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1.
Recent studies in northern Switzerland have shown that epicontinental areas thought to have been tectonically stable during the Mesozoic were not necessarily as rigid as presumed. By comparing Oxfordian facies boundaries and depocenters in their palinspastic position with known faults in the basement, a direct relationship between the two can be demonstrated. Previously, the lack of obvious synsedimentary tectonic features has lulled scientists into believing that the realm of the Swiss Jura was tectonically stable during the Mesozoic. However, it can be shown that facies and sedimentary structures are largely influenced by tectonics. Subsurface data provide evidence for the presence of Paleozoic troughs in the basement which, apparently, were prone to reactivation during the Pan-European stress-field reorganization taking place in the Late Jurassic. This led to differential subsidence along pre-existing lineaments within the study area, which can be recognized in the distribution of Oxfordian epicontinental basins and their coeval shallow-water counterparts. Eustatic sea-level fluctuations played an important role in the development of shallow-water facies patterns, but a subordinate role in the control of accommodation space in basins.

While tectonic activity is often recorded in the sedimentary record in the form of platform break-ups and associated sedimentary debris, more subtle indicators may be overlooked or even misinterpreted. Sedimentary structures and isopach maps, as well as subsurface data in the study area suggest that subtle synsedimentary tectonic movements led to the formation of two shallow, diachronous epicontinental basins during the Late Jurassic. It becomes possible to recognize and differentiate the combined effects of local and regional tectonism, eustasy and sedimentation.  相似文献   


2.
During the Early Jurassic (lasting?~?27 Myr) only thin deposits (mostly ca. 30–50 m) of the Staffelegg Formation accumulated in wide parts of NW Switzerland while sea-level rise was in the range of?~?60 m. Isopach and facies patterns provide clear evidence of differential subsidence while faults that formed in the basement during the late Palaeozoic became reactivated. Orientation of many relative thickness minima and maxima follows faults constituting either the Rhenish Lineament or the North Swiss Permo-Carboniferous Trough. Such pattern is seen on the isopach maps of the Schambelen, Beggingen, Weissenstein, Frick, Fasiswald, Mt. Terri, Breitenmatt, Rickenbach, Rietheim and Gross Wolf members of the Staffelegg Formation, independently upon if the individual lithostratigraphic units are condensed or display somewhat enhanced thickness. Onto a general trend of decreasing thickness to the S, often isopach anomalies of small areal extension are superimposed. They suggest that localized strike-slip movements affected a mosaic of basement blocks. Reactivation of faults in the basement during the Early Jurassic is also evidenced by temporally enhanced hydrothermal activity as documented by chronometric ages of veins and mineral alterations.  相似文献   

3.
Structural trends in the Celtic Sea area indicate that Variscan deformation patterns were inherited from Caledonian basement structures, and that the regional fold alignment is arcuate with a regional WSW-ENE direction rather than WNW-ESE (Armorican). There is no lateral structural continuity between Southern Ireland and South Wales-Southwest England. Three major structural provinces arranged en échelon across the Variscan foldbelt are recognised: (a) Southwest England, where there was complex deformation of a major basin; (b) the South Wales-Mendips foreland area, with strong basement/cover interaction and (c) the Southern Ireland graben and flanking platform province. Late Palaeozoic depositional patterns indicate that Southern Ireland and Southwest England were separated by a WSW-ENE trending platform bounded on the north by the inherited Wexford Boundary Lineament and to the south by a previously unidentified major Palaeozoic fault zone, here termed the Bristol Channel Lineament. The South Wales-Mendips Variscan successions accumulated on this intervening Wales-Celtic Sea platform, and were partly influenced by rejuvenated Caledonian fault lines. It is suggested that the northern margin of the Rheno-Hercynian foldbelt (the Variscan Front) be taken along the Bristol Channel Lineament, which can be traced for some 400 km southwestwards towards the Goban Spur on the continental margin. This permits a rationalisation of both tectonic and major facies boundaries in locating the front. It is also suggested that the structurally localised nature of the Southern Ireland basin be recognised by designating it as the Southern Ireland Zone of the Variscan foldbelt.The sites of Mesozoic rifting in the Celtic Sea and adjacent areas, although complex in detail, appear to have been located along the Wexford Boundary and Bristol Channel Lineaments.  相似文献   

