The criteria for the biogeneicity of microbially induced sedimentary structures (MISS) in Archean and younger, sandy deposits

The identification of fossils or biogenic sedimentary structures in rocks of Archean age is difficult, because similar lithological features could rise from purely physical or chemical processes alone. Therefore it is important to define criteria that serve the secure definition of a fossil or structure in question as of biological origin. Such criteria have been established for stromatolites and microfossils.This contribution discusses the 6 criteria of biogeneicity of ‘microbially induced sedimentary structures’ (MISS). Those structures are found in sandy deposits of early Archean age to the present, and rise from the interaction of benthic microbiota with physical sediment dynamics. The six criteria for their biogeneicity are: (i) MISS occur in rocks of not more than lower greenschist facies; (ii) in stratigraphic sections, MISS correlate with turning points of regression–trangressions; (iii), MISS correlate with a characteristic depositional facies that enhances the development and the preservation of microbial mats; (iv), the distribution of MISS correlates with the ancient average hydraulic pattern; (v), the geometries and dimensions of fossil MISS correspond to that of the modern ones; (vi), the MISS include at least one of 9 specific microtextures.     

豫西苗岭统馒头组二段皱饰构造与遗迹化石共生特征*

埃迪卡拉纪以来,微生物与后生动物之间呈此消彼长的关系,但在寒武纪苗岭世却出现了微生物成因沉积构造和后生动物扰动构造短暂共存的现象。笔者在豫西馒头组二段下部识别出包括皱饰构造与微生物席裂构造在内的2种微生物成因沉积构造,对皱饰构造与遗迹化石的共生关系进行了分类,建立了席上足辙迹(Monomorphichnus henanensis)与牧食迹(Jinningichnus badaowanensis)、席下水平漫游迹(Planolites montanus)、席下深层泥岩中生物扰动共3种微生物席与后生动物的共生模式和生态演化模型。上述研究表明,具有特殊环境耐受性的“机会主义”动物在食物来源较为宽松的潮坪环境中与微生物席共存,这种微生物席与后生动物短暂而“和谐”的共存关系不仅延续了埃迪卡拉纪双方的部分共生特征,且在以混合底为主导的显生宙生态环境中得到了进一步变化与发展。     

Neoproterozoic trace fossils vs. microbial mat structures: Examples from the Tandilia Belt of Argentina

The Tandilia Belt in northeast Argentina includes a Neoproterozoic sequence of sediments (Sierras Bayas Group), in which the Cerro Largo Formation, ca. 750 Ma in age, forms a siliciclastic, shallowing upward succession of subtidal nearshore to tidal flat deposits. Trace fossils Palaeophycus isp. and Didymaulichnus isp. have been described from the upper part of this succession. Specific sedimentary structures consisting of round-crested bulges, arranged in a reticulate pattern, and networks of curved cracks are associated with the trace fossils. These structures are considered to be related to epibenthic microbial mats that once colonized the sediment surface. They reflect stages of mat growth and mat destruction, if compared to analogous structures in modern cyanobacterial mats of peritidal, siliciclastic depositional systems. Also the trace fossils are interpreted as mat-related structures, partly forming components of networks of shrinkage cracks, partly representing the upturned and involute margins of shrinkage cracks or circular openings in desiccating and shrinking, thin microbial mats.

The definition of Didymaulichnus miettensis Young as a Terminal Proterozoic trace fossil is questioned, and it may be considered to interpret the ‘bilobate’ structure as the upturned, opposite margins of microbial shrinkage cracks which have been brought back into contact by compaction after burial.     

Characteristic and Geological Significance of Microbially Induced Sedimentary Structures(MISS) in Terrestrial P-T Boundary in Xingyang,Western He’nan Province

Microbially Induced Sedimentary Structures (MISS) are primary sedimentary structures that arise syndepositionally from microbial community activity. Especially valuable are MISS for the analysis of early Archean (and extraterrestrial) deposits. However, most reports of MISS have focused on the Precambrian and Phanerozoic mass extinction marine sediments, and only a few and terrestrial MISS have been studied. The MISS presented in this paper, which mainly consists of mat growth feature, mat destruction feature and mat decay feature, are well preserved in terrestrial clastic rocks around the P-T boundary in Xiyang area, western Henan. Large U ridges, oriented sand quartz, mica grains and thin clayey laminae arranged parallel to bedding plane are the main features visible under the microscope. Several lines of evidence indicate that the Xingyang MISS are of biogenic origin. Abundant MISS in Xingyang may indicate the degradation of terrestrial ecosystems and proliferation of microbial mats immediately after the severe Permian-Triassic mass extinction. Study aiming at MISS helps to analyze their space distribution in the globe and to probe into links between microbial proliferation and environmental stresses following the end-Permian mass extinction in terrestrial ecosystems.     

