pyrite mineralization in microbial mats from the mid proterozoic newland formation belt supergroup montana u s a abstract the mid proterozoic newland formation a shale dominated unit of the belt supergroup was deposited in an eastern extension of the belt basin the helena embayment a variety of different shale facies types can be distinguished of particular interest for this study is a shale facies that has been interpreted to be the result of microbial mat growth resulting in carbonaceous shale beds interrupted by storm deposition causing deposition of graded silt mud couplets alternation of carbonaceous beds with silt mud couplets gives these shales a characteristic striped appearance along the basin margins a pyrite rich sub facies of these striped shales is found locally consisting of laminated pyrite beds that alternate with non pyritic silt mud couplets laminated pyrite beds in pyritic striped shales are interpreted as mineralized microbial mats because of wavy crinkly internal laminae and because of the direct association with unmineralized striped shales that contain microbial mat deposits excess iron in pyritic shale horizons was probably supplied by terrestrial runoff in colloidal form iron hydroxides introduced by rivers into basin marginal lagoons flocculated and were then incorporated into microbial mats and reduced to pyrite upon burial

the validity of flow approximations when simulating catchment integrated flash floods abstract within hydrological models flow approximations are commonly used to reduce computation time the validity of these approximations is strongly determined by flow height flow velocity and the spatial resolution of the model in this presentation the validity and performance of the kinematic diffusive and dynamic flow approximations are investigated for use in a catchment based flood model particularly the validity during flood events and for varying spatial resolutions is investigated the openlisem hydrological model is extended to implement both these flow approximations and channel flooding based on dynamic flow the flow approximations are used to recreate measured discharge in three catchments among which is the hydrograph of the 2003 flood event in the fella river basin furthermore spatial resolutions are varied for the flood simulation in order to investigate the influence of spatial resolution on these flow approximations results show that the kinematic diffusive and dynamic flow approximation provide least to highest accuracy respectively in recreating measured discharge kinematic flow which is commonly used in hydrological modelling substantially over estimates hydrological connectivity in the simulations with a spatial resolution of below 30 m since spatial resolutions of models have strongly increased over the past decades usage of routed kinematic flow should be reconsidered the combination of diffusive or dynamic overland flow and dynamic channel flooding provides high accuracy in recreating the 2003 fella river flood event finally in the case of flood events spatial modelling of kinematic flow substantially over estimates hydrological connectivity and flow concentration since pressure forces are removed leading to significant errors

evidence for microbes in early neoproterozoic stromatolites abstract the biogenesis of stromatolites has long been discussed since many lack convincing evidence of their biological origin this has particularly been the case with older precambrian examples where widespread diagenetic and metamorphic processes have commonly destroyed microbial relics in some cases however evidence has been preserved through very early mineralisation precambrian stromatolites are relatively abundant but it is extremely rare that they contain calcified or dolomitized cyanobacteria and biofilms this study provides evidence from early neoproterozoic columnar stromatolites in the jiuliqiao formation from the southeastern margin of the north china platform for fossilized extracellular polymeric substances eps and cyanobacteria along with nanospheres which may represent permineralised viruses or viral like particles a similar chemical composition and colour along with their embedded and cross cutting relationships with the matrix suggest they are syn depositional products and not modern artefacts or the result of sample preparation the interweaving of cyanobacterial filaments with detrital grains such as quartz and intraclasts indicates trapping baffling and binding processes the presence of virus like particles and mineralized eps with anhedral fine grained calcite suggests they may have provided initial nucleation sites for subsequent carbonate precipitation this study demonstrates the use of a high definition scanning electron microscope to detect fossilized calcified filamentous and spheroidal bacteriomorphs within ancient stromatolites in order to confirm their biogenesis

impacts of convectively coupled kelvin waves on environmental conditions for atlantic tropical cyclogenesis abstracthigh amplitude convectively coupled equatorial atmospheric kelvin waves cckws are explored over the tropical atlantic during the boreal summer 1989 2009 focus is given to the atmospheric environmental conditions that are important for tropical cyclogenesis cckws are characterized by deep westerly vertical wind shear to the east of its convectively active phase and easterly vertical wind shear to the west of it this dynamical signature increases vertical wind shear over the western tropical atlantic ahead of the convectively active phase and reduces vertical wind shear after its passage the opposite is true over the eastern tropical atlantic where the climatological vertical wind shear is easterly positive total column water vapor tcwv anomalies progress eastward with the convectively active phase of the cckw whereas negative tcwv anomalies progress eastward with the convectively suppressed phase during the passage of the convectively active phase of the cckw a zonally oriented strip o

two dimensional kinematic wave model of overland flow a two dimensional kinematic wave model was developed for simulating runoff generation and flow concentration on an experimental infiltrating hillslope receiving artificial rainfall experimental observations on runoff generation and flow concentration on irregular hillslopes showed that the topography of the slope surface controlled the direction and flow lines of overland flow the model simulated results satisfactorily compared with experimental observations the erosive ability of the concentrated flow was found to mainly depend on the ratio of the width and depth of confluent grooves

fossil microbial communities in neoproterozoic interglacial rocks maikhanuul formation zavkhan basin western mongolia abstract glaciogenic deposits are widely distributed in the neoproterozoic successions around the world but only few of them are associated with occurrences of authentic macroscopic fossils problematical circular remains recovered from intertillite beds of the neoproterozoic maikhanuul formation zavkhan basin western mongolia may be a new record of biogenic structures in ancient glacial rocks the maikhanuul tillites were deposited between 732 and 777 ma the underlying volcanic rocks of the neoproterozoic dzabkhan formation and 632 14 ma the overlying limestones of the ediacaran nemakit daldynian tsagaanolom formation the assemblage of microfossils from the tsagaanolom formation is comparable to the assemblage known from the 635 551 ma doushantuo formation of south china the maikhanuul glacial event may therefore be correlated with the 635 ma nantuo glaciation morphological taphonomic biometric and geochemical observations have allowed us to interpret the problematical circular remains from the maikhanuul tillites as microbial communities preserved in situ on the floor of an ancient glacial basin many discoidal fossils from precambrian strata have been compared with extant microbial colonies that have a similar external morphology however ultrastructure of the hypothetical precambrian microbial communities to the best of our knowledge has not previously been reported scanning electron microscopy of the circular remains from the maikhanuul tillites revealed rod shaped filamentous and star shaped bacteriomorph structures some microremains and especially the star shaped particles are considerably enriched in iron up to 50 that may be attributed to bacterial activity furthermore the star shaped microremains can be compared with modern star shaped bacteria known from freshwater and terrestrial environments and with aggregates of biogenic nanohematite although the presence of microbial communities could not be used for global correlation it does provide information on prokaryotic diversity and ecology as well as on palaeoenvironmental conditions

a microscopic sedimentary succession of graded sand and microbial mats in modern siliciclastic tidal flats microscopic studies of thin sections from modern siliciclastic tidal flat sediments in the southern north sea demonstrate the significant role of microbial mats in the buildup of sedimentary sequences this is documented by a unit only a few millimetres thick it starts at the base with a fine to medium grained quartz sand often containing secondary pores fenestrae type merging gradually into finer sediments the lower siliciclastic part is superposed by an upper organically dominated layer built by microbial mats within the organic material single quartz grains without any contact to each other are oriented with their long axes parallel to the bedding planes each siliciclastic part in the lower section of the unit indicates the initial deposition of coarser grains in a stronger flow regime followed by gradually decreasing flow velocities each microbial mat in the upper part essentially represents a period of low sedimentation rate during its growth grains still settle down onto the mat and become bound in the organic matrix the orientation of these grains with their long axes parallel to the bedding plane points to an energetically suitable position to gravity achieved by the friction reduction of the soft organic matter repeated depositional events followed by low rate deposition cause the buildup of various units there is no visible reworking of the former surfaces since the microbial mats prevent erosion during periods of increased flow the buildup is characteristic of siliciclastic sediments repeatedly occupied stabilized and fixed by microbial films or mats

multifractal characterization of microbially induced magnesian calcite formation in recent tidal flat sediments abstract structures resulting from biogenic carbonate cementation of microbial mats in recent siliciclastic tidal flat sediments of the north sea are analyzed quantitatively by a novel combination of scanning electron microscopy and energy dispersive x ray spectrometry sem edx imaging and subsequent multifractal analysis evaluation of calcium distribution patterns and their links to sediment intrinsic mineralization processes show that the applied geometrical technique is an efficient tool for detecting microscopic variations in elemental distributions and related minerals within sedimentary matrices two main conclusions can be drawn i magnesian calcite is a rapidly formed product of the early diagenesis of organic matter in recent bioactive marine sediments and ii multifractal spectra are measures for the spatial inhomogeneity of authigenic calcification processes acting on the sedimentary structure this implies that elemental distribution patterns in a sedimentary system are scale independent phenomena processes causing such patterns have occurred over certain periods with varying rates and on different scales the detection of multifractal measures also opens a way towards a systematic survey of dynamic processes occurring in sedimentary structures

