carbon and strontium isotopes and global correlation of cambrian series 2 series 3 carbonate rocks in the keping area of the northwestern tarim basin nw china abstract one hundred and ten carbon and nineteen strontium isotopic values of outcropping cambrian series 2 and series 3 carbonate rocks in the penglaiba section of the keping area were analyzed effective isotopic data with little influence of diagenesis were used to address the global correlation the 13 c values exhibit two major positive excursions peaking at 3 1 and 3 3 and three major negative excursions peaking at 3 0 4 2 and 3 2 the carbon isotope excursions peaking at 3 0 and 4 2 across the cambrian series 2 series 3 boundary show good correlations with similar variations reported in siberia laurentia north china and south china in contrast the other three carbon isotope excursions peaking at 3 1 3 3 and 3 2 do not have a fairly good global correlation because of the lack of biostratigraphic data with respect to the 87 sr 86 sr ratios they show good correlation with those reported for laurentia and further support the global 13 c comparison on the basis of these new data it is showed that the combination of 13 c curves and 87 sr 86 sr variations serves as a powerful tool for correlation and subdivision of cambrian strata in the tarim basin of northwest china and provides new data for global correlation

novel paleoecology of a postextinction reef famennian late devonian of the canning basin northwestern australia reefs are widely supposed to be particularly susceptible to mass extinction events and to survive only as low diversity remnant communities dominated by holdover or disaster taxa famennian late devonian reefs exposed in the windjana limestone of the canning basin northwestern australia demonstrate however that a novel reef ecology was established in the immediate aftermath of the frasnian famennian mass extinction here diverse calcimicrobes including rothpletzella spp shuguria spp ortonella and girvanella together with bryozoans brachiopods and stromatoporoid sphinctozoan and lithistid sponges grew as complex framework intergrowths in previously undocumented morphological forms forming spectacular elevated laminar to platy structures to 3 m in diameter and 0 35 m thick at least 15 morphospecies of lithistids are now identified where only two were previously documented these communities show no substantial reduction in biodiversity compared to frasnian counterparts nor any change in tiering or loss of complex ecological interactions these observations suggest that where stable carbonate platforms persisted after mass extinction events reef building could continue more important they demonstrate that no protracted interval of time was necessarily required either for recovery to ecological stability or for completely new reef ecologies to assemble such studies highlight the need to document ecosystem recovery after mass extinction events using detailed paleoecological analyses in addition to simple compilations of global biodiversity changes

microbial mats as bioreactors populations processes and products microbial mats are dynamic and complex ecosystems exhibiting spatial and temporal heterogeneity the physical chemical environment is typified by steep gradients and distinct microenvironments these microenvironments support a great diversity of species with a wide range of metabolic processes these processes often result in coupled reactions and biogeochemical cycles and produce important end products such as trace gases and mineral precipitates the latter can impact the composition and character of the sediment imparting a biosignature these biosignatures can be preserved in the rock record and are useful in the interpretation of fossil record on earth and possibly as an indication of life on other planetary bodies the modern marine stromatolites of the exuma cays bahamas provide an ideal system for studying the populations processes and products in a microbial ecosystem using a multidisciplinary approach in order to acquire redox energy microbial populations need to carry out metabolic reactions at rates faster than the equivalent chemical abiotic reactions as such microbes can be viewed as bioreactors that preferably oxidize carbon to co2 to maximize the energy yield the study of the microbial role in carbonate sedimentation and lithification in these stromatolites provides a picture of microbial mats as bioreactors producing a biosignature

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

calcification of cyanobacterial filaments girvanella and the origin of lower paleozoic lime mud the origin of lime mud in ancient shallow marine carbonate platforms is one of the most vexing mysteries in sedimentary geology possible sources previously suggested include the physical and biological disintegration of animal and algal bioclasts mineralizing pelagic organisms and spontaneous whitings from either abiotic precipitation or calcification of suspended picoplankton and organic matter the styles of occurrence of micrite walled tubes referred to girvanella in lower paleozoic limestones argue that occasional permineralization of mucilaginous sheaths of the benthic filamentous cyanobacteria precursor could have produced lime mud when the tubes fell apart estimated volumes are comparable to those calculated for the modern bahama platform the copious growth of cyanobacteria typical in shallow marine settings indicates that this mechanism could account for a considerable amount of lime mud especially in the early paleozoic

