The Ediacara member of the Rawnsley quartzite: The context of the Ediacara assemblage (late precambrian,flinders ranges)

The Ediacara fossil assemblage occurs widely in the Flinders Ranges, South Australia, in a single, readily mappable stratigraphic interval—the Ediacara Member of the Rawnsley Quartzite, which is part of the Pound Subgroup of the Wilpena Group. The Member occurs low in the Rawnsley Quartzite and consists of siltstones, medium‐ to thick‐bedded sandstones, and heterolithic units of intercalated siltstone and sandstone. Features such as rhythmical bedding and flaser bedding, interference and flat‐topped ripples, winnowed coarse sand residues, abundant clay galls, and rare desiccation cracks suggest that the heterolithic siltstone/sandstone units represent intertidal deposits. The rich body‐fossil assemblage occurs chiefly in these deposits of probable intertidal origin, and for the most part appears to represent organisms stranded by the tide away from their normal habitat. Associated bioturbation structures include horizontal, penetrative (post‐depositional) burrows, but vertical dwelling burrows have not been found; the Pound Subgroup evidently pre‐dates their widespread appearance.

The Rawnsley Quartzite appears to have been deposited during cycles of marine transgression, with the Ediacara Member inferred to have accumulated in environments varying from shallow shelf to tidally influenced lagoons sheltered by barrier bars.     

Textured organic surfaces associated with the Ediacara biota in South Australia

The Ediacaran Period takes its name from the fossils of the Ediacara biota, which represent the first appearance of large and diverse assemblages of organisms in the fossil record. Although the global record of these distinctive body fossils is now well known, a previously unrecognized megascopic organic record of textured organic surfaces (TOS) occurs in the Ediacara biota. However, TOS is also a feature over a wider range of paleoenvironmental settings, where body fossils are unknown, in Ediacaran siliciclastic successions that have been studied in Australia, Namibia and western North America.Paleoecological analysis of successive bedding planes of strata from the late Ediacaran Rawnsley Quartzite in the Flinders Ranges of South Australia, reveals that TOS represent the most common organic features in bedding-surface assemblages of the Ediacara biota. The TOS consist of preserved, patterned assemblages of textured organic mats, fibers and simple tubular body fossils. Complex Ediacara body fossils while striking for their distinctive body plans, and dominating some of the beds, are relatively minor components of combined overall surface area. Many elements of TOS have previously been miss-diagnosed as trace fossils, which are in practice limited to two or at most three morphotypes that indicate the presence of Bilateria. Although TOS represent a simpler grade of organismic construction than discrete and more complex Ediacara body fossils, they were preserved in a similar manner. Marked variability in all components of the biota between successive surfaces suggests that Ediacara ecologies fluctuated at short intervals despite an apparently consistent sedimentary regime.     

湘西震旦纪武陵山生物群的化石形态学特征和归属

湘西桃源理公港震旦系留茶坡组中部黑色页岩中的炭质压膜化石,为研究末前寒武纪晚期生物学提供了一个稀有的布吉斯页岩型分类学窗口。根据已知属种和新获材料的研究,确定了17个明显的形态类型,讨论了每种形态类型特征及其可能的生物学属性,指出除个别化石可能为两侧对称动物外,其余绝大多数化石可以解释为原核生物或多细胞藻类,系统发育上与绿藻、褐藻、蓝藻细菌等相关。具固着器、叶状体为球状或具同心纹构造的Apsidiumsphaericus的发现,进一步证明典型埃迪卡拉动物群(或白海生物群)中简单的圆盘状化石可能为多细胞藻类,而不是水母。武陵山生物群中具同心纹结构的大型圆盘状化石的出现及其共生生物特点,指示该生物群是埃迪卡拉期生物分异发展阶段的产物,是末前寒武纪晚期一个以多细胞藻类发育为特色的新型生物群。     

There is no such thing as the ‘Ediacara Biota'

