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1.
《Geodinamica Acta》2013,26(1-3):83-100
The Magura Basin domain developed in its initial stage as a Jurassic-Early Cretaceous rifted passive margin that faced the eastern parts of the oceanic Alpine Tethys. In the pre- and syn-orogenic evolution of the Magura Basin the following prominent periods can be distinguished: Middle Jurassic-Early Cretaceous syn-rift opening of basins (1) followed by Early Cretaceous post-rift thermal subsidence (2), latest Cretaceous–Paleocene syn-collisional inversion (3), Late Paleocene to Middle Eocene flexural subsidence (4) and Late Eocene - Early Miocene synorogenic closing of the basin (5). The driving forces of tectonic subsidence of the basin were syn-rift and thermal post-rift processes, as well as tectonic loads related to the emplacement of accretionary wedge. This process was initiated at the end of the Paleocene at the Pieniny Klippen Belt (PKB)/Magura Basin boundary and was completed during Late Oligocene in the northern part of the Magura Basin. During Early Miocene the Magura Basin was finally folded, thrusted and uplifted as the Magura Nappe. 相似文献
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3.
Stable C and O isotope records were obtained from carbonate rocks spanning the Hauterivian to Cenomanian interval collected in several sections from the carbonate platform of Pădurea Craiului (Apuseni Mountains, Romania). In the absence of some key biostratigraphic marker species, stable isotopes were applied as a tool for stratigraphic correlation and dating. The composite δ13C and δ18O curves for the Early Cretaceous shows variable conditions with large positive and negative excursions and provide information on past environmental changes. The Hauterivian and the Barremian limestones (Blid Formation) display lower δ13C values (−2.8‰ to +2.9‰) relative to the Aptian–Albian deposits (−2.6‰ to +5.4‰) (Ecleja, Valea Măgurii and Vârciorog Formations). The red detrital formation (Albian–Cenomanian) is characterized by a highly variable distribution of the δ13C values (−3.5‰ to +3.9‰). Based on the similarities between the C-isotope curve established in Pădurea Craiului and from other sections in the Tethyan and the Pacific regions, two major oceanic anoxic events characterized by δ13C positive excursions were clearly recognized. The first is the OAE1a event (Early Aptian) in the upper part of the Ecleja Formation and the Valea Măgurii Formation. The second is the OAE1b event (Late Aptian–Albian) in the upper part of the Vârciorog Formation and in the Subpiatră Member. The position of the Aptian/Albian boundary is estimated to be at the upper part of the Vârciorog Formation, immediately after the beginning of the δ13C positive excursion. The δ13C data show major negative excursions during the Barremian (Blid Formation), Early Aptian (Ecleja Formation), and Late Aptian (Vârciorog Formation). The O isotope variation pattern (−10.2‰ to −2.1‰) is consistent with progressively warming temperatures during the Early Barremian followed by a cooling period. A subsequent warming period culminated in the Early Aptian. A significant cooling phase corresponds to the Late Aptian and Early Albian and the climate cooled again during the Late Albian and into the Early Cenomanian stage. The data provide a better understanding of the Early Cretaceous sedimentation cycles in Pădurea Craiului and create a more reliable framework for regional correlations. 相似文献
4.
内蒙古二连盆地早白垩世砂岩型铀矿目的层时代探讨 总被引：4，自引：0，他引：4
赛汉高毕和巴彦乌拉地区是二连盆地两个新近突破的砂岩型铀矿区,分属于两个不同的二级构造单元,前者位于乌兰察布坳陷的东北角,后者位于马尼特坳陷的西南角,中间由贺根山断裂分隔。由于两个地区的含矿目的层的厚度、岩性、岩石颜色、沉积相和沉积环境等存在一定的差别,故而引起了两地的含矿目的层时代的争论。为了解决这一问题,在砂岩型铀矿区部分钻孔进行了古地磁采样、分析,结果表明:地磁极性序列变化基本相似,相当于国际标准年表的阿普第—阿尔必期。同时,在两个地区采集的部分孢粉样品分析结果显示,均获得较多早白垩世的标志分子,组合面貌与我国北方早白垩世赛汉塔拉组Cicatricosisporites-Disacciatrileti孢粉植物群的特征非常相符。古地磁和孢粉分析资料共同有力地证实了二连盆地的这两个地区砂岩型铀矿的目的层属于同一个层位,即下白垩统赛汉塔拉组。 相似文献
5.
