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

impressions of algal mats from the middle proterozoic belt supergroup northwestern montana u s a irregular low relief bedding plane markings which probably represent impressions of thin wrinkled algal mats have recently been detected in mudstones from the 1100 m y old snowslip formation belt supergroup glacier national park montana algal mat impressions are rarely reported from ancient strata yet algal mats are common in certain modern environments originating primarily in moist settings and in relatively quiescent shallow water settings such structures may be of some value in interpreting ancient depositional environments

environmental interpretation and a sequence stratigraphic framework for the terminal proterozoic ediacara member within the rawnsley quartzite south australia abstract fossils of the ediacara biota are confined to preservational windows in the ediacara member of the rawnsley quartzite pound subgroup from the flinders ranges south australia the base of the ediacara member is a type 1 sequence boundary incised into the partly lithified chace quartzite member of the rawnsley quartzite the ediacara member and the upper half of the rawnsley quartzite comprise the rawnsley depositional sequence bounded above by the early cambrian uratanna depositional sequence the rawnsley sequence developed over an erosional surface cut into the chace quartzite member with some 250 m of relief southeasterly directed palaeovalleys are filled with a sequence of massive sandstone and laminated siltstone passing up into well bedded sandstone at lowstand local channels were filled by massive sand the highstand systems tract consists of several parasequence sets of laminated siltstone and channelized amalgamated massive sandstone overlain by interbedded siltstone and sandstone grading up into well bedded clean sandstone impressions of soft bodied ediacaran organisms are preserved above the valley fill facies on sandstone partings within upward shoaling delta front environments between storm and fairweather wavebase the ediacara member is in places conformably overlain by up to 500 m of sandstone of the same lithofacies as those underlying the member distinctive microbial mat bound sand laminae described as petee structures are characteristic of the rawnsley quartzite above and below the ediacara member during deposition of the ediacara member colonization of the deeper substrates by microbial mat communities enabled preservation of the ediacara biota the erosional surface at the base of the ediacara member is one of at least four incision events recorded in the terminal proterozoic and early cambrian succession of the adelaide geosyncline the similarity of incision filling lithofacies of the rawnsley and uratanna sequences has in condensed sections led to confusion between the depositional sequences characteristic trace and body fossil assemblages provide the only clear distinction between depositional cycles spanning the proterozoic cambrian boundary

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

precise u pb titanite age constraints on the emplacement of the bushveld complex south africa the c 2 06 ga bushveld complex intrudes the transvaal supergroup south africa calcsilicate xenoliths within the mafic phase of the bushveld complex rustenburg layered suite or rls preserve calcsilicate xenoliths with high temperature c 1200 c mineralogies that were later metasomatized by hydrous retrograde c 600 700 c fluids whose timing has been unconstrained new u pb isotope data from newly grown titanite within a completely retrogressed xenolith indicates that retrogression occurred at 2058 9 0 8 ma this suggests that retrogression was due to hydrothermal circulation associated with the cooling rls and not slightly later bushveld related granites the new data place a tight constraint on the minimum age of emplacement of the rls

fate of outflow channel effluents in the northern lowlands of mars the vastitas borealis formation as a sublimation residue from frozen ponded bodies of water 1 we analyze the fate of the hesperian aged outflow channel effluents emplaced into the northern lowlands of mars we have modeled the evolution of these effluents under the assumption that they were emplaced under a range of atmospheric conditions comparable to those of today and thought to have prevailed in the hesperian under these conditions we find that the evolution of the sediment loaded water after it left the channels includes three phases phase 1 emplacement and intensive cooling violent emplacement of water followed by a short period of intensive evaporation from the surface and near surface layer and intensive convection during this phase the water maintained and redistributed its large suspended sediment load water vapor strongly influenced the climate at least for a geologically short time when the temperature of the water reached the temperature of the maximum density or the freezing point boiling and intensive convection ceased and the water deposited the sediments phase 2 freezing solid geologically rapid freezing of the water body accompanied by weak convective water movement occurred over a period of the order of 104 years phase 3 sublimation and loss this period involved sublimation of the ice and lasted longer than the freezing phase the rate and latitudinal dependence of the sublimation as well as the location of water vapor condensation crucially depend on the planetary obliquity climate and sedimentary veneering of the ice phase 3 would have been very short geologically 105 106 years if an insulating sedimentary layer did not build up rapidly if such an insulating layer did form rapidly sublimation could cease and residual ice hundreds of meters thick could remain below the surface today the northern lowlands of mars are largely covered by the late hesperian aged vastitas borealis formation vbf which has sharp boundaries clearly seen in the map of kilometer scale roughness and a distinctive kilometer scale roughness signature we examine detrended topography data and find evidence that the vbf is underlain at very shallow depths by an early hesperian ridged volcanic plains substrate rather than frozen water deposits remaining from the outflow channel events analysis of the vbf roughness characteristics suggests at least 100 m thickness of sediments on top of the underlying volcanic ridged plains the total inferred volume of the vbf material approximately corresponds to the volume of material removed from the outflow channels these results support a model in which the vastitas borealis formation predominantly represents the sedimentary residue remaining after the sediment laden water effluents of the outflow channels ponded in the northern lowlands and rapidly froze solid and sublimed the distinctive facies of the vbf are interpreted to be related to the freezing sublimation and residue of the outflow channel effluents ridged facies are dominantly marginal and are interpreted to be related to ice sheet lateral retreat knobby facies occur throughout and are interpreted to be due to a variety of causes including dewatering de icing and brine related processes and kame like ice residues grooved facies are interpreted to represent postsublimation uplift and fracturing due to load removal the mottled facies may represent bright ejecta whose albedo is related to buried sedimentary or evaporitic residues presently the most likely sites to find frozen remnants of the hesperian ocean are below the floors of stealth craters underlying the vbf on the basis of these findings and interpretations we make predictions for the fate of the outflow channel water vapor and the nature of the martian hydrologic cycle during the hesperian if noachian aged oceans existed conditions at that time would be similar to those described for a hesperian ocean as soon as a global cryosphere was formed if any residual deposits remain in the northern lowlands from a proposed noachian ocean they would lie below both the vbf and the underlying sequence of hesperian ridged plains

inverse maximum gross bedform normal transport 2 application to a dune field in ganges chasma mars and comparison with hirise repeat imagery and mrams abstract inverse maximum gross bedform normal transport imgbnt analysis has been applied to context camera ctx images of the largest dune field in ganges chasma on mars the dune field was selected for its position in a likely complex multi directional wind regime results indicate that four main winds are responsible for simultaneous construction of the dune field including along chasma winds from the ese winds blowing down a nearby re entrant from the ne winds blowing down the adjacent chasma wall from the nw and chasma floor winds from the sw each wind represents a transport vector that dominates dune morphology at its respective edge of the dune field such that the central axis of the dune field reflects the convergence of the three most prominent winds ese nw and sw the mars regional atmospheric modeling system mrams was run at twelve times throughout the martian year to provide context for the local wind patterns potential sand fluxes calculated from mrams output show that three major air flows from the ene e nne ne and nnw n converge near the location of the dune field these flows likely correspond to the ese ne and nw winds identified from imgbnt analysis respectively mrams output shows that the flows with major northerly components are produced by larger scale hadley return flow constructively combining with nighttime downslope winds the flow with a major easterly component is likely produced by equatorial easterly trade winds constructively combining with the diurnal tide and or local topography although the model correctly predicts the major elements of the local wind pattern some aspects are either over or underrepresented demonstrating the value of using aeolian morphological analysis to conclusively constrain the major sand moving winds on mars overlapping high resolution imaging experiment hirise images of barchanoid dunes at the northernmost edge of the dune field indicate that these dunes are currently migrating southward at 5 m mars year 2 6 m earth year the direction of migration is consistent with both mrams predictions in this location and the nw ne winds found from imgbnt analysis dune morphology suggests that sand in the northwestern part of the dune field is likely to be derived from the adjacent chasma wall to the north and northwest and sand in the southeastern part of the dune field was probably transported from farther east along the main chasma floor

