Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.
{"title":"Microfossils, High-Resolution Stratigraphy, Geochemistry and Lithology of the Upper Jurassic and Lower Cretaceous (Urdyuk-Khaya and Paksa Formations) in the Nordvik Peninsula, Anabar Bay, Laptev Sea","authors":"B.L. Nikitenko, E.B. Pestchevitskaya, V.A. Kashirtsev, E.A. Fursenko, A.Yu. Popov, S.N. Khafaeva, V.Yu. Bragin","doi":"10.2113/rgg20234612","DOIUrl":"https://doi.org/10.2113/rgg20234612","url":null,"abstract":"Abstract —The goal of this study was to improve the high-resolution biostratigraphy of the Upper Jurassic and Lower Cretaceous in the type section on the Nordvik Peninsula, Anabar Bay, Laptev Sea. The results were used to identify a succession of 13 foraminiferal biostratigraphic units, 9 dinocyst units, and 8 palynofloral biostratigraphic units in the rank of zones and local zones. Based on new data, the stratigraphic continuity of this section is proved for the Lower and Middle Volgian, where a major stratigraphic hiatus was previously assumed. The established zones have variable correlation potential. Different versions of the subdivision of the section based on ammonites are discussed and the proposed scale is justified. A reference level based on calcispheres/calcareous dinocysts is defined providing global correlations and calibration of beds near Jurassic–Cretaceous boundary in the Tethyan and Arctic regions. The magnetostratigraphic subdivision of the studied section and its comparison with the Tethyan regions are discussed. Together with biostratigraphic data, the proposed δ13Corg curve in the Upper Jurassic and lower part of the Valanginian can be a tool for detailed correlations in different regions of the Northern Hemisphere. The cyclicity of carbon isotope composition in the Upper Volgian and Boreal Berriasian and isotope events in the Volgian and Lower Valanginian are determined within the Arctic region. The distribution of geochemical parameters (Corg, δ13Corg and hydrogen index) is determined in studied section, geochemical stratification of the section and variations in major oxide compositions are demonstrated. A sharp change in geochemical parameters is identified at the base of the Paksa Formation (Upper Volgian). The distribution interval of the “subsurface chlorophyll maximum” is determined. The study shows that high concentrations of isotopically light organic carbon in the first diasterene geochemical subhorizon were caused by high phytoplankton productivity and were deposited under reducing conditions favorable for preservation of organic matter. The analysis of major oxide compositions of the studied rocks revealed that variations in the chemical composition of the studied rocks reflect changes in their mineralogy and petrography.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"63 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135062779","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —The Vendian oil and gas complex (OGC) consists of the Vilyuchan, Nepa, and Tira stratigraphic horizons. The horizons are divided into correlation layers, stratigraphic charts are refined, cyclometric stratigraphic charts of oil and gas-bearing areas of the southern part of the Lena–Tunguska province are constructed. The lower boundary of the Vendian oil and gas complex and the base of the Vendian system are established in the Nuj zone of the Nepa–Botuoba and Irkutsk zones of the Angara–Lena oil and gas region (OGR) at the end of the pre-Vendian break in sedimentation. In the Angara–Lena OGR, the Typta Formation lies after a break both on different formations of the Baikalian system, and on the basement, and it is covered by sandstones of the Vendian Nepa horizon. The Typta Formation is assigned to the Vendian system, to the Vilyuchan horizon. In the Nepa–Botuoba OGR, a long pre-Vendian break divided the Talakan Formation into an upper Vendian and a lower Riphean parts. The name Talakan is left for the Vendian strata, the lower part is divided into three strata of the Baikalian system. The cyclometric stratigraphic scale is based on repetitions of cyclically constructed sections of horizons and their parts. Repetitions are considered as the result of oscillatory movements of the Earth, which take place at different intervals of time. The ranks of movements are planetary (40 Myr), long-period (20 Myr), and regional. In these ranks of time, nexacylites, horizons and regocyclites were formed. The horizons linked the regional and cyclometric stratigraphic scales. Breaks in the sedimentation of the Vendian OGC are divided by duration into short-term separating regocyclites, long-term separating horizons and two breaks – pre-Vendian and pre-Danilovo, the duration of which reaches 10–20 Myr.