Syn-rift shallow-marine carbonates of Late Aptian to Early Albian age in the southern Maestrat Basin (E Spain) register the thickest Aptian sedimentary record of the basin, and one of the most complete carbonate successions of this age reported in the northern Tethyan margin. The host limestones (Benassal Formation) are partially replaced by dolostones providing a new case study of fault-controlled hydrothermal dolomitization. The syn-rift sediments filled a graben controlled by normal basement faults. The Benassal Fm was deposited in a carbonate ramp with scarce siliciclastic input. The lithofacies are mainly characterized by the presence of orbitolinid foraminifera, corals and rudist bivalves fauna. The succession is stacked in three transgressive–regressive sequences (T–R) bounded by surfaces with sequence stratigraphic significance. The third sequence, which is reported for the first time in the basin, is formed by fully marine lithofacies of Albian age and represents the marine equivalent to the continental deposits of the Escucha Fm in the rest of the basin.The dolomitization of the host rock is spatially associated with the basement faults, and thus is fault-controlled. The dolostone forms seismic-scale stratabound tabular geobodies that extend several kilometres away from the fault zones, mostly in the hanging wall blocks, and host Mississippi Valley Type (MVT) deposits. The dolostones preferentially replaced middle to inner ramp grain-dominated facies from the third T–R sequences consisting of bioclastic packestones and peloidal grainstones. Field and petrology data indicate that the replacement took place after early calcite cementation and compaction, most likely during the Late Cretaceous post-rift stage of the basin. The dolostone registers the typical hydrothermal paragenesis constituted by the host limestone replacement, dolomite cementation and sulfide MVT mineralization. The Aptian succession studied provides a stratigraphic framework that can be used for oil exploration in age-equivalent rocks, especially in the València Trough, offshore Spain. Moreover, this new case study constitutes a world class outcrop analogue for similar partially stratabound, dolomitized limestone reservoirs worldwide. 相似文献
6.
根据非海相与海相,特别是共同的海相和非海相软体动物化石的对比,并结合放射性同位素测年,中国东北黑龙江东部和辽宁西部,韩国东南部庆尚盆地,日本西南部内带岐阜县北部牧户/庄川地区和外带四国德岛和物部地区早白垩世地层得到了对比,产自这些地层的非海相软体动物的时代也因此受到了约束。著名的中国东北含煤地层龙爪沟和鸡西群,盛产热河生物群/动物群的热河群的时代均为欧特里沃期/巴列姆期阿普特期,它们的上覆地层桦山群和孙家湾组为阿尔必期。韩国西南部新洞群和除金洞组以外的河阳群为阿普特期阿尔必期,不整合于新洞群之下的卯谷组主要为欧特里沃期。日本西南部内带的牧户/庄川地区的手取群和外带德岛和物部地区的物部川群均为欧特里沃期阿尔必期。Cuniopsis kihongi,Nakamuranaia leei,Koreanaia cheongi和Trigonioides(Wakinoa)tetoriensis的时代为欧特里沃期早巴列姆期。Viviparus onogoensis,Unio ogamigoensis,Myrene(Mesocorbicular)tetoriensis及Tetoria(Tetoria)yokoyami为欧特里沃期阿普特期。Arguniella cf.quadrata,A.cf.ventricosa,Sphaerium(Sphaerium)anderssoni,Probaicalia vitimensis和Pr.gerassimovi为欧特里沃期/巴列姆期阿普特期。Nakamuranaia chingshanensis,Plicatounio(Plicatounio)multiplicatus,Sphaerium(Sphaerium)coreanicum和Micromelania?katoensis为阿普特期阿尔必期。Nippononaia sinensis,Nip.tetoriensis,Nip.ryosekiana和Trigo-nioides(Wakinoa)wakinoensis是阿普特期的标志。Trigonioides(Trigonioides)quadratus,T.(T.)heilongjiangensis,Plicatounio(Plicatounio)naktongensis,Unio longus与Sphaerium(Sphaerium)chintaoense为晚阿普特期阿尔必期或阿尔必期的标志化石。我国东北、韩国东南和日本西南部非海相,特别是淡水软体动物接近的相似性表明这三地区在早白垩世时相连,并处于同一水系。但是,在欧特里沃期阿尔必期期间,这一陆块的东部,即频临古太平洋的日本西南部的外带因地势低而多被海水覆盖,在牧户/庄川和黑龙江东部存有遭受海侵的浅而窄的海湾,凡兰吟期,特别是欧特里沃期/巴列姆期之前,中国东北韩国东南部日本西南部陆块为受造山运动引起的隆起和沉降活动影响的高低不平的高原,经受了广泛而长期的剥蚀。多数含有包括熔岩和凝灰岩在内的火山岩,并与北东北北东方向的断裂带近于平行分布的非海相白垩纪盆地直至欧特里沃期/早巴列期(有些地区可能稍早(凡兰吟期))(134～126Ma),即华北克拉通破坏的高峰期(130～120Ma)才形成。这一现象表明,这些盆地受断裂,特别是伴随有强烈火山喷发和时而局部海侵的沿着古太平洋西北缘和郯庐断裂带的构造运动的控制。 相似文献
7.