Comparative study of two relatives,MISS and Stromatolites: example from the Proterozoic Kunihar Formation,Simla Group,Lesser Himalaya

Comparison of microbially induced sedimentary structures (MISS) and stromatolitic bearing horizons from the Proterozoic Kunihar Formation, Simla Group, Lesser Himalaya, has been scrutinised to understand the formative processes and controls on MISS and stromatolites in the context of sedimentary facies and response to sea level fluctuations. MISS structures recorded are wrinkle structures, Kinneyia ripples, load casts, domal structures, sand chips, palimpsest and patchy ripples with limited desiccation cracks. Stromatolitic morphotypes recorded are solitary, branching, wavy and domal forms of stromatolites associated with ooids, peloids and fenestral laminae. MISS structures flourished within tidal flats to shallow intertidal while stromatolites mushroomed in environments ranging from tidal to deep subtidal. MISS structures were favoured by resistant substratum, low energy conditions, consistent water supply and low terrigenous input. Stromatolites boomed when the volume of carbonate accumulation exceeded siliciclastic deposition. Fluctuating environmental conditions and sediment budget controlled morphology of stromatolites. Owing to limited siliciclastic input during deposition of dolomudstones (characterizes transgressive systems tract), microbial growth was enhanced. Calcareous shales were deposited over dolomudstones which marks the maximum flooding surface (MFS) indicating the culmination of transgression. Deposition of storm-dominated sandstone-siltstone (FA1), wave-rippled sandstones (FA2), tide-dominated sandstones (FA3), heteroliths (FA4), wackestone-packestone (FA6), boundstone (FA7) and ooid-peloid grainstone (FA8) on top of the MFS reflects initiation of highstand systems tract (HST) which is mainly characterized by stromatolitic horizons, alternation of carbonates and siliciclastics with flourishing microbial activity. Eventually, increased sedimentation in upper part of Kunihar Formation marks late stage of regression.     

Topographic control on distribution of modern microbially induced sedimentary structures (MISS): A case study from Texas coast

Modern back-barrier tidal flats of Galveston Island, Follets Island, and Matagorda Peninsula of the Texas coast are dominated by mud- to fine sand-sized siliciclastic sediments and prolific microbial mats. These microbial mats modify sediment behavior and result in a variety of microbially induced sedimentary structures (MISS). Common structures include: knobby surfaces, reticulated surfaces, gas domes, mat-cracks, sieve-like surfaces, erosional pockets, wrinkles, and mat chips. In general, mat thicknesses increase from ～ 1 mm in the upper supratidal to ～ 3 cm (maximum) in the lower supratidal and then decrease to ～ 2 mm in the lower intertidal areas. This same wedge-shaped pattern is displayed by detailed measurements of mat thicknesses from the rims into the deeper centers of depressions (pools) on the supratidal flats. Measurements of 175 mat-cracks show that height of the curled edges of the mat-crack polygons increases with increase in mat thickness. Similarly, measurements of 150 gas domes reveal that the size of the gas domes also increases with increasing thickness of the associated mats. Because mat thickness varies with elevation on the tidal flat, curl height of the mat-cracks and size of the gas domes are also related to elevation.Six zones were identified based on the occurrence of MISS within the supratidal (zone-I) to upper subtidal (zone-VI) areas. At the highest elevation, knobby surfaces characterize zone-I whereas zone-II is defined by reticulated surfaces. Along with reticulated surfaces, gas domes and mat-cracks characterize zone-III and zone-IV, respectively. Association of sieve-like surfaces with mat-cracks typifies zone-V whereas mat deformation structures and sieve-like surfaces define zone-VI. Boundaries between the MISS-zones in general are parallel and related to tidal zones. The distribution patterns of the MISS-zones are strongly controlled by local topography of the sediment surface because the degree of inundation is the primary controlling factor for the mat growth and resultant MISS. Therefore, distribution of the microbially induced sedimentary structures in siliciclastics, along with the dimension of the mat-cracks and gas domes, can be potentially helpful in interpretation of topography of paleodepositional surfaces.     