{"title":"Stratigraphic Structure of the Vendian Oil and Gas Complex of the Southern Oil and Gas Regions of the Lena–Tunguska Province of the Siberian Platform","authors":"N.V. Mel’nikov","doi":"10.2113/rgg20234646","DOIUrl":"https://doi.org/10.2113/rgg20234646","url":null,"abstract":"Abstract —The Vendian oil and gas complex (OGC) consists of the Vilyuchan, Nepa, and Tira stratigraphic horizons. The horizons are divided into correlation layers, stratigraphic charts are refined, cyclometric stratigraphic charts of oil and gas-bearing areas of the southern part of the Lena–Tunguska province are constructed. The lower boundary of the Vendian oil and gas complex and the base of the Vendian system are established in the Nuj zone of the Nepa–Botuoba and Irkutsk zones of the Angara–Lena oil and gas region (OGR) at the end of the pre-Vendian break in sedimentation. In the Angara–Lena OGR, the Typta Formation lies after a break both on different formations of the Baikalian system, and on the basement, and it is covered by sandstones of the Vendian Nepa horizon. The Typta Formation is assigned to the Vendian system, to the Vilyuchan horizon. In the Nepa–Botuoba OGR, a long pre-Vendian break divided the Talakan Formation into an upper Vendian and a lower Riphean parts. The name Talakan is left for the Vendian strata, the lower part is divided into three strata of the Baikalian system. The cyclometric stratigraphic scale is based on repetitions of cyclically constructed sections of horizons and their parts. Repetitions are considered as the result of oscillatory movements of the Earth, which take place at different intervals of time. The ranks of movements are planetary (40 Myr), long-period (20 Myr), and regional. In these ranks of time, nexacylites, horizons and regocyclites were formed. The horizons linked the regional and cyclometric stratigraphic scales. Breaks in the sedimentation of the Vendian OGC are divided by duration into short-term separating regocyclites, long-term separating horizons and two breaks – pre-Vendian and pre-Danilovo, the duration of which reaches 10–20 Myr.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"315 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135459908","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —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.
{"title":"Myauchan Ore Field (Northeastern Asia), an Example of Weakly Eroded Ag–Pb–Zn Volcanoplutonic Mineralization","authors":"A.N. Glukhov, E.E. Kolova, A.V. Sobolev","doi":"10.2113/rgg20234596","DOIUrl":"https://doi.org/10.2113/rgg20234596","url":null,"abstract":"Abstract —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 &lt; 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.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"81 1-2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135461751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —The results of regional geological exploration over the past 18 years within the Aldan–Maya potential petroleum area were used as the basis for the refinement of the geological structure of the study area. The study considers the key structural features of the sedimentary cover of the Aldan–Maya region and major tectonic events that affected its structure. The generalization and interpretation of regional seismic survey data provided the basis for building a series of geoseismic sections and structure maps, which, in turn, were used in structural tectonic zoning of the study area. The map showing outcrops of Riphean formations and groups on the pre-Vendian erosion surface was complied. Tectonic schemes for three structural levels (upper Karelian–Lower Riphean, Middle–Upper Riphean and Vendian–Cambrian) confirmed their fundamental difference. In particular, the large Maya inclined swell was detected only in the topography of the Lower Riphean and is absent in the overlying structures of Middle Riphean–Vendian age, which are represented by weakly differentiated monoclines. The parameters of the major tectonic elements were determined.