could bacteria have formed the precambrian banded iron formations banded iron formations bifs are prominent sedimentary deposits of the precambrian but despite a century of endeavor the mechanisms of their deposition are still unresolved interactions between microorganisms and dissolved ferrous iron in the ancient oceans offer one plausible means of mineral precipitation in which bacteria directly generate ferric iron either by chemolithoautotrophic iron oxidation or by photoferrotrophy on the basis of chemical analyses from bif units of the 2 5 ga hamersley group western australia we show here that even during periods of maximum iron precipitation most if not all of the iron in bifs could be precipitated by iron oxidizing bacteria in cell densities considerably less than those found in modern fe rich aqueous environments those ancient microorganisms would also have been easily supported by the concentrations of nutrients p and trace metals v mn co zn and mo found within the same iron rich bands these calculations highlight the potential importance of early microbial activity on ancient metal cycling

the influence of air sea roughness sea spray and storm translation speed on waves in north atlantic storms abstract a coupled atmosphere wave sea spray model system is used to evaluate the impact of sea spray and wave drag on storm generated waves their height variations and directional wave spectra in relation to the storm location and translation speed results suggest that the decrease or increase of significant wave height due to spray and wave drag is most significant in high wind regions to the right of the storm track these processes are modulations on the maximum wave region and tend to occur several hours after the peak wind events depending on the storm translation velocity the translation speed of the storm is important the directional variation between local winds and wind generated waves within rapidly moving storms that outrun the waves is notably different from that of trapped waves when the dominant waves group velocity approximates the storm translation speed while wave drag and spray can increase or reduce the magnitudes of wind and significant wave height their nondirectional formu

microbial mat control on siliciclastic precambrian sequence stratigraphic architecture examples from india abstract an attempt has been made to understand within a cause and effect framework the sequence building pattern in proterozoic time that witnessed non uniformiteranean microbial mat growth and epeiric sea development marine or marginal marine successions in three neoproterozoic formations the sonia sandstone in western india and the sirbu shale and upper bhander sandstone in central india have been examined here for this purpose the strikingly common feature of all three formations is vertical stacking of highstand systems tracts without intervention of any significant transgressive deposits in one instance only the transgressive systems tract is represented by a thin granular transgressive lag and in all other cases the evidence of transgression is simply marked by the presence of marine flooding surfaces the absence of transgressive strata relates to the low sea floor gradients which facilitated rapid transgressions combined with a generally low sediment supply aggradation under normal regressive highstand conditions in spite of the low sediment supply was promoted by the prolific growth of microbial mats which reduced the effects of wave and current reworking by organic binding of clastic particles

major influences on the evolution of the 2 67 2 1 ga transvaal basin kaapvaal craton abstract the transvaal is one of three structural basins of the transvaal supergroup preserved on the kaapvaal craton the evolution of the neoarchaean palaeoproterozoic transvaal basin is ascribed predominantly to magmatism palaeoclimate and eustasy with plate tectonics playing a sporadic role the supergroup comprises basal protobasinal rocks followed by the black reef formation chuniespoort group and uppermost pretoria group immature siliciclastic and bimodal volcanic rocks of the protobasinal unit reflect a wide zone of rifting related to the c 2 7 ga ventersdorp supergroup mantle plume individual protobasinal successions were laid down in separate fault bounded basins controlled at least partially by greenstone belt orientations in the kaapvaal basement post magmatic post rifting thermal subsidence accommodated black reef fluvial sheet sandstones and the subsequent thick carbonate bif epeiric platform succession of the chuniespoort group subordinate mechanical subsidence accompanied this long lived thermal relaxation intense weathering due to neoarchaean atmosphere composition greatly reduced clastic sedimentation and the greenhouse palaeoclimate further encouraged carbonate sedimentation globally enhanced sea levels due to enhanced mid ocean ridge growth consequent upon either global magmatic events or supercontinent break up also played a pivotal role in chuniespoort epeiric basin evolution pretoria group sedimentation is ascribed to two cycles of rifting and subsequent thermal subsidence the first cycle appears to reflect plate tectonically induced rifting with an epeiric sea drowning the rift basin despite reduced sea levels due to the first major global glaciation the second pretoria cycle is most likely related to a major continental flood basalt event with thermal subsidence allowing a second and probably larger epeiric sea to advance onto the northern kaapvaal craton evaluation of the inferred relatively minor importance of plate tectonics in the evolution of the essentially intracratonic transvaal basin depends to a large degree on the age assigned to the limpopo orogeny during which the zimbabwe and kaapvaal cratons collided recent evidence for a c 2 0 ga collision supports the concept that catastrophic global magmatic events gradually gave way to plate tectonics during transvaal basin evolution

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

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

fill and spill of giant lakes in the eastern valles marineris region of mars the existence of hesperian age 3 7 3 4 ga surface water bodies on mars is a contentious issue often conflicting with favored climate models extensive lakes are proposed to have filled parts of valles marineris during this period yet evidence for their presence and temporal continuity is poorly constrained here we report geomorphic and chronologic evidence for the initiation and demise of a voluminous lake system within the basins of eastern valles marineris we find that independent kilometer deep lakes were present here well after the wetter global climate optimum that characterized the previous noachian epoch 4 1 3 7 ga relative and impact crater chronologies of flood channels emerging from lake basins indicate relatively late lake spillover in the early amazonian ca 3 0 ga drawdown of the lake and cessation of interbasin sedimentation may be recorded by a similar early amazonian ca 3 1 ga crater retention age on the surface of capri mensa a 4 km tall sulfate bearing interior layered deposit the topography data demonstrate that incision of the bedrock barriers between the basins during spillover was driven by a dramatic local base level difference between the lake surface and downstream basin floors we postulate that the lake spillover process created an integrated drainage routing system between a voluminous equatorial water supply and the northern plains basin

mars outflow channels a reappraisal of the estimation of water flow velocities from water depths regional slopes and channel floor properties methods used so far to assess the flow velocities of the water commonly assumed to be responsible for forming the major outflow channel systems on mars have relied widely on various versions of the manning equation this has led to problems in allowing for the difference between the accelerations due to gravity on mars and earth and for the differences of scale between martian floods and most river systems on earth we reanalyze the problem of estimating water flow velocities in martian outflow channels using equations based on the darcy weisbach friction factor instead of the manning n factor we give simplified formulae appropriate to mars for the darcy weisbach friction coefficient as a function of bedrock size distribution for a given channel floor slope and water flood depth similar mean flow velocities are implied for a wide range of values of the ratio of bed roughness to water depth relevant to martian outflow channels using a recent rederivation of manning s equation based on turbulence theory we obtain a new value of 0 0545 s m 1 3 for the manning n coefficient appropriate to martian channels and show that previous analyses have generally overestimated though in some cases underestimated water flow velocities on mars by a factor of order two combining the consequences of this flow velocity overestimate with likely overestimates of flow depth from assuming bank full flow we show that discharges may have been overestimated by a factor of up to 25 leading to corresponding overestimates of subsurface aquifer permeabilities rates of filling of depressions with water and grain sizes of sediments on channel floors despite the availability of an improved value for the manning n coefficient for mars we strongly recommend that modified forms of the original version of the manning equation should be replaced by the modern form or preferably by the darcy weisbach equation in future work