The Early Cretaceous was a time with super-greenhouse conditions and episodic global oceanic anoxic events. However, relative timing of atmospheric CO2 emissions and oceanic anoxic events, and their causal relationships remain matters of debate. Using the stomatal index approach, well-preserved fossil cuticles of Ginkgo from the Lower Cretaceous Changcai Formation, eastern Jilin, and from the Lower Cretaceous Yingcheng Formation, central Jilin, Northeast China, were investigated to reconstruct atmospheric CO2 concentrations during the Aptian and earliest Albian (Early Cretaceous). The results indicate that the CO2 concentrations reached 1098–1142 ppmv (Carboniferous standardization) or 970–1305 ppmv (regression function) during the Aptian and earliest Albian. Our estimates of palaeoatmospheric CO2 concentrations during the earliest Albian (OAE 1b) are slightly higher than the data between the early Aptian Selli (OAE 1a) and the middle Aptian Fallot OAEs; this may indicate the absence of any great emissions of CO2 during the latest Aptian and earliest Albian. 相似文献
8.
《Cretaceous Research》2002,23(3):409-438
Four transgressive-regressive (T-R) cycles and five T-R subcycles have been recognized in Lower Cretaceous strata of the northeastern Gulf of Mexico. These T-R cycles are the LKEGR-TR 1 (Lower Cretaceous, Eastern Gulf Region) (upper Valanginian–upper Aptian), the LKEGR-TR 2 (upper Aptian–middle Albian), the LKEGR-TR 3 (middle–upper Albian), and the LKEGR-TR 4 (upper Albian–lower Cenomanian) cycles. The LKEGR-TR 1 Cycle consists of three subcycles: LKEGR-TR 1–1 (upper Valanginian–lower Aptian), LKEGR-TR 1–2 (lower Aptian) and LKEGR-TR 1–3 (upper Aptian) subcycles. The LKEGR-TR 2–1 (upper Aptian–lower Albian) and the LKEGR-TR 2–2 (lower–middle Albian) subcycles constitute the LKEGR-TR 2 Cycle. The LKEGR-TR 3 and the LKEGR-TR 4 cycles consist of a single T-R cycle.Recognition of these T-R cycles is based upon stratal geometries, nature of cycle boundaries, facies stacking patterns within cycles, and large-scale shifts in major facies belts. The T-R subcycles are characterized by shifts in major facies belts that are not of the magnitude of a T-R cycle. The cycle boundary may be marked by a subaerial unconformity, ravinement surface, transgressive surface or surface of maximum regression. A single T-R cycle consists of an upward-deepening event (transgressive aggrading and backstepping phases) and an upward-shallowing event (regressive infilling phase). These events are separated by a surface of maximum transgression. The aggrading phase marks the change from base-level fall and erosion to base-level rise and sediment accumulation; this phase signals the initiation of the creation of shelf-accommodation space. The marine transgressive and flooding events of the backstepping phase are widespread and provide regional correlation datums. Therefore, these T-R cycles and subcycles can be identified, mapped, and correlated in the northeastern Gulf of Mexico area. The progradational events associated with the regressive infilling phase represent a major influx of siliciclastic sediments into the basin, the development of major reef build-ups at the shelf margin, and a significant loss of shelf-accommodation space. These T-R cycles are interpreted to be the result of the amount of and change in shelf-accommodation due to a combination of post-rift tectonics, loading subsidence, variations in siliciclastic sediment supply and dispersal systems, carbonate productivity and eustasy associated with a passive continental margin. The T-R cycles, where integrated with biostratigraphic data, can be correlated throughout the northern Gulf of Mexico region and have the potential for global correlation of Lower Cretaceous strata. 相似文献
9.