on the appearance of cyanobacterial calcification in modern stromatolites abstract in august 1991 calcified magnesian calcite filamentous cyanobacteria scytonema mirabile appeared on the surface of a modern lacustrine stromatolite lake r2 rangiroa atoll tuamotu archipelago french polynesia previously the topmost photosynthetic layer of this sediment was devoid of such microbial biomineralisers the calcified cyanobacteria are accompanied by magnesian calcite grains which are evocative of bacterial precipitates although the appearance of cyanobacterial calcification might be related to environmental changes in the lake in particular a decrease in water salinity the persistence of non calcified specimens of a filamentous cyanobacteria phormidium crossbyanum which was once a dominant species of the lake benthos shows that calcification and environmental conditions might be only indirectly related thus attempts to use the fossil record of calcareous cyanobacterial skeletons to infer changes in the chemical composition of past oceans cannot be made without due regard of biological processes like the appearance of new competitors

microbial biomineralization processes forming modern ca mg carbonate stromatolites abstract modern ca mg carbonate stromatolites form in association with the microbialmat in the hypersaline coastal lagoon lagoa vermelha brazil thestromatolites although showing diversi ed fabrics characterized by thin orcrude lamination and or thrombolitic clotting exhibit a pervasive peloidalmicrofabric the peloidal texture consists of dark micritic aggregates of veryhigh mg calcite and or ca dolomite formed by an iso oriented assemblage ofsub micron trigonal polyhedrons and organic matter limpid acicular crystalsof aragonite arranged in spherulites surround these aggregates unlike thearagonite crystals organic matter is present consistently in the dark micriticcarbonate comprising the peloids this organic matter is observed as sub micron at and lamentous mucus like structures inside the interspaces of thehigh mg calcite and ca dolomite crystals and is interpreted as the remains ofdegraded extracellular polymeric substances moreover many fossilizedbacterial cells are associated strictly with both carbonate phases these cellsconsist mainly of 0ae2to4lm in diameter sub spherical rod like and lamentous forms isolated or in colony like clusters the co existence offossil extracellular polymeric substances and bacterial bodies associated withthe polyhedrons of ca mg carbonate implies that the organic matter andmicrobial metabolism played a fundamental role in the precipitation of theminerals that form the peloids by contrast the lack of extracellular polymericsubstances in the aragonitic phase indicates an additional precipitationmechanism the complex processes that induce mineral precipitation in themodern lagoa vermelha microbial mat appear to be recorded in the studiedlithi ed stromatolites sub micron polyhedral crystal formation of high mgcalcite and or ca dolomite results from the coalescence of carbonatenanoglobules around degraded organic matter nuclei sub micron polyhedralcrystals aggregate to form larger ovoidal crystals that constitute peloids subsequent precipitation of aragonitic spherulites around peloids occurs asmicro environmental water conditions around the peloids change keywords bacterial fossils biomineralization microbialite nanoglobules peloids stromatolites

origin of annual laminations in tufa deposits southwest japan abstract laminated tufas and a tufa depositing stream in sw japan shirokawa ehime prefecture were studied monthly over a 3 yr period a series of samples from the tufa clearly reveals the pattern of annual laminations the annual layering pattern was primarily controlled by changes in the rate of calcite precipitation as calculated from water chemistry the concentration of dissolved caco 3 which correlates with the precipitation rate was high in summer autumn and low in winter spring owing to changes in the partial pressure of co 2 in underground air regular seasonal changes in underground pco 2 probably resulted from two temperature dependent processes the diffusion of soil co 2 and the ventilation of underground air these changes in addition to water temperature changes altered the precipitation rate which has a clear seasonal pattern especially in the lower stream the seasonal precipitation rate was high in summer autumn and low in winter spring which is consistent with the seasonal lamination pattern seen in the tufas the textures of collected samples show that the laminations consist of densely calcified summer autumn june october laminae and lightly calcified winter spring november may laminae we infer that the increased precipitation rate stimulated thick calcite encrustation on cyanobacterial filaments to produce the dense textures this interpretation is supported by the lowered organic inorganic carbon production ratio in summer autumn seasonal variations in cyanobacterial assemblages are present but do not reflect the seasonal lamination pattern because the relevant processes are temperature dependent the seasonal lamination pattern at shirokawa is thought to generally apply to other laminated tufas deposited in temperate climates however a reversed pattern can result from local and climatic circumstances dense laminae were deposited in winter near the source of the spring at shirokawa because calcite precipitation was high owing to low underground pco 2 in winter reversed patterns reported from northwestern europe were probably influenced by seasonal rainfall which is reflected in hydrological conditions