山西黎城中元古界常州沟组微生物成因构造(MISS)及其地质意义

在山西黎城县西井镇彭庄至大井盘公路旁剖面以及黄崖洞景区发育大量的微生物成因构造(MISS),多发育在砂岩表面。由于构造形态奇特,被误以为各种遗迹化石或是不规则的泥裂构造。依据其形态特征、成因构造和前人分类方案,将研究区此类构造分为3种类型,即微生物席生长构造、微生物席破坏构造和微生物席腐烂构造,以及9个不同形态构造,即小瘤状突起、圆顶大瘤状突起、不规则侧向生长脊、大脊状生长构造、纺锤状脱水裂痕、多边形网状脱水裂痕、曲形脱水裂痕、微生物席砂片、砂火山构造,对9种不同形态的MISS进行了详细的论述。对研究区微生物成因构造(MISS)的成因进行了探讨,与豫西鲁山地区、贺兰山苏峪口地区、北京南口地区、河北兴隆地区发育的MISS及地层特征进行类比,认为MISS对华北地台中元古代地层对比以及古环境研究有重要的指导意义。     

The oldest record of Ediacaran macrofossils in Gondwana (~563 Ma,Itajaí Basin,Brazil)

The Avalon biota (Ediacaran Period, 570–559 Ma) marks the first appearance of macroscopic and complex benthic communities in the fossil record. This assemblage is known from a few localities worldwide, mainly in Canada and England. Here, we report for the first time the presence of Ediacaran macrofossils in deposits of similar age from Gondwana (Itajaí Basin, southern Brazil). Our new radiometric date (~563 Ma) indicates that the Itajaí Basin can be chronocorrelated with the classic Avalonian deposits and thus represents one of the oldest records of the Ediacaran biota in Gondwana. We describe the presence of the Ediacaran genus Palaeopascichnus, as well as discs (Aspidella and Nimbia), and other problematic forms. Contrary to the deep-marine macroorganisms of the Avalon Assemblage, the Itajaí fossils are associated with abundant and exceptionally preserved three-dimensional microbial mats and microbially induced sedimentary structures (MISS) in relatively shallow settings (upper slope and distal delta front deposits). In this sense, the Itajaí biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later White Sea Assemblage.     

贺兰山地区中元古代微生物席成因构造

贺兰山中段中元古界黄旗口组石英砂岩中发现丰富的微生物席成因构造(MISS),包括由微生物席生长、破坏和腐烂过程形成的3种类型、9种不同形态的构造;与华北大红峪组发现的同类构造在成因类型与多样性方面具有很强的可对比性.砂岩中发育双向交错层理、冲洗层理、高角度单斜层理系和波痕,泥质粉砂岩夹层中发育波痕与泥裂,表明微生物席主要发育于潮间带上部至潮上带下部环境.MISS构造在华北地台长城系下部砂岩中的广泛存在表明在1.6 Ga前以蓝细菌为主的微生物群在环潮坪碎屑环境也很活跃.可能代表了微生物由海洋向陆地环境发展的过渡阶段.具光合作用功能的制氧蓝细菌的蓬勃发展可能是引发中元古代海洋化学条件发生转变、含氧量增高的重要原因,并为真核生物及宏观藻类的兴起创造了条件.研究表明,黄旗口组与华北大红峪组大致同时,反映了Columbia超大陆裂解期华北地台开始拉伸-张裂、缓慢沉降的构造古地理背景.     

