共查询到20条相似文献，搜索用时 31 毫秒
1.
2.
东昆仑南带加嗡门地区碳酸盐岩地层中发现的中元古代晚期-新元古代早期叠层石组合以大型锥叠层石及其相关的分子Conophyton garganicus var. inkeni,C. cf. ressoti Menchikov, Jacutophyton f. 和Conicodomenia cf. longotenuia等最丰富, 并与Baicalia共生, 故可视之为Conophyton-Baicalia组合.这叠层石组合可以与天山、华北等地蓟县系中部-青白口系中部叠层石组合对比,尤其酷似于天山地区蓟县系的爱尔基干组合和华北蓟县系的闪坡岭叠层石组合,而显著有别于华南地块.它还可以与南乌拉尔、西伯利亚、北美、北非和阿拉斯加半岛等地区的中里菲界上部--上里菲界下部层位中的叠层石组合对比.加嗡门叠层石组合的时限为距今1 300～850 Ma,大致为蓟县纪中期-青白口纪中期或中里菲晚期-晚里菲早期.东昆仑南带存在前寒武纪微地块,当时此微地块的古地理和古环境与天山、华北、西伯利亚和阿拉斯加半岛等地区的前寒武纪地块相似,均位于低纬度区,其上均广泛发育适宜叠层石繁育的温暖陆表海,它们可能共同处于罗迪尼亚超大陆的低纬度大陆边缘部位,与华南地块的不同.这对本区和东昆仑地层和大地构造研究,以及对罗迪尼亚超大陆重建提供了新的古生物约束. 相似文献
3.
3D models of apparent magnetization and density of rocks allow us to provide insights into the deep structure of the Volga-Ural, Pericaspian, and Fore-Caucasus petroliferous basins. In the Volga-Ural Basin, some Riphean rifts reveal close spatial relations to Paleoproterozoic linear zones, presumably of the rift nature as well. The structure of the Paleoproterozoic Toropets-Serdobsk Belt is interpreted in detail. Rocks with petrophysical properties inherent to basic volcanics are established in the pre-Paleozoic basement of the marginal zone of the Pericaspian Basin. These rocks locally spread beyond the boundary escarpment and may be regarded as a part of the Riphean plume-related basaltic province. It is shown that the Pericaspian Basin was formed on the place of a triple junction of Riphean rifts: the Sarpa and Central Pericaspian oceanic branches and the continental branch of the Pachelma Aulacogen. The drastically different petrophysical properties of the basement beneath Baltica and the Astrakhan Arch indicate that this arch is an element of the large terrane that was attached to Baltica in the Vendian. The suture along which the Astrachan Terrane is conjugated with the basement of the central and southern segments of the Karpinsky Ridge is traced beneath the Paleozoic complex. A system of northwest-verging thrust faults formed during the collision between Scythia and Eurasia is mapped in the basement of the junction zone between the Karpinsky Ridge and Scythian Platform (Terrane). According to geological data, this event took place in the Early Paleozoic. 相似文献
4.
M. E. Raaben 《Stratigraphy and Geological Correlation》2007,15(1):30-40
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. 相似文献
5.
1 Introduction The stromatolites of the Jiawengmen area in the southern belt of the Eastern Kunlun orogen were initially interpreted as vortex structures by the Regional Geological Survey Team, Qinghai Bureau of Geology and Mineral Resources in 1973; these samples were then identified as algal fossils of Sinian age by the Nanjing Institute of Geology and Paleontology (Qinghai Bureau of Geology and Mineral Resources, 1973). In 1994, Chen and Luo (1998) discovered some stromatolites, i… 相似文献
6.
Most of the Proterozoic carbonate formations of Peninsular India, and the so-called ‘unfossiliferous’ carbonates of the Sub- and Lesser Himalaya, contain abundant columnar and branching stromatolites. Systematic study of some of these stromatolites supports their use in biostratigraphy and reveals their Riphean—Proterozoic affinity. A synthesis of stromatolite studies in India has been attempted. A biostratigraphic correlation of the stromatolitic formations of Sub- and Lesser Himalaya extending from Jammu in the west to Buxa in the eastern Himalaya has been established. A probable correlation of those of Peninsular India has been indicated, based on available information. A bibliography on Indian stromatolites is appended. 相似文献
7.