hydrometeorological controls and erosive response of an extreme alpine debris flow on 29 august 2003 an intense convective storm system affected the fella river basin in the eastern italian alps producing rainfall peaks of approximately 390 mm in 12 h the storm triggered an unusually large debris flow in the ungauged rio cucco basin 0 65 km2 with a volume of approximately 78 000 m3 the analysis of the time evolution of the rainstorm over the basin has been based on rainfall estimates from radar observations and data recorded by a raingauge network detailed geomorphological field surveys carried out both before and after the flood of august 2003 and the application of a distributed hydrological model have enabled assessment of flood response estimation of erosion volumes and sediment supply to the channel network the accounts of two eyewitnesses have provided useful elements for reconstructing the time evolution and the flow processes involved in the event liquid peak discharge estimates cluster around 20 m3 s 1 km 2 placing this event on the flood envelope curve for the eastern italian alps the hydrological analysis has shown that the major controls of the flood response were the exceptional cumulated rainfall amount required to exceed the large initial losses and the large rainfall intensities at hourly temporal scales required to generate high flood response at the considered basin scale observations on the deposits accumulated on the alluvial fan indicate that although the dominant flow process was a debris flow sheetflood also contributed to fan aggradation and fluvial reworking had an important role in winnowing debris flow lobes and redistributing sediment on the fan surface this points out to the large discharge values during the recession phase of the flood implying an important role for subsurface flow on runoff generation of this extreme flash flood event copyright 2009 john wiley sons ltd

stromatolites the challenge of a term in space and time abstract several definitions of stromatolites are discussed and kalkowsky s most important statements about stromatolites are translated from german to english a new definition for stromatolites is proposed namely stromatolites are laminated rocks the origin of which can clearly be related to the activity of microbial communities which by their morphology physiology and arrangement in space and time interact with the physical and chemical environment to produce a laminated pattern which is retained in the final rock structure unconsolidated laminated systems clearly related to the activity of microbial communities and often called recent stromatolites or living stromatolites are defined as potential stromatolites the main microbial activities which are important in the formation of potential stromatolites and stromatolites are described and examples of stromatolites of various types including iron stromatolites are also described

textured organic surfaces associated with the ediacara biota in south australia abstract 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

extensive microbial mats and their influences on the erosional and depositional dynamics of a siliciclastic cold water environment lower arenigian montagne noire france abstract lower arenigian ordovician rocks of the montagne noire france represent a shallow marine environment of a high latitude position along the northern margin of gondwana within the weakly metamorphosed siliciclastics six depositional units were recognized 1 outer shelf 2 foreshore zone below wave base 3 foreshore zone above wave base 4 sand bars of shoreface zone 5 intertidal deposits and 6 lagoonal zone wrinkle structures and various other phenomena were mediated by coherent cyano bacterial mats the structures can be related to the different facies zones of the paleoenvironment whereas the muddy outer shelf and the high energetic sand bars were not overgrown by any mat constructing microbial populations fine sands of the foreshore zone the tidal flats and lagoonal areas were widely colonized restriction of mats due to competition of space by endobenthic macroorganisms or by grazers was low the microbially induced structures are composed of organic material pyrite clay minerals illite chamsonite chlorite and chert the minerals precipitated in situ during degradation of the organic layers by the activity of heterotrophic bacteria at low temperatures because the microorganisms formed a dense organic carpet covering extensive areas of the ancient sea bottom they influenced significantly the erosional and depositional dynamics of the sedimentary system of the local arenigian biostabilization counteracted erosion and baffling trapping and binding enriched mineral particles additionally the in situ formed minerals contributed to the total amount of sediment the biotic influence lead to increased accumulation of sediment within the depositional area the study shows that microbial mats of great extension occur within phanerozoic siliciclastics of cold paleoclimate zones and that preservation of the mat fabrics was possible the significant mats influenced the local sedimentary system an aspect scarcely taken into account for such paleoenvironments

modern microbial mats in siliciclastic tidal flats evolution structure and the role of hydrodynamics microbial mats in coastal environments play an important role in both stabilizing the sediment and preserving sedimentary structures they represent the first biological systems that appeared on earth even forming large fossils in carbonate settings known as stromatolites however microbial mats have also been recognized for siliciclastic environments as sandy mat structures in particular mats are the primary element of the so called microbially induced sedimentary structures miss and their various types represent very useful proxies for the interpretation of the environmental conditions in which they were formed the objectives of this paper are twofold the first is to provide a general background review of microbial mats in tidal flats including their evolution structure and morphology the second objective is to provide a modern case study in which we examine the role of storms relative to day to day tidal currents although tidal currents could be an important eroding factor we demonstrate that waves no matter their magnitude play a significant role in developing different types of miss such as wrinkle structures and eroding mats into flipped over fragments furthermore we also show the significance of wave induced pressure onto groundwater in forming other types of miss as kinneya structures and petee ridges knowing the environmental conditions to which present day microbial mats are subject and how they evolve upon drastic changes in those conditions i e storm events represent an important basis for the interpretation of fossil miss

resolving miss conceptions and misconceptions a geological approach to sedimentary surface textures generated by microbial and abiotic processes the rock record contains a rich variety of sedimentary surface textures on siliciclastic sandstone siltstone and mudstone bedding planes in recent years an increasing number of these textures have been attributed to surficial microbial mats at the time of deposition resulting in their classification as microbially induced sedimentary structures or miss research into miss has developed at a rapid rate resulting in a number of misconceptions in the literature here we attempt to rectify these miss misunderstandings the first part of this paper surveys the stratigraphic and environmental range of reported miss revealing that contrary to popular belief there are more reported miss bearing rock units of phanerozoic than precambrian age furthermore miss exhibit a pan environmental and almost continuous record since the archean claims for the stratigraphic restriction of miss to intervals prior to the evolution of grazing organisms or after mass extinction events as well as claims for the environmental restriction of miss appear to result from sampling bias in the second part of the paper we suggest that raised awareness of miss has come at the cost of a decreasing appreciation of abiotic processes that may create morphologically similar features by introducing the umbrella term sedimentary surface textures of which miss are one subset we suggest a practical methodology for classifying such structures in the geological record we illustrate how elucidating the formative mechanisms of ancient sedimentary surface textures usually requires consideration of a suite of sedimentological evidence from surrounding strata resultant interpretations microbial or non microbial should be couched within a reasonable degree of uncertainty this approach recognizes that morphological similarity alone does not constitute scientific proof of a common origin and reinstates a passive descriptive terminology for sedimentary surface textures that cannot be achieved with the current miss lexicon it is hoped that this new terminology will reduce the number of overly sensational and misleading claims of miss occurrence and permit the means to practically separate initial observation from interpretation furthermore this methodology offers a scientific approach that appreciates the low likelihood of conclusively identifying microbial structures from visual appearance alone informing the search for true miss in earth s geological record and potentially on other planetary bodies such as mars

modelling gully erosion for a small catchment on the chinese loess plateau the rolling hills region of the chinese loess plateau is one of the areas with the highest erosion rates on earth a striking feature of this area is the occurrence of many large permanent gullies a 3 5 km2 catchment was selected to study the processes of erosion and to adapt the storm based limburg soil erosion model lisem to the conditions prevailing on the loess plateau part of this work consisted of mapping and measuring the largest gully headcuts the amount of loose soil material beneath the headcuts was also estimated observations suggest that gully headcuts are relatively stable i e do not migrate rapidly but that gullies can nevertheless produce significant amounts of sediment during overland flow events erosion of headcuts occurs mainly by soil falls in between storms the loose soil material produced by these soil falls accumulates on the gully bottom as the lisem simulates storm erosion the development of gullies over time can be ignored and only the amount of material produced by them during runoff events needs to be studied a digital elevation model dem was used to estimate the position of existing gully heads by applying an adapted form of the montgomery and dietrich science 255 1992 826 index using the assumption that headcuts are vertical it is possible to calculate headcut height from the slope angle map a simple stability model which assumes soil falls on gully headcuts to be a function of soil moisture content and headcut height was applied this daily based model can then be used to simulate the accumulation of loose soil material below the headcut the results show that while the dem is not accurate enough to allow the detection of individual headcuts this method can be used to produce a reasonable estimate of the amount of loose soil material available a map showing the amount of loose soil material accumulated can then serve as input for a storm based erosion model such as lisem

searching for travertines calcretes and speleothems in deep time processes appearances predictions and the impact of plants common models for modern calcite precipitation in and around caves soils springs and streams involve co 2 supplied by thick high p co 2 biogenic soils which were probably thin or non existent before vascular plants indeed plant influenced chemical weathering might have caused accelerated terrestrial carbonate production from the devonian onwards however terrestrial carbonates have also been documented from the archaean proterozoic cambrian ordovician and silurian mechanisms which could have caused non marine carbonates to precipitate without organic rich soils are described and some geological events likely to have influenced non marine carbonate precipitation up to the origin of vascular plants are highlighted as organisms have evolved so have the petrographic characteristics of non marine carbonates some examples of this are also given here

microbial sand chips a non actualistic sedimentary structure abstract microbial mats show a marked decline with the transition from the precambrian to the phanerozoic most likely due to the advent of effective benthic grazing organisms hitherto most aquatic sediments up to sand grade were commonly coagulated by organic material allowing reworking to form intraclasts new term microbial sand chips presence of a microbial mat is indicated 1 by refractory remains of organic matter in the laminated parent sediment 2 by the concentration of early diagenetic pyrite associated with sandy intraclasts in quartzites indicating a concentration of organic matter in the clast and 3 by plastic deformation of the clasts during the erosive event as bioturbation spread into most aquatic depositional environments during the phanerozoic the formation of microbial sand chips became restricted to habitats where bioturbation and grazing are limited by environmental stress and where the preservation potential for microbial sand chips is very low therefore the widespread formation of microbial sand chips in precambrian sandy subaqueous sediments is non actualistic

