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1.
After the severest mass extinction event in the Phanerozoic, biotic recovery from the extinction at the Permian–Triassic boundary required approximately 5 my, which covers the entire Early Triassic. It is important to obtain information on the superocean Panthalassa, which occupied most of the world ocean, to explore paleoenvironmental changes during the Early Triassic at the global scale. In order to establish the continuous lithostratigraphy of pelagic sediments in Panthalassa during the Early Triassic, high‐resolution reconstruction of the Lower Triassic pelagic sequence in Japan was conducted for the first time based on detailed field mapping and lithostratigraphic correlation in the Inuyama area, central Japan. The reconstructed Early Triassic sequence is approximately 9.5 m thick, consists of five rock types, and is divided into eight lithological units. For the reconstructed continuous sequence, measurement of carbon isotopic composition of sedimentary organic matter (δ13Corg) was carried out. Stratigraphic variation of the δ13Corg value shows large‐amplitude fluctuations between ?34.4 and ?21.0‰ throughout the sequence. In order to establish a higher resolution age model for the reconstructed Lower Triassic pelagic sequence, we correlated δ13Corg records in the Inuyama area with high‐resolution isotopic profiles of carbonate carbon (δ13Ccarb) from shallow‐marine carbonate sequences in southern China based on the similarity in general variation patterns with age constraints by radiolarian and conodont biostratigraphy. The result provides a high‐resolution time scale for the pelagic sequence of Panthalassa during the Smithian and Spathian. The age model suggests a drastic increase in sedimentation rate during the late Smithian, which should have been caused by the increase in terrigenous input to this site.  相似文献   

2.
Succeeding to multiply collisions of different blocks in Late Paleozoic[1―5], complex intracontinental structural deformation occurred in the Tianshan area during Mesozoic-Cenozoic[6―16], which controlled coeval basin-range evolution and resulted in intensive modi- fication and adjustment of the Paleozoic oil-gas reser- voirs[17―19]. The Kuqa Depression is a secendary struc- tural unit of the Tarim basin, in which Mesozoic- Ce- nozoic deposits occur in thickness of 6000―7000 m. The Kuq…  相似文献   

3.
Jurassic sedimentary features and tectonic settings of southeastern China   总被引：1，自引：0，他引：1  
Two types of the Jurassic basins are distinguished in SE China based on their geodynamic features: the Late Triassic-Early Jurassic post-orogenic basins and the Middle Jurassic intra-continental extensional basins. The Lower Jurassic sequence shows a change from coarse- to fine-grained accumulation, suggesting a gradually deepening depositional environment from river to shore-lake and to deep-water lake. In contrast, the Middle Jurassic accumulation was changed from claystone to conglomerate along the coastal provinces in SE China, indicative of an initial crustal uplift. The Wuyi Mountains have been a paleogeograghic separating zone since the Middle Jurassic. The Late Jurassic strata are absent in most areas of SE China. A large-scale bimodal intra-continental rift-type volcanism occurred during the Middle Jurassic along a 40–60 km wide and 200 km long area in western Fujian and southern Jiangxi provinces, which is most likely the strongest volcanism in SE China since the Cambrian. The SHRIMP zircon U-Pb analyses on the rhyolite from the Dongkeng basin in the southern Jiangxi area yield a concord U-Pb age of 160±0.5 Ma, providing an upper age limit for the bimodal volcanic eruption. The analyses of the basin features indicate a change of the depositional environment during the interval from Middle Triassic to Late Triassic from a shallow-sea to an intra-continent in SE China in response to the strong collision between the Yangtze and North China Blocks. Sedimentary structures record a southward direction of Early Jurassic paleo-currents, reflecting that their source areas were to the north side. We propose that the Wuyi region was uplifted as early as Middle Jurassic, followed by a wide E-W-trending extended depression and bimodal volcanism in the western foot of the Wuyi Mountains. Presumably the uplift of the Wuyi domain changed the Middle Jurassic paleogeographic outline and formed the transformational tectonic regime from compression to extension as a tectonic response to the Pacific plate subduction.  相似文献   

4.

