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11.
用化学地层学研究新元古代地层划分和对比 总被引：3，自引：0，他引：3
随着传统地层学向多学科相互渗透的综合地层学方向的发展,笔者开展了湖北峡东地区新元古界震旦系和南华系的化学地层学研究。分别介绍了碳酸盐岩地层的稳定同位素和碎屑岩化学蚀变指数的研究方法和成果并依此提出新元古界划分和对比方案。震旦系碳酸盐岩中所获得的δ13C变化曲线和87Sr/86Sr比值与世界诸多剖面的变化曲线基本一致。南华系碎屑岩的化学蚀变指数(CIA)的特征是莲沱组下部CIA值为55~65(代表寒冷环境的CIA值),莲沱组上部CIA值则增至65~75(代表温湿环境),而莲沱组顶部两个样品的CIA值再次降为寒冷指数60~65;南沱组CIA值均为60~65,除了顶部(接近震旦系)的两个样品分别为69·4和70·9。上述CIA值的变化表明南华系以寒冷气侯为主,并且经历过“寒冷—温湿—寒冷”气候的演变条件下的沉积物。沉积相的多样性说明即使在“冰期”期间古构造、古地理环境对沉积物特征的影响依然存在。 相似文献
12.
Pirajno FRANCO 《《地质学报》英文版》2004,78(1):61-67
The Late Permian Emeishan Large Igneous Province (ELIP) is commonly regarded as being located in the western part of the Yangtze craton, SW China, with an asymmetrical shape and a small area. This area, however, is just a maximum estimation because some parts of the ELIP were not recognized or dismembered and destroyed during the Triassic to Cenozoic tectonism. In this paper, the chemostratigraphical data of the Zongza block, the Garze-Litang belt and the Songpan-Garze block suggest that the Late Permian basalts in these areas have remarkable similarities to the ELIP basalts in petrography and geochemistry. Flood basalts in the Sanjiangkou area are composed of the lower part of the low-Ti (LT) tholeiite and the upper part of the high-Ti (HT) tholeiite, which is the same as the flood basalts on the western margin of the Yangtze craton. Flood basalts in the Zongza and Songpan-Garze areas, which are far from the Yangtze craton, consist of HT tholeiite only. This is the same as the flood basalts within the Y 相似文献
13.
The Yenisei Range and the adjacent territories in the east are subdivided into (1) the Mid-Angara intracratonic depression; (2) the Yenisei pericratonic trough; and 3) a marginal oceanic block, the Isakovka-Predivinsk area. The lower part of the Riphean succession is subdivided into two principally different sedimentary complexes — the Lower Sukhoi Pit Subgroup and the Upper Sukhoi Pit Subgroup (the Pogoryui-Alad'in interval of the succession). The fundamental nature of the events that separate these two complexes and the characteristic, rhythmically bedded structure of the Upper Sukhoi Pit Subgroup allow the latter to be ranked a separate straton, the Bol'shoi Pit Group. Its lower boundary is associated with the Grenvillian events commencing with the emplacement of the Teya granite-gneiss domes and other intrusive complexes dated at 1100–1000 Ma. In the sedimentation record these events are manifested as a sudden change from the slate complex, for which we keep the name Sukhoi Pit Group, to the rhythmically bedded succession of the Bol'shoi Pit Group. The latter is interpreted as a product of uproofing of an elevated hinterland to the west. Insofar as the amplitude of this elevated area decreases progressively toward the Mid-Angara trough, the Bol'shoi Pit erosional unconformity and the associated interval of nondeposition are absent from the area. In the west of the Yenisei Range, in contrast, there is a major stratigraphic gap in the sequence, which is associated with the aforementioned events. The hypothesis on intensive events separating the deposition of the Bol'shoi Pit Group of the Kerpylian Horizon and the Tungusik Group of the Lakhandinian Horizon is not supported by the new data. The change from carbonate facies into siliciclastics in the west was misinterpreted as an erosional unconformity, with basal deposits corresponding to the lower boundary of the Tungusik Group. The occurrence of the Upper Tungusik deposits overlying much older rocks is a result of the pre-Bol'shoi Pit erosion and the gradual expansion of the Tungusik transgression. Thus, there are no grounds to argue for significant pre-Lakhandinian events in the region. Hence, the Kerpylian and Lakhandinian in the Yenisei Range, as well as in other parts of the Siberian Craton, constitute two parts of a larger supraregional straton, which corresponds to the lower half of the Upper Riphean and is designated here the Mayanian. The fundamentally different nature of the events associated with the next, Baikalian stage of the development allows its tripartite subdivision in the region. Deposition of the Lower Baikalian (the Oslyanka Group) was preceded by the crustal extension at the junction between the continental and oceanic blocks and, possibly, the formation of one of the Yenisei Range ophiolite complexes, followed by the emplacement of the Tatarka-Ayakhta batholiths at around 850 Ma. Fragments of both complexes are found as clasts in the basal conglomerates of the Middle Baikalian Chingasan Horizon. The specific character of the pre-Baikalian events determines their apparently poor expression in the sedimentation (weaker metamorphism of the Oslyanka deposits compared with the Tungusik Group). Even the activity leading to the formation of the Tatarka-Ayakhta granites cannot be regarded as a full-scale orogenic process. Collisional events separating the Lower and Middle Baikalian are manifested as the erosional unconformity at the base of the Chingasan Group and the emplacement of the Glushikha granites (760–730 Ma). The Middle Baikalian age of the Chingasan deposits is constrained by the data from paleontology, historical geology, and geochronology. Furthermore, the presence of glacial deposits renders this straton as a global stratigraphic marker. Further expansion of transgression in the Upper Baikalian is linked to another important event, but additional paleontological and geochronological information is needed to date the Upper Baikalian (Chapa Group) more accurately. The Baikalian events synchronously manifested themselves in all structural-facies zones of the Yenisei Range and are coeval to structural complexes from adjacent areas of the Siberian Craton. The tripartite Baikalian, therefore, has a potential for being included into the General Scale of the upper Upper Riphean. 相似文献
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15.