豫西鲁山汝阳群微生物成因构造宏观特征分析及其沉积环境演化

豫西鲁山地区汝阳群发育了形态特征多样的大量微生物成因构造,主要为多边形网格状脱水裂痕和纺锤形脱水裂痕。通过对微生物成因构造宏观特征的描述和统计分析,探讨了微生物成因构造与沉积环境之间的关系,认为微生物成因构造的总体特征演化规律与汝阳群趋于稳定的沉积环境演化一致,其形态特征与微生物席厚、暴露时间频繁有着密切的关系。     

微生物席成因构造形态组合的古环境意义: 以华北南缘中-新元古代为例

微生物席成因构造(microbially induced sedimentary structures, MISS)是由微生物与沉积物相互作用形成的生物-沉积构造, 可作为早期微生物群活动的重要标识, 但对其指示古环境的研究尚显不足.华北地台南部中-新元古代汝阳群(Pt₂)和洛峪群(Pt₃)以近岸浅水陆源碎屑沉积为主, 其中发育大量MISS, 包括多向波痕、微生物席稳化波痕、微生物席碎片、微生物席平滑波痕、多种微生物席脱水形成的砂裂及不规则网状生长脊等.研究表明, 在潮坪环境中MISS最为发育.地势差异对水动力、基底暴露、水分补给和沉积条件等环境因素具有显著控制作用, 影响微生物席的发育与结构, 因此, MISS的形态组合特征能够反映沉积微相变化.研究发现, 在潮上带以微生物席脱水形成的砂裂构造为主, 潮间带上部以破坏-改造型构造为主, 潮间带下部-潮下带一般少见原位MISS, 但可见再沉积微生物席碎片.据潮间带下部至潮上带上部MISS产出类型及其形态组合分析, 识别了4个MISS形态组合带, MISS形态组合由潮间带下部至潮上带上部的变化反映了古地形由低到高的明显变化.      

豫西鲁山汝阳群微生物成因构造宏观特征分析及其环境演化

豫西鲁山地区汝阳群发育了大量形态特征多样的微生物成因构造（microbially induced sedimentary struc-tures）,简称MISS,是微生物席或微生物膜与其他物理作用营力（如剥蚀作用、沉积作用、搬运作用和变形作用）相互作用的产物,也可被视为一种广义的遗迹化石,其最主要的两种类型是多边形网格...     

东濮凹陷两种新储层类型——沙河街组河口湾体系的识别与储层预测

东濮凹陷沙河街组河口湾环境发育的最初征兆是出现震积岩（Seismites）和水下脱水收缩裂隙（Synaeresis）,预示其基底有构造性下沉,海水在间歇性地灌入,接着淡水介形类开始大量死亡。与海水有关的生物痕迹如Ophiomorpha、Tigillites屡屡出现,说明此时此地淡水水体已被河口湾咸水水体所取代,最后剖面中见到滨海高能环境下的生物痕迹Arenicolites和鲕粒砂岩、介壳碎屑层等,指示潮道和潮汐坝的存在。至此,这一地区的河口湾以陆相（分流河道）－陆海混合相（河口湾点坝）－海相（潮道）为代表的三元结构,便完整地记录了一次海面升降周期。由陆相动物活动痕迹、植物活动痕迹和古土壤识别出的陆相部分在沙河街组有10层（开31井）,由海相生物痕迹、海相生物及海相内源沉积物识别出的海相部分有12层（开31井、新胡4井）,说明沙河街组沉积期曾有过10次以上的海面升降过程。海面下降时,河流沿兰聊断裂和内黄凸起间断裂谷地侵蚀切割两岸形成可容空间;海面上升期,此可容空间部分或全部被不同类型的沉积物所充填,形成了分流河道、河口湾点坝砂为代表的下切谷型储层和以潮道、滩坝砂体为代表的超覆型储层。     

从微观角度认识微生物席在中元古代的繁盛--以豫西云梦山组为例

豫西云梦山组发育了大量的微生物成因沉积构造（MISS）。在地层纵剖面上,毫米级的深色沉积物层和浅色的石英颗粒层交替出现,形成典型的微生物席纹层,代表着微生物席在沉积表面的多次生长和埋藏。深色层包含有泥质物和细砂-粉砂颗粒,被认为是先前微生物席的残留区;浅色层则是较纯净的石英颗粒,由物理沉积作用形成。进一步对纹层区的薄片...     

