surface area control of shallow cratonic to deep marine carbonate accumulation sites of calcium magnesium carbonate accumulation have been shifting from shallow shelf to deep marine settings since the late cretaceous during this time total area of flooded epicratonic shelf has decreased about 50 and areas of shelf carbonate deposition have declined from 27 106 km to present areas of 1 4 106 km while the maximum extent of platform carbonate accumulation has decreased from about 50 to 28 north latitude in terms of cratonic carbonate this decrease in tropical shelf area has resulted in a sixfold reduction in shoal water limestone accumulation from a cretaceous rate of 0 6 km m y to a present value of about 0 1 106 km m y over the same time period the global carbonate compensation depth has deepened by about 1 5 km attendant with a threefold areal increase of calcite ooze depositionn 40 to 130 106 km this expansion has resulted in an eightfold increase in pelagic limestone accumulation from a cretaceous rate of 0 05 106 km m y to a present rate of about 0 4 106 km m y transfer of accumulation from shallow cratonic to deep marine depositional settings records the central role of sedimentary environment surface area in predicating the differential partitioning of finite carbonate fluxes to phanerozoic global oceans

paleolatitude distribution of phanerozoic marine ooids and cements opdyke b n and wilkinson b h 1990 paleolatitude distribution of phanerozoic marine ooids and cements palaeogeogr palaeoclimatol palaeoecol 78 135 148 data on 493 phanerozoic marine ooid and cement occurrences indicate that the dominance of calcite versus aragonite in tropical marine settings has changed in response to variation in atmospheric co2 and or oceanic temperature gradient holocene ooid and cement precipitation occurs over similar latitudes with means centered around 24 and 28 respectively aragonite and calcite also display roughly comparable distributions with average occurrences between 25 and 28 surface seawater saturation values requisite for ooid cement carbonate precipitation are at least 3 8 rs for aragonite and 3 4 a s for calcite ancient ooid cement occurrences vary in space and time with depositional zones generally closer to the equator during continental emergence greatest extent correlates with periods of maximum transgression aragonite formation is favored in more equatorial localities than calcite when cement ooid distributions are narrow and continents are emergent similarity of latitude distribution of marine ooids cement and biogenic carbonate suggests that physicochemical processes that control levels of carbonate saturation were more important in predicating sites of limestone accumulation in phanerozoic seas than biological processes related to net productivity of various carbonate platform communities continental position and tropical shelf area available for carbonate accumulation dictates the relative abundance of shallow water inorganic carbonate precipitates in space and time

paleobotanical evidence for near present day levels of atmospheric co2 during part of the tertiary understanding the link between the greenhouse gas carbon dioxide co 2 and earth9s temperature underpins much of paleoclimatology and our predictions of future global warming here we use the inverse relationship between leaf stomatal indices and the partial pressure of co 2 in modern ginkgo biloba and metasequoia glyptostroboides to develop a co 2 reconstruction based on fossil ginkgo and metasequoia cuticles for the middle paleocene to early eocene and middle miocene our reconstruction indicates that co 2 remained between 300 and 450 parts per million by volume for these intervals with the exception of a single high estimate near the paleocene eocene boundary these results suggest that factors in addition to co 2 are required to explain these past intervals of global warmth

an oscillating trend in phanerozoic non skeletal carbonate mineralogy textural and compositional data on ancient ooids and cements suggest the existence of an oscillating phanerozoic temporal trend in non skeletal carbonate mineralogy the trend shows good correlation with eustatic climatic oscillations proposed by others the most likely mechanism appears to be plate tectonically influenced oscillations in pco2 the vapour pressure of co2 rather than change in oceanic mg ca ratio

relative precipitation rates of aragonite and mg calcite from seawater temperature or carbonate ion control the temperature and degree of carbonate mineral supersaturation co3 2 ion concentration of seawater are the two most likely controlling variables on the compositions of recent marine carbonate cements the relative importance of these variables is difficult to assess in nature because they have similar trends with depth 0 1500 m and latitude in modern oceans we carried out laboratory experiments to investigate the relative growth rates of calcite mg calcite and aragonite in seawater as functions of both temperature 5 25 and 37 c and of carbonate ion concentration 2 5 to 15 times supersaturated with respect to calcite the precipitation rates of aragonite relative to those of calcite increase strongly with increasing temperature and are not affected greatly by changes in saturation state at 5 c calcite precipitation rates are nearly equivalent to those of aragonite regardless of the degree of saturation at both 25 and 37 c aragonite precipitation rates are much more rapid than those of calcite up to a factor of 4 except at very low saturation states calcite compositions vary from less than 5 mol mgco3 at 5 c to 14 mol mgco3 at 37 c our results suggest that the well documented shift toward precipitation of lower mol mg calcite and the decrease in abundance of aragonite cements with increasing oceanic depth and latitude can be attributed largely to lower temperatures

giant holocene freshwater microbialites laguna bacalar quintana roo mexico with more than 10 km of total length holocene microbialites in laguna bacalar mexico belong to the largest freshwater microbialite occurrences microbialites include domes ledges and oncolites domal forms can grow to diameters and heights of 3 m microbialites are composed of low magnesium calcite which is to a large extent precipitated due to the metabolic activity of the cyanobacteria homeothrix and leptolyngbya and associated diatoms photosynthesis removes carbon dioxide and triggers carbonate precipitation also an elevated carbonate concentration in lagoon waters derived from dissolution of cenozoic limestone in a karst system supports carbonate precipitation trapping and binding of detrital grains is also observed but is not as common as precipitation bacalar microbialites are largely thrombolitic however stromatolitic sections occur as well the bulk of bacalar microbialites probably formed in the late holocene ca 1 kyr bp until present according to 14c dating microbialites accreted 9 to 8 cal kyr bp however these ages may be too old as a result of a strong hard water effect this effect is seen in 14c ages of living bivalve and gastropod mollusc shells from bacalar lagoon which are 8 to 7 cal kyr bp the modern associated fauna of microbialites is characterized by low diversity and high abundance of the bivalve mollusc dreissena sp and the gastropod pomacea sp the abundant grazing gastropods presumably hamper modern microbialite formation a comparison of bacalar microbialites with other modern microbialite occurrences worldwide shows only a few patterns sizes shapes microbial taxa mineralogy type of accretion and settings including water properties of microbialite occurrences exhibit high variability a trend may be seen in the grazing metazoa which are rare to absent in the marine and brackish examples but apparently present in all the freshwater occurrences of microbialites also freshwater examples are usually characterized by elevated concentrations of carbonate and or calcium ions in the surrounding waters