华南埃迪卡拉纪陡山沱海洋中无机碳同位素组成变化 总被引：3，自引：1，他引：2
报道了贵州江口桃映深水相剖面陡山沱组碳酸盐岩δ13C值的变化特征,结合其他已报道的数据,分析了华南扬子地区埃迪卡拉纪陡山沱海洋不同沉积环境,包括盆地相、斜坡相、台地相、台地边缘相碳酸盐岩中δ13C变化趋势及绝对值的异同,发现浅水区剖面记录的δ13C漂移次数多于深水区剖面,且不同相区δ13C值也有差异。δ13C值的差异与埃迪卡拉纪陡山沱海洋的阶段性演化密切相关。基于不同相区的δ13C值变化,埃迪卡拉纪陡山沱海洋的演化历史可分为3个时期:1)陡山沱组1段盖帽白云岩沉积期华南扬子地区很可能为一个开阔台地,白云岩中δ13C值可能继承于幔源CO2的碳同位素特征,深水区和浅水区碳酸盐中δ13C值无显著差异;2)陡山沱组2段和陡山沱组3段下部沉积时期盆地深水区中δ13C值显著低于浅水区,且深水区δ13C值与陡山沱组1段时期无显著差异,浅水区的δ13C值则显著升高;3)陡山沱组3段上部和陡山沱组4段沉积时期陡山沱盆地中δ13C值均显著下降,且不同沉积环境中的δ13C值差异度降低。盖帽后埃迪卡拉纪陡山沱海洋阶段性演化主要与不同时期深水区DOC库的逐步氧化有关。 相似文献
16.
Stable carbon‐isotope record of shallow‐marine evaporative epicratonic basin carbonates,Ordovician Williston Basin,North America 
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下载免费PDF全文 Secular variations in stable carbon‐isotope values of marine carbonates are used widely to correlate successions that lack high‐resolution index fossils. Various environmental processes, however, commonly may affect and alter the primary marine carbon‐isotope signal in shallow epicratonic basins. This study focuses on the marine carbon‐isotope record from the carbonate–evaporite succession of the upper Katian (Upper Ordovician) Red River Formation of the shallow epicratonic Williston Basin, USA. It documents the carbon‐isotope signal between the two major Ordovician positive shifts in δ13C, the early Katian Guttenberg and the Hirnantian excursions. Eight δ13C stages are identified based on positive excursions, shifts from positive to negative values and relatively uniform δ13Ccarb values. A correlation between carbon‐isotope trends and the relative sea‐level changes based on gross facies stacking patterns shows no clear relation. Based on the available biostratigraphy and δ13C trends, the studied Williston Basin curves are tied to the isotope curves from the North American Midcontinent, Québec (Anticosti Island) and Estonia, which confirm the Late Katian age (Aphelognathus divergens Conodont Zone) of the upper Red River Formation. The differences in the δ13C overall trend and absolute values, coupled with the petrographic and cathodoluminescence evidence, suggest that the carbon‐isotope record has been affected by the syndepositional environmental processes in the shallow and periodically isolated Williston Basin, and stabilized by later burial diagenesis under reducing conditions and the presence of isotopically more negative fluids. 相似文献
17.
