No 2 (2019)

Terrigenous sedimentation on the submarine Shirshov Ridge (Bering Sea) during the last deglaciation
Murdmaa I.O., Dorokhova E.V., Ovsepyan E.A., Dara O.M., Nürnberg D.

The submarine Shirshov Ridge is an independent system of terrigenous sedimentation, which is geomorphologically isolated from bottom terrigenous influx into the deep-water basin of the Bering Sea. Using the ridge as example, we studied background hemipelagic sedimentation of the finely dispersed terrigenous suspended material from water column and deposition of the coarser grained ice-rafted material in the western part of the deep-water basin. The grain-size and mineral composition of postglacial sediments of the Shirshov Ridge was studied in cores SO201-2-85KL and SO201-2-77KL taken from local basins in the central and southern parts of the ridge, respectively. Statistic treatment of uninterrupted grain-size distributions (GD) of terrigenous component of the postglacial sediments by end-member (EM) modelling revealed that the grain-size distributions of terrigenous sediments from two cores are determined by the mixing of three EMs. EM-1 and EM-2 reflect the hemipelagic sedimentation with and without bottom currents influence respectively, while EM-3 with mode at fine-grained sand characterizes GD of the ice-rafted material. Reconstructed mechanisms of terrigenous influx on the Shirshov Ridge involve advection of the suspended matter with surface and intermediate water masses and ice-rafting. The relative role of both mechanisms of the terrigenous sedimentation under the influence of varying bottom current velocities for intervals of Last Glacial Maximum, early deglaciation, Heinrich event 1, Bølling–Allerød, Younger Dryas, and Early Holocene is estimated. It is ascertained that the grain-size distribution of terrigenous component is defined by climate variations, sea ice coverage, sea ice drift pathways, conditions of fast ice melting, and mobility of bottom waters. High concentrations of drifting ice or seasonal sea ice cover likely existed above the southern part of the ridge during the second half of the Heinrich 1 event. The low mobility of bottom waters facilitated only the subice hemipelagic sedimentation of fine fractions from the background reserve of suspended material. A sharp reduction of ice-rafted flux was reconstructed for the Bølling–Allerød warming interval. Bottom currents affected sedimentation in the central part of the ridge during the entire deglaciation (in addition to the second half of the Heinrich 1 event), and in the southern part during the Bølling–Allerød, Younger Dryas, and Early Holocene.

Литология и полезные ископаемые. 2019;(2):102-118
Geological and biological reasons for the collapse of reef formation, Paleozoic
Kuznetsov V.G., Zhuravleva L.M.

Paleozoic reef formation developed cyclically, and its global termination has been caused by the biological reasons — biotic crises and mass extinctions near the borders early and middle Cambrian, Ordovician and Silurian, Frasnian and Famennian, Serpukhovian and Bashkirian, Permian and Triassic. The Early Cambrian reef formation has ended along with disappearance of archaeocyathid. In the later stages reefs were much more difficult ecosystems, and they stopped developing before the full extinction of the reef-building communities. The interruption of reef formations within the separate stages have been connected with the geological and paleogeographic reasons – volcanism, regression, climate aridization etc.

Литология и полезные ископаемые. 2019;(2):119-129
Thermobaric depth settings of sedimentary rock basins and their fluid dynamics: Communication 3. Superhigh pressures in the stratisphere and salt diapirs
Kholodov V.N.

The article discusses the patterns of location and the conditions for the formation of salt diapirs. Their formation is associated with thick salt cjmpleses in which phase transformations within closed physicochemical systems form ultrahigh pressures. The latter are the cause of the flow of salts and their penetration through tectonic cracks and fractures to the earth's surface. The similarity of the formation of salt diapirs and mud volcanoes is emphasized. The possibility of the influence of ultrahigh pressures on the autonomous folding of the sedimentary cover is assumed.

Литология и полезные ископаемые. 2019;(2):130-148
Мetasomatic rocks after shungite-bearing rocks of the Maksovo Deposit, Onega Structure, Karelia
Kuleshevich L.V., Filippov М.М., Goltsin N.А., Krymsky R.S., Lokhov K.I.

