FTIR microspectroscopy of Ediacaran phosphatized microfossils from the Doushantuo Formation,Weng'an,South China

Phosphatized microfossils from ca. 580 Ma from the Doushantuo Formation in the Weng'an region of South China were analyzed by Fourier transform infrared (FTIR) microspectroscopy for their chemical characterization. Two morpho-types of phosphatized embryo-like fossils (Megasphaera and Megaclonophycus) were analyzed, together with algal fossils. Transmission IR spectra of the microfossils have absorption bands of around 2960 cm^− 1 and 2925 cm^− 1, indicating the presence of aliphatic hydrocarbon (anti-symmetric aliphatic CH₃ and aliphatic CH₂), and have an additional band of around 1595 cm^− 1, probably derived from aromatic moieties (aromatic CC). In addition, IR microscopic mapping shows that aliphatic hydrocarbon and aromatics are distributed inside the embryo-like fossils. The embryo-like fossils appear to show three types of CH₃/CH₂ peak height ratios (R_3/2) and aromatic CC/CH₂ peak height ratios (R_CC/2 values): (1) high-R_3/2/low-R_CC/2 type (R_3/2 = ~ 0.2–1.0 and R_CC/2 ~ 0–2), (2) low-R_3/2/medium-R_CC/2 type (R_3/2 = ~ 0.2–0.6 and R_CC/2 = ~ 1–4); and (3) low-R_3/2/high-R_CC/2 type (R_3/2 = ~ 0.2–0.6 and R_CC/2 ~ 1–8). All three types are contained in both Megasphaera and Megaclonophycus. Raman spectra for the carbonaceous matter within the rock sample show a similar degree of thermal alteration, indicating that the organics were embedded in situ prior to thermal maturation. The IR spectroscopic differences might reflect differences in original organic compositions of microorganisms, and/or immediate post-mortem alteration. This suggests that the origins of phosphatized embryo-like fossils are more diverse than was previously recognized on the basis of their morphology. A comparison of R_3/2 and R_CC/2 values in the embryo-like fossils with those of the algal fossils and the extant microorganisms indicates the possible interpretation that some of the embryo-like fossils belong to animal embryo, others are algae, but none of them originate from bacteria.     

华南埃迪卡拉(震旦)系陡山沱组生物地层学研究的新进展

本文重点介绍华南地区埃迪卡拉(震旦)系陡山沱组生物地层学研究的新进展:(1)贵州江口陡山沱组上部黑色页岩中发现保存完美的八辐射螺旋结构的埃迪卡拉型动物化石--八臂仙母虫,首次确立陡山沱组上部庙河生物群层位有埃迪卡拉型动物化石的存在,为该层位与澳大利亚典型埃迪卡拉动物群层位对比提供了重要证据.(2)陡山沱组第二段首次发现有饰天柱山藻,确立了陡山沱组中下部出现的以Tianzhushania属为特征的具刺疑源类下组合带,为同期地层的对比提供了新依据.(3)在峡东地区陡山沱组第三段发现以Tanarium属为特征的具刺疑源类上组合带,它们与断面呈圆形和方形的管状化石共生,层位稳定,分布广泛.这些新古生物的发现,不仅进一步完善了我国埃迪卡拉(震旦)系陡山沱组的生物地层序列,而且为解决全球埃迪卡拉系划分和对比提供了可靠的古生物依据.     