genesis of large siliceous stromatolites at frying pan lake waimangu geothermal field north island new zealand lilypad stromatolites up to 3 m long and 1ae5 m wide were found to be actively growing in the shallow marginal waters of frying pan lake and its outflow channel these stromatolites composed of phormidium 90 fischerella and a variety of other microbes develop through a series of distinct growth stages dark green microbial mats cover the floor of the outflow channel and give rise to columns of various sizes and shapes in the shallower marginal waters once the columns reach the water level the mats spread laterally to form a lilypad stromatolite the lilypads are characterized by a raised dark green rim 4 5 mm high that encircles a flat interior covered with a distinctive orange red mat the microbes forming the columns and lilypad plate are being actively silicified the stromatolites are formed of i flat lying phormidium filaments p laminae ii upright filaments of phormidium that are commonly associated with fischerella u laminae and iii mucus diatoms and pyrite framboids m laminae p laminae dominate most of the columns with tripartite cycles of p u to m laminae being found mostly in the upper parts of the stromatolites the transition from the p to u laminae is marked by a change in the growth pattern of the phormidium and branching of fischerella which was probably triggered by a change in environmental conditions in the frying pan lake outflow channel this change may be related to fluctuations in water level and flow rates that are caused by periods of heavy rain seasonal changes long term variations in rainfall and or the unique 40 day hydrological cycle that exists between frying pan lake and inferno crater which is a nearby hydrothermal crater lake

modelling precipitation streamflow processes in karst basin the case of the jordan river sources israel summary a system approach daily precipitation streamflow model was developed for both the base and the surface flow components of large scale karst basins long term streamflow data were separated to baseflow and surface flow using the recursive digital filter method which provides time series for model calibration the hydrological model for karst environment hymke includes attributes to large scale preferential flow that recharge the groundwater and solve the problem of uncorrelated baseflow and surface flow in a karst environment hymke was applied simultaneously to the three major tributaries of the upper catchment of the jordan river which originate in the karstic region of the hermon mountain northern israel it was verified by comparing the calculated surface flow and baseflow with the daily time series of the baseflow separation procedure and demonstrated good agreement of both the surface r2 0 6 and baseflow r2 0 77 components of each stream

reconstructing marine redox conditions for the transition between cambrian series 2 and cambrian series 3 kaili area yangtze platform evidence from biogenic sulfur and degree of pyritization the transition between series 2 and series 3 of the cambrian period was a time of environmental perturbations and biological innovations a generally positive sulfur isotopic composition of sedimentary pyrite with delta s 34 pyrite values between 1 7 and 373 is consistent with a biological origin via reduction of strongly s 34 enriched seawater sulfate no substantial changes in the redox conditions of the water column are discernible from the dop record and the sulfide sulfur isotopic composition is independent of dop in particular an excursion towards less is enriched values immediately preceding the proposed level of the cambrian series 2 to cambrian series 3 transition this level is also characterized by a negative carbonate carbon isotope excursion believed to reflect the transgressive flooding of the shelf with basinal anoxic waters low dop values would suggest that these might have been ferruginous rather than sulfidic c 2013 elsevier b v all rights reserved

semi distributed lumped model of a karst system under active management summary in this paper inverse modeling is used to characterize the regime of a karst aquifer subjected to extensive pumping in a conduit located upstream of its main outlet the systemic approach uses a transfer model that is based on computing the convolution integral of up to several signals e g efficient rainfall pumping to simulate flow rates and groundwater levels in both the karst conduit and the carbonate matrix at the aquifer outlet and in several parts of the catchment area the model is a semi distributed lumped model which simulates the hydrological response of a heterogeneous karst aquifer made up of different hydrologic compartments and is applied to the lez karst system france groundwater is abstracted near the system s major outlet at a higher rate than the low water spring discharge thereby mobilizing stored groundwater during low water periods active management the model s results are very satisfactory especially for the karst system outlet where the water levels are particularly well reproduced the model can also simulate the natural i e non pumping state of the karst system and thereby estimate the impact of active management on the water resource