aragonite calcite seas quantifying the gray area oscillations between the dominance of aragonite and calcite in abiotic marine caco3 precipitates throughout earth history are closely coupled with the evolution of earth s seawater composition and represent the environmental context in which organisms evolved their ability to biomineralize the most important factor controlling these phanerozoic oscillations in caco3 polymorph composition is the ratio of mg ca in seawater which is thought to separate aragonite and calcite precipitation along a distinct temperature controlled threshold a sharp threshold however is contradicted by overlapping aragonite and calcite precipitation fields at a range of experimental conditions here we present experimental data that enable us to quantify the proportions of caco3 polymorphs as a function of mg ca ratio and temperature this allows us to convert published mg ca ratio proxy data and models of the phanerozoic mg ca ratio into proportions of abiotic caco3 polymorphs at a given temperature and thus provides a temperature corrected view of aragonite calcite sea conditions in this revised view abiotic calcite precipitation was inhibited during aragonite sea intervals at temperatures above 20 c whereas calcite sea intervals were characterized by the co precipitation of aragonite and calcite in environments above 20 c this continuous prominence of aragonite precipitation in phanerozoic warm water environments explains the phanerozoic increase of aragonite over calcite skeletal composition in calcifying organisms

microbial carbonates the geological record of the calcified bacterial algal mats and biofilms summary deposits produced by microbial growth and metabolism have been important components of carbonate sediments since the archaean geologically best known in seas and lakes microbial carbonates are also important at the present day in fluviatile spring cave and soil environments the principal organisms involved are bacteria particularly cyanobacteria small algae and fungi that participate in the growth of microbial biofilms and mats grain trapping is locally important but the key process is precipitation producing reefal accumulations of calcified microbes and enhancing mat accretion and preservation various metabolic processes such as photosynthetic uptake of co2 and or hco3 by cyanobacteria and ammonification denitrification and sulphate reduction by other bacteria can increase alkalinity and stimulate carbonate precipitation extracellular polymeric substances widely produced by microbes for attachment and protection are important in providing nucleation sites and facilitating sediment trapping microbial carbonate microfabrics are heterogeneous they commonly incorporate trapped particles and in situ algae and invertebrates and crystals form around bacterial cells but the main component is dense clotted or peloidal micrite resulting from calcification of bacterial cells sheaths and biofilm and from phytoplankton stimulated whiting nucleation interpretation of these texturally convergent and often inscrutable fabrics is a challenge conspicuous accumulations are large domes and columns with laminated stromatolite clotted thrombolite and other macrofabrics which may be either agglutinated or mainly composed of calcified or spar encrusted microbes stromatolite lamination appears to be primary but clotted thrombolite fabrics can be primary or secondary microbial precipitation also contributes to hot spring travertine cold spring mound calcrete cave crust and coated grain deposits as well as influencing carbonate cementation recrystallization and replacement microbial carbonate is biologically stimulated but also requires favourable saturation state in ambient water and thus relies uniquely on a combination of biotic and abiotic factors this overriding environmental control is seen at the present day by the localization of microbial carbonates in calcareous streams and springs and in shallow tropical seas and in the past by temporal variation in abundance of marine microbial carbonates patterns of cyanobacterial calcification and microbial dome formation through time appear to reflect fluctuations in seawater chemistry stromatolites appeared at 3450 ma and were generally diverse and abundant from 2800 to 1000 ma inception of a proterozoic decline variously identified at 2000 1000 and 675 ma has been attributed to eukaryote competition and or reduced lithification thrombolites and dendrolites mainly formed by calcified cyanobacteria became important early in the palaeozoic and reappeared in the late devonian microbial carbonates retained importance through much of the mesozoic became scarcer in marine environments in the cenozoic but locally re emerged as large agglutinated domes possibly reflecting increased algal involvement and thick micritic reef crusts in the late neogene famous modern examples at shark bay and lee stocking island are composite coarse agglutinated domes and columns with complex bacterial algal mats occurring in environments that are both stressed and current swept products of mat evolution ecological refugia sites of enhanced early lithification or all three

temporal variation in calcification in marine cyanobacteria periods of widespread abundance of calcified cyanobacteria in marine environments are here termed cyanobacterial calcification episodes cces intense such episodes occurred in the cambrian early ordovician late devonian and mid late triassic mild episodes occurred during the early carboniferous and jurassic early cretaceous possible episodes during parts of the silurian and permian await confirmation cyanobacterial calcification is not obligate but is dependent upon environmental factors favouring carbonate precipitation cyanobacterial calcification episodes are therefore interpreted as reflecting periods of increased marine carbonate precipitation this is supported by the general abundance of marine carbonate cements and oolites during cyanobacterial calcification episodes cyanobacterial calcification episodes correspond with phanerozoic periods for which elevated global temperatures have been inferred they do not appear to correlate closely with inferred changes in aragonite calcite facilitation the sandberg curve and p co2 through time it is concluded that variations in the precipitation rates of abiotic and quasi abiotic marine carbonates through time have been controlled primarily by temperature the mineralogy of these precipitates appears instead to have been mainly influenced by p co2 and the mg ca ratio also linked to sea level through plate tectonic processes thus the controls on rate and mineralogy of precipitation were independent of one another

the concept of joint saturation and its application two of the major joint driving mechanisms are joint normal stretching and poroelastic shrinkage and these lead to joint sets commonly associated with structural bending and natural hydraulic fracturing respectively regardless of joint driving mechanism joint infilling is a nonhomogeneous poisson process in the presence of stress shadows through probability modeling we show that in all cases joint spacing is best fit with gamma distributions the shape parameter of the best fit gamma distribution to joint spacing data is a quantitative means to assess the extent of saturation which is represented in a new parameter the joint saturation ratio jsr to test the utility of jsr we call upon published structural bending joint data elk basin lilstock and rives plate bending experiment the shape parameters for these well developed structural bending joints are equal to around three corresponding to a jsr of approximately 30p using the same analysis on the spacing of natural hydraulic fractures collected from outcrops in the gas prone devonian sections of the appalachian basin we find that natural hydraulic fractures differ in two aspects from structural bending joints first the joint spacing is proportional to bed thickness in bedded rocks but not in gas shale sections second the joint saturation of natural hydraulic fractures is generally lower than in well developed structural bending joints thus the jsr is a means to distinguish the joint driving mechanism and to represent joint saturation level independent of bed thickness effects it can be used to distinguish natural fractures from drilling induced fractures and to improve the fracture network modeling