扬子板块埃迪卡拉系(震旦系)陡山沱组层序地层划分与对比

在对扬子板块埃迪卡拉系陡山沱组不同相区的25条代表性剖面野外研究基础上,通过沉积岩石学和岩相序列特征的系统分析,认为陡山沱组沉积时期曾发生3次二级海平面升降事件。依据3个海平面升降转换面,可识别出3个层序底界面:(1)陡山沱组底部与下伏南华系南沱组及其同期层位的冰碛杂砾岩之间的界面;(2)在浅水沉积区陡山沱组中部和上部分别出现喀斯特侵蚀面;(3)在深水沉积区相应层序界面为岩相结构转换面。依据火山灰锆石U-Pb同位素年龄,可将陡山沱组层序地层划分为2个半二级层序或超层序(SS1,SS2和SS3-TST),其中SS1时限为35Ma(635~600Ma),SS2时限为35Ma(600~565Ma),SS3-TST时限为14Ma(565~551Ma)。陡山沱组底部广泛发育的盖帽白云岩底和3个层序内的最大海泛面可以作为4个相对等时面,结合事件沉积标志层,可建立扬子板块陡山沱组从浅水沉积区至深水沉积区等时性二级层序地层划分对比格架。研究结果表明,三峡地区陡山沱组四段式划分方案不适用于整个扬子板块内陡山沱组的区域地层划分和对比。因而,建议扬子板块陡山沱组应该以二级层序地层为基础,结合化学地层和生物地层进行综合划分和对比。陡山沱组新的地层划分对比格架为研究陡山沱组古地理演变和编制该时期高精度的岩相古地理图奠定了基础。     

华南震旦系陡山沱组磷质震积岩及其与多细胞生物群相关性初探

埃迪卡拉纪（震旦纪）陡山沱期是Rodinia超大陆裂离的重要地质时期,是多细胞生物起源和发展的重要转折时期和磷质聚集时期,也是化学、气候和环境变化的剧烈时期。液化岩脉、液化角砾岩、脉化变形构造、以及阶梯状层内断层等磷质震积岩的发现,表明扬子地区在陡山沱期晚期至少发生过两次以上的地震事件。地震构造运动将地球内部积累能量快速地释放,可能是磷质来源和热水活动一种重要的方式或通道。海水中磷等无机营养盐分的增加,海水温度的升高,有利于多细胞生物的起源和发展,同时多细胞生物的繁盛又有利于磷的聚集。     

Microfossils from the Upper Sinian (Late Neoproterozoic) Doushantuo Formation in Changyang, Western Hubei, China

l.IntroductionIn1978,YinLeimingandLiZaipingreportedonProterozoicmicroplansinsouthwestChina.Alt-houghmostwerefoundinmacerationofsiliclasticsandcarbonates,thinsectionsoftheDoushantuochertfromtheTianzhushandistrictnearChangyang(samples#TianR.l9and#TianR.29,inL.YinandLi,l978)containedtwolargespinosespeciesfAs-lerocaPsoidessinensis(upto325Umindiameter)andTianzhushaniasPinosa(45opmindiameter).Subsequentst-UdiesoftheDoushantuoFormationindicatethatthemicrofossilsintheDoushantuochertandphosph…     

湖北峡东地区埃迪卡拉系陡山沱组微体化石的新材料

通过对牛坪剖面和新测的晓峰河剖面燧石结核和条带的切片研究,进一步证实峡东地区陡山沱组下部和上部分别含有不同的微体化石组合。下组合以大型具刺疑源类Tianzhushania为主,包括疑源类Appendisphaera magnifica、Leiosphaeridia tenuissima、Meghystrichosphaeridium chadianensis、Tanarium sp.、Tianzhushania fissura、T.spinosa、T.sp.、Unnamed A;丝状蓝藻Oscillatoriopsis longa、Polytrichoides induviatus、Salome hubeiensis、Siphonophycus kestron、S.robustum;多细胞藻类Sarcinophycus palilloformis、Unnamed multicelluar alga A。上组合以出现大量个体介于50～140μm的呈聚集保存的球状膜壳为特征,包括疑源类Leiosphaeridia tenuissima、Knollisphaeridium maximum、K.sp.、Meghystrichosphaeridium perfectum及Unnamed B、C。本文的两个微体化石组合与Yin等(2011)和Liu等(2013)的组合特征基本一致。     

Sedimentary lithofacies characteristics and sweet-spot interval characterization of the Sinian Doushantuo Formation in Upper Yangtze Platform,South China