Wide regions of Morocco, from the Meseta to the High Atlas, have experienced km-scale upward vertical movements during Middle Jurassic to Early Cretaceous times following the appearance of oceanic crust in the Central Atlantic. The area experiencing exhumation was flanked to the W by a domain of continuous subsidence, part of which is named the Essaouira-Agadir basin. Comparison with vertical movement curves predicted by lithospheric thinning models shows that only 50–60?% of the subsidence documented in the Essaouira basin can be explained by post-rift thermal relaxation and that <30–40?% of the observed exhumation can be explained by processes (in)directly related to the evolution of the Central Atlantic rifted margin. Syn-sedimentary structures in Middle Jurassic to Lower Cretaceous formations of the Eassouira-Agadir basin are common and range from m-scale folds and thrusts to km-scale sedimentary wedges. These structures systematically document coeval shortening generally oriented at high angle to the present margin. As a working hypothesis, it is suggested that regional shortening can explain the structural observations and the enigmatic vertical movements. 相似文献
10.
In the southern Tethyan margin, the Essaouira-Agadir Basin (EAB), south of Morocco, exhibits well-exposed and fossiliferous sections of Aptian–Albian age. Biostratigraphy by ammonoids and sedimentological analysis have been realized for five sections located along an E-W transect in the EAB. The studied successions were dated from the latest Early Aptian to the Early Albian and are characterized by five major sedimentary discontinuities defining at least four main sedimentary sequences. The Late Aptian–Early Albian succession can be considered a gently westward-dipping ramp, marked by a deepening upward evolution. A quantitative study of calcareous nannofossils and calcium carbonate content has been performed on three of these sections. At this time, the EAB was located in the tropical-equatorial hot arid belt. The decrease in both calcium carbonate content and Nannoconus abundances at the Aptian–Albian transition could be the result of cooler climatic conditions recognized in the EAB, and/or of the associated increasing terrigenous input and nutrients, which hindered carbonate production. In the EAB, the nannofossil productivity is higher below the deposition of dark levels, which are coeval with the Niveau Paquier, recognized as the expression in southern France of the OAE 1b (Early Albian). During the Early Albian, the EAB was characterized by nannofossil fluxes two times lower than the upwelling-influenced Mazagan Plateau (southern Tethyan margin) and eight times lower than the Vocontian Basin (northern Tethyan margin). These results show that, with respect to the northern Tethyan margin, trophic conditions in sea surface waters of the pelagic realm of the southern Tethyan margin were lower. Comparable results obtained by Heldt et al. in the neritic realm of the southern Tethyan margin have been ascribed to more arid climatic conditions. 相似文献
11.
《International Geology Review》2012,54(5):541-548
A study of the Lower Cretaceous deposits of the northwestern Pacific province reveals Inoceramus zones in arenaceous-argillaceous sequences traceable over most of the area, representing the Hauterivian, Barrermian, Aptian, and Albian stages. Inoceramus was found to occur very rarely in the Valanginian. – IGR Staff. 相似文献
12.
