sp.,M. spinulan. sp.,M. stegosauriformisn. sp.,M. triangularisn. sp.,M. uniformisn. sp.,Sinosphaera asteriformisn. sp.,Tanarium acusn. sp.,T. elegansn. sp.,T. longitubularen. sp.,T.?minimumn. sp.,T. obesumn. sp.,T. variumn. sp.,Urasphaera fungiformisn. sp.,U. nuptan. sp.,Yushengia ramispinan. gen. n. sp.,Granitunica mcfaddeniaen. gen. n. sp.,Osculosphaera arcelliformisn. sp., andO. membraniferan. sp.