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1.
Facies, cycles, and controls on the evolution of a keep-up carbonate platform (Kimmeridgian, Swiss Jura) 总被引：2，自引：0，他引：2
During the Late Jurassic, accelerated ocean-floor spreading and associated sea-level rise were responsible for a worldwide transgression, which reached its maximum in the Late Kimmeridgian. In many Western European basins, this major sea-level rise led to the formation of marly and condensed sections. In the Swiss Jura, however, a shallow carbonate platform kept growing and only subtle changes in the stratigraphic record suggest an increasingly open-marine influence. Field observations and thin-section analyses reveal that the central Swiss Jura was at that time occupied by tidal flats and by more or less open marine lagoons where shoals and bioherms developed. The evolution through time of sedimentary facies and bed thicknesses permits the definition of small-, medium-, and large-scale depositional sequences. The diagnostic features of these sequences are independent of scale and seem largely controlled by the Kimmeridgian second-order transgression. A high-resolution sequence-stratigraphic correlation with biostratigraphically well-dated hemipelagic and pelagic sections in the Vocontian Basin in France reveals that: (i) The most important increase in accommodation recorded in the Kimmeridgian of the central Swiss Jura occurs in the Eudoxus ammonite zone (Late Kimmeridgian) and corresponds to the second-order maximum flooding recognized in many sedimentary basins. (ii) The small- and medium-scale sequences have time durations corresponding to the first and second orbital eccentricity cycle (i.e. 100 and 400 ka, respectively), suggesting that sedimentation on the platform and in the basin was at least partly controlled by cyclic environmental changes induced by insolation variations in the Milankovitch frequency band. The comparison of the high-resolution temporal framework defined in the Swiss Jura and Vocontian Basin with the sequence-stratigraphic interpretation realized in other Western European basins shows that the large-scale sequence boundaries defined in the Kimmeridgian of the Swiss Jura appear in comparable biostratigraphic positions in most Western European basins. Discrepancies that occur are probably because of local or regional tectonics. 相似文献
2.
3.
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
4.
High-resolution clay-mineral analyses were performed on upper Hauterivian to lower Aptian sediments along a platform-to-basin transect through the northern Tethyan margin from the Neuchâtel area (Switzerland), to the Vocontian Trough (France) in order to investigate links between climate change, carbonate platform evolution, and fractionation patterns in clay minerals during their transport.During the Hauterivian, the northern Tethyan carbonate platform developed in a heterozoan mode, and the associated ramp-like topography facilitated the export of detrital material into the adjacent basin, where clay-mineral assemblages are dominated by smectite and kaolinite is almost absent, thereby suggesting dry-seasonal conditions. During the Late Hauterivian Balearites balearis ammonite zone, a change to a more humid climate is documented by the appearance of kaolinite, which reaches up to 30% of the clay fraction in sediments in the Vocontian Trough. This prominent change just preceded the Faraoni Oceanic Anoxic Event and the onset of the demise of the Helvetic Carbonate Platform, which lasted to the late early Barremian.From the Late Barremian onwards, the renewed growth of the northern Tethyan carbonate platform in a photozoan mode and the associated development of a marginally confined platform topography fractionated the clay-mineral assemblages exported into hemipelagic settings: kaolinite particles were preferentially retained in proximal, platform settings, due to their size and their relatively high specific weight. In the inner platform environment preserved in the Swiss Jura, an average of 32% of kaolinite in the clay fraction is observed during the latest Barremian–earliest Aptian, whereas clay-mineral assemblages of coeval sediments from deeper depositional settings are dominated by smectite and show only minor amounts of kaolinite.This signifies that besides palaeoclimate conditions, the morphology and ecology of the carbonate platform had a significant effect on the distribution and composition of clay assemblages during the Late Hauterivian–Early Aptian along the northern Tethyan margin. 相似文献
5.