I. K. Kozakov E. B. Sal’nikova V. V. Yarmolyuk A. M. Kozlovsky V. P. Kovach P. Ya. Azimov I. V. Anisimova V. I. Lebedev G. Enjin Ch. Erdenejargal Yu. V. Plotkina A. M. Fedoseenko S. Z. Yakovleva 《Geotectonics》2012,46(1):16-36
Fragments of the crystalline complexes where Vendian metamorphism of moderate and elevated pressure predated Early Paleozoic metamorphism have been established in the accretionary-collisional domain of the eastern segment of the Central Asian Foldbelt (Early Caledonian superterrane of Central Asia). The geodynamic setting of the Vendian (??560?C570 Ma) South Hangay metamorphic belt located in the junction zone of the Baydrag Block and the Late Riphean (??665 Ma) ophiolite complex of the Bayanhongor Zone is considered. The origination of this belt was related to the formation of the convergent boundary in the framework of the Zabhan microcontinent about 570 Ma ago. At the same time, an island-arc complex was formed in the paleo-oceanic domain. Metamorphism of elevated pressure indicates that Vendian structures with sufficiently thick continental crust were formed in the framework of the continental blocks. Vendian metamorphism is also established in the Tuva-Mongolia Massif and the Kan Block of the Eastern Sayan. These data show that the Late Baikalian stage predated the evolution of the Early Caledonian superterrane of Central Asia. The development of its accretionary-collisional structure was accompanied by Late Cambrian-Early Ordovician low-pressure regional metamorphism. Granulite-facies conditions were reached only at the deep levels of the accretionary-collisional edifice. The outcrops of crystalline complexes in the southern framework of the Caledonian paleocontinent are regarded as fragments of the Early Paleozoic Central Mongolian metamorphic belt. 相似文献
8.
I. K. Kozakov E. B. Sal’nikova V. P. Kovach V. V. Yarmolyuk I. V. Anisimova A. M. Kozlovskii Yu. V. Plotkina T. A. Myskova A. M. Fedoseenko S. Z. Yakovleva A. M. Sugorakova 《Stratigraphy and Geological Correlation》2008,16(4):360-382
Granitoids and metamorphic rocks of the Baidarik basement block of the Dzabkhan microcontinent are studied in terms of geology, geochronology (U-Pb dating of zircon microfractions and individual grains) and Nd isotopic-geochemical systematics. As is established, the formation history of metamorphic belt (disthene-sillimanite facies) in junction zone of the Baidarik block and Bayankhongor zone of the Late Riphean (～665 Ma) ophiolite association characterizes development of the Vendian (～560–570 Ma) active continental margin. The high-P metamorphic rocks of that time span evidence formation of structures with the Earth’s crust of considerable thickness. In Central Asia, events of the Vendian low-gradient metamorphism are established also in the Tuva-Mongolian massif, Kan block of the East Sayan Mountains, and South Chuya inlier of the Caledonides in the Altai Mountains. Based on these data, it is possible to distinguish the Late Baikalian stage in development of the Early Caledonian superterrane of Central Asia, which antedated the subsequent evolution of this structure during the Late Cambrian-Ordovician. The high-gradient metamorphism that affected most intensively the southeastern part of the Baidarik block can be correlated with the Early Paleozoic (525–540 Ma) evolution of active continental margin and associated development of the Vendian oceanic basins and island arcs of the Ozernaya zone. 相似文献
9.
Kheraskova T. N. Volozh Yu. A. Vorontsov A. K. Pevzner L. A. Sychkin N. I. 《Lithology and Mineral Resources》2002,37(1):68-81
Recent lithological and geophysical studies of Riphean and Lower Vendian sedimentary rocks in the Kresttsy and Mid-Russian (Soligalich) aulacogens resulted in the recognition of four stages in the evolution of the East European Platform in the Late Proterozoic: (1) late Early Proterozoic–Early Riphean stage (formation of the protoplatform cover); (2) Middle Riphean stage (rifting only at platform margins); (3) late Middle Riphean–initial late Riphean stage (formation of the paleoplatform cover related to the existence of the epi-Grenville Rodinia supercontinent, which united all continents of the Earth at that time); (4) latest Riphean–early Vendian stage (rifting and origination of the Central Russian aulacogen system during the breakup of Rodinia and Cadomian orogeny. 相似文献
10.