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

oceans on mars an assessment of the observational evidence and possible fate the edges of the northern plains and interpreted to be shorelines remaining from these former standing bodies of water we examine the elevations and geologic relations along these contacts in detail and find little support for their interpretation as shorelines some contacts are clearly of volcanic origin and all have significant variations in elevation better support for the former presence of water over large parts of the northern plains is provided by the vastitas borealis formation vbf most of the post noachian fill within the northern basin is ridged plains of lower hesperian age interpreted to be volcanic in origin overlying the ridged plains is the vbf a thin veneer of material of upper hesperian age the vbf may have been deposited from large floods support for this interpretation is the similarity in age between the outflow channels and the vbf the presence of the vbf at the lower ends of the outflow channels and identification of numerous features in the outcrop areas of the vbf that are suggestive of basal melting of an ice sheet to cover all the area over which the vbf is exposed would require 2 3 10 7 km 3 of water spread over the entire surface of mars this volume is equal to a global layer global equivalent layer or gel 156 m deep we find no support for the larger estimates of ocean volumes that range up to 3 10 8 km 3 and which imply comparable amounts of water per unit area as are currently present on the surface of the earth under present climatic conditions on mars an ocean would freeze in a geologically short time period 10 4 years then would sublimate away at rates strongly dependent on the presence or absence of debris on the ice surface the present vbf is interpreted as a sublimation residue from the ponded outflow channel effluents the fate of a volume of water thought to have been emplaced by the outflow channels 2 3 10 7 km 3 is largely accounted for by the presence of other existing reservoirs on the planet an approximately 20 30 m gel of water is estimated to be in the present polar caps and a 50 m gel may have escaped to space since the hesperian leaving 80 m gel unaccounted for this amount may be partly trapped in other volatile rich deposits on the surface and a significant amount could have reentered the groundwater system by south polar basal melting and been progressively cold trapped at the base of a growing cryosphere on the basis of our assessment of the hesperian aged deposits we predict that testing of the clifford and parker 2001 hypothesis that a noachian aged ocean covered up to one third of the surface of mars will be made very difficult by the enhanced degradation rates in the noachian and subsequent geological events in the northern lowlands index terms 6225 planetology solar system objects mars 4267 oceanography general paleoceanography 5407 planetary sciences atmospheres evolution 5470 planetary sciences surface materials and properties 1635 global change oceans 4203 keywords mars oceans channels shorelines hesperian

the ongeluk basaltic andesite formation in griqualand west south africa submarine alteration in a 2222 ma proterozoic sea abstract the ongeluk lavas form part of the palaeoproterozoic transvaal griqualand west supracrustal sequence of the archaean kaapvaal craton of south africa they form a thick shallow marine volcanic sequence of pillow lava massive flows and hyaloclastite which together with their comagmatic subaerial hekpoort correlate once covered most of the craton in this study the magmatic composition and alteration features of ongeluk samples were distinguished using geochemistry and radiogenic isotopes the ongeluk hekpoort magma was a basaltic andesite derived from anomalous kaapvaal craton lithosphere with a long history of high u pb high rb sr and chur like sm nd ratios little evidence for magmatic fractionation was found although contamination of the lower lavas with cr rich material is evident in both hekpoort and ongeluk sequences the alteration of ongeluk lavas is characterised using diagrams which compare pillow core rim pairs hyaloclastite and massive lava samples with the estimated original magma composition alteration is ascribed to a shallow 87 sr 86 sr ratios decreased from magmatic 0 7071 towards seawater 0 7025 during submarine alteration the rb sr system also reveals a much later 1200 ma phase of ca and rb mobility in a few samples in contrast the submarine alteration affected pb isotope ratios so little that a 2222 13 ma isochron age is regarded as a refinement of earlier dates for the ongeluk hekpoort extrusion the ongeluk hyaloclastites acted as a sink for k and rb in the overlying sea while the mn and ca entering the sea could have contributed to the overlying kalahari manganese deposits

sedimentology of hot spring systems hot springs and geysers hold a special fascination for many people to the casual visitor and tourist they provide a powerful visual display of nature at work if their temperature is tolerable taking the waters can provide relaxation comfort and alleged health benefits to the scientist however terrestrial hydrothermal systems are of major importance in many disciplines they serve as models for understanding the processes in the shallowest part of the geothermal systems that produce epithermal mineral deposits they are commonly the surface manifestation of large subsurface geothermal systems that may be tapped for geothermal energy their fascinating ecosystems are dominated by diverse arrays of microorganisms many of which thrive in waters of extremely high temperatures and compositions that are toxic to all other organisms although the life of a geothermal system may be geologically brief typically lasting only a few hundred to a few hundred thousand years many hot springs leave a tangible record of former activity in the deposits that were precipitated in and around their vents these hot spring deposits which are composed mainly of calcium carbonate travertine and silica siliceous sinter are the topic of this special issue hot spring deposits have been studied seriously for more than a century the pioneer of their detailed study was walter harvey weed who in the 1880s was one of the first to examine the deposits of siliceous sinter and travertine at yellowstone national park in wyoming u s a more than a century ago weed 1889 a 1889 b 1889 c recognized that the abundant microorganisms that inhabit spring environments may play a role in the formation of travertine and sinter the subsurface geothermal systems that feed hot springs were widely studied with a view to understanding and predicting epithermal mineralization interest in surface hot spring deposits however

