lower paleozoic
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Author(s):  
И.А. Богуш ◽  
Г.В. Рябов ◽  
В.И. Черкашин ◽  
Н.А. Исаева

Ультрабазиты Северного Кавказа являются древнейшими магматическими породами, возраст которых определяется как нижнепалеозойский (ордовик-силур). Эти породы играют ключевую роль в металлогении благородных металлов Кавказа. С ультрабазитами связаны гигантские запасы металлов в региональной углеродсодержащей девонской черносланцевой толще Северного Кавказа. Практическое значение имеют пермскские пропилиты (Чучкурское месторождение) и металлоносные юрские коры выветривания ультрабазитовых массивов. До настоящего времени не оценены благородные металлы лиственитов Северного Кавказа, сопровождающих ультрабазиты. Цель работы. Показать, что ультраосновные породы являются донорами благородных металлов (Au, Pt, Pd) для Северного Кавказа на протяжении всего фанерозоя. Подтвердить пространственно-временную связь ультрабазитов с благороднометалльным оруденением в черных сланцах Кавказа. Доказать на примере Беденского массива ультрабазитов наличие рудоносной коры выветривания, залегающей на размытой поверхности серпентинитов. Методы исследований. Сделан краткий исторический обзор исследований ультрабазитов с ориентацией на генетические связи благородных металлов (Au, Pt, Pd) с ультрабазитовой магмой. Проведен анализ геологических материалов по наиболее крупным на Северном Кавказе Беденскому и Малкинскому ультрабазитовым массивам - их составу, геохимическим особенностям и потенциальной рудоносности. Результаты работы. По химическому составу ультрабазиты Северного Кавказа отнесены к альпинотипному формационному типу. Установлена рудообразующая роль альпинотипных ультрабазитов для благородных металлов в осадочных и метаморфических толщах фанерозоя региона. Благородные металлы активно проявляются в металлогении фанерозойских геотектонических эпох: каледонской, герцинской, киммерийской и альпийской, имея единый первичный ультрабазитовый источник. Свежие, неизмененные серпентиниты в настоящее время не обнаруживают аномальные содержания благородных металлов, представляющих промышленный интерес. Насыщение серпентинитов благородными металлами проявляется при их экзогенной переработке в обогащенных продуктах их разрушения. Потенциально промышленными осадочными комплексами, состоящими из обогащенных продуктов разрушения серпентинитов, являются коры выветривания серпентинитов и осадочные черносланцевые толщи Северного Кавказа. Ультрабазитовая магма на Северном Кавказе послужила первичным глубинным источником благородных металлов в осадочных и метаморфогенных фанерозойских толщах Кавказа The ultrabasites of the North Caucasus are the oldest igneous rocks, whose age is defined as the Lower Paleozoic (Ordovician-Silurian). These rocks play a key role in the metallogeny of the noble metals of the Caucasus. Huge reserves of metals in the regional carbonaceous Devonian black shale stratum of the North Caucasus are associated with ultrabasites. Permian propylites (Chuchkurskoye deposit) and metal-bearing Jurassic crusts of weathering of ultrabasic massifs are of practical importance. To date, the noble metals of the listvenites of the North Caucasus accompanying ultrabasites have not been evaluated. Aim. Show that ultrabasic rocks are donors of noble metals (Au, Pt, Pd) for the North Caucasus throughout the entire Phanerozoic. Confirm the spatio-temporal relationship of ultrabasic rocks with noble metal mineralization in the black shales of the Caucasus. Prove the presence of an ore-bearing weathering crust on the eroded surface of serpentinites using the example of the Bedensky ultrabasic massif. Methods. A brief historical review of ultrabasite studies with a focus on the genetic relationships of noble metals (Au, Pt, Pd) with ultrabasite magma is made. The analysis of geological materials on the Bedene and Malkin ultrabasite massifs, the largest in the North Caucasus, is carried out - their composition, geochemical features and potential ore content. Results. According to the chemical composition, the ultrabasites of the North Caucasus are attributed to the alpinotype formation type. The ore-forming role of alpinotype ultrabasites for noble metals in sedimentary and metamorphic strata of the Phanerozoic region has been established. Noble metals are actively manifested in the metallogeny of the Phanerozoic Geotectonic epochs: Caledonian, Hercynian, Cimmerian and Alpine, having a single primary ultrabasic source. Fresh, unaltered serpentinites do not currently show anomalous contents of noble metals of industrial interest. The saturation of serpentinite with noble metals is manifested during their exogenous processing in the enriched products of their destruction. Potentially industrial sedimentary complexes consisting of enriched products of destruction of serpentinites are the weathering crusts of serpentinites and sedimentary black-shale strata of the North Caucasus. Ultrabasic magma in the North Caucasus served as the primary deep-seated source of precious metals in sedimentary and metamorphogenic Phanerozoic strata of the Caucasus


