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陕南镇巴地区早寒武世地层—火烧店组的建立及其地层学意义 总被引：1，自引：0，他引：1
火烧店组的建组地点在陕南镇巴县小洋坝乡火烧店附近。该组下伏地层是灯影组(包括上震旦统的灯影峡阶和下寒武统的天柱山段),上覆地层是下寒武统水井沱组。火烧店组由碳酸盐岩组成,可分上、下两部分。下部相当于滇东筇竹寺组的八道湾段;上部相当于玉案山段的下部。该组时代应归于梅树村期晚期—筇竹寺期早期。这一地层单位的建立,对进一步研究上扬子区的早寒武世早期地层有一定意义。 相似文献
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1980—1982年间,我们在研究滇东震旦系与寒武系之间界线时,曾将晚震旦世至早寒武世过渡地层渔户村组由下至上划分为旧城段、白岩哨段、小歪头山段、中谊村段及大海段,筇竹寺组分为八道湾段和玉案山段等岩石地层单元(罗惠麟等,1982)。经过近10年的实践,证明这一划分基本合理,并为云南省地矿局区调队及第一地质大队广泛采用。由于八道湾段与新疆乌鲁木齐附近的侏罗系八道湾组重名,罗惠麟等(1990)建议改称为石 相似文献
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云南省德泽地区筇竹寺组黑色岩系位于扬子陆块南缘下寒武统黑色页岩分布带的西端, 不同于该带中段湘黔地区的牛蹄塘组, 它发育有两个多金属富集层位, 其中, 石岩头段黑色碳质粉砂岩底部富集V、U、Ag和Pd, 玉案山段黑色页岩底部富集Mo、Ni、Pt和Pd.筇竹寺组黑色岩系整体上富集V-Ni-Mo-U-Ag-Pt-Pd, 而牛蹄塘组黑色岩系则富Ni-Zn-Co-Pt-Pd-Ag-Pb, 但它们都经历了相似的缺氧环境, 且具有相同的PGE和Ni、Mo富集机制, 是一种重要的非传统矿产资源类型. 相似文献
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滇东下寒武统含磷岩系底部火山喷发事件沉积及其意义 总被引：8，自引：0，他引：8
云南曲靖德泽剖面下寒武统梅树村组待补段底和晋宁梅树村剖面小歪头山段底粘土岩层的岩石、矿物和元素地球化学特征表明，这些粘土岩层是由酸性火山灰蚀变而成的变斑脱岩。它们是同期火山喷发事件沉积的标志，也是滇东地区下寒武统梅树村组底界等时对比的标志层。根据这个标志层以及小歪头山段和待补段沉积序列的对比，梅树村剖面小歪头山段仅相当于小江断裂以东地区的待补段下部白云岩层，缺失上部硅质岩层，因而它不能代表滇东地区下寒武统梅树村组下段的沉积序列。 相似文献
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云南昆阳磷矿黑色页岩微量元素特征及其地质意义 总被引：5，自引：1，他引：4
昆阳磷矿是我国下寒武统黑色页岩中赋存的最大的磷块岩矿床。为了探讨磷块岩及上覆黑色页岩的源区性质及古海洋的氧化还原环境,本文对梅树村组中谊村段的磷块岩、石岩头段的黑色页岩以及筇竹寺组玉案山段的砂质黑色页岩的地层剖面进行了岩石地球化学研究。发现昆阳剖面磷矿区的下寒武统黑色页岩Th-Zr和Th-Y/Ho比值以及Y-Y/Ho比值与陆源碎屑物质更为接近,石岩头段黑色页岩样品的稀土元素总量平均为174×10-6,与大陆壳稀土总量的平均丰度基本一致。稀土配分模式也十分类似,说明陆源碎屑物质来源比海水自生来源占的比重更大。受陆源碎屑物质的影响,Ni/Co,V/Cr和V/（V+Ni）等氧化还原敏感元素比值并不能很好的指示古海洋的沉积环境。但石岩头段黑色页岩的氧化还原敏感元素相对大陆壳具有一定程度的富集,并且富集程度不强烈,Ce具有轻微的负异常,反映了黑色页岩可能形成于次氧化环境。 相似文献
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贵州瓮安地区上震旦统碳同位素特征 总被引：12，自引：2，他引：12
贵州瓮安磷矿上震旦统碳同位素组成显示，δ１３Ｃ值在垂向地层序列中的变化有明显的规律性。陡山沱组底部白云岩δ１３Ｃ为负值，向上碳同位素值发生显著正飘移，然后，除在陡山沱组中部δ１３Ｃ值有所下降外，δ１３Ｃ值基本上保持在＋２‰左右，一直持续到灯影组。瓮安地区上震旦统碳同位素剖面表现出与湖北峡东及世界其它地区同期碳同位素剖面极大的相似性，显示它们反映了末元古代海水碳同位素值的长期变化趋势。 相似文献
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以云南晋宁梅树村和海口尖山剖面肖滩阶顶部的生屑富集层为研究对象,通过对其野外观察认为,在原"玉案山段"底部生屑富集层,与下伏泥质粉砂岩之间存在沉积间断。本文认同陈均远等(1996)和朱茂炎等(2001)的观点,筇竹寺组建组条件不足,应该废弃,"石岩头段"和"玉案山段"应更名为石岩头组和玉案山组。肖滩阶顶部生屑层很可能为风暴作用后,在海侵过程中形成的半局限潮坪洼地沉积。通过岩石光薄片、光面和揭片观察,认为唐努乌拉尔壳在玉案山组底部小壳化石富集层中的丰度最大,其次是软舌螺和开腔骨骨针,藻类和赫尔克特壳在玉案山组底部地层中也偶尔可见,拉普渥斯壳、牙形类、刺胞类?、腕足动物和其他难以识别的生物骨骼碎片则极少见。通过X射线光电子能谱分析认为,玉案山组底部的生屑富集层中含丰富有机质、铝硅酸盐岩、金属碳酸盐、金属磷酸盐、铁氧化物和硫化物等。所谓的"生屑磷块岩"中磷主要分布于磷质团块和生物骨骼等碎屑颗粒外表面和内部,围岩中磷的原子百分含量极低或为0。其全岩P2O5的重量百分含量很可能低于6%,宜根据其中铝硅酸盐和金属碳酸盐含量的相对多少将"生屑磷块岩"更名为含磷碳质生屑白云岩或含磷碳质白云质粉砂岩。滇东肖滩阶顶部的磷沉积可能与有机质的大量存在和频繁变化的水动力条件有重要关系。 相似文献
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YU Wen 《《地质学报》英文版》2014,88(4):1262-1287