early middle triassic stromatolites from the luoping area yunnan province southwest china geobiologic features and environmental implications abstract an early middle triassic stromatolite deposit is documented from the guanling formation of the luoping area yunnan sw china the luoping stromatolite shows five types of constructional microbial forms in various magnifications 1 typical stratified columnar structures up to 20 cm high with crinkled laminae dark coloured laminae 1 mm thick are composed of upright filamentous tubes averagely 29 4 m in diameter showing a vertical growth fabric 2 laminoid fenestrae 0 5 1 mm wide and 3 prostrate filaments which are reflected by strong fluorescence in sharp contrast to dolomite cement in fluorescent images 4 rod like aggregates 4 6 18 m in diameter composed of minute dolomite rhombs are very common in stromatolitic laminae they resemble present day cyanobacterial trichome and thus may represent putative fossilized cyanobacteria 5 moreover small pits coccoid like spheroids calcified biofilms and fibrous structures are also common in stromatolitic laminae the last two may represent calcified extracellular polymeric substances eps that contributed to the development and lithification of stromatolites authigenic quartz grains are common and may also have involved biological processes in stromatolite formation of these microbial functional groups driving accretion and lithification processes of stromatolite documented in literature both lithified cyanobacteria oxygenic phototrophs and possible sulfate reducing bacteria srb which induced microbial formation of dolomite and contributed to the accretion of the luoping stromatolite are suggestive of biogenic origin the luoping stromatolite differs from the permian triassic boundary microbialites ptbms in having abundant filamentous structures and growing in an oxic marine environment both sedimentary facies analysis and abundant fossilized cyanobacteria may indicate proliferation of oxygenic phototrophs in a normal oxic habitat during the middle anisian early middle triassic a period when hospitable environments coupled with biotic diversification prevailed in south china and set an agenda for the full recovery of marine ecosystems in middle late anisian however the post extinction stromatolites and other anachronistic facies are not necessarily indicative of anoxic or oxic conditions and their environmental settings are much more complex than previously thought

upper lower triassic stromatolite from anhui south china geobiologic features and paleoenvironmental implications abstract widespread stromatolites and other microbialite deposits characterize lower triassic marine successions worldwide this study documents a stromatolite deposit 1 1 m thick from the upper spathian lower triassic of the susong area south china the stromatolite comprises distinct laminated domes in the basal part and columns at the upper part dark laminae are loosely spaced and interlayered with thicker light colored laminae diffusive dark colored laminae are composed of peloidal micrite that grade locally into microclotted structures and yield copies of bacteria clump like and coccoid like spheroid aggregates the former are characterized by cloudy micrite nuclei rimmed by coarse grained euhedral sparry calcite crystals while the latter are comprised of solid calcite crystal nuclei coated with rather thin micrite envelopes the cloudy micrite nuclei resemble bacteria clump like structures observed in present day travertine both the coccoid like spheroids and bacteria clump like structures are surrounded by coarse grained euhedral calcite crystals suggesting a similar accretion mechanism both spherical structures therefore could be crucial in the accretion of the susong stromatolite the laminated microclotted structures are interpreted as the result of variation in timing of lithification relative to the timing of the decay of microbes micro analysis also unravels the common occurrence of authigenic micro quartz crystals in association with fe bearing illite clay minerals in the stromatolite columns their coalescing nature with each other together with the associated pyrite grains strongly support the formation of micro quartz crystals from microbial reduction of an fe bearing smectite precursor by sulfate reducing bacteria a comparison of the susong stromatolite with its counterparts from the upper lower triassic strata in dajiang south china reveals many similarities in stromatolite microstructures suggesting that a harsh euxinic anoxic environment resulting in the bloom of sulfate reducing bacteria most likely extended into the latest spathian in south china

development of phylloid algal carbonate mounds during regression expanding the build and fill model abstract the build and fill model for mixed carbonate clastic systems was originally developed to explain thin widespread icehouse depositional sequences that maintain more or less equal thickness over wide areas despite complex internal architecture that includes both topography building and topography filling depositional phases lithologic heterogeneity in each small scale sequence is driven largely by carbonate deposition providing localized relief above surrounding sediment and the eventual infilling of that relief by siliciclastics or a combination of carbonates and siliciclastics phylloid algal carbonate mounds are a critical component of these small scale sequences cyclothems during the late paleozoic ice age pennsylvanian permian and have been ascribed to both relief building and relief filling phases of build and fill which hinders the use of this model as a predictor of lithofacies distribution and geometry and limits its broader application to other carbonate mound settings this study includes detailed remapping of upper pennsylvanian outcrop and subsurface strata over roughly 3 000 km 2 of northeastern kansas which includes the type strata for the paleozoic example of the original build and fill model the dominant depositional motif for the phylloid algal lithofacies is that of relief builder with only moderate relief filling as carbonate mounds switched from aggradation to progradation during continued regression phylloid algal lithofacies in the iola wyandotte farley and plattsburg cyclothems upper missourian stage were predominantly aggradational and developed mound geometries relief building during regression as the base of the photic zone fell to a position low enough to encourage red and green algae dominated typically micritic bafflestone lithologies to develop on pre existing topographic highs as accommodation space continued to decrease mound development switched from aggradational to progradational before further regression brought nearshore shales into the basin which filled in bathymetric lows produced between adjacent mounds the revisions to build and fill presented here serve to expand the model and highlight the influence that the dominant relief building mechanism frame building binding vs baffling sequence stratigraphic position transgression vs falling stage and interplay between antecedent topography and rate of sea level rise and fall can have on interpretation of these mixed carbonate clastic depositional systems relief building can occur during both transgression and regression relief filling is largely limited to regression the timing of relief building within each sequence tst vs fsst is a result of the interplay between the dominant relief building organisms basin and or slope geometry pre existing accommodation space i e water depth vs antecedent topography and the rates of relative sea level rise and fall

carbonate deposition climate stability and neoproterozoic ice ages the evolutionary success of planktic calcifiers during the phanerozoic stabilized the climate system by introducing a new mechanism that acts to buffer ocean carbonate ion concentration the saturation dependent preservation of carbonate in sea floor sediments before this buffering was primarily accomplished by adjustment of shallow water carbonate deposition to balance oceanic inputs from weathering on land neoproterozoic ice ages of near global extent and multimillion year duration and the formation of distinctive sedimentary cap carbonates can thus be understood in terms of the greater sensitivity of the precambrian carbon cycle to the loss of shallow water environments and co 2 climate feedback on ice sheet growth

a diverse calcified cyanobacteria assemblage in the latest ediacaran abstract a three dimensionally preserved phosphatized cyanobacterial fossil assemblage tentatively identified as a distinct calcified cyanobacterial combination of oscillatorialeans and rivulariacean is recognized in the latest ediacaran in the southern shaanxi province china based on the morphological and preservation modes oscillatorialean cyanobacteria herein contain 3 genera which are girvanella obruchevella and subtifloria with thin walled tubes tangled coiled or aligned a kind of fan shaped fossils composed of filaments with tapered trichomes and pseudo branches cambricodium is clarified as calcified rivulariacean cyanobacteria prosperous calcified cyanobacteria co occurring with the earliest mineralized skeletal tubular fossils cloudina and sinotubulites in addition to contributing new morphological and preservation information the discovery of these cyanobacteria perhaps strengthens the case for prosperity in cyanobacterial calcification in the terminal neoproterozoic