Daniel Tyborowski Błażej Błażejowski 《Proceedings of the Geologists' Association. Geologists' Association》2019,130(6):741-751
A new marine vertebrate assemblage from the Late Jurassic (late Kimmeridgian) at Krzy?anowice near I??a in the NE margin of the Holy Cross Mountains in Poland is described. This new locality is rich in fossils of coastal and pelagic reptiles. The most frequent fossils are plesiochelyid turtle shell fragments and pliosaurid skull bones and teeth. The Krzy?anowice vertebrate assemblage is similar to the Late Jurassic Boreal/Sub-Boreal localities of the Kimmeridge Clay in Great Britain and Svalbard Archipelago in the Arctic, in the presence of pliosaurids and long-necked plesiosaurids. However, plesiochelyid turtles and crocodylomorphs are similar to those from the Mediterranean/Sub-Mediterranean sites of the northern border of the Tethys Ocean, as, for example, in the Swiss Jura Mountains and Southern Germany. This unique composition of the Krzy?anowice vertebrate fauna demonstrates that, during the Late Jurassic this new locality was located in the transitional palaeobiogeographic line referred to in this paper as the “Matyja-Wierzbowski Line”. The new palaeobiogeographical reconstructions of Late Jurassic of Europe are based on the composition of the Krzy?anowice locality and other sites with similar turtle-pliosaurid faunas which formed a long-term, stable ecological sympatry in marine ecosystems of the European Archipelago. 相似文献
6.
Damien Carcel Claude Colombié Fabienne Giraud Bernard Courtinat 《Sedimentary Geology》2010,223(3-4):334-359
Boreal and Tethyan realms of Western Europe present significant sedimentological, paleontological, and stratigraphic differences. The purpose of this study is to constrain regional versus global controls on the dynamics of a sedimentary system located at the interface of these two realms in order to better understand the origin of their differences. Detailed sedimentological, palynofacies and calcareous nannofossil analyses were performed on two sections from the La Rochelle platform (western France). The Pas section includes part of the Late Oxfordian and Early Kimmeridgian, and the Rocher d'Yves section is assigned to the Late Kimmeridgian. They correspond to monotonous marl–argillaceous limestone alternations. Limestones are essentially mudstones with echinoderms, bivalves and foraminifera that suggest low-energy, open-marine conditions. Highly bioclastic and/or peloidal deposits occur commonly, and show wackestones to wacke-pack-grainstones textures. These deposits indicate frequent high-energy events, and are interpreted as storm deposits. Marls dominate in the most proximal depositional environments, while calcareous deposits are more important in more distal environments. The Rocher d'Yves section is globally more marly than the Pas section, suggesting a more proximal setting. Palynofacies are dominated by woody particles, suggesting shallow-water, proximal depositional environments. Calcareous nannofossils are ascidian spicules, coccoliths, and schizospheres. Watznaueria britannica dominate calcareous nannofossil assemblages in the Pas section. The Rocher d'Yves assemblages are quasi-exclusively composed of Cyclagelosphaera margerelii, and indicate more proximal paleoenvironments than those of the Pas section. Different orders of depositional sequences are defined, with sequence boundaries corresponding to the most rapid relative sea-level falls. They are hierarchically stacked, and correlate, on the basis of ammonite zones, with the sequences of contemporaneous sections from Tethyan and boreal realms. The stacking pattern of these sequences suggests an orbital control on sedimentation. Small-, medium- and large-scale sequences correspond to precession (20 ky) cycles and to 100 ky and 400 ky eccentricity cycles, respectively. The elementary sequences have durations shorter than 20 ky. The Kimmeridgian was a period of global sea-level rise that ended in the Late Kimmeridgian. More proximal depositional environments in the Rocher d'Yves section (Late Kimmeridgian) than in the Pas section (Early Kimmeridgian) imply a progradation of the La Rochelle platform during the Kimmeridgian. This progradation resulted from a slowdown of the subsidence in the Aquitaine Basin during the Kimmeridgian, corresponding to the first steps of Atlantic Ocean opening. High-frequency cycles on the La Rochelle platform formed in sync with Milankovitch orbital cycles, while tectonics controlled the formation of the low-frequency cycles. 相似文献
7.
