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1.
Members Ⅰ-Ⅳ of the Wumishan Formation of the Jixian System are exposed respectively in Mt. Cuihua and Mt. Hushan in the Ming Tombs, Beijing. Black banded cherts which are extensively developed in this formation contain an abundance ofmicrofossils that are well preserved and variable in form. A study of thin sections shows that the microfossils include 10 genera, 12 species, 3 of. species, 2 indeterminate species and 1 unnamed form, of which 1 genus and 7 species are newly erected. The present assemblage is morphologically comparable to those from the Wumishan Formation in the Western Hills of Beijing, Jixian County of Tianjin and Kuancheng of Hebei Province.  相似文献   

2.
Conodont Evidence for the Age of the Panxian Fauna,Guizhou, China   总被引：1，自引：0，他引：1  
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3.
According to differences of the protolith formations, the early Precambrian strata in the northern part ofthe North China platform may be divided into the stable stratigraphic region in the west and the mobilestratigraphic region in the east. Based on unconformities, either stratiragphic or tectonic, as well as significantmetamorphic thermal events, the two regions may be stratigraphically defined as follows: 1) the middleArchaean Fuping Supergroup composed of the Chenzhuang and Wanzi Groups (stable areas), and the middleArchaean Qianxi Group (mobile area), whose upper limits are all dated at 2800 Ma; and 2) the upper ArchaeanWutai Supergroup composed of the Longquanguan, Shizui and Taihuai Groups (stable areas), and the upperArchaean Zunhua, Dantazi and Zhuzhangzi Groups (mobile areas). whose upper limits are all dated at 2500Ma. A correlation of the above-mentioned units is also made. The lower Proterozoic Hutuo Group of the sta-ble region is adjusted to comprise the Gaofan, Doucun, Dongye and Guojiazhai Groups. The upper limit of theGaofan Group is placed at 2350 Ma, Dongye 1850 Ma and Guojiazhai (the lower limit of the Changcheng Sys-tem) 1700 Ma.  相似文献   

4.
1. IntroductionThe Tarim basin, one of the most developed and important areas of marine Cretaceous-Tertiary in China except for south Tibet, is very rich in oil and gas, such as Kekeya oilfield in southwestern Tarim and Kela2 gas field in northeastern Tarim. Because of the expansion, subduction of the oceanic crust of the Tethys and the collision between the India plate and the Eurasia plate during the Cretaceous-Tertiary, the Tethys transgressed into the Tarim basin from west to east fr…  相似文献   

5.
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6.
The Huanghuachang section near Yichang, southern China meets the requirements of Global Stratotype Section and Point (GSSP) for the base of the Middle Ordovician Series and the yet-to-be-named third stage of the Ordovician System (or lower stage of Middle Ordovician Series). The conodont succession at the section is complete across the Lower to Middle Ordovician series boundary and several excellent phylogenetic lineages of Baltoniodus, Trapezognathus, Periodon, and Microzarkodina are represented. The definition of the base of the Middle Ordovician is proposed to be the first appearance datum (FAD) of Baltoniodus? triangularis in the section. It is followed closely by the FAD of Microzarkodina flabellum, which is taken as a reasonable proxy for the boundary. This level approximates the boundary between the lower and upper intervals of the Azygograptus suecicus graptolite Biozone, and nearly coincides with the base of the Belonechitina henryi chitinozoan Biozone.The proposed GSSP for the base of the international Middle Ordovician Series is located in a roadside exposure at the base of Bed (SHod) 16, 10.57 m above the base of the Dawan Formation in the measured Huanghuachang section near Yichang City, southern China. The same faunal succession is also recorded from the Chenjiahe (formerly Daping) section, 5 km to the north of the Huanghuachang section. The proposed boundary horizon can be recognized and correlated globally with high precision in both relatively shallow-water carbonate facies as well as in deep-water graptolite facies.  相似文献   