a case study of microbial mat related features in coastal epeiric sandstones from the paleoproterozoic pretoria group transvaal supergroup kaapvaal craton south africa the effect of preservation reflecting sequence stratigraphic models on the relationship between mat features and inferred paleoenvironment abstract the magaliesberg formation sandstones within the upper part of the pretoria group are interpreted as a second order highstand systems tract within an overall clastic epeiric marine setting where episodic braided fluvial systems fed sediment directly into a tidally dominated coastline setting mat related features are abundantly preserved within the inferred tidal flat and supratidal deposits the daspoort formation sandstones at a lower stratigraphic level are ascribed to a closely analogous paleoenvironmental setting yet have hardly any preserved mat features at all they are ascribed to a second order transgressive systems tract in a sequence stratigraphic framework during highstand the depositional systems are inferred to have aggraded thus preserving the mat related features formed in magaliesberg intertidal supratidal environments during second order transgression the formation of the wave tidal ravinement surface in the subtidal intertidal environments largely obliterated the features of the daspoort intertidal and supratidal environments leading to a paucity of mat related structures in the preserved daspoort succession this case study thus supports the application of mat related features to integrated paleoenvironmental and sequence stratigraphic analysis while emphasizing the role of preservation

wrinkle structures microbially mediated sedimentary structures common in subtidal siliciclastic settings at the proterozoic phanerozoic transition sedimentary structures produced by microbial activity are well known from ancient carbonate facies but little is known about equivalent microbial structures in ancient siliciclastic facies wrinkle marks and kinneyia ripples are closely related sedimentary structures that are commonly found in ancient siliciclastics and they may represent microbial activity to evaluate this possibility these structures were studied in vendian cambrian strata of north america and compared to structures formed by modern microbial mat communities in redfish bay texas striking similarities in sedimentologic petrographic and morphologic characteristics of modern and ancient occurrences suggest that the enigmatic but widespread ancient structures could have been formed by microbial processes the relative abundance of these structures in siliciclastic facies of this interval further suggests that prior to the onset of relatively intense bioturbation in the ordovician microbial mats could have played a significant role in the evolution and diversification of early life in a broad variety of sea floor environments

advanced analytical techniques for studying the morphology and chemistry of proterozoic microfossils this paper outlines the suite of advanced multi scalar techniques currently available in the toolkit of the modern proterozoic palaeobiologist these include non intrusive and non destructive optical laser and x ray techniques plus more destructive ion beam and electron beam methods together these provide morphological mineralogical and biochemical data at flexible spatial scales from that of an individual atom to the largest proterozoic microfossils an overview is given of each technique and a case study from the exceptionally well preserved torridonian biota of nw scotland is presented this microfossil assemblage was first recognized over a century ago but its great diversity and evolutionary importance has only recently come to light due in no small part to the research efforts of martin brasier

bacterially mediated authigenesis of clays in phosphate stromatolites authigenic clays in close textural relation to carbonate fluorapatite within finely laminated phosphate stromatolites of upper jurassic age have been studied using scanning electron microscopy sem transmission electron microscopy tem and analytical electron microscopy aem stromatolite laminae consist of hexagonal prisms of francolite sizes ranging between 0 1 and 1 m that are surrounded by poorly crystalline smectite and amorphous fe si al oxyhydroxides microanalyses show that smectite is fe rich with highly variable composition particularly regarding fe and si contents smectite has significant beidellitic montmorillonitic and non tronitic substitutions although the lack of fringe contrast in some areas adjacent to the smectite packets with 1 0 1 3 nm spacing is due to differences in orientation of layers textural and analytical data clearly indicate the presence of fe si al amorphous phases intimately intergrown with smectite the occurrence of poorly crystalline smectite and associated amorphous phases within microbially precipitated stromatolite laminae both as envelopes around and as pore fillings between extremely small calcium phosphate crystals demonstrates authigenic smectite growth from a precursor fe si al amorphous material this material is formed in close association with a phosphate rich precursor the textural and structural relations the preservation of chemical precursors of glauconite such as nontronitic montmorillonite and the presence of fe si al amorphous mineral phases imply crystallization of the observed crystalline phases from synsedimentary bacterially precipitated amorphous precursors during early diagenesis in postoxic environments carbonate fluorapatite was the first phase to crystallize from the primary gel smectite and associated amorphous fe si al oxyhydroxides were the residual material of the crystallization process the slow rate of transformation at low temperatures from fe si al rich gels to smectite explains the textural relations between the poorly crystalline phases and the phosphate crystals as well as the preservation of amorphous substances in relation to clays authigenic smectite represents the first step in glauconitization

evidence for microbial life in synsedimentary cavities from 2 75 ga terrestrial environments fluviolacustrine sediments of the 2 75 ga hardey formation fortescue group australia preserve pendant columnar structures with stromatolitic lamination within synsedimentary cavities the millimeter sized finger like columns strongly resemble microbialites from modern basaltic caves and indicate the likely presence of microbial biofilms the ancient microbial columns are preserved by chert and locally occur as reworked clasts indicating a near depositional age for the structures sulfur isotopic analysis of pyrite in the columns and adjacent carbonaceous matrix yields 34scdt cdt canyon diablo troilite values between 8 5 and 19 showing significant fractionation characteristic of biological cycling of sulfur organic matter in cavity ceilings and shale matrix has 13cpdb pdb peedee belemnite values between 55 and 43 suggesting the presence of methanotrophs our results suggest that 2 75 ga terrestrial environments supported a microbial ecosystem including microbes that inhabited synsedimentary hollows extending the fossil record of coelobionts by 1 5 b y subsurface cavities represent a new habitable microenvironment for early life on earth and an analogue for ancient life on mars

remarkably preserved prokaryote and eukaryote microfossils within 1ga old lake phosphates of the torridon group nw scotland abstract the 1000 ma torridon group of northwest scotland are here shown to contain a rich diversity of organic walled microfossils preserved in exceptional detail within sedimentary phosphate the phosphatic nodules and bands in which they occur are autochthonous as are the organic fossils they contain the associated sedimentology of this phosphate is shown to be consistent with a lacustrine setting informal taxonomic treatment of the microfossils allows statistical assessment of the relative abundances of different morphotypes across a range of lacustrine environments exceptional preservation of pristine organic walled eukaryotes and prokaryotes together with a taphonomic spectrum in both physicochemical and biological degradational conditions allows a picture to be built of the earliest lacustrine ecological communities

facies and origin of shales from the mid proterozoic newland formation belt basin montana usa shales constitute more than 60 of the world s sediments yet while facies models for sandstones and carbonates are at a high level of sophistication the study of shales has clearly lagged behind in the mid proterozoic newland formation six major shale facies types deposited in nearshore to basinal environments are distinguished on the basis of bedding characteristics textural features and the proportions of silt clay and carbonate textural features of these shale types are related to sedimentary environments as deduced from associated lithologies the shales are undisturbed by bioturbation and their textural and sedimentary characteristics reflect subaqueous growth of microbial mats erosion and deposition by storms deposition of flocculated vs dispersed clays continuous slow background sedimentation winnowing by waves or currents and subaerial exposure

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

possible indicators of microbial mat deposits in shales and sandstones examples from the mid proterozoic belt supergroup montana u s a abstract it has been suspected for some time that microbial mats probably colonized sediment surfaces in many terrigenous clastic sedimentary environments during the proterozoic however domination of mat morphology by depositional processes post depositional compaction and poor potential for cellular preservation of mat building organisms make their positive identification a formidable challenge within terrigenous clastics of the mid proterozoic belt supergroup a variety of sedimentary structures and textural features have been observed that can be interpreted as the result of microbial colonization of sediment surfaces among these are a domal buildups resembling stromatolites in carbonates b cohesive behaviour of laminae during soft sediment deformation erosion and transport c wavy crinkly character of laminae d bed surfaces with pustular wrinkled appearance e rippled patches on otherwise smooth surfaces f laminae with mica enrichment and or randomly oriented micas g irregular curved wrinkled impressions on bedding planes h uparched laminae near mud cracks resembling growth ridges of polygonal stromatolites and i lamina specific distribution of certain early diagenetic minerals dolomite ferroan carbonates pyrite although in none of the described examples can it irrefutably be proven that they are microbial mat deposits the observed features are consistent with such an interpretation and should be considered indicators of possible microbial mat presence in other proterozoic sequences

organic rich biolaminated facies from a kimmeridgian lagoonal environment in the french southern jura mountains a way of estimating accumulation rate variations abstract during kimmeridgian times the present day southern jura was a carbonate platform in the palaeolagoon at the village of orbagnoux organic matter was deposited giving birth to calcareous laminites with organic carbon reaching 12 three facies may be distinguished two types of laminites are encountered one made of parallel laminae and the other made of undulating laminae the laminites alternate with massive limestone beds in which no internal structure may be seen the lithology sedimentology and the faunal floral and organic content of laminites and of massive limestones was thoroughly investigated at different scales using various methods field observation transmitted light and scanning electron microscopy rock eval pyrolysis biomarkers infrared study of kerogen palynofacies observation it is suggested that the different types of laminites parallel or undulating may reflect variations in the accumulation rates linked with the carbonate and organic matter productions undulating laminae would correspond to periods of lack of sedimentation whereas parallel laminae would reflect alternations of periods of sedimentation and periods of non sedimentation these variations might in turn reflect climatic changes affecting the emerged lands supplying the lagoon with detrital products organic or inorganic the accumulation and preservation of organic matter were made possible by the development of microbial mats building oxygen tight barriers at the water sediment interface these barriers separated overlying oxygenated water from anaerobic sediments these phenomena may explain one way in which potential hydrocarbon source rocks can form under a poorly oxygenated water column