topography of valles marineris implications for erosional and structural history compilation of a simplified geologic geomorphic map onto digital terrain models of the valles marineris permitted an evaluation of elevations in the vicinity of the troughs and the calculation of depth of troughs below surrounding plateaus thickness of deposits inside the troughs volumes of void spaces above geologic geomorphic units and volumes of deposits the central troughs north ophir north and central candor and north melas chasmata lie as much as 11 km below the adjacent plateaus in ophir and candor chasmata interior layered deposits reach 8 km in elevation if the deposits are lacustrine and if all troughs were interconnected lake waters standing 8 km high would have spilled out of coprates chasma onto the surrounding plateaus having surface elevations of only 4 5 km in this case interior deposits above about 4 km in the central troughs would not be lacustrine they could be volcanic on the other hand the troughs may not have been interconnected at the time of interior deposit emplacement they may have formed isolated ancestral basins the existence of such basins is supported by independent structural and stratigraphic evidence the ancestral basins may have eventually merged perhaps through renewed faulting to form northern subsidiary troughs in ophir and candor chasmata and the coprates north melas ius graben system the peripheral troughs are only 2 5 km deep shallower than the central troughs they may have formed from a combination of erosional collapse and structural activity chaotic terrain is seen in the peripheral troughs near a common contour level of about 4 km on the adjacent plateaus which supports the idea of release of water under artesian pressure from confined aquifers the layered deposits in the peripheral troughs may have formed in isolated depressions that harbored lakes and predated the formation of the deep outflow channels if these layered deposits are of volcanic origin they may have been emplaced beneath ice in the manner of table mountains areal and volumetric computations show that erosion widened the troughs by about one third and that deposits occupy one sixth of the interior space even though the volume eroded is larger than the volume deposited topographic and geologic considerations imply that material eroded from trough walls was probably part of the interior layered deposits but not their sole source additional material may have come from subterranean piping from reworking of local disintegration products on the floors such as chaotic materials or from eolian influx but overall it is likely that the additional material is volcanic and that it forms mostly the upper more diversely bedded layers of the interior deposits

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

on the dependence of sea surface roughness on wave development abstract the aerodynamic roughness of the sea surface z0 is investigated using data from lake ontario from the north sea near the dutch coast and from an exposed site in the atlantic ocean off the coast of nova scotia scaling z0 by rms wave height gives consistent results for all three datasets except where wave heights in the atlantic ocean are dominated by swell the normalized roughness depends strongly on wave age younger waves traveling slower than the wind are rougher than mature waves alternatively the roughness may be normalized using the friction velocity u of the wind stress again young waves are rougher than mature waves this contradicts some recent deductions in the literature but the contradiction arises from attempts to describe z0 in laboratory tanks and in the field with a single simple parameterization here it is demonstrated that laboratory waves are inappropriate for direct comparison with field data being much smoother than their field equivalents in the open ocea

terminal proterozoic mid shelf benthic microbial mats in the centralian superbasin and their environmental significance abstract a combined sedimentological and biogeochemical study has been conducted on several terminal proterozoic mid shelf microbial mat facies from the centralian super basin isotopic and organic geochemical analysis of the bitumen and kerogen indicated that two sources of organic matter from planktonic and benthic microbial mat populations contributed to the sediment the planktonic source provided a suite of n alkanes with c20 whereas the benthic source contributed an overlay of n alkanes c20 with a strong even preference together with mid chain methyl alkanes kerogen and biomarkers derived from the microbial mat were found to be depleted in 13c relative to planktonic material pyrite in the micorbial mats was also found to be depleted in 34s compared to surrounding facies the combination of these observations suggested that the mats may have been at least partly composed of sulfide oxidising bacteria these organisms have specific environmental tolerances that set limits on palaeo environment their requirement for oxygen indicates that the water column above the mid shelf could not have been anoxic accordingly from the results and age determinations reported here it would appear that mid shelf environments of the centralian superbasin of australia were seeing significant levels of oxygen through the ediacarian

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

ripple marks in quartz arenites of the hurwitz group northwest territories canada evidence for sedimentation in a vast early proterozoic shallow fresh water lake abstract supermature quartz arenites of the whiterock member deposited in the early proterozoic intracratonic hurwitz basin have a maximum thickness of 400 m and a minimum areal extent of 100 000 km2 the unit is unusual in that it is virtually devoid of other rock types and displays sedimentary structures that consist almost entirely of short spaced ripple marks and parallel stratification both formed by oscillatory flow the ripples have spacings that are consistently small average

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

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

wave dependence of sea surface wind stress abstract distribution of the wind stress over the oceans is usually estimated by using a bulk formula it contains the squared 10 m wind speed multiplied by the drag coefficient which has been assumed in many cases to be a weak function of the 10 m wind speed over land the important role of thermal stratification has been clearly recognized but over the sea the influence of wind waves is less well documented this paper presents evidence showing the likelihood that the influence of the wind waves can also be large charnock proposed an expression for the marine atmospheric boundary layer roughness parameter z0 which depended only on the wind friction velocity u and the acceleration of gravity g toba and koga have recently proposed an alternative expression for flow over growing wind waves which are in local equilibrium with the wind given by a form including the wind wave spectral peak frequency explicity the criterion for local equilibrium of the wave field with the wind is its consistency wi

interior trough deposits on mars subice volcanoes widespread several kilometer thick successions of layered deposits occur as mounds that partly fill the troughs or chasmata that compose the valles marineris on mars like terrestrial subice volcanoes the layered deposits occur in a volcano tectonic setting within basins that may have held ponded water or ice on the basis of their dimensions morphologies and associated catastrophic floods and other geologic events as shown in viking and new mars global surveyor mgs data sets we suggest that the interior deposits are volcanic in origin and possibly generated by subice eruptions a tuya origin for the mounds can explain the lack of external sediment mound heights that can rival the plateau local flat topped mesas morphologically distinct mounds of different ages horizontal to steep dips fine grained materials indications of rare volcanic vents and lava flows and spectral composition the extremely diverse layering of west candor chasma and possible volcanic cones in melas may have formed by related subaerial eruptions consistent with the suggestion that interior deposits are eroding out of the wall rock some deposits could have been erupted from sites along the walls

neoproterozoic substrate condition vis a vis microbial mat structure and its implications sonia sandstone rajasthan india dst fast track project young scientist scheme no sr ftp es 03 2011 cas phase v upe ii programme of jadavpur university national research foundation and university of pretoria south africa

a sulfur isotope study of pyrite genesis the mid proterozoic newland formation belt supergroup montana abstract different generations of sedimentary pyrite from the mid proterozoic newland formation usa have been analysed for their sulfur isotopic compositions the results indicate bacterial sulfate reduction as the pyrite forming process the 34 s values for early diagenetic pyrite around 14 are in contrast to dominantly more positive values for many other middle proterozoic units a progressive reduction of sulfate availability during diagenesis can be recognized by an increase in 34 s content rayleigh distillation as well as through detailed petrographic observations contemporaneous seawater had a sulfur isotopic ratio between 14 and 18 as measured from sedimentary barite within the unit

evidence for ponding and catastrophic floods in central valles marineris mars abstract the valles marineris canyon system of mars is closely related to large flood channels some of which emerge full born from chaotic terrain in canyon floors coprates chasma one of the largest valles marineris canyons is connected at its west end to melas chasma and on its east end to chaotic terrain filled capri and eos chasmata the area from central melas to eos chasmata contains a 1500 km long and about 1 km deep depression in its floor despite the large volumes of groundwater that likely discharged from chaotic terrain in this depression no evidence of related fluvial activity has thus far been reported we present an analysis of the regional topography which together with photogeologic interpretation of available imagery suggests that ponding due to late hesperian discharge of water possibly produced a lake mean depth 842 m spanning parts of the valles marineris depression vmd overflow of this lake at its eastern end resulted in delivery of water to downstream chaos regions and outflow channels our ponding hypothesis is motivated primarily by the identification of scarp and terrace features which despite a lateral spread of about 1500 km have similar elevations furthermore these elevations correspond to the maximum ponding elevation of the region 3560 m simulated ponding in the vmd yields an overflow point at its eastern extremity in eos chasma the neighborhood of this overflow point contains clear indicators of fluvial erosion in a consistent east west orientation

