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1.
In this paper we discuss the timing of final closure of the Paleo-Asian Ocean based on the field investigations of the Carboniferous–Permian stratigraphic sequences and sedimentary environments in southeastern Inner Mongolia combined with the geology of its neighboring areas. Studies show that during the Carboniferous–Permian in the eastern segment of the Tianshan-Hinggan Orogenic System, there was a giant ENE–NE-trending littoral-neritic to continental sedimentary basin, starting in the west from Ejinqi eastwards through southeastern Inner Mongolia into Jilin and Heilongjiang. The distribution of the Lower Carboniferous in the vast area is sparse. The Late Carboniferous or Permian volcanic-sedimentary rocks always unconformably overlie the Devonian or older units. The Upper Carboniferous–Middle Permian is dominated by littoral-neritic deposits and the Upper Permian, by continental deposits. The Late Carboniferous–Permian has no trace of subduction-collision orogeny, implying the basin gradually disappeared by shrinking and shallowing. In addition, it is of interest to note that the Ondor Sum and Hegenshan ophiolitic mélanges were formed in the pre-Late Silurian and pre-Late Devonian respectively, and the Solonker ophiolitic mélange formed in the pre-Late Carboniferous. All the evidence indicates that the eastern segment of the Paleo-Asian Ocean had closed before the Late Carboniferous, and most likely before the latest Devonian (Famennian).  相似文献   

2.
A great number of magmatic Cu-Ni deposits(including Kalatongke in Xinjiang and Hongqiling in Jilin) are distributed over a distance of almost 3000 km across the Tianshan-Xingmeng Orogenic Belt, from Tianshan Mountains in Xinjiang in the west, to Jilin in eastern China in the east. These deposits were formed during a range of magmatic episodes from the Devonian to the Triassic. Significant magmatic Cu-Ni-Co-PGE deposits were formed from the Devonian period in the Nalati arc(e.g. Jingbulake Cu-Ni in Xinjiang), Carboniferous period in the Puerjin-Ertai arc(e.g. Kalatongke Cu-Ni-Co-PGE in Xinjiang), Carboniferous period in the Dananhu-Touquan arc(e.g. Huangshandong, Xiangshan and Tulaergen in estern Tianshan, Xinjiang) to Triassic period in the Hulan arc(e.g. Hongqiling Cu-Ni in Jilin). In addition to the overall tectonic, geologic and distribution of magmatic Cu-Ni deposits in the Tianshan-Xingmeng Orogenic Belt, the metallogenic setting, deposit geology and mineralization characteristics of each deposit mentioned above are summarized in this paper. Geochronologic data of Cu-Ni deposits indicate that, from west to east, the metallogenic ages in the Tianshan-Xingmeng Orogenic Belt changed with time, namely, from the Late Caledonian(～440 Ma), through the Late Hercynian(300–265 Ma) to the Late Indosinian(225–200 Ma). Such variation could reflect a gradual scissor type closure of the paleo Asian ocean between the Siberia Craton and the North China Craton from west to east.  相似文献   

3.
Two Upper Devonian to Lower Carboniferous sections, namely the Bulongguoer and Haer(Gennaren area) in the Junggar Basin, Central Asian Orogenic Belt, in northwestern China were examined with regard to ichnology and palynology. The deposits of the Hongguleleng Formation and Namu Member of the Heishantou Formation, respectively, are mostly unbioturbated or poorly bioturbated, with poorly diversified trace fossils, which indicate unfavourable conditions for the burrowing benthic community during the Late Devonian and Early Carboniferous. The main factor governing the growth of the bioturbating population was the rapid sedimentation of fine-grained, volcanic material documented as tempestites, which buried the benthic fauna. In the Bulongguoer section, the presence of miospores Teichertospora torquata and Grandispora gracilis enabled identification of the broad Teichertospora torquata–Grandispora gracilis Miospore Zone from the transitional Frasnian/Famennian interval. More accurate identification of palynostratigraphical levels(DE and CZ Miospore zones) is only tentative. On the basis of palynofacies analysis, samples from the lower Bulongguoer section indicate deposition in more proximal conditions, whereas samples from the top of the section indicate deposition in a more distal environment. In the Haer section, only a general biostratigraphic indication for the Tournaisian was possible, owing to poor preservation of organic matter.  相似文献   

