Gleization and paleosoils in Devonian red rocks of the Middle Timan region

Study of the lithological features of Devonian red rocks in the Middle Timan region and paleopedogenic complexes therein coupled with analysis of the localization of buried plant remains and gleization zones made it possible to reconstruct onthogenesis of the sedimentary sequence. It is concluded that processes of pedogenesis and gleization were separated in time.     

Y–REE-Rich zircons of the Timan region: Geochemistry and economic significance

Mineralogical–geochemical studies of zircon from the Ichet’yu occurrence revealed unusually high Y and HREE contents (correlative with the P content) in the inner parts and zones of approximately 10% of the grains. They represent the intermediate members of the zircon–xenotime join with a heterovalent scheme of isomorphism Zr⁴⁺ + Si⁴⁺ → (Y + HREE)³⁺ + P⁵⁺. Geochronological and mineralogical–geochemical data suggest that the Middle Timan basement (the most probable source of zircon of the Ichet’yu occurrence) is made up of the Paleoproterozoic rocks and possibly represents a continuation beneath the Mezen syneclise and Middle Timan of the Paleoproterozoic collisional structure, to which the Arkhangelsk diamond province is confined.     

Chemical composition,isotopic U–Pb age,and source of zircon from polymineralic ichet’yu occurrence,Mobile Timan

This study focuses on the morphological features, color cathodoluminescence, chemical composition, age, and source of zircons from the Ichet’yu occurrence. The isotopic U–Pb age of Paleo–Mezoproterozoic zircon grains varies within an interval of ~700 Ma from 2247 to 1478 Ma. The average roundness and well-preserved integrity of zircon grains allow us to suggest their proximal source. The available data show that the basement of the Middle Timan, composed of continental Paleo–Mezoproterozoic igneous rocks, is the most probable source of zircon in the Ichet’yu occurrence. These rocks are apparently a continuation of the Archean–Proterozoic Arkhangel’sk Mobile Belt.     

Zircon U-Pb Chronology and Geological Significance of Mesozoic Volcanic Rocks from Naozhi Copper-Gold Mining Area

Large deposits of diamonds are associated mainly with kimberlites (and related rocks) of the cratons, but they are also known in the folded belts surrounding them. As an example is the Baltica craton and the surrounding its the Ural‐Timan (UT) folded belt. With the first object are associated diamonds of the Arkhangelsk (kimberlites and placers) provinces, and with the second one ‐ mostly placer deposits of the UT province, the probable source of which are also kimberlites. The structural position, composition and age of the potentially diamond‐bearing complexes of the Urals and Timan make it possible to propose a new petrological‐geodynamic interpretation of their formation. According to this model, during the Vendian‐Cambrian subduction of the Pechora Ocean crust, several different depth complexes have been formed, being changed in the western direction. At a shallow depth level the oceanic crust subduction is accompanied only by fluid processing, without the magmatism participation. As a result, this process leads to the formation of fluidizate‐explosive rocks of the Sertynya complex, which marks the outlet of the ancient subduction zone into the surface. At a moderately deep (up to 100–150 km) level melts are being produced, the derivatives of which are not diamond‐bearing depleted kimberlites of the Khartes (V‐Cm) complex. Apparently by the beginning of the Ordovician the active subduction of the Pechora Ocean stops. It occurs an opening of a new Ural paleoocean, and the earlier submerged the oceanic slab continues moving under the Baltica craton. At a deep (above 150 km) level the slab interaction with the mantle produces typical kimberlite magmas (from the Ordovician to the Middle Devonian) transporting diamonds to the surface of the Ural‐Timan province proper.     