LITOSFERA ◽  
2021 ◽  
Vol 21 (6) ◽  
pp. 867-883
Author(s):  
A. I. Rusin ◽  
A. A. Zvorygina ◽  
P. M. Valizer

Research subject. This article presents mineralogical, petrological and geochemical studies of lawsonite eclogites and metasomatites of the Utarbayev Аssociation of the Maksyutov complex. The Utarbayev Association forms an independent unit in the Maksyutovsky complex accretion structure. This Association features a variety of lawsonite-bearing metasomatites that form zonal halos in the frame of block-like diopside-grossular bodies included in the antigorite-serpentinite melange. The Utarbayev Association differs from typical lawsonite-blue shale complexes of collisional oro genes by the absence of mineral parageneses of lawsonite-bearing rocks of blue amphibolites.Methods. A microprobe analysis of the mineral composition was performed using a Cameca SX-100 microanalyzer. The content of petrogenic, rare and rare-earth elements was determined by X-ray spectroscopy (CPM-18) and mass spectroscopy (ICP-MS, ELAN-90). Results. An indicator mine ral paragenesis (Grt + Omp + Lws + Di) ± (Coe-Qz + Ttn) that characterizes lawsonite eclogite was found. Omphacite (Jd38–44) and unchanged lawsonite (Н2O-OH – 11.8%, Ca/Al = 0.48–0.51 и Fe/Al = 0.01 0.02%) are represented as inclusions in grossular-almandine garnet (Alm39–46Grs41–51), coesite – as microinclusions in omphacite. Thermobarometry (Grt-Omp, Grt-Omp-Ph) showed the following formation conditions of lawsonite paragenesis: T = 495–622°C under P = 2.2–2.4 GPa. The age of crystallization of lawsonite eclogite was found to be Lower Paleozoic (471–444 Ma).Conclusions. The lawsonite eclogite of the Utarbayev Association is similar to the complexes of «cold» eclogites, which are formed under the conditions of a very low geothermal gradient and are rarely preserved when removed into the upper crust. The latest review published in the «Journal of Metamorphic Geology» (2014) mentions 19 sites, where lawsonite eclogites were discovered on the earth’s surface. Тhe HP-UHP lawsonitebearing Utarbayev Rock Association complements this list.


Resources ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 3
Author(s):  
Oleg Prischepa ◽  
Yury Nefedov ◽  
Victoria Nikiforova

The Timan–Pechora oil and gas province (TPP), despite the good geological and geophysical knowledge of its central and southern regions, remains poorly studied in the extreme northwestern part within the north of the Izhma–Pechora depression and the Malozemelsk–Kolguev monocline, and in the extreme northeast within the Predpaikhoisky depression. Assessing the oil and gas potential of the Lower Paleozoic part of the section is urgently required in the northwestern part of the TPP, the productivity of which has been proven at the border and in the more eastern regions of the province (Pechora–Kolva, Khoreyverskaya, Varandei–Adzva regions), that have been evaluated ambiguously. A comprehensive interpretation of the seismic exploration of regional works was carried out, with the wells significantly clarifying the structural basis and the boundaries of the distribution of the main seismic facies’ complexes. The capabilities of potentially oil- and gas-producing strata in the Silurian–Lower Devonian were studied. An analysis of migration routes in transit strata used for basin modeling in order to reconstruct the conditions of oil and gas formation that are common in the land and water areas of the Arctic zone of the TPP was carried out. Modeling allowed us to reach an understanding of the formation of large zones with possible accumulations of hydrocarbons, including the time at which the formation occurred and under what conditions, to establish space–time links with possible centers of generation to identify migration directions and, based on a comparison with periods of intensive generation of hydrocarbons both directly located within the work area and beyond (noting the possible migration), to identify zones of the paleoaccumulation of hydrocarbons. The body of existing literature on the subject made it possible to outline promising oil and gas accumulation zones, with the allocation of target objects for further exploration in the Lower Paleozoic part of the section.