The early Vendian microfossils first found in the Russian plate: Taxonomic composition and biostratigraphic significance 总被引：1，自引：0，他引：1
A. F. Veis N. G. Vorob’eva E. Yu. Golubkova 《Stratigraphy and Geological Correlation》2006,14(4):368-385
The microfossils studied are discovered for the first time in the Riphean-Lower Vendian deposits, which have been recovered in 2002 by the Kel’tminskaya-1 deep parametric borehole in the Vychegda depression, the northeastern margin of the East European platform. The sampled interval of core section (4825–2347 m) consists of three units: the lower (depth range 4825–3995 m, 5 samples) and middle (depth range 3687–2961 m, 17 samples) carbonate successions overlain by sandstone-siltstone beds (depth range 2907–2347 m, 58 samples). Based on lithological criteria and/or composition of stromatolites, the carbonate successions are correlative with the Yshkemes and Vapol formations of the Upper Riphean of the Timan ridge succession, while the overlying, mostly siltstone succession was correlated with the Vychegda Formation of the southern Timan according to similarity in lithology and mineral composition. Microfossils found in 56 samples occur at 20 microphytological levels and represent different microbiotas. The Yshkemes and Vapol microbiotas of low diversity characterize six lower levels and represent one assemblage, while the diverse and abundant Vychegda microbiota typical of fourteen upper levels is divisible into three successive assemblages. The Vapol stromatolites Inzeria djejimii and Poludia polymorpha along with giant Chuaria and Navifusa present in the Yshkemes-Vapol assemblage suggest that their host deposits correspond to the upper Upper Riphean. The Vychegda assemblages, each of peculiar biostratigraphic specifics and unique in composition, consist of different morphotypes, primarily of large acanthomorphic acritarchs Cavaspina, Polyhedrosphaeridium, Cymatiosphaeridium, Asterocapsoides, and Tanarium, which are known in Scandinavia, Siberia, China, Australia, and India only in the Lower Vendian microbiotas of the Perthatataka type. The comprehensive microphytological characterization of the Lower Vendian in the Vychegda depression and earlier data on the Middle-Upper Riphean microbiotas from the adjacent Mezen syneclise enable a high-resolution biostratigraphic subdivision of the Riphean and Vendian successions in the vast region under consideration. 相似文献
11.
J. William Schopf 《Precambrian Research》1977,5(2):143-173
Diverse, cellularly preserved microbial communities are now known from stromatolitic sediments of at least twenty-eight Precambrian formations. These fossiliferous deposits, principally cherts and cherty portions of carbonate units, range in age from Early Proterozoic (Transvaal Dolomite, ca. 2250 Ma old) to Vendian (Chichkan Formation, ca. 650 Ma old) and include units from Australia, India, Canada, South Africa, Greenland, the United States and the Soviet Union. More than three-quarters of these microbiotas have been discovered since 1970. Although few, therefore, have as yet been studied in detail, virtually all of the assemblages are known to be dominated by prokaryotic (bacterial and blue-green algal) microorganisms and to contain three major categories of microfossils: spheroidal unicells, cylindrical tube-like sheaths, and cellular trichomic filaments. Analyses of data now available (including measurements of more than 7800 fossil unicells) indicate that each of these three types of microfossils exhibited a gradual, but marked, increase in mean diameter and size range during the Proterozoic and that taxonomic diversity apparently also increased, especially beginning about 1400 Ma ago. Thus, it now seems evident that (i) the microbial components of Proterozoic stomatolitic assemblages have varied systematically as a function of geologic age and that (ii) such communities are both more abundant and more widespread than had previously been recognized. These observations augur well for the future use of such assemblages in Precambrian biostratigraphy. At present, however, data are sufficient to warrant the provisional establishment of only a few microfossil-based subdivisions of the Proterozoic. Such zones, necessarily relatively long-ranging, are here tentatively defined; it is of interest to note that boundaries between certain of these microfossil-based subdivisions appear to coincide, at least approximately, with previously suggested stromatolite-based boundaries. To some extent, therefore, results of this study seem consistent with, and may be supportive of, the concept of stromatolite-based biostratigraphy. At the same time, however, the study seems to indicate that stromatolites of markedly differing age, whether of similar or of dissimilar morphology, were probably formed by distinctly differing microbiotas. Data are as yet insufficient to indicate whether differing types of coetaneous, stratigraphically useful, stromatolites were formed by differing microbial communities and two what extent the “evolution” of stromatolite morphology was a result of the biologic evolution of stromatolite-building microorganisms. There is thus continued need for investigation of the potential biostratigraphic usefulness of stromatolitic microbiotas and, especially, for more effective integration of results of such studies with those available from studies of stromatolites without preserved microbiotas and from studies of the acritarchs preserved in Proterozoic shales. 相似文献
12.
