Home – Home – Jornals – Russian Geology and Geophysics 2024 number 4

The Myauchan ore field located in the Omsukchan zone of the Okhotsk-Chukotka Volcanic Belt is described. The Korennoe and Malyutka Ag-Pb-Zn ore occurrences forming this field are localized at the center of anticlinal fold of NW strike made up of Upper Triassic carbonate-terrigenous deposits intruded by stock-like bodies and dikes of Upper Cretaceous andesite, monzodiorite, granite-porphyry, and rhyolite-porphyry. Sulfide-carbonate-fluorite-quartz veins and vein-veinlet zones with arsenopyrite, pyrite, sphalerite, galena, chalcopyrite, and Ag-tetrahedrite are localized both in intrusions and in terrigenous strata. The field bears As-Sb-Ag-Pb-Au-Bi-Cu-Zn-W mineralization. Study of fluid inclusions and REE and ore element patterns show that the field ores formed from chloride solutions with the participation of surface waters in hydrothermal-magmatic system under epithermal conditions. The ores were deposited from solutions with TDS = 0.5-9.0 wt.% NaCl equiv. in the temperature range 106-287 ºC. The ores containing ca. 70 ppm Ag and up to 1.2% Pb formed through boiling-off of solutions enriched in iron salts. The ores with Ag < 7 ppm and Pb ≤ 25 ppm were generated from diluted hydrothermal solutions with predominant sodium salts and potassium admixture. Mineralization of the Myauchan ore field marks the upper level of the Ag-Pb-Zn ore system similar to the Gol’tsovoe deposit.

We studied geochemical compositions of the early Paleocene basaltic and andesite dikes associated to linear zones of the Lankovo-Omolon shearing system (Northern Okhotsk region) and basalts of the Evdyreveem volcanic field associated to the Okhotsk-Penzhinsk fault system, and compared them to other synchronous manifestations of basic volcanism: andesibasalts and andesites of the studied earlier Garmanda field, as well as with the Late Cretaceous basalts of the Mygdykit Formation of the Northern Okhotsk region, roofing the Okhotsk-Chukotka volcanic belt. The isotopic composition of Sr and Nd in dikes, the distribution of major and trace elements with the ratios of noncoherent elements indicate the formation of volcanic bodies in the environment of continental margin rifting, which is confirmed by the combination of depleted, intraplate and above subduction geochemical features of their composition. Such behavior of the elements indicates multi-stage processes of the earlier Mesozoic supra-subduction fluid metasomatosis. Melting of an ancient buried Cretaceous slab may explain the appearance of such “above subduction” marks as the Nb-Ta negative anomalies in the studied basaltoids. Andesite dikes are characterized by higher isotope ratios of Nd and lower Sr, with lower absolute concentrations of trace elements and more pronounced anomalies on spider plots.

We report results of a systematic paleomagnetic study of the Abinskaya Group of the Kuznetsk depression, including a typical volcanic complex that reflects important features of the evolution of the Permian-Triassic Siberian large igneous province (LIP). Four zones of magnetic polarity have been established in the group’s deposits. We revise the correlation of the volcanic sheets of the Mal’tsevo Formation (Fm.) at the base of the group with the Ivakinsky Fm. of the Norilsk region, which is linked to the initiation of trap magmatism. The beginning of the eruption of the Saltymak complex volcanic rocks in the Kuznetsk area corresponds to the boundary between subchrons LT1n.1n and LT1n.1r (251.2 Ma) within the Kedrovka sub-formation of the Mal’tsevo Fm. This boundary was traced in the magnetostratigraphic sections of the Maimecha-Kotui, Koltogor-Urengoy, Western Taimyr, and Norilsk regions of the Siberian LIP and suggests a correlation of the Mal’tsevo Fm. volcanic rocks with the upper part of the undifferentiated interval of the Onkuchak - Tyvankit (?) Fms., the base of the Korotchaev Fm., the Verkhnetam Fm. and the top of the Samoed Fm. The duration of this main pulse of volcanism in the Kuznetsk depression did not exceed 0.1 Myr. The volcanic sheets of the second, significantly weaker pulse of the Yamin Fm. are compared with the Maimecha Fm. of the Maimecha-Kotui area and the top of the Korotchaev Fm. of the Koltogor-Urengoy area. Thus, the accumulation of the entire Abinskaya Group, including the sedimentary complex of the Sosnovka Fm., lasted no more than 1.5 Myr. Except for the initial stage, this coincided with the eruption of most of the Maimecha-Kotui and Koltogor-Urengoy trap sections. The early magmatism of the Ivakinsky time and its analogs in other areas of the Siberian province during the Permian-Triassic boundary in the Kuznetsk depression probably corresponds to the break between the Tailugan Fm. and the Abinskaya Group. The mean paleomagnetic pole (PLat = 59.0°, PLon = 160.3°, A95 = 5.7°, N = 33) calculated for the entire studied section reflects the paleogeography of the Kuznetsk depression and can be considered a reference pole for the Permian-Triassic boundary.