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

initial assessment of the carbon emission rate and climatic consequences during the end permian mass extinction numerous lines of geochemical and stable isotopic evidence indicate that the end permian mass extinction was accompanied by abrupt climate change induced by co2 addition catastrophic end permian siberian volcanism may have released a large amount of co2 into the atmosphere and pushed the earth s system beyond a critical threshold causing the mass extinction however the injection rate total amount and source of co2 are largely unknown we conducted a suite of simulations using the recently published carbon isotope records and u pb ages from meishan section in zhejiang province china an earth system model of intermediate complexity cgenie http www genie ac uk was used to extract the pattern of co2 release needed to replicate the observed carbon isotope excursion across the permian triassic boundary this analysis leads us to suggest that the source of co2 must have been significantly heavier than typical biogenic or thermogenic methane to explain the significant warming that occurred during and after the extinction event nevertheless as with the paleocene eocene thermal maximum end permian rates of co2 addition were likely small compared with modern fossil fuel burning but considerably more protracted such that the likely total co2 emitted significantly exceeded the modern fossil fuel reserves peak emission rates corresponded to the onset of the maximum extinction interval consistent with carbon cycle disruption including volcanogenic co2 induced warming and perhaps ocean acidification as a trigger for the end permian mass extinction

cryptic biostalactites in a submerged karst cave of the belize barrier reef revisited pendant bioconstructions cemented by microbial micrite abstract microbial carbonates are important components of postglacial tropical coral reef frameworks curious calcium carbonate protrusions in a submarine karst cave in the belize barrier reef platform were initially interpreted as being largely the product of physicochemical precipitation around a meshwork of serpulid tubes new petrographical mineralogical geochronological and inorganic and organic geochemical data suggest that sulfate reducing bacteria played a substantial role in carbonate formation just as in cryptic settings of other modern tropical coralgal reefs the bacterial involvement in carbonate authigenesis is indicated by the content and isotopic composition of carbonate associated sulfate the presence of non isoprenoidal sn 1 mono o alkyl glycerol monoethers mages and terminally branched fatty acids and the observation that the majority of molecular fossils assigned to sulfate reducing bacteria are tightly associated with the carbonate mineral lattice the carbonate protrusions that were formerly named pseudostalactites are termed biostalactites here to underline the significance of biological activity during carbonate formation the belize biostalactites are composed of four carbonate phases including serpulid tubes lithified sediment and microbial carbonate as well as unconsolidated sediment usually found in macroborings of bivalve molluscs lithified sediment and microbial carbonate are fine grained with clotted mottled and peloidal textures while serpulid tubes are aragonitic lithified sediment and microbial carbonates are mixtures of high magnesium calcite and aragonite magnesium calcite content increases with increasing consolidation lithified sediment and microbial carbonate are interpreted as fine biodetrital sediment that was subsequently cemented by authigenic micrite scalenohedral high magnesium calcite and acicular aragonite cements played a subordinate role in cementation carbon and oxygen stable isotope ratios of lithified sediment and microbial carbonate exhibit similar ranges as modern reefal microbialites our study exemplifies that heterotrophic bacteria can be a crucial agent that contributes to the formation of carbonate build ups by cementing skeletal frameworks in cryptic environments

stromatolite decline a reconsideration the prevailing concept of phanerozoic stromatolite decline is considered too simplistic changes in stromatolite character and proportion to other lithologies after the precambrian can be explained as responses to substrate competition and changing sedimentological conditions caused by the evolution of skeletal metazoans grazing pressure was likely insignificant as a limiting factor

environmental covariation of metazoans and microbialites in the lower ordovician boat harbour formation newfoundland abstract an antagonistic view of the relationship between microbialites and metazoans has long been inferred in part because of the large scale anticorrelation of these two groups through geologic time the nexus of this relationship occurs in the early paleozoic era stromatolites declined in abundance as complex animals and algae diversified but thrombolites a type of microbialite little known before the proterozoic cambrian boundary proliferated for the first time well preserved parasequences in the basal portion of the lower ordovician boat harbour formation western newfoundland contain a succession of stromatolites and thrombolites that permit an investigation into the role metazoans played in shaping the nature and abundance of microbialites in early paleozoic carbonate seas sessile benthic animals colonized thrombolite surfaces but are nearly absent from stromatolites bioturbation rarely co occurred with microbialites but is widespread in clastic carbonates that lack microbialites our results thus support the hypothesis of ecological antagonism between microbial communities and motile benthic animals but also demonstrate biological facilitation between thrombolites and both sessile benthic animals and nekton

glacial to holocene redistribution of carbonate ion in the deep sea we have reconstructed the glacial age distribution of carbonate ion concentration in the deep waters of the equatorial ocean on the basis of differences in weight between glacial and holocene foraminifera shells picked from a series of cores spanning a range of water depth on the western atlantic s ceara rise and the western pacific s ontong java plateau the results suggest that unlike today s ocean sizable vertical gradients in the carbonate ion concentration existed in the glacial age deep ocean in the equatorial pacific the concentration increased with depth and in the atlantic it decreased with depth in addition the contrast between the carbonate ion concentration in deep waters produced in the northern atlantic and deep water in the pacific appears to have been larger than in today s ocean

accumulation rates of carbonate platforms the growth potential of carbonate platforms i e the maximum rate at which they can aggrade vertically is difficult to assess to estimate the growth potential from the conservative side and search for variations with time we have compiled published accumulation rates from the phanerozoic accumulation rates vary in a pattern with maximum rates up to 200 m ma or more not corrected for compaction in the late devonian permian late triassic late jurassic and mid cretaceous separated by intervals of reduced rates e g carboniferous early jurassic and late cretaceous the most dramatic drop occurs at the permo triassic boundary after which there is no documented platform growth this pattern resembles the evolutionary rhythm of bloom and demise of reefs and reef builders the observed maximum accumulation rate of 200 m ma over 10 6 10 7 yr is probably imposed by the maximum rate of long term relative sea level rise on passive margins the most favorable site for carbonate platform deve

development of middle cambrian leiolitic bioherms dominated by calcified microbes a case study of the xinji section north china platform abstract among the varieties of microbial carbonate rocks leiolites are rare in ancient rock records and have only few examples in the modern environment which makes them difficult to study this study documents the sedimentary environment characteristics and composition of microbial carbonates dominated by calcified microbes which developed in the cambrian miaolingian xuzhuang formation on the north china platform the upper part of the formation in the xinji section of lushan city henan province is bounded by a drowning unconformity surface of a third order depositional sequence beside the development of an ooid shoal in response to sea level fall a bioherm dominated by leiolite also developed in the upper part of the xuzhuang formation these leiolites represent special sedimentary phenomena due to their occurrence with high energy ooid shoals microscopically they are characterized by abundant calcified cyanobacteria fossils such as dichotomous branching epiphyton and filamentous cyanobacteria thus showing the diversity and complexity of the cyanobacterial microbial mats that predominate the leolitic bioherm four groups are confirmed for epiphyton based on the morphological characteristics of calcified filaments the filamentous cyanobacteria can be divided into girvanella and subtifloria and their possible forming mechanisms are discussed the macroscopic and microscopic characteristics of the current leiolites provide important research clues and typical examples for understanding the origin of the miaolingian leiolitic bioherm and its paleoenvironmental significance