Stromatolite morphology is usually controlled by a number of biological and environmental factors. In the south‐eastern part of the Korean Peninsula, three stromatolite units of the Cretaceous Sinyangdong Formation have been studied with regard to the effect of diagenesis on their morphology. Here, it is proposed that subaerial exposure and meteoric diagenesis are the most significant factors in shaping the stromatolites of the Cretaceous Sinyangdong Formation. Most previous palaeontological and sedimentological studies on stromatolites have concentrated on the environmental and biogenic controls on stromatolite morphology. These include extrinsic factors such as sedimentation rates or current velocities. The main controlling factor on the morphology of the stromatolites in the Sinyangdong Formation is apparently transient subaerial exposure and related meteoric diagenesis. Textural examination of stromatolite samples from three stratigraphic horizons shows a characteristic repetitive pattern of cycles with gradual transition from fibrous calcite to micrite layers, reflecting changes in the hydrological cycle of the lake in which the stromatolites grew. Stromatolite growth was terminated by corroded surfaces indicative of subaerial exposure related to a fall in lake level. The growth pattern of the stromatolites was mostly determined by the morphology of the corroded substrates during subaerial exposure. Furthermore, the internal stromatolite structure was strongly modified by the process of leaching. As a result, growth forms mostly changed from stratiform to columnar mesostructure. This study strongly implies that diagenesis could make a very significant influence on the morphogenesis of lacustrine stromatolites in the geological past. 相似文献
13.
A biostratigraphic model of the temporal distribution of distinctive Proterozoic microfossil assemblages is suggested, based on studies of upper Precambrian chert-embedded and compression-preserved organic-walled microfossils from the reference sections of Eurasia, North America and Australia. Microfossils from 2.0 to 0.542 Ga can be divided into seven successive informal global units which can be compared to standard units of the International and Russian time scales. Each unit is characterized by a particular association of taxa, typified by the fossil assemblage that gives it its name. These form broad biostratigraphic units comparable to assemblage zones of Phanerozoic successions; in general (but with minor differences) they correspond to chronostratigraphic units accepted by the Internal Commission on Stratigraphy. The units are: (1) Labradorian, the upper part of the Paleoproterozoic (Orosirian and Statherian), 2.0–1.65 Ga; (2) Anabarian, lower Mesoproterozoic (Calymmian–Ectasian)/Lower Riphean–lower Middle Riphean, 1.65–1.2 Ga; (3) Turukhanian, upper Mesoproterozoic (Stenian)/upper Middle Riphean, 1.2–1.03 Ga; (4) Uchuromayan, lower Neoproterozoic (late Stenian–Tonian)/lower Upper Riphean, 1.03–0.85 Ga; (5) Yuzhnouralian, upper Neoproterozoic (Cryogenian)/upper Upper Riphean, 0.85–0.63 Ga; (6) Amadeusian, lower Ediacaran/lower Vendian, 0.63–0.55 Ga; (7) Belomorian, upper Ediacaran/upper Vendian, 0.55–0.542 Ga. 相似文献
14.
五台山古元古代巨型叠层石的结构特征及成因意义 总被引：1，自引：0，他引：1
山西省五台山地区的古元古代滹沱群地层中发育大量各种形态和大小的叠层石,最近在东冶亚群地层中发现体量巨大的叠层石。本文在对其进行形态学分析、显微结构分析、地质剖面实测以及生长环境特征分析研究后认为,这一宏观上的穹窿形叠层石是由柱状叠层石组成的生物岩礁,柱体在底质基础上放射状生长,其表面圆形、长条形的凸起为叠层石柱体顶部横断面及斜切面形态。通过标本切片,镜下观察到组成柱体并充填柱间的均为泥晶方解石,并发现纤细的丝状微生物遗迹,这些丝状体相互交织构成暗层的重要组分。叠层石体量巨大,需要较长时间内相对稳定的深水环境;泥晶方解石结晶较好,指示水动力条件相对较弱、沉积速率较快的温暖浅海环境,可能形成于潮下带。 相似文献
15.