7.
Reconstructions of the Cambrian–Silurian tectonic evolution of eastern Gondwanaland, when the Australian Tasmanides and Antarctic Ross Orogen developed, rely on correlation between structural elements in SE Australia and Northern Victoria Land (NVL), Antarctica. A variety of published models exist but none completely solve the tectonic puzzle that is the Delamerian–Lachlan transition in the Tasmanides. This paper summarizes the understanding of Cambrian (Delamerian) to Silurian (Lachlan) geological evolution of the eastern Tasmanides, taking into account new deep seismic data that clarifies the geological connection between Victoria and Tasmania — the ‘Selwyn Block’ model. It evaluates previous attempts at correlation between NVL, Tasmania and Victoria, and presents a new scenario that encompasses the most robust correlations. Tasmania together with the Selwyn Block is reinterpreted as an exotic Proterozoic microcontinental block – ‘VanDieland’ – that collided into the east Gondwanaland margin south of western Victoria, and north of NVL in the Late Cambrian, perhaps terminating the Delamerian Orogeny in SE Australia. Subsequent north-east ‘tectonic escape’ of VanDieland in the Early Ordovician explains the present-day outboard position of Tasmania with respect to the rest of the Delamerian orogen, the origin of the hiatus that separates the Delamerian and Lachlan orogenic cycles in Australia, and how western Lachlan oceanic crust developed as a ‘trapped plate-segment’. The model establishes a new structural template for subsequent Lachlan Orogen development and Mesozoic Australia–Antarctica separation.  相似文献   

8.
The western segment of the East Kunlun Mountains is one of the poorly studied regions in northwestern China. Through a structural analysis of the typical sections, we have the following views: (1) There is a very well developed fault system in the western segment of the East Kunlun Mountains and thrust propagation, normal slip and decoupling are the chief deformation events in this area. (2) Although the thrusting started in the Late Carboniferous and Late Triassic-Early Jurassic, strong activity took place in the Miocene-Quaternary when the Kumkol basin was strongly downwarped. (3) The tectonic pattern of coexistence of N-directed thrust propagation and S-directed normal slip in this area is consistent with the general tectonic pattern of the northern Qinghai-Tibet plateau and also very similar to that of the Himalayan region on the southern margin of the Qinghai-Tibet plateau, but their directions between the thrust propagation are opposite and all the strong thrust propagations occurred from the Mioc  相似文献   

9.
Integrative methods of chemostratigraphy and biostratigraphy were used in the study of microtektites and moderate nickel-iridium anomaly beds in the Devonian-Carboniferous boundary beds at Huangmao (Guangxi Autonomous Region) and Muhua (Guizhou Province) in southern China. Microtektites provide evidence for meteoritic impact event(s), whereas the minerals and the chemical composition of the Ni-Ir anomaly beds likely display a submarine hydrothermal origin. It is postulated that the intensification of the rifting-hydrothermal process, and the ensuing pollution, might have been responsible for the Devonian-Carboniferous biotic crisis. This process began in the late Famennian expansa zone, lasted to the Tournaisian duplicata zone, and produced the largest manganese ore deposits of China.  相似文献   

10.
《International Geology Review》2012,54(12):1504-1520
This study presents new data relating to the tectonic evolution of the Zhonggang ocean island, within the Mesozoic Banggongco–Nujiang suture zone of northern Tibet, and discusses the implications of these data for the evolution of this region. Thirteen basalt and ten gabbro samples were collected from a sampling transect through this area; these samples have light rare earth element (LREE)-enriched chondrite-normalized REE patterns, and are enriched in highly incompatible elements, yielding primitive-mantle-normalized trace-element variation patterns that are similar to ocean island basalts (OIB). A gabbro dike intruded into basalt of the Zhonggang ocean island and was overlain by basaltic conglomerate, suggesting that this dike was formed after the basalt, but before the basaltic conglomerate. The gabbro dike yields an LA–ICP–MS zircon U–Pb age of 116.2 ± 4.1 Ma, indicating the timing of formation of the Zhonggang ocean island, and suggesting in turn that the Banggongco–Nujiang Neo-Tethys Ocean remained open at this time. These data, combined with the geological history of the region, indicates that the Banggongco–Nujiang Neo-Tethys Ocean opened between the late Permian and the Early Triassic, expanded rapidly between Late Triassic and Middle Jurassic time, and finally closed between the late Early and early Late Cretaceous.  相似文献   