藏南聂拉木北部喜马拉雅山主脊带侏罗系重解 总被引：1，自引：0，他引：1
通过野外调查和地层系统校正,认为前人在该区划分的侏罗纪地层系统存在偏差。下侏罗统在喜马拉雅山主脊带南北两侧岩相变化较大,普普嘎组可能穿时;中上侏罗统岩相变化较小;侏罗系总厚度不超过1400m。中侏罗统鲕粒铁质岩所对应的岩石地层单元按命名先后原则应为定结组,形成于外陆棚环境,可能与全球侏罗纪海泛时期洋流涌入有关,代表特提斯喜马拉雅地区中侏罗世晚巴通期一次沉积地质事件;晚侏罗世基末利期在特提斯喜马拉雅可能存在与欧洲同期的缺氧事件。 相似文献
8.
滇中地区上侏罗统叶肢介化石及其地层学意义 总被引：3，自引：4，他引：3
在回顾似东方叶肢介科(新科)Eosestlherlopseidae Niu(fam．nov．)内各属的特征、产出层位和分布的基础上，探讨了该科与真叶肢介科的亲缘关系，该科的起源，地层间的沉积间断和该科的迁移，以及Chuanjieestheria(gen．nov．)，Eosestheriopsis，Yunnanograpta(gen．nov．)等属在滇中上侏罗统中的层位演化关系，首次提出麻地山组至安宁组和蛇店组至妥甸组的时代可能为晚侏罗世早期的意见．大体可与中国北方土城子组对比。Eosestheriopsis群和Pseudograpta群分别为中国南方特提斯区和北方太平洋区2个不同生物地理区的产物。这些成果对中国陆相侏罗纪地层划分与对比、生物地理区及其变迁、古构造研究等，都具有理论意义和实际价值。文中还描述了叶肢介的一些新属种。 相似文献
9.
Lower Cretaceous carbonate deposits historically called “Urgonian limestones” are widely exposed around the margins of the Vocontian basin in southeastern France and in the adjacent Swiss Jura. This paper presents the history of their rise, growth and sudden demise. Eleven maps were constructed for deposits ranging in age from the Late Hauterivian pro parte to the Early Aptian (Bedoulian) pro parte. Based on sequential interpretations, they illustrate the present geographical distribution of the inner platform facies (Urgonian limestones stricto sensu, with rudists), the outer platform facies (essentially bioclastic deposits) and the basinal facies (slope, hemipelagic, pelagic deposits). These maps depict only the final terms of each successive sequence (the late highstand intervals). Chronostratigraphy is constrained by ammonites found mainly in basinal deposits, by echinoids, by rudists and to a lesser extent by dinoflagellates and calcareous nannoplancton. Inner platform, outer platform and slope (talus) deposits are dated by rich assemblages of orbitolinids and dasycladalean algae. Currently 39 species of orbitolinids have been recognized and their ranges collated with those of the ammonites in the area.In the Jura and in Provence the oldest Urgonian deposits are dated early Late Hauterivian, thus showing the synchroneity of the onset of platform carbonates development on both the southern and northern margins of the basin. Thereafter, growth of the platforms led a clearly regressive shallowing-upward trend, resulting from a stepwise progradation toward the center of the Vocontian area, coordinated with cyclical exposures in the inner platform areas. The maximum reduction of the platform deposits occurred early in Late Barremian times, coeval with a noticeable turnover in the orbitolinids assemblages.Thereafter, carbonate platform deposition shifted toward the margins of the Vocontian basin. In Early Aptian time, a well-dated discontinuity of regional extent marks the sudden, almost synchronous disappearance of the Urgonian deposits. 相似文献
10.