Triassic sequences in both the western Qinling and Songpan terrane are composed mostly of deep-marine sediments. A detailed study was carried out on main sedimentary facies of Triassic successions, showing that they resulted from diverse sedimentary processes, such as submarine debris-flows, turbidity currents, bottom-flows, suspension fallout, and fluidized sediment flows. Debris-flows are dividable into two types, gravelly and sandy debris-flows, respectively, and the sandy debris-flow deposits make up considerable portion of the Triassic successions concerned. Turbidite is characterized by occurrence of normal grading, and the whole Bouma sequences, though widely developed, are not totally attributed to true turbidity currents. The non-graded Ta division is thought to originate from sandy debris flows, whereas the rest divisions result from low-density currents or from bottom-current modification if they contain sedimentary structures related to traction currents. Four types of facies associations are distinguished within Triassic deep-marine successions: massive and thick-bedded coarse-grained facies association, medium- and thick-bedded sandstone with interlayered fine-grained facies association, interlayered thin-bedded fine-grained facies association, and syn-sedimentary slump/breccia facies association. Spatial distribution of the different facies associations suggests that Lower Triassic sedimentation occurred primarily in continental slope, submarine channels, and base-of-slope aprons in the Hezuo-Jianzha region of the western Qinling, whereas the Middle Triassic consists mainly of sedimentary facies of base-of-slope aprons and submarine incised valleys. The counterparts in the Dangchang-Diebu region, in contrast, are characterized by platform carbonates. The shallow-marine carbonates evolved into deep-marine facies since the Ladinian, indicative of rapid drowning of the Carnian carbonate platform in Middle Triassic times. Depositional history of Lower Triassic and lower portion of Middle Triassic successions in the northern Songpan terrane is similar to that of the Dangchang-Diebu region of the western Qinling, as manifested by development of Lower-early Middle Triassic shallow-marine carbonate and a rapid shift to base-of-slope apron sediments since the Ladinian.

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5.
The site of Bonneval (France) exhibits a 6 m thick stratigraphical sequence in which Middle and Lower Palaeolithic artefacts were discovered. The stratigraphy of the site consists of an alternation of loess-like silt layers deposited along glacial stages, and paleosoil horizons corresponding to the vegetal stabilization of the area during interglacials. These layers hence provide past environmental informations and can be used as stratigraphical markers and compared with well dated sequences of Northern France. Eight sediment samples from this Middle and Upper Pleistocene sequence were dated using the recuperated optically stimulated luminescence (Re-OSL) signal of quartz grains. The middle-size fraction (40–63 μm) shows a good reproducibility of the OSL signals which allows the application of a multiple-aliquot additive-dose approach for De determination. For all samples, the growth curves are linear up to an accumulated dose of 3000 Gy. The Re-OSL ages range from ～100 to ～450 ka and are in good agreement with the independent chronological information; they establish when handaxe industries have been made during the Middle and Upper Pleistocene in the Paris Basin.  相似文献   

6.
Age determinations of the Triassic lithostratigraphic units of the Yanshan belt were previously based on plant fossils and regional correlations of lithologies. The Liujiagou and Heshanggou Formations were assigned as the Lower Triassic, and the Ermaying Formation was regarded as the Middle Triassic. We carried out a geochronologic study of detrital zircon grains from the Triassic sandstone in the Xiabancheng and Yingzi basins in northern Hebei where the Triassic strata are exceptionally well preserved. The results show that the Liujiagou, Heshanggou, and Ermaying Formations are all Late Triassic in age. The ages of detrital zircons also revealed that the upper part of the Shihezi Formation and the overlying Sunjiagou Formation, both of which were thought to be the Middle-Late Permian units, are actually late Early to Middle Triassic deposits. This study combines the upper Shihezi and Sunjiagou Formations into a single unit termed as the Yingzi Formation. We also substitute the widely-used Liujiagou, Heshanggou, and Ermaying Formations with the Dingjiagou, Xiabancheng, and Huzhangzi Formations, respectively. Field observations and facies analysis show that the top of the Shihezi Formation is an erosive surface, marking a parallel unconformity between the Middle Permian and Lower Triassic. The Yingzi Formation is composed mainly of meandering river deposits, indicative of tectonic quiescence and low-relief landform in the Early to Middle Triassic. In contrast, the Dingjiagou, Xiabancheng, and Huzhangzi Formations are interpreted as the deposits of sandy/gravelly braided rivers, alluvial fans, fan deltas, and deep lakes in association with volcanism, thus indicating an intense rifting setting. A new Triassic lithostratigraphic division is proposed according to age constraints and facies analysis, and the results are of significance for understanding the early Mesozoic tectonic evolution of the Yanshan belt.  相似文献   

