峡东地区埃迪卡拉系陡山沱组碳同位素特征研究进展与国内外对比

本文重点通过研究峡东地区埃迪卡拉系陡山沱组碳同位素的变化规律,来探讨其全球地层对比意义.峡东地区埃迪卡拉系陡山沱组经历了三次比较显著的碳同位素负漂移(EN1~EN3)和两次正漂移(EP1、EP2).第一次碳同位素负漂移(ENI)发生在南沱冰期之后陡山沱组底部盖帽碳酸盐岩层位及其上部的白云岩,与世界其他地区Marinoan冰期之后盖帽碳酸盐岩的碳同位素负漂移可进行对比;第二次碳同位素负漂移(EN2)发生在陡山沱组中部;第三次负漂移(EN3)发生在陡山沱组顶部,是该地质历史时期持续时间最长的一期碳同位素负漂移,同澳大利亚、阿曼、纳米比亚、加里福尼亚、西伯利亚、苏格兰等地碳同位素异常均可进行对比.两次正漂移(EP1、EP2)分别位于第二段中部和第三段的下部,分别与陡山沱组所含的两个疑源类组合具有很好的对应关系;而EN3则与陡山沱组上部所含的宏体化石组合(庙河生物群)相对应;表明碳同位素的变化与生物演化具有一定的对应关系.研究表明,利用碳同位素变化特征进行埃迪卡拉纪地层洲际对比是行之有效的手段之一.     

Quantitative evaluation of the biostratigraphic distribution of acanthomorphic acritarchs in the Ediacaran Doushantuo Formation in the Yangtze Gorges area, South China

Doushantuo acanthomorphic acritarchs are large morphologically complex organic-walled microfossils broadly constrained between the 635 Ma Nantuo glaciation and the 551 Ma Miaohe Biota. They are potential biostratigraphic tools for subdivision and correlation of the Ediacaran System in South China. However, major variations in sedimentary facies and stratigraphic thickness present challenges in understanding the spatial and temporal distribution of these acritarchs. Further, the distribution of acritarchs in the Doushantuo Formation is associated with the presence of early diagenetic chert and phosphate, implying a certain degree of preservational bias and/or environmental control. The purpose of this paper is to document the stratigraphic distribution of Doushantuo acritarchs and to quantitatively evaluate their biostratigraphic significance and possible taphonomic–environmental biases, based on high-resolution paleontological data from six sections over 100 km in the Yangtze Gorges area, South China.A total of 1082 acritarch fossils were recorded from 84 chert horizons in the six sections of the study area. These chert horizons are not uniformly distributed throughout the Doushantuo Formation, thus the presence/absence of early diagenetic chert does play a role in controlling the distribution of acritarchs. The sampled chert horizons can be grouped into two stratigraphic intervals in the lower and upper Doushantuo Formation, respectively, based on regional stratigraphic correlation. Quantitative analysis shows that the two intervals are distinct taxonomically and largely independent of taphonomic or facies controls. Thus, the two intervals can be regarded as assemblage biozones. The lower biozone (biozone 1) is numerically dominated by Tianzhushania spinosa (n = 587; 68.3%) and Meghystrichosphaeridium magnificum (n = 74; 8.6%), whereas the upper biozone (biozone 2) is dominated by Ericiasphaera rigida (n = 104; 47.1%) and Tianzhushania spinosa (n = 34; 14.1%). The three most common genera, Meghystrichosphaeridium, Tianzhushania, and Ericiasphaera, have been identified in all sections. Correspondence analysis (CA), detrended correspondence analysis (DCA), discriminant analysis (DA), and pairwise comparisons of samples (Spearman rank coefficient and Jaccard–Chao index), all consistently support biostratigraphic zonations. Thus, the distribution of the Doushantuo acanthomorphs is primarily controlled by biostratigraphic position of samples, with facies and taphonomic differences playing a secondary role. Our case study suggests that acanthomorphic acritarchs can offer a viable tool for regional correlation of the Ediacaran System.     

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。     

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.     