4.
塔里木盆地库车坳陷西秋古隆起的形成及其演化   总被引：1，自引：0，他引：1       下载免费PDF全文
重力异常资料显示,库车坳陷南缘西秋构造带深层发育有基底隆起。本文通过地震资料解释确认了西秋构造带深层占隆起的结构,分析了占隆起的形成和演化过程。西秋构造带南侧边缘存在一条区域性基底断裂,断裂北侧新生界下伏中生界、古生界明显减薄或地层缺失,总体上表现为断背斜形态的古隆起构造。结合区域构造演化分析认为,泥盆纪~石炭纪(D-C)塔里木克拉通边缘隆升、二叠纪-三叠纪(P-T)受南天山负荷影响产生的克拉通边缘压陷的构造演化过程中,西秋构造带处于"跷跷板"式地壳升降运动的"支点"部位,发育古隆起和基底卷入高角度断层,晚期南天山隆升向南斜向推挤的挤压剪切应力场使古隆起边界断层复活,基底断裂活动并在新生界之下形成冲断隆起。  相似文献   

5.
Southern Egypt is mostly covered by clastic sediments belonging to the Paleozoic and the Mesozoic. The Precambrian basement rocks bound the Etbai area to the east and Gabgaba area to the west. The basement extends further west forming dissected small and major exposures in southern Egypt, south of latitude 23° 30′ N but are covered by Cretaceous-Lower Tertiary sediments further north, the Western Limestone Plateau. The clastic sediments in southeast Egypt, on the western side of the basement rocks in-between latitudes 22° N and 24° 35′ N, built two sub-basins, Kom Ombo (Garara) sub-basin in the north and south Nile Valley sub-basin in the south. These are separated by a dissected basement wall. The two sub-basins have different lithostratigraphic successions, Paleozoic (Early to Late) in the south Nile Valley sub-basin whereas Late Paleozoic-Mesozoic-Tertairy in the Kom Ombo sub-basin. The platform clastic sediments within both sub-basins were possibly supplied from an easterly located Paleotethys extending to North Gondwana. The Oxfordian opening of the Indian Ocean associated with rise in sea level supplied more waters to the north and sediments by passed the filled southern Nile Valley sub-basin and reached the adjacent Kom Ombo sub-basin defining a depositional shift. On the other hand, during the Jurassic, Northern Egypt received Neotethys waters that filled deeper sub-basins (e.g., the Maghara sub-basin), hence the difference in lithology between Jurassic northern and southern sediments. Since the Jurassic, most of Egypt received Tethys waters. In the drilled wells studied, the younger top sediments surrounding the well sites are related to the Tethys geostratigraphy. The sub-basins in southern Egypt are controlled by N-S faults defining constant subsiding basins. The E-W Guinea–Nubia Lineament bounds the northern side of the Kom Ombo sub-basin, where it is closed by a northern basement arch.  相似文献   