3d simulation of vajont disaster part 1 numerical formulation and validation abstract this work presents a numerical method for the simulation of landslides generated impulse waves and its application to the historical vajont case study the computational tool is based on the particle finite element method pfem a lagrangian strategy that combines the finite element solution of the governing equations with an efficient remeshing strategy to deal with large deformation problems after presenting the numerical formulation different landslide impulse wave problems with froude number ranging from 0 5 to 2 8 are analyzed to validate the proposed methodology the computational method is shown to be able to reproduce accurately the landslide runout the momentum transfer between the sliding material and the impounded water and the consequent wave propagation observed in experimental physical models then the pfem model is applied to the numerical simulation of the vajont disaster which is analyzed with a fully resolved three dimensional model the numerical results are discussed and compared to the post event observations and the numerical results of other computational methods the results in terms of landslide velocity and runout geometry of the deposit maximum water runup dam overtopping wave and water discharge in the downstream valley are in good agreement with observations and reconstructions the calibration and validation performed for this study form the basis for the pfem analyses presented in a companion paper finalized to simulate different scenarios of the vajont rockslide considered in the experimental tests done a year before the disaster

high resolution carbon isotope changes in the permian triassic boundary interval chongqing south china implications for control and growth of earliest triassic microbialites abstract high resolution 13 c carb analysis of the permian triassic boundary ptb interval at the laolongdong section beibei near the city of chongqing south china encompasses the latest permian and earliest triassic major facies changes in the south china block scb microbialites form a distinctive unit in the lowermost 190 cm above the top of the changhsing formation latest permian at laolongdong comparable to a range of earliest triassic sites in low latitudes in the tethyan area the data show that declining values of 13 c carb well known globally began at the base of the microbialite high positive values 3 to 4 ppt of 13 c carb in the late permian are interpreted to indicate storage of 12 c in the deep waters of a stratified ocean that was released during ocean overturn in the earliest triassic contributing to the distinctive fall in isotope values this interpretation has been stated by other authors and is followed here the 13 c carb curve shows fluctuations within the microbialite unit which are not reflected in the microbialite structure comparisons between microbialite branches and adjacent micritic sediment show little difference in 13 c carb demonstrating that the microbialite grew in equilibrium with surrounding seawater the early triassic microbialites are interpreted to be a response to upwelling of bicarbonate rich poorly oxygenated water in low latitudes of tethys ocean consistent with current ocean models for the ptb interval however the decline of 13 c carb may be due to a combination of processes including productivity collapse resulting from mass extinction return of deep water to ocean surface oxidation of methane released from methane hydrate destabilisation and atmospheric deterioration nevertheless build up of bicarbonate rich anoxic deep waters may be expected as a result of the partial isolation of tethys due to continental geography release of bicarbonate rich deep water by ocean upwelling in the earliest triassic may have been an inevitable consequence of this combination of circumstances

environmental change during the triassic jurassic boundary interval of an equatorial carbonate platform sedimentology and chemostratigraphy of the ghalilah formation united arab emirates abstract the sedimentology and chemostratigraphy 13ccarb 13corg sr concentrations of the triassic jurassic tr j boundary interval has been investigated in detail in sections of the ghalilah formation exposed in wadi ghalilah wadi milaha and wadi naqab northeastern united arab emirates the sequence of events recorded across the tr j boundary interval in ras al khaimah reflects significant environmental change that can ultimately be related to camp volcanism uppermost triassic limestones of the sumra member rich in coral calcareous sponges and large size bivalves are interbedded with siliciclastic mudstones and deposited in an open lagoonal environment these are abruptly followed by oolites with intercalated calcareous mudstones of the sakhra member that are devoid of macrofossil thrombolitic microbialites that occur in the lowermost sakhra member are interpreted to reflect the demise of hypercalcifying marine biota during the tr j boundary interval the oolites of the sakhra member are capped by a subaerial exposure surface followed by peritidal deposits of the shuba member the available sparse biostratigraphic data of the ghalilah formation are critically discussed and support a position of the tr j boundary at the base of the sakhra member a negative excursion in 13corg occurs in the upper sumra member and possibly correlates with the late triassic spelae carbon isotope event the 13ccarb and 13corg values increase across the boundary interval and an extended positive excursion in 13ccarb occurs in the oolites of the sakhra member sr concentrations increase in the bioclastic limestones of the uppermost sumra member and peak in the oolites of the upper sakhra member high sr concentrations also occur at correlative stratigraphical levels in the lombardy basin italy and are interpreted as an early hettangian seawater signal reflecting the global scale reduction of biological aragonite precipitation and an increased continental weathering flux

provenance of microcrystalline carbonate cement in limestone marl alternations lma aragonite mud or molluscs aragonite derived from marine molluscs is evaluated as the source for microcrystalline carbonate cements of limestone marl alternations lma calculations demonstrate that extremely low levels of mollusc derived aragonite well below the production rates of molluscs in modern marine settings could have provided sufficient carbonate to cement examples of ordovician silurian and jurassic lma in non tropical or tropical settings it is likely that even in the palaeozoic molluscs provided sufficient carbonate entirely to source microcrystalline cements of lma autochthonous molluscan aragonite is the only viable aragonite precursor for lma microcrystalline cements of cool water settings where temperatures precluded calcified algae and abiotic carbonate precipitation in calcite seas where mg ca ratios inhibited both abiogenic aragonite precipitation and aragonite generation by calcified algae molluscan aragonite was again the most likely main contributor in some epeiric seas where brackish wedges switched off the shallow water carbonate mud factories molluscan aragonite is the parsimonious source of carbonate for lma microcrystalline cements