{"title":"Structure–Tectonic Characteristics of the Aldan–Maya Potential Petroleum Area Based on the Interpretation of Regional Seismic Data","authors":"I.A. Gubin, A.E. Kontorovich, L.N. Konstantinova, S.A. Moiseev, A.M. Fomin","doi":"10.2113/rgg20234645","DOIUrl":"https://doi.org/10.2113/rgg20234645","url":null,"abstract":"Abstract —The results of regional geological exploration over the past 18 years within the Aldan–Maya potential petroleum area were used as the basis for the refinement of the geological structure of the study area. The study considers the key structural features of the sedimentary cover of the Aldan–Maya region and major tectonic events that affected its structure. The generalization and interpretation of regional seismic survey data provided the basis for building a series of geoseismic sections and structure maps, which, in turn, were used in structural tectonic zoning of the study area. The map showing outcrops of Riphean formations and groups on the pre-Vendian erosion surface was complied. Tectonic schemes for three structural levels (upper Karelian–Lower Riphean, Middle–Upper Riphean and Vendian–Cambrian) confirmed their fundamental difference. In particular, the large Maya inclined swell was detected only in the topography of the Lower Riphean and is absent in the overlying structures of Middle Riphean–Vendian age, which are represented by weakly differentiated monoclines. The parameters of the major tectonic elements were determined.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"98 2","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135461757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —Multidirectional dynamics of changes in the chemical composition of the water of the only runoff of Lake Baikal, the Angara River, has been established. The cyclic-wave change in the interannual chemical composition of the Baikal water has been revealed, which indicates a long-term memory effect in the chemical time series of elements. Positive and negative temperature and chemical trends in the state of the water in the source of the Angara are observed, which are due to climate changes, the confinement of Baikal to the rift zone, and the composition of the enclosing rocks. It is shown that the current concentrations of monitored elements in the Angara source water depend also on their past concentrations but can change dramatically in the case of catastrophic environmental disturbances caused by natural and anthropogenic disasters (fires, drought, floods, earthquakes, etc.). The relationship between the elevated concentrations of uranium in the water and the seismic process in the Baikal area has been traced. The data obtained are based on the long-term (1950–2021) monitoring of the chemical composition of water in the Baikal ecosystem (Baikal, its tributaries, and Angara source).
{"title":"Different Dynamics of the Chemical Composition of Water in the Baikal Ecosystem (Baikal, Its Tributaries, and the Source of the Angara River)","authors":"V.I. Grebenshchikova, M.I. Kuzmin, V.M. Demyanovich","doi":"10.2113/rgg20234650","DOIUrl":"https://doi.org/10.2113/rgg20234650","url":null,"abstract":"Abstract —Multidirectional dynamics of changes in the chemical composition of the water of the only runoff of Lake Baikal, the Angara River, has been established. The cyclic-wave change in the interannual chemical composition of the Baikal water has been revealed, which indicates a long-term memory effect in the chemical time series of elements. Positive and negative temperature and chemical trends in the state of the water in the source of the Angara are observed, which are due to climate changes, the confinement of Baikal to the rift zone, and the composition of the enclosing rocks. It is shown that the current concentrations of monitored elements in the Angara source water depend also on their past concentrations but can change dramatically in the case of catastrophic environmental disturbances caused by natural and anthropogenic disasters (fires, drought, floods, earthquakes, etc.). The relationship between the elevated concentrations of uranium in the water and the seismic process in the Baikal area has been traced. The data obtained are based on the long-term (1950–2021) monitoring of the chemical composition of water in the Baikal ecosystem (Baikal, its tributaries, and Angara source).","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"183 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135889427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —Radiometric dating of zircon grains from crustal xenoliths in kimberlites of the Yakutian diamond province show that most of the Daldyn and Markha terranes were formed in Paleoarchean but preserve some fragments of Eaoachean and possibly even Hadean crust recycled in several tectonothermal events. The oldest zircons were crystallized about 3.2 Ga and recrystallized during later activity stages of 2.9, 2.8–2.7, and 1.9 Ga, whereby they gained radiogenic hafnium produced by 176Lu decay in the rock. The degrees crust rework and the tectonothermal stages varied across the Anabar tectonic province. The earliest events of 3.2 and 2.9 Ga left record in zircons from kimberlites in the Nakyn field, while the signatures of the 2.7 Ga activity are best pronounced in zircons from kimberlites sampled in the Upper Muna and Nakyn fields. On the other hand, zircons from lower crustal mafic granulite xenoliths in the Daldyn and Alakit-Markha kimberlites lack traces of the earliest crust history and only evidence of the last 1.9 Ga event, which remained mute in xenolith samples from the Upper Muna field. Zircons from felsic granulite and metadiorite xenoliths in the Udachnaya kimberlite, which represent middle and upper crust, show a peak at 2.6 Ga besides that of 1.9 Ga. The synthesized available data support several previous inferences: vertical and lateral heterogeneity of the crust in the Yakutian diamond province; absence of linkage between the crust recycling degree and major collisional zones of the Siberian craton; absence of the separate Markha terrane. Correlation of age peaks corresponding to thermal events in the crust history of the Anabar tectonic province with those of large igneous provinces allows a hypothesis that the revealed tectonothermal events may be related with the activity of superplumes.