spatially averaged conservation equations for interacting rill interrill area overland flows the modeling of flows at hillslope scale over land surfaces that contain rills and interrill areas is presented the flow in rills is treated as one dimensional channel flow the flow at interrill areas is treated as two dimensional sheet flow sheet flow equations are averaged along the interrill area width local averaging to account for the interaction between interrill and rill sections the flow depth at the interrill area outlet section is derived by assuming that the flow profile of the interrill area section has the profile of a sine function to minimize computational efforts and economize on the number of model parameters locally averaged rill and sheet flow equations are then averaged over the transects of a hillsope large scale averaging the expectations of the terms containing more than one variable are obtained through the taylor series expansion around their mean values only the first two moments of the series expansion are considered the results of the model are in good agreemen

structural diversity of biogenic carbonate particles in microbial mats non skeletal carbonate particles in microbial mats were studied using thin sections and scanning electron microscopy the microbial mats form biolaminated units so called potential stromatolites in salterns this study emphasizes the coexistence of different particle forms and makes a genetic connection between the heterogeneity of the organic substrate built by bacteria and diatoms and their extracellular polymeric substances eps whereas allochthonous particles are scarce lanzarote microbial mats provide various autochthonous surfaces for the attachment of cells and eps including sheaths and capsules of cyanobacteria frustules of diatoms metabolic products such as gas bubbles liquid globules and faecal pellets as well as the carbonate precipitates themselves morphologically different carbonate precipitates are i calcified organic clumps peloids ii particles composed of concentric aragonite and biofilm laminae ooids and oncoids hi isolated particles floating in gel supported mats and coated by rims of fibrous cement cortoids iv particles bound by cryptocrystalline matrices or cement resulting in aggregate grains and v lobate cement which fills out spaces and pores and fixes the particles peloids are suggested to represent faecal pellets although microbial systems also generate cell clumps by non faecal processes ooid and oncoid constructions clearly record alternating processes of biofilm accumulation and aragonite encrustation further characteristic features of carbonate particles generated within a microbial mat are i an irregular distribution ranging from isolated particles floating within the gel like matrix to closely packed particles ii the amalgamation of different particle types e g peloids and ooids in aggregate grains iii the heterogeneous nature of nuclei comprising bacterial clumps intraclasts individual cells cell colonies and bubbles iv the enrichment of remains casts and imprints of cells within precipitates and v deformation e g truncated cortices of particles

erosional remnants and pockets evolving from biotic physical interactions in a recent lower supratidal environment abstract sedimentary structures characterizing tidal depositional systems are not in all cases produced by physical dynamics alone the activities of epibenthic cyanobacteria such as biostabilization or surface levelling may also play a significant role in structure formation one example of bio induced structures are erosional remnants and pockets a specific surface morphology that can be observed in the lower supratidal zone of mellum island southern north sea this surface relief rises from partwise erosion of a microbial mat covered and biostabilized tidal surface on the basis of detailed field measurements of the geometric dimensions of the surface relief the tidal current system of the area and the history of formation of the morphology can be reconstructed erosional remnants and pockets are highly facies indicative and fossil occurrences would help in reconstruction paleo environments

fine grained agglutinated elongate columnar stromatolites tieling formation ca 1420 ma north china the mesoproterozoic tieling formation near jixian northern china contains thick beds of vertically branched laterally elongate columnar stromatolites carbonate mud is the primary component of both the stromatolites and their intervening matrix its abundance is attributed to water column whiting precipitation stimulated by cyanobacterial photosynthesis neomorphic microspar gives the stromatolites a streaky microfabric and small mud flakes are common in the matrix the columns consist of low relief mainly non enveloping laminae that show erosive truncation and well defined repetitive lamination in plan view the columns form disjunct elongate ridges 10 cm wide separated by narrow matrix filled runnels the stromatolite surfaces were initially cohesive rather than rigid and prone to scour and are interpreted as current aligned microbial mats that trapped carbonate mud the pervasive ridge runnel system suggests scale dependent biophysical feedback between i carbonate mud supply ii current duration strength and direction and iii growth and trapping by prolific mat growth together these factors determined the size morphology and arrangement of the stromatolite columns and their laminae as well as their branching patterns alignment and ridge runnel spacing ridge runnel surfaces resemble ripple mark patterns but whether currents were parallel and or normal to stromatolite alignment remains unclear the formation and preservation of tieling columns required plentiful supply of carbonate mud mat building microbes well adapted to cope with this abundant sediment and absence of both significant early lithification and bioturbation these factors were time limited and tieling stromatolites closely resemble coeval examples in the belt purcell supergroup of laurentia the dynamic interactions between mat growth currents and sediment supply that determined the shape of tieling columns contributed to the morphotypical diversity that characterizes mid late proterozoic branched stromatolites this article is protected by copyright all rights reserved

paleoproterozoic microbially induced sedimentary structures from lagoonal depositional settings in northern china abstract microbially induced sand cracks crack fills occur extensively on the top surface of fine sandstone beds of the paleoproterozoic zhaojiazhuang formation changcheng group 1 7 ga around the cangyan mountain hebei province northern china detailed field and microscopic petrographical evidence reveal that these sand cracks crack fills possibly resulted from dehydration and desiccation of microbial mats the age and peculiar morphology of these microbially induced sedimentary structures do not allow comparison with trace fossils or purely physical desiccation cracks the fine sandstone beds on the surfaces of which these microbially induced sedimentary structures formed were deposited in a lagoon brackish depositional setting marine to non marine transitional setting with episodic injection of marine water as such these microbially induced sedimentary structures suggest the colonization of the marine to non marine transitional settings in the paleoproterozoic period and that the search for evidence of early microbial life should be sought in the marine to non marine transitional settings these broad habitats suggest these microbes could have been eurytopic organisms capable of adapting to varying extents of salt and oxygen content variations like their modern counterparts

discussion were the ediacaran siliciclastics of south australia coastal or deep marine by retallack et al sedimentology 59 1208 1236 richard h t callow martin d brasier and duncan mcilroy department of geology and petroleum geology university of aberdeen meston building aberdeen ab24 3ue uk e mail r callow abdn ac uk department of earth sciences university of oxford south parks road oxford ox1 3an uk department of earth sciences memorial university of newfoundland 300 prince philip drive st john s nl a1b 3x5 canadaintroductionthe late ediacaran period is a critical interval inthe history of life on earth and its poorly under stood fossils have potential to shape our under standing of early biosphere evolution critical tothis process is an accurate assessment of theenvironments in which these organisms our ished prior to the radiation of animal life duringthe cambrian explosion few successions can bemore historically important for this than theediacara member of the rawnsley quarzite inthe flinders ranges south australia glaessner 1984 the depositional settings for these rockshave hitherto been established and widelyaccepted as being below fair weather wave base delta front prodelta shoreface to intertidal gehling 2000 the new interpretation advancedby retallack 2012 is thought provoking andincludes a diverse dataset which is used to arguefor deposition of the ediacara member within ashallow marine coastal and subaerial suite ofenvironments this discussion examines a num berofthe conclusions insupportofthatclaim andconsiders that the established marine depositionalsetting of the ediacara member remains valid deep marine context of theediacara memberthe title of the paper implies that gehling 2000 interpreted the ediacara member to be a deepmarine unit see also mount 1989 the term deep marine is rarely used in a strict sense bygeologists it has been used variously to refereither to environments situated beyond the shelfbreak e g pickering et al 1989 or to environ ments affected by processes that are typical ofslope and basin oor environments i e sedimentgravity ows the depositional environmentsrecognized by gehling 2000 include sandstonedeposition below fair weather wave base inincised valley lls palaeovalleys delta front topro delta palaeoenvironments delta top sandsheets braid deltas and intertidal ats it is clearfrom this list of palaeoenvironmental interpreta tions that gehling 2000 did not consider theediacara member as deep marine for example intertidal environments were identi ed from theinference of ancient microbial mats and sandgypsum crystals gehling 2000 gehling dro ser 2009 most importantly the fossiliferousbeds were interpreted as tempestites that formedin delta front palaeoenvironments between stormand fair weather wave base gehling 2000 sediment gravity ows including but not lim ited to turbidites were identi ed as componentsof the succession by gehling 2000 as parts offacies associations c d and e however it wasstated explicitly that the massive channelizedsands 0ae5 to 8 m thick beds were not depositedin a basinal setting but rather in sub wave basesubmarine channels similarly the micro turbi dites facies association e were interpreted aspart of a distal pro delta environment suchshelfal prodelta turbidites are common in depo sitional systems with high sediment supply andhigh rates of accommodation generation e g mcilroy et al 2005 we concur with gehling 2000 that the thick bedded massive and dewa tered channelized sandstones are not readilycompatible with uvial facies models and aremore consistent with deposition from submarine ows e g kneller branney 1995 the pres ence of hummocky cross strati ed beds gehling 2000 g 10d has been con rmed by manyauthors such bedforms were not observed bysedimentology 2013 60 624 627

what do models tell us about water and sediment connectivity connectivity has been embraced by the geosciences community as a useful concept to understand and describe hydrological functioning and sediment movement through catchments mathematical modelling has been used for decades to quantify and predict erosion and transport of sediments e g in scenarios of land use change or conservation measures being intrigued by both models and the connectivity concept as a group of modellers we aimed at investigating what different models could tell us about connectivity therefore we evaluated the response of contrasted spatially distributed models to landscape connectivity features and explained the differences based on different model structures a total of 53 scenarios were built with varying field sizes and orientations as well as the implementation of soil conservation measures these scenarios were simulated for two rainfall intensities with five event and process based water and soil erosion models erosion3d fullswof 2d landsoil openlisem and watersed results showed that rainfall amount plays the most important role in determining relative export and connected area of runoff and sediment in all models indicating that functional aspects of connectivity were more important than structural connectivity as for the role of structural landscape elements there was no overall agreement between models regarding the effects of field sizes crop allocation pattern and conservation practices agreement was also low on the spatial patterns of connectivity this overall disagreement between models was unexpected the results of this exercise suggest that the correct parameterization of runoff and sediment production and of routing patterns may be an important issue thus incorporating connectivity functions based on routing would help modelling forward our results also suggest that structural connectivity indices may not suffice to represent connectivity in this type of catchment relatively simple and monotonous land cover and functional connectivity indices should be applied