2021 ◽  
Vol 147 (6) ◽  
pp. 04021045
Author(s):  
Chengsheng Chen ◽  
Haizu Zhang ◽  
Yunpeng Wang ◽  
Lingling Liao ◽  
Shuyong Shi ◽  
...  

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7603
Author(s):  
Xiaoyan Zou ◽  
Xianqing Li ◽  
Jizhen Zhang ◽  
Huantong Li ◽  
Man Guo ◽  
...  

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.


2021 ◽  
Author(s):  
◽  
Roger Alan Cooper

<p>Eleven graptolite zones are recognized in New Zealand and are considered to represent most of the Ordovician Period. The most complete fossiliferous section, at Aorangi Mine in Northwest Nelson, is described in detail. New fossiliferous Ordovician sections at Wangapeka Valley and Hailes Knob, in Northwest Nelson, are described and the previously Known sections at Cobb Valley (Northwest Nelson) and the Cape Providence - Preservation Inlet region (Southwest Otago) are discussed The New Zealand zones are correlated with those of Victoria, Australia, and the Victorian stage nomenclature is adopted for New Zealand. In upward sequence the stages and zones are: Lancefieldian (zones 1, Adelograptus, and 2, T.approximatus), Bendigonian (zone 3, T.fruticosus), Chewtonian (zone 4, D.protobifidus), Castlemainian (zones 5, I.c.lunata, and 6, I.c.maximodivergens), Yapeenian (zone 7,Oncograptus), Darriwilian (zones 8, P.etheridgei, and 9, D.decoratus), Gisbornian (zone 10, N.gracilis), Eastonian (zone 11, Orthograptus - lower part) and Bolindian (zone 11, Orthograptus - upper part?). Fossils of lowermost Lancefieldian and uppermost Bolindian age are not yet known in New Zealand. Diagnostic Silurian fossils are also unknown and the next youngest New Zealand fossils are Lower Devonian (Gedinnian?). Previous Work in the Aorangi Mine area is outlined, the geology illustrated by a map, and the stratigraphic column shown to include both older, and younger beds than were previously known. About 8500ft thick, the column comprises, in upward sequence, Webb Formation, Aorangi Mine Formation (with four informal members), Formation A (new and informal, with three members), and Formation B (new and informal). Graptolites are confined to the three younger formations and represent zones 1 to 10, ranging in age from Lancefieldian to Gisbornian. The structure is outlined and illustrated by cross-sections. In Wangapeka Valley, argillites of the Wangapeka Formation contain zone 11 graptolites of Eastonian and lower Bolindian age, and are overlain by 1500ft of quartzite of the Ellis Formation, which has yielded no diagnostic fossils but which is inferred to represent at least part of the Silurian Period. Lower Devonian brachiopods, bivalves, corals and trilobites are known from the uppermost beds of the Ellis Formation, about 1550ft above its base. At Hailes knob, Mount Arthur Marble with fossils of uppermost Ordovician age is overlain by Hailes Knob Quartzite of probable Silurian age. From the Aorangi Mine and Wangapeka areas, one hundred and thirteen graptolite species and subspecies, representing 35 geners, are described. They include one named new species and 49 new records for New Zealand. Stratigraphic and geographic distribution elsewhere in the world is noted. The geners Isograptus Moberg and Paraglossograptus Mu are reviewed, and their New Zealand members described and discussed in detail. The important zonal species and subspecies are also described in detail; the remainder are briefly discussed. One hundred and six taxa are figured. Fossil localities in the areas described are listed with their fossils in appendix I, and details of measured sections are given in appendix II. A summary of Lower Paleozoic fossil localities of Northwest Nelson is given in a supporting paper.</p>