4.
Abstract: The Caiziyan Middle and Upper Devonian boundary section is located approximately 30 km northeast of Guilin. It hosts relatively abundant benthic and common–rare pelagic fossils, including brachiopods, corals, tentaculites, and conodonts, which may serve as a better suitable section for pelagic and neritic stratigraphic correlation. In this section, 10 “standard” conodont zones are recognized across the Givetian–Frasnian boundary, including, in descending order, the Lower hassi Zone, punctata Zone, transitans Zone, the Upper falsiovalis Zone, the Lower falsiovalis Zone, disparilis Zone, the Upper hermanni–cristatus Zone, the Lower hermanni–cristatus Zone, the Upper varcus Zone, and the Middle varcus Zone, all of which are defined by the first occurrence of their defining conodont species. The Middle–Upper Devonian (Givetian–Frasnian) boundary is defined by the first occurrence of Ancyrodella pristina in accordance with the Global Stratotype Section and Point (GSSP), which is assigned at 6.2m above the base of bed 19 in the Caiziyan section.  相似文献   

5.
The Central Asian metallogenic domain (CAMD) is a multi-core metallogenic system controlled by boundary strike-slip fault systems. The Balkhash metallogenic belt in Kazakhstan, in which occur many large and super-large porphyritic Cu–Mo deposits and some quartz vein- and greisen-type W–Mo deposits, is a well-known porphyritic Cu–Mo metallogenic belt in the CAMD. In this paper 11 molybdenite samples from the western segment of the Balkhash metallogenic belt are selected for Re–Os compositional analyses and Re–Os isotopic dating. Molybdenites from the Borly porphyry Cu deposit and the three quartz vein-greisen W–Mo deposits—East Kounrad, Akshatau and Zhanet—all have relatively high Re contents (2712–2772 μg/g for Borly and 2.267–31.50 μg/g for the other three W–Mo deposits), and lower common Os contents (0.670–2.696 ng/g for Borly and 0.0051–0.056 ng/g for the other three). The molybdenites from the Borly porphyry Cu–Mo deposit and the East Kounrad, Zhanet, and Akshatau quartz vein- and greisen-type W–Mo deposits give average model Re–Os ages of 315.9 Ma, 298.0 Ma, 295.0 Ma, and 289.3 Ma respectively. Meanwhile, molybdenites from the East Kounrad, Zhanet, and Akshatau W–Mo deposits give a Re–Os isochron age of 297.9 Ma, with an MSWD value of 0.97. Re–Os dating of the molybdenites indicates that Cu–W–Mo metallogenesis in the western Balkhash metallogenic belt occurred during Late Carboniferous to Early Permian (315.9–289.3 Ma), while the porphyry Cu–Mo deposits formed at 316 Ma, and the quartz vein-greisen W–Mo deposits formed at 298 Ma. The Re–Os model and isochron ages thus suggest that Late Carboniferous porphyry granitoid and pegmatite magmatism took place during the late Hercynian movement. Compared to the Junggar-East Tianshan porphyry Cu metallogenic belt in northwestern China, the formation of the Cu–Mo metallogenesis in the Balkhash metallogenic belt occurred between that of the Tuwu-Yandong in East Tianshan and the Baogutu porphyry Cu deposits in West Junggar. Collectively, the large-scale Late Carboniferous porphyry Cu–Mo metallogenesis in the Central Asian metallogenic domain is related to Hercynian tectono-magmatic activities.  相似文献   

6.
The Daposhang section at Muhua, Changshun. Guizhou. is an excellent and attractive DevonianCarboniferous boundary section. The transitional beds between the Devonian and Carboniferous of the sectionare continuous and well exposed. belonging to the deep-water basin facies Abundant fossil groups have beendiscovered from this section: conodonts. ammonoids. trilobites. ostracods. vertebrate microfossils and so on.So far as known. it has the most continuous and complete conodont zonation for the Devonian-Carboniferousboundary beds in the world. It is especially worth pointing out that both typical Siponodella pracsulcata andthe transitional forms between S. praesulcata and S. sulcata have been found from the upper pracsulcata Zoneof the Daposhang section. Evidently. we can not only prove the actual existence of the evolutionary lineagefrom S. praesulcata to S. sulcata, but also exactly define the level of the Devonian-Carboniferous boundary. Inthis paper. the development of the Devonian-Carboniferous boundary beds at the Daposhang section is dealtwith and the section is compared with the Muhua section and the Nanbiancun section which are the candidatesfor the Devonian-Carboniferous boundary stratotype. In the authous opinion the Daposhang section is obvi-ously better than the Muhua and the Nanbiancun sections. hence it can be recommended as one of the candi-dates for the international Devonian-Carboniferous boundary stratotype.  相似文献   