Roberto Graziano 《地学学报》2001,13(2):110-116
Huge megabreccias occur at the eastern margin of the Cretaceous Apulia Carbonate Platform (Gargano Promontory, southern Italy). Their stratigraphic and genetic meaning are controversial in the debated geological evolution of the Apulia Platform. New stratigraphic analyses have revealed that three distinct megabreccia levels occur within the coarse debrites that were previously interpreted to be the result of repeated collapses of a scalloped platform margin during the late Albian–Cenomanian. Each level has peculiar chronostratigraphic distribution, geometry, composition and genetic features. They are the Posta Manganaro Megabreccias (late early Aptian to late Albian pp. ), Monte S. Angelo Megabreccias (early–middle Cenomanian) and Belvedere di Ruggiano Megabreccias (middle Turonian). These deposits overlie regional, tectonically enhanced unconformities of late early Aptian, late Albian and late Cenomanian age. These megabreccias, which were formed, respectively, during drowning, prograding and exposure events of the Apulia Platform, reflect important turning points in its Cretaceous geodynamic evolution. 相似文献
13.
《地学前缘(英文版)》2022,13(3):101377
Tectonic transition from a syn-rift stage to subsequent post-rift stage is an important mechanism in the evolution of extensional basins. The sedimentary infill records the crustal response to this process. We have obtained new detrital zircon U-Pb and Lu-Hf signatures from the Lower Cretaceous stratigraphic successions encompassing the commonly accepted syn- to post-rift transition boundary, the T4 unconformity, in the Songliao Basin, NE China. These constrain the Songliao Basin’s evolution from its center to distal margins, providing insights into the sediment provenance and dispersal pattern over the tectonic transition. Analysis of zircons from the syn-rift (the Shahezi and Yingcheng formations) and immediate post-rift (the Lower and Middle Denglouku Formation) stages reveals Phanerozoic age populations with positive ?Hf(t) values, which were derived from the proximal juvenile mantle-derived melt origin bedrocks of the Songliao Block. In contrast, the overlying samples from the Upper Denglouku Formation deposited in the subsequent post-rift stage contain exotic and ancient zircon populations with ages of 2.5 Ga & 1.8 Ga and complex hafnium signatures, characteristic of a mixed origin. These are interpreted to be transported from distant cratonic terranes via larger drainage networks. It is obvious that the sediment dispersal pattern switched from being a local and hydrologically closed “intraregional” pattern to a “transcontinental” pattern during the transition. The time lag between the development of the T4 unconformity and the drainage reorganization also ensures a distinguishable ～3 Myr (106103 Ma, Late Albian) transition period of regional extent. During this transition stage, syn-rift faulting was replaced by post-rift thermal subsidence, exhibiting a uniform sag configuration. Our new findings are important for understanding other continental rift basins during syn- to post-rift transition, which often demonstrates a complex interaction between the linkage and integration of sub-basins, and the reorganization of fluvial drainages and catchment systems. 相似文献
14.
东尼日尔Termit盆地是中西非裂谷系中典型的中—新生代裂谷盆地。在充分应用钻井和地震解释资料的基础上,根据构造、沉积充填及主要区域性不整合面的特征,分析了该盆地的演化过程。盆地内主要发育两类断层,第一类断层形成于早白垩世,于古近纪发生继承性活动,第二类断层为形成于古近纪的新生断层。全盆地普遍存在4个主要区域性不整合面,分别位于下白垩统、上白垩统、古近系、新近系—第四系底部。下白垩统和古近系沉积特征受断层活动控制明显,上白垩统和新近系沉积中心位于盆地中部,在其沉积时构造活动较弱。构造和沉积充填特征表明,Termit盆地经历了白垩纪和古近纪—第四纪两期裂谷旋回叠置的演化过程。下白垩统和古近系沉积于同裂谷期,沉积充填受断层活动控制;上白垩统和新近系—第四系沉积于后裂谷期,以热沉降拗陷作用为主。 相似文献
15.
《International Geology Review》2012,54(3):416-426
The area is divided into two parts: 1) elevated Precambrian basement with platform-type structures, and 2) an area of subsidence occupied by the Pricaspian depression; these structural subdivisions are separated by an escarpment. The Cretaceous stratigraphic section is subdivided into groups, based on lithological (geoelectrical) and faunal properties, correlated between the uplifted and down-warped areas. Eleven and twelve groups have been defined in the Lower and Upper Cretaceous, respectively. Variations in lithologles of the groups were controlled by the Voronezh massif and the Pricaspian depression. There was a gradual transgression of the Cretaceous sea from basin to elevated areas, on which some groups were bevelled by erosion. Deep downwarping of the salt dome area took place in the Valanginian and Hauterivian. The area near the Voronezh massif also subsided in the Hauterivian. Sedimentation took place on a geotectonically levelled surface during the greater part of the Barremian, Aptian, Touronian-Coniacian, Santonian and, partially, in the Cenomanian and Campanian stages. Intense warping of the Pricaspian depression occurred in the Albian and Maestrichtian and is marked by a sudden increase in the thickness of deposits of these ages and the appearance of Danian rocks. Thinning occurs on the Uzen-Ichinsk uplift and in the Upper Cretaceous, in the region of the marginal escarpment. — J.D. Haun 相似文献
16.