mat related sedimentary structures in neoproterozoic peritidal passive margin deposits of the west african craton anti atlas morocco abstract proterozoic inliers in the central anti atlas mountains expose predominantly siliciclastic sedimentary successions deposited in peritidal zones along the neoproterozoic continental margin of the west african craton wac the low grade metamorphic and modestly deformed sediments contain a wealth of sedimentary structures related to the former presence and activities of microbial mats and respective physicobiological processes the well preserved structures include wrinkle structures erosion marks microbial sand chips spindle shaped and subcircular microbial shrinkage cracks and possibly gas domes and cabbage head structures thin sections exhibit mat fragments and dispersed grains of hematite limonite after pyrite in fine grained quartzitic storm deposits post storm layers frequently consist of matrix supported sand sized to silt sized grains and are overlain by argillaceous veneers including isolated silt sized grains and black carbonaceous laminae the muddy veneers are considered to represent compacted stacks of microbial mats biolaminites which colonized and biostabilized storm and post storm layers and thus prevented them from eroding in the absence of grazing and burrowing organisms and at suitable depositional and hydrodynamic conditions it may be expected that proterozoic microbial mats extensively grew from the supratidal to the intertidal zones and occasionally e g behind protective barriers in the subtidal zone and beyond mat related structures however need specific conditions for their formation and preservation wrinkle structures erosion marks and microbial sand chips require tractional currents and soon deposition and burial respectively such conditions are preferably met in intertidal and supratidal zones spindle shaped and subcircular cracks require mat shrinkage due to either desiccation or syneresis crack propagation implies progressive shrinkage while superposition of crack generations indicates repeated alternation between mat exposure and flooding respective conditions prevail in the upper intertidal zone gas domes and cabbage head structures are related to the production of gas from decaying organic material beneath a sealing cohesive mat they may be some of the first features formed during genesis of petee structures in the intertidal to lower supratidal zones mat related structures may serve as sensitive facies indicators once their modes of formation are revealed

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

benthic cyanobacteria and their influence on the sedimentary dynamics of peritidal depositional systems siliciclastic evaporitic salty and evaporitic carbonatic abstract peritidal sedimentary systems are widely colonized by benthic cyanobacteria that form biofilms and microbial mats the bacterial communities interfere with physical and chemical sedimentary dynamics which is documented by the formation of microbially induced sedimentary structures miss the structures form a new fifth category in the existing classification of primary sedimentary structures siliciclastic depositional systems are dominated by physical dynamics by biostabilization cyanobacteria shelter their substrata against erosion during periods of intensive hydraulic reworking or they permit flexible deformation of sandy sediments during low hydrodynamic disturbance the bacteria enhance deposition of sediments by baffling trapping and binding such biotic physical interference is recorded by miss such as erosional remnants and pockets or planar stromatolites chemical depositional systems include i evaporitic salty environments characterized by evaporation and dissolution and ii evaporitic carbonatic environments that include evaporation dissolution and in situ lithification of organic matter here cyanobacterial mats experience periodical desiccation or evaporation of crystals and mat related structures such as petees and polygonal patterns of cracks are formed cyanobacteria and heterotrophic bacteria provide a chemical microenvironment that supports in situ lithification of organic matter in thin sections carbonate precipitates as ooids or lines of decaying filaments are visible miss occur in modern and ancient depositional systems they record i biological abilities of benthic cyanobacteria to cope with sedimentary dynamics and ii paleoclimate and paleoenvironmental conditions during earth history similar structures are also expected in extraterrestrial paleo environments

proliferation of early triassic wrinkle structures implications for environmental stress following the end permian mass extinction lower triassic strata in the western united states and northern italy have yielded the first reported occurrence of microbially mediated wrinkle structures in shallow subtidal siliciclastic paleoenvironments since the cambrian we hypothesize that wrinkle structures formed under reduced infaunalization conditions during the aftermath of the end permian mass extinction these wrinkle structures occur in siliciclastic sedimentary rocks in association with hummocky cross stratification and in some cases trace fossils such as asteriacites rhizocorallium planolites and gyrochorte that indicate a subtidal paleoenvironment wrinkle structures were found in the campil member in the werfen formation of northern italy and in the virgin limestone member of the moenkopi formation and the upper member of the thaynes formation exposed in the western united states the presence of wrinkle structures is likely related to a unique taphonomic window that allowed for the preservation of these delicate features on storm dominated siliciclastic shelves wrinkle structures commonly formed in a variety of subtidal paleoenvironments during the proterozoic cambrian but thereafter became restricted to intertidal supratidal and deep sea environments this restriction has been attributed to the increase in infaunalization of metazoans following the cambrian radiation the proliferation of wrinkle structures in subtidal settings during the early triassic suggests that infaunal bioturbation was reduced after the end permian mass extinction and that this reduction lasted for millions of years

coupled atmosphere ocean wave simulations under high wind conditions abstract the impact of ocean surface waves on the structure and intensity of three tropical cyclones and a topographically forced bora event is investigated using a coupled atmosphere ocean wave modeling system the coupled system is capable of representing surface momentum fluxes that are enhanced due to young ocean waves in fetch limited conditions which yield surface roughness lengths that significantly depart from the conventional charnock type formulation in general the impact of ocean wave induced stress on the tropical cyclone central pressure was quite variable with ocean wave feedback resulting in changes ranging from 8 hpa deeper to 3 hpa shallower the increased low level stress due to the ocean waves reduced the near surface winds by 2 3 m s 1 with local differences in excess of 10 m s 1 which directly led to a 10 reduction in the significant wave height maxima the reduced significant wave heights in the coupled model were in closer agreement with observations for tropical cyclone bonni

chryse planitia mars topographic configuration outflow channel continuity and sequence and tests for hypothesized ancient bodies of water using mars orbiter laser altimeter mola data many of the largest and most prominent outflow channels on mars debouch into chryse planitia pre mars global surveyor topographic data show chryse to be a closed depression almost 2000 km in diameter new mars orbiter laser altimeter mola data reveal the following 1 chryse is not a locally closed basin but instead opens into the north polar basin 2 the highly distinctive morphology of the six largest predominantly hesperian aged channels kasei maja simud tiu ares and mawrth disappears into the northern lowlands at average elevations that all occur within less than 170 m of a mean elevation of 3742 sd 153 m over a lateral distance in excess of 2500 km 3 the elevations where the distinctive morphology of each channel disappears all fall within 190 m of contact 2 a boundary mapped by parker et al 1993 and interpreted to represent an ancient shoreline and the mean elevation values of contact 2 and circum chryse channel termini fall within 18 m of each other in contrast the termini of seven later amazonian aged channels emerging from elysium into utopia planitia are spread over a vertical range of 1500 m 4 topographic evidence of the continuation of some of the outflow channels can be observed for distances of 250 450 km into the north polar basin but the morphology is subdued and distinctly different 5 the nature of this less distinctive topography and its crosscutting relationships show that simud and tiu are likely to represent the youngest activity specifically crosscutting ares valles 6 the distinctive change in channel morphology is consistent with rapid loss of energy encountered at base level subaerial submarine boundary and emplacement into a shallow submarine environment channel characteristics lack of distinctive deltas or lobes and continuation of subdued channel morphology suggest hyperpychnal flow and the possibility of density turbidity currents estimates of the volumes of individual channel events are wide ranging the minimum volume estimates of carr 1996 suggest that 46 such events would be required to fill the basin to the level of contact 2 and thus that the channels may have emptied into an existing standing body of water volume estimates of baker et al 1991 assume that single individual events may have filled the basin to the level of contact 2 thus requiring significant water loss between events and refilling during subsequent events to essentially the same level in both end member cases these observations are consistent with the presence of large standing bodies of water in the northern lowlands in hesperian early amazonian times