7.
The research on Paleozoic tectonics and endogenic metallogeny in the Tianshan-Altay region of Central Asia is an important and significant project. The Altay region, as a collision zone of the Early Paleozoic(500–397 Ma), and the Tianshan region, as a collision zone of the early period in the Late Paleozoic(Late Devonian-Early Carboniferous, 385–323 Ma), are all the result of nearly N-S trending shortening and collision(according to recent magnetic orientation). In the Late Devonian-Early Carboniferous period(385–323 Ma), regional NW trending faults displayed features of dextral strike-slip motion in the Altay and Junggar regions. In the Tianshan region, nearly EW-trending regional faults are motions of the thrusts. However, in the Late Carboniferous-Early Permian period(323–260 Ma), influenced by the long-distance effect induced from the Ural collision zone, those areas suffered weaker eastward compression, the existing NW trending faults converted into sinistral strike-slip in the Altay and Junggar regions, and the existing nearly E-W trending faults transferred into dextral strike-slip faults in the Tianshan region. The Rocks of those regions in the Late Carboniferous-Early Permian period(323–260 Ma) were moderately ruptured to a certain tension-shear, and thus formed a number of world famous giant endogenic metal ore deposits in the Tianshan-Altay region. As to the Central Asian continent, the most powerful collision period may not coincide with the most favorable endogenic metallogenic period. It should be treated to "the orogenic metallogeny hypothesis" with caution in that region.  相似文献   

8.
Late Paleozoic supra-subduction zone(SSZ)-type ophiolites and intra-oceanic arc igneous petrotectonic assemblages are developed in the Erenhot-Hegenshan suture zone(EHSZ)in the eastern part of the Central Asian Orogenic Belt(CAOB).which contains information about the Late Paleozoic tectonic evolution of the Paleo-Asian Ocean(PAO)in the eastern CAOB.However,there are two main views and associated controversies about the closure time of the PAO in the eastern CAOB,which are“collision suture from Late Devonian to Early Carboniferous”and“final suture from Late Permian to Early Triassic”.  相似文献   

9.
The age of the Yukiang (Yujiang) Formation has been shrouded in controversy for more than 75 years. New investigation at the Liujing section, Hengxian County, Guangxi, has revealed a conodont sequence assignable to two Early Devonian conodont zonations: the Eognathodus kindlei?–Polygnathus pireneae Zone and the Polygnathus nothoperbonus Zone from oldest to youngest. The Gaoling and Mahuangling members of the Nahkaoling (Nagaoling) Formation and the overlying Xiayiling Member and lower part of the Shizhou Member of the Yukiang Formation are proven to belong to the Pragian Eognathodus kindlei?–Polygnathus pireneae Zone. The co-occurrence of Polygnathus pireneae and Pol. sokolovi in the lower part of the Shizhou Member demonstrates that this interval can be approximately correlated with the uppermost part of the Polygnathus pireneae Zone. However, precise level identification of the Pragian–Emsian Boundary (PEB) in the Liujing section remains dfficult due to the scarcity of suitable limestone samples for conodont analysis from the middle and upper parts of the Shizhou Member. The Daliancun and Liujing members of the Yukiang Formation and the lower part of the overlying Moding Formation are assigned to the Polygnathus nothoperbonus Zone with the nominal species of this biozone ranging from the bottom of the Daliancun Member to the lower part of the Moding Formation.  相似文献   