The term‘Ediacara Biota’(or many variants thereof)is commonly used to refer to certain megascopic fossils of Precambrian and early Palaeozoic age e but what does the term actually mean?What differentiates a non-Ediacaran‘Ediacaran’and an Ediacaran‘Ediacaran’from an Ediacaran non-‘Ediacaran’?Historically,the term has been used in either a geographic,stratigraphic,taphonomic,or biologic sense.More recent research and new discoveries,however,mean that the term cannot actually be defned on any of these bases,or any combination thereof.Indeed,the term is now used and understood in a manner which is internally inconsistent,and unintentionally implies that these fossils are somehow distinct from other fossil assemblages,which is simply not the case.Continued use of the term is a historical relic,which has led in part to incorrect assumptions that the‘Ediacara Biota’can be treated as a single coherent group,has obscured our understanding of the biological change over the PrecambrianeCambrian boundary,and has confused research on the early evolution of the Metazoa.In the future,the term‘Ediacaran’should be restricted to purely stratigraphic usage,regardless of affnity,geography,or taphonomy;suffcient terminology also exists where reference to specimens on a geographic,taphonomic,or biologic basis is required.It is therefore time to abandon the term‘Ediacara Biota’and to instead treat equally all of the fossils of the Ediacaran System.     

Were Ediacaran siliciclastics of South Australia coastal or deep marine?

The Late Neoproterozoic Ediacara Member of the Rawnsley Quartzite in South Australia has been considered aeolian, fluvial, intertidal and deep marine by various authors. Palaeosols would not be expected for the deep marine interpretation, but some palaeosols should be evident for the aeolian–fluvial–intertidal interpretations, and this is the first study to examine the Ediacara Member at a petrographic and geochemical scale appropriate to recognize potential palaeosols. Recognition of palaeosols and floodplain facies in Neoproterozoic rocks is a challenge because such rocks are too ancient for diagnostic non‐marine fossils such as root traces. The varied thickness of Ediacara Member red siltstones and white sandstones is distinct from laterally persistent overlying and underlying grey shales and limestones with acritarchs, stromatolites and other marine fossils. The sandstones are trough cross‐bedded and fill palaeovalleys. The red siltstones have poorly sorted, highly angular, silt‐size grains characteristic of loess. Particular sandy and silty beds were sampled for detailed petrographic and geochemical studies, because they include desiccation cracks, sand crystals, ice cracks, carbonate nodules and soft‐sediment deformation like those of palaeosols. Chemical and grain‐size variations within these beds reveal surficial clay formation and oxidation from feldspar as in soils. Petrographic studies also revealed surficial disruption of these palaeosols by filamentous structures comparable with microbial ropes of biological soil crusts. This array of palaeosol features may be of use for recognizing palaeosols in other Neoproterozoic siliciclastic sequences.     

辽宁省本溪期-山西期沉积岩相古地理分析

辽宁省本溪期-山西期沉积地层主要分布于太子河地层小区,少量见于大连地层小区,零星出露于辽西锦州、朝阳、凌源和葫芦岛一带.根据其岩性组合、沉积构造、指相化石及沉积矿产等特征,对该期沉积环境进行较深入的研究,划分为三角洲相、障壁海岸相和海湾陆棚相3个沉积相,进而对本期岩相古地理特征进行分析研究.     

辽西地区义县组岩相古地理特征

义县组广泛发育于辽西地区晚中生代盆地中,为一套以陆相火山喷发为主,夹多层沉积岩层的火山--沉积岩系。其沉积层中富含热河生物群化石。通过岩相古地理和火山岩相等研究方法,把义县组自下而上分为4个岩性段,各段的岩相特征为:一段主要为河流相,由复成分细砾岩组成;二段湖泊相广泛分布,形成了一套含珍稀化石的湖相沉积层;三段以河流相为主;四段为湖泊相、河流相和冲积扇相,均小面积发育。4个岩性段均不同程度发育火山岩相(包括各火山亚相)。与土城子期对比,义县期的古地貌不会高于土城子时期,古水流主要来自火山盆地坳陷湖的四周。     