microbialites of the neoproterozoic beck spring dolomite southern california ancient microbialites reflect interactions between microbial communities and environmental conditions however evaluating the relative roles of microbial community processes and environmental influences on microbialite morphology and internal fabric in the rock record can be challenging the neoproterozoic beck spring dolomite preserves diverse microbialites and thus provides an opportunity to explore the factors that influenced microbialite development locally stromatolitic thrombolitic and composite microbialites are abundant in subtidal to upper intertidal carbonates in the beck spring dolomite thrombolitic and composite microbialites have not been recognized previously in this unit but compose much of the newly defined thrombolitic member stratigraphic relationships demonstrate that these three types of microbialites formed in close spatial and temporal association in subtidal to intertidal environments the relative proportions and distributions of stromatolitic and thrombolitic microbialites vary with depositional environment stromatolitic microbialites dominate in deeper intertidal to subtidal facies whereas thrombolitic textures are more abundant in upper intertidal facies composite microbialites composed of intermingled clotted and laminated textures formed in all environments but are most abundant in intertidal facies the broad environmental distribution of stromatolitic thrombolitic and composite microbialites and the intermingling of textures suggest that laminated and clotted textures reflect diverse microbial community morphologies rather than environmental variations furthermore the ca 750 ma age of thrombolitic microbialites in the beck spring dolomite requires that they formed without the influence of calcimicrobes or metazoans colonizing and grazing the microbial mat surface thus these thrombolites provide further evidence that the biostratigraphic distribution of thrombolites cannot be uniquely attributed to evolution of calcifying and grazing organisms in the earliest cambrian and that older microbial communities were capable of producing clotted textures

lower permian oncolites from south china implications for equatorial sea level responses to late palaeozoic gondwanan glaciation the oncoid bearing chuanshan formation is a regionally extensive carbonate deposit of predominantly asselian to early sakmarian early permian age in south china occupying an area of some 500 000 km2 throughout south china the oncoid bearing horizons are generally stable and broadly comparable in lithology fossil content and the morphology of the oncoid grains four types of microfacies are recognized from the oncolite succession and overall they suggest a moderate to high energy wave agitated shallow marine carbonate platform environment an analysis of the stratigraphic distribution of oncoid grain size density thickness and the bedding structures of the oncolite beds and the number of coating laminae indicate the presence of metre scale cyclothems suggestive of possible high frequency cycles of sea level fluctuation compared to carbonate successions above and below that lack oncolites and in conjunction with evidence from sequence stratigraphic and isotopic geochemical analyses of coeval carbonate deposits in south china and elsewhere the origin of the chuanshan oncolites is linked to a drastic drop in global sea level at the pennsylvanian permian boundary that can be correlated closely in timing with the zenith of the late palaeozoic gondwanan glaciation it is further suggested that the eustatic changes apparent from the deposition of the chuanshan oncolites and similar coeval deposits in lower palaeolatitudes were coupled with and influenced by the contemporaneous high latitude gondwanan glaciation the largest and longest known such event in phanerozoic earth history

textural transition in an aragonite travertine formed under various flow conditions at pancuran pitu central java indonesia abstract a large travertine mound at pancuran pitu central java indonesia displays various types of lamination reflecting different hydrological conditions to understand the geomicrobiological processes of the laminated travertines we investigated the mound s hydrology water chemistry texture microbial composition and volume percentage of carbonate mineral vpc we identified four types of travertines dense travertine 80 vpc flow rate 200 cm s lithified microbial travertine 60 vpc flow rate 70 cm s fragile microbial travertine 30 vpc flow rate 10 cm s and poorly lithified microbial mat

cambrian chronostratigraphy current state and future plans abstract important steps have been made by the international subcommission on cambrian stratigraphy iscs toward global chronostratigraphic subdivision of the cambrian the consensus of opinion is that the system should be subdivided into four series representing subequal spans of time the lower two series will correspond approximately to the traditional lower cambrian the third series will correspond approximately to the traditional middle cambrian and the fourth series corresponds approximately to the traditional upper cambrian the fourth series called the furongian series was ratified by the international commission on stratigraphy ics and the international union of geological sciences iugs in 2003 selection of horizons representing evolutionary events that can be correlated on a global scale and which can be used as stage or series boundaries is much more difficult for the lower two series intervals of the cambrian than it is for the upper two series intervals of the cambrian the most practical concept for subdividing the system into stages involves the establishment of two stages each for the first and second series and the establishment of three stages each for the third and fourth series the lowermost stage of the furongian called the paibian stage has been ratified by the ics and the iugs