10.
《地学前缘(英文版)》2020,11(5):1711-1725
The tectonic setting of the northern Alxa region during the Late Paleozoic is highly controversial.The key to resolve this controversy is to recognize the Late Paleozoic magmatic processes in the northern Alxa.In this paper,we present new zircon U-Pb ages,Hf-isotopic compositions and whole-rock geochemical data of four granitoids along the Zhusileng-Hangwula Tectonic Belt in the northern Alxa region that could provide critical information about the tectonic evolution of this region.The zircon U-Pb data could be grouped as two phases:Late Devonian granite and diorite(ca.373-360 Ma),and Late Carboniferous granodiorite(ca.318 Ma).The Late Devonian granites and diorites are metaluminous to slightly peraluminous,with A/CNK and A/NK ratios of 0.90-1.11 and0.95-2.19,respectively.The Late Devonian diorites are characterized by high MgO,Cr and Ni contents and MgO#values,together with variable ε_(Hf)(t) values from-1.0 to+1.3 and old T_(DM2) ages varied from 1283 Ma to 1426 Ma,indicating the primary magma was potentially derived from magma mixing of depleted mantle with Mesoproterozoic continental crust.Even though the Late Devonian granites yielded most positive and minor negative e_(Hf)(t) values between-1.1 to+5.7(three grains are negative) with two-stage model ages(T_(DM2)) of 1003-1438 Ma,they display low MgO,Cr and Ni contents and MgO#values,suggesting that they were mainly derived from juvenile crustal materials,mixed with a small amount of ancient crust.The Late Carboniferous granitoids are metaluminous and medium-K calc-alkaline series,with A/CNK and A/NK ratios ranging from 0.88 to 0.95 and1.75 to 1.90,respectively.These rocks were potentially derived from juvenile crustal materials mixed with depleted mantle,as evidenced by their high ε_(Hf)(t) values(+11.6 to+14.1) and young TDM2 ages(427 Ma to 586 Ma),as well as high Mg#values,and MgO,Ni and Cr contents.Our data,along with available sedimentary evidence and previous researches,indicate that the Late Devonian and Late Carboniferous rocks are arc-related granitoids under the subduction setting.The identification of arc-related granitoids in the northern Alxa region not only reveals the Late Paleozoic magmatic process in response to the subduction of Paleo Asian Ocean,but also provide significant constrains to the tectonic evolution of the Central Asian Orogenic Belt.  相似文献   

11.
Based on detailed and systematic researches of the geology of ore deposits, fluid inclusions and isotope geochemistry etc., and regarding the Late Paleozoic fluid system of the Yuebei Basin as an integrated object in this paper, we have revealed the temporo-spatial evolution law of the basin＇s fluid system and discussed its ore-forming effects by simulating and analyzing the distribution of ore-forming elements, the fluid thermodynamics and dynamics of evolution processes of this basin. The results show that Late Paleozoic ore-forming fluid systems of the Yuebei Basin include four basic types as follows. （1） The sea floor volcanic-exhalation system developed during the rapid basin slip-extension stage in the Mid-Late Devonian, which affected the Dabaoshan region. It thus formed the Dabaoshan-type Cu-Pb-Zn-Fe sea floor volcanic-exhalation sedimentary deposits. （2） The compaction fluid system developed during the stable spreading and thermal subsidence-compression stage of the basin in the Mid-Late Devonian. The range of its effects extended all over the whole basin. It resulted in filling-metasomatic deposits, such as the Hongyan-type pyrite deposits and pyrite sheet within the Fankou-type Cu-Pb-Zn-S deposits. （3） The hot water circulation system of sea floor developed during the stage of basin uplifting and micro-aulacogen from the late Late Carboniferous to Middle Carboniferous. The range of its effects covered the Fankou region. It thus formed MVT deposits, such as the main orebody of the Fankou-type Pb-Zn-S deposits. （4） The gravity fluid system developed during the stage of fold uplifting and the basin closed from Middle Triassic to Jurassic, forming groundwater hydrothermal deposits, e.g. the veinlet Pb-Zn-calcite orebodies of the Fankou-type Pb-Zn- S deposits. Migration and concentration of the ore-forming fluids were constrained by the state of temporo-spatial distribution of its fluid potential. Growth faults not only converged the fluids and drove them to move upwards, but also the fluids often crossed the faults to the edges of the basin at the bottom of these faults and the lithologic interfaces, and even migrated to the basin＇s edges from top to bottom along the faults, which may be one of the basic reasons for the stratabound deposits to cluster mainly along the contemporaneous faults on the inner border of the basin. The superposed mineralization resulting from the multi-stage activity of contemporaneous faults and ore-forming fluid systems in the basin may be one of the key factors for forming superlarge ore deposits.  相似文献   