7.
Some fundamental problems in outcrop sequence stratigraphy   总被引：4，自引：1，他引：3  
Some fundamental problems in outcrop sequence stratigraphy are discussed, and the following ideas are obtained: (i) Detailed sedimentary facies analysis and study on stacking pattern of parasequences, careful and accurate study of biostratigraphy, and stratigraphical correlation of different facies areas are the essential conditions for proper identification of sequences. (ii) The first flooding surface may be an ideal sequence boundary in outcrop sequence stratigraphy, where the most distinct palaeontological and sedimentary changes take place and make the surface readily recognizable in outcmp. (iii) The distribution in space, specially in different facies belts, is regarded as an important criterion for defining and recognizing the various orders of sequences. The third-order sequence is probably global in nature, which may be discerned in various depositional facies belts at least on one continental margin, and can be correlated over long distances, sometimes worldwide. (iv) The first flooding surface may be used as a useful reference marker in optimizing chronostratigraphic boundaries. Project jointly supported by the SSER, the Ministry of Science and Technology of China, and the Ministry of Land and Natural Resources of China.  相似文献   

8.
The Early Triassic is a critical period in earth his- tory. A series of events such as volcano eruptions[1,2], sea-level fluctuations, changes in environmental con- ditions[3], mass extinctions[4,5] as well as global negative carbon isotope excursions[6-9] have been discovered in the uppermost Permian or across the Permian-Triassic boundary. Large scale sea-level rise[10-12], restoration of environment conditions, re- covery of ecosystem[13], including gradual carbon iso- tope rise[14] occur…  相似文献   

9.
Most geologists believe that there are no Early and Middle Triassic strata in the W. Gandisê stratigraphic subregion, but the present authors have found Early Triassic conodonts for the first time in the Shiquanhe area, including five conodonts genera (Form genera): Pachycladina, Neohindeodella, Cornudina, Hadrodontina and Hibbardella sp. etc. Then we affirm that Early Triassic deposits exist in the Gandisê stratigraphic subregion, and establish the Tangnale Formation. The conclusion is new important complementary basal data for Triassic stratigraphy division of Gangdisê, reconstructing palaogeography and studying Gangdisê from Paleozoic to Mesozoic island-arc evolution and transi-tion.  相似文献   

10.
The present study focuses on the morphotectonic evolution of the axial portion of the Southern Apennine chain between the lower Calore River valley and the northern Camposauro mountain front (Campania Region). A multidisciplinary approach was used, including geomorphological, field‐geology, stratigraphical, morphotectonic, structural, 40Ar/39Ar and tephrostratigraphical data. Results indicate that, from the Lower Pleistocene onwards, this sector of the chain was affected by extensional tectonics responsible for the onset of the sedimentation of Quaternary fluvial, alluvial fan and slope deposits. Fault systems are mainly composed of NW‐SE, NE–SW and W‐E trending strike‐slip and normal faults, associated to NW‐SE and NE–SW oriented extensions. Fault scarps, stratigraphical and structural data and morphotectonic indicators suggest that these faults affected the wide piedmont area of the northern Camposauro mountain front in the Lower Pleistocene–Upper Pleistocene time span. Faults affected both the oldest Quaternary slope deposits (Laiano Synthem, Lower Pleistocene) and the overlying alluvial fan system deposits constrained between the late Middle Pleistocene and the Holocene. The latter are geomorphologically and chrono‐stratigraphically grouped into four generations, I generation: late Middle Pleistocene–early Upper Pleistocene, with tephra layers 40Ar/39Ar dated to 158±6 and 113±7 ka; II generation: Upper Pleistocene, with tephra layers correlated with the Campanian Ignimbrite (39 ka) and with the slightly older Campi Flegrei activity (40Ar/39Ar age 48±7 ka); III generation: late Upper Pleistocene–Lower Holocene, with tephra layers correlated with the Neapolitan Yellow Tuff (~15 ka); IV generation: Holocene in age. The evolution of the first three generations was controlled by Middle Pleistocene extensional tectonics, while Holocene fans do not show evidence of tectonic activity. Nevertheless, considering the moderate to high magnitude historical seismicity of the study area, we cannot rule out that some of the recognized faults may still be active. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