crystal fabrics and microbiota in large pisoliths from laguna pastos grandes bolivia large pisoliths from the laguna pastos grandes playa in the bolivian altiplano have a wide diversity of cortical fabrics and variable mineralogical composition the cortical laminae are composed of radial calcite bundles spar calcite micrite amorphous silica mixed micrite amorphous silica quartz gypsum and halite diatoms are common in the outer parts of some radial calcite laminae and amorphous silica laminae but cyanobacterial filaments are rare although the organization of the cortical laminae is highly variable some repetitive sequences of different laminae are present cavities in and between pisoliths contain micrite detrital grains calcite bundles and peloids morphologically similar to those found in marine reefs the pisoliths grow in shallow ephemeral pools fed by hot springs radial bundles of calcite precipitate rapidly by degassing and photosynthetic removal of co2 following spring snowmelt conditions for micrite precipitation are unclear but there is evidence to suggest formation in partially stagnant waters some of elevated salinity amorphous silica laminae precipitate mainly by evaporative concentration quartz may precipitate from warm silica rich spring waters that remain below amorphous silica saturation the evaporite minerals form during desiccation of the pools or from spray the peloids in cavities are probably primary precipitates different types of laminae may form simultaneously in different pools because of the highly variable conditions across the playa lateral migration of spring locations through time has created a complex carbonate silica pavement large spherical pisoliths form in outflow channels near spring orifices and across discharge aprons where waters are several decimetres deep with mineral precipitation channels are filled and become shallow producing discoid pisoliths and crusts in shallow waters and on distal aprons only small pisolith gravels form as spring pools fill with deposits their locations shift laterally new pisoliths form elsewhere or precipitation may recommence on older abandoned pisoliths

formation of silica oncoids around geysers and hot springs at el tatio northern chile siliceous oncoids up to 4 cm in diameter are common on the laterally extensive sinter aprons that surround the spectacular geysers and hot springs at el tatio in northern chile many of these complex oncoids developed close to geyser and spring vents that discharge boiling water internally the oncoids which are composed of precipitated amorphous silica are formed of complex arrays of spicules and concentric laminae as well as detrital volcanic grains spicular growth is dominant in most examples the formation and growth of the spicules and concentric laminae were mediated by a microbial community which included filamentous microbes mucus and possibly bacteria the microbes and mucus were silicified by replacement and encrustation in some laminae the filamentous microbes lay parallel to the growth surface in other laminae most filaments forming the thin mats were suberect amorphous silica precipitated between the filaments occluded porosity and commonly disguised the microbial fabric the oncoids grew on the proximal sinter aprons around the geyser vents and hot spring pools most growth took place subaerially with the silica delivered to the precipitation sites by splashing water from the geysers and or periodic shallow flooding of the discharge aprons unlike silica oncoids at other geothermal sites vertical growth of oncoids that formed in some rimstone pools was not limited by water depth

microbialites in a modern lagoonal environment nature and distribution tikehau atoll french polynesia abstract microbialites including stromatolitic structures gelatinous masses and mats develop in tikehau lagoon tuamotu french polynesia on the flanks and slopes of numerous pinnacles and motu islets between 0 and 25 m deep on coral colonies algal tufts or on lagoonal sediments individual stromatolitic structures consist of hemispherical domes and are produced by monospecific populations of filamentous cyanobacteria belonging to three distinctive phormidium species symploca and possibly to one new species of schizothrix gelatinous masses hanging from the ceiling of caverns are produced by phormidium laysanense microbial mats are well developed at all depths on pinnacle slopes and are produced by either monospecific or mixed cyanobacterial populations the study of micro and ultrastructure of stromatolites reveals that they result both from trapping and binding of sediments and from carbonate precipitation in addition to phototrophic biomineralization pervasive carbonate precipitation occurred in association with decaying organic matter the basic constructional elements of the precipitated carbonate consist of 0 1 0 2 m rounded bodies that form very fine anhedral to subhedral micrite their surfaces comprise extremely small carbonate granules 20 50 nm gradual changes ageing in the ultrastructure of carbonate precipitates include the precipitation of successive euhedral calcite layers around these grains widespread development of microbialites in this pristine lagoonal environment results from rapid blooms of microbial benthic communities possibly induced by temporary and local nutrient pulses nutrients seem to undergo a restricted circulation between the sediment and pinnacle reef frameworks pinnacles and reef islets are repeatedly affected by catastrophic storm events which cause redistribution of sediments and nutrients