Yangtzeconus priscus-Archaeospira ornata, an important earliest Cambrian benthonic Assemblage of the Yangtze micromolluscan fauna, occurs mainly in the Lower Cambrian Zhongyicun and Dahai Members of the Yuhucun Formation in E Yunnan, the Tianzhushan Member （=Huangshandong Member） of the Dengying Formation in W Hubei and the Maidiping Member of the Hungchunping Formation in C Sichuan, China. About 90% of the genera of this Assemblage are unknown from the Nemakit-Daldynian and Tommotian molluscan Assemblages of the Siberian Platform, Russia. About 90% of the Siberian molluscan genera do not occur in the Zhongyicun and Dahai Members in the Meishucun section and in the corresponding beds of the Yangtze Platform, because the Tommotian molluscan Assemblage is characterizedly abundant archaeocyathids. It is clearly indicated that the Yangtze and Siberian molluscan Assemblages represent different bio- and lithofacies and ages. The age of the pre-trilobitic Yangtzeconus priscus-Archaeospira ornata Assemblage is older than that of the Nemakit-Daldynian and Tommotian molluscan Assemblages and referable to the Earliest Cambrian. Two new genera Mcnamaraconus and Zhangwentangoconus are herein proposed. 相似文献
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云南东部上新元古界-下寒武统地层碳同位素变化 总被引：1，自引：0，他引：1
云南东部上新元古界-下寒武统沉积序列中碳酸盐岩较多，本文研究的三条剖面上厚约500m，包括：东龙潭组、渔户村组及筇竹寺组底部，覆于海相冰水沉积之上，反映了从潮上蒸发至浅水相环境。已获得的δ^13C和δ^18O值显示出较大的变化范围，分别是-7．33～ 2．64(‰)和-14．98～ 0．78(‰)。依靠δ^13C测试，结合岩矿鉴定，发现梅树村震旦系．寒武系界线层型剖面岩石成岩作用中有改造现象。显然，δ^13C总的变化范围及变化模式比世界其它地区小，但却包含一个δ^13C负异常，直接位于古生物学上的前寒武系-寒武系界线之下。 相似文献
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陆相渐新统划分中的问题及新进展 总被引：18，自引：1，他引：18
近年来国际上关于始新世－渐新世界线的研究取得了重大进展，其同位素年龄被确认为３４Ｍａ，北美哺乳动物年代表已据此重新厘定。通过对哺乳动物群的分析和对比，论证了我国原认为是早渐新世的乌兰戈楚期和呼尔井期的时代应改归晚始新世，原认为是中渐新世的三达河期的时代应为早渐新世。在亚洲始新世－渐新世的界线不是在乌兰戈楚期之末，而是在呼尔井期与三达河期之间。 相似文献
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《International Geology Review》2012,54(15):1909-1921
This paper reports the carbon and oxygen isotope compositions of lacustrine carbonate sediments from the Palaeogene Shahejie Formation, Qikou depression, Bohaiwan Basin, with the aim of determining the palaeoenvironmental conditions in the region. Results from Es2, the second member of the Shahejie Formation, showed values of δ13C and δ18O from –1.2‰ to +2.4‰ (average +0.6‰) and from –6.8‰ to –4.7‰ (average –5.7‰), respectively, suggesting a relatively hot climate attending deposition. The slightly closed nature of the lake, which contains brackish water, resulted in higher carbonate δ13C and δ18O values than in a meteoric environment. The values of δ13C and δ18O preserved within the carbonates of the overlying lower Shahejie I (Es1) varied between +1.3‰ and +4.9‰ (average +3.2‰) and from ?4.4‰ to ?1.8‰ (average ?3.1‰), respectively, indicating that the climate became colder at that time. Subsequently, a marine transgression caused the salinity of the lake water to increase. The values of δ13C and δ18O were controlled by salinity. The high δ13C values were also influenced by the rapid burial of the lake organisms and by algal photosynthesis. Values of δ13C and δ18O from carbonates in upper Es1 ranged from ?8.0‰ to +11.0‰ (average +10.1‰) and from ?5.0‰ to ?1.5‰ (average ?3.4‰), respectively, indicating a slight increase in the temperature over time. In the closed and reducing environment, extremes in δ13C values resulted from biochemical fermentation. The positive δ13C excursion recorded in the carbonates of the Shahejie Formation in the Qikou depression indicates that the palaeoclimate underwent a significant transformation during the Eocene and the Oligocene. 相似文献
