No 6 (2019)

Cretaceous-Paleogene (K/T) boundary in the North-Eastern Caucasus (Dagestan): sedimentology, geochemistry and biota
Gavrilov Y.О., Shcherbinina E.A., Shchepetova Е.V., Golovanova O.V., Pokrovsky B.G.

The Cretaceous/Paleogene (K/T) boundary interval was studied in the Okhli and Gubden sections, northeastern Caucasus. Two sediment successions represented in these sections were accumulated in different zones of the paleobasin and distinguished by their lithological and geochemical characteristics. The high-resolution study of nannofossils revealed very gradual changes in nannoplankton community at the Cretaceous/Paleogene transition. The nannofossil assemblage becomes poor from the level ca. 4 m below K/T boundary and it is very scarce in the last 2.5 m of uppermost Maastrichtian. The significant sea-level fall is evidenced in the beginning of the K/T event. It led to erosion and redeposition of Maastrichtian calcareous sediments within the thin layer of clay, covering erosional surface in the Okhli section. The clay mineral assemblage, starting from this surface contains palygorskite. The concentrations of coprolites (Decapoda?) and microspherulas (diagenetic microconcretions) with higher content of some trace elements were found within the small red lenses at the base of the clay layer overlying the Maastrichtian erosional surface. The reliable evidence of impact event are not recognized. The evolutional trends which are recorded within the Cretaceous/Paleogene transitional interval in the Okhli and Gubden sections are similar to trends recognized in studied sections of the K/T event on the adjacent territories of the North-Eastern Peri-Tethys (e.g., southern Turkmenistan and Mangyshlak Peninsula).

Литология и полезные ископаемые. 2019;(6):497-517
Mineralogical and geochemical features of pyrite nodules of sulfide turbidites from the Talgan Cu–Zn massive sulfide deposit (South Urals)
Ayupova N.R., Maslennikov V.V., Artemyev D.A., Blinov I.A.

Pyrite nodules were found in thin-layered sulfide ores localized at the flanks of the Talgan Cu‒Zn massive sulfide deposit (South Urals). The nodules consist of (1) an inner core of microgranular pyrite with inclusions of authigenic sulfides and host rock minerals, (2) an intermediate zone of anhedral and subhedral pyrite metacrystals, (3) an outer zone formed by parallel subhedral pyrite crystals and (4) dioctahedral chlorite rimming the pyrite crystals of zone 3. Each zone exhibits specific trace element association, which is identified using LA ICP-MS micromapping. The trace element content of pyrite significantly (by 1–3 orders of magnitude) decreases in a range of microgranular pyrite of the core → an- and subhedral pyrite crystals of the intermediate zone → subhedral pyrite crystals of the outer zone (average values, ppm): 13106–9 Zn, 24100–1783 Pb, 1323–134 As, 1027–1.81 Co, 456–4 Ni, 390–38 Ag, 0.1–0.01 Au, 55–0.6 Te, 9.8–0.6 Bi. The subhedral pyrite crystals of the outer zone are enriched (ppm, up to) in Cu (8367), Sb (1627) and Mn (734) relative to microgranular pyrite of the core. The extremely high trace element contents are related to the inclusions of authigenic chalcopyrite, sphalerite, fahlore, gold and silver minerals. The host rock components of the nodules include quartz, calcite, chlorite, illite and REE minerals. The ore clasts of distal sulfide turbidites mixed with hyaloclastites, which were altered during dia- and anadiagenesis, were the source of ore material for the nodules.

Литология и полезные ископаемые. 2019;(6):518-539
Structural-lithological geological-genetic model and mineral composition of Krasnokutskaya rare-metal-titanium placer deposits (Ukraine)
Ganja E.A., Lalomov A.V., Chefranova A.V., Grigor’eva A.V., Magazina L.O.

