Bionomic description of the Fammenian basin on western slope of the Central and South Urals

Three major facies types are developed: shoal facies, consisting of thick beds of limestone and dolomite with some anhydrite; depression facies, consisting of black bituminous limestones, cherty mudstones and black shales; intermediate facies, consisting of interbedded types from the other two facies. The principal biocoenoses of each facies and its variants are discussed and the faunas and floras tabulated. — D. J. McLaren.     

The early Precambrian history of rock metamorphism in the Urals segment of crust

Early Precambrian rock units in the Urals are present in several polymetamorphic complexes, which are exposed in the Urals in the form of small (<1500 km²) tectonic blocks. Their ages are Archaean (as old as 3.5 Ga) and Palaeoproterozoic. During the formation of these complexes in the early Precambrian, two stages of ultra-high-temperature (granulite) metamorphism occurred. The maximum age of the early Neoarchaean stage of metamorphism is 2.79 Ga. Evidence of this metamorphic event includes the dating of the Taratash gneiss-granulite complex of the South Urals. Gneiss-migmatite complexes, which dominate the lower Precambrian section of the Urals, were formed in the Palaeoproterozoic during the sequential appearance of granulite facies metamorphism followed by amphibolite facies metamorphism and accompanying granitization. The maximum age of the Palaeoproterozoic stage of granulite metamorphism in the Alexandrov gneiss-migmatite complex, the most well-studied complex in the South Urals, is 2.08 Ga.     

The ordovician-silurian boundary on the western slope of the Subpolar Urals

Data obtained using different methods: paleontological, sedimentological, event stratigraphy and C-isotope chemostratigraphy of a unique succession of the Upper Ordovician and lower Silurian, located on the western slope of the Subpolar Urals, are presented in this work. The data obtained made it possible to revise some existing ideas about the texture of the Upper Ordovician succession and clarify the position of the Ordovician-Silurian boundary in the region. In addition, the Upper Ordovician Yaptiknyrd Formation was correlated with the synchronous formations in Scotland and Estonia.     

松辽盆地西斜坡中—晚二叠世古沉积环境演化及油气地质意义

大兴安岭南部—松辽盆地西斜坡晚二叠世古沉积环境一直以来备受争议,关于该地区中—晚二叠世古环境演化方面的研究也鲜见报道。本文采用元素地球化学和有机地球化学相结合的研究方法,对松辽盆地西斜坡蒙科地1井中—晚二叠世古沉积环境演化特征进行综合研究。结果表明,中二叠世为明显的海相沉积,沉积水体相对较深,期间可能存在多次干热—暖湿波动,其中中二叠世ZSI晚期—ZSII早期较为明显,水体性质体现为咸水—微咸水—半咸水,水体还原性—偏氧化性—还原性,气候干热—温湿—干热。晚二叠世早期为微咸水—半咸水海相沉积,至晚二叠世晚期转变为淡水—微咸水海陆过渡相沉积,期间存在两次明显的气候环境波动,与中二叠世哲斯组沉积中期气候环境变化相似,表现为水体变浅、咸度降低、还原性减弱,气候由干热转向温湿。晚二叠世以来气候逐渐向温暖湿热转变,水体逐渐变浅,可能与二叠纪—三叠纪之交气候变暖有关。至三叠纪、侏罗纪时期,区域处于构造抬升阶段,沉积环境由海陆过渡相环境转变为陆相沉积。结合TOC、古生产力指标分析得出,中二叠世ZSI晚期—ZSII2早期、晚二叠世LXI晚期、晚二叠世LXII中期、晚二叠世LXIII沉积期偏湿润的气候条件和低咸度、弱还原—偏氧化性的沉积水体环境,是形成厚度较大、富有机质烃源岩的有利的气候环境条件。     

Late Precambrian Scissors--Type Opening--Closing Tectonics and Its Dynamics in South China