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《China Geology》2020,3(4):558-566
It has been an intense debate on the exact boundary between Ediacaran and Cambrian in the southwest Yangtze Block. The calibration of this critical boundary has a remarkable influence on the further investigation of the break-up of the Rodinia Supercontinent, the early life evolution, and the mechanism of the phosphorite deposit. Ediacaran and Cambrian strata and fossils are widely distributed in Anning, Yunnan Province in China. In recent years, the Xiaowaitoushan Member from the Lower Yuhucun Formation has been studied. Through this interval with continuous collections, the first appearance datums (FADs) of the protoconodont (Fomitchella cf. inchoate Yang et He, Protohertzina cf. anabarica Missarzhevsky) and globular embryos fossil (Olivooides sp.) earlier than these in the Lower Cambrian strata of the Meishucun Formation were discovered. This discovery indicates that the Xiaowaitoushan Member has included more FADs than the previously discovered single FAD of Anabarites primitivus Qian et Jiang, and the Ediacaran–Cambrian boundary in southwest China should be replaced below the Point “A” of the Meishucun Formation in Yunnan Province. The Point “B” of the Meishucun Formation is younger than the suggested age 541 Ma of the Ediacaran–Cambrian boundary and can no longer reference the Global Boundary Stratotype Section and Point (GSSP) correlation in southwest China. It can be suggested based on the previous stratigraphy and palaeontology studies from northern Sichuan and southern Shaanxi and the FAD of the globular embryos fossils that the Ediacaran−Cambrian boundary in the southwest Yangtze Block should be placed at the base of the Xiaowaitoushan Member; other phosphorite strata refer to Xiaowaitoushan Member. The discovery of the FADs of the shelly fossils in the Xiaowaitoushan Member provides new evidence for the global correlation of the Ediacaran –Cambrian boundary in the southwest Yangtze Block. The conodont discoloration index (CAI) of the specimens in Anning is between 2 and 3, which indicates that the organic matter in Xiaowaitoushan Member is matured and has high potential to form a shale gas reservoir. 相似文献
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Luo Huilin Jiang Zhiwen Wu Xiche Ouyang Lin Song Xueliang Xue Xiaofeng 《《地质学报》英文版》1992,66(2):197-207