古元古代末浅海赤铁矿化微生物席: 标识与意义*

微生物活动导致铁氧化被认为是前寒武纪铁建造和红层形成的重要机制之一,但是地质记录中却鲜有相关证据。针对这一问题,本研究选择华北古元古代末的大红峪组微生物席成因构造(MISS)为研究对象,通过沉积学和矿物学的综合研究,揭示微生物活动在前寒武纪铁循环中的关键作用。研究表明:华北井陉大红峪组发育大量以砂裂为代表的MISS,指示当时潮间带至潮上带广泛发育微生物席;非微生物席层发育大量原位和近距离搬运的海绿石,指示低氧富铁的浅海和孔隙水化学条件,而相邻微生物席层则发生了显著的赤铁矿化,指示相对更氧化的沉积环境。考虑到微生物席层与相邻(厘米级)非微生物席层间微生物活动与矿物组成的明显差异,笔者提出微生物活动可能是导致当时低氧铁化浅海环境局部铁氧化的重要机制。本研究提供了微生物参与Fe²⁺离子氧化的重要证据,对揭示前寒武纪红层和大规模铁建造形成机制具有启示意义。     

Mass occurrence of benthic coccoid cyanobacteria and their role in the production of Neoarchean carbonates of South Africa

The sparse Archean fossil record is based almost entirely on carbonaceous remnants of microorganisms cellularly preserved due to their early post-mortem silicification. Hitherto as an exception, sedimentary carbonate rocks from the Neoarchean Nauga Formation of South Africa contain calcified microbial mats composed of microbiota closely resembling modern benthic colonial cyanobacteria (Chroococcales and Pleurocapsales). Their remains, visible under the scanning electron microscope (SEM) after etching of polished rock samples, comprise capsular envelopes, mucilage sheaths, and groups of cells mineralized by calcium carbonate with an admixture of Al–K–Mg–Fe silicates. The capsular organization of the mucilaginous sheaths surrounding individual cells and cell clusters forming colonies and the mode of mineralization are the characteristic common features of the Neoarchean microbiota described and their modern analogues. The new findings indicate massive production of calcium carbonates by benthic coccoid cyanobacteria in the Neoarchean, and offer a solution to the problem of the origin of Archean carbonate platforms, stromatolites and microbial reefs.     

前寒武纪与微生物席相关的粉砂岩岩墙——以天津蓟县古元古界串岭沟组为例

在天津蓟县剖面古元古界串岭沟组下部的环潮坪相粉砂质泥页岩细粒沉积中,发育许多粉砂岩岩墙。由于该粉砂岩岩墙在层面上和层内具有特别的形态,因而对其成因具有多种解释:在层面上呈纺锤状粉砂岩裂缝以及在层内呈砂质充填管形态,从而被认为是最古老的后生动物遗迹化石;在层内呈弯弯曲曲的粉砂岩岩墙以及明显的流体化作用特点,所以又被解释为地震振荡作用形成的液化砂岩脉。显微镜下,这种岩墙具有明显的富残余有机质构成的边界,以及由粉砂颗粒相对聚集所显示出的明显的流体化作用特征;再加上与这种粉砂岩岩墙共生的沉积构造主要是皱饰构造,局部还发育变余波痕,由此表明沉积面上曾经发育过微生物席。因此,这种粉砂岩岩墙应该解释为沉积面在曾经被微生物席封闭的情况下,相对富含有机质的细粒沉积物在早期成岩作用过程中所发生的脱气作用和脱水作用的产物,最终可以归为由微生物形成的沉积构造的一种类型。     

Deep-rooted piercement structures in deep sedimentary basins — Manifestations of supercritical water generation at depth?

Deep-rooted enigmatic piercement structures in sedimentary basins, including ‘mud volcanoes’, ‘shale diapirs’, ‘salt diapirs’, and ‘asphalt volcanoes’, range in size from less than 1 km², surface area, up to 64 km², and have often an unknown depth of penetration due to incomplete imaging. We propose that they form a family associated with fluid flow. Our argument is based partly on their inferred location (above deep faults) and on the chemical analysis of emitted products, which includes liquid clays, brines and other substances from salt diapirs, and asphalt and light oils from the asphalt volcanoes. We explain these compositions by chemical alteration caused partly by supercritical water, a phase of water existent at high pressure and temperature, locally and temporarily achieved at depths generally beyond 10 km below surface, i.e., at the sediment–crust boundary. Our hypothesis overcomes some of the problems with interpreting fluid flow products, which are otherwise very difficult to explain. In case this hypothesis can be further verified, the family could perhaps be called ‘hydrothermally associated piercement structures’.     