sedimentary carbonates through phanerozoic time plate tectonic processes play a critical role in the origin and distribution of sedimentary carbonates through phanerozoic time the phanerozoic age distribution of sedimentary properties like calcite dolomite ratio inferred ooid and cement mineralogy and survival rate of continental carbonates is cyclic the cycles appear to be coupled to plate tectonic processes that give rise to global sea level change and changes in the properties of the ocean atmosphere system first order changes in sea level are driven by the accretion of mid ocean ridges high accretion rate high sea level low accretion rate low sea level although correlations between sea level and sedimentary carbonate properties are not strong high sea level over an extended period of time appears to be correlated with low calcite dolomite ratios lack of inferred aragonite ooids and cements and maxima in the survival rate of continental carbonates the opposite is true for extended periods of low mid ocean ridge accretion rates and global sea levels the lack of strong correlations may reflect an insufficient data base and the possibility of lags between sea level change and change in carbonate properties furthermore the survival rate of continental carbonates appears to be affected by differential cycling and therefore may not be directly related to accumulation rate it appears that the environmental conditions for early dolomitization and calcite ooid and cement formation are best met during extended times of high sea level when atmospheric co2 levels are high and the saturation state of seawater with respect to carbonate minerals relatively low during low sea levels early dolomitization is less favored and aragonite precipitates are more abundant because of low atmospheric co2 levels and enhanced seawater carbonate saturation states differential cycling has modified the phanerozoic sedimentary carbonate mass age distribution because of erosion of younger units within continental carbonate cycles it may be difficult to derive an unequivocal record of the partitioning of carbonate between the deep sea and shallow water realms of deposition during the phanerozoic this difficulty must be considered in further quantification of geochemical models describing the geologic history of atmospheric co2 and climate change

seawater ph and isotopic paleotemperatures of cretaceous oceans abstract stable oxygen isotope ratios 18 o of foraminifera are widely used to reconstruct the climatic history of earth it is well known that temperature reconstructions based on 18 o are complicated by factors such as the unknown isotopic composition of the ocean in addition recent experimental and theoretical work has shown that the seawater ph has a marked effect on the 18 o of foraminifera here i employ this effect to demonstrate that reconstructions based on 18 o of foraminifera may underestimate sea surface temperatures in the geological past ocean surface temperatures for the mid cretaceous are estimated to have been 2 3 5 c higher than previously thought

stromatolitic biotic systems in the mid triassic of israel a product of stress on an epicontinental margin abstract phanerozoic microbialites are carbonate precipitating biotic forms that are often described in modern systems from inter or supratidal hypersaline or fresh water environments and from beds associated with a variety of ecologically stressed environments over geologic time middle to late triassic microbialitic successions from southern israel were commonly subtidal and thrived under cryptic ecological stress conditions related to the regional configuration of the levant margin at that time the ladinian and carnian sequence at the ramon outcrop contains 18 successions with 28 microbialitic horizons these microbialites form isolated patches small bioherms and biostromes interleaved with other calcareous sediments including poorly diverse molluscan accumulations three distinct microbialitic facies and two associated molluscan facies were identified most were distinctly subtidal the two associated molluscan biofacies include a subtidal bivalve boundstone forming mounds and a bedded packstone of minute gastropods the ladinian carnian microbialites were not climatically forced environmental stress was caused by partial restriction of marine circulation due to tectonic movements and biotic accumulation on the outer edge of the levant margin comparison of coeval successions from central and northern israel and the north calcareous alps and southern alps in europe indicates a tethyan or global carbonate system of microbial producers separated from the open marine environment by shelf edge barriers therefore we conclude that the ramon microbialites represent a response to ecological stress of the carbonate system within the subtidal environment rather than solely to normal stresses of the intertidal environment

early triassic stromatolites as post mass extinction disaster forms aftermaths of mass extinctions have been thought to be characterized by relaxation of ecological constraints accompanied by increased prominence of opportunistic generalists such taxa termed disaster forms have been shown to increase dramatically in range and abundance after several mass extinction events the cambrian ordovician stromatolite decline in normal marine level bottom environments has been explained as a direct or indirect consequence of increases in ecological constraints such as greater levels of predation and or bioturbation of microbial communities caused by early paleozoic benthic invertebrate evolution and diversification thus one would predict that in post ordovician strata stromatolites might appear in normal marine level bottom environments as disaster forms in the aftermaths of mass extinction particularly devastating to the benthic biota such as during early triassic time mounded stromatolites are present in two beds up to 1 5 m thick of the lower triassic spathian virgin limestone member moenkopi formation in the southwestern spring mountains of nevada stromatolites from level bottom normal marine subtidal environments have also been described from other lower triassic strata in north america europe and asia these stromatolites unusual in level bottom normal marine settings may have developed locally during the long aftermath 4 5 m y of the permian triassic mass extinction because of partial relaxation of the ecological constraintsmore that typically restricted them from unstressed subtidal normal marine level bottom environments less

paleoenvironmental implications of an extensive maceriate microbialite bed in the furongian chaomidian formation shandong province china abstract this study focuses on the unique occurrence of an extensive microbialite bed 10 20 m thick in the chaomidian formation furongian in shandong province china in order to understand its paleoenvironmental implications the microbialite bed can be traced for over 6000 km2 in area the microbialites are characterized by centimeter to decimeter scale branching maze like constituents maceriae of microbial and muddy sediments with chaotic texture including tabular maceriate microbialite type 1 columnar maceriate microbialite type 2 and columnar chaotic microbialite type 3 within the bed each microbialite unit is generally well correlated for tens of kilometers the entire bed is bounded by limestone marlstone alternation at the base and an erosional surface at the top that is subsequently overlain by a grainstone bed of various thicknesses the microbialite bed formed when the seafloor reached suitable water depth for the microbial growth during sea level rise accompanied with carbonate production the maze like maceria structures formed to acquire a larger surface area under a relatively large input of lime mud the tabular maceriate microbialites initially formed in relatively deep water environments and flourished on broad and flat seafloor whereas the columnar microbialites types 2 and 3 developed under the influence of strong waves and currents the microbialite bed was eroded and terminated by frequent storm events and buried under the reworked grainstone further rise in sea level and increased metazoan activities afterwards limited the resurgence of microbes in the late furongian

alternation of microbial mounds and ooid shoals middle jurasssic morocco response to paleoenvironmental changes abstract the occurrence of neritic microbial carbonates is often related to ecological refuges where grazers and other competitors are reduced by environmental conditions or to post extinction events e g in the late devonian early triassic here we present evidence for middle jurassic bajocian microbial mounds formed in the normal marine shallow neritic setting of an inner ramp system from the high atlas of morocco the microbial mounds are embedded in cross bedded oolitic facies individual mounds show low relief domal geometries up to 3 m high and 4 5 m across but occasionally a second generation of mounds exhibits tabular geometries