The Sinian Doushantuo Formation is the oldest shale gas reservoir discovered in the world, which contains good shale gas shows as the Eyangye-1 and Zidi-1 wells in the Yichang Region of western Hubei province, China. The shales in the Doushantuo Formation feature considerable thickness (135 m), high gas content (4.83 m³/t) and high fragile mineral content (up to 75%). Due to the influences of the sedimentary environment, the shale reservoirs here have high dolomitic content (54%) and abruptly changes in vertical lithofacies. Moreover, the characteristics of the shale sweet-spot differ significantly from that in the Wufeng Formation and Longmaxi Formation in southeast Sichuan Basin. A high-resolution sequence stratigraphic correlation was performed on the shales of the Doushantuo Formation at the Eyangye-1 well, Zidi-1 well, Zidi-2 well and some outcrop profiles in Yichang area for the identification of their sedimentary microfacies characteristics. A comprehensive comparative analysis was made by incorporating the elemental geochemistry, wireline and mud logging data of the well to further identify the sweet-spot interval therein. With the analysis of Eyangye-1 well, the sweet-spot interval of the Doushantuo Formation is 3360−3408 m, of which sedimentary microfacies is deepwater reduced environment with many pyrite laminaes, and the TOC is high to 3.42%, the Ro is 3.3%, the organic and matrix pore are well developed and the aperture more than 50 nm, the porosity is 2.7%, the desorption gas content average is 2.16%, and the main mineral is dolomitic (54%) and siliceous quartz (21%). Additionally, these parameters combined with previous studies will shed light on evaluating and characterizing the layers therein, also provide referential geological data for the following exploration and development activities of this shale system.     

The Sinian microfossils from Jinning,Yunnan, south west China

A microfossil assemblage has been detected in phosphorite cherts from the Dengying and Meishucun Formations (610 Ma) of the Sinian System in Jinning County, Yunnan Province, southwest China.A unique type (mode) of microfossil preservation — collophanite or apatite, or even in rare cases, chert-replacement — is reported here for the first time.The size frequency statistics for the assemblage are consistent with the results obtained by Schopf. The assemblage includes 18 genera and 20 species, among which 4 genera and 10 species are new. The assemblage consists of solitary and colonial spheroidal cells and septate or non-septate filaments, mainly Cyanophyta, especially Chroococaceae, Oscillatoriaceae and Nostocaceae.The microfossils described are Bigeminococcus grandis n. sp., Myxococcoides kingii, Myxococcoides grandis, Palaeoanacystis vulgaris, Archaeophycus venustus n.g. et sp., Eomycetopsis robusta, Circulinema jinningense n.g. et sp., Circulinema muirae n.g. et sp., Cyanonema infliatum, Obruchevella parva, Oscillatoriopsis awramikii n. sp., Palaeolyngbya oehlerii n. sp., Palaeolyngbya spiralis n. sp., Palaeotubulus lamellosus n.g. et sp., Veteronostocale sp. 1, Veteronostocale sp. 2, Allantomorphus septatus n.g. et sp., Clonophycus vacus n. sp., Archaeotrichion contortum, Rhienonema antiquum, Micrhystridium setulerum and Protosphaeridium densum.     

鄂西地区震旦系陡山沱组二段页岩气储层测井评价初探

鄂西地区震旦系陡山沱组是中国页岩气勘查的新层系,其页岩储层矿物成分以白云石为主,测井响应特征与奥陶系五峰组—志留系龙马溪组、寒武系牛蹄塘组硅质页岩明显不同,原有储层"七性"关系测井评价对于陡山沱组页岩储层精细刻画和压裂施工解释评价存在一定的不适用性。本文以鄂阳页1井为例,综合利用常规测井、特殊测井和样品测试分析资料,研究发现不同于五峰组—龙马溪组和牛蹄塘组硅质页岩"四高四低"测井响应特征,陡山沱组二段云质页岩具有低伽马、低铀、低声波时差、低中子,高电阻率、高密度"四低两高"测井响应特征,认为元素测井是评价陡山沱组二段页岩地层总有机碳含量最直接和有效的方法,MRIL-P型核磁测井适用于该地层孔隙度参数评价。通过拟合计算完善了适用于该地层的含气量估算方法,获取了有利页岩储层评价参数,研究成果将为同类型页岩储层测井评价提供参考依据。     

