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1.
中国晚寒武世长山期最大海泛事件及其全球对比意义 总被引：2，自引：0，他引：2
在华北地台寒武-奥陶系层序地层研究中发现了不同层序中的海绿石质凝缩层。长山期最大海泛凝缩层系以富钾海绿右的双层结构复合层系为特征,富集多种金属元素和磷、锰、K_2O为特点。长山期海泛事件具有全球对比意义。笔者已在北欧,北美及亚洲26个洲际剖面点发现了长山事件记录。详细的比较沉积学、微相、米级旋回和Fischer图解研究均证明长山期最大海泛事件系起因干二级与三、四级海平面变化周期复合叠加作用,形成时限为1.2-3Ma,最后提出长山期全球海泛事件的洲际模式。 相似文献
2.
At least seven different types of ore bodies, with an ore stock of Ba, F, Fe, Pb, Zn, Cu and Sb occur in Paleozoic rocks (Lower-Middle Cambrian and Ordovician) in an ?15 km2 area north of the Narcao village (SW Sardinia, Italy). The ore bodies are related both to syngenetic accumulations, and later epigenetic recirculation of the primary ores. In the Lower Cambrian the area studied shows evidence of synsedimentary tectonic instability, probably related to carbonate shelf margin features. The Upper Cambrian is lacking and the transgressive Ordovician sediments cover large areas of the previously gently folded Cambrian rocks (Sardic phase of Caledonian orogenesis). The main Hercynian tectonic phases had a much stronger compressive folding that is mirrored in a sequence of tight folds and upthrusts. The geometric setting resulting from the tectonic frame of the Cambrian and Ordovician sediments must be taken into account to understand the distribution and the genesis of most of the ore bodies. 相似文献
3.
The recognition of ice‐related unconformities is of prime importance when dealing with the sequential architecture of pre‐Pleistocene glacial successions. Late Ordovician striated surfaces strikingly preserved in North Gondwana were long considered as abrasion surfaces at the sole of a grounded glacier overriding unlithified sediments, or having resulted from the scouring action of drifting icebergs. Field observations from Mauritania and Libya show that these striated surfaces require an alternative interpretation, which can be applied to similar surfaces described elsewhere, such as in Permo‐Carboniferous or Neoproterozoic glacial sequences. A new model is proposed that involves superimposed concurrent décollement planes within a subglacial brittle shear zone in unlithified sand beds. Shear zones in subglacial sediments are well known in Quaternary deposits but, to date, it has not been demonstrated that they may form striated surfaces occurring at continent scale with orientations consistent with palaeo ice‐flow reconstructions based on larger‐scale indicators. 相似文献
4.
5.
J. B. Jago 《Australian Journal of Earth Sciences》2013,60(5-6):223-230
In Tasmania shelly fossils are known from Middle and Upper Cambrian sediments of the Dundas Trough, Fossey Mountain Trough, Dial Range Trough, Beaconsfield Trough, Smithton Basin, Adamsfield Trough and from within sediments associated with the Mount Read Volcanics of Western Tasmania. In the Dundas Trough fossils range in age from early Middle Cambrian (Ptychagnostus gibbus Zone) to the middle Late Cambrian (pre‐Payntonian A or B). Late Middle Cambrian fossils occur in sediments associated with the Mount Read Volcanics in two places in Western Tasmania. Late Middle Cambrian fossils only are known from the Smithton Basin and the Beaconsfield Trough. Late Middle to early Late Cambrian faunas are known from the Dial Range Trough; the Adamsfield Trough contains middle Middle to middle Late Cambrian fossils. Tasmanian Cambrian faunas show affinities with those of Queensland, China, the northwest Siberian Platform and northern Victoria Land, Antarctica. 相似文献
6.