pendant bioconstructions cemented by microbial carbonate in submerged marine caves holocene se sicily abstract unusual pendant bioconstructions occur within two submerged caves in the plemmirio marine protected area south of syracuse se sicily these cm to dm sized bioconstructions project downward from the cave roofs the main framework builders are serpulids belonging to the genera protula semivermilia and josephella encrusting bryozoans corals hydrozoans and sponges are subordinately present whereas bivalves and brachiopods are overall rare these faunal associations are characteristic of the studied caves but only in some places they form small bioconstructions that are cemented by microbial carbonates made up by autochthonous peloidal to clotted peloidal and aphanitic micrite the autochthonous micrite stabilizes the pendant bioconstructions herein referred to as biostalactites the microbial carbonate reveals high contents of bacterial lipid biomarkers among the most abundant compounds are mono o alkyl glycerol ethers mages and branched fatty acids 10 me c16 0 iso and anteiso c15 0 and c17 0 interpreted as biomarkers of sulfate reducing bacteria other compounds preserved in the autochthonous carbonates include lipids derived from marine zoo and phytoplankton brassicasterol dinosterol and monounsaturated short chain fatty acids unspecified marine bacteria saturated and monounsaturated short chain fatty acids and land plants long chain fatty acids long chain alcohols stigmasterol sitosterol and campesterol the observed lipid biomarker signatures are remarkably similar to those of post glacial reefal microbialites where microbialite formation in cavities of the coral framework was also mediated by sulfate reducing bacteria in the submerged caves of plemmirio marine protected area serpulid colonies apparently occur preferentially where freshwater is seeping through crevices in the limestone the consequent nutrification is believed to favor serpulid aggregation and the growth of other skeletal i e bryozoans and corals and soft bodied organisms i e sponges and ascidiae the resultant accumulation of biomass and its taphonomy provide niches for sulfate reducing bacteria which induce carbonate precipitation cementing and stabilizing the biostalactites the finding of pendant cemented bioconstructions in the mazzere and granchi caves of the plemmirio marine protected area reveals that sulfate reducing bacteria are involved in microbialite formation in various cryptic environments the formation of such peloidal to clotted peloidal microcrystalline carbonates in cryptic ecosystems is a significant factor for the stabilization of different kinds of bioconstructions spanning from small biostalactites to large reefs

secular oscillations in the carbonate mineralogy of reef building and sediment producing organisms driven by tectonically forced shifts in seawater chemistry the primary mineralogy of oolites and early marine carbonate cements led sandberg nature 305 1983 19 22 to divide the phanerozoic eon into three intervals of aragonite seas and two intervals of calcite seas hardie geology 24 1996 279 283 has shown that these oscillations together with synchronous oscillations in the mineralogy of marine potash evaporites can be explained by secular shifts in the mg ca ratio of seawater driven by changes in spreading rates along mid ocean ridges the hardie model also predicts that high mg calcite should precipitate along with aragonite as it does in today s aragonite sea we have uncovered oscillations in the carbonate mineralogy of hypercalcifying organisms ones that have produced massive skeletons large reefs or voluminous bodies of sediment that correspond to sandberg s aragonite seas and calcite seas and that are predicted by the hardie model particular groups of corals sponges and algae appear to have been dominant reef builders only when favored by an appropriate mg ca ratio in seawater in early and middle paleozoic calcite seas calcite i reefs were dominated by calcitic tabulate heliolitid and rugose corals and calcitic stromatoporoids in contrast during the period of late paleozoic early mesozoic aragonite seas aragonite ii aragonitic groups of sponges scleractinian corals and phylloid algae as well as high mg calcitic red algae were principal reef builders during late cretaceous time at the acme of calcite ii massive rudists displaced aragonitic hermatypic corals in today s aragonite sea aragonite iii scleractinian corals are again dominant reef builders along with high mg calcitic coralline algae major sediment producing algae exhibit temporal patterns similar to those of reef builders calcitic receptaculitids flourished during calcite i whereas aragonitic dasycladaceans did not become dominant rock formers until aragonite ii during calcite ii calcitic nannoplankton formed massive coccolith chalks in warm shallow seas of the late cretaceous after the mg ca ratio of seawater had reached a very low value and calcium concentration a very high value as the mg ca ratio of seawater rose and calcium concentration fell during the cenozoic era individual coccoliths on average became less massive and encrusted cells less thickly by pliocene time during aragonite iii the prominent genus discoaster secreted only narrow rayed coccoliths that covered less than 25 of the cell surface also during aragonite iii the aragonitic green alga halimeda emerged as the dominant skeletal sediment producer in reef tracts the influence of seawater chemistry on skeletal secretion appears to have been especially strong for morphologically simple taxa that exert relatively weak control over their own calcification such groups include algae sponges corals and bryozoans morphological simplicity also permits these groups to adopt vegetative or colonial modes of growth that confer success in competition for space on reefs this linkage in addition to the basic chemical demands of hypercalcification has given the mg ca ratio of seawater strong control over the success of individual reef building taxa more generally this ratio appears to have strongly influenced evolutionary changes in the skeletal mineralogy of sponges and cheilostome bryozoans throughout their history we conclude that throughout phanerozoic time a chain of causation has extended from mid ocean ridge processes via seawater chemistry to the mineralogical and biological composition of reef communities and bioclastic carbonate deposits

the implication of the oxygen isotope records in coexisting cherts and phosphates 18 o values have been determined for 53 coexisting chert phosphate pairs from the phanerozoic and precambrian in addition 18 o values were also determined for 18 biogenic phosphates from the phanerozoic the oxygen isotope data for the chert phosphate pairs permit the calculation of the temperatures of formation of the chert phosphate pairs as well as the 18 o of the waters in which they equilibrated in turn the calculated 18 o of the waters permit the calculation of temperatures from the isotopic data of the biogenic phosphates the temperatures for the tertiary and mesozoic samples are compatible with the literature values determined from oxygen isotope data for well preserved calcareous marine skeletal remains the temperatures calculated from the chert phosphate pairs of the paleozoic are usually higher and vary in cycles of about a 150 million year period the early precambrian temperatures are as high as 80 c and decrease with time the use of chert phosphate pairs for temperature determinations are sufficiently promising to warrant further investigations of this type on well preserved chert phosphate or carbonate phosphate pairs