6.
《Geodinamica Acta》2001,14(6):361-372
The Mamora  area (Morocco) is located in the northern part of the Meseta and the southern part of Rharb. The recent formations (Mesozoic to Quaternary) lie unconformably on a Paleozoic basement. This study based on hydrogeological, sedimentological, drilling data and seismic reflection profiles interpretation, proposes new interpretations of geodynamical evolution of this area particularly in terms of tectonic patterns. The most ancient formations recognized in this region are Paleozoic schists and quartzites in the Tiflete sector. They represent the basement of the basin on which Triassic conglomerates and red mudstones associated with basalts lie unconformably. Jurassic and Cretaceous sediments are limestones and marls. The Mio-pliocene formations are open marine blue marls. Plio-quaternary sediments are limestones and sands containing gravel and pebbles. Miocene to Pliocene blue marls facies corresponds to deep marine marls (bathyal as indicated by planctonic foraminifers) with an attributed age from upper Miocene 〚9〛 to middle Pliocene 〚7〛. A facies distribution map of the top of the blue marls has been realized where four main facies - conglomerate, shelly sandstone, limestone and marls - indicate a major regression in the Mamora basin. The datation of the formations was mostly realized by Wernli 〚22〛, 〚23〛, 〚24〛, 〚25〛, and Cirac 〚10〛. In the Mamora area, Hercynian faults show two main structural directions, N020°E-N040°E (Agadir-Rabat), N120°E (Rabat-Tiflète) 〚5〛, and a new major Hercynian fault (K2S). The seismic profiles have been studied between Sidi Slimane and Sidi Yahia area, to illustrate the structure of the Mamora, and to replace it, in the geodynamical evolution. The seismic reflection lines and drilling data show that the eastern Mamora was subdivided into two sectors : i) the southern sector is affected by Hercynian faults which create horsts and grabens in the Paleozoic. Mio-Pliocene formations infill these depressions and are covered by Quaternary sediments ; ii) the northern sector is constituted by various formations : 1. Paleozoic formation as basement covered by autochthonous Mesozoic to Miocene, 2. Prerifain nappes (marls and evaporites), 3. Mio-Plio-Pleistocene formations as subautochthonous to autochthonous. These two sectors are separated by a major fault (K2S). On the other hand, in the occidental Mamora, the facies distribution and the Plio-Pleistocene thickening seem to be induced by faults with a NE-SW and NW-SE trends which affect the Paleozoic basement. Then, between the Meseta domain and the septentrional Rharb basin, two major Hercynian initially dextral shear zones, Rabat-Tiflete and K2S, have been recognised. During the Atlantic Ocean opening, they are probably senestral shear zones. At the same time the subsidence in Rharb basin is active, major action of these faults is normal. Therefore, Mamora represents a real hinge between stable Meseta and unstable septentrional Rharb basin.  相似文献   

7.
The Harz Mountains and the adjacent Subhercynian Cretaceous Basin figure as the most prominent surface representative for Late Cretaceous inversion structures in Central Europe. Facies, depositional architecture and provenance of the basin fill reflect mechanisms and timing of the exhumation of the Harz. From Hauterivian to Early Santonian there is no evidence for detrital input from the nearby Harz area. Sediments are mature quartzarenites derived from Paleozoic basement rocks and/or recycled Permian to Mesozoic sedimentary rocks. This situation changed drastically in Middle to Late Santonian when freshly exhumed and eroded Mesozoic sedimentary cover rocks of the Harz were delivered into the basin. Feldspar and lithoclasts reflect erosion of Triassic and, in places, Jurassic to Turonian strata. Apatite and garnet in heavy mineral spectra are derived from largely unweathered Lower Triassic Buntsandstein as indicated by apatite and garnet chemistry. In Early Campanian, Paleozoic lithoclasts indicate erosion cutting down into the basement of the Harz. Simultaneous strong decrease of feldspar, garnet and apatite suggest an almost complete removal of the 2–3 km thick Mesozoic cover of the Harz within only 2–4 Myr. This translates into an exhumation rate of approximately 1 mm/a consistent with apatite fission track data from granitoid rocks of the Harz Mountains.  相似文献   

8.
The Baoshan block of the Tethyan Yunnan, southwestern China, is considered as northern part of the Sibumasu microcontinent. Basement of this block that comprises presumably greenschist-facies Neoproterozoic metamorphic rocks is covered by Paleozoic to Mesozoic low-grade metamorphic sedimentary rocks. This study presents zircon ages and Nd–Hf isotopic composition of granites generated from crustal reworking to reveal geochemical feature of the underlying basement. Dating results obtained using the single zircon U–Pb isotopic dilution method show that granites exposed in the study area formed in early Paleozoic (about 470 Ma; Pingdajie granite) and in late Yanshanian (about 78–61 Ma, Late Cretaceous to Early Tertiary; Huataolin granite). The early Paleozoic granite contains Archean to Mesoproterozoic inherited zircons and the late Yanshanian granite contains late Proterozoic to early Paleozoic zircon cores. Both granites have similar geochemical and Nd–Hf isotopic charateristics, indicating similar magma sources. They have whole-rock T DM(Nd) values of around 2,000 Ma and zircon T DM(Hf) values clustering around 1,900–1,800 and 1,600–1,400 Ma. The Nd–Hf isotopic data imply Paleoproterozoic to Mesoproterozoic crustal material as the major components of the underlying basement, being consistent with a derivation from Archean and Paleoproterozoic terrains of India or NW Australia. Both granites formed in two different tectonic events similarly originated from intra-crustal reworking. Temporally, the late Yanshanian magmatism is probably related to the closure of the Neotethys ocean. The early Paleozoic magmatism traced in the Baoshan block indicates a comparable history of the basements during early Paleozoic between the SE Asia and the western Tethyan belt, such as the basement outcrops in the Alpine belt and probably in the European Variscides that are considered as continental blocks drifting from Gondwana prior to or simultaneously with those of the SE Asia.  相似文献   