柴北缘地区层序格架下的沉积特征

中国中西部含油气沉积盆地大多具有前陆盆地层序组合特征,可以识别出前陆层序和非前陆层序。柴达木盆地柴北缘层序地层格架主要包括非前陆层序的侏罗系和古近系以及前陆层序的新近系。通过井剖面层序分析结合有限的地震剖面,可以对柴达木北缘侏罗系划分7套III级层序。古近系—第四系划分11套III级层序。侏罗系属于非前陆期沉积,新近系属于前陆期沉积。通过柴北缘地区层序框架下沉积特征的解剖,表明柴北缘地区非前陆期遗迹化石以缺氧环境化石群为主,沉积相以河流-湖沼体系为特征。前陆期遗迹化石以陆相氧化河湖相环境化石群为主,湖退体系域(RST)冲积扇-河流三角洲-滨浅湖相沉积体系非常发育。柴达木盆地的沉积层序表现为受构造强烈活动和气候变化的影响,强烈活动期潮湿气候下层序表现为山前带发育进积式准层序组,凹陷区形成退积式准层序组。干旱气候配合下的层序表现为多物源更加明显,山前带沉积物供应更加迅速,且沉积中心迁移强烈。     

Note on the palaeoenvironmental significance of the nuccaleena formation (upper Precambrian), central Flinders Ranges,South Australia

Four distinct sedimentary facies have been recognized within the upper Precambrian Nuccaleena Formation in the central Flinders Ranges of South Australia. Three dolomite facies, containing tepee structures within either well‐laminated or stromatolitic dolomite, were deposited within supratidal and intertidal environments, whilst an interbedded shale and dolomite facies originated under very shallow submerged conditions.     

西藏西部昂拉仁错地区下白垩统岩石地层特征及空间变化规律

将西藏昂拉仁错地区下白垩统划分为则弄群、多尼组、郎山组和捷嘎组4个正式岩石地层单位。讨论了各组段的空间分布、岩石组合特征、沉积环境及横向变化规律。认为多尼组仅分布于班戈-八宿地层分区的东部,在改则厚齿玛里以西相变尖灭,与则弄群二段既有上下层位关系又呈横向相变关系。郎山组为只见于昂拉仁错北部班戈-八宿地层分区内的一套稳定碳酸盐台地相沉积,而捷嘎组为只见于昂拉仁错中南部措勤-申扎地层分区内的较活动的火山活动碳酸盐台地相沉积。郎山组与捷嘎组为同时异相关系。     

Nature and significance of the Neoproterozoic Sturtian–Marinoan Boundary,Northern Adelaide Geosyncline,South Australia

The Cryogenian succession of the Northern Flinders Ranges reveals a complex sedimentary record between the Sturtian and Marinoan glacial deposits. A major unconformity separates the Sturtian and Marinoan-aged sedimentary successions in the area. This forms a subaerial erosion surface with terrestrial and marginal marine infill directly above the Angepena and Balcanoona Formations in their respective localities. This exposure surface is here correlated with the previously documented submarine unconformity between the Yankaninna Formation and the underlying deep marine Tapley Hill Formation. This erosional event provides a chronostratigraphic marker horizon that coincides approximately with thepreviously defined Sturtian–Marinoan Time Series boundary in the Northern Flinders Ranges. These stratigraphic relationships also constrain lateral facies relationships between the Oodnaminta ReefComplex (Balcanoona Formation) and the Angepena Formation. Similarly, the shallow-water Weetootla Dolomite is correlated with the deeper water carbonates of the Yankaninna Formation.     

湘西-黔东地区寒武系都匀阶清虚洞期 岩相古地理与铅锌成矿关系研究

依据地层记录中的两种相变面和两种穿时性,结合上扬子地区寒武系十余条代表性剖面的沉积特征及其横向展布规律,应用等时面优势相成图方法编制了寒武系都匀阶清虚洞期岩相古地理图.区内古地理格局具有西高东低、北浅南深(水深)的特点,沉积自北西向南东超覆,层位逐渐抬高穿时;岩性、厚度、颜色和沉积相类型上的差异是统一沉积背景下沉积物相变、穿时的结果.清虚洞组由灰岩段和白云岩段组成,以发育缓坡型碳酸盐台地为特征,纵向上构成总体向上变浅的沉积相序列,同时反映了缓坡型碳酸盐台地的生长发育过程;横向上从北西至南东发育从混积潮坪相、浅缓坡相、中缓坡相、深缓坡相和陆棚-盆地等沉积.岩相古地理对层控铅锌矿具有明显的控制作用,主要分布于中缓坡相藻灰岩微晶丘中,浊积岩、微晶丘、砾(粒)屑灰岩构成一完整的铅锌控矿序列.     