2021 ◽  
Author(s):  
◽  
Roger Alan Cooper

<p>Eleven graptolite zones are recognized in New Zealand and are considered to represent most of the Ordovician Period. The most complete fossiliferous section, at Aorangi Mine in Northwest Nelson, is described in detail. New fossiliferous Ordovician sections at Wangapeka Valley and Hailes Knob, in Northwest Nelson, are described and the previously Known sections at Cobb Valley (Northwest Nelson) and the Cape Providence - Preservation Inlet region (Southwest Otago) are discussed The New Zealand zones are correlated with those of Victoria, Australia, and the Victorian stage nomenclature is adopted for New Zealand. In upward sequence the stages and zones are: Lancefieldian (zones 1, Adelograptus, and 2, T.approximatus), Bendigonian (zone 3, T.fruticosus), Chewtonian (zone 4, D.protobifidus), Castlemainian (zones 5, I.c.lunata, and 6, I.c.maximodivergens), Yapeenian (zone 7,Oncograptus), Darriwilian (zones 8, P.etheridgei, and 9, D.decoratus), Gisbornian (zone 10, N.gracilis), Eastonian (zone 11, Orthograptus - lower part) and Bolindian (zone 11, Orthograptus - upper part?). Fossils of lowermost Lancefieldian and uppermost Bolindian age are not yet known in New Zealand. Diagnostic Silurian fossils are also unknown and the next youngest New Zealand fossils are Lower Devonian (Gedinnian?). Previous Work in the Aorangi Mine area is outlined, the geology illustrated by a map, and the stratigraphic column shown to include both older, and younger beds than were previously known. About 8500ft thick, the column comprises, in upward sequence, Webb Formation, Aorangi Mine Formation (with four informal members), Formation A (new and informal, with three members), and Formation B (new and informal). Graptolites are confined to the three younger formations and represent zones 1 to 10, ranging in age from Lancefieldian to Gisbornian. The structure is outlined and illustrated by cross-sections. In Wangapeka Valley, argillites of the Wangapeka Formation contain zone 11 graptolites of Eastonian and lower Bolindian age, and are overlain by 1500ft of quartzite of the Ellis Formation, which has yielded no diagnostic fossils but which is inferred to represent at least part of the Silurian Period. Lower Devonian brachiopods, bivalves, corals and trilobites are known from the uppermost beds of the Ellis Formation, about 1550ft above its base. At Hailes knob, Mount Arthur Marble with fossils of uppermost Ordovician age is overlain by Hailes Knob Quartzite of probable Silurian age. From the Aorangi Mine and Wangapeka areas, one hundred and thirteen graptolite species and subspecies, representing 35 geners, are described. They include one named new species and 49 new records for New Zealand. Stratigraphic and geographic distribution elsewhere in the world is noted. The geners Isograptus Moberg and Paraglossograptus Mu are reviewed, and their New Zealand members described and discussed in detail. The important zonal species and subspecies are also described in detail; the remainder are briefly discussed. One hundred and six taxa are figured. Fossil localities in the areas described are listed with their fossils in appendix I, and details of measured sections are given in appendix II. A summary of Lower Paleozoic fossil localities of Northwest Nelson is given in a supporting paper.</p>


2021 ◽  
pp. 82-91
Author(s):  
Petr Ignatov ◽  
Nail Zaripov ◽  
Konstantin Novikov ◽  
Alexander Tolstov

Drag folds were revealed in Lower Paleozoic sedimentary strata of Mirny, Nakyn and Syuldyukar diamondiferous fields, West Yakutia. They consist of minor anticlinal forms (3-5 to 15-20 cm thick) and cut marl, clayey limestone and dolomite bands located between monolith seams of carbonate rocks. Some folds as monocline, flexures and S- or Z-shaped folds reflect the degree of shearrelated interlayer offset. Drag folds are among shear zone occurrences including microfaults, slickensides with slip groove horizontal planes, and schistosity zones. Drag folds reflect local extension points while schistosity zones indicate compression points. For Syuldyukar field, detailed mapping results for drag folds and schistosity zones are provided at 3 scales: across 20 × 20 m observation grid within a local 2 km2 site; across 200 × 200 m grid within 20 km2 area; across 500 × 500 m grid within ~100 km2 territory. For all scales, drag fold halos are restricted to schistosity zones. Within a local site adjacent to kimberlites, drag folds mark ore-hosting fault controlling long axes of kimberlite areal projections. Within large areas, drag fold halos are 1,2-2 km, which compares with kimberlite group areal parameters. Drag fold halos reflect shear junctions, with some of them hosting kimberlites. Local occurrences of drag folds mark a major shear hosting a kimberlite body. Drag fold analysis combined with other evidence should be used as an indirect prospecting indicator of concealed shears and local extension areas controlling kimberlites.


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