11.
The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on me  相似文献   

12.
1INTRODUCTION THELATEPRECAMBRIANGRANITOIDSOFTHEARABONU BIANSHIELDINEGYPTWEREEXPOSEDBYEARLYTOMIDDLE TERTIARYUPLIFTANDENSUINGEROSIONDURINGTHEREDSEA RIFTINGEVENT(GREENBERG,1981).THEREAREANUMBER OFEFFECTIVEANDRELATIVELYSUCCESSFULSCHEMESFORTHE CLASSIFICATIONOF…  相似文献   

13.
Data on the distribution of radiolarians and planktonic and benthic foraminifers are obtained for the first time from the Alan-Kyr Section (Coniacian–Campanian), in the central regions of the Crimean Mountains. Radiolarian biostrata, previously established from Ak-Kaya Mountain (central regions of the Crimean Mountains) were traced: Alievium praegallowayi–Crucella plana (upper Coniacian–lower Santonian), Alievium gallowayi–Crucella espartoensis (upper Santonian without the topmost part), and Dictyocephalus (Dictyocryphalus) (?) legumen–Spongosaturninus parvulus (upper part of the upper Santonian). Radiolarians from the Santonian–Campanian boundary beds of the Crimean Mountains are studied for the first time, and Prunobrachium sp. ex gr. crassum–Diacanthocapsa acanthica Beds (uppermost Santonian–lower Campanian) are recognized. Bolivinoides strigillatus Beds (upper Santonian) and Stensioeina pommerana–Anomalinoides (?) insignis Beds (upper part of the upper Santonian–lower part of the lower Campanian) are recognized. Eouvigerina aspera denticulocarinata Beds (middle and upper parts of the lower Campanian) and Angulogavelinella gracilis Beds (upper part of the upper Campanian are recognized on the basis of benthic foraminifers. These beds correspond to the synchronous biostrata of the East European Platform and Mangyshlak. Marginotruncana coronata-Concavatotruncana concavata Beds (Coniacian–upper Santonian), Globotruncanita elevata Beds (terminal Santonian), and Globotruncana arca Beds (lower Campanian) are recognized on the basis of planktonic foraminifers. Radiolarian and planktonic and benthic foraminiferal data agree with one another. The position of the Santonian–Campanian boundary in the Alan-Kyr Section, which is located stratigraphically above the levels of the latest occurrence of Concavatotruncana concavata and representatives of the genus Marginotruncana, is refined, i.e., at the level of the first appearance of Globotruncana arca. A gap in the Middle Campanian–lower part of the upper Campanian is established on the basis of planktonic and benthic foraminifers. The Santonian–Campanian beds of the Alan-Kyr Section, on the basis of planktonic foraminifers and radiolarians, positively correlate with synchronous beds of the Crimean-Caucasian region, and beyond. Benthic foraminifers suggest a connection with the basins of the East European Platform.  相似文献   