下扬子区早三叠世风暴沉积及其特征

<正> 早三叠世,下扬子区为位于华北古陆与华夏古陆之间的陆表海,其中发育一套以碳酸盐岩为主的海相沉积物。近年来,笔者在该区(图1)工作期间,发现在早三叠世时,沿皖南到苏南的广大区域内,风暴沉积作用产生的特征十分显著,风暴岩广为发育。     

The nature of Mawsonites (Ediacara fauna)

Some representatives of the Ediacara fauna have been later re-interpreted as pseudofossils. This was recently also done for Mawsonites, which was re-interpreted as a sedimentary structure formed due to interaction of a sand volcano (or water-escape structure) and a biomat. This sedimentary genesis appears not to be tenable, as several physical processes should have been involved, none of which is known from modern times or the geological past. It is concluded that Mawsonites must be considered as a fossil, either an imprint or a true fossil. This interpretation may be tested on one or more fragments of the structure.     

Shaanxilithes在贵州的发现及其意义

贵州清镇桃子冲组发现了保存精美的 Shaanxilithes,其特征与陕南高家山生物群中的相同分子基本一致 ,结合瓶状化石资料 ,初步推断桃子冲组下段的下部可与高家山段对比 ,与南澳的“可疑构造”在形态上的相似性进一步证实 Shaanxilithes具有较为稳定的地史分布 ,可以作为新元古代末期地层对比的一个潜在的重要标志。对Shaanxilithes的深入研究排除了其为遗迹化石或蠕形动物的可能 ,推测它可能是一类钙化的藻类化石碎片     

Eastern Mississippi delta: late Wisconsin unconformity, overlying transgressive facies, sea level and subsidence

Analysis of 92 engineering core logs located in the Balize sector of the eastern Mississippi delta focuses on the late Wisconsin unconformity and lithofacies of strata lying immediately below and above this stratigraphic horizon. This major sequence boundary is a key feature used to correlate strata across shelf and slope to the basin. Observations emphasize lithofacies distributions of the latest Pleistocene sediments underlying the unconformity, the late Pleistocene to early Holocene transgressive facies, and the immediately overlying deltaic deposits. Maps and a cross-section compiled with this information highlight the critical relation between lithofacies distributions and late Wisconsin sea-level oscillations. Core analysis reveals that the transgressive facies comprises distinct environments of deposition, offshore to onshore. Findings identify criteria to determine the approximate position of the shoreline at the late Wisconsin maximum sea-level lowstand and at the extent of early Holocene maximum marine inundation in the Balize complex. Mapping of lithologies along the late Wisconsin unconformity serves to improve correlation of sediment facies with changes in acoustic response along high-resolution seismic profiles. An estimate of long-term averaged land subsidence suggests lowering of at least 1 mm/year near the shelfedge during the past 18 000 years. This mapping also refines sea-level response models for the Mississippi delta, including criteria to locate key paleogeographic features such as shelfedges and maximum flooding surfaces in other Recent marine deltas and in older, stacked deltaic sequences.     