12.
Paleozoic Tectono-Metallogeny in the Tianshan-Altay Region, Central Asia   总被引：1，自引：0，他引：1  
The research on Paleozoic tectonics and endogenic metallogeny in the Tianshan-Altay region of Central Asia is an important and significant project. The Altay region, as a collision zone of the Early Paleozoic (500–397 Ma), and the Tianshan region, as a collision zone of the early period in the Late Paleozoic (Late Devonian-Early Carboniferous, 385–323 Ma), are all the result of nearly N-S trending shortening and collision (according to recent magnetic orientation). In the Late Devonian-Early Carboniferous period (385–323 Ma), regional NW trending faults displayed features of dextral strike-slip motion in the Altay and Junggar regions. In the Tianshan region, nearly EW-trending regional faults are motions of the thrusts. However, in the Late Carboniferous-Early Permian period (323–260 Ma), influenced by the long-distance effect induced from the Ural collision zone, those areas suffered weaker eastward compression, the existing NW trending faults converted into sinistral strike-slip in the Altay and Junggar regions, and the existing nearly E-W trending faults transferred into dextral strike-slip faults in the Tianshan region. The Rocks of those regions in the Late Carboniferous-Early Permian period (323–260 Ma) were moderately ruptured to a certain tension-shear, and thus formed a number of world famous giant endogenic metal ore deposits in the Tianshan-Altay region. As to the Central Asian continent, the most powerful collision period may not coincide with the most favorable endogenic metallogenic period. It should be treated to “the orogenic metallogeny hypothesis” with caution in that region.  相似文献   

13.
The adakites rocks are typically considered as direct diagnostic evidence for subduction and continental growth, as well as the important evidence to determine the location of the major oceanic basin and evolution history of lost oceanic basins, which are longstanding conundrums for understanding the tectonics of the Paleo-Asian Ocean (PAO). As the processor of the Altaids, the PAO was a long-lived ocean, and its multiple subductions led to substantial continental growth in the Central Asian continent. Here we report our newly discovered Paleozoic adakitic rocks (granite and dacite) developed in Jijitaizi in the Eastern Tianshan of the southern Altaids to address the above issues. The Jijitaizi granite and dacite contain high concentrations of Sr (203–343 ppm) and low concentrations of Y (3.00–6.36 ppm) and Yb (0.23–0.62 ppm), indicative of the adakitic affinity. Zircon U-Pb dating results show that the adakitic rocks were formed in three episodes at 372.26 ± 1.51 Ma, 356.02 ± 1.11 Ma and 334.51 ± 0.68 Ma from the Late Devonian to Carboniferous. The rocks are depleted in Nb, P and Ti, and possess variable Mg# values (28.51–57.22), high Na2O/K2O ratios (1.39–4.94), as well as relatively depleted Hf isotopic compositions, all of which point to a subduction origin from slab melting. Our new finding with the date from the Jijitaizi complex (ca. 321 Ma) suggests continuing subduction of the Paleo-Asian oceanic slab beneath the Central Tianshan from the Late Devonian to Carboniferous. Our work provides a solid line of key evidence demonstrating that continuous oceanic subduction of the major PAO evolved into its mature stage following subducting beneath the Central Tianshan from ca. 372 to 321 Ma.  相似文献   

14.
The global Hangenberg Crisis or Hangenberg Extinction is a mass extinction near the Devonian–Carboniferous boundary. Comprehensive research of petrology and geochemistry on the Devonian–Carboniferous boundary, as exposed in the Nanbiancun auxiliary stratotype section, South China, elucidates paleoenvironmental changes and controls on marine strontium (87Sr/86Sr) and carbonate carbon (δ13Ccarb) isotopes during the Hangenberg Crisis. The new 87Sr/86Sr data reveal a regression in the Middle Siphonodella praesulcata Zone, while the Hangenberg Extinction was occurring in South China. Moreover, the δ13Ccarb data records a negative excursion near the base of the Middle Siphonodella praesulcata Zone that may have been connected with the Hangenberg Extinction. A positive δ13Ccarb excursion, corresponding with the Upper Siphonodella praesulcata Zone, may reflect the effects of a vigorous biological pump. The magnitude of the Hangenberg Carbon Isotopic Excursion in peak δ13carb values and δ13Ccarb gradient in carbonate Devonian–Carboniferous boundary sections of the South China Craton during the Hangenberg Crisis, are a function of depositional water depth and distance from the shore. The carbon cycling during the Hangenberg Carbon Isotopic Excursion had a much stronger impact on oceanic surface waters than on the deep ocean and the δ13Ccarb gradient of local seawater was likely caused by enhanced marine productivity, associated with biological recovery in platform sediments during the Hangenberg Crisis.  相似文献   