the anatomy of a sulphate platform and adjacent basin system in the leba sub basin of the lower werra anhydrite zechstein upper permian northern poland the lower werra anhydrite zechstein upper permian deposits of the teba area originated in a deep basin setting in shallow to deep water conditions facies changes occur within small distances and suggest fluctuating boundaries between well defined basins and platforms this pattern of local platforms and adjacent basins developed during deposition in basinal areas the sequence is clearly transgressive whereas on platforms accumulation kept pace with subsidence after an initial transgression nodular anhydrite represents a polygenetic deposit which formed at different times with respect to deposition massive anhydrite with pseudomorphs after upright growth gypsum crystals suggest rapid precipitation in a subaqueous environment and or fluctuating but generally high salinity conditions massive clastic sulphate originated due to periodic high energy events and resedimentation or due to brecciation possibly connected with salinity fluctuations and the dissolution of halite massive textureless anhydrite is locally porous and passes upward into breccia indicating a strongly saline environment bedded anhydrite is considered to form in shallow water environments and laminated anhydrite in deep water bedded anhydrites contain portions which are graded intercalations of sulphate turbidites and upright growth gypsum suggest fluctuating water depths with comparatively deep water during turbidite deposition but shallower conditions during upright growth gypsum deposition the sequence observed in slope zones at platform basin margins detrital parautochthonous sulphate sand to graded beds to basinal laminites indicates that redistribution processes were important at the onset of the lower werra anhydrite deposition bathymetric relief existed between the central part of the basin and its margins where carbonate platforms remained subaerially exposed formation of local platforms and adjacent basins required a relatively high subsidence rate as pre existing relief cannot account for the total accumulated thickness of the lower werra anhydrite deposits one implication of this is that the main argument against the shallow water shallow basin evaporite basin model i e a very fast rate of subsidence may not be valid for the eba lower werra anhydrite basin

the criteria for the biogeneicity of microbially induced sedimentary structures miss in archean and younger sandy deposits abstract 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

atlantic hurricane activity following two major volcanic eruptions 1 in 1982 and 1991 two major volcanic eruptions loaded the stratosphere with long lived sulfate aerosols altering the global climate by redistributing longwave and shortwave radiation at the surface and throughout the atmosphere cooling the surface and subsurface waters of the tropical oceans theory and observations demonstrate through direct and indirect mechanisms a causal relationship between tropical north atlantic sea surface temperatures and seasonal atlantic hurricane frequency duration and intensity therefore it is plausible that hurricane activity in the seasons immediately following these eruptions is diminished however to date such a theory remains untested here i use observations reanalysis data and output from a numerical model to suggest that the number duration and intensity of hurricanes in the years following the eruptions of el chichon 1982 and mount pinatubo 1991 decreased via the aerosol direct effect determining the effects of each eruption on seasonal cyclone activity is complicated by simultaneous positive enso events thus further study of the relationship between atlantic tropical cyclones and major volcanic eruptions is warranted

multidecadal variability in north atlantic tropical cyclone activity abstract recent increases in atlantic basin tropical cyclone activity since 1995 and the associated destructive u s landfall events in 2004 and 2005 have generated considerable interest into why there has been such a sharp upturn natural variability human induced global warming or a combination of both factors have been suggested several previous studies have discussed observed multidecadal variability in the north atlantic over 25 40 yr time scales this study using data from 1878 to the present creates a metric based on far north atlantic sea surface temperature anomalies and basinwide north atlantic sea level pressure anomalies that shows remarkable agreement with observed multidecadal variability in both atlantic basin tropical cyclone activity and in u s landfall frequency

algen als faziesindikatoren bioherme und biostrome im unter kambrium von sw sardinien archaeocythan limestones of the lower cambrian nebida fm sw sardinia form bioherms lower nebida fm matoppa mbr as well as biostromes upper nebida fm punta manna mbr in both cases algae are the main rock forming organisms they act as sediment binding and sediment baffling organisms and thus are responsible for the growth of these carbonates

remarkable preservation of microbial mats in neoproterozoic siliciclastic settings implications for ediacaran taphonomic models abstract it is beyond doubt that the appearance of infaunal bioturbation and metazoan biomineralization across the ediacaran cambrian transition irreversibly affected the nature of marine sediment architecture and biogeochemistry here we review those changes in relation to their likely effect upon the processes of fossil preservation especially within siliciclastic sediments processes of soft tissue preservation in siliciclastic settings from the ediacaran period including microbes and microbial mats as well as ediacaran macrofossils are here reviewed within this context highlighted examples include the exceptional preservation of microbes found in association with wrinkle structures and ediacaran macrofossils in england and newfoundland replicated by silicate minerals and in the white sea region of russia replicated by iron sulphide these occurrences show that soft tissue preservation in siliciclastic settings went well beyond that typical for ediacaran macrofossils alone and also extended to similar modes of preservation in associated microbes using these new observations it can be argued that several existing explanations for ediacaran fossil preservation can be united within a biogeochemical model that involves evolution of the sediment mixed layer across this transition

life on land in the proterozoic evidence from the torridonian rocks of northwest scotland the stoer group and diabaig formation of the torridonian succession in northwest scotland are late mesoproterozoic to early neoproterozoic ca 1200 1000 ma features preserved on the top surfaces of fine to medium grained sandstone beds in a number of stratigraphically and geographically separated localities are attributable to microbially induced sedimentary structures these include wrinkle structures remnants of apparent microbial crusts and indications of original cohesiveness and pliancy in sand sized sediment the surfaces on which the microbial structures formed were exposed subaerially abundant deep desiccation cracks and locally pedogenic structures in alluvial interfluve and lacustrine margin settings and many of the structures developed in areas well away from the perennially wetted regions adjacent to shorelines and fluvial channels thus these features indicate that earth9s biosphere had adapted to and colonized land surfaces many hundreds of millions of years before the dawn of the phanerozoic

microbial mats in the terrestrial lower triassic of north china and implications for the permian triassic mass extinction abstract evidence for microbial mats has been reported repeatedly from marine lower triassic rocks but scarcely mentioned in post mass extinction terrestrial facies here we report from the terrestrial lower triassic liujiagou formation in north china the presence of five kinds of microbially induced sedimentary structures miss or sedimentary surface textures including old elephant skin textures wrinkle structures palimpsest ripples manchuriophycus structures and sand cracks terrestrial microbial communities that produced these miss adapted not only to periodically desiccated conditions but also to the storm dominated palaeoenvironments in the liujiagou formation the permian triassic mass extinction ptme in north china is marked by the die off of plants disappearance of coal beds extinction of pareiasaurs among tetrapods decreased bioturbation levels and a dramatic change of sedimentary systems through the sunjiagou formation the sunjiagou formation recorded the turnover from an ever wet to a progressively drier and hotter climate and it spans the ptme in north china following this mass extinction miss became much more common and widespread suggesting that the mass extinction provided favourable biological and environmental conditions for the development of the miss in terrestrial ecosystems especially the decreased bioturbation intensity and grazing pressure associated with increased temperature and climatic drying in the upper part of the liujiagou formation and overlying heshanggou formation the disappearance of miss coupled with increased bioturbation might indicate an improvement of terrestrial ecosystems and the beginning of the triassic biotic recovery however as the investigation of miss in space and time through the geological record is in its early stages further geobiologic and geochemical studies as well as high precision isotopic dating from permian triassic terrestrial successions are needed to fully reveal the timing and pattern of the early triassic terrestrial ecosystem reconstruction

enhanced organic carbon burial in large proterozoic lakes implications for atmospheric oxygenation abstract the burial of organic carbon in sedimentary systems has been a fundamental part of the carbon cycle throughout the geological record and was instrumental in major oxygenations of the atmosphere in the early palaeoproterozoic and neoproterozoic while much focus has been placed on the burial of carbon in precambrian marine carbonate and organic carbon rich rocks deposited around the time of these major oxygenations such deposits yield little information on the evolution of the atmosphere in the significant time between there is however growing evidence from terrestrially deposited sediments to suggest the surface environment may have been at least intermittently well oxygenated from the late mesoproterozoic hence proterozoic sediments deposited in terrestrial near surface environments are useful targets for the study of atmospheric evolution during a time which is hitherto poorly understood thus far little attention has been paid to the contribution of large lakes and intercontinental basins to the global burial of organic carbon and thus the progressive oxygenation of the atmosphere especially given that the highest rates of organic carbon burial in modern aquatic environments occur in lacustrine settings in stark contrast to the low rates observed in the contemporary marine realm here we report high burial rates of organic carbon in large lacustrine systems of late mesoproterozoic to early neoproterozoic age which are comparable with modern lacustrine systems and significantly higher than modern and ancient marine deposits these data emphasise the significance of lakes as a global repository for organic carbon and imply proterozoic lakes were at least as efficient and perhaps as important as modern lakes in the global burial of organic carbon such findings suggest large proterozoic lakes and epicontinental basins played a crucial role in the progressive oxygenation of the atmosphere before the major neoproterozoic oxygenation