Marine sediments of Early Cretaceous age (Berriasian–Albian) have a widespread distribution in the Lower Saxony Basin of northern Germany. This basin, which is about 400 km long and 100 km wide, formed the southernmost extension of the North Sea Basin. Sediments attaining a maximum thickness of up to several hundred metres are represented by shallow marine siliciclastics in the west, south and easternmost part of the basin. These interfinger with the basin facies represented by dark mudstones up to 2000 m thick. The distribution and facies patterns of the sediments as well as thicknesses are related to three factors: differential subsidence, local tectonics and sea-level changes. For various parts of the basin and certain stratigraphic intervals it is possible to distinguish between these causes. Sedimentary thicknesses are clearly a result of differential subsidence from Kimmeridgian to Albian times onwards, being controlled by tectonic movements along northwest–southeast trending faults. These result in an asymmetric trough, bound to the north and south by synsedimentary faults with sedimentation rates highest in the north. Local tectonics are clearly caused by salt diapirs mainly in the eastern part of the basin and along the western, southern and eastern margins. These areas in particular include parts of the western Emsland and the Salzgitter area. Sedimentary patterns vary considerably over less than a kilometre, showing an extreme range of different lithologies. This is ideally observed in the Salzgitter area. Sea-level changes finally are reflected by widespread facies patterns and particularly by fossils of different provenance. The following sea-level-related events can be followed throughout the basin: the Wealden regressive phase, the Early Valanginian transgression, the early Late Valanginian transgression, the mid Hauterivian transgression, the Barremian regression, deposition of the Early Aptian anoxic sediments, and accumulation of the mid Albian hemipelagic marls. 相似文献
17.
列举并尝试对比了非洲早白垩世脊椎动物化石的主要产地。晚侏罗世(坦桑尼亚的敦达古鲁基默里奇期提塘期)至白垩纪最早期(南非的阿尔戈阿盆地凡兰吟期)的组合中含有剑龙、腕龙和梁龙,到前阿普特期(欧特里沃期巴列姆期?)被另一组合所取代。这一更年轻的组合中含有重爪龙亚科棘龙类、大头鳄类鳄鱼Sarcosuchus以及大型禽龙,它们主要来自尼日尔(ElRhaz组和喀麦隆(Koum组),部分来自利比亚(Cabao组)和突尼斯(Douiret组),后两组中还含有鲨鱼Priohybodus ar ambourgi。阿普特期(?)至早阿尔必期组合中仍含有禽龙,但是棘龙科棘龙类取代了重爪龙亚科。早塞诺曼期组合(Bahariya,Kem Kem)以恐龙Spinosaurus、Carcharodonto saurus,鲨鱼(Onchopris tisnumidus)和鳄鱼(利比亚鳄类、无棘腔鳄类)为特征。由此可知,中非的一些原先被认为是早白垩世的地层(坦桑尼亚的Galula组、马拉维的含恐龙层)为晚白垩世。脊椎动物化石在非洲陆相地层的对比中具有重要作用。 相似文献
18.
F. A. Middlemiss 《Cretaceous Research》1981,2(3-4)
Brachiopod events in the European Middle Cretaceous (Aptian-Cenomanian). Brachiopod species proliferated in the Late Aptian and Cenomanian. Significant palaeobiogeographical events took place during the Middle Cretaceous, in particular during Early and Late Albian time. 相似文献
19.