In this paper the author first reviews 6 major advances in the study of Precambrian geologyand tectonics of South China during the last decade, and then proposes the following new modelof Late Precambrian scissors-type opening-closing tectonic evolution in the region. (1) Besidesthe Middle-Late Proterozoic low-grade metamorphic basement, there existed a LateArchaean-Early Proterozoic medium- to high-garde metamorphic basement in South China;both of them formed the united Yangtze-Cathaysia (craton) at the end of the Early Proterozoic,with the Jiangxi-Anhui-Zhejiang palaeogulf extending into the inland and the Jiangxi-Anhui-Jiangsu Peninsula lying on the northern side of the palaeogulf.(2) From the Middle Proterozoic,the present Guangxi-Guizhou-Hunan area in the western-central oldland was subjected toextensional rifting and became a rift trough, thus resulting in counterclockwise rotation of the"Cathaysian block" and clockwise rotation of the "Yangtze block"; moreover, the southwardcompression of the Dabie-Jiaonan block which split from the southern margin of the NorthChina plate and was accreted to the northern margin of the Jiangxi-Anhui-Jiangsu Peninsula ledto the scissors-type closing of the Jiangxi-Anhui-Zhejiang palaeogulf during the Middle-earlyLate Proterozoic, which further influenced the Early Palaeozoic tectonic evolution of the region.     

湘西晚前寒武纪层状硅质岩的热水沉积地球化学标志及其环境意义

湘西晚前寒武纪层状硅质岩化学成分纯净,硅质矿物平均含量９５％以上。岩石富Ｆｅ、Ｍｎ,相对贫Ａｌ、Ｔｉ、Ｍｇ,富含Ｂａ、Ａｓ、Ｓｂ、Ａｇ、Ｕ等微量元素。Ｆｅ／Ｔｉ、（Ｆｅ＋Ｍｎ）／Ｔｉ、Ａｌ／（Ａｌ＋Ｆｅ＋Ｍｎ）、Ｕ／Ｔｈ比值及ＡｌＦｅＭｎ、ＦｅＭｎ（Ｎｉ＋Ｃｏ＋Ｃｕ）三角图均表明岩石为热水来源沉积岩。稀土元素总量低,Ｃｅ负异常,重稀土相对富集,显示主要为热水沉积作用的产物。δ３０Ｓｉ、δ１８Ｏ值及岩石的形成温度清楚地表明组成岩石的二氧化硅来源于热水。岩石的ＭｎＯ／ＴｉＯ２、δＣｅ及δ３０Ｓｉ值分析表明硅质岩沉积于大陆边缘斜坡半深海至大洋盆地深海环境中     

New data on geology of the Shatak Complex (western slope of the Southern Urals)

The comprehensive study of sections of the Shatak Complex has revealed that conglomerates at the base of Middle Riphean rocks are not basal but intraformational rocks. Previously described angular unconformities between shales of the Sukhin Subformation (Yusha Formation, R₁) and conglomerates of the Kuz”elga Subformation (Mashak Formation, R₂) are related to late tectonic movements. Magmatic rocks developed at the base of the Middle Riphean section are represented by sheet intrusions formed in the course of emplacement of a fluid-saturated magmatic melt into partially or completely lithified terrigenous rocks at the graben formation stage during the origination of synkinematic faults that served as magma conduits. It is inferred that distribution of provenances of clastic materials and sedimentation basins in the Burzyanian and Yurmatian should be scrutinized in the study region, because the normal regressive sequence of rocks from the uppermost Yusha Formation to the lowermost Mashak Formation, which was established in the Shatak Ridge, eliminates a clear boundary distinguished between them at present. The idea about an older age of the Mashak conglomerates is substantiated.     

The Lower Precambrian in the Structure of Paleozoids of the Subpolar Urals

Doklady Earth Sciences - Rocks of Early Precambrian age have been established in many polymetamorphic complexes of the Urals. However, there is no doubt that only two polymetamorphic complexes...     