14.
The paper presents original authors' data on the O, H, C, S, and Sr isotopic composition of water and sediments from the basins into which the Aral Sea split after its catastrophic shoaling: Chernyshev Bay (CB), the basin of the Great Aral in the north, Lake Tshchebas (LT), and Minor Sea (MS). The data indicate that the δ18О, δD, δ13C, and δ34S of the water correlate with the mineralization (S) of the basins (as of 2014): for CB, S = 135.6‰, δ18О = 4.8 ± 0.1‰, δD = 5 ± 2‰, δ13C (dissolved inorganic carbon, DIC) = 3.5 ± 0.1‰, δ34S = 14.5‰; for LT, S = 83.8‰, δ18О = 2.0 ± 0.1‰, δD =–13.5 ± 1.5‰, δ13C = 2.0 ± 0.1‰, δ34S = 14.2‰; and for MS, S = 9.2‰, δ18О =–2.0 ± 0.1‰, δD =–29 ± 1‰, δ13C =–0.5 ± 0.5‰, δ34S = 13.1‰. The oxygen and hydrogen isotopic composition of the groundwaters are similar to those in MS and principally different from the artesian waters fed by atmospheric precipitation. The mineralization, δ13С, and δ34S of the groundwaters broadly vary, reflecting interaction with the host rocks. The average δ13С values of the shell and detrital carbonates sampled at the modern dried off zones of the basins are similar: 0.8 ± 0.8‰ for CB, 0.8 ± 1.4‰ for LT, and –0.4 ± 0.3‰ for MS. The oxygen isotopic composition of the carbonates varies much more broadly, and the average values are as follows: 34.2 ± 0.2‰ for CB, 32.0 ± 2.2‰ for LT, and 28.2 ± 0.9‰ for MS. These values correlate with the δ18O of the water of the corresponding basins. The carbonate cement of the Late Eocene sandstone of the Chengan Formation, which makes up the wave-cut terrace at CB, has anomalously low δ13С up to –38.5‰, suggesting origin near a submarine methane seep. The δ34S of the mirabilite and gypsum (11.0 to 16.6‰) from the bottom sediments and young dried off zone also decrease from CB to MS in response to increasing content of sulfates brought by the Syr-Darya River (δ34S = 9.1 to 9.9‰) and weakening sulfate reduction. The 87Sr/86Sr ratio in the water and carbonates of the Aral basins do not differ, within the analytical error, and is 0.70914 ± 0.00003 on average. This value indicate that the dominant Sr source of the Aral Sea is Mesozoic–Cenozoic carbonate rocks. The Rb–Sr systems of the silicate component of the bottom silt (which is likely dominated by eolian sediments) of MS and LT plot on the Т = 160 ± 5 Ma, I0 = 0.7091 ± 0.0001, pseudochron. The Rb–Sr systems of CB are less ordered, and the silt is likely a mixture of eolian and alluvial sediments.  相似文献   

15.
The Chah-Bazargan gabbroic intrusions are located in the south of Sanandaj–Sirjan zone. Precise U–Pb zircon SHRIMP ages of the intrusions show magmatic ages of 170.5 ± 1.9 Ma. These intrusions consist primarily of gabbros, interspersed with lenticular bodies of anorthosite, troctolite, clinopyroxenite, and wehrlite. The lenticular bodies show gradational or sharp boundaries with the gabbros. In the gradational boundaries, gabbros are mineralogically transformed into anorthosites, wehrlites, and/or clinopyroxenites. On the other hand, where the boundaries are sharp, the mineral assemblages change abruptly. There is no obvious deformation in the intrusions. Hence, the changes in mineral compositions are interpreted as the result of crystallization processes, such as fractionation in the magma chamber. Rock types with sharp boundaries show abrupt chemical changes, but the changes exhibit the same patterns of increasing and decreasing elements, especially of rare earth elements, as the gradational boundaries. Therefore, it is possible that all parts of the intrusions were formed from the same parental magma. Parts showing signs of nonequilibrium crystallization, such as cumulate features and sub-solidification, underwent fracturing and were interspersed throughout the magma chamber by late injection pulses or mechanical movements under mush conditions. The geological and age data show that the intrusions were formed from an Al-, Sr-, Fe-enriched and K-, Nb-depleted tholeiitic magma. The magma resulted from the partial melting of a metasomatized spinel demonstrated by negative Nb, P, Hf, and Ti, and positive Ba, Sr, and U anomalies typical of subduction-related magmas.  相似文献   