A regional fluid inclusion study of Cu-Au (+Zn-Pb) mineralisation in the Harlech Dome area, North Wales, gives support to the concept of two distinct metallogenic episodes. The inclusion assemblages associated with the porphyry copper mineralisation at Coed-y-Brenin are consistent with a genetic model of early potassic-propylitic alteration overprinted by later phyllic alteration. High salinity fluids, normally characteristic of potassic alteration, are confined to the host rock quartz. The meteoric/hydrothermal system is closely linked to the emplacement of late-Cambrian diorites. Integrated fluid inclusion and mineralogical studies of the Gold-belt veins suggest that the mineralising fluids were probably dehydration waters released from weakly metamorphosed Cambrian and perhaps Precambrian sediments during hydraulic fracturing in a tensional zone at the close of the Caledonian orogeny. Localisation of economic concentrations of gold in veins at the level of the Clogau Formation is ascribed to a destabilisation of metal complexes caused by a change in fluid buffering from a pyrite-magnetite assemblage in the Lower Cambrian sediments to a pyrite-pyrrhotite-graphite assemblage in the Upper Cambrian sediments. Veining associated with the Coed-y-Brenin porphyry copper deposit and related breccia pipes can be distinguished from the copper-gold veins of the coextensive Dolgellau Gold-belt by the presence in the former of inclusions notably richer in CO2. Furthermore the Gold-belt fluids have a distinctive low CO2/CH4+N2+H2 ratio. 相似文献
7.
T. P. Crimes 《Geological Journal》1966,5(1):33-42
A new classification of concretions is suggested. Some concretions are described from the Upper Cambrian (Maentwrog) sediments of St. Tudwal's Peninsula, southwest Caernarvonshire, and their age relative to that of the surrounding sediments is discussed. 相似文献
8.
Maxwell R. Banks H. A. Bartlett K. L. Burns B. Campana I. B. Jennings D. King 《Australian Journal of Earth Sciences》2013,60(2):127-135
At some time prior to the Ptychagnostus gibbus Zone of the Middle Cambrian the area of deposition of Upper Precambrian (or Lower Cambrian) well‐sorted sands, silts and dolomite was affected by tectonic movements producing uplift of the Tyennan Geanticline and change in the shape of the depositional basin (Spry, Chapter I). Continued tectonic activity and more rapid sinking of the sea floor resulted in a change in sedimentary association from well‐sorted sediments of the orthoquartzite‐limestone suite to poorly sorted sediments of the greywacke suite. Initially siltstone was the main deposit in the Dundas, Huskisson River, Ulverstone, Deloraine and Beaconsfield areas and this has been likened to the initial euxinic phase of geosynclinical development elsewhere (Campana, 1961b). Silt seems to have been the predominant normal deposit during the Middle and early Upper Cambrian, but siliceous oozes and some limestone were also formed. Carbonaceous, pyritic and calcareous silts were deposited. Inter‐bedded with the silts are poorly‐sorted greywackes and greywacke conglomerates with a disrupted framework and graded bedding. Banks and Jennings interpret these as mostly turbidity current deposits. The proportion of greywacke and conglomerate varies through the successions in a cyclic manner (Carey and Banks, 1954; Banks, 1956) such that a conglomerate‐rich section is followed by a greywacke‐rich section and this by a predominantly lutaceous section. These cycles may be interpreted as due to tectonic instability and variation in height of the source area. Faulting of Upper Middle Cambrian and Lower Dresbachian age has been demonstrated near Ulverstone. Campana and King