fossils and matgrounds from the neoproterozoic longmyndian supergroup shropshire uk body and trace fossils of ediacaran affinity are described from strata of the late neoproterozoic longmyndian supergroup exposed near church stretton shropshire uk the almost spherical soft bodied ediacaran fossil beltanelliformis brunsae menner occurs rarely in the burway formation but much smaller simpler discoidal structures are common in both the burway and synalds formations and are referred to beltanelliformis minutae sp nov similar discoidal structures but with a distinct central depression are included in intrites punctatus fedonkin and are common at several horizons two blocks with numerous examples of medusinites aff asteroides sprigg glaessner wade were recovered from the burway formation the purported ediacaran body fossil arumberia glaessner walter is common at several horizons but its biogenicity is not accepted herein arumberia is thus treated along with evidence for microbially bound sediment surfaces or matgrounds that have been suggested by several authors to be necessary for some types of ediacaran preservation the assemblage of simple trace and body fossils along with matgrounds is typical of latest neoproterozoic time though some elements range into the phanerozoic

morphogenesis and facies relationships of thrombolites and siliciclastic stromatolites in a cambrian tidal sequence elat area southern israel abstract thrombolites and siliciclastic stromatolites occur within the lower cambrian marine timna formation in the elat area southern israel this rock succession consists of four consecutive stratal suites which together represent a transgressive regressive cycle within a peritidal depositional system the thrombolites are associated with the sea ingression stage and occur as a series of massive bedded strata with laminoid fenestral layers and with a microclotted peloidal fabric of the micritic material sem eds study of the clotted and peloidal micrite reveals a calcitic framework of pitted polygonally shaped units 2 m wide together with a few groups of compressed large hollow structures these forms are interpreted as the possible remnants of bacterial decomposers and of coccoid dominated mat forming unicells respectively the intimate structural connection between the carbonate fraction and the microbe structures suggest in situ carbonate production through bacterial decay of the cyanobacterial material during its self burial with carbonate precipitating as solid phases on vacant extracellular envelopes the siliciclastic stromatolites developed during seashore progradation and now occur as rare laterally linked columnar forms within channelled cross stratified sandstones at the top of the timna succession they are finely laminated with a low to moderate degree of inheritance of the laminae and are partly burrowed by skolithos textures and the geometry of the siliciclastic stromatolites suggest that they were formed through binding of transported quartz sand sized particles by bottom dwelling filamentous microorganisms sediment production and the growth pattern of the two structures within the timna sequence seem to have been regulated by different microbial assemblages which shifted in response to changes in environmental factors through time and space the differential distribution of the two buildups in the sedimentary sequence reflects the difference in balance between the biological attributes of the two biotas and the physical environment pitted architectures such as those displayed by the timna thrombolites could be an ontogenetic fingerprint of microbially constructed rocks which might help to recognize them in the fossil record when other evidence is lacking

morphogenetic impact of microbial mats on surface structures of kimmeridgian micritic limestones cerin france for several years palaeoecological research has been conducted on micritic limestones of late kimmeridgian age in the southern jura mountains the sedimentary environment is that of a lagoon with an irregular bottom which was repeatedly exposed between two stages of lime deposition a microbial mat grew over the muddy surface giving cohesion to the sediment restraining erosion and preserving fossil remains and reptile tracks various structures at the microbial mat surface can be observed crescentic wavy radial wavy torn petee and mixed structures they imply the presence of desiccation periods and a slight bottom slope leading to a downward sliding of the microbial mat such features may also be generalised to explain superficial microbial structures of other shallow carbonate mud environnements

hydraulic characterization of river networks based on flow patterns simulated by 2 d shallow water modeling scaling properties multifractal interpretation and perspectives for channel heads detection

post mortem onshore transportation of epiphytic foraminifera recent example from the tunisian coastline abstract the barrier island system that connects jerba island to the tunisian coastline is composed mainly of carbonate bioclastic sands well preserved tests of dead epiphytic foraminifera are abundant on the foreshore and backshore but they are scattered and poorly preserved on the shoreface where very fine sand size eolian quartz peloids and broken bioclasts are the main components the reason for this paradoxical pattern is that most epiphytic foraminifera are very easily removed as suspended load by storm generated currents and concentrated on beaches washover fans and small eolian dunes kilometers away from their original life environment similar bioaccumulations are common in the fossil record and have often been interpreted incorrectly as prolific biocoenoses

a review of north atlantic modes of natural variability and their driving mechanisms 1 this paper reviews three modes of natural variability that have been identified in the north atlantic ocean namely the north atlantic oscillation nao the atlantic multidecadal oscillation amo and the atlantic meridional mode amm this manuscript focuses on the multidecadal fluctuations of these three modes a range of different mechanisms to initiate phase reversals in these modes on multidecadal timescales has been suggested previously we propose a systematic grouping of these mechanisms into three types that involve respectively 1 the dependency of the atlantic thermohaline circulation thc on salinity 2 the sensitivity of the thc to changes in ocean heat transport and 3 the dependency of the nao to changes in the atlantic meridional temperature gradient some new density data is also provided demonstrating physical links between the thc and the amo

suitability of transport equations in modelling soil erosion for a small loess plateau catchment erosion models have not often been applied to very steep terrain such as the gully catchments of the chinese loess plateau the purpose of this research was to evaluate the suitability of a number of transport equations for use in erosion modelling under loess plateau conditions to do this the equations were programmed into the lisem model which was applied to the 3 5 km2 danangou catchment in the rolling hills region of the loess plateau previous evaluations of transport equations used either flume tests or river sections and did no spatial modelling the results show that some equations predicted physically impossible concentrations defined as above 1060 g l the results were evaluated by using two methods 1 by comparing predicted and measured sedigraphs and sediment yield at the catchment outlet and 2 by comparing the fraction of the catchment in which physically impossible transport capacities occurred the results indicated that for the small grain sizes high density flows and steep slopes of the gully catchments on the loess plateau the shields parameter attained very high values furthermore the transport threshold can usually be neglected in the equations most of the resulting equations were too sensitive to slope angle abrahams schoklitsch yalin bagnold low and rickenmann so that transport rates were overpredicted for steep slopes and underpredicted for gentle slopes the yang equation appeared to be too sensitive to grainsize the govers equation performed best mainly because of its low slope dependency and is therefore recommended for erosion models that simulate sediment transport by flowing water in conditions with small grain sizes and steep slopes

tropical and subtropical north atlantic vertical wind shear and seasonal tropical cyclone activity abstractgiven recent insights into the role of anticyclonic rossby wave breaking awb in driving subseasonal and seasonal north atlantic tropical cyclone tc activity this study further examines

evidence for 2 0 ga continental microbial mats in a paleodesert setting abstract early evolved microbial communities characterized the initial biological invasion of precambrian continental landscapes in modern arid settings microbial mats and biological soil crusts are well developed and stabilize sediment the paleoproterozoic makgabeng formation in south africa is one of the oldest and best preserved dryland systems on earth six types of microbial mat related structures are now recognized within these depositional systems this paper presents three newly discovered structures that include tufted microbial mat biological soil crusts and gas escape features in addition to three previously documented structures that include roll up features sand cracks and wrinkled features these discoveries demonstrate that microbial communities were well established and inhabited diverse continental settings by 2 0 ga approximately 200 million years after the onset of the great oxidation event

suspected microbial mat related crack like sedimentary structures in the palaeoproterozoic magaliesberg formation sandstones south africa abstract the occurrence of patchy preservation of ripples and of palimpsest ripples on many sandstone bed surfaces of the c 2 1 ga magaliesberg formation pretoria group transvaal supergroup south africa suggests that microbial mats grew within the upper parts of sandy deposits of the braid deltaic tidally controlled epeiric marine coastline palaeoenvironment inferred for this stratigraphic unit recently limited occurrences of petee ridges cracked sand layers elephant skin textures wrinkle structures and manchuriophycus like cracks have been found substantiating the envisaged role for microbial mats binding sandy sediment and providing cohesion during active sedimentation by fluvial and tidal processes ripple marks associated with most of these biogenic sedimentary structures enable evaluation of genetic processes for the ripples currents waves wind as well as estimation of wave heights and water depths cf tanner w f 1967 ripple mark indices and their uses sedimentology 9 89 104 tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 the petee ridges are interpreted as reflecting spring low tidal desiccation which cracked the mats followed by disruption of sand beneath the mat due to loading from incoming tides or subsequent deposits slightly sinuous sand cracks on ripple crests are related to a similar combination of low tidal desiccation and formation of wind ripples with subsequent high tides providing the deeper water conditions and larger wave heights calculated from the tanner w f 1971 numerical estimates of ancient waves water depths and fetch sedimentology 16 71 88 formula synaeresis cracking is inferred for both elephant skin cracks and manchuriophycus structures these inferred suspect microbial sedimentary structures when studied in relation to data derived from associated ripples thus enable better estimation of depositional conditions within the magaliesberg palaeoenvironment and indicate minimum epeiric tidal ranges of c 112 cm in general these structures are found associated with evidence for shallower water and higher energy conditions which probably protected the microbial mats from degradation by heterotrophic bacteria through fast burial a possible association of such mat related structures with epeiric marine or passive margin coastline conditions may be pertinent for much of the precambrian clastic record