16.
Seismogenesis of aftershocks occurring in the Kachchh seismic zone for more than last 10?years is investigated through modeling of fractal dimensions, b-value, seismic velocities, stress inversion, and Coulomb failure stresses, using aftershock data of the 2001 Bhuj earthquake. Three-dimensional mapping of b-values, fractal dimensions, and seismic velocities clearly delineate an area of high b-, D-, and Vp/Vs ratio values at 15?C35?km depth below the main rupture zone (MRZ) of the 2001 mainshock, which is attributed to higher material heterogeneities in the vicinity of the MRZ or deep fluid enrichment due to the release of aqueous fluid/volatile CO2 from the eclogitisation of the olivine-rich lower crustal rocks. We notice that several aftershocks are occurred near the contacts between high (mafic brittle rocks) and low velocity regions while many of the aftershocks including the 2001 Bhuj mainshock are occurred in the zones of low velocity (low dVp, low dVs and large Vp/Vs) in the 15?C35?km depth range, which are inferred to be the fractured rock matrixes filled with aqueous fluid or volatiles containing CO2. Further support for this model comes from the presence of hydrous eclogitic layer at sub-lithospheric depths (34?C42?km). The depth-wise stress inversions using the P- and T-axes data of the focal mechanisms reveal an increase in heterogeneity (i.e., misfit) with an almost N?CS ??1 orientation up to 30?km depth. Then, the misfit decreases to a minimum value in the 30?C40?km depth range, where a 60o rotation in the ??1 orientation is also noticed that can be explained in terms of the fluid enrichment in that particular layer. The modeling of Coulomb failure stress changes (??CFS) considering three tectonic faults [i.e., NWF, GF, and Allah bund fault (ABF)] and the slip distribution of the 2001 mainshock on NWF could successfully explain the occurrences of moderate size events (during 2006?C2008) in terms of increase in positive ??CFS on GF and ABF. In a nutshell, we propose that the fluid-filled mafic intrusives are acting as stress accentuators below the Kachchh seismic zone, which generate crustal earthquakes while the uninterrupted occurrence of aftershocks is triggered by stress transfer and aqueous fluid or volatile CO2 flow mechanisms. Further, our results on the 3-D crustal seismic velocity structure, focal mechanisms, and b-value mapping will form key inputs for understanding wave propagation and earthquake hazard-related risk associated with the Kachchh basin.  相似文献   

17.
International Journal of Earth Sciences - The Žermanice locality represents the best-exposed example of the meta-basaltoid/meta-gabbroic rock type of the teschenite association. It forms a...  相似文献   

18.
正The Eglab-Yetti region of southwestern Algeria is a main part of the Reguibat shield of the West African craton(WAC)which consists of Archean to Paleoprotzrozoic basement.The region hosts numerous  相似文献   

19.
In the middle and lower reaches of the Salawusu River. the Salawusu Formation regarded traditionallyas fluvio-lacustrine deposits actually includes a series of strata which mainly consist of eolian sandy depositsnamed as "Chengchuan Formation" by the authors. The eolian sand of the Chengchuan Formation and theMalan loess distributed in the upper reaches of the Salawusu River are deposits of sand and loess faciesformed by wind action during the same period. The relationship of the Chengchuan Formation and theMalan Loess with the Salawusu Formation which is really of fluvio-lacustrine deposits is that the formertwo superpose the latter. This can be demonstrated by the difference of the extinct species proportion of thefaunas in different strata. In this area. the Salawusu formed during the early period of Late Pleistocene.while the Malan Loess and the Chengchuan Formation deposited during the late period of the LatePleistocene.  相似文献   

20.
The ‘silent revolution’ is a phenomenon describing the individualistic behaviour of farmers in the adoption of intensive groundwater abstraction technologies, which in some cases has led to groundwater over-abstraction and environmental degradation in semiarid areas such as La Mancha, Spain. However, a lacuna exists as to the extent to which state politics have affected the development of groundwater abstraction technologies in Spain. With new quantitative and qualitative data from the irrigation community of Manzanares and public irrigation and colonisation plans, this report studies the adoption of groundwater abstraction technology and investigates the historical role of the state in the development of modern groundwater-fed irrigation socio-ecologies in the semiarid area of La Mancha in Spain.  相似文献   

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