state: “The proportion of coarse material increases upwards in the Dundas and Huskisson successions at least.” Turbidity currents brought fragments of grey, red, black and banded cherts, banded slate, quartzite, basalt and golden mica (this last presumably from breakdown of Precambrian mica schist) to the Dundas area. In view of the known distribution of chert in western Tasmania a westerly or north‐westerly source is likely. Turbidity currents deposited fragments of chert, claystone, quartzite, slate, greywacke, quartz mica schist, chloritised basic lava and spilite in the Deloraine area indicating a source area with Precambrian rocks and earlier Cambrian sediments and lavas. Near Rocky Boat Harbour the source area contained dolomite, ultrabasic rocks, granite, and Precambrian quartzites and schists. A difference between the fauna in the silts and in the greywackes is evident in the Hodge Slate at Dundas and the Kateena Formation near Ulverstone at least. The “dendroids” in the Hodge Slate are in the siltstone and the fragmentary trilobites and cystoids in the greywacke. This suggests that the fossils in the greywackes are thanatocoenotic as might be expected and introduces the possibility of remanié fossils and of shallow water fauna intercalated with deeper water fauna. The bathymetric conditions suggested by Hills and Thomas (1954) for the Cambrian of Victoria may thus not be applicable to Tasmania. Deposition was also interrupted from time to time by lava flows, some of them, at least, submarine. The Mt. Read Volcanics may be Lower Cambrian but acid and basic lavas and pyroclastic rocks are interbedded with or overlie Middle and Upper Cambrian sediments at Zeehan, Dundas, Ulverstone, Smithton and Beaconsfield. Acid volcanic rocks are commoner near the Tyennan Geanticline and basic rocks further away. Possibly during the Dresbachian ultrabasic rocks were intruded as sheets and dykes into Precambrian and earlier Cambrian rocks and by Franconian time were exposed to erosion at Adamsfield. Deposition may have commenced later at Smithton (Upper Middle Cambrian), Beaconsfield (Lower Dresbachian) and Adamsfield (Lower Franconian) than at Dundas (Lower Middle Cambrian). Campana and King express the thoughts of Bradley (1957, pp. 114–115) and the author when they state: “The Dundas Group reflects a eugeosynclinical cyclic sedimentation under unstable tectonic conditions. The group is no doubt a synorogenic suite comparable with the Flysch as it was deposited in the narrow subsiding Dundas Trough which developed along the Mt. Read Volcanic Arc, and which is similar to the present deeps of archipelago areas. Such a comparison is enhanced by the succeeding Ordovician conglomerates and sandstones, comparable in some respects with the molassic deposits which displaced the Flysch sedimentation in the Pre‐Alpine troughs (Fig. 12).” The Cambrian rocks were folded or tilted at least along the western and northern margin of the Tyennan Geanticline and near New River Lagoon, the Tyennan Geanticline was rejuvenated, the Asbestos Range Geanticline raised and the highland areas near Ulverstone and Zeehan uplifted late in the Cambrian or very early in the Ordovician. 相似文献
9.
早寒武世晚期-奥陶纪华北陆台为陆表海,沉积稳定型建造,蒙古-吉黑洋优地斜继续发展,堆积大洋玄武岩系和岛弧火山岩系。志留纪系蒙古-吉黑洋优地斜沉积复理石建造,对陆台俯冲作用加强,促使陆台隆起剥蚀,缺失志留系-泥盆系。石炭纪一二叠纪蒙古-吉黑洋变为冒地斜,与陆台同时出现北东向隆起和裂陷。三叠纪印支运动使蒙古-吉黑洋封闭,与华北陆台古生代地层同时褶皱隆起,联合组成亚洲陆台。 相似文献
10.
本文对华北陆块、秦岭陆块以及扬子陆块内的70个采样点,474个标本进行了古地磁研究,利用16个采样点,112个标本中所获得的原生剩磁,重点分析了三陆块自寒武纪以来的古地磁极位置、古地磁偏角以及古纬度的变化特点。结果表明,三陆块为不同地质构造单元;寒武纪以来,华北陆块、秦岭陆块以及扬子陆块自北到南顺序排列;寒武纪时,秦岭陆块北侧和南侧分别存在一古洋盆,此时华北陆块和扬子陆块相距约1060km,三陆块向北漂移的过程中伴随着旋转运动,其中华北陆块和秦岭陆块以反时针旋转占优势,扬子陆块以顺时针旋转占优势;三陆块完全拼合时间在早三叠世至晚白垩世之间。 相似文献
11.