11.
New progresses on geothermal history of Turpan-Hami Basin, Xinjiang, China   总被引：2，自引：0，他引：2  
A comprehensive study on geothermal history of the Turpan-Hami Basin by vitrinite reflectance, fluid inclusion geothermometry, apatite fission track and40Ar-39Ar dating displays that the main effects influencing geotemperature distribution are burial depth of the basement, heat flow, magmatic activities, as well as tectonic movement, having a rugulation to be higher in the east and north, lower in the west and south, as well as higher in the past and lower at the present. The heat of the mantle source and the Indo-China tectonic thermal event have extremely influenced maturation of source rocks of the upper Lower Permian and the Middle and Upper Triassic in the lndo-China epoch. While, the geothermal gradient and the weak tectonic geothermal event of the Early Yanshan Movement provided necessary heat for the maturation of source rock in coal-bearing strata of the Middle and Lower Jurassic.  相似文献   

12.
The Lower Triassic Xikou Formation in southwestern Fujian, China is a set of complex deep-water sediments which includes turbidites, sandy contourites and isolated olistoliths. Five facies and seven subfacies are recognized in the deep-water turbidites, which are considered to belong to five facies associations of upper, middle and lower fans, respectively. The sandy contourites, which occur within turbidites as isolated thin layers with structures of traction current, are formed by reworking turbidites. They occur in discrete units, not as a part of a vertical sequence of structures, such as Bouma sequence. Paleocurrent directions derived from sandy contourites are perpendicular to or at a large angle of those derived from turbidites. In some areas, within the Formation there exist large oolitic limestone blocks slided from shallow sea. The temporal-spatial distribution of three types of sediments mentioned above and the related evidences could indicate that a passive continental margin from shallow sea to bathyal-abyssal region, dipping toward southeast, once occurred in study area during the early Triassic. The early Triassic represents a period of sealevel uprising. The uprising of sea level and the development of isolated olistoliths probably imply gradual shrinking of an ocean basin at that time. Project supported by the National Natural Science Foundation of China (Grant Nos. 49490011, 49702036).  相似文献   

13.
The Hruškovec quarry of basaltoid rocks is situated on the northwestern slopes of Mt. Kalnik, within the Zagorje–Mid-Transdanubian zone, a part of the North-western Dinarides. The basaltoids are inter-bedded with radiolarites of the Middle and Upper Triassic age (Langobardian, Carnian–Norian). Spilites, altered diabases and meta-basalts form part of Triassic volcanic-sedimentary sequence, made of sandstones, shales, micritic limestone, altered vitric tuffs and radiolarian cherts, incorporated tectonically into the Jurassic–Cretaceous mélange.  相似文献   