evidence that floodwaters filled and overflowed capri chasma mars 1 erosional features on a plateau in the valles marineris provide evidence that a lake filled capri chasma until it overflowed its eastern rim carving two large spillover channels the floodwaters surged into the adjacent lowlands of ancestral ganges chasma and eastern eos chasma the channel floor elevation and depth of incision at daga vallis reveal that a 1200 m deep lake water column was drained by the flooding the width depth and steep energy slope 0 02 of daga vallis and the existence of several cataracts including a 500 m high dry falls demonstrate the power of the floodwaters we estimate a possible peak discharge rate of 1 6 108 m3 s 1 the catastrophic flows may have been triggered by the collapse of topographic barriers in eastern coprates chasma providing a gateway for lake waters in the central valles marineris to pour eastward toward capri chasma and the lowlands beyond these may have been among the earliest flows in simud tiu valles contributing discharge to a possible sea in the northern plains of mars

high outflow channels on mars indicate hesperian recharge at low latitudes and the presence of canyon lakes abstract a number of martian outflow channels were carved by discharges from large dilational fault zones these channels were sourced by groundwater not surface water and when observed on high standing plateaus they provide indicators of elevated paleo groundwater levels we identify three outflow channels of hesperian age that issued from a 750 km long fault zone extending from candor chasma to ganges chasma two of these channels allegheny vallis and walla walla vallis have sources 2500 m above the topographic datum too high to be explained by discharge from a global aquifer that was recharged solely in the south polar region the indicated groundwater levels likely required regional sources of recharge at low latitudes the floodwaters that erupted from ophir cavus to form allegheny vallis encountered two ridges that restricted the flow forming temporary lakes the flow probably breached or overtopped these obstructions quickly catastrophically draining the lakes and carving several scablands after the last obstacle had been breached a single main channel formed that captured all subsequent flow we performed hydrologic analyses of this intermediate phase of the flooding prior to incision of the channel to its present depth using floodwater depths of 30 60 m we calculated flow velocities of 6 15 m s 1 and discharges in the range of 0 7 3 10 6 m 3 s 1 locally higher flow velocities and discharges likely occurred when the transient lakes were drained variable erosion at the channel and scabland crossing of mola pass 10644 suggests that the upper 25 30 m may consist of poorly consolidated surface materials underlain by more cohesive bedrock we infer that an ice covered lake with a surface elevation 2500 m probably existed in eastern candor chasma because this canyon is intersected by the ophir catenae fault system from which allegheny vallis and walla walla vallis originated we introduce a new hydrology concept for mars in which the groundwater system was augmented by recharge from canyon lakes that were formed when water was released by catastrophic melting of former ice sheets in tharsis by effusions of flood basalts this model could help to reconcile the expected presence of a thick cryosphere during the hesperian with the abundant evidence for groundwater as a source for some of the circum chryse outflow channels

microbial silicification in iodine pool waimangu geothermal area north island new zealand implications for recognition and identification of ancient silicified microbes silicified microbes provide evidence for some of the earliest life forms on earth they are extremely important to understanding the early development of life and the conditions that allowed its development such discussions commonly rely on comparisons with extant taxa and therefore depend upon the preservation style of the microbes and in particular the preservation of the taxonomically important features silicified microbes are deceptive they commonly appear to be well preserved even though their taxonomically critical features have been destroyed by silicification an understanding of the early taphonomic processes that influence microbial silicification can be obtained by studying extant microbes that are being silicified in modern hot spring pools iodine pool located in the waimangu geothermal area on the north island of new zealand is ideal for this purpose the spring water has a temperature of 69 100 c a ph of 8 3 9 0 and 440 457 ppm sio 2 glass slides left in the shallow marginal waters of this pool for 90 h became covered with thin layers of opaline silica discrete opal a spheres unsilicified microbes pseudofilaments partly silicified microbes and silicified microbes the rapidly silicified microbes appear well preserved with their general morphology diameter length and presence or absence of septa being readily apparent most of the silicified microbes however lack the key features that would allow accurate comparisons with extant taxa only two of the silicified microbes can be tentatively allied with the unsilicified forms despite being found side by side on the same glass slide these problems in identifying modern rapidly silicified microbes suggest that identifications of ancient silicified microbes can be problematic and must be treated with caution

chronological correlations between the pilbara and kaapvaal cratons abstract the early geological development of the pilbara and kaapvaal cratons has many features in common attempts have been made to correlate geologically similar features of the two cratons and it has been postulated that they originated as contiguous components of a single continent vaalbara during this time the early geological histories of the pilbara and kaapvaal cratons are here compared in detail and the evidence that they were initially contiguous is assessed these comparisons indicate significant differences in the chronologies of magmatic events within the granite greenstone crusts of the pilbara and kaapvaal cratons in addition igneous correlatives emplaced during ca 2985 and 2782 ma magmatic events on the kaapvaal craton have not been identified on the pilbara craton and a well defined 2760 ma magmatic event manifest as widespread emplacement of granitic rocks into the pilbara granite greenstone basement and eruption of flood basalts of the lower part of the fortescue group is absent from the kaapvaal craton furthermore similarities in first and second order transgression regression cycles within the sedimentary supracrustal sequences may be attributable to global sea level fluctuations and thus may be irrevelant to the question of former contiguity however similarities in some aspects of the geological development of the pilbara and kaapvaal cratons imply that there were periods extending for between 60 and 200 ma of the archaean era during which the style of crust formation intensity of volcanism and subaerial erosion and magnitude of sea level fluctuations may have varied on a global scale such similarities include the overall duration of formation of the granite greenstone crusts from ca 3650 to 3100 ma the onset of craton wide erosion in the interval ca 3125 to 3000 ma the major episodes of flood basaltic volcanism between 2760 and 2680 ma the predominance of chemical carbonate and banded iron formation sedimentation between ca 2630 and 2440 ma and the transition to widespread clastic sedimentation within the interval 2440 to 2200 ma