分析了华北克拉通新太古代—三叠纪 16个碎屑沉积岩组合样品。与Taylor和McLennan等提出的太古宙—元古宙界线前后沉积岩及上地壳化学组成变化不同 ,新太古代五台群沉积岩具明显负Eu异常 ,相容元素含量很低 ,不相容元素含量较高 ,与典型后太古宙沉积物组成类似。而古元古代沉积岩比五台群显示出异常高的Eu/Eu 值 ,w(Sc) /w(Th) ,w(Cr) /w (Th)比值。青白口纪、寒武纪、石炭纪和二叠纪沉积岩显示正常的后太古宙沉积岩特征。三叠纪沉积岩的Eu/Eu 值 ,w (Sc) /w (Th) ,w(Cr) /w(Th)比值再次显著升高 ,推测与华北和扬子克拉通最终的陆陆碰撞作用有关。因此 ,太古宙—元古宙界线并不一致对应于上地壳演化程度迅速增高。大陆上地壳并非总是向着分异程度提高的方向演化 ,而是部分时期可出现演化程度降低的异常现象。 相似文献
12.
通过对柴达木盆地北缘欧龙布鲁克微地块的野外地质调查及精细观察,根据剖面中发育的岩石组合关系、沉积构造特征以及地层接触关系,对该区早古生代寒武纪—早奥陶世沉积及岩相古地理特征进行了详细研究。认为早古生代欧龙布鲁克微地块处于火山岛弧弧后区域,柴北缘洋俯冲及陆陆碰撞控制了该时期的盆山格局与沉积充填演化。欧龙布鲁克微地块下古生界主要发育一套海相碳酸盐岩建造,仅在寒武系底部以及下奥陶统存在陆源碎屑沉积。从岩石组合来看,沉积相类型大致可划分为蒸发潮坪相、局限台地相、开阔台地相、台地边缘相和复理石盆地沉积5大类及相应的亚类。研究区早古生代整体处于海侵状态,欧龙布鲁克微地块早寒武世经历蒸发潮坪沉积,中、晚寒武世海侵范围逐步扩大,研究区接受了一套以浅海碳酸盐岩建造为特点的局限台地—开阔台地沉积。早奥陶世基本继承了寒武纪海侵范围,欧龙布鲁克微地块沉积环境向台地边缘浅滩—前缘斜坡转变,直至早奥陶世晚期台地相向中南方向迁移而形成于高海平面下的台缘斜坡—欠补偿深水陆棚沉积环境。 相似文献
13.
E. V. Arkhipova A. D. Zhigalin L. I. Morozova A. V. Nikolaev 《Doklady Earth Sciences》2012,446(2):1176-1179
A measurable effect of mass bombing on weak to moderate seismicity, endogenous microseism intensity, and acceleration of tectonic processes has been found. This effect is seen in the regime of strong and catastrophic earthquakes, a decrease in magnitude and time for their preparation, and lesser seismic hazard. The M = 7.8 Van Earthquake on October 23, 2011, was induced to occur early due to mass bombing in Libya and other regions of North Africa; however, the induced character caused its magnitude to be less by several tenths than it might have been. 相似文献
14.
The Cadomian basement and the Cambro-Ordovician overstep sequence in Saxo-Thuringia is characterized by clastic sedimentation from the Late Neoproterozoic to the Ordovician. Magmatism in the Avalonian–Cadomian Arc preserved in Saxo-Thuringia occurred between ca. 570 and 540 Ma. Peri-Gondwanan basin remnants with Cadomian to Early Palaeozoic rocks are exposed as very low-grade metamorphosed rocks in six areas (Schwarzburg Anticline, Berga Anticline, Doberlug Syncline, North Saxon Anticline, Lausitz Anticline, and Elbe Zone). A hiatus in sedimentation between 540 and 530 Ma (Cadomian unconformity) is related to the Cadomian Orogeny. A second gap in sedimentation occurred during the Upper Cambrian (500 to 490 Ma) and is documented by a disconformity between Lower to Middle Cambrian rocks and overlying Tremadocian sediments. Major and trace-element signatures of the Cadomian sediments reflect an active margin (“continental arc”), those of the Ordovician sediments a passive margin. The Cambrian sediments have inherited the arc signature through the input of relatively unaltered Cadomian detritus. Initial Nd and Pb isotope data from the six Saxo-Thuringian areas demonstrate that there is no change in source area with time for each location, but that there are minor contrasts among the locations. (1) Cadomian sediments from