14.
The Permian-Triassic Boundary Stratigraphic Set (PTBST), characteristic of the GSSP section of Meishan and widespread in marine Permian-Triassic Boundary (PTB) sequences of South China, is used to trace and recognize the PTB in a continental sequence at Chahe (Beds 66f―68c). Diversified Permian plant fossils extended to the PTBST, and a few relicts survived above that level. Sporomorphs are dominated by fern spores of Permian nature below the PTBST, above which they are replaced by gymnosperm pollen of Triassic aspect. In the nearby Zhejue Section, the continental PTBST is charac- terized by the fungal 'spike' recorded in many places throughout the world. The boundary claybeds (66f and 68a,c) of the PTBST are composed of mixed illite-montmorillonite layers analogous with those at Meishan. They contain volcanogenic minerals such as β quartz and zircon. U/Pb dating of the upper claybed gives ages of 247.5 and 252.6 Ma for Beds 68a and 68c respectively, averaging 250 Ma. In con- trast to the situation in Xinjiang and South Africa, the sediment sequence of the Permian-Triassic tran- sition in the Chahe section (Beds 56―80) become finer upward. Shallowing and coarsening upward is not, therefore, characteristic of the Permian-Triassic transition everywhere. The occurrence of relicts of the Gigantopteris Flora in the Kayitou Fm. indicates that, unlike most marine biota, relicts of this pa- leophytic flora survived into the earliest Triassic. It is concluded that Bed 67 at Chahe corresponds to Bed 27 at Meishan, and that the PTB should be put within the 60-cm-thick Bed 67b④, now put at its base tentatively. This is the most accurate correlation of the PTB in continental facies with that in the marine GSSP.  相似文献   

15.
“Milanggouwan stratigraphical section” named lately takes down 27 cycles of alternately evolutionary histories of desert depositions in the Mu Us area with the fluviolacustrine facies and palaeosols since 150 ka B. P. Studies show that the sedimentary form was induced by the growth and decline and confrontation each other between the winter monsoon and the summer monsoon of East Asia in the past 150 ka. Project supported by the National Natural Science Foundation of China (Grant No. 49473192).  相似文献   

16.
Proposed new Lower Triassic stages in South China   总被引：5，自引：1，他引：5  
As the global Lower Triassic stages are not properly defined, a Chinese scheme of the Lower Triassic subdivision was recently proposed to meet the insistent need of the general investigation in China. The Lower Triassic sequences of South China are briefly summarized and the twofold Lower Triassic subdivision is discussed. The type sections of the two Chinese Lower Triassic stages, Yinkengian and Chaohuan, and their definitions are stated.  相似文献   

17.
The Upper Permian Dalong Formation (P2d) and Changxing Formation (P2C), and the Lower Triassic Zhengtang Formation (Tlz) are of deep-water turbidites. The sedimentary features of the NW Zhejiang are of SE-dipping passive continental margin from the Paleozoic to the early Triassic. Together with the foreland molasse basin during the late Triassic (T3w), the tectonics of the NW Zhejiang is characterised by a tectogenesis which took place in the middle Triassic. From SE to NW, the structural style varies from multi-duplex, antiformal stack to imbricate fans, and then to Jura Mountain-type fold zone with fold-style varying gradually from large-scale tight fold to midscale chevron fold, then to cylindrical fold, reviewing a preliminary scenario of foreland fold and thrust belt. The space-distributed structures and the tectonic vergence indicate the significance of deformation in (T1-T3). Project supported by the National Natural Science Foundation of China and Chinese Academy of Sciences.  相似文献   

18.
鄂尔多斯地块构造演化的古地磁学研究   总被引：15，自引：0，他引：15       下载免费PDF全文
鄂尔多斯地块与中朝地台其它地区相同时代地层的古地磁结果基本一致表明:晚二叠世以来,中朝地台经历了从低纬度(19°左右)向中纬度的北移过程,并伴有50°左右的逆时针旋转;晚二叠世—中三叠世地台北移10°(1000km)左右,而方位基本未变;中三叠世—中侏罗世主要发生50°左右的逆时针旋转,而北向位移不明显,这一旋转可能与杨子地台和中朝地台碰撞拼合有关,或者说是印支运动在该地区的反应,中侏罗世—早白垩世地块已基本和现代位置一致  相似文献   

19.
Paleomagnetic measurements have been carried out on six samples of Early Triassic age and five samples of Middle Triassic age from East Greenland. The mean stable remanent magnetization directions obtained after alternating-field demagnetization tests give the virtual geomagnetic pole positions as: (1) 49°N, 158°E for the Middle Triassic and (2) 34° 30′N, 176°W for the Early Triassic. The Greenland Triassic paleomagnetic results have been compared with those for Europe and North America. It is inferred from this comparison that these preliminary results for Greenland do not conform with the requirements of a reconstruction based on a geometrical fit of the three landmasses.  相似文献   

20.
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