《International Geology Review》2012,54(16):2065-2066
ABSTRACTMetasedimentary rocks from the El Triunfo Complex (Jocote Unit) in the southern Chiapas Massif (SE México) are constituted mainly by sillimanite-rich micaschist, locally intercalated with marble and calc-silicate rocks. Mafic rocks (now amphibolite) intruded the sequence prior to deformation and folding. Peak metamorphic conditions are estimated by geothermobaromerty at ~6.0 kbar and ~650ºC. The timing of the metamorphic event is dated by LA-MC-ICPMS analysis on zircon rims at 438+23/–12 Ma. Furthermore, detrital zircon grains yield mainly Stenian–Tonian and minor early Mesoproterozoic ages, indicating provenance from Grenville-type orogens (such as Oaxaquia) and some older cratonic sources. The 87Sr/86Sr values of 0.70775–0.70777 and the δ13C values from +1.9‰ to +2.7‰ in associated calcite marble define the time of deposition between 600 and 580 Ma. Geochemical markers from metapelite samples (such as La/Th > 3.94, La/Sc > 3.72, Th/U > 8.19, Th/Co > 0.42 and CIA = 74 to 83), as well as Sm–Nd isotope data (εNdi = ?8.1 to ?4.0, TDM(Nd) = 1.65–1.32 Ga) suggest weathering of Mesoproterozoic felsic rocks during temperate to warm climate. Furthermore, Zr/Sc values (9.1–21.0), chondrite-normalized REE patterns [La/Yb]N = 10.3–23.3, Eu/Eu* < 0.64), and ΔHf values (1.98–10.02) are indicative of pelagic and zircon-depleted sediments of a passive margin. The results suggest that the Jocote Unit was deposited during the opening of the Eastern Iapetus Ocean in the Ediacaran Period. This is the first evidence for Rodinia breakup in southern México. Besides that, the Ordovician tectonothermal event is probably related to compression during subduction and accretion along the western margin of Gondwana. 相似文献
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Dominik Hennhoefer Aisha Al Suwaidi Cinzia Bottini Emina Helja Thomas Steuber 《Sedimentology》2019,66(2):536-555
The sedimentary record of the Arabian Shelf offers a unique opportunity to study the Cretaceous (Albian–Turonian) greenhouse climate from a palaeoequatorial perspective. In particular, hemipelagic to pelagic carbonate successions from the extensive Shilaif intra‐shelf basin have the potential to produce an excellent record of carbon cycle perturbations during this interval. This study presents a 269 m thick chemostratigraphic (carbonate δ13C and δ18O) record from the Middle Albian to Early Turonian of central Abu Dhabi (United Arab Emirates), representing over 14 Myr of uninterrupted carbonate sedimentation. The Mauddud to Shilaif formations represent outer ramp to basinal intra‐shelf carbonates with variations from laminated organic‐rich to clean bioturbated intervals. Isotopic evidence of the latest Albian Anoxic Event (Oceanic Anoxic Event 1d), Middle Cenomanian Event I and the Cenomanian–Turonian Anoxic Event (Oceanic Anoxic Event 2) are confirmed and biostratigraphically calibrated by means of calcareous nannofossils. The carbon isotope record allows correlation with other regional records and well‐calibrated records across the Tethyan Ocean and represents a significant improvement of the chronostratigraphic framework of the United Arab Emirates (Shilaif) and Oman (Natih) intra‐shelf basins. The study further confirms that low carbon isotope values corresponding to the two source rock intervals in the Shilaif Formation clearly precede the isotopic expressions of Oceanic Anoxic Event 1d and Oceanic Anoxic Event 2. 相似文献
19.
湖北宜昌茅坪泗溪剖面埃迪卡拉系岩石地层和碳同位素地层研究 总被引：2，自引：0，他引：2
华南埃迪卡拉系陡山沱组上部的δ13C巨大负异常事件(DOUNCE)是当前埃迪卡拉系研究最受关注的焦点之一。在对湖北宜昌茅坪泗溪剖面埃迪卡拉系开展高精度的岩石地层和碳氧同位素研究的基础上,通过与黄陵背斜周缘其他剖面的对比,表明峡区陡山沱晚期DOUNCE事件的δ13C值变化由下降—负漂移—短期正漂移—回升4个阶段构成,但DOUNCE事件在不同剖面上的表现存在明显差异。详细的沉积岩相分析和地层对比表明,各剖面δ13C演化差异是由岩相变化导致的岩石地层发育差异引起的。泗溪剖面DOUNCE事件主体部分缺失与该剖面位于台内盆地斜坡环境,发育多层滑塌构造造成的地层缺失有关。研究结果表明在缺乏生物地层控制的埃迪卡拉系,δ13C同位素地层是揭示沉积相变化造成的岩石地层差异和地层对比的重要手段。 相似文献
20.
Atena Shizuya Masahiro Oba Takuto Ando Yukari Ogata Reishi Takashima Hiroshi Nishi Toshifumi Komatsu Phong D. Nguyen 《Island Arc》2020,29(1)
The Hangenberg Crisis at the Devonian–Carboniferous boundary is known as a polyphase extinction event that affected more than 45 % of marine and terrestrial genera. As the cause of this event is still debated, analyses were carried out on sedimentary samples from the Devonian–Carboniferous Pho Han Formation in northeastern Vietnam to reconstruct the paleoenvironment around the time of this event using stable carbon isotopes; total sulfur; manganese; vanadium; molybdenum; and sedimentary organic matter, such as dibenzothiophenes, cadalene, and regular steranes. These geochemical signatures provide a high‐resolution redox history for this section and show that transgression‐driven high primary productivity, possibly enhanced by terrestrial input, caused severe oxygen depletion along the continental margin of the South China block during the Hangenberg Crisis. 相似文献