Provenance composition and features of geological evolution of the Late Vendian foreland basin of the Timan orogen

The provenance composition and geological evolution of different segments in the distal zone of the Late Vendian foreland basin of the Timan orogen were deciphered on the basis of sequence stratigraphic reconstructions and precision geochemical data on the Upper Vendian fine-grained terrigenous rocks from the Southeast White Sea region, Vychegda, Verkhnekama, and Shkapovo-Shikhan basins, and the Kvarkush-Kamennogorsk and Bashkirian meganticlinoriums. The Upper Vendian of the Southeast White Sea region is subdivided into four sequences: Agma, Solza, Zimnie Gory, and Erga. The tracing of sequence boundaries and lateral facies associations from the Southeast White Sea Region to the South Urals made it possible to identify the main stages of the evolution of sedimentary filling of the foreland basin: (I) shallow water epiplatformal basin, (II) isolated basin, (III) lowstand system tract, and (IV) progradation of delta platforms. Position of data points of the Upper Vendian shales, silty mudstones, and mudstones plotted in the diagrams Th-La, Ni-Cr, Gd_N/Yb_N-Eu/Eu*, Sc-Th/Sc, La/Sm-Sc/Th, and Co/Hf-Ce/Cr, together with their REE systematics and data on Nd model ages indicates that the Proterozoic, including Neoproterozoic rocks of the Timan thrust-folded belt served as the main source for fine aluminosiliciclastic material in the distal zones of the Timan foreland basin. Obtained results are consistent with the concept that the Vendian stage of the evolution of the Eastern European platform is related to the intense input of allochthonous material in its peripheral area owing to the activation of orogenic processes in the adjacent mobile belts and allow us to significantly specify the paleogeographical reconstructions.     

Late Pleistocene glacial and lake history of northwestern Russia

Five regionally significant Weichselian glacial events, each separated by terrestrial and marine interstadial conditions, are described from northwestern Russia. The first glacial event took place in the Early Weichselian. An ice sheet centred in the Kara Sea area dammed up a large lake in the Pechora lowland. Water was discharged across a threshold on the Timan Ridge and via an ice-free corridor between the Scandinavian Ice Sheet and the Kara Sea Ice Sheet to the west and north into the Barents Sea. The next glaciation occurred around 75-70 kyr BP after an interstadial episode that lasted c. 15 kyr. A local ice cap developed over the Timan Ridge at the transition to the Middle Weichselian. Shortly after deglaciation of the Timan ice cap, an ice sheet centred in the Barents Sea reached the area. The configuration of this ice sheet suggests that it was confluent with the Scandinavian Ice Sheet. Consequently, around 70-65 kyr BP a huge ice-dammed lake formed in the White Sea basin (the 'White Sea Lake'), only now the outlet across the Timan Ridge discharged water eastward into the Pechora area. The Barents Sea Ice Sheet likely suffered marine down-draw that led to its rapid collapse. The White Sea Lake drained into the Barents Sea, and marine inundation and interstadial conditions followed between 65 and 55 kyr BP. The glaciation that followed was centred in the Kara Sea area around 55-45 kyr BP. Northward directed fluvial runoff in the Arkhangelsk region indicates that the Kara Sea Ice Sheet was independent of the Scandinavian Ice Sheet and that the Barents Sea remained ice free. This glaciation was succeeded by a c. 20-kyr-long ice-free and periglacial period before the Scandinavian Ice Sheet invaded from the west, and joined with the Barents Sea Ice Sheet in the northernmost areas of northwestern Russia. The study area seems to be the only region that was invaded by all three ice sheets during the Weichselian. A general increase in ice-sheet size and the westwards migrating ice-sheet dominance with time was reversed in Middle Weichselian time to an easterly dominated ice-sheet configuration. This sequence of events resulted in a complex lake history with spillways being re-used and ice-dammed lakes appearing at different places along the ice margins at different times.     

Preservation conditions of in situ root systems in Devonian sections of the middle Timan region

Upper Devonian terrigenous red rocks in the middle Timan region enclose many paleopedocomplexes. Some sections include both paleosoil profiles with well-preserved coalified organic matter of in situ root systems and profiles lacking these features. Lithological investigations revealed that sedimentary beds are mostly composed of sand-to gravel-sized clay clasts (with small pebbles) and characterized by subaerial spasmodic proluvial genesis. The pelitic-silty bedded sediments accumulated in water basins with calm hydrodynamics are less widespread. It is established that organic matter of roots is preserved only if they are rapidly overlain by sediments of debris flows.     