The Maksovo metasapropelite deposit, which contains shungite matter and is called maksovite, is located in the eastern Onega structure. The deposit is a diapiric fold which formed ca. 2070±10 Ma ago. It is underlain by carbonate rocks and overlain by tuff siltstones and is cross-cut by 1956±5 Ma gabbro-dolerites. Unaltered maksovites are pelitomorphic rocks with a massive to mildly layered texture and moderate concentrations of all petrogenic components and Сorg of about 30%. Fe-Mg rich and alkaline metasomatic rocks evolve after maksovites and mafic and carbonate tuff siltstones in the northwestern part of the deposit within a multiple ridge-like fold after brecciation zones. They differ from unaltered sedimentary rocks in heterogeneous (brecciated, streaky) textures, mineral and chemical composition and are saturated with numerous sulphide, carbonate, quartz and albite veinlets. They are identified by intense biotitization, chloritization and the presence of calcite, microcline metacrystals, albite-carbonate metacrystals with apatite and carbonate-quartz metacrystals with sulphides and rutile, veinlets and disseminated mineralization. Na concentration rises to 5.67% and K concentration to 7.57%. P and Ti concentrations, accompanying alkaline metasomatism, as well as Mg-Fe and ore-bearing components (often incompatible), increase locally. Metasomatic rocks evolve heterogeneously and are represented by breccia zones. Their slightly elevated radioactivity disturbs the qualitative characteristics of primary maksovite as a useful mineral. Maksovites were dated at 1558±61 Ma by the Re-Os method from sulphides.

Литология и полезные ископаемые. 2019;(2):149-164
The Nadeiyakha Ore occurrence (Pai-Khoi, Russia): an example of ferromanganese metasediments in carbonaceous dolomitic shales
Brusnitsyn A.I., Starikova E.V., Ignatova M.V., Kuleshov V.N.

The paper presents the results of study of metalliferous (ferromanganese and manganese) rocks at the Nadeiyakha ore occurrence (Pai-Khoi) discovered in 2010. The metalliferous deposit represents a stratiform body lying conformably in the Upper Devonian carbonaceous siliceous and clayey–carbonate–siliceous shales. The ore bed occurs 180 m below the regional Famennian manganiferous rock association in Pai-Khoi. Discovery of the Nadeiyakha ore occurrence suggests the existence of an additional age interval of Mn accumulation within the Devonian sequence of this region. The studied metalliferous rocks display structures and textures typical of the metasedimentary rocks. In terms of composition, they are divided into two varieties: (i) ferromanganese (quartz–carbonate) rocks composed of quartz, dolomite, kutnahorite, rhodochrosite, siderite, and calcite; (ii) manganiferous (quartz–rhodochrosite–silicate) rocks composed of quartz, rhodochrosite, tephroite, sonolite, and pyroxmangite. The Nadeiyakha ore occurrence is marked by the abundance of dolomite in the ferromanganese rocks and host shales. In terms of the relationship of indicator elements (Al, Ti, Fe, and Mn), ferromanganese and manganese rocks are comparable with the recent metalliferous and ore-bearing sediments. The carbon isotope composition in carbonates (δ13C from –16.4 to –7.8‰ PDB) corresponds to authigenic carbonates related to the involvement of carbon dioxide produced during the microbial decomposition of organic matter at the stage of dia- and/or catagenesis. Geological and petrographic observations show that the ferruginous and manganiferous sediments were deposited synchronously with the terrigenous–carbonate–siliceous sediments. Fe and Mn could be sourced from hydrothermal solutions or interstitial diagenetic waters. The latter version seems to be more probable. Metals were accumulated in a depression-trap characterized by a periodic stagnation of bottom waters. Such sedimentation setting promoted the formation of paragenetic association of ferruginous and manganiferous sediments with the carbonaceous sediments and fostered reductive conditions during the postsedimentary mineral formation. Calcium carbonates contained in the primary rocks were subjected to dolomitization during the dia- or catagenesis. This process was promoted by the mobilization of Mg released during the transformation of clay minerals owing to the montmorillonite–illite transition. Iron and manganese carbonates were formed during the later replacement of oxides of Mn3+, Mn4+, and Fe3+. Crystallization of manganese silicates also started at early stages of lithogenesis and terminated during the regional metamorphism of metalliferous rocks.

Литология и полезные ископаемые. 2019;(2):165-192
Ural lithological biennale-2018
Maslov A.V., Badida L.V., Alekseev V.P., Tuchkova M.I.

The 12th Ural lithological meeting “Sedimentary geology of the Urals and surrounding regions: today and tomorrow” and the 3rd All-Russian School of students, graduate students, young scientists and specialists on lithology “Lithology and me: from idea to conclusions” took place in Yekaterinburg, in the oldest in the region Ural State Mining University (USMU), united by the common name “Ural lithological Biennale-2018” in October 22–26, 2018. The events were organized by the Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences and the USMU. Financial support for the Organizing Committees of the lithological meeting and the School was provided by the RFBR.

Литология и полезные ископаемые. 2019;(2):193-196

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