The conditions of the occurrence, structure, material composition and controlling factors of Krasnokutsky rare-metal-titanium placer deposit localized in the Miocene sediments of the North-Eastern slope of the Dnieper-Donets basin are investigated. Distinguished lithofacies complexes (alluvial-deltaic, coastal and shallow marine, aeolian) correspond to the Lower (Aquitanian), Middle (Burdigalian) and Upper (Langhian) members of Novopetrovskaya Formation of Miocene. Placer bodies are localized in the littoral marine-coastal complexes of Middle Novopetrovskaya sub-formation. Placer–forming process is related to phases of stabilization of the shoreline of the regressive phase of the Sub-Paratetic basin. Main search and forecasting criteria for the identification of promising sites within the Kharkiv-Sumy placer-bearing zone are stabilization of the shoreline in the Middle Novopetrovskaya time simultaneously with development of transverse thereto alluvial-deltaic structures that supply weak mineralized sediments. Also, the deltaic ledge breaking the monotony coastal migration and playing the role of structural-sedimentary traps. The developed digital structural-lithological model of the Krasnokutskoye mineral deposit allows us to offer a set of criteria for comparative evaluation of different placer-bearing areas in order to determine the order of their development. The mineral composition of productive deposits is typical for the placers of the region and for rare-metal-titanium placers as a whole; the increased content of rutile and zircon, which rise the industrial value of placers of this zone, are associated with the influence of crystalline rocks of the Voronezh massif.

Литология и полезные ископаемые. 2019;(6):540-556
Мicrobiota of bauxites in the Eva deposit (Guinea-Bissau)
Georgievskiy A.F., Zhegallo E.A., Bugina V.M.

The important role of the biogenic factor in sedimentary ore genesis now, after more than a hundred years after the publication of V. I. Vernadsky’s and Ya. V. Samoylov’s papers, has become an indisputable fact for everyone. Discussions mainly take place as to how productive the activity of organisms was in the formation of specific exploitable minerals. In 2004, a joint monograph of Russian geologists “Biomorphic Structures in Bauxite” was published. Using the examples of dozens of deposits of a huge stratigraphic range from the Late Proterozoic age to the Quaternary period and wide geographic range (Africa, Eurasia, Australia and America), active participation of various microbial communities in the bauxite formation was shown in the monograph. This article demonstrates new results of electron microscopic study of ores from Eva bauxite deposit, which is little known in Russia, and continues researching this topic, which was initiated by E. L. Shkolnik.

Литология и полезные ископаемые. 2019;(6):557-567
Isotope features (δ13С, δ18О) of continental carbonates from Permian and Triassic boundary deposits Northeast of Russian plate: paleoclimatic and biotic causes, chemostratigraphy
Kuleshov V.N., Arefiev M.P., Pokrovsky B.G.

The carbon and oxygen isotopic composition were determined in pedogenic, sedimentary and organogenic carbonates of continental deposits of the Upper Permian (Vyatkian stage) and lower Triassic (Induan stage) of the northeastern part of the Moscow Syneclise. It is assumed that variations in δ18О (18.0 …29.1‰ SMOW) and δ13С (-8.8 …0.7‰ PDB) values in them could be associated with both regional climate fluctuations and perturbation of the global carbon cycle at the Permian and Triassic boundary. The decrease in δ18О values in the pedogenic carbonates of the roof sequence of the Vyatkian stage, apparently, was due to the cooling in the northeast of the Pangea supercontinent. The negative excursion of δ13С values at this stratigraphic level is correlated with a similar excursion found in the Paleo-and Neotetis marine carbonates and corresponds to the Late Permian biotic event.

Литология и полезные ископаемые. 2019;(6):568-591
The influence of fluids on the species composition and preservation of microfossils in biogenic carbonate sediments by hydrothermal cluster “Pobeda” (Mid-Atlantic ridge)
Gablina I.F., Dmitrenko O.B., Khusid T.A., Libina N.V.

The species composition, distribution and preservation of carbonate shells of nanno — and microfossils of biogenic bottom sediments within the hydrothermal cluster “Pobeda” (17°07.45´–17°08.7´ n) were studied on the basis of materials obtained in flight No. 37 of NIS “Professor Logachev” in the Russian exploration area (Mid-Atlantic ridge). Physical-chemical parameters and the total carbonate content of sediments were measured, their changes in column sections were revealed. For complexes of coccoliths studied precipitation is attributed to the top (acme) biostratigraphic zone of Emiliania huxleyi. It is established that within the zone of hydrothermal activity (ore cluster “Pobeda”) the total number of microorganisms decreases and their species diversity decreases, as a rule, in the lower part of the columns. Down the column section also decreases the Eh, pH and carbonate precipitation. These changes are explained by the influence of diffuse hydrothermal fluids.

Литология и полезные ископаемые. 2019;(6):592-606

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