At many North Atlantic continental margins, the early Neocomian is characterized by a major stratigraphic turning point from Late Jurassic-Berriasian carbonate bank/pelagic carbonate deposition to Valanginian-Barremian hemipelagic sedimentation with thick Wealden-type deltaic to deep-sea fan sequences. The stratigraphy and structure of the very old, starved passive margin of the Mazagan Plateau and adjacent steep escarpment off Morocco was studied during the French-German CYAMAZ deep diving campaign. The drowning of the Late Jurassic-early Berriasian carbonate platform was strongly influenced by a global late Berriasian sea level fall which was followed by a rapid late Valanginian sea level rise and/or by a major regional blockfaul ting event with accelerated subsidence rates. Upper Berriasian to (?) Hauterivian quartz-bearing bioclastic wackestones document the transition from the carbonate platform to the hemipelagic deposition on the drowned platform margin. Seawards, these deposits are correlated with a deep sea fan sequence. We discuss also an example from the Tarfaya Basin-Fuerteventura area further south. A 300 m thick succession of organic-rich claystone and sandstone turbidites (including m-thick debris flow units) of Hauterivian to Barremian age was an unexpected discovery at DSDP Site 603 off North Carolina (Leg 93). We discuss a tectonically confined fan model with laterally migrating channels, influenced by sea level fluctuations and varying terrigenous supply. During the Valanginian to Barremian time of high-standing (or rising) sea level, shelf construction (Wealden-type deltas) coincided with subdued, resedimentation-starved turbiditic system on the continental rise. Extensive unconsolidated sands, however, reflect sudden input of shelfal material into the basin during a mid-Aptian sea level lowstand (shelf destruction). The following global late Aptian transgression terminated the clastic fan deposition, raised the CCD and started the deposition of organic-rich shales. 相似文献
20.
The Mesozoic sediments of Thakkhola (central Nepal) were deposited on a broad eastern north Gondwanan passive margin at mid-latitudes (28–41 °S) facing the Southern Tethys ocean to the north. The facies is strikingly similar over a distance of several thousand kilometres from Ladakh in the west to Tibet and to the paleogeographically adjacent north-west Australian margin (Exmouth Plateau, ODP Legs 122/123) and Timor in the east. Late Paleozoic rifting led to the opening of the Neo-Tethys ocean in Early Triassic times. An almost uninterrupted about 2 km thick sequence of syn-rift sediments was deposited on a slowly subsiding shelf and slope from Early Triassic to late Valanginian times when break-up between Gondwana (north-west Australia) and Greater India formed the proto-Indian Ocean. The sedimentation is controlled by (1) global events (eustasy; climatic/oceanographic changes due to latitudinal drift; plate reorganization leading to rift-type block-faulting) and (2) local factors, such as varying fluvio-deltaic sediment input, especially during Permian and late Norian times. Sea level was extremely low in Permian, high in Carnian and low again during Rhaeto-Liassic times. Third-order sea-level cycles may have occurred in the Early Triassic and late Norian to Rhaeto-Liassic. During the Permian pure quartz sand and gravel were deposited as shallowing upward series of submarine channel or barrier island sands. The high compositional maturity is typical of a stable craton-type hinterland, uplifted during a major rifting episode. During the early Triassic a 20–30 m thick condensed sequence of nodular ‘ammonitico rosso’-type marlstone with a ‘pelagic’ fauna was deposited (Tamba Kurkur Formation). This indicates tectonic subsidence and sediment starvation during the transgression of the Neo-Tethys ocean. During Carnian times a 400 m thick sequence of fining upward, filament-rich wackestone/shale cycles was deposited in a bathyal environment (Mukut Formation). This is overlain by about 300 m of sandy shale and siltstone intercalated with quartz-rich bioclastic grain- to rudstone (Tarap Shale Formation, late Carnian-Norian). The upper Norian to (?lower) Rhaetian Quartzite Formation consists of (sub)arkosic sandstones and pure quartz arenites, indicating different sediment sources. The fluvio-deltaic sandstones are intercalated with silty shale, coal and bioclastic limestone, as well as mixed siliciclastic-bioclastic rocks. The depositional environment was marginal marine to shallow subtidal. The fluvio-deltaic influence decreased towards the overlying carbonates of Rhaeto-Liassic (?) age (Jomosom Formation correlative with the Kioto Limestone), when the region entered tropical paleolatitudes resulting in platform carbonates. 相似文献