9.
Abstract

The Mamora area (Morocco) is located in the northern part of the Meseta and the southern part of Rharb. The recent formations (Mesozoic to Quaternary) lie unconformably on a Paleozoic basement. This study based on hydrogeological, sedimentological, drilling data and seismic reflection profiles interpretation, proposes new interpretations of geodynamical evolution of this area particularly in terms of tectonic patterns. The most ancient formations recognized in this region are Paleozoic schists and quartzites in the Tifíete sector. They represent the basement of the basin on which Triassic conglomerates and red mudstones associated with basalts lie unconformably. Jurassic and Cretaceous sediments are limestones and marls. The Mio-pliocene formations are open marine blue marls. Plio-quaternary sediments are limestones and sands containing gravel and pebbles. Miocene to Pliocene blue marls facies corresponds to deep marine marls (bathyal as indicated by planctonic foraminifers) with an attributed age from upper Miocene [9] to middle Pliocene [7]. A facies distribution map of the top of the blue marls has been realized where four main facies—conglomerate, shelly sandstone, limestone and marls—indicate a major regression in the Mamora basin. The datation of the formations was mostly realized by Wernli [22, 23, 24, 25], and Cirac [10], In the Mamora area, Hercynian faults show two main structural directions, N020°E-N040°E (Agadir-Rabat), N120°E (Rabat- Tiflète) [5], and a new major Hercynian fault (K2S). The seismic profiles have been studied between Sidi Slimane and Sidi Yahia area, to illustrate the structure of the Mamora, and to replace it, in the geodynamical evolution. The seismic reflection lines and drilling data show that the eastern Mamora was subdivided into two sectors: i) the southern sector is affected by Hercynian faults which create horsts and grabens in the Paleozoic. Mio-Pliocene formations infill these depressions and are covered by Quaternary sediments; ii) the northern sector is constituted by various formations: 1. Paleozoic formation as basement covered by autochthonous Mesozoic to Miocene, 2. Prerifain nappes (marls and evaporites), 3. Mio-Plio-Pleistocene formations as subautochthonous to autochthonous. These two sectors are separated by a major fault (K2S). On the other hand, in the occidental Mamora, the facies distribution and the Plio-Pleistocene thickening seem to be induced by faults with a NE-SW and NW-SE trends which affect the Paleozoic basement. Then, between the Meseta domain and the septentrional Rharb basin, two major Hercynian initially dextral shear zones, Rabat- Tiflete and K2S, have been recognised. During the Atlantic Ocean opening, they are probably senestral shear zones. At the same time the subsidence in Rharb basin is active, major action of these faults is normal. Therefore, Mamora represents a real hinge between stable Meseta and unstable septentrional Rharb basin. © 2001 Éditions scientifiques et médicales Elsevier SAS  相似文献   

10.
The Late Permian/Early Triassic succession of the Central European Basin (CEB) was repeatedly affected by the tectonic pulses associated with the earliest phases of Tethyan and Arctic–North Atlantic rifting. Effects of the differential tectonic subsidence are particularly well recorded by unconformities, which form widespread sequence boundaries. Such unconformities are most obvious in areas occupied by fault-controlled intra-basinal highs (swells). In that areas, stratigraphic loss may comprise entire Lower and Middle Buntsandstein formations and in places remnant Middle Buntsandstein successions directly rest on Permian strata. Analysis of 3D-seismic data and well logs combined with high-resolution sedimentological logging of drillcores at the western margin of the Ems Trough (NW Germany) reveals details of synsedimentary tectonic control on sequence development. Early Triassic extensional faulting of basement blocks provided stepwise addition of accommodation space for continental sequences by growth faulting along north–south oriented fault zones blocks on the flanks of the East Netherlands High. This process is most evident during the development of the Hardegsen Unconformity, which is characterised by an amalgamation of succeeding unconformity surfaces in areas of structurally controlled intrabasinal highs.  相似文献   