evaluating iron as a biomarker of rhythmites an example from the last paleozoic ice age of gondwana abstract microorganisms play a significant role in mineral precipitation but detecting them in the fossil record is still a challenge here we offer an example of how the detection of biological activity in the sedimentary environment can modify a classical depositional model this study describes the activity of microorganisms in sedimentary structures and the iron mineral formation during the last paleozoic ice age in southwestern gondwana recorded by the itu rhythmites parana basin brazil the itu rhythmites have been considered to be varve type deposits that present alternating dark laminae clay silt size sediments and light layers sand gravel size sediments of varied thickness forming couplets earlier studies focused on abiotic processes of these structures we applied different techniques and analytical approaches were used such as synchrotron based techniques and rock magnetic techniques in order to test the biogenicity of iron minerals contained in putative microbially induced sedimentary structures by detecting biominerals in this rock succession the depositional model had to be reconsidered taking into account the biological activity the limitations on the specific conditions for bacterial growth and for mineral precipitation therefore we offer a new depositional model that considers the role of microorganisms in formation of these laminae and this model can be considered for other iron rich rhythmic deposits in other places of the world considering the effects of temperature and other factors in the bacterial productivity the deposition of the latest couplets in the outcrop occurred in different seasons and by different depositional processes corroborating with the non periodicity of 1 year per lithological couplet

holocene stromatolites and microbial laminites associated with lenticular gypsum in a marine dominated environment ras el shetan area gulf of aqaba egypt field and petrographic investigations of holocene evaporites in the ras el shetan area gulf of aqaba egypt indicate the presence of microbial mats either in the form of laminites or stromatolites the morphology of microbial mats and gypsum crystal size characterize the following lithofacies 1 slump stromatolitic gypsarenite 2 random gypsrudite 3 stromatolitic gypsarenite and 4 microbially laminated gypsrudite these evaporite lithofacies are formed above pre evaporitic mudstones rich in disrupted cyanobacterial filaments burrows and cerithid gastropods the morphology of the gypsum crystals is mainly lenticular indicating enrichment of dissolved organic compounds in the depositional environment the difference in size of the lenticular gypsum crystals is related to minor changes in salinity and temperature of the parent brine fluid inclusions in gypsum crystals indicate their formation at low temperature 50 c in a seawater sourced brine that evaporated to gypsum saturation or higher the brine salinities range from 10 62 to 12 99 equivalent wt nacl and the brine densities range from 1 08 to 1 11 g cm3 the change in morphology of the microbial mats stromatolites and laminites is related mainly to changes in water depth from a very shallow salina to a coastal sabkha lenticular gypsum nucleated displacively in the microbial mats from saline oxygenated groundwater that seeped from the sea through a barrier

earth s earliest microbial mats in a siliciclastic marine environment 2 9 ga mozaan group south africa this study provides evidence for the existence of filamentous cyano bacteria forming sediment stabilizing mats in shelf environments at 2 9 ga the oldest known occurrence of microbial mats in siliciclastic rocks the mesoarchean mozaan group south africa features fine grained quartzites of an ancient shallow shelf environment these sandstones contain wrinkle structures which in thin section reveal filamentous textures forming carpet like microbial mat fabrics the textures resemble the trichomes of modern cyanobacteria chloroflexi or sulfur oxidizing proteobacteria mineralogical geochemical and isotopic analyses acre consistent with a biological origin of the filament like textures carbon filaments with biogenic isotopic signatures 1 3 c 24 2 0 5 are closely associated with hematite goethite and chert minerals which may derive from the former presence of oxygen within the microbial mats detrital quartz zircon and rutile in the mats could indicate baffling trapping and binding of the bacterial communities

tufted microbial cyanobacterial mats from the proterozoic stoer group scotland upward thinning stellate and polygonal carbonate structures are described and compared to modern and ancient stromatolites although tufted microbial mats are common in modern settings they have rarely been described from ancient rocks owing to their poor preservation potential the preservation of these from the stoer group is due to early replacement by calcite before their original tufted relief could be obliterated by compaction associated limestones with some similar features are interpreted as flat to mamillated microbial mats

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

the oldest record of ediacaran macrofossils in gondwana 563 ma itajai basin brazil abstract 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 itajai basin southern brazil our new radiometric date 563 ma indicates that the itajai 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 itajai 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 itajai biota could represent early adaptations of benthic macrobiota to the shallower and more photic environments that characterize the later white sea assemblage

on the madden julian oscillation atlantic hurricane relationship abstract the large scale equatorial circulation known as the madden julian oscillation mjo has been shown to impact tropical cyclone activity in several basins around the globe in this paper the author utilizes an mjo index created by wheeler and hendon to examine its impacts on tropical genesis and intensification in the atlantic large differences in frequency and intensity of tropical cyclone activity are seen both in the tropical atlantic as well as in the northwest caribbean and gulf of mexico depending on the mjo phase coherent changes in upper and lower level winds and relative humidity are likely responsible for these differences since the mjo shows potential predictability out to about two weeks the relationships discussed in this paper may be useful for short term predictions of the probability of tropical cyclone activity in the atlantic as a complement to the already available longer term seasonal predictions

the hydrological significance of holocene tepees stromatolites and boxwork limestones in coastal salinas in south australia abstract holocene groundwater lakes salinas are common in the coastal zone of south australia they usually contain an evaporitic carbonate sequence that surrounds a central gypsum unit to form a bull s eye pattern of sediment distribution in the salina the evaporitic carbonates can be subdivided into three units a boxwork boundstone unit a veneer boundstone unit and an algal boundstone unit these units contain many interesting structures including tepees stromatolites and mound springs all of which show a megapolygonal outcrop pattern the salina carbonates have formed under a hydrological regime that has changed little since its inception some 6000 years ago consequently it has been possible to interpret the hydrological significance of the salina carbonates the salinas are fil ed by schizohaline surface waters whose water levels and salinities fluctuate seasonally all of the salina carbonates form where marine derived groundwater resurges from a surrounding dune aquifer into the margin of the salina tepee structures form in the veneer boundstone as a response to groundwater induced seasonal changes in the pore pressures of the underlying boxwork sediments the recognition of such groundwater tepees or other groundwater controlled structures in ancient carbonate sequences could aid paleohydrological interpretation of the ancient basin

high energy flood events recorded in the mesoproterozoic meall dearg formation nw scotland their recognition and implications for the study of pre vegetation alluvium the mesoproterozoic neoproterozoic torridonian sandstone of nw scotland has renewed sedimentological significance following recent advances in the understanding of pre vegetation alluvium as it is one of the most extensive and easily accessible successions of such strata worldwide this paper presents the first modern sedimentological analysis of the unit9s constituent meall dearg formation late mesoproterozoic recognizing a dominance of alluvial facies with subordinate aeolian facies alluvial strata within the meall dearg formation contain direct evidence for event deposition by high energy floods including the following 1 widespread upper and transitional upper flow regime elements 2 frequent stacking of successively lower flow regime elements 3 common subcritical subaqueous dune fields with superimposed ripple marks 4 occasional thin desiccated mudstones 5 evidence that microbial mats colonized substrates during intervals of sedimentary stasis together these strands of primary sedimentary geological evidence indicate that the alluvial deposition of the meall dearg formation was typified by supercritical flows during high energy floods punctuated by prolonged intervals of sedimentary stasis the preservation potential of all of the features was boosted by highly aggradational sedimentary conditions these primary observations have implications for the norm in pre vegetation alluvium and confirm that despite increasing recognition of diversity within precambrian fluvial systems classical pre vegetation motifs of high energy alluvial flood deposits preserved as sheet braided alluvium are still an archetypal sedimentary signature in some instances using supportive evidence from the meall dearg formation we recommend that the term sheet braided be used in inverted commas in future studies this emphasizes the polygenetic depositional nature of the 20 1 width thickness fluvial style while maintaining the value of the term in the isolation of a key characteristic of pre vegetation sedimentary architecture

microbial structures in oolitic iron formations ferriferous ooids and microoncoids occur in many sedimentary iron formations these ferriferous coated grains are found in fine grained carbonate rich groundmasses iron mineral encrusted microbiota are observed in both the coated grains and the groundmass the branching nature and other morphological features of the microorganisms suggest fungal origins for the oolitic iron ores particularly of the lower jurassic lorraine minette the similarity of the microbial structures in coated grains and their groundmasses suggests that both had developed within microbial mats growing under calm environmental conditions the contribution of stromatolitic marine fungal mats to the fast extraction and immobilization of iron and thus to the genesis of iron ores is demonstrated observations on well preserved freshwater derived fungal stromatolites of the tertiary and laboratory experiments with organotrophic fungal mats confirm the findings on the jurassic and imply a general role of microorganisms in the formation of such deposits

ediacaran biota in the aftermath of the kotlinian crisis asha group of the south urals abstract the asha group of the south urals is dominated by laminated shales and thin siltstone sandstone alternations interpreted as a prograding low energy inner shelf depositional system the succession includes several thick sharp based sandstone bodies comprising interstratified fine to medium grained fine laminated planar laminated hummocky convolute and wave bedded planar and trough cross bedded sandstones occasionally pebble to boulder conglomerates regarded as tidal deltaic and shoreface depositional systems the sandstone shoreface bodies are interpreted as forced regressive deposits stranded in offshore positions during subsequent transgressions although palaeoecological and taphonomic context of the asha group is favourable for the ediacara type biofacies the associated fossil assemblages nevertheless are depauperate and consist of frondomorph holdfast structures palaeopascichnids microbial colonies arumberiamorph structures as well as lithified microbial substrates shagreen texture biolaminites in terms of fidelity and fossil completeness preservation of ediacaran fossils in the asha group is by no means inferior to that seen in other ediacaran macrofossil localities the low biodiversity of ediacaran macrofossils can be attributed to a relatively young ediacaran age of the asha group which is constrained by a u pb zircon date of 547 6 3 8 ma from an ash bed in the lower part of the sedimentary succession the uppermost part of the asha group has yielded bilobed burrows with a backfill structure suggesting an affinity with the ichnogenus didymaulichnus from the ediacaran cambrian boundary strata the asha group therefore offers an important glimpse into the history of the edacaran biota in the aftermath of the kotlinian crisis that caused extinction of dickinsoniomorphs tribrachiomorphs and bilateralomorphs in wave and current agitated shoreface depositional systems 550 million years ago but did not significantly affect frondomorphs and palaeopascichnids