K. E. Degtyarev 《Geotectonics》2011,45(1):23-50
The extended Saryarka and Shyngyz-North Tien Shan volcanic belts that underwent secondary deformation are traced in the Caledonides
of Kazakhstan and the North Tien Shan. These belts are composed of igneous rocks pertaining to Early Paleozoic island-arc
systems of various types and the conjugated basins with oceanic crust. The Saryarka volcanic belt has a complex fold-nappe
structure formed in the middle Arenigian-middle Llanvirnian as a result of the tectonic juxtaposition of Early-Middle Cambrian
and Late Cambrian-Early Ordovician complexes of ensimatic island arcs and basins with oceanic crust. The Shyngyz-North Tien
Shan volcanic belt is characterized by a rather simple fold structure and consists of Middle-Late Ordovician volcanic and
plutonic associations of ensialic island arcs developing on heterogeneous basement, which is composed of complexes belonging
to the Saryarka belt and Precambrian sialic massifs. The structure and isotopic composition of the Paleozoic igneous complexes
provide evidence for the heterogeneous structure of the continental crust in various segments of the Kazakh Caledonides. The
upper crust of the Shyngyz segment consists of Early Paleozoic island-arc complexes and basins with oceanic crust related
to the Saryarka and Shyngyz-North Tien Shan volcanic belts in combination with Middle and Late Paleozoic continental igneous
rocks. The deep crustal units of this segment are dominated by mafic rocks of Early Paleozoic suprasubduction complexes. The
upper continental crust of the Stepnyak segment is composed of Middle-Late Ordovician island-arc complexes of the Shyngyz-North
Tien Shan volcanic belt and Early Ordovician rift-related volcanics. The middle crustal units are composed of Riphean, Paleoproterozoic,
and probably Archean sialic rocks, whereas the lower crustal units are composed of Neoproterozoic mafic rocks. 相似文献
16.
I.V. Gordienko A.N. Bulgatov S.V. Ruzhentsev O.R. Minina V.S. Klimuk L.I. Vetluzhskikh G.E. Nekrasov N.I. Lastochkin V.S. Sitnikova D.V. Metelkin T.A. Goneger E.N. Lepekhina 《Russian Geology and Geophysics》2010,51(5):461-481
New structural, petrological, chemical, isotope, and paleomagnetic data have provided clues to the Late Riphean–Paleozoic history of the Uda–Vitim island arc system (UVIAS) in the Transbaikalian sector of the Paleoasian ocean, as part of the Transbaikalian zone of Paleozoids. The island arc system consists of three units corresponding to main evolution stages: (i) Upper Riphean (Late Baikalian), (ii) Vendian–Lower Paleozoic (Caledonian), and (iii) Middle–Upper Paleozoic (Hercynian). The earliest stage produced the base of the system composed of Late Riphean ophiolite (971–892 Ma, U-Pb) and volcanic (837–789 Ma, U-Pb) and sedimentary rocks (hemipelagic siliceous sediments and dolerite sills) which represent the Barguzin–Vitim oceanic basin and the Kelyana island arc. The main event of the second stage was the formation of the large UVIAS structure (over 150,000 km2) which comprised the Transbaikalian oceanic basin, the forearc and backarc basins, and the volcanic arc itself, and consisted of many volcanic-tectonic units exceeding 100 km2 in area (Eravna, Oldynda, Abaga, etc.). Lithology, stratigraphy, major–element compositions, and isotope ages of Vendian–Cambrian volcanic rocks and associated sediments indicate strong differentiation of calc-alkaline series and the origin of the island arc system upon oceanic crust, in a setting similar to that of the today’s Kuriles–Kamchatka island arc system. The Middle–Upper Paleozoic stage completed the long UVIAS history and left its imprint in sedimentary and volcanic rocks in superposed trough basins. The rocks were studied in terms of their biostratigraphic and isotope age constraints, as well as major- and trace-element compositions, and were interpreted as products of weathering and tectonic-magmatic rework of the UVIAS units. 相似文献
17.