{"title":"Eoarchean to Paleoproterozoic Crust History in the Yakutian Diamond Province: Evidence from U–Th–Pb (LA-ICP-MS) and Lu–Hf Dating of Zircons from Crustal Xenoliths in Kimberlite Pipes","authors":"V.S. Shatsky, A.L. Ragozin, Q. Wang","doi":"10.2113/rgg20234651","DOIUrl":"https://doi.org/10.2113/rgg20234651","url":null,"abstract":"Abstract —Radiometric dating of zircon grains from crustal xenoliths in kimberlites of the Yakutian diamond province show that most of the Daldyn and Markha terranes were formed in Paleoarchean but preserve some fragments of Eaoachean and possibly even Hadean crust recycled in several tectonothermal events. The oldest zircons were crystallized about 3.2 Ga and recrystallized during later activity stages of 2.9, 2.8–2.7, and 1.9 Ga, whereby they gained radiogenic hafnium produced by 176Lu decay in the rock. The degrees crust rework and the tectonothermal stages varied across the Anabar tectonic province. The earliest events of 3.2 and 2.9 Ga left record in zircons from kimberlites in the Nakyn field, while the signatures of the 2.7 Ga activity are best pronounced in zircons from kimberlites sampled in the Upper Muna and Nakyn fields. On the other hand, zircons from lower crustal mafic granulite xenoliths in the Daldyn and Alakit-Markha kimberlites lack traces of the earliest crust history and only evidence of the last 1.9 Ga event, which remained mute in xenolith samples from the Upper Muna field. Zircons from felsic granulite and metadiorite xenoliths in the Udachnaya kimberlite, which represent middle and upper crust, show a peak at 2.6 Ga besides that of 1.9 Ga. The synthesized available data support several previous inferences: vertical and lateral heterogeneity of the crust in the Yakutian diamond province; absence of linkage between the crust recycling degree and major collisional zones of the Siberian craton; absence of the separate Markha terrane. Correlation of age peaks corresponding to thermal events in the crust history of the Anabar tectonic province with those of large igneous provinces allows a hypothesis that the revealed tectonothermal events may be related with the activity of superplumes.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"30 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136038540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —We have studied biostratigraphy, lithology and geochemistry of drill cores from the Kyulenke River basin. The study of fossil remains and rock compositions, the analysis of trilobite distributions and changes in the lithological and geochemical characteristics of the sediments made it possible to identify structural features of the marker horizons, to correlate borehole sections and outcrops, to compare individual Cambrian intervals and the regional zones of the Yudoma–Olenek facies region of the Siberian Platform. The study has shown rocks of the Kuonamka Fomation to be enriched in uranium (U) and revealed a direct relationship between the contents of U and organic carbon (Corg) in the analyzed rocks, typical for the lower and middle Cambrian black shale deposits sampled from the outcrops in the eastern parts of the Siberian Platform. For the first time, a relationship of rock radioactivity by gamma-ray logging with the contents of U and Corg in Cambrian rocks was established.
{"title":"Biostratigraphy, Lithology and Geochemistry of the Lower and Middle Cambrian Rocks in the Kyulenke River Basin: First Results of Borehole Core Study","authors":"I.V. Korovnikov, I.V. Varaksina, A.E. Kontorovich, T.M. Parfenova","doi":"10.2113/rgg20234630","DOIUrl":"https://doi.org/10.2113/rgg20234630","url":null,"abstract":"Abstract —We have studied biostratigraphy, lithology and geochemistry of drill cores from the Kyulenke River basin. The study of fossil remains and rock compositions, the analysis of trilobite distributions and changes in the lithological and geochemical characteristics of the sediments made it possible to identify structural features of the marker horizons, to correlate borehole sections and outcrops, to compare individual Cambrian intervals and the regional zones of the Yudoma–Olenek facies region of the Siberian Platform. The study has shown rocks of the Kuonamka Fomation to be enriched in uranium (U) and revealed a direct relationship between the contents of U and organic carbon (Corg) in the analyzed rocks, typical for the lower and middle Cambrian black shale deposits sampled from the outcrops in the eastern parts of the Siberian Platform. For the first time, a relationship of rock radioactivity by gamma-ray logging with the contents of U and Corg in Cambrian rocks was established.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"26 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"136038542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —The Bachat earthquake (M = 6.1) with the epicenter coordinates of 54.29° N, 86.17° E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world’s largest earthquake induced while mining solid minerals. More than 5000 aftershocks were registered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward directions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1–3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.