diverse microbially induced sedimentary structures from 1 ga lakes of the diabaig formation torridon group northwest scotland abstract the siliciclastic lacustrine rocks of the 1000 ma diabaig formation northwest scotland contain a remarkable diversity of macroscopic structures on bedding planes that can be compared with various kinds of microbially induced sedimentary structures miss field sedimentological investigations combined with laboratory analysis of bedding planes and petrographic study of thin sections have allowed us to characterise a range of depositional environments and document the spectrum of biological structures miss are reported from frequently subaerial environments through commonly submerged facies and down to permanently sub wavebase settings palaeoenvironmental conditions water depth exposure hydrodynamic energy control the distribution of miss within these facies this demonstrates that mat forming microbial communities were arguably well adapted to low light levels or periodic exposure some miss from the diabaig formation are typical of precambrian microbial mats including reticulate fabrics and old elephant skin textures in addition to these a number of new and unusual fabrics of putative microbial origin are described including linear arrays of ridges and grooves cf arumberia and discoidal structures that are comparable with younger ediacaran fossils such as beltanelliformis these observations indicate that benthic microbial ecosystems were thriving in freshwater lake systems 1000 ma and indicate how microbially induced sedimentary structures may be applied as facies indicators for proterozoic lacustrine environments the discovery of structures closely resembling ediacaran fossils cf beltanelliformis also serves to highlight the difficulty of interpreting simple discoidal bedding plane structures as metazoan fossils

arumberia glaessner walter a review of its potential for correlation in the region of the precambrian cambrian boundary arumberia is a large impression fossil which may be allied to the ediacaran fossils ernietta and pteridinium new finds and published evidence suggest that it was restricted to very shallow possibly non marine environments and to rocks of latest precambrian to lower cambrian age well preserved material from the longmyndian shows that it was associated with numerous small spherical structures at present it is only of broad stratigraphic use but as the wide range of characters observed becomes better understood it may prove more valuable especially as it occurs in otherwise poorly fossiliferous environments

significance of styles of epicontinental shale sedimentation in the belt basin mid proterozoic of montana u s a abstract within the strongly shale dominated sediment fill of the mid proterozoic belt basin a large variety of shale types can be distinguished sedimentological investigations of several formations have yielded valuable data about lateral associations of shale types as well as about the principal mechanisms of shale deposition depositional environments of shales in the belt basin range from red bed mudstones of ancient flood plains to deep water mudstones in a turbidite setting graded silt mud couplets are ubiquitous in most shales of the belt basin however they differ in detail and can be related to a variety of depositional processes such as low density turbidity currents sheet floods storms and wave reworking in several formations there is evidence that microbial mats colonized the sediment surface and probably protected the sediment surface from erosion shales from comparable phanerozoic settings generally lack the silt mud couplets that are so commonly observed in shales from the belt basin and other proterozoic epicontinental basins this difference probably reflects the proliferation of bioturbating organisms in the phanerozoic the absence of benthic microbial mats in phanerozoic shales is probably due to the evolution of metazoan grazers towards the end of the proterozoic

a quantitative approach to sedimentary surface structures contoured by the interplay of microbial colonization and physical dynamics in the tidal flats of mellum island southern north sea biofilms and microbial mats generated largely by cyanobacteria colonize the sedimentary surfaces biostabilization effects and biomass enrichment influence erosional and depositional dynamics resulting from tidal flushing and storm surges the overlapping of both biological and physical forces causes the development of characteristic sedimentary structures to obtain a quantitative expression of the degree of effectiveness of microbial colonization in the formation of structures in an extended tidal area a modification index mod i was developed based on the following values i the proportion of mat covered area related to a defined investigation area ia ii the degree of steepness of slope angles of raised erosional remnants is and iii the degree of microbial levelling of a rippled sedimentary surface in the mod i was calculated for several defined regions within the study area and both winter and summer situations were considered the mod i values show first that the lower intertidal zone is characterized by index values approaching zero this implies that microbially induced effects in this zone are negligible even in summer second the upper intertidal zone is characterized by lower index values in winter and relatively high values in summer this implies a predominantly seasonal control on the biofilm development in this zone third in the lower supratidal zone the index values are almost identical during both winter and summer this implies non seasonal biological effects in this zone concomitant empirical studies on the composition of microbial mats and films suggest that the dominant microbial type influences the mod i value

multidirected ripple marks rising from biological and sedimentological processes in modern lower supratidal deposits mellum island southern north sea the sandy lower supratidal zone called westplate of mellum island southern north sea is colonized by epipsammic cyanobacteria the microbes form habitats of different stages of development adjacent to each other biofilms initial stages mats mature stages whereas biofilms do not contribute much to cohesion of sedimentary grains mats significantly stabilize the supratidal surface which leads to local conservation of a former physically shaped surface relief at microbially overgrown sites in fall the westplate is covered by variously orientated ripple marks termed multidirected ripple marks field measurements and investigations on the epipsammon revealed that ripple marks of similar orientations were covered by microbial assemblages of similar stages of development the results permit the following interpretation the sediments of the westplate are reworked by high water spring tide flood currents the directions of which are frequently changed by strong winds because the water depth of the flood current is very shallow some parts of the uneven sedimentary surface are more affected by hydrodynamic stress than others at sites of calmer hydrodynamic conditions predominantly filamentous cyanobacteria settle in time forming mats constant physical reworking of slightly deeper parts of the supratidal surface however only permits the development of less sediment stabilizing biofilms composed mainly of coccoid cyanobacteria after the supratidal area drains the deeper parts are also colonized by mat constructing cyanobacteria and the ripple marks become consolidated by the organic layer repetition of these interactive processes of physical reworking and microbial colonization is documented by the patchy ripple structure of the supratidal surface

life on land in the precambrian microfossils have been discovered in cavity fill and replacement silica that occurs between chert breccia clasts in 1200 million year old paleokarst at the top of the mescal limestone central arizona and in 800 million year old paleokarst at the top of the beck spring dolomite southeastern california microbial communities on precambrian g550 million years ago land may have been extensive enough to affect weathering erosion sedimentation and geochemical processes

microbially induced sedimentary structures in archean sandstones a new window into early life abstract until now the most valuable information on the early life on the archean earth derived from bacterial fossils and stromatolites preserved in precipitated lithologies such as chert or carbonates also shales contain complex biomarker molecules and specific isotopes constitute an important evidence for biogeneicity in contrast because of their low potential of fossil preservation sandstones have been less investigated but recent studies revealed a variety of microbially induced sedimentary structures miss that differ greatly from any other fossils or sedimentary structures wrinkle structures multidirected ripple marks biolaminites and other macrostructures indicate the former presence of photoautotrophic microbial mats in shallow marine to tidal paleoenvironments the miss form by the mechanical interaction of microbial mats with physical sediment dynamics that is the erosion and deposition by water agitation the structures occur not only in archean tidal flats but in equivalent settings throughout earth history until today miss are not identified alone by their macroscopic morphologies in thin sections the structures display the carpet like fabrics of intertwined filaments of the ancient mat constructing microorganisms geochemical analyses of the filaments proof their composition of iron minerals associated with organic carbon in conclusion microbial mats colonize sandy tidal settings at least for 3 2 ga years therefore archean sandstones constitute an important archive for the exploration of early life

siderite concretions indicators of early diagenesis in the gammon shale cretaceous the upper cretaceous gammon shale in the northern great plains contains abundant siderite concretions that formed during the early compactional history of the fine grained marine sediments the relative depth of siderite precipitation can be estimated on the basis of textural mineralogical and isotopic evidence siderite concretions that formed at shallow depths in the sediment column contain a large volume percent carbonate 75 85 preserve uncompacted sediment textures and have oxygen isotope ratios similar to those of carbonates precipitated in equilibrium with seawater delta 18 o nearly equal e 0 to 2 per thousand pdb in contrast lower volume percent carbonate values 55 75 and relative decreases in 18 o 16 o values characterize concretions that formed longer after deposition and or at greater depths in the accumulating sediments both volume percent carbonate and delta 18 o values are strongly correlated with independently determined sediment accumulation rates concretions in rapidly deposited sediments formed at shallow depths 200 m later in the burial history the gammon served as both source rock and reservoir for accumulations of biogenic methane and like the siderite concretions the methane was generated during early diagenesis both siderite precipitation and methane accumulation require interstitial pore waters that have sufficiently high bicarbonate activities and that are depleted in dissolved sulfur and free oxygen because of chemical requirements siderite did not precipitate until after the onset of methane generation therefore if the depth of siderite formation is known the minimum depth for the onset of methane accumulation can be inferred the presence of abundant pyrite in slowly accumulated gammon sediments suggests by analogy to data from recent sediments that the depth of siderite precipitation and methane accumulation was controlled by the sedimentation rate in slowly accumulating sediments most organic matter was probably consumed by aerobic organisms and sulfate reducing anaerobic bacteria whereas in areas of more rapid deposition large quantities of organic matter were available for methane generation