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。     

华南黄陵背斜西翼兴山地区乡儿湾剖面埃迪卡拉系陡山沱组微体化石

本文首次报道并描述了华南黄陵背斜西翼湖北宜昌兴山县乡儿湾剖面埃迪卡拉系陡山沱组二段中上部的燧石结核和条带中的疑源类微体化石,经系统鉴定共识别出8属8种,包括Appendisphaera grandis,Crassimembrana multitunica,Leiosphaeridia minutissima,Megasphaera inornata,Schizofusa zangwenlongii,Symphysosphaera basimembrana,Urasphaera nupta,Variomargosphaeridium gracile。该化石组合包含Liu Pengju and Moczyd?owska (2019)所建立的第二生物组合带(Tanarium tuberosum-Schizofusa zangwenlongii组合带)的特征分子Schizofusa zangwenlongii,因此,可尝试性地与第二生物组合带相对比,但未见黄陵背斜东南翼陡山沱组二段的常见属Tianzhushania,据此推测黄陵背斜两翼在古环境上可能有所差异。     

华南埃迪卡拉纪陡山沱组物源风化对全球性成磷事件的启示

华南埃迪卡拉纪陡山沱组沉积于原始地球-生命系统向现代地球-生命系统过渡的关键时期,该套地层记录了地质历史时期一次大规模成磷事件,但关于该次成磷事件中磷元素的来源仍存在诸多争议。浅海区磷元素主要来源于由河流搬运的陆表含磷矿物风化产物及上升流作用所带来的其他海域含磷水体,这两种来源可以通过全岩碎屑元素(Al、Fe、Th等)和稀土元素的含量及其分布特征进行区分。本文通过对上扬子地区乡党坪剖面和四斗坪剖面的陡山沱组主、微量元素特征的综合分析,恢复了该地区的物源体系及其风化作用过程。较高的P₂O₅-Al₂O₃、P₂O₅-Fe₂O₃相关性,表明该时期磷来源于陆地风化而非上升流;较低的Th/Co、La/Sc、Th/Cr等比值,TiO₂-Zr相关性以及Th-Hf-Co、La-Th-Sc三角图分布关系,表明研究区内陡山沱组的物源体系主要为玄武岩;较高的化学蚀变指数(CIA)和较低的Sr/Cu值,表明物源区当时...     

峡东埃迪卡拉系陡山沱组稳定碳同位素记录及其年代地层意义

基于峡东秭归青林口、泗溪和宜昌晓峰河埃迪卡拉系下部陡山沱组剖面岩石、层序和精细的碳同位素地层研究,在埃迪卡拉系下部陡山沱组底部、下部、中部、上部和顶部分别识别出5次以灰岩出现或黑色页岩增厚为标志的海侵事件,划分出5个可以进行区域对比的三级层序,自下而上分别命名为BDSS,LDSS,MDSS,UDSS和TDSS。以层序界面为对比标志,峡东埃迪卡拉纪不同古地理部位碳同位素组成变化的对比显示峡东埃迪卡拉系陡山沱组中内部发育5次可以进行区域乃至全球对比的碳同位素负异常,分别是分布在BDSS下部的SN1,LDSS上部的SN2,MDSS上部和顶部的SN3和SN4,以及分布在UDSS上部的SN5。其中SN1和SN4碳同位素负偏离最为明显,最小δ13C分别达到-4‰~-5‰和-9‰~-10‰,分别与Marinoan冰期上覆盖帽白云岩以及Gaskier冰碛沉积上、下地层中的碳同位素组成特点接近。SN4是埃迪卡拉系最晚冰期的产物。与SN1是埃迪卡拉系底界划分对比的标志相对比,SN4的出现应该是埃迪卡拉系内部再划分中另一个不可忽视的界线标志。     

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,...     

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。     

黔东北伊迪卡拉纪陡山沱组的宏体藻类

宏体生物广泛地生活于扬子地区伊迪卡拉纪陡山沱期的海洋中,它们为后生动物的快速发展和演化奠定了一个崭新的环境和一个新生态链的基础.产自于黔东北伊迪卡拉系陡山沱组的瓮会生物群生活环境应在贫氧的、透光性良好的浅海低能环境,以宏体藻类为主,共描述15属18种(其中包括3个新属、5个新种、2个修定属和4个修定种)和1个未命名藻以及不明藻类固着器,另包含有宏体后生动物,可能的后生动物以及遗迹化石.瓮会生物群不但含有鄂西庙河生物群和皖南蓝田植物群的分子,也有南澳大利亚Ediacara生物群和俄罗斯WhiteSea生物群的分子,而且具有自已的特征而有别于其他伊迪卡拉期的生物群.其宏体藻类形态变化较大,组织器官和功能已出现明显的分化,并与高等植物之间存在一定的演化关系.宏体藻类多为直立固着于海底,提高了光合作用的效率,增加了水体中的含氧量.同时,宏体藻类作为生态系统中的初级生产者成为一种新的食物,改变了后生动物的食谱.因此,陡山沱期的宏体植物不仅改善了环境,为依赖一定氧而生活、生长和繁殖的后生动物给予了必要的支持,而且作为生态系统中的必要基础,为宏体后生动物的快速发展和演化提供了一个新的食物源.另外,宏体生物群的繁盛不仅提高了有机质的生产率,而且促进了富有机碳的沉积和保存.     