Cosmogenic 10Be exposure age dating across Early to Late Weichselian ice-marginal zones in northwestern Russia

Rock samples from the Kanin Peninsula and the Timan Ridge were analysed for in situ cosmogenic ¹⁰Be for exposure age dating purposes. Crystalline rocks were sampled at four sites on the Kanin Peninsula, either from bedrock outcrops or from glacial erratics, giving overall similar ¹⁰Be ages. Outcropping sandstone and crystalline erratics were available from three sites at the Timan Ridge. The highly weathered sandstone gives substantially younger ¹⁰Be ages than the adjacent erratics. The exposure ages from the Kanin Peninsula suggest that the last deglaciation of this area took place between 55 and 37 ¹⁰Be kyr ago, in agreement with a preceding Kara Sea glaciation (55-45 kyr BP). The northwest coast of the peninsula was probably just outside the maximum limit of the last Scandinavian glaciation (20-17 kyr BP). Glacial erratic exposure ages from the Timan Ridge suggest that the 55-45 kyr BP Kara Sea glaciation reached the northern part of the ridge. The exposure dates do not show conclusive evidence regarding the existence of a Timan Ridge ice cap.     

Tsilmanite as a new type of jet

A new type of jet from continental Devonian deposits of the Middle Timan is described. Fragments of Archaeopteris were the substrate for jet formation. Fossils in sandstone layers are characterized by a peculiar spheroidal jointing of organic matter; the material is fusainized completely. The jet is characterized by integration of the properties of classic jet and inertinite. The proper name tsilmanite is suggested for the new type of jet after the place of its discovery.     

First finding of Archaeopteridaceae wood in the Upper Devonian deposits of the Middle Timan Region

Stem remains of Archaeopteridaceae with a well-preserved anatomical structure were firstly found in the Upper Devonian deposits of the Middle Timan Region. The wood was studied under SEM and REM and was identified as Callixylon trifilievii Zalessky. Previous findings of Archaeopteridaceae in the northern part of European Russia and some taxonomic problems of the species were discussed.     

The provenance of terrigenous rocks of the basal horizons of the Uralides of the Baidarata Allochthon (Polar Urals) according to the U–Pb isotope age of detrital zircons

The U–Pb (LA–ICP–MS) age of detrital zircons from the Upper Cambrian–Lower Ordovician terrigenous rocks of the Baidarata Allochthon, which is located in the northern part of the Polar Urals, is determined. The analysis of the youngest zircon population indicates a broad occurrence of the Uralides in this area rather than Pre-Uralides, as was considered previously. The Bedamel island-arc rocks (rather than Timan orogen) were probably the major provenance for the studied sequences. The results of statistical processing of the U–Pb ages of zircons from coeval rocks of Arctic regions suggest similar provenances for the Baidarata Allochthon and Novaya Zemlya and Severnaya Zemlya archipelagoes.     

右江盆地中三叠统细碎屑岩地球化学特征及其对物源区、构造背景的指示

右江盆地位于华南板块西南缘与印支板块的结合部位,于中三叠世沉积了一套以细碎屑岩为主的巨厚浊积岩。研究区中三叠统细碎屑岩的主量、微量和稀土元素分析表明,细碎屑岩以杂砂岩和岩屑砂岩为主,其源岩来自大陆上地壳,物源区岩石类型主要为长英质沉积岩和火成岩,岩石风化程度中等偏高,构造背景为大陆岛弧和活动大陆边缘。综合细碎屑岩稀土元素特征及前人对该区中三叠统古流向和碎屑锆石U-Pb年代学研究,认为中三叠统碎屑物来源复杂,云开地区、江南造山带和越北地块是主要的物源区。     

河北省兴隆地区大红峪组沉积古环境研究

大红峪组为燕山地区惟一中、新元古界碎屑岩与碳酸盐岩混合沉积地层。根据“岩性—岩相—相序”的研究思路与方法 ,在详细研究成因单元基础之上 ,将大红峪组地层叠置规律归纳为碎屑岩型、混合岩型、碳酸盐岩型三种相序 ,横向上划分为两个相区 :东部相区以碎屑岩为主、西部相区以碳酸盐岩为主 ,沉积环境表现为由东部靠近陆源区缓斜坡砂质海滩向西部过渡为浅水碳酸盐台地型相模式 ,沉积作用以潮汐作用为主 ,偶见浅水风暴沉积     

U-Pb dating and provenance of detrital zircons from the Upper Precambrian deposits of North Timan