the Lausitz Anticline, the Doberlug Syncline and the Elbe Zone have lower 207Pb/204Pb than all other areas. (2) The core of the Schwarzburg Anticline, which is overprinted by greenschist facies conditions and detached, is isotopically heterogeneous. One part of its metasedimentary units has less radiogenic Nd than sediments from other low-grade units of similar age in the same area. (3) Cadomian sediments from the Schwarzburg Anticline show an input of younger felsic crust. (4) The Rothstein Group shows distinct input of young volcanic material. Also, (5) Cadomian sediments from the Lausitz Anticline, the Elbe Zone and parts of the North Saxon Anticline are characterized by input from an old mafic crust. Nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1.5–1.9 Ga, which suggests derivation from an old craton as found for other parts of the Iberian–Armorican Terrane Collage. Similarly, the Pb isotope data of all areas indicate sediment provenance from an old craton.The rapid change of lithologies from greywacke to quartzite from the Late Neoproterozoic (Cadomian basement) to the Ordovician does not reflect changes in sediment provenance, but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation. This change in sediment maturity takes its chemical expression in lower overall trace-element contents in the quartzite (dilution effect by quartz) and relative enrichment of some trace-elements (Zr, MREE, HREE due to detrital zircon and garnet). The Rb–Sr systematics of the quartzites and one Ordovician tuffite was disturbed (most likely during the Variscan Orogeny), which suggests a lithology-controlled mobility of alkali and calc-alkali elements. By comparison with available data, it seems unlikely that only Nd TDM model ages are useful to distinguish between West African and Amazonian provenance. Nd TDM model ages of 1.5 to 1.9 Ga in combination with paleobiogeographic aspects, age data from detrital zircon, and palaeogeographic constraints, especially through tillites of the Saharan glaciation in the Hirnantian, strongly indicate a provenance of Saxo-Thuringia from the West African Craton. 相似文献
15.
文章对采自华北板块山东潍坊、河北唐山和辽宁大连的寒武系开腔骨类化石的新材料进行了研究，这些化石鉴定为
Chancelloria 属。辽宁大连地区的Chancelloria 产自寒武系第二统第四阶馒头组下部的黄绿色页岩；山东潍坊地区的
Chancelloria 产自苗岭统乌溜阶馒头组上部的黄绿色页岩和鼓山阶张夏组的深灰色中厚层灰岩；河北唐山地区的Chancelloria
产于芙蓉统江山阶长山组的薄层灰岩，该层位是目前Chancelloria 属在中国产出的最高层位，也是全球的最高层位之一。这
些来自华北寒武系第二统—芙蓉统的Chancelloria 骨片与早期的骨片相比，展现出骨片形态趋于规则、基面从浑圆趋于平
整、骨片整合度提升的特点，进一步印证了之前关于此类问题的研究结论。 相似文献
16.
文章对采自华北板块山东潍坊、河北唐山和辽宁大连的寒武系开腔骨类化石的新材料进行了研究,这些化石鉴定为
Chancelloria 属。辽宁大连地区的Chancelloria 产自寒武系第二统第四阶馒头组下部的黄绿色页岩;山东潍坊地区的
Chancelloria 产自苗岭统乌溜阶馒头组上部的黄绿色页岩和鼓山阶张夏组的深灰色中厚层灰岩;河北唐山地区的Chancelloria
产于芙蓉统江山阶长山组的薄层灰岩,该层位是目前Chancelloria 属在中国产出的最高层位,也是全球的最高层位之一。这
些来自华北寒武系第二统-芙蓉统的Chancelloria 骨片与早期的骨片相比,展现出骨片形态趋于规则、基面从浑圆趋于平
整、骨片整合度提升的特点,进一步印证了之前关于此类问题的研究结论。 相似文献
17.