nucleation of calcium carbonate on bacterial nanoglobules nucleation of calcium carbonate on microbial cell material may have been the dominant mode of microbial carbonate formation during most of earth s history current knowledge predicts that nucleation takes place on the cell surface or on extracellular polymeric substances however the initial nucleation steps have not been described in detail and the process remains elusive here we describe the bacterial nucleation of calcium carbonate at the nanometer scale in our precipitation experiment with sulfate reducing bacteria srb the bulk of calcium carbonate precipitates on hundreds of individual globules 60 200 nm in diameter globules originate from the srb cell surface but calcify significantly only when released to the culture medium similar globules have been observed albeit at a much larger scale in other bacterial precipitation experiments and in many natural microbial carbonates suggesting that the process we describe could be an important step in microbial calcification

a chronology of paleozoic sea level changes sea levels have been determined for most of the paleozoic era 542 to 251 million years ago but an integrated history of sea levels has remained unrealized we reconstructed a history of sea level fluctuations for the entire paleozoic by using stratigraphic sections from pericratonic and cratonic basins evaluation of the timing and amplitude of individual sea level events reveals that the magnitude of change is the most problematic to estimate accurately the long term sea level shows a gradual rise through the cambrian reaching a zenith in the late ordovician then a short lived but prominent withdrawal in response to hirnantian glaciation subsequent but decreasingly substantial eustatic highs occurred in the mid silurian near the middle late devonian boundary and in the latest carboniferous eustatic lows are recorded in the early devonian near the mississippian pennsylvanian boundary and in the late permian one hundred and seventy two eustatic events are documented for the paleozoic varying in magnitude from a few tens of meters to 125 meters

microbially induced fe and mn oxides in condensed pelagic sediments middle upper jurassic western sicily abstract this article presents a petrographic comparison of the rosso ammonitico facies of western sicily and the original rosso ammonitico veronese of northern italy based on a total of 27 sections the rosso ammonitico has been the subject of numerous controversies that range from bathyal to shallow water platform sedimentation therefore it seemed interesting to verify if the term rosso ammonitico has the same geologic connotation from region to region the middle upper jurassic rosso ammonitico of western sicily is a condensed succession formed during a period of extensional synsedimentary tectonics related to the spreading of the ionian ocean slope to basin or pelagic carbonate deposits characterize the sedimentation which consists of reddish mudstones and wackestones the abundant fauna is composed of radiolarians protoglobigerinids saccocoma bositra associated with ammonites a few ferruginous hardgrounds fe mn oxide crusts and mn coated condensation horizons are also present the red matrices contain abundant fe mn encrusted microbored and bioeroded bioclasts sporadic fe mn oncolites composed of amorphous mn minerals and goethite are also conspicuous the matrix as well as the shells and the fillings of the complex associated veinlets are frequently altered into calcite microsparite submicronic iron bacterial and fungal filaments associated with mineralized extracellular polymeric substances eps are observed in the matrix they record dysaerobic microenvironments at or near the sediment water interfaces early mineralized discontinuities enhanced by subsequent pressure dissolution are reported in the succession mn ni bacterial filaments are exceptionally observed in the cortex of the fe mn oncolites as a consequence of an early lithification the mn filaments are poorly preserved the pigmentation of the rock is due to the dispersion of submicronic oxyhydroxides now goethite and amorphous iron formed by bacterial mediation during early diagenesis in microaerophilitic environments as in the case of the original rosso ammonitico veronese fe and mn bacteria fungi were able to produce bioconstructions which have no bathymetric significance the limiting factor must have been the oxygen content which was low in these very quiet and relatively deep environments thus the rosso ammonitico of northern and southern italy have a number of points in common but some obvious dissimilarities are observed that explain some of the various sedimentological interpretations among them the chemical composition is of particular importance more fe is present in veneto northern italy while mn is associated with the sicilian rosso ammonitico the sicilian localities were more proximal to oceanic magmatic sources which were related to the activity of the oceanic crust