15.
The central part of South Mongolia, located to the north of the Solonker Suture, is a key region for studying the late Paleozoic tectonic evolution of the Central Asian Orogenic Belt(CAOB). Voluminous late Paleozoic granitic rocks,especially of Carboniferous age, were intruded in this area. However, these granitoids have not been well studied and there is a lack of precise ages and isotopic data. This has hampered our understanding of the tectonic evolution of southeastern Mongolia, and even the entire CAOB. In this paper, we provide new U-Pb isotopic ages and geochemical analyses for these Carboniferous granites. One granite from the Ulaanbadrakh pluton yielded a zircon U-Pb age of 326 Ma, which indicates emplacement in the Early Carboniferous, and three other granites from the Khatanbulag region gave zircon U-Pb ages of316 Ma, 315 Ma, and 311 Ma, which indicate emplacement in the Late Carboniferous. The Early Carboniferous granite has SiO2 contents of 70.04–70.39 wt% and K2 O + Na2 O contents of 6.48–6.63 wt%, whereas the Late Carboniferous granites have more variable compositions(SiO2 = 65.29–77.91 wt% and K2 O + Na2 O = 5.30–7.27 wt%). All the granites are weakly-peraluminous I-types that are relatively enriched in U, Th, K, Zr, Hf, and LREEs. The whole rock Sr-Nd and zircon in situ Lu-Hf isotope analyses for the Early Carboniferous granite gave positive values of εNd(t)(2.87) and εHf(t)(4.31–12.37) with young Nd(TDM = 860 Ma) and Hf(TDMc = 1367–637 Ma) two-stage model ages, indicating derivation from juvenile crustal material. In contrast, the Late Carboniferous granites had more diverse values of εNd(t)(–4.03 to 2.18) and εHf(t)(–12.69 to5.04) with old Nd(TDM = 1358–1225 Ma) and Hf(TDMc = 2881–1294 Ma) depleted mantle two-stage model ages,suggesting derivation from remelting of Precambrian basement. Based on the existing results, the tectonic setting of the Late Carboniferous granites in the central part of South Mongolia is known for its diversity, and this paper believes that the tectonic background of the carboniferous granite records the tectonic transition from a continental-margin-arc to a postcollisional extensional setting during the Late Carboniferous–Permian.  相似文献   

16.
Well-preserved and diversified spores, cryptospores, and acritarchs have been recorded from a relatively continuous sequence that encompasses the Silurian–Devonian boundary in Qujing, Yunnan, southwest China. Four spore assemblage zones from Late Silurian to Early Devonian in age are proposed based on the first appearance datum (FAD) of characteristic spore species. In ascending stratigraphic order, they are Ambitisporites dilutus–Apiculiretusispora synorea (DS; Late Ludfordian to Early Pridoli), Synorisporites verrucatus–Apiculiretusispora plicata (VP; Pridoli), Apiculiretusispora minuta–Leiotriletes ornatus (MO; Lochkovian), and Verrucosisporites polygonalis–Dibolisporites wetteldorfensis (PW; Pragian). The acritarch assemblage from the upper part of the Yulongsi Formation, the Xiaxishancun Formation, and the lower–middle parts of the Xitun Formation indicates an age of Late Silurian. Based on palynological evidence, the upper part of the Yulongsi Formation is considered Late Ludfordian to Early Pridoli in age; the Xiaxishancun Formation is believed to be Pridoli in age; the Xitun Formation is considered Late Pridoli to Early Lochkovian in age; the Guijiatun Formation is considered Lochkovian in age; and the Xujiachong Formation is Late Lochkovian to Pragian in age. The Silurian-Devonian boundary is recognized between the VP and the MO spore biozones, and occurs within the middle part of the Xitun Formation.  相似文献   