甘肃省的三叠系

根据地层区划分原则,将省内三叠系划分为海、陆2个地层区和6个地层小区,阐述了各地层区特征,对顶、底界及统界进行了合理划分并提出了一些新的划分意见,对个别地层时代,据新资料进行了修改、厘定;建立了地层系统和地层层序,统一了地层单位和名称,选出代表性剖面,系统论述了岩性、岩相、厚度、古生物组合、接触关系及合矿性等特征;首次将三叠纪划分为海、陆两大生物区系,南部海相区,早、中三叠世主要属特提斯型生物区系,混有少量北方及环太平洋区系分子,北部陆相区的三叠纪及南部的南祁连小区和西秦岭小区的晚三叠世主要属北方型植物区系,仅西秦岭小区属不典型的南方型植物区系,两区间为混合型植物区系;按海、陆相各世分别总结了各门类古生物组合特征及与国内、外进行了对比;按海、陆相三叠系分别与国内、外有关地层进行了概略对比;按世分别编制了岩相古地理略图,并探讨了各地层小区内岩相古地理及古气候特征;概述了三叠纪沉积矿产煤、石油及层控矿产汞、锑等13种矿产的分布、含矿岩系及储存层位等特征。     

上扬子区寒武系娄山关群白云岩层序地层格架及其古地理背景

上扬子区特别是贵州及其邻区的寒武系娄山关群发育一套化石贫乏的浅水台地相白云岩,横跨中、上寒武统,厚度上千米,自北西向南东随着沉积环境水体的加深逐渐相变为开阔海台地相灰岩、陆棚相泥页岩等。由于化石贫乏难以进行详尽的年代地层划分,但是发育石盐假晶泥晶白云岩所反映的沉积环境水体变浅以及发育颗粒白云岩所反映的水体加深,表明可以应用从岩相序列到沉积相序列的方法对该套白云岩进行层序地层划分,成为在“海平面变化的框架内探讨沉积相迁移”的典型代表。巨厚的贫乏化石的娄山关群白云岩与下伏厚度较小、产三叶虫化石的陡坡寺组白云质细粒混合岩系形成了鲜明的对照,它们组成了1个二级层序,并可以划分为7个三级层序。陡坡寺组细粒混合岩系代表了二级海侵作用所造成的水体加深,而娄山关群白云岩自北西向南东进积尖灭则代表了二级海退过程所造成的水体变浅。该二级层序本身即是1个总体向上变浅的沉积相序列,其相序组构与三级层序相似,三级层序的相序组构与那些由岩相序列所组成的若干环潮坪型米级旋回也具有相似性。因此研究区娄山关群白云岩构成了1个复杂而有规律的、独特的层序地层格架,并由此反映了沉积物的时间演变序列和沉积相的空间展布特征具有一定的规律性,代表了其古地理演变过程既受制于海侵加深和海退变浅的时间过程,同时又受控于沉积环境水体自北西向南东由浅变深的空间变化过程。娄山关群白云岩的层序地层研究表明：层序地层学研究的核心是沉积物的时间演变序列以及沉积相的空间展布形式所代表的规律性,并根据这种规律性进行地层划分和对比。     

First known Cretaceous glaciation: Livingston Tillite Member of the Cadna‐owie Formation,South Australia

A 2 m‐thick diamictite occurs near the base of the Cretaceous Eromanga Basin succession at Trinity Well, at the northern extremity of the Flinders Ranges in South Australia. The diamictite consists of a matrix of silt‐ and clay‐size particles and a framework of sand and coarser materials up to small boulder size. Scanning electron microscope study reveals the presence of numerous quartz grains displaying extreme angularity and surface textures attributed to glacial crushing. Sandy sediments considered as fluvioglacial in origin and a locally developed facies displaying flow structures attributed to solifluction processes constitute the basal 3–5 m of the sequence. In places these directly underlie the diamictite and rest with angularity on Neoproterozoic Adelaidean strata. Conformably above the diamictite at the type locality ‘Recorder Hill’ is a sequence approximately 15 m thick of fine sand and silt units containing lonestones up to ～70 cm diameter and hummocky cross‐stratification. These sediments have been assigned to the Cadna‐owie Formation and are dated on palynology as Berriasian to Valanginian. The occurrence of diamictite containing glacially affected quartz grains contributes to our interpretation that the southern margin of the Eromanga Basin, and at least the adjacent part of the northern Flinders Ranges, were affected by glaciation in the Early Cretaceous. The associated dropstone and solifluction facies and nearby glendonite pseudomorphs after ikaite are further evidence of at least intermittent cold climates at this time.