architectural elements from lower proterozoic braid delta and high energy tidal flat deposits in the magaliesberg formation transvaal supergroup south africa abstract three architectural elements are identified in the lower proterozoic magaliesberg formation pretoria group transvaal supergroup of the kaapvaal craton south africa 1 medium to coarse grained sandstone sheets 2 fine to medium grained sandstone sheets and 3 mudrock elements both sandstone sheet elements are characterised by horizontal lamination and planar cross bedding with lesser trough cross bedding channel fills and wave ripples as well as minor desiccated mudrock partings double crested and flat topped ripples due to the local unimodal palaeocurrent patterns in the medium to coarse grained sandstone sheets they are interpreted as ephemeral braid delta deposits which were subjected to minor marine reworking the predominantly bimodal to polymodal palaeocurrent trends in the fine to medium grained sandstone sheets are inferred to reflect high energy macrotidal processes and more complete reworking of braid delta sands the suspension deposits of mudrocks point to either braid delta channel abandonment or uppermost tidal flat sedimentation the depositional model comprises ephemeral braid delta systems which debouched into a high energy peritidal environment around the margins of a shallow epeiric sea on the kaapvaal craton braid delta and tidal channel dynamics are inferred to have been similar fine material in the magaliesberg formation peritidal complexes indicates that extensive aeolian removal of clay does not seem applicable to this example of the early proterozoic

negligible microbial matground influence on pre vegetation river functioning evidence from the ediacaran lower cambrian series rouge france supported by shell international exploration and production b v under research framework agreement pt38181

an overview of the geology of the transvaal sequence and bushveld complex south africa the late archaean early proterozoic transvaal sequence is preserved within the transvaal kanye and griqualand west basins with the 2050 ma bushveld complex intrusive into the upper portion of the succession within the transvaal basin both transvaal and bushveld rocks are extensively mineralized the former containing large deposits of iron manganese asbestos andalusite gold fluorine lead zinc and tin ores and the latter some of the world s major occurrences of pge chromium and vanadium ores transvaal sedimentation began with thin predominantly clastic sedimentary rocks black reef vryburg formations which grade up into a thick package of carbonate rocks and bif chuniespoort ghaap taupone groups these lithologies reflect a carbonate bif platform sequence which covered much of the kaapvaal craton in reaction to thermal subsidence above ventersdorp aged rift related fault systems an erosional hiatus was followed by deposition of the clastic sedimentary rocks and volcanics of the pretoria postmasburg segwagwa groups within the three basins under largely closed basin conditions an uppermost predominantly volcanic succession rooiberg group loskop formation is restricted to the transvaal basin a common continental rift setting is thought to have controlled pretoria group sedimentation rooiberg volcanism and the intrusion of the mafic rocks of the rustenburg layered suite of the bushveld complex the dipping sheets of the rustenburg magmas cut across the upper pretoria group stratigraphy and lifted up the rooiberg lithologies to form the roof to the complex subsequent granitic rocks of the lebowa and rashoop suites of the bushveld complex intruded both upper rustenburg rocks and the rooiberg felsites

paleontology of proterozoic shales and mudstones examples from the belt supergroup chuar group and pahrump group western usa abstract proterozoic black shales and other fine grained siliciclastic rocks contain a variety of fossils these fossils are illustrated by examples from three proterozoic units in the western usa the belt supergroup middle proterozoic the chuar group late proterozoic and the upper pahrump group late proterozoic a variety of microfossils and megafossils occur in the belt supergroup western montana acritarchs and filamentous microfossils are moderately well preserved in sub greenschist facies black shale in the little belt mountains the biologic affinity of the acritarchs is uncertain they could represent the vegetative or encystment stage of eukaryotic algae or the outer envelope of colonial coccoid cyanobacteria most of the filaments in these shales are of a size and morphology that is consistent with prokaryotic affinities however rare 20 and 40 m wide filaments could be either prokaryotic or eukaryotic higher grade sub greenschist facies dark gray to black mudstones in glacier national park contain poorly preserved acritarchs and spheroidal and filamentous pseudomicrofossils they are of interest because they provide information useful for distinguishing authentic microfossils from pseudofossils in mudstones and shales that have undergone substantial burial metamorphism several authentic megafossils occur in lower belt shales in the little belt and big belt mountains montana one of these is the carbonaceous compression beltina danai which could represent either fragments of a microbial mat or fragments of a sheet like megascopic alga the megafossil grypania spiralis has the form of a coiled ribbon and tentatively is interpreted as a megascopic alga green to purple mudstones and muddy sandstones in the lower belt supergroup in glacier national park contain markings that resemble a string of beads they are interpreted as megafossils that may have eukaryotic algal affinities black shales in the late proterozoic kwagunt formation chuar group grand canyon arizona contain a variety of acritarchs and filamentous microfossils of special interest is the vase shaped microfossil melanocyrillium which is interpreted as the sporangium of a eukaryotic and probably megascopic alga melanocyrillium also occurs in black mudstone in the late proterozoic pahrump group southeastern california

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

examination of the impact of a coupled atmospheric and ocean wave system part i atmospheric aspects abstract to take into account the change of surface roughness length induced by ocean waves a coupled atmospheric and ocean wave model system is developed a two way coupling is done between a mesoscale atmospheric model mc2 and an oceanic wave model a regional version of wam cycle 4 two different approaches based on the wave age of smith et al and the wave induced stress of janssen are used to compute a coupling parameter called the charnock parameter expressed as the nondimensional surface roughness length the coupling between the two models is accomplished by the use of this parameter which is a function of sea state instead of the constant value obtained from empirical studies using the well known charnock relation the coupled atmospheric and ocean wave system was applied to four intense storms in the western atlantic to examine the impact of the two way interaction using real midlatitude storm cases in part i the atmospheric forecasts resulting from this two way coupling are discusse

wrinkle marks an intertidal sedimentary structure due to aseismic soft sediment loading abstract the structures have a wide distribution intertidally in the macrotidal severn estuary and inner bristol channel occurring on the active sedimentary surface chiefly in association with a millimetre scale sand over mud doublet the sand surface is marked by depressions and ridges of a wide variety of shapes and orientations relative to slope that are matched antithetically by ridges and depressions on the mud sand interface below the sand layer consequently takes the form of a series of touching to detached pillow shaped masses whose centres lie 2 4 sand layer thicknesses apart wrinkle marks originate soon after the emergence of the sedimentary surface into the atmosphere and are considered to be soft sediment deformation structures on account of their 1 occasional displacement and or severance of early emergence surface organic trails and feeding marks 2 similarity in shape and internal structure to pseudo nodules recorded from the field and produced experimentally and 3 association with gravitationally unstable sediment layers in settings that favour the vigorous seepage of pore water through water logged sediments owing to their origin at the sedimentary surface wrinkle marks appear to be preserved mainly as surface markings on eroded and discordantly reburied mud sand interfaces