11.
青藏高原拉萨地体北部的前寒武纪变质作用及构造意义   总被引：12，自引：0，他引：12  
张泽明  董昕  耿官升  王伟  于飞  刘峰 《地质学报》2010,84(4):449-456
青藏高原南部拉萨地体中分布的角闪岩相至麻粒岩相变质岩一直被认为是前寒武纪变质基底,但并没有获得可靠的年代学证据。本文运用原位锆石U-Pb定年方法,在拉萨地体北部那果地区的变质岩中获得了约720Ma的变质年龄,从而证明拉萨地体北部在新古元代经历了角闪岩相变质作用和近同期的岩浆作用。基于这一成果和在拉萨地体中、南部高级变质岩中陆续获得的中、新生代变质年龄,对拉萨地体变质作用的时、空变化及其成因进行了初步探讨。  相似文献   

12.
合肥盆地基底构造属性   总被引：33，自引：4，他引：29       下载免费PDF全文
根据合肥盆地及周边地表地质、地震剖面、同位素测年及MT等新资料的综合研究,提出中-新生代合肥盆地的基底是一个不同构造类型基底的叠合与复合.上古生界以前的基底以六安断裂为界,其北为华北板块陆壳型-过渡壳型结晶基底及其上的华北克拉通-被动大陆边缘盆地沉积的上元古-下古生界基底;其南为大别型结晶基底及其上的北淮阳弧后盆地沉积的上元古-下古生界变质基底,而上古生界基底属于弧后前陆盆地型沉积.六安断裂是合肥盆地部位北大别弧、北淮阳晚元古-早古生代弧后盆地在早古生代晚期-晚古生代早期与华北板块的弧-陆碰撞缝合线.  相似文献   

13.
Formation of Mesozoic western China, which was dominated by tectonic amalgamation along its southern margin and associated intracontinental tectonisms, holds a key for interpreting the succedent Cenozoic evolution. This paper presents new data including lithology, sedimentary facies, stratigraphic contact, seismic interpretation and paleo-structures within the Upper Jurassic-Lower Cretaceous strata in the northern Qaidam Basin, NW China. These data all account for a contractional tectonic deformation in the earliest Cretaceous. The South Qilian Shan, according to the sedimentary features and provenance analysis, reactivated and exhumated during the deformation, controlling the deposition of the Lower Cretaceous sequences. A simplified model for the Late Jurassic-Early Cretaceous paleogeography and tectonics of the northern Qaidam Basin is accordingly proposed. The results also support a ∼25° clockwise rotation of the Qaidam Basin since the Early Cretaceous and a more accurate Mesozoic evolution process for the basin. This earliest Cretaceous deformation, associated with the reactivation of the South Qilian Shan at the time, are part of the intracontinental tectonisms in central Asia during the Mesozoic, and probably driven by both the closure of the Mongol-Okhostk Ocean to the north and the collision of the Lhasa and the Qiangtang blocks to the south.  相似文献   

14.
Basement fault reactivation is now recognized as an important control on sedimentation and fault propagation in intracratonic basins. In southern Ontario, the basement consists of complexly structured mid-Proterozoic (ca. 1.2 Ga) crystalline rocks and metasedimentary rocks that are overlain by up to 1500 m of Paleozoic sedimentary strata. Reactivation of basement structures is suspected to control the location of Paleozoic fault and fracture systems, but evaluation has been hindered by a limited understanding of the regional structural characteristics of the buried basement. New aeromagnetic- and gravimetric-lineament mapping presented in this paper better resolves the location of basement discontinuities and provides further evidence for basement controls on the distribution of Paleozoic fault and fracture systems. Lineament mapping was facilitated by reprocessing and digital image enhancement (micro-levelling, regional residual separation, derivative filtering) of existing regional gravity and aeromagnetic datasets. Reprocessed images identify new details of the structural fabric of the basement below southern Ontario and delineate several previously unrecognized aeromagnetic and gravity lineaments and linear zones. Linear zones parallel the projected trends of mid-Proterozoic terrane boundaries identified by field mapping on the exposed shield to the north of the study area, and are interpreted as zones of shearing and basement faulting. Mapped aeromagnetic and gravity lineaments show similar trends to Paleozoic faults and fracture networks and broad zones of seismicity in southern Ontario. These new data support an ‘inheritance model’ for Paleozoic faulting, involving repeated reactivation and upward propagation of basement faults and fractures into overlying cover strata.  相似文献   