V. A. Nikishin N. A. Malyshev A. M. Nikishin D. Yu. Golovanov V. F. Proskurnin A. V. Soloviev R. F. Kulemin E. S. Morgunova G. V. Ulyanov P. A. Fokin 《Doklady Earth Sciences》2017,473(2):402-405
New data on the ages of detrital zircons from folded basement rocks and cover sediments of the Severnaya Zemlya archipelago and Izvestiy TSIK islands have been obtained. The basement age is defined as Cambrian (pre-Ordovician). The Ordovician and Silurian sandstones were mainly formed by erosion of the basement rocks. The Devonian sandstones were formed by debris sourced from the Caledonian orogen. The Carboniferous–Early Permian molasse was formed simultaneously with the erosion of the Carboniferous granitoids and weathering of the Ordovician volcanic arc rocks and the Cambrian basement. The North Kara basin was formed in the Ordovician as a back-arc basin. It experienced its main compression deformations at the boundary of the Devonian and Carboniferous and in the Carboniferous. 相似文献
18.
Primary aragonite and high‐Mg calcite in the late Cambrian (Furongian). Potential evidence from marine carbonates in Oman 
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下载免费PDF全文 Transient aragonite seas occurred in the early Cambrian but several models suggest the late Cambrian was a time of calcite seas. Here, evidence is presented from the Andam Group, Huqf High, Oman (Gondwana) that suggests a transient Furongian (late Cambrian) aragonite sea, characterized by the precipitation of aragonite and high‐Mg calcite ooids and aragonite isopachous, fibrous, cements. Stable carbon isotope data suggest that precipitation occurred just before and during the SPICE (Steptoean Positive Carbonate Isotope Excursion). Aragonite and high‐Mg calcite precipitation can be accounted for if mMg:Ca ratios were around 1.2 given the very high atmospheric CO2 at that time and if precipitation occurred in warm waters associated with the SPICE. This, together with reported occurrences of early Furongian aragonite ooids from various locations in North America (Laurentia), suggests that aragonite and high‐Mg calcite precipitation from seawater may have been more than just a local phenomenon. 相似文献
19.
到目前为止本省内早寒武世尚未发现有梅树村期和筇竹寺期沉积,仅有沧浪铺期和龙王庙期沉积存在。在济源—博爱—武陟一线以南地区有沧浪铺阶辛集组、朱砂洞组和龙王庙阶馒头组。该线以北只有龙王庙阶辛集组和馒头组。辛集组是个受特定环境控制的穿时地层单元。早寒武世沧浪铺早—中期(辛集组)沉积环境是潮下浅水陆棚和滨岸潮下带、滨岸潮坪潮间带。沧浪铺中—晚期(朱砂洞组)沉积环境是滨岸碳酸盐潮坪缓坡—潮间—潮上蒸发坪和潮间蒸发岩洼地以及潮下碳酸盐浅水缓坡。龙王庙期(馒头组)沉积环境是滨岸碳酸盐岩潮坪缓坡和潮下碳酸盐岩浅水缓坡。早寒武世痕迹化石主要产于三个层位,可分为H-T组合和L-B组合。前者为潮下浅水陆棚风暴环境痕迹组合,后者为潮间—潮上低能泥坪环境痕迹组合。早寒武世痕迹化石共11属(1新属)、16种(1新种、1相似种、10未定种)。 相似文献
20.
《International Geology Review》2012,54(6):566-574
During the early stages of North Atlantic rifting, in the Late Triassic and Early Liassic, intracontinental basins with the eruption of tholeiitic lavas developed along the Atlantic margin of Morocco and in the Atlas domain. K-Ar dating of different grain-size fractions of Cambrian schists from the Hercynian basement and of sediments from the Triassic cover yield apparent ages which decrease with grain size, from 330-300 Ma for the coarse fractions to about 220-200 Ma for the clay-size fractions. These apparent ages indicate either K-Ar resetting of Hercynian minerals, or the development of new minerals during one or more Upper Triassic to Lower Liassic thermal or hydrothermal events. Theoretical calculations indicate that a temperature of 185-210 ° C maintained for 15 ± 10 m.y. can account for the isotopic rehomogenization of the fine-grained Hercynian micas of the High Atlas. The probable cause was a rise of the upper mantle in a thin continental crust during the first stages of Atlantic rifting. 相似文献