{"title":"Volumetric Structure of the Bachat Earthquake (Kuzbass) Aftershock Area and Stress State of Rock Mass under Open-Pit Mine","authors":"A.A. Emanov, A.F. Emanov, E.V. Shevkunovа, A.V. Fateev, Yu.L. Rebetsky","doi":"10.2113/rgg20234624","DOIUrl":"https://doi.org/10.2113/rgg20234624","url":null,"abstract":"Abstract —The Bachat earthquake (M = 6.1) with the epicenter coordinates of 54.29° N, 86.17° E occurred on June, 18 2013 near the Bachatsky coal strip mine, is the world’s largest earthquake induced while mining solid minerals. More than 5000 aftershocks were registered and the spatial volumetric structure of the aftershock area was investigated. The Bachat coal field is located in the Salair zone of the Kuznetsk Depression and is represented by a brachysynclinal fold of a very complex structure characterized by the damage and fracturing behaviors of rocks. The main event is confined to the coal-mine pit wall, with the greatest density of aftershocks observed in its middle portion. In the cross section, aftershocks form a wide area with its deepened portion shifted towards the Kuznetsk Depression, while large faults bounding the depression dip down under the Salair Ridge. In the exposed pit wall, at a depth of 4 km, the activated area resembles a rhombus whose horizontal diagonal line runs across the entire length of the mine pit and decreases both in upward and downward directions. The area is seismically activated to a depth of 6 km, with more intense activation of rock mass observed within the 1–3 km depth interval. Results of the study of the mechanisms of aftershock sources revealed a disagreement between the stress state of rock mass of the Bachatsky open-pit coal mine modeled from the mechanisms of aftershocks, and the mainshock mechanism of the Bachat earthquake.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"94 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-10-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135147140","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract —The digital elevation model (SRTM03) of the central part of the Lower Amur province is analyzed. The Limuri–Amgun ring structure is identified on the basis of a set of features, and it is also the location of the Pilda–Limuri and Kherpuchin–V’yunsky gold-ore regions, as well as the Albazino deposit, known for large industrial gold deposits and many small deposits and ore occurrences. The distribution of linear and ring elements of the relief is analyzed and geologically interpreted, and its spatial relationship with gold deposits and ore occurrences is shown. The relationship between the morphological severity of the ring structure and the deep structure of the region is shown. It is revealed that the structure is magmatic and characterized by a high concentration of intrusive bodies. According to the reference data on the age and composition of the igneous complexes of the region, the formation of the ring structure is associated with the processes of formation and transformation of the Earth’s crust and upper mantle during the end of the Late Cretaceous and the onset of the Paleocene in a suprasubduction geodynamic setting.
{"title":"Use of Digital Elevation Models in Metallogenic Investigations on the Example of the Central Part of the Lower Amur Province","authors":"G.Z. Gil’manova, M.Yu. Nosyrev, A.N. Didenko","doi":"10.2113/rgg20234574","DOIUrl":"https://doi.org/10.2113/rgg20234574","url":null,"abstract":"Abstract —The digital elevation model (SRTM03) of the central part of the Lower Amur province is analyzed. The Limuri–Amgun ring structure is identified on the basis of a set of features, and it is also the location of the Pilda–Limuri and Kherpuchin–V’yunsky gold-ore regions, as well as the Albazino deposit, known for large industrial gold deposits and many small deposits and ore occurrences. The distribution of linear and ring elements of the relief is analyzed and geologically interpreted, and its spatial relationship with gold deposits and ore occurrences is shown. The relationship between the morphological severity of the ring structure and the deep structure of the region is shown. It is revealed that the structure is magmatic and characterized by a high concentration of intrusive bodies. According to the reference data on the age and composition of the igneous complexes of the region, the formation of the ring structure is associated with the processes of formation and transformation of the Earth’s crust and upper mantle during the end of the Late Cretaceous and the onset of the Paleocene in a suprasubduction geodynamic setting.