15.
Due to the political boundaries between the Central European countries, on one hand, and the thick Tertiary cover in the Pannonian Basin, on the other, the eastward continuation of the Alpine and Dinaridic units has been ambiguous and poorly documented. Based on comparative analyses, the aim of the present paper is to define the pre-Tertiary structural units in the junction area of the Alpine, Dinaridic, and Pannonian regions, in the SW part of the Pannonian Basin, and to draw conclusions on the continuation of the Alpine and Dinaridic units. According to diagnostic characteristics of the Periadriatic Lineament system, the Balaton Lineament system may be considered as its direct eastern continuation. North of the Periadriatic–Balaton Lineament system, the Transdanubian Range Unit, due to its pre-Tertiary paleogeographic setting, shows mainly South Alpine facies relations; however, its present structural position is identical to that of the Upper Austroalpine nappes. Between the Periadriatic–Balaton and Zagreb–Zemplin Lineament systems heterogeneous structural units are juxtaposed, forming the Sava Composite Unit. In the northern part of this composite unit non-metamorphosed nappes occur which can be considered the eastern continuation of the South Alpine units. These nappes are overthrust onto Internal Dinaridic units in the Tertiary. The Zagreb–Zemplin (Mid-Hungarian) Lineament separates the Sava Unit from the Tisza Unit showing close affinity to the Tethyan margin of the Eurasian plate during the early stage of the Alpine evolution. Received: 1 June 1999 / Accepted: 14 March 2000  相似文献   

16.
The European Hercynides are considered the collisional result of Baltica and the microcontinents of Southern Europe, after subduction destroyed the intervening Rheic Ocean during the early Paleozoic. Their geotectonic development is assumed to consist of four overlapping stages:
1. (1) lithospheric thinning, upwelling of hot asthenospheric material, subsidence along listric faults, and basinal and geosynclinal development on the opposing shelves of the Rheic Ocean starting in pre-Devonian time;
2. (2) intermittent subduction of the Rheic Ocean interspersed with episodes of fracturing, volcanism, local uplift and subsidence, and basement reactivation as a result of compression with dextral megashear, particularly since the earliest Devonian;
3. (3) several phases of folding with a northward vergence, and thrusting and overthrusting along listric surfaces, the true orogenic stage;
4. (4) post-orogenic stage of massive granite intrusions and subsequent volcanism in the Permo-Triassic
.The high clastic content (as opposed to carbonates) of the sedimentary sequences involved in the subduction and folding processes and the consequent release of large amounts of meteoric water are held responsible for the synorogenic and post-orogenic magma rise, and for the wide zone of anatectic granites and migmatites. The dominant dextral megashear, the constant re-adjustment of the microcontinents of Southern Europe (oblique collision) and the scarcity of back-arc basins, oceanic plateaus and microcontinents led to the poor preservation of ophiolites and ultrabasic rocks, and to a wide (over 1500 km) Hercynian Foldbelt.During the Paleozoic, the depositional center of the Rhenish Massif shifted from south polar latitudes in the early Ordovician to tropical positions within a period of about 100 m.y. The sediment facies reflects this paleogeographic development.  相似文献   