系统性地对湖北松滋地区下奥陶统叠层石特征进行的详细研究。结果显示,叠层石在研究区下奥陶统南津关组、分乡组和红花园组均有分布,在纵向上具有规模、厚度和数量逐渐减小的特征,横向上叠层石类型也发生有规律的变化,由水平层状、波状逐渐变为柱状的类型。新发现并命名了两种叠层石类型,即凝块状叠层石和双锥柱状叠层石。根据几何形态特征,可以将研究区的叠层石分为层状、波状、柱状、丘状以及凝块状五种类型。在对各类型叠层石的沉积特征进行详细阐述基础上,根据叠层石发育的形态类型,结合不同类型叠层石内部的岩性、微相及显微特征,对研究区各类叠层石沉积环境进行了分析,并总结了研究区叠层石的沉积模式。根据中奥陶世初期后生动物的大量增加与叠层石突然减少的对应关系,结合研究区叠层石中发现大量后生底栖食草腹足类Ecculiomphalus化石等现象,认为叠层石的逐渐减少、衰退与后生动物丰度增加有一定关系,食草动物不仅啃食了形成叠层石的菌藻类微生物,造成叠层石数量的不断减少,而且破坏了叠层石的生长状态,并形成了独具研究区特征的凝块状叠层石。此外,研究认为,中奥陶世开始,海平面的快速上升也是研究区叠层石减少直至消失的原因之一。 相似文献
18.
PETER N. SOUTHGATE 《Sedimentology》1989,36(2):323-339
Stromatolite biostromes and bioherms in the lower two units of the Late Proterozoic Loves Creek Member of the Bitter Springs Formation represent shallowing upward and deepening upward sequences. In the central unit stromatolite form is governed by relative position in an asymmetric shallowing upward sequence. Ooid and/or peloid-intraclast grainstones and small, irregular bulbous and columnar stromatolites characterize the basal, transgressive portion of cycles. Domal, columnar and stratiform stromatolites comprise the bulk of the cycle. These forms accreted in a gradually shallowing epeiric sea. Domal stromatolites predominate in the deeper parts of cycles. Here synoptic relief gradually increases upwards. Columnar and stratiform stromatolites predominate in the shallower parts of cycles, where synoptic relief rapidly diminishes upwards. In thin-bedded dolo-mudstones at the tops of cycles the co-occurrence of desiccation cracks, tepee structures, scalloped dissolution surfaces, gypsum moulds and anhydrite nodule pseudomorphs provides evidence for subaerial exposure. In contrast, stromatolites in a unit at the base of the Loves Creek Member accreted during a gradual rise in sealevel. Stratiform, columnar and domal stromatolitic building blocks of the shallowing upward cycle are present in this deepening sequence, but only the lower half of the shallowing upward cycle is represented. Synoptic relief of the stromatolitic laminae gradually increases upward throughout the basal stromatolitic unit. Recognition of a deepening upward stromatolite sequence at the base of the Loves Creek Member, and a disconformity surface between this sequence and the underlying Gillen Member, permits palaeoenvironmental re-interpretation of the Loves Creek Member as a single ‘large scale’ sea-level cycle. 相似文献
19.
20.
Based on the LA-ICP-MS data, detrital zircons from the tillite-type conglomerates of the Tanin Formation (Serebryanka Group)
on the western slope of the Central Urals include approximately equal proportions of crystals with Neoarchean and Paleoproterozoic
U-Pb ages. Therefore, we can assume that crystalline rocks of the basement beneath the eastern part of the East European Craton
served as a provenance for aluminosilicate clastics in the initial Serebryanka period. Detrital zircons from sandstones of
the Kernos Formation have the Meso-Neoarchean (∼15%), Paleoproterozoic (∼60%), and Mesoproterozoic (∼26%) age. Comparison
of the obtained data with the results of the study of detrital zircons from Riphean and Vendian sandstones of the Southern
Urals shows that the Riphean and Lower Vendian rocks are mainly represented by erosional products of Middle and Upper Paleoproterozoic
crystalline rocks that constitute the basement of the East European Craton. In addition, a notable role belonged to older
(Lower Proterozoic, Neoarchean and Mesoarchean) rock associations during the formation of the Serebryanka Group. The terminal
Serebryanka time (Kernos Age) differed from its initial stage (Tanin Age) by the appearance of Mesoproterozoic complexes in
provenances. According to available data, these complexes played an insignificant role in the formation of Riphean-Vendian
rocks in the neighboring South Uralian segment. This implies a spatiotemporal diversity of clastic material sources for Upper
Precambrian rocks in the western megazone of the Southern and Central Urals. 相似文献