Timan comprises the southwest edge of the Pechora Plate. The plate basement is composed of variably metamorphosed sedimentary, mainly terrigenous, and igneous rocks of the Late Precambrian age that are generally overlain by Ordovician-Cenozoic platform cover. Poor exposition and discontinuous distribution of the Upper Precambrian outcrops of dominantly fossil-free sedimentary rocks cause considerable disagreements in stratigraphic correlation. This applies equally to North Timan, which represents an uplifted block of basement, in which sedimentary-metamorphic rocks form the Barminskaya Group (～5000 m thick), previously dated as Early Riphean to Vendian. Earlier Rb-Sr and Sm-Nd isotope dating of schist and cross-cutting gabbro-dolerite and dolerite established the timing of greenschist facies metamorphism at 700 Ma. Thus, Late Riphean age of the Barminskaya Group has been suggested. Results of local U-Pb dating of detrital zircon from silty sandstones of the Malochernoretskaya Formation, which constitutes the middle part of the outcropping section of the Barminskaya Group, confirm this conclusion. Age data for 95 zircon grains cover the range of 1035–2883 Ma with age peaks at 1150, 1350, 1550, 1780, and 1885 Ma. The minimum age of zircons, considered as the lower age constraint on sediment deposition, provides grounds to date the Barminskaya Group as Late Riphean and indicates eroded rock complexes of the Fennoscandian Shield as the possible provenance areas.     

川西磷酸岩

川西磷酸岩的特征,对阐明磷的沉积作用和磷块岩的成因,有一定的重要性。多年来,四川省地质局在该区作了大量的详细的勘查和研究。这里仅就我们的工作所及,讨论磷酸岩的一些沉积学问题。一、含磷岩系的岩性序列与岩相系列掌握含矿岩系本身在纵横两个方向上变化更替的规律,对沉积矿床的勘查是很重要的。这种变化规律,可以用岩性序列与岩相系列表示之。岩性序列是含矿岩系的各个岩类在纵剖面上转换的次序,反映它成生时期沉积盆地的地质、自然地理、物理、化学和生物等诸方面的状况及其在时间上的演化;而岩相系列则是含矿岩系的各个岩类及其组合在横向上的转换次序,反映上述诸方面状况在空间上的演变。     

Copper sulfide pseudomorphs after phytodetritus in Devonian sedimentary rocks of the Middle Timan region

Copper sulfide pseudomorphs after phytodetritus in ore-bearing sedimentary rocks of the Middle Timan region were studied by ore microscopy, X-ray methods, electron scanning microscopy (microprobe), and chemical analysis. It was established that jurleite rather than chalcocite, as was previously assumed, is the major copper sulfide in pseudomorphs. Other copper sulfides detected in microscopic amounts are inferior to jurleite in abundance. Two types of jurleite—white and light blue—can be distinguished under an ore microscope. In addition to color, jurleite varieties differ in size of crystals and hardness. White jurleite occurs as large grains in superficial crusts and pith pseudomorphs or fills contraction fissures in plant tissue. Light blue jurleite segregations are combined with microgranular units and altered wood. Part of the light blue jurleite replaces the white variety. Light blue jurleite has a higher relief on a polished surface. The common crystallographic orientation of sulfide grains in pseudomorphs was noted for all modes of occurrence of jurleite. Jurleite grains of various shapes and different hardness may be detected in the same sample. In general, copper sulfides were formed in the following sequence: (i) filling of fissures and interstices in wood, (ii) formation of superficial crusts composed of white jurleite, (iii) joining of fissures by pseudomorphs after organic matter and partial replacement of white jurleite with the light blue variety, and (iv) secondary transformation of light blue jurleite with partial redistribution of its constituents between less frequent copper sulfides.     