17.
WANG Xu-ri  JI Qiang 《地质通报》2013,32(7):977-987
This paper introduces a new section of the Devonian-Carboniferous boundary in Huohua area, Ziyun County, Guizhou Province, South China. The Huohua section of Upper Devonian and Lower Carboniferous is well-outcropped along a new countryside road. In this section, the D-C boundary beds can be grouped into three litho-units: the Daihua Formation, the Changshun Shale and the "Wangyou Formation", from which more than 30 conodont samples were collected and processed. According to our current study, some important conodonts in the Daihua Formation and the Changshun Shale have been recognized, such as Palmatolepis tenuipunctata, Pa. glabra, Pa. marginifera, Pa. gracilis, Polygnathus vogesi and Polygnathus purus purus. A few conodonts have been found from the Wangyou Formation, such as Polygnathus communis and Hindeodella subtilis. Based on the comparison with the Muhua section in Changshun county and the Hasselbachtal section in Germany in lithology, sedimentology and conodont biostratigraphy, the D-C boundary could be temporarily placed between Bed 25 and Bed 26, namely between the Changshun Shale and the Wangyou Formation.  相似文献   

18.
238 marine carbonate samples were collected from seven sedimentary sections ofthe entire late Palaeozoic (Permian, Carboniferous and Devonian) in the Upper Yangtze Plat-form, southwest China. Based on the absence of cathodoluminescence and very low Mn (gener-ally<50 ppm) contents of the samples, it is thought that they contain information on the orig-inal sea water geochemistry. The results of isotopic analyses of these samples are presented interms of δ~(13)C and ~(87)Sr/~(86)Sr ratios versus geological time. The strontium data, consistent withother similar data based on samples from North America, Europe, Africa and other areas inAsia, support the notion of a global consistency in strontium isotope composition of marinecarbonates. The strontium data exhibit three intervals of relatively low ~(87)Sr/~(86)Sr ratios in thelate Middle Devonian to early Late Devonian, Early Carboniferous and Early Permian, corre-sponding to global eustatic high sea level stands. The lowest ~(87)Sr/~(86)Sr ratio recorded in theLate Permian was probably caused by substantial basalt eruptions in the Upper Yangtze Plat-form at the time. Three corresponding periods of relatively high δ~(13)C values at roughly the samethe intervals were caused by a relatively high rate of accumulation of organic carbon duringsea level rises at these times. The deposition of coal was probably responsible for the increaseof sea water δ~(13)C at other times. The δ~(13)C values drop dramatically near theDevonian/Carboniferous, Carboniferous/Permian and Permian/Triassic boundaries, con-sistent with other similar data, which further support the notion that geological time boundariesare associated with mass extinction and subsequent rejuvenation.  相似文献   

19.
Most of the hinterland of the North China platform is devoid of Late Ordovician strata. The BaiyanhuaMountain section at Shetai Town is a standard section of the Upper Ordovician newly established in recentyears at the northernmost margin of the platform. This establishment directly involved the determination of thenorth boundary of the platform and the understanding of its evolutionary Listory. The area is quite differentfrom the binterland of the platform in Middle Ordovician rock types and sedimentary environments, with theformer characterized by frequent slope deposits and the latter consisting almost entirely of platform deposits.The present paper focuses on the petrographic features and sedimentary ervironments of the Middle-UpperOrdovician strata in the area, providing further theoretical support to the establishment of the section and fil-ling the gap in this respect.  相似文献   

20.
The hydrocarbon potential of the Hangjinqi area in the northern Ordos Basin is not well known, compared to the other areas of the basin, despite its substantial petroleum system.Restoration of a depth-converted seismic profile across the Hangjinqi Fault Zone(HFZ) in the eastern Hangjinqi area shows one compression that created anticlinal structures in the Late Triassic, and two extensions in ~Middle Jurassic and Late Early Cretaceous, which were interrupted by inversions in the Late Jurassic–Early Early Cretaceous and Late Cretaceous, respectively.Hydrocarbon generation at the well locations in the Central Ordos Basin(COB) began in the Late Triassic.Basin modeling of Well Zhao-4 suggests that hydrocarbon generation from the Late Carboniferous–Early Permian coal measures of the northern Shanbei Slope peaked in the Early Cretaceous, predating the inversion in the Late Cretaceous.Most source rocks in the Shanbei Slope passed the main gas-migration phase except for the Hangjinqi area source rocks(Well Jin-48).Hydrocarbons generated from the COB are likely to have migrated northward toward the anticlinal structures and traps along the HFZ because the basin-fill strata are dipping south.Faulting that continued during the extensional phase(Late Early Cretaceous) of the Hangjinqi area probably acted as conduits for the migration of hydrocarbons.Thus, the anticlinal structures and associated traps to the north of the HFZ might have trapped hydrocarbons that were charged from the Late Carboniferous–Early Permian coal measures in the COB since the Middle Jurassic.  相似文献   

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