Geochemistry of the Late Precambrian Sturt Tillite,Flinders Ranges,South Australia

Analyses of major oxides and some trace elements (Ga, Rb, Sr, and B) were carried out on 25 samples of tillite matrix materials of the major Late Precambrian glacial episode in South Australia. The results indicate the dominantly granitic nature of the source rocks and suggest deposition under marine glacial conditions.     

Late Neoproterozoic to Holocene thermal history of the Precambrian Georgetown Inlier,northeast Australia

Carboniferous‐Permian volcanic complexes and isolated patches of Upper Jurassic — Lower Cretaceous sedimentary units provide a means to qualitatively assess the exhumation history of the Georgetown Inlier since ca 350 Ma. However, it is difficult to quantify its exhumation and tectonic history for earlier times. Thermochronological methods provide a means for assessing this problem. Biotite and alkali feldspar ⁴⁰Ar/³⁹Ar and apatite fission track data from the inlier record a protracted and non‐linear cooling history since ca 750 Ma. ⁴⁰Ar/³⁹Ar ages vary from 380 to 735 Ma, apatite fission track ages vary between 132 and 258 Ma and mean track lengths vary between 10.89 and 13.11 μm. These results record up to four periods of localised accelerated cooling within the temperature range of ～320–60°C and up to ～14 km of crustal exhumation in parts of the inlier since the Neoproterozoic, depending on how the geotherm varied with time. Accelerated cooling and exhumation rates (0.19–0.05 km/10⁶ years) are observed to have occurred during the Devonian, late Carboniferous‐Permian and mid‐Cretaceous — Holocene periods. A more poorly defined Neoproterozoic cooling event was possibly a response to the separation of Laurentia and Gondwana. The inlier may also have been reactivated in response to Delamerian‐age orogenesis. The Late Palaeozoic events were associated with tectonic accretion of terranes east of the Proterozoic basement. Post mid‐Cretaceous exhumation may be a far‐field response to extensional tectonism at the southern and eastern margins of the Australian plate. The spatial variation in data from the present‐day erosion surface suggests small‐scale fault‐bounded blocks experienced variable cooling histories. This is attributed to vertical displacement of up to ～2 km on faults, including sections of the Delaney Fault, during Late Palaeozoic and mid‐Cretaceous times.     

Conditions of formation of igneous rocks in plume magmatism at the example of the western slope of the Southern Urals

This work presents new data on the conditions of formation of igneous rocks on the western slope of the Southern Urals and the adjacent part of the East European Platform. Based on the calculated P–T melting parameters of the mantle substrate, it is shown that plume magmatism leads to the formation of similar rocks (picrites and picrite-dolerites), while the genesis of them is quite different. The first type of rocks is a product of crystallization of the undifferentiated mantle-derived melt in the upper horizons of the crust; the rocks of the second type are formed as a result of magma differentiation in large intracrustal magma chambers.     

New paleomagnetic data on baltica based on upper ediacaran deposits on the western slope of the Middle Urals

The latest concepts about the Earth’s paleogeography for the period of 700–500 million years are quite contradictory. Reliable paleomagnetic data are quite scarce for the Ediacaran-Cambrian of the majority of continental plates, which means that making any reliable global paleogeographic and paleotectonic reconstructions is impossible. According to various authors, Baltica within this time, for example, could have been located at any latitudes from the South Pole to the equator. Making correct reconstructions requires new paleomagnetic data; however, almost all objects that are applicable for such studies within Baltica have already been studied. A possible solution is to study the deformed margins of the plate, in particular, the western megazone of the Middle Urals, where the lower and upper Ediacaran volcanogenic-sedimentary and sedimentary sections are known within the Kvarkushsko-Kamennogorskii anticlinorium [1, 2] (Fig. 1). This paper presents the first paleomagnetic results obtained for the sedimentary rocks of the Upper Ediacaran Chernokamenskaya suite. They are consistent with the group of six poles of the same age [3–7], by which Baltica was located at the subequatorial latitudes at the end of the Educarian.