Megascopic Symmetrical Metazoans from the Ediacaran Doushantuo Formation in the Northeastern Guizhou, South China

In South China, various megascopic symmetrical metazoan fossils were found in the upper Doushantuo (陡山沱)Formation of the Neoproterozoic Ediacaran.The worm-like fossil is characterized by modern taxological annelid, for many metameres, parapodia, one possible tentale, an alimentary canal, and a dorsal vessel. The triradiate discoidal fossil is belong to Trilobozoa, and the octaradiate discoidal fossil might be Ctenophora. All these fossils indicate that the megascopic metazoans have appeared in the Doushantuoian of Eidacaran and imply that the symmetrical metazoans must have originated at least 550 Ma ago.     

Organic Carbon Isotope Geochemistry of the Neoproterozoic Doushantuo Formation, South China

The Neoproterozoic Doushantuo Formation on the Yangtze Platform, South China, documents a sedimentary succession with different sedimentary facies from carbonate platform to slope and to deep sea basin, and hosts one of the world-class phosphorite deposits. In these strata, exquisitely preserved fossils have been discovered： the Weng＇an biota. This study presents carbon isotope geochemistry which is associated paired carbonate and organic matter from the Weng＇an section of a carbonate platform （shelf of the Yangtze Platform, Guizhou Province） from the Songtao section and Nanming section of a transition belt （slope of the Yangtze Platform, Guizhou Province） and from the Yanwutan section （basin area of the Yangtze Platform, Hunan Province）. Environmental variations and bio-events on the Yangtze Platform during the Late Neoproterozoic and their causal relationship are discussed. Negative carbon isotope values for carbonate and organic carbon （mean δ^13Corg = -35.0‰） from the uppermost Nantuo Formation are followed by an overall increase in δ^13C up-section. Carbon isotope values vary between -9.9‰ and 3.6‰ for carbonate and between -35.6‰ and -21.5‰ for organic carbon, respectively. Heavier δ^13Ccarb values suggest an increase in organic carbon burial, possibly related to increasing productivity （such as the Weng＇an biota）. The δ^13C values of the sediments from the Doushantuo Formation decreased from the platform via the slope to basin, reflecting a reduced environment with minor dissolved inorganic carbon possibly due to a lower primary productivity. It is deduced that the classical upwelling process, the stratification structure and the hydrothermal eruption are principally important mechanisms to interpret the carbon isotopic compositions of the sediments from the Doushantuo Formation.     

湘西北地区震旦纪陡山陀组页岩气储层特征

对湘西北下震旦统陡山陀组页岩气有利层位进行相应的地球化学、物性特性分析,并结合地质保存条件等因素对含气页岩层进行了综合评价,得到区内页岩主要物化指数:TOC为0.52%~6.79%,均值为2.25%;Ro为2.38%~2.87%,均值为2.56%,干酪根类型为Ⅰ型;孔隙度为0.6%~8.7%,平均为3.9%,渗透率均小于0.04×10-3μm2,属低孔低渗类型。页岩埋深主要在2000~5000m,且有效厚度基本大于20m,具有页岩气成藏条件,页岩气勘探开发前景良好。     

贵州震旦系陡山沱组磷块岩成磷作用及与新元古代末期氧化事件(NOE)的耦合

贵州地区埃迪卡拉系陡山沱组磷矿床沉积是新元古代晚期全球性成磷事件的典型代表,与气候突变及生命演化等存在密切联系。然而,目前对磷矿床沉积的研究仅局限于成磷机制和磷质来源等问题,而通过同位素地球化学指标研究该矿床成磷过程及与同期古海洋环境的关联研究较为薄弱。本文以贵州省息烽地区陡山沱组磷块岩为研究对象,在野外剖面观察和镜下岩石学特征研究基础上,利用元素分析仪-同位素质谱(EA-IRMS)连续流分析技术精确测得陡山沱组磷块岩的硫酸根硫同位素变化范围为32.7‰~36.9‰(n=32,平均值34.1‰),比同时期海水的硫同位素值低11‰,两者的差异表明磷块岩中的硫并不全部来自表层海水。理想化早期海洋(>520Ma)化学分带模型指示同时期海水中存在相对亏损³⁴S的H₂S带,结合磷块岩中磷质来源与上升流关系密切的认识,可以认为陡山沱组磷块岩的硫酸根硫同位素组成代表了表层海水和上升流的混合信号。