Ulla Schudack Michael Schudack Daniel Marty Gaël Comment 《Swiss Journal of Geoscience》2013,106(2):371-395
Ostracods are a common microfaunal element of the Kimmeridgian of the Jura Mountains in NW Switzerland. The stratigraphical subdivision within the Kimmeridgian can as clearly be inferred from ostracods as it is the case from the ammonite biozonation. This proves the utiliy of the ostracod biozonation, especially where ammonites are not available or rare. The ostracod-bearing layers of the sequence under study (middle part of the Reuchenette Formation = Banné Member, Courtedoux Member and Lower Virgula Marls) have been deposited in waters with highly brackish to marine salinities (high in the pliohaline range to—predominanttly—brachyhaline according to the Venice System, Oertli 1964). From the base of the section (base of the Banné Member, high brachyhaline in average), salinities slowly decreased, with lowest salinities in the lower dinosaur track levels of Courtedoux Member (high pliohaline on average). They then increased again to higher salinities (high brachyhaline on average) above the upper dinosaur track levels of the Courtedoux Member and the Lower Virgula Marls (lowermost A. eudoxus Zone). These trends perfectly correlate with the increased occurence of ammonites above the upper dinosaur track levels. In terms of Kimmeridgian ostracod palaeobiogeography, the fauna of the NW Swiss Jura Mountains described in this work is most similar to the Aquitan and Paris Basins, a little less to Northern Germany, and even less (with not even half of the species in common) to Southern Germany. The NW Swiss Jura Mountains still belong to a largely boreally influenced “Western and Central European subprovince”, whereas Southern Germany (though located more to the north) was subjected to an enhanced tethyan influence. 相似文献
11.
Cretaceous Oceanic Red Beds: Distribution, Lithostratigraphy and Paleoenvironments 总被引：1，自引：0，他引：1 
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下载免费PDF全文 Chen Xi WANG Chengshan HU Xiumian HUANG Yongjian WANG Pingkang Luba JANSA ZENG Xuan 《《地质学报》英文版》2007,81(6):1070-1086
Cretaceous oceanic red beds (CORBs) represented by red shales and marls, were deposited during the Cretaceous and early Paleocene, predominantly in the Tethyan realm, in lower slope and abyssal basin environments. Detailed studies of CORBs are rare; therefore, we compiled CORBs data from deep sea ocean drilling cores and outcrops of Cretaceous rocks subaerially exposed in southern Europe, northwestern Germany, Asia and New Zealand. In the Tethyan realm, CORBs mainly consist of reddish or pink shales, limestones and marlstones. By contrast, marlstones and chalks are rare in deep-ocean drilling cores. Upper Cretaceous marine sediments in cores from the Atlantic Ocean are predominantly various shades of brown, reddish brown, yellowish brown and pale brown in color. A few red, pink, yellow and orange Cretaceous sediments are also present. The commonest age of CORBs is early Campanian to Maastrichtian, with the onset mostly of oxic deposition often after Oceanic Anoxic Events (OAEs), during the early Aptian, late Albian-early Turonian and Campanian. This suggests an indicated and previously not recognized relationship between OAEs, black shales deposition and CORBs. CORBs even though globally distributed, are most common in the North Atlantic and Tethyan realms, in low to mid latitudes of the northern hemisphere; in the South Atlantic and Indian Ocean in the mid to high latitudes of the southern hemisphere; and are less frequent in the central Pacific Ocean. Their widespread occurrence during the late Cretaceous might have been the result of establishing a connection for deep oceanic current circulation between the Pacific and the evolving connection between South and North Atlantic and changes in oceanic basins ventilation. 相似文献
12.