The purpose of this paper is to present the results of sequence stratigraphic modeling of subcontinental reservoirs of the Tanopcha Formation upper part (Lower Cretaceous) of the Minkhov field, located in the northern part of the Messov oil and gas region of the Gydan oil and gas region. The study is vital due to the need for additional exploration and commissioning of hydrocarbon reserves in the lower part of the Pokur suprahorizon in the north of Western Siberia. The modeling is based on sedimentological columns for four wells, in which the object of study was characterized by a core with sufficient completeness. The structure of seven sequences has been studied. Sequences PK 2-2, 2-3, 2-4, 2-5, 2-6, and PK 3-1, in accordance with the classical concept, are divided into three systems tracts: lowstand (LST), transgressive (TST), highstand (HST). The boundaries of the sequences are outlined along the erosive surfaces in the bottom of the alluvial complexes. LST tops - on contacts of alluvial facies with tidal, marsh, lake sediments, indicating flooding of the coastal plain at the beginning of transgressions. TST tops - on contacts of facies of the tidal plain with alluvial deposits, indicating the beginning of normal regressions. The main reservoirs of the object are large belts and covers of alluvium of amalgamating channels as part of the LST. Additional reservoirs are thin bodies of tidal genesis in the composition of TST, and alluvial genesis in the composition of HST. The bottom of the PK 3-2 sequence was outlined on the contacts of coastal-marine TST sandstones with tidal and marsh facies, indicating the event transgression of the coastline. One of the main reservoirs of the field, the TP₁ formation, is connected to the TST of the PK 3-2 sequence. The boundaries of the selected sequences can be traced on seismic sections of acoustic impedance. Depending on the temporary thickness in the impedance field, the sequences are displayed as two-, three- and four-layer sequences of layers, which opens up the possibility of their further study by the method of wave field inversion

This study presents the results of recent regional seismic exploration and deep drilling efforts in the Sayan-Yenisei syneclise and adjacent areas of the Lena-Tunguska petroleum province. These results were used to build a series of structure maps for Riphean, Vendian and Lower Cambrian reflectors; thickness maps of the Riphean and Vendian terrigenous geoseismic sequences within the syneclise, and a tectonic map of the Vendian-Paleozoic structural stage of the Sayan-Yenisei syneclise. The proposed oil and gas geological zoning of the Sayan-Yenisei potential petroleum area enabled us to identify eight potential petroleum regions and perform a quantitative assessment of the hydrocarbon potential. The original in-place resources of the Sayan-Yenisei potential petroleum area are estimated to be 3 billion 231 million tons of hydrocarbon equivalent, including 3 trillion 39 billion m³ of gas and 192.7 million tons of condensate. It is shown that over next 15-20 years, up to 1 trillion m³ gas reserves can be explored in the Sayan-Yenisei potential petroleum area. It is proposed to consider the Boguchany village as a large gas conversion and helium production center.