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

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

sedimentation rates basin analysis and regional correlations of three neoarchaean and palaeoproterozoic sub basins of the kaapvaal craton as inferred from precise u pb zircon ages from volcaniclastic sediments abstract calculation of sedimentation rates of neoarchaean and palaeoproterozoic siliciclastic and chemical sediments covering the kaapvaal craton imply sedimentation rates comparable to their modern facies equivalents zircons from tuff beds in carbonate facies of the campbellrand subgroup in the ghaap plateau region of the griqualand west basin transvaal supergroup south africa were dated using the perth consortium sensitive high resolution ion microprobe ii shrimp ii dates of 2588 6 ma and 2549 7 ma for the middle and the upper part of the nauga formation indicate that the decompacted sedimentation rate for the peritidal flat to subtidal below wave base stratifera and clastic carbonate facies southwest of the ghaap plateau at prieska was of up to 10 m ma when not corrected for times of erosion and non deposition dates of 2516 4 ma for the upper gamohaan formation and 2555 19 for the upper monteville formation indicate that some 2000 m of carbonate and subordinate shale sedimentation occurred during 16 ma to 62 ma on the ghaap plateau for these predominantly peritidal stromatolitic carbonates decompacted sedimentation rates were of 40 m ma to over 150 m ma bubnoff units the mixed siliciclastic and carbonate shelf facies of the schmidtsdrif subgroup and monteville formation accumulated with decompacted sedimentation rates of around 20 b for the kuruman banded iron formation a decompacted sedimentation rate of up to 60 b can be calculated thus for the entire examined deep shelf to tidal facies range archaean and phanerozoic chemical and clastic sedimentation rates are comparable four major transgressive phases over the kaapvaal craton followed by shallowing upward sedimentation can be recognized in the prieska and ghaap plateau sub basins in griqualand west and partly also in the transvaal basin and are attributed to second order cycles of crustal evolution first order cycles of duration longer than 50 ma can also be identified the calculated sedimentation rates reflect the rate of subsidence of a rift related basin and can be ascribed to tectonic and thermal subsidence comparison of the calculated sedimentation rates to published data from other archaean and proterozoic basins allows discussion of general precambrian basin development siliciclastic and carbonate sedimentation rates of archaean and palaeoproterozoic basins equivalent to those of younger systems suggest that similar mechanical chemical and biological processes were active in the precambrian as found for the phanerozoic particularly for stromatolitic carbonates matching modern and neoarchaean sedimentation rates are interpreted as a strong hint of a similar evolutionary stage of stromatolite building microbiota the new data also allow for improved regional correlations across the griqualand west basin and with the malmani subgroup carbonates in the transvaal basin the nauga formation carbonates in the southwest of the griqualand west basin are significantly older than the gamohaan formation in the ghaap plateau region of this basin but are in part correlatives of the oaktree formation in the transvaal and of parts of the monteville formation on the ghaap plateau

the sequence stratigraphic concept and the precambrian rock record an example from the 2 7 2 1 ga transvaal supergroup kaapvaal craton abstract sequence stratigraphic concepts are applied to the 2 7 2 1 ga transvaal supergroup which constitutes the sedimentary floor to the bushveld igneous complex the transvaal succeeds the foreland fill of the witwatersrand supergroup and in its lowermost portions is partly synchronous with the ventersdorp supergroup lavas that followed upon the witwatersrand sediments in the stratigraphic record the unconformable contacts at the base and the top of the transvaal supergroup mark significant changes in the overall tectonic setting which qualifies them as first order sequence boundaries sedimentation within the transvaal basin was controlled by cycles of extensional and or thermal subsidence resulting in the accumulation of sequences separated by stages of base level fall generating sequence bounding subaerial unconformities the transvaal first order sequence is subdivided into five second order unconformity bounded depositional sequences i e the protobasinal black reef chuniespoort rooihoogte timeball hill and boshoek houtenbek sequences the span of time of these second order sequences averaging 130 ma is much longer than the duration of the second order phanerozoic cycles which is explained by the less evolved and thus slower plate tectonic processes that dominated the late archaean early proterozoic times each transvaal second order sequence preserves a variable number of systems tracts mainly as a function of the strength of the erosional processes associated with the ravinement surfaces and subaerial unconformities in a complete succession a sequence would include a basal lowstand systems tract lst followed by transgressive tst highstand hst and falling stage fsst systems tracts the protobasinal and rooihoogte timeball hill sequences only preserve the lst and tst due to the strong post depositional erosion the black reef sequence is composed of lst tst and hst the chuniespoort sequence preserves the tst hst and fsst but lacks the lst due to ravinement erosion the boshoek houtenbek sequence develops the complete succession of systems tracts common features may be emphasized between the same types of systems tract developed within different sequences the lst includes high energy coarse prograding facies such as alluvial fans and fan delta systems that fill the irregularities of the pre existing topography and lead to the peneplanation of the depositional areas the tst may be recognized from retrogradational stacking patterns that are associated with the transgression of marine environments the hst marks the normal regression of the previous marine environments which assumes coeval aggradation of fluvial and basinal facies within an overall progradational framework the fsst would normally include only basinal facies age equivalent with the correlative subaerial unconformities in our case study the stages of base level fall resulted invariably in fully nonmarine environments within the transvaal area generally leading to the development of subaerial unconformities in particular circumstances the nonmarine environment may still accumulate and preserve fluvial alluvial fan or lacustrine sediments as a function of the relative position between topography and local equilibrium profiles and base levels the interpretations of base level rise and fall resulting from the application of the sequence stratigraphic concept to the 2 7 2 1 ga transvaal supergroup enable estimation of sea level changes during deposition of this succession with an understanding of local tectonic conditions on the kaapvaal craton and of coeval sedimentation elsewhere in africa eustatic and relative sea level changes and variation in continental freeboard conditions may be suggested for the transvaal supergroup

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

examination of the impact of a coupled atmospheric and ocean wave system part ii ocean wave aspects a coupled atmospheric and ocean wave system has been developed to study the impact of changes of surface roughness length induced by ocean waves a two way coupling between a mesoscale atmospheric model mc2 and an oceanic wave model a regional version of wam cycle 4 was designed to ensure consistency in the treatment of the atmospheric boundary layer parameterizations between the two models two different approaches based on the wave age of smith et al and the wave induced stress of janssen are used to compute a coupling parameter called the charnock parameter expressed as the nondimensional surface roughness length the coupling between the two models is accomplished by the use of this parameter which is a function of sea state instead of the constant value obtained from empirical studies using the well known charnock relation the impacts on the atmospheric forecasts are discussed in part i in part ii the ocean wave forecasts resulting from this two way coupling are discussed for four different real cases the two approaches are evaluated by comparing ocean wave model outputs obtained from the coupled and uncoupled systems against buoy observations the coupling has some beneficial impact especially in areas of extreme sea states the significant wave heights are reduced in the coupled runs and generally show better agreement with the buoy observations the impact of the coupling also exhibits some dependence on the intensity of the cyclone development with larger changes occurring in the case of rapidly deepening storms

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

a regional climate model coupled to ocean waves synoptic to multimonthly simulations the ncar regional climate model regcm is coupled to the wam ocean model using the sea state dependent roughness parameterization derived in the hexos experiment coupled model simulations are shown to give reduced wind speeds u10 compared to uncoupled simulations this is in accord with other recent studies however the wave atmosphere coupling is effected through the friction velocity field u rather than through the wind field u10 thus because the coupling gives enhanced resistive friction u10 is weakened whereas u is enhanced wave heights driven by u are also increased in our coupled model simulations compared to uncoupled model simulations coupled model outputs are shown to compare favorably with air sea observations collected during the recent labrador sea deep convection experiment in 1997 both for synoptic storm timescales and for seasonal timescales

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