Microbial signatures in peritidal siliciclastic sediments: a catalogue

A catalogue of microbial structural signatures is presented, based upon the coupling of fundamental biogeochemical–microbial processes and local morphogenetic determinants. It summarizes a collection of sedimentary structures obtained from two modern siliciclastic peritidal environments in different climatic zones (temperate humid: Mellum Island, southern North Sea; subtropical arid: coast of southern Tunisia). Textural geometries reveal a high structural diversity, but their determinants are primarily based upon six major parameters: (1) intrinsic biofactors: structural diversification of sedimentary microbial films and mats inherent in the organisms, i.e. their construction morphology, growth, taxis and behaviour, and local abundance of specific morphotypes. Most prominent are the ensheathed filamentous cyanobacteria Microcoleus chthonoplastes and Lyngbya aestuarii, and the sheathless filamentous cyanobacterium Oscillatoria limosa. (2) Biological response to physical disturbances: sediment supply, erosion and fracturing of surface layers resulting from desiccation cause growth responses of biofilms and microbial mats. (3) Trapping/binding effects: physicobiological processes give rise to grain orientations and wavy to lenticular lamina, lamina‐specific grain arrangements and ‘sucrose’ calcium carbonate accumulations. (4) Secondary physical deformation of biogenic build‐ups: mechanical stresses acting upon sediments overgrown and biostabilized by biofilms and mats produce erosional and overthrust structures. (5) Post‐burial processes: textural fabrics that evolve from mechanical effects of gas formation from decaying mats, and features related to the formation of authigenic minerals (calcium carbonates, calcium sulphates, pyrite). (6) Bioturbation and grazing: post‐depositional structures, such as Skolithos‐type dwellings, traces of burrowing insects, gastropod grazing traces and faecal pellets. In synopsis, the catalogue firstly comprises a sound set of ubiquitous signatures. This uniformity in architectural characteristics is attributed to the presence and local dominance of certain microbes throughout the different settings. The catalogue secondly documents signatures that are extremely sensitive to tidal position, hydrodynamic regime and overall climatic conditions. These kinds of signature indicate narrow facies zones, which often coincide with the activity or dominance zones of certain organisms. An overview of structures of microbial origin from the fossil record underlines the potential of many of the signatures included in this catalogue to become fossilized and provide strong indicators of former siliciclastic tidal settings.     

前寒武纪海侵砂岩中的微生物砂质碎片：以北京南口虎峪剖面大红峪组为例

碎屑岩中微生物形成的原生沉积构造,由于缺乏直接的微生物证据,其识别常常比较困难。位于北京西北郊的南口虎峪一带,古元古代晚期的大红峪组(1650～1600Ma),海侵体系域砂岩地层与高水位体系域砂泥质白云岩和叠层石白云岩组成了较为有规律的沉积相序特征,成为将大红峪组划分为三个三级层序的主要标志。在大洪峪组的海侵体系域砂岩层中,一种类似于碳酸盐岩中的“内碎屑”的奇特的砂质碎片,代表了前寒武纪海侵砂岩沉积面上曾经发育过微生物席;该砂质碎片与变余波痕和皱饰构造组成系列席底构造,特殊的形态和产出特点成为窥视前寒武纪砂岩中微生物席发育的一种典型标志。因此,南口虎峪剖面大红峪组海侵砂岩中的微生物砂质碎片及其相关的席底构造的发现,有益于今后对类似沉积构造的阐释与研究,特别是那些常常被厘定为前寒武纪古老的后生动物遗迹化石的沉积构造;同时也表明,在前寒武纪地层之中,除了要关注叠层石之类的微生物沉积构造以外,碎屑岩中也存在微生物活动的若干证据即席底构造(第五类原生沉积构造),这些特别的沉积构造对前寒武纪沉积环境重塑具有重要意义。