mass occurrence of oncoids at the cambrian series 2 series 3 transition implications for microbial resurgence following an early cambrian extinction abstract the traditional lower middle cambrian transition cambrian series 2 series 3 transition is marked by the first major biotic extinction of the phanerozoic eon this biotic crisis has been arguably linked to changes in ocean chemistry and or marine environments but their casual relationships remain controversial to better understand the microbial responses to paleoceanographic changes across this critical transition we have studied the environmental conditions for mass occurrence of oncoids in the western north china platform oncoids at the lower middle cambrian transition form 1 to 3 m thick massive beds show spherical subspherical morphology and contain 8 14 light dark cortical laminar couplets the light laminae are thicker and contain densely intertwined filamentous cyanobacteria that have calcified sheaths and a prostrate growth pattern the dark laminae are thinner and rich in organic matter relics pyrite framboids and heterotrophic bacteria in most oncoids cortical laminae show the same growth orientation for more than five light dark laminar couplets suggesting much less frequent grain overturning than generally thought both light and dark laminae contain well preserved organomineralization fabrics textures including extracellular polymeric substances epss nanoglobules polyhedrons and micropeloids suggesting oncoid formation in shallow marine environments with high alkalinity and active sulfate reduction the presence of pyrite framboids and heterotrophic bacterial relics implies anoxic dysoxic bottom water conditions stratigraphic correlation indicates that time equivalent oncolites and other microbialites are widespread not only in north china but also in other early cambrian successions globally the mass occurrence of oncoids coincides with the kalkarindji large igneous province of australia a prominent negative 13 c excursion roece or redlichiid olenellid extinction carbon isotope excursion a significant increase in 87 sr 86 sr and a large positive shift in 34 s the coincidence of these events suggests that the early cambrian biotic crisis may have been caused by an ocean anoxic event resulting from enhanced volcanic release of co 2 global warming and increased continental weathering preservation of massive oncolites is likely related to decreased metazoan grazing following an early cambrian biotic crisis during which archaeocyathids and many early cambrian trilobite taxa went to extinction the oncoid mass occurrence provides evidence for the resurgence of microbial life in anoxic dysoxic marine shelf environments concomitant with the early cambrian extinction event

simulation of the development of karst aquifers using a coupled continuum pipe flow model 1 this paper is intended to provide insight into the controlling mechanisms of karst genesis based on an advanced modeling approach covering the characteristic hydraulics in karst systems the dissolution kinetics and the associated temporal decrease in flow resistance karst water hydraulics is strongly governed by the interaction between a highly conductive low storage conduit network and a low conductive high storage rock matrix under variable boundary conditions only if this coupling of flow mechanisms is considered can an appropriate representation of other relevant processes be achieved e g carbonate dissolution transport of dissolved solids and limited groundwater recharge here a parameter study performed with the numerical model carbonate aquifer void evolution cave is presented which allows the simulation of the genesis of karst aquifers during geologic time periods cave integrates several important features relevant for different scenarios of karst evolution 1 the complex hydraulic interplay between flow in the karst conduits and in the small fissures of the rock matrix 2 laminar as well as turbulent flow conditions 3 time dependent and nonuniform recharge to both flow systems 4 the widening of the conduits accounting for appropriate physicochemical relationships governing calcite dissolution kinetics this is achieved by predefining an initial network of karst conduits protoconduits which are allowed to grow according to the amount of aggressive water available due to hydraulic boundary conditions the increase in conduit transmissivity is associated with an increase in conduit diameters while the conductivity of the fissured system is assumed to be constant in time the importance of various parameters controlling karst genesis is demonstrated in a parameter study covering the recharge distribution the upgradient boundary conditions for the conduit system and the hydraulic coupling between the conduit network and the rock matrix in particular it is shown that conduit diameters increase in downgradient or upgradient direction depending on the spatial distribution local versus uniform of the recharge component which directly enters the conduit system

constrained deformable layer tomostatics although first arrival tomography provides an effective waytoestimatenear surfacevelocitiesandstaticcorrections the undulation of velocity interfaces such as the base of the weatheredzonemaynotbeeasilydeterminedbythismethod the main reason is that first arrivals are insensitive to small geometric changes in velocity interfaces because their raypaths tend to traverse along those interfaces to improve the solution of interface geometry we developed a deformable layer tomostatics method that approximates the near surface velocity field as several layers of constant velocity and variablethicknessthatcanbeinvertedforthegeometryofthevelocityinterfaces weuseamultiscalemodelparameterization in the inversion for interface geometry synthetic and field datatestsshowedthatthemethodcandeterminetheinterface geometry constraining the depth range of the basal boundary of the weathered zone increases the convergence rate of the iterative inversion process tests on field data showed greater reflection coherency in a stacked section based on constrainedstaticcorrectionsthaninonefromunconstrained static corrections the method yielded a better match with statics computed from sand dune curves than does a match obtained by using two commercial grid tomography packages