     

重庆城口震旦系下统陡山沱组层序地层分析

重庆城口震旦系下统陡山沱组共分两段,主要发育浅海陆棚沉积相,包括过渡相和滨外陆棚两个微相。对区内钻井剖面及露头剖面进行分析,识别出岩性岩相转换面、陡山沱组与观音崖组之间界面两种层序界面类型,将陡山沱组划分为4个Ⅱ型三级层序。其中层序1为陡山沱组第一段底部,层序2为陡山沱组第一段中部,层序3为陡山沱组第一段上部和第二段底部,层序4为自陡山沱组第二段下部至灯影组第一段底部中厚层状白云岩。基于浅海陆棚的背景,研究区陡山沱组第四次海平面广泛上升至最大海泛面滞后时段内,在深水、还原、偏碱性的浅海滨外陆棚环境下锰矿才开始聚集,且在高燕、修齐等锰矿区成为重要的开采矿床。     

Germanium/silica ratios in diagenetic chert nodules from the Ediacaran Doushantuo Formation,South China

Germanium/silica (Ge/Si) ratios of dolostone- and mudstone-hosted chert nodules from the Ediacaran (635–542 Ma) Doushantuo Formation in the Yangtze Gorges area, South China, are reported. These chert nodules typically have a calcite rim, a pyrite rim, and a silica core, the latter sometimes containing disseminated pyrite. The silica core was precipitated by early diagenetic replacement of carbonate and silty/muddy sediments. Two types of chert nodules are identified based on their mineralogy and geochemistry. Type-1 chert nodules are poor in disseminated pyrite in the silica core. They also have low Al, and show a strong positive correlation between Al contents and Ge/Si with a near-zero or negative intercept. In contrast, Type-2 chert nodules contain abundant disseminated pyrite in the silica core and show a weakly positive correlation between Ge/Si ratios and Al contents (with a large positive intercept on the Ge/Si axis). The Ge/Si of Doushantuo nodules are greater than those of Cretaceous deep-sea cherts, suggesting that the Ge/Si ratio of Ediacaran seawater/porewater was greater than the Cretaceous due to the more effective discrimination against Ge by inorganic opal precipitation relative to biogenic opal precipitation. The positive correlation between Ge/Si and Al can be interpreted using a mixing model with a pure chert (characterized by a low Ge/Si ratio) and an Al-rich endmember (characterized by a high Ge/Si ratio). The latter is most likely represented by a clay component, but the model-based estimate of the Ge/Si ratio inferred for the Al-rich (clay) endmember is much higher than that of Phanerozoic clay minerals. These high Ge/Si ratios for the clay endmember may be related to the generally high Ge/Si ratio of Ediacaran seawater, but could also be related to clay–organic matter interactions. Organic matter absorbed to clays could provide an additional source of Ge because certain organic molecules are known to have a high affinity for Ge due to their strong metal ion-chelating properties. The high Ge/Si ratio of the Al-rich endmember in Type-1 chert nodules suggests that Ge in porewaters from which these cherts precipitated may have been dominated by Ge–organic complexes. The low Ge/Si ratio inferred for the Al-rich endmember in Type-2 chert nodules is therefore taken to indicate that Ge was released from organic matter, perhaps due to anaerobic degradation of organic matter (accompanied by the formation of pyrite), and was redistributed between clay–organic endmembers and pure chert, resulting in a non-zero intercept in the Ge/Si vs. Al₂O₃ plots. These observations suggest that a strong terrestrial influence in a restricted sedimentary basin or a high content of dissolved organic carbon in Ediacaran seawater and porewater may have contributed to the dominance of Ge–organic complexes in the Doushantuo basin in the Yangtze Gorges area.     