青海省南部侏罗纪地层问题讨论 总被引：9，自引：1，他引：8
青海省南部侏罗纪海相双壳类异常丰富.根据近年来新测制的地层剖面和化石资料,本文分析了该区双壳类动物群的时代意义,从而确立了本区侏罗系应包括中,上侏罗统;海相侏罗纪沉积大致自巴柔阶到基末里阶.东特提斯区北缘的弧形地带,诸如青海南部、藏东、藏北、滇西,缅甸掸邦和泰国呵叻等地在中,晚侏罗世基本上属于同一个生态环境较特殊的双壳类生物地理分区,双壳类动物群表现出强烈的地方性色彩,特别是淡水双壳类动物群cuneopsis—Psilunio—Lamprotula组合,半咸水动物群Corbula—Neomindon组合以及淡水（微咸水）动物群Peregrinococha组合完全是该区特有的土著分子,从时代对比意义上来说,它们之间可对比度更高.云南和平乡组双壳类动物群和本区相比较后表明,和平乡组沉积时代大致相当于巴柔期（含早巴通期）.缅甸南瑶系中的双壳类动物群时代不应晚于巴通期.藏东和青海南部产出的奇异蛤动物群时代则应不早于基末里期. 相似文献
13.
前人(张研等,1983)曾将珠斯愣海尔罕地区的泥岔系分为4个组:珠斯楞组、依克乌苏组、卧驼山组和西屏山组,分别属于埃姆斯期、艾菲尔期、吉维特期和弗拉斯期。本文描述了该区中、上泥盆统4个剖面,将其划分为4个沉积旋网,每个旋回构成一组,自下而上依次为依克乌苏组、卧驼山组、下西屏山组和上西屏山组。根据四射珊瑚组合和其它共生化石,把依克乌苏组上部到下西屏山组下部归入吉维持期,下西屏山组上部相上西屏山组的时代为弗拉斯期,木区缺乏法门期的沉积。 关于珠斯楞海尔罕地区所在的北方槽区泥盆纪的生物地理区系特征尚无统一认识。作者根据四射珊瑚动物群的地方性分子含量,Otsuka相似性系数和构造古地理,将中同泥岔纪的珊瑚分为3个大区:北方大区、北特提斯大区和南特提斯大区。这种划分方案也非常适用于吉维特期和弗拉斯期。 吉维持期到弗拉斯期,巴丹吉林区和扬子区珊瑚群的关系最为密切,与北天山——准噶尔区和内蒙古——兴安区共同的属很少。因此,广大的北方槽区属于两个不同的生物大区,北方大区和北特提斯大区,二者的界线是居延海——林西地壳对接带。这种认识与王鸿祯(1981)所划分的中国大地构造单元一致。 相似文献
14.
Based on a well-established bio- and sequence-stratigraphic framework, a narrow time window in the Bimammatum ammonite zone
(Late Oxfordian) is investigated in six Swiss Jura sections representing a shallow-water carbonate platform. From the detailed
facies and microfacies analysis of oncoid-rich (Hauptmumienbank Member) and ooid-rich (Steinebach Member) limestones, a microfacies
classification is established, depositional environments are interpreted, and a depositional model for the Swiss Jura platform
is proposed. The sequence- and cyclostratigraphic interpretation has been performed for the transgressive part of the medium-scale
sequence Ox6+, independently for each section, with a very high time resolution at the scale of elementary depositional sequences.
The good correlation of the elementary and small-scale sequences between the six studied sections and the similar number of
elementary sequences in all sections strongly suggest that allocyclic processes were involved in their formation. The hierarchically
stacked depositional sequences (small-scale and elementary sequences) result from orbitally controlled sea-level changes with
periodicities of 100 and 20 kyr, respectively. Thickness variations in the correlated small-scale and elementary sequences
imply variable sedimentation rates, probably resulting from differential subsidence due to the activity of tectonic blocks.
The tectonically controlled platform morphology contributed significantly to the general pattern of depositional environments
and, combined with high-frequency sea-level fluctuations, created a complex facies distribution in time and space on the Swiss
Jura carbonate platform. 相似文献
15.
BIOGEOGRAPHIC RELATIONS OF THE JURASSIC PECTINOIDA AND OSTREOIDA (BIVALVIA) BETWEEN TANGGULA AND OTHER AREAS 总被引：2，自引：0，他引：2
Sha Jingeng 《地学前缘》2000,(Z1)
BIOGEOGRAPHIC RELATIONS OF THE JURASSIC PECTINOIDA AND OSTREOIDA (BIVALVIA) BETWEEN TANGGULA AND OTHER AREAS 相似文献
16.