stable isotope geochemistry of the lower cambrian sekwi formation northwest territories canada implications for ocean chemistry and secular curve generation abstract three curves delineating 13 c variations across the early cambrian sekwi formation carbonate ramp mackenzie mountains northwest territories canada are incorporated into a biostratigraphic and sequence stratigraphic framework that provides a higher resolution temporal and spatial framework for the sekwi formation the three 13 c curves were correlated across a range of depositional environments from tidal flat to deep subtidal on the sekwi carbonate ramp eight 13 c cycles in the curves a h were correlated across the basin complimenting the sequence stratigraphic framework the most complete 13 c curve from the sekwi formation correlates well with a composite early cambrian 13 c curve from the siberian platform however the differing magnitude and absolute timing of some of the correlative isotopic excursions records the influence of regional tectonism sea level changes and diagenesis on the sekwi ramp additionally the sekwi formation 13 c curve has more high frequency variations than the siberian curve due in part to the higher sample density used to construct the sekwi curve the early middle cambrian boundary was not sampled in this study but a large negative isotopic excursion in the very latest early cambrian coincides with a regional drowning that may be correlative throughout western laurentia but recognizing this event globally is problematic

multiple δ13c excursions spanning the cambrian explosion to the botomian crisis in siberia new high resolution 13 c data through the lower cambrian of siberia reveal multiple positive excursions coincident with phases in the explosion of invertebrate phyla nemakit daldynian to middle botomian stages comparison of the 18 o and trace element mg fe mu sr chemistry indicate that six new 13 c cycles are primary rather than diagenetic features with potential for global correlation positive 13 c excursions up to 3 indicate that fractional organic carbon burial rates were high but variable through the cambrian explosion values for 13 c dropped sharply from around 2 2 to 1 6 in botomian time coincident with mass extinction of the archaeocyathan reef biota the rapid fluctuation of the 13 c signal and the temporal coincidence of the pronounced negative shift with the extinction event hint that the 13 c record may record productivity variations during the early cambrian radiation

pyrite morphology and redox fluctuations recorded in the ediacaran doushantuo formation abstract recent geochemical studies of the doushantuo formation ca 635 551 ma in south china suggested that the ediacaran ocean was strongly stratified with an oxic surface layer above a euxinic wedge that was sandwiched within ferruginous deep waters this ocean redox model however was derived largely from the data obtained from stratigraphic sections in the yangtze gorges area that according to recent paleogeographic reconstruction were deposited in a restricted intrashelf lagoon in order to test the redox conditions in open ocean deep water environments we have conducted a detailed morphological analysis of authigenic pyrites from the upper to lower slope sections of the doushantuo formation in analogy to modern euxinic basins such as the black sea framboidal pyrites with smaller and less variable size distribution are taken as evidence for sulfide precipitation in euxinic water column while larger and more variable framboidal and euhedral pyrites are formed or diagenetically altered in sediments with an overlying oxic dysoxic water column except for a few brief intervals pyrites from the doushantuo formation in upper slope sections siduping and taoying sections are mainly of early diagenetic origin and do not record water column euxinia during deposition in contrast pyrites from the doushantuo formation in the lower slope section wuhe section are dominated by fine grained framboids indicative of pervasive water column euxinia below chemocline in both upper and lower slope sections temporal changes in genetic pyrite types occur at centimeter to decameter scales suggesting frequent chemocline fluctuations the overall decrease in abundance of framboidal pyrites toward the upper doushantuo formation in upper slope sections suggests increasing water column oxygenation and deepening of the chemocline macroalgae and metazoan fossils are found mainly from shale intervals without syngenetic pyrites in upper slope sections indicating the sensitivity of macroscopic eukaryotes to the ocean chemocline the redox fluctuations recorded by the doushantuo pyrites compels for comprehensive geochemical data in deep water successions to further test the existing paleoceanographic models of the ediacaran ocean