This paper gives a brief report on the latest results in litho-, bio-, and chrono-stratigraphy obtained fromthe authors' further research on the Meishucun section during 1987-1988. More attention was paid to the studyof the microtexture of Lapworthella and some new materials of trace fossils. Phycodes pendum Seilacher, animportant index for correlation, was also discovered in the Zhongyicun Member. In the Yu' anshan Membermany worms, medusas and arthropods of the Chengjiang fauna have been found by other workers. Asupplemental study was made on the fossil zones of the Meishucunian stage. Based on new isotopic data, theage of the Precambrian-Cambrian boundary should now be 597 Ma. It is further suggested that point "B" re-mains as an optimum selection for defining the Precambrian-Cambrian boundary. 相似文献
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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
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The age of the Katera Group, which occupies a large area in the western North Muya Range and occurs 100–150 km east of the Uakit Group, is a debatable issue. Based on geological correlations with reference sections of the Baikal Group and Patom Complex, the Katera and Uakit groups were previously considered nearly coeval units and assigned to Late Precambrian (Khomentovskii and Postnikov, 2002; Salop, 1964). This was supported partly by the Sm–Nd model datings (Rytsk et al., 2007, 2009, 2011). Finds of the Paleozoic flora substantiated the revision of age of the Uakit Group and its assignment to the Late Devonian–Early Carboniferous (Gordienko et al., 2010; Minina, 2003, 2012, 2014). We have established that Sr and C isotopic compositions in carbonates of these groups differ drastically, as suggested by their different ages. Sediments of the Nyandoni Formation (Katera Group), which contains carbonates characterized by minimum values of 87Sr/86Sr = 0.7056 and maximum values of δ13C = 4.9‰, were accumulated in the first half of Late Riphean (800–850 Ma ago), whereas the overlying Barguzin Formation (87Sr/86Srmin = 0.70715, δ13Cmax= 10.5‰) was deposited at the end of Late Riphean (700–750 Ma). Judging from the isotope data, the Nerunda Formation (Uakit Group), which contains carbonates with characteristics matching the most rigorous criteria of fitness for the chemostratigraphic correlation (Sr content up to 4390 μg/g, Mn/Sr < 0.1, δ18O = 23.0 ± 1.8‰), was deposited at the end of Vendian ~550–540 Ma ago). The sequence includes thick typical carbonate horizons with very contrast carbon isotopic compositions: the lower unit has anomalous high δ13C values (5.8 ± 1.0‰); the upper unit, by anomalous low δ13C values (–5.2 ± 0.5‰]). Their Sr isotopic composition is relatively homogeneous (87Sr/86Sr = 0.7084 ± 0.0001) that is typical of the Late Vendian ocean. The S isotopic composition of pyrites from the Nyandoni Formation (Katera Group) (δ34S = 14.1 ± 6.8‰) and pyrites from the Mukhtunny Formation (Uakit Group) (δ34S = 0.7 ± 1.4‰) does not contradict the C and Sr isotopic stratigraphic data. 相似文献