In bottom sediments of the New Siberian sedimentary basin and adjacent geostructures of the East Siberian Sea, we identified СН₄, as well as its limit and unsaturated homologues (up to and including C₅H₁₂), CO₂, CO, H₂, He, H₂S, O₂, N₂, and Ar. Isotope-gas-geochemical parameters δ¹³С СО₂, СН₄ and С₂Н₆, of the molecular mass of hydrocarbon fraction and genetic coefficients indicate the presence of both syngenetic and epigenetic gases of various gas sources in sediments, including recent sediments, peatlands, coal-bearing and gas-bearing formations, solid bitumen, igneous formations, accumulations of gas hydrates and prognostic condensate-gas, condensate, oil-and-gas and gas-and-oil reservoirs. Concentrations of CO₂ and CO reach 29.25 and 0.06 cm³/kg, CH₄ and the sum of its homologues - 5.93 and 0.031, Н₂ and He - 0.78 and 0.318, H₂S - 0.092 cm³/kg; this indicates that gas-geochemical anomalies, exceeding the anomaly criteria by 6-124 times, form in bottom sediments. The formation and distribution of abnormal concentrations of natural gases depend on the complex influence of gas-controlling factors - geological structure, fold and fault tectonics, magmatism, coal-oil-gas content, bituminous content, organic saturation, lithological composition, water-physical and reservoir properties of sediments, hydrogeological, geocryological and other conditions for accumulation of natural gases or their degassing.

Investigating Early Eocene and Paleocene deposits within the Punjab Platform, Pakistan, involved comprehensive analysis using advanced geochemical and petrophysical techniques. This study evaluates the source potential of three formations: Nammal and Sakesar of Early Eocene age and Dungan and Ranikot of Palaeocene age. The Sakesar Formation, a reservoir rock, was evaluated through interpretation of wireline logs to estimate key petrophysical properties-porosity, water saturation, and hydrocarbon saturation. Geochemical investigations focused on total organic carbon content and Rock-Eval pyrolysis of twenty-one cutting samples from a well. These samples displayed TOC values ranging from 0.21 to 2.04 wt.% and S2 values ranging from 0.09 to 2.14 mg HC/g rock. Analysis positioned all samples within the immature window zone with Type II/III and Type III kerogen, suggesting limited generative potential. Findings suggest limited hydrocarbon generation from these formations. Petrophysical analysis indicated average porosity of 11.2%, water saturation of 32.58%, and hydrocarbon saturation of 67.42% for the Sakesar Formation, categorizing it as average to good reservoir potential. This study highlights complex geochemical and petrophysical characteristics of these formations. While Sakesar shows promising reservoir qualities, significant hydrocarbon generation potential from Nammal, Dungan, and Ranikot formations is constrained. Informed decision-making is crucial when considering these formations as hydrocarbon sources.

The Lucaogou Formation in Jimsar sag is an important shale oil-producing layer in the Junggar basin. In this paper, core data, organic carbon, rock pyrolysis, biomarker compounds, and organic matter group component separation were used to study the sedimentary environment, parent material type, organic maturity and oil-bearing property of mud shale of the Second member of the Lucaogou Formation. The results showed that the sedimentary environment is a semi-oxidation and semi-reduction environment. The parent material is mainly aquatic with minor input of higher plants. The average TOC is 7.43%, the average value of hydrocarbon generation potential ( S ₁+ S ₂) is 50.54 mg/g, and the average value of T_max is 446 °C, showing high maturity of the mud shale. The chloroform bitumen “A” features high saturated hydrocarbon content (34.10% on average), low aromatic hydrocarbon content (15.39% on average), and high saturated/aromatic ratio (2.54). The carbon number of saturated hydrocarbons is distributed between n-C₁₃ and n-C₃₃. Their peak are mainly n-C₁₇ and n-C₂₃, which are biased toward medium-low molecular weight alkanes. The average of the ΣC^-₂₁/ΣC⁺₂₂ is 1.19, indicating that the alkane has advantage of short chain. The mud shale in the Second member of the Lucaogou Formation has a large sedimentary thickness, high organic matter content, and high oil generation potential. It is an important replacement target for shale oil in Jimsar sag and has important exploration significance in the future.