贵州江口震旦系陡山沱组沉积层序和沉积环境分析

通过对贵州江口桃映及邻区的坝黄、石竹溪的陡山沱组剖面的沉积序列研究,将陡山沱组划分为2个海侵-海退层序,并根据层序对比认为陡山沱期的生物群均产于陡山沱期第二次海平面开始上升之后形成的沉积中.从晚震旦世陡山沱期的第二次海侵开始是多细胞藻类、后生动物的第一次"爆发".桃映陡山沱组剖面产庙河生物群分子的沉积为局限滞流海盆沉积,进一步证明了庙河生物群型宏体生物的生存、保存环境模式仅限于局限滞流海盆中,为贫氧环境.     

中国华南陡山沱组烃源岩的形成机制与分布预测

震旦系(埃迪卡拉系)陡山沱组是成冰系(南华系)极端冰期事件结束后首次沉积的泥岩和碳酸盐岩地层,大规模的海侵活动导致在全球广泛发育富有机质黑色页岩,可能是未来深层油气和页岩气勘探的重要烃源岩层.中国华南陡山沱组烃源岩分布广泛,由于受古构造格局、沉积相带等因素影响,烃源岩非均质性强、平面上分布差异大.本文在前人研究基础上,...     

中扬子地区震旦系陡山沱组页岩储层孔隙结构特征

通过氩离子抛光-SEM技术,分析了中扬子地区震旦系陡山沱组页岩储层孔隙类型、孔隙形态、孔径和面孔率特征,探讨了这些孔隙的油气地质意义。研究认为,陡山沱组页岩储层发育有机质孔隙、粒间孔隙、粒内孔隙和微裂缝4种孔隙类型。页岩孔隙形态可分为不规则多边形孔、圆形或椭圆形孔、复杂网状孔、串珠状孔、长条形孔、线状孔6种类型,其中复杂网状孔的连通性最好,有利于压差传递,可提高页岩气的解吸效率和储层的渗透率。页岩孔径为10~2 000 nm,主体范围为20~200 nm,平均面孔率为1.4%~6.2%。不同类型的孔隙能够为页岩气的赋存提供不同尺度的储集空间,微裂缝和粒间孔隙对页岩气的运移最为有利。     

湖北宜昌樟村坪埃迪卡拉系陡山沱组硅磷质结核中的微体化石

本文报道的微体化石产于湖北宜昌樟村坪万家沟剖面埃迪卡拉纪陡山沱组第10层的硅磷质结核中,化石组合包括疑源类Appendisphaera grandis、Ericiasphaera spjeldnaesii、Knollisphaeridium maxi mum、Leiosphaeridia tenuissi ma、Meghystrichosphaeridium perfectum、Tianzhushania polysiphonia、T.spinosa、T.ornata;丝状蓝藻Oscillatoriopsis obtusa、Polytrichoides induviatus、P.lineatus、Salome hubeiensis、Siphonophycustypicum;多细胞藻类Sarcinophycus palilloformis、Wengania minuta。该微体化石组合面貌与黄陵背斜东、南翼陡山沱组二段硅质结核中以大型具刺疑源类Tianzhushania为特征的组合相同,与贵州瓮安地区陡山沱组上磷块岩下部保存的微体化石组合面貌基本一致。     

黔东北伊迪卡拉（震旦）纪陡山沱期的古地理环境

南沱冰期后的伊迪卡拉纪陡山沱期,全球海平面逐渐上升,宏体生物群（包括蓝田生物群、瓮会生物和庙河生物群等）广泛出现在扬子地区,使扬子地区陡山沱期的古地理研究成为目前研究的热点之一。在黔东北江口一铜仁地区的陡山沱组中产有丰富的宏体生物（“瓮会生物群”）和圆柱状叠层石,同时通过对遵义一铜仁陡山沱组多剖面岩性及岩性组合特征的分析和研究,认为在江口德旺地区可能存在有隆起的大陆边缘,其东侧为大陆边缘前缓斜坡相,西侧为半封闭台地相。