T. V. Klets 《Stratigraphy and Geological Correlation》2008,16(5):467-489
Geographic differentiation of conodontophorids between northern and southern latitudes commenced in the Triassic since the early Induan. Cosmopolitan long-lived genera of predominantly smooth morphotypes without sculpturing were characteristic of high-latitude basins of the Panboreal Superrealm. Since the early Olenekian until the Carnian inclusive, this superrealm consisted of the Siberian Realm that extended over Northeast Asia and the Canada-Svalbard Realm that included the Svalbard Archipelago and northern regions of Canada. Throughout the Triassic period, conodontophorids characteristic of the Tethys-Panthalassa Superrealm spanning the Tethys and low-latitude zones of the Pacific were highly endemic, very diverse in taxonomic aspect, having well-developed sculpturing and tempos of morphological transformations. Distinctions between the Early-Middle Triassic conodontophorids from northern and southern zones were not as great as afterward, and their impoverished assemblages from southern Tethyan basins were close in some respects to the Boreal ones. Their habitat basins of that time can be grouped into the Mediterranean-Pacific and India-Pakistan realms. Hence, the extent of geographic differentiation of conodontophorids was not constant and gradually grew, as their taxonomic diversity was reducing in northern basins but relatively increasing in southern ones. The Panboreal e Tethys-Panthalassa superrealms of conodontophorids, which are most clearly recognizable, are close to first-rank paleobiochores (superrealms) established earlier for ammonoids and bivalve mollusks. Main factor that controlled geographic differentiation of Triassic conodontophorids was climatic zoning. Initially lower diversity of southern Tethyan assemblages points probably to relatively cooler water regime in the peri-Gondwanan part of the Tethys. The established patterns in geographic distribution of conodontophorids characterize most likely the real trend of their differentiation and evolution, i.e., the distribution area contraction prior to complete extinction at the end of the Triassic 相似文献
17.
AbstractDivergent and convergent margins actualistic models arc reviewed and applied to the history of the western Alps. Tethyan rifting history and geometry are analyzed : (he northern European margin is considered as an upper plate whereas the southern Apulian margin is a lower plate; the Bréche basin is regarded as the former break-away trough; the internal Bríançonnais domain represents the northern rift shoulder whilst the more external domains are regarded as the infill of a complex rim basin locally affected by important extension (Valaisan and Vocontian trough).The Schistes lustres and ophioliles of the Tsaté nappe are compared to an accretionary prism : the imbrication of this nappe elements is regarded as a direct consequence of the accretionary phenomena already active in early Cretaceous; the Gels/Simme complex could originate from a more internal part of the accretionary prism. Some eclogitic basements represent the former Apulian margin substratum (Sesia) others (Mont-Rose) are interpreted as the former edge of the European margin. The history of the closing Tethyan domain is analyzed and the remaining problems concerning the cinematics, the presence/absence of a volcanic arc and the eoalpine melamorphism are discussed. 相似文献
18.
Nathan Looser Elke Schneebeli-Hermann Heinz Furrer Thomas M. Blattmann Stefano M. Bernasconi 《Swiss Journal of Geoscience》2018,111(3):445-460
The Triassic–Jurassic boundary is characterized by strong perturbations of the global carbon cycle, triggered by massive volcanic eruptions related to the onset of the Central Atlantic Magmatic Province. These perturbations are recorded by negative carbon isotope excursions (CIEs) which have been reported worldwide. In this study, Triassic–Jurassic boundary sections from the southern margin of the Central European Basin (CEB) located in northern Switzerland are analyzed for organic carbon and nitrogen isotopes in combination with particulate organic matter (POM) analyses. We reconstruct the evolution of the depositional environment from Late Triassic to Early Jurassic in northern Switzerland and show that observed negative shifts in δ13C of the total organic carbon (δ13CTOC) in the sediment are only subordinately influenced by varying organic matter (OM) composition and primarily reflect global changes in the carbon cycle. Based on palynology and the stratigraphic positions of isotopic shifts, the δ13CTOC record of the studied sections is correlated with the GSSP section at Kuhjoch (Tethyan realm) in Austria and with the St. Audrie’s Bay section (CEB realm) in southwest England. We also show that in contrast to POM analyses the applicability of organic carbon/total nitrogen (OC/TN) atomic ratios and stable isotopes of total nitrogen (δ15NTN) for detecting changes in source of OM is limited in marginal depositional environments with frequent changes in lithology and OM contents. 相似文献
19.