New Data of Macrofossils in the Ediacaran Wenghui Biota from Guizhou, South China

The abundance and diversity of macrofossils in the Ediacaran have attracted much attention. The upper Doushantuo macrobiotas in South China, including the Miaohe biota from Hubei and the Wenghui biota from Guizhou, are mainly preserved as the carbonaceous compressions and dominated by macroscopic algae and metazoans. Here, we describe 10 genera and 10 species (including 6 new genera and species) of macrofossils from the Wenghui biota. At present, the Wenghui biota yields macrofossils in more than 31 genera and 33 species, excluding those given no image and established on a few unascertained specimens. Based on the occurrence and distribution of macrofossils in both Miaohe and Wenghui areas, the middle-late Ediacaran (back shales of the upper Doushantuo Formation) in South China can be subdivided into two assemblage biozones in biostratigraphy: (i) the Protoconites–Linbotulitaenia–Eoandromeda–Anomalophton assemblage biozone characterized by abundant and diverse macrofossils and by the ranges of Protoconites, Linbotulitaenia and Anomalophton; and (ii) the Baculiphyca–Gesinella–Cucullus–Beltanelliformis assemblage biozone characterized by the acme of the longer macrofossils Baculiphyca and Gesinella, and by few shorter and discoidal macrofossils.     

扬子克拉通埃迪卡拉系陡山沱组构造-岩相古地理恢复及油气意义*

近年来,随着扬子克拉通埃迪卡拉系陡山沱组页岩气勘探获得重大突破,深入和细化陡山沱期构造-岩相古地理就显得迫在眉睫。基于大量野外露头和最新钻井资料,结合前人研究成果,作者对陡山沱期构造-岩相古地理进行了分析、研究和图件编制。研究认为: 扬子克拉通埃迪卡拉纪陡山沱期,受控处于罗迪尼亚超大陆西北边缘的古地理位置和超大陆大规模裂解之后的热沉降作用初期的成盆构造环境,其古地理特征总体呈现出西高东低、北高南低,四古陆剥蚀区(汉南、康滇、牛首山和江南古陆)、三台地区(上扬子、中下扬子和浙北台地)与四盆地区(扬子东南缘与北缘坳陷、万源—达州和湘鄂西内裂陷)相间的沉积面貌和格局。其中,台地区以局限—开阔台地,盆地区以台缘斜坡、陆棚和半深海等为主要优势相。4个古陆是扬子陡山沱组主要的碎屑物源区,下伏裂谷盆地构造和陡山沱期发育的同沉积断裂,共同控制了埃迪卡拉系陡山沱组构造-沉积特征。提出陕南、川东北、鄂西和湘黔渝临区是最有利的陡山沱组烃源岩分布区,其次是浙北—皖南地区。有利烃源岩分布区及其邻区是扬子深层—超深层常规天然气或页岩气勘探值得高度关注的区域。     

Tectonic-lithofacies palaeogeographic reconstruction of the Yangtze Craton of the Ediacaran Doushantuo Formation and its oil and gas significance