Characteristics and evaluation of Mesozoic source rocks in the southeastern East China Sea continental shelf

Source rocks are the material basis of oil and gas generation and determine the potential resources of exploration blocks and have important research value. This paper studies the lithology, thickness, and geochemistry of Mesozoic source rocks in the southeastern East China Sea continental shelf. The results show that the Mesozoic source rocks are mainly dark mudstone and coal-bearing strata. The total thickness of Lower–Middle Jurassic source rocks ranges from 100 m to 700 m, and that of Lower Cretaceous source rocks ranges from 50 m to 350 m. The overall thickness of Mesozoic source rocks is distributed in the NE direction and their thickness center is located in the Jilong Depression. The Lower–Middle Jurassic source rocks are mainly developed shallow marine dark mudstone and transitional coal measure strata. Those of the Lower Cretaceous are mainly mudstone of a fan delta front. Lower–Middle Jurassic and Lower Cretaceous hydrocarbon source rocks are dominated by type III kerogen, with Lower–Middle Jurassic hydrocarbon source rocks having high organic matter abundance and being medium–good hydrocarbon source rocks, while Lower Cretaceous hydrocarbon source rocks have relatively poor quality. From northwest to southeast, the vitrinite reflectance Ro of Mesozoic source rocks increases gradually. Source rocks in the study area are divided into three types. The first hydrocarbon-generating area is mainly located in the southeastern region of the study area, and the Jilong Depression is the hydrocarbon-generating center. The results of this study can provide a basis for exploration of Mesozoic oil and gas resources in the southeastern East China Sea continental shelf.© 2019 China Geology Editorial Office.     

兴蒙造山带东段火成岩构造组合、构造岩浆阶段及大地构造演化

以火成岩构造组合的概念和方法为指导,以近几年在嘉荫、伊春、鹤岗、鸡西、牡丹江等地区开展的1∶5万、1∶25万区调研究为基础,基于侵入岩锆石U-Pb年龄,建立了研究区古生代构造岩浆阶段划分的初步方案.划分出与洋壳俯冲事件有关的火成岩构造组合5期,分别为加里东期早寒武世、早中奥陶世、中志留世,华力西期晚石炭世和晚二叠世.与...     

The study of Neo-Tethys Paleogeography in Marri-Asbkeshan area, north-northwest Doruneh–Kashmar subzone (Khartouran)

The study area is a small part of the Sabzevar structural zone, and is confined between Semnan and Khorasan provinces. The oldest sedimentary rocks of this region are Middle Jurassic in age with horizons of calc-alkaline rhyolitic-rhyodacitic lavas in between. First alkaline basaltic lavas accompanied by diabasic dikes in this region appeared along with Early Cretaceous lime-stone. Late Cretaceous rocks are composed of volu-minous calc-alkaline rhyodacitic-rhyolitic and trachy-andesitic lavas and dikes, and basaltic dikes. With abundance pinkish-cream plagic limestone this has been overlain by Paleocene rocks.     

Riphean stromatolitic formations fringing the East European platform

Riphean stromatolitic formations flank the East European epi-Karelian platform only in the east and northeast. They are traceable as long (over 3600 km) relatively narrow belt consisting of two rectilinear segments, one running along the Urals western flank from southern extremity of the Bashkirian meganticlinorium to the Polyudov Ridge and the other one extending from the southern and central Timan to the Kil’din Island and northern Norway. Within the belt there are known stromatolitic formations of all Riphean erathems: the Lower and Middle Riphean stromatolitic buildups are confined to the eastern segment of its southern part only, while the Upper Riphean occur everywhere. Their distribution conformable to large structural elements of the plaform margin being replaced by carbonate-terrigenous rocks almost lacking stromatolites westward and southwestward in the Kama-Belaya aulacogen system and by substantially siliciclastic succession eastward and northeastward. The distribution area of Upper Riphean stromatolitic formations includes the Karatavian stratotype region, where 12 stromatolite beds ranging in age from ≥900 to 620 Ma are established. Many of the beds are traceable along the strike far beyond the stratotype region. Representing relatively small reference units, the beds facilitate reconstruction of distribution dynamics of the Upper Riphean stromatolites. Distribution area of the latter was always parallel to marginal structures of the platform, though being of changeable size, particularly of length. Originated in the stratotype region eastern part, stromatolites first advanced into northeastern areas never crossing boundaries of the Upper Riphean distribution area during the Early Karatavian. In the initial Late Karatavian, they occupied a longest distribution area that was sharply reduced at the end of that period. According to distribution peculiarities in space and with time, the Upper Riphean stromatolitic formations accumulated likely in peripheral areas of an open sea or oceanic basin adjacent to the East European platform, rather than in closed epiplatform basins.