羌塘盆地地处藏北高原,其南北界分别为班公错-怒江缝合带与拉竹龙-金沙江缝合带,盆地面积约180 000 km2.进一步可分为羌北坳陷、中央隆起带和羌南坳陷3个二级构造单元.双湖托纳木地区地处羌北坳陷与中央隆起带毗连地带,索瓦组分布于研究区北部大部分地区,根据地层层序及岩性组合特征,同时结合岩石、古生物、沉积旋回、接触关系等对地层进行了较系统的划分,将索瓦组划分为4个岩性段;索瓦组一段到四段自下而上反映出一个完整的海侵-海退序列,分别为碳酸盐台地-混积缓坡-混积碳酸盐台地-混积外滨浅水陆棚沉积环境;索瓦组三段礁灰岩和油页岩的发现对古环境的恢复以及油气的生储盖研究都具有重要意义;根据区内索瓦组的古生物地层分布和组合特征,建立了珊瑚组合带和双壳类组合带,确定索瓦组为上侏罗统,大致与Oxfordian-Kimmeridgian相当. 相似文献
20.
The planktic foraminifera of the Chuangde Formation (Upper Cretaceous Oceanic Red Beds, CORBs) as exposed at Tianbadong section, Kangmar, southern Tibet has been firstly studied for a detailed for a detailed biostratigraphy elaboration. A rich and well-preserved planktic foraminifera were recovered from the Chuangde Formation of the Tianbadong section and the Globotruncanita elevata, Globotruncana ventricosa, Radotruncana calcarata, Globotruncanella havanensis, Globotruncana aegyptiaca, Gansserina gansseri and Abathomphalus mayaroensis zones have been recognized. The planktic foraminiferal assemblage points to an early Campanian to Maastrichitian age for the CORBs of the eastern North Tethyan Himalayan sub-belt, which also provides a better understanding of the shifting progress of the Indian Plate to the north and the evolution of the Neotethyan ocean. The lithostratigraphy of the Chuangde Formation of the Tianbadong section comprises two lithological sequences observed in ascending succession: a lower unit (the Shale Member) mainly composed of purple (cherry-red, violet-red) shales with interbedded siltstones and siliceous rocks; and an upper unit (the Limestone Member) of variegated limestones. The strata of the Chuangde Formation in the Tianbadong section are similar to CORBs in other parts of the northern Tethyan Himalaya area of Asia (Gyangze, Sa’gya, Sangdanlin, northern Zanskar, etc.). The fossil contents of the Chuangde Formation in the sections (CORBs) studied provide a means of correlation with the zonation schemes for those of the northern Tethyan Himalayan sub-belt and the Upper Cretaceous of the southern Tethyan Himalayan sub-belt. Paleogeographic reconstruction for the Late Cretaceous indicates that the Upper Cretaceous Chuangde Formation (CORBs) and correlatable strata in northern Zanskar were representative of slope to basinal deposits, which were situated in the northern Tethyan Belt. Correlatable Cretaceous strata in Spiti and Gamba situated in the southern Tethyan Belt in contrast were deposited in shelf environments along the Tethyan Himalayan passive margin. CORBs are most likely formed by the oxidation of Fe(II)-enriched, anoxic deep ocean water near the chemocline that separated the oxic oceanic surface from the anoxic. 相似文献