Recently,great breakthroughs have been obtained in shale gas exploration in the Ediacaran Doushantuo Formation in the Yangtze Craton. Thus,the tectonic-lithofacies palaeogeography of the Yangtze Craton during the Doushantuo depositional period was in urgent need to be further studied. Based on a large number of outcrop sections,latest drilling data,numerous previous studies,we reconstructed the tectonic-lithofacies palaeogeography of the Yangtze Craton. The results indicated that,during the Ediacaran Doushantuo Period,the tectonic background of the Yangtze Craton was not only controlled by its palaeogeographic location(at the northwest of the supercontinent Rodinia),but also by the thermal sedimentation after the continental rifting. The tectonic-lithofacies palaeogeography of the Yangtze Craton generally showed higher terrain in the west and the north,and lower in the east and the south,with four oldlands developed namely the Hannan,Kangdian,Niushoushan and Jiangnan oldlands. The sedimentary pattern was featured by three platforms(in the Upper Yangtze,Middle-Lower Yangtze,and northern Zhejiang regions)alternated with four basins(in the Wanyuan-Dazhou,west Hubei-Hunan,southeastern and northern Yangtze margins). The three platforms were dominated by restricted-open platform facies; the four basins were dominated by platform margin slope,shelf and bathyal facies. The four oldlands(provided the main detrital provenance),together with the syn-depositional faults and the palaeostructure of the underlying rift basins,controlled the tectonic-sedimentary characteristics of the Yangtze Craton during the Ediacaran Doushantuo Period. The paper has proposed that the southern Shaanxi,northeastern Sichuan,western Hubei,and the adjacent area of the Hunan,Guizhou and Chongqing are the most favorable distribution areas of the Doushantuo source rocks;the northern Zhejiang and southern Anhui areas are the secondary favorable distribution areas. These favorable distribution areas and their adjacent areas are considered to be favorable regions for deepening the deep natural gas exploration in the Yangtze Craton.     

关于峡东陡山沱组具刺疑源类化石研究的补充

在峡东陡山沱组黑色燧石中前人报道了多种多样的具刺疑源类化石，笔者最近重新研究了陡山沱组岩石切片中的具刺疑源类，发现微化石三维地保存了几乎没蚀变的条件下，这个生物群落包括Filis phaeridi-um,Baltisphaeridium,Comasphaeridium和Tianzhushania等分子，它们中的Tianzhushania在外表及形态上可与产自挪威斯瓦尔巴德群岛晚里菲岩层中的Trachyhstrichosphaera aimika比较，Trachyhystrichosphaera aimika是晚前寒武纪最特殊和分布最广的一个分子，目前已知至少产自世界上15个地区的晚里菲岩层中，对于新古元代前文德地层似乎是一个出色的指示化石，产自陡山沱组的Tianzhushania似乎支持Butterfield的观点，即：陡山沱组硅化碳酸盐沉积的年代早于伊迪卡拉后生物多样化的时期，但是，由于化石只发展于少数岩石薄片中，因此，这些化石或许只代表峡东陡山沱组局部的生态环境。文中还讨论了陡山沱组的沉积环境及化石的保存。     

湖北峡东地区牛坪剖面埃迪卡拉系碳同位素组成及地质意义

对湖北宜昌埃迪卡拉系牛坪剖面碳酸盐岩进行了高精度的碳、氧同位素分析,微量元素测定。碳同位素演化趋势研究表明,牛坪剖面陡山沱组与灯影组下部存在2 次碳同位素负漂移和3 次显著的碳同位素正漂移。负漂移分别位于陡山沱组底部( EN1) 和陡山沱组中部( EN2) ,δ13C 值分别降低到－ 3. 6‰、－ 2‰。正漂移分别位于陡山沱组下部( EP1) 、上部( EP2) 以及陡山沱组和灯影组界线处( EP3) ,δ13C 分别上升到6. 7‰、7. 1‰、8. 2‰。牛坪剖面埃迪卡拉系δ13C 的演化趋势可与黄陵背斜周缘埃迪卡拉系碳同位素演化趋势对比,表明至少区域上碳同位素化学地层学在埃迪卡拉系划分和对比中具有重要意义。     

华南峡东地区埃迪卡拉(震旦)纪年代地层划分初探

华南峡东地区埃迪卡拉纪地层连续,出露完整,化石丰富,顶、底界线清楚,是世界上同时代地层最具代表性的序列之一,也是解决埃迪卡拉纪年代地层划分、竞争相关界线层型剖面的最理想地区之一.根据近年来峡东地区埃迪卡拉系的同位素年代学、生物地层学和化学地层学等方面的研究积累.本文以生物地层序列(生物演化阶段)为基础标志,以碳稳定同位素组成的重要变化界面为辅助标志,对峡东地区埃迪卡拉纪地层进行年代地层的划分,提出2统5阶方案.下统名称建议用峡东统,下分九龙湾阶和陈家园子阶;上统名称建议用扬子统,下分吊崖坡阶、第四阶和第五阶.在此基础上,根据生物地层和碳稳定同位素地层学的特征,初步探讨了与其他地区埃迪卡拉系的对比关系.这一划分和对比方案只是目前研究的阶段性认识,更完整的划分对比意见还有待今后的进一步完善.     

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.