17.
青藏高原北羌塘地区晚三叠世地层展布和沉积型式   总被引：10，自引：3，他引：10  
北羌塘盆地地处拉竹龙-金沙江缝合带和双湖构造混杂岩带之间,自北向南可划分出5个沉积相带/岩石地层单位：以砂泥质复理石-洋岛、岛弧型火山岩-大理岩岩石组合沉积为特征的若拉岗日群,以深水复理石盆地相沉积为特征的藏夏河组,以深水暗色细碎屑岩盆地相沉积为特征的结扎群,以开阔台地相/缓坡相碳酸盐岩沉积为特征的菊花山组,以三角洲相含煤碎屑岩系沉积为特征的土门格拉群.晚三叠世北羌塘盆地显示为南缓北陡的箕状沉积格局,盆地内充填物为南薄北厚的楔形沉积体,且双物源、沉降中心和沉积中心不一致,表明其具有前陆盆地的一系列沉积特征.  相似文献   

18.
In Central Switzerland, Mesozoic sedimentation began after erosion and peneplainisation of the Hercynian relief and late Paleozoic continental deposition in SW-NE striking pull-apart basins. The first Triassic sedimentary sequence overlaying a weathered crystalline basement consists of a relatively thin (<10 m), lithologically highly variable unit with coarse-grained siliciclastic deposits at the base, grading into a mixed sandstone/shale-dolomite sequence followed by well-bedded dolomites with chert nodules.Sedimentary texture analyses and petrological investigations revealed four different sedimentary units starting at the base with a regolith unit that represents the weathered crystalline basement. It is overlain by terrestrial plain deposits, followed by mixed siliciclastic-carbonaceous sediments and a sequence of dolomites, deposited between the supralittoral and eulittoral zones of a tidal flat (Mels-Formation), and the eulittoral to sublittoral zones of a carbonate tidal flat environment (Röti-Dolomit), respectively.Palynological data from four localities in Central Switzerland indicate a heterochronous early Anisian age (Aegean – Bithynian/Pelsonian) for the supra- to eulittoral mixed siliciclastic-carbonaceous sediments. These new biostratigraphic ages suggest that the first Triassic marine transgression in Central Switzerland is time equivalent with those of the basal Wellendolomit in Northern Switzerland but slightly older than in the Germanic Basin. Consequently, Central Switzerland was located at this time at the northern shoreline of the Tethys and not on the southern limit of the Germanic Basin.  相似文献   

19.
苏北盆地为一新生代形成的拉张盆地,震旦纪至白垩纪地层构成了盆地的基底,本文对中、古生界碳酸盐岩盆地基底演化和盆地形成进行了四个阶段的古地热史恢复和生烃史模拟并依次叠加,得到了部分钻井的有机质的成熟度（Ｒ０值）。其结果基本上与地层实测（Ｒ０）值相吻合,为构造演化复杂的苏北地区中、古生界烃源岩成熟度提供了一些新的消息,并可作为该区进一步油气远景评价的参考。  相似文献   

20.
安徽的地壳演化:Sr,Nd同位素证据   总被引：13，自引：0，他引：13  
陈江峰  谢智  张巽  周泰禧 《安徽地质》2001,11(2):123-130
在地壳(幔)演化和板块构遣的框架内，评述了有关安徽南部(扬子地块东部，包括大别遣山带和江南遣山带)的同位素地质年代学和Nd，Sr同位素地球化学示踪研究的成果。该地区出露地表的中元古界溪口群浅变质岩代表皖南的基底，沿江地区和大别山区的基底包舍太古宇或／和古元古界古老岩石。此格局还影响到从震旦纪到古生代沉积岩的物源区，江南深断裂以北的沉积岩中有古老岩石的贡献，而以南的物源主要来自出露的中元古界岩石。扬子陆块南北缘(大别和江南遣山带)的晋宁期演化可能与罗迪尼亚超大陆演化有密切关系，但有关研究开展很少。三叠纪大陆深俯冲和超高压变质作用研究已成为国际地球科学的热点。晚中生代(120-140Ma)本区发生强烈的岩浆活动，并伴有重要矿床的形成。中酸性岩的形成是一种壳幔物质混合的过程。沿江地区陆下地幔具有富集特征，为扬子型岩石圈地幔与软流圈地幔混合的产物。从晚中生代到第四纪，基性岩指示其源区的地球化学性质有随时间变得越来越亏损的趋势。  相似文献   

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