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

causes and consequences of the relation between area and age of the ocean floor the distribution of area of the ocean floor with age t is approximately described by da dt c0 1 t tm where c0 is the rate of crustal generation and tm the maximum age a linear differential area versus age relation can be explained by a balance between crustal generation and consumption where consumption is uniformly distributed with age the present distribution of consumption with age was estimated from the isochron map used to derive the area age relation and a recently published set of angular velocity vectors describing present plate motions the rate of consumption per unit age shows considerable scatter about a mean value equal to c0 tm 1 7 10 8 km2 yr2 but consumption is sufficiently close to being uniformly distributed with age to explain the observed degree of approximation to a linear differential area age relation the trenches appear to be distributed randomly with respect to age provinces in the oceans it was not possible to discern any trend of mean subduction velocities with age apart from the smaller velocities observed for the two youngest age provinces 0 9 ma changes in the rate of plate generation and the distribution of consumption with age result in shifts in the area age distribution in turn these shifts produce changes in the plate driving forces which act to restore the rate of plate generation and distribution of consumption to their initial states the ridge pushing force for example decreases as the rate of crustal generation increases this coupling between driving forces and the area age distribution provides a feedback mechanism limiting the extent of any changes a measure of the magnitude of shifts in the area age distribution is given by global changes in sea level if long term changes in sea level are less than 150 m as suggested by recent estimates then only small changes 12 in the rate of plate generation and distribution of consumption with age are required sea level changes as large as 300 m require about a 50 change in the rate of crustal generation the above area age relation can be combined with simple expressions for depth and heat flow versus age to obtain an empirical hypsometric distribution parameterized in terms of age and exact expressions for the heat loss from the ocean floor the latter is estimated to be 2 9 1013 w with 25 of this heat being lost by seafloor younger than 5 ma of the total heat loss from the mantle 26 is estimated to be transported by small scale convection

a global marine sedimentary response to the end permian mass extinction examples from southern turkey and the western united states the end permian mass extinction greatly diminished marine diversity and brought about a whole scale restructuring of marine ecosystems these ecosystem changes also profoundly affected the sedimentary record data presented here attained through facies analyses of strata deposited during the immediate aftermath of the end permian mass extinction southern turkey and at the close of the early triassic southwestern united states in combination with a literature review show that sedimentary systems were profoundly affected by 1 a reduction in biotic diversity and abundance and 2 long term environmental fluctuations that resulted from the end permian crisis lower triassic strata display widespread microbialite and carbonate seafloor fan development and contain indicators of suppressed infaunal bioturbation such as flat pebble conglomerates and wrinkle structures facies considered unusual in post cambrian subtidal deposits our observations suggest that depositional systems too respond to biotic crises and that certain facies may act as barometers of ecologic and environmental change independent of fossil assemblage analyses close investigation of facies changes during other critical times in earth history may serve as an important tool in interpreting the ecology of metazoans and their environment

geobiology of microbial carbonates metazoan and seawater saturation state influences on secular trends during the phanerozoic abstract microbial carbonates are long ranging essentially bacterial aquatic sediments their calcification is dependent on ambient water chemistry and their growth is influenced by competition with other organisms such as metazoans in this paper these relationships are examined by comparing the geological record of microbial carbonates with metazoan history and secular variations in caco3 saturation state of seawater marine abundance data show that microbial carbonates episodically declined during the phanerozoic eon past 545 myr from a peak 500 myr ago this abundance trend is generally inverse to that of marine metazoan taxonomic diversity supporting the view that metazoan competition has progressively limited the formation of microbial carbonates lack of empirical values concerning variables such as seawater ionic composition atmospheric partial pressure of co2 and ph currently restricts calculation of caco3 saturation state for the phanerozoic as a whole to the use of modeled values these data together with palaeotemperature data from oxygen isotope analyses allow calculation of seawater caco3 saturation trends microbial carbonate abundance shows broad positive correspondence with calculated seawater saturation state for caco3 minerals during the interval 150 545 myr ago consistent with the likelihood that seawater chemistry has influenced the calcification and therefore accretion and preservation of microbial carbonates these comparisons suggest that both metazoan influence and seawater saturation state have combined to determine the broad pattern of marine microbial carbonate abundance throughout much of the phanerozoic in contrast for the major part of the precambrian it would seem reasonable to expect that seawater saturation state together with microbial evolution was the principal factor determining microbial carbonate development interrelationships such as these with feedbacks influencing organisms sediments and the environment are central to geobiology

enhanced nitrogen fixation in the immediate aftermath of the latest permian marine mass extinction the carbon 13 c org and nitrogen 15 n isotopic compositions of bulk organic matter were analyzed in two high resolution permian triassic transitional sections containing microbialite in south china the results from these shallow marine sections show that an abrupt negative shift in 15 n from 3 to 0 occurred immediately after the latest permian mass extinction lpe in both sections concurrent with a distinct negative shift in 13 c org the persistently low values of 15 n suggest that following the lpe microbial nitrogen fixation became the main source of biologically available nitrogen in the nanpanjiang basin and perhaps over a broader region of the eastern paleotethys ocean enhanced n fixation is probably indicative of the prevalence of stratified anoxic water masses characterized by intense denitrification and or anaerobic ammonium oxidation at the time perturbation of the marine nitrogen cycle might have contributed to high temperatures following the main marine mass extinction through the release of the greenhouse gas n 2 o the sharp declines in 15 n and 13 c org may be ascribed to an abrupt change in shallow water microbial communities which differed in composition from contemporaneous deep water communities

rare earth and trace elements of microbialites in upper jurassic coral and sponge microbialite reefs major trace y zr pb th and u rare earth element ree and sm nd isotope analyses were carried out on microbialites and detrital carbonate sediments collected in upper jurassic coral and sponge microbialite reef settings selected bioconstructions developed in various palaeogeographic settings and depositional environments on northwestern tethys and eastern atlantic margins pure carbonate lagoon carbonate dominated deep shelf to epicontinental basin and mixed carbonate siliciclastic shallow ramp and lagoon the proximity to terrigenous sources directly controlled ree patterns of carbonate samples lateral and intrareef sediments and to a lesser degree stromatolitic microbial crusts are more susceptible to contamination by terrigenous material than are microbialites of thrombolitic fabric in mixed carbonate siliciclastic settings microbialites display a flat shale normalized ree pattern in pure carbonate lagoonal settings microbialites have shale normalized ree patterns similar to those of modern seawaters with a negative ce anomaly ce ce up to 0 14 positive la and gd anomalies and light ree depletion relative to heavy ree these data imply that similar ree chemistry than modern seawater already occurred on the northwestern tethys margin at the upper jurassic strong negative ce anomalies b0 4 imply microbialite formation in well oxygenated seawaters both in coral reefs of pure carbonate lagoonal environments pagny sur meuse and sponge bioherms of deep shelf settings plettenberg absence of positive ce anomalies rules out an influence of alkaline and high ph seawaters thus ree patterns and nd isotopic signatures which are in perfect agreement with existing results for tethysian seawater confirm that microbialites can be used as proxies of palaeoenvironmental seawater chemical characteristics