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"24 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135866092","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Abstract ––The Early Devonian Altai–Sayan rift system (ASRS) has spread to the structures of East and West Sayan, Kuznetsk Alatau, and Mongolian Altay. Its largest fragments are the Tuva, Delyun–Yustyd, Kan, Agul, and Minusa basins as well as depressions in north-western Mongolia. The paper summarizes the geologic, geochemical, and Sr–Nd isotope characteristics of the ASRS mafic rocks represented by nappes of moderately alkaline and alkali basalts and their subvolcanic and intrusive rock analogues. They are present in all magmatic associations and are divided into low-Ti (TiO2 = 0.2–2.2 wt.%) and high-Ti (TiO2 = 2.2–4.3 wt.%) subgroups. These rocks are characterized by wide variations in Sr isotope characteristics (εSr(T) = –16 to +30). High-Ti mafic rocks are common at the southern segment of the ASRS; they show a weak positive Ta–Nb anomaly (La/Nb = 0.8–1.1) and are relatively enriched in LREE ((La/Yb)N = 6–14) and radiogenic Nd (εNd(T) = 3.8–8.7). Low-Ti varieties are confined to the northwestern segment of the ASRS; they are enriched in Ba but depleted in Th, U, Nb, Ta (La/Nb = 1.2–2.2), Zr, Hf, LREE ((La/Yb)N = 3–7), and radiogenic Nd (εNd(T) = 2.0–6.0). Taking into account the existence of different terranes, which were combined in the structure of the Altai–Sayan folded area during accretion (ca. 500–480 Ma), we propose a model suggesting different environments of magma formation at the southern and northwestern segments of the ASRS and the relationship of magmatism with a mantle plume within the ASRS. In composition the plume corresponds to the sources of high-Ti magmas. The effect of the melted lithospheric mantle of different compositions beneath different groups of terranes led to the observed isotope-geochemical heterogeneity of mafic rocks within the ASRS, in particular, the absence of high-Ti mafic rocks from the Minusa basin.
{"title":"Geological and Isotope-Geochemical Indicators of Early Devonian Plume–Lithosphere Interactions in the Southwestern Framing of the Siberian Craton: Data Synthesis for Magmatic Associations of the Altai–Sayan Rift System","authors":"A.A. Vorontsov, D.V. Kovalenko, V.V. Yarmolyuk, A.V. Nikiforov, O.Yu. Perfilova","doi":"10.2113/rgg20234605","DOIUrl":"https://doi.org/10.2113/rgg20234605","url":null,"abstract":"Abstract ––The Early Devonian Altai–Sayan rift system (ASRS) has spread to the structures of East and West Sayan, Kuznetsk Alatau, and Mongolian Altay. Its largest fragments are the Tuva, Delyun–Yustyd, Kan, Agul, and Minusa basins as well as depressions in north-western Mongolia. The paper summarizes the geologic, geochemical, and Sr–Nd isotope characteristics of the ASRS mafic rocks represented by nappes of moderately alkaline and alkali basalts and their subvolcanic and intrusive rock analogues. They are present in all magmatic associations and are divided into low-Ti (TiO2 = 0.2–2.2 wt.%) and high-Ti (TiO2 = 2.2–4.3 wt.%) subgroups. These rocks are characterized by wide variations in Sr isotope characteristics (εSr(T) = –16 to +30). High-Ti mafic rocks are common at the southern segment of the ASRS; they show a weak positive Ta–Nb anomaly (La/Nb = 0.8–1.1) and are relatively enriched in LREE ((La/Yb)N = 6–14) and radiogenic Nd (εNd(T) = 3.8–8.7). Low-Ti varieties are confined to the northwestern segment of the ASRS; they are enriched in Ba but depleted in Th, U, Nb, Ta (La/Nb = 1.2–2.2), Zr, Hf, LREE ((La/Yb)N = 3–7), and radiogenic Nd (εNd(T) = 2.0–6.0). Taking into account the existence of different terranes, which were combined in the structure of the Altai–Sayan folded area during accretion (ca. 500–480 Ma), we propose a model suggesting different environments of magma formation at the southern and northwestern segments of the ASRS and the relationship of magmatism with a mantle plume within the ASRS. In composition the plume corresponds to the sources of high-Ti magmas. The effect of the melted lithospheric mantle of different compositions beneath different groups of terranes led to the observed isotope-geochemical heterogeneity of mafic rocks within the ASRS, in particular, the absence of high-Ti mafic rocks from the Minusa basin.","PeriodicalId":49587,"journal":{"name":"Russian Geology and Geophysics","volume":"131 1","pages":"0"},"PeriodicalIF":0.0,"publicationDate":"2023-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"135966754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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