climate warming in the latest permian and the permian triassic mass extinction high resolution oxygen isotope records document the timing and magnitude of global warming across the permian triassic p tr boundary oxygen isotope ratios measured on phosphate bound oxygen in conodont apatite from the meishan and shangsi sections south china decrease by 2 in the latest permian translating into low latitude surface water warming of 8 c the oxygen isotope shift coincides with the negative shift in carbon isotope ratios of carbonates suggesting that the addition of isotopically light carbon to the ocean atmosphere system by siberian traps volcanism and related processes resulted in higher greenhouse gas levels and global warming the major temperature rise started immediately before the main extinction phase with maximum and harmful temperatures documented in the latest permian meishan bed 27 the coincidence of climate warming and the main pulse of extinction suggest that global warming was one of the causes of the collapse of the marine and terrestrial ecosystems in addition very warm climate conditions in the early triassic may have played a major role in the delayed recovery in the aftermath of the permian triassic crisis

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

foreslope stromatoporoid renalcid bioherm with evidence of early cementation devonian ancient wall reef complex rocky mountains a small mound 4 x 23 m in size on the fore reef slope of the ancient wall reef complex at mouni haultain alberta consists of fenestral renalcid micrite and wac kestone stroniatoporoids are the most abundant skeletal component but do not form an organic framework renalcids together with early micrite cementation performed a supporting and stabilizing role but only rarely directly encrusted skeletal material many of the primary shelter voids interparticle voids and fenestrae were filled with internal sediments and submarine micrite cements a considerable proportion of the micrite matrix appears to be cement the location and development of the bioherm was controlled by a local hard substrate and suitable environmental conditions the mound developed on and around a large block within an underlying megabreccia bed soon after it was deposited in a debris flow on the fore reef slope it formed near wave base in about 30 50 m water depth and was subject to gentle current action laminar stromatoporoids grew on the flanks and top of the mound and fenestral renalcid micrite and wackestone accumulated in the central part deepening water and increased rates of mud accumulation terminated further build up of the bioherm and it was buried by basin mud fenestral renalcid micrite occurs in a number of devonian and lower palaeozoic organic mounds this study suggests that early submarine cementation was a significant factor in the developmen and preservation of this distinctive lithotype

distribution of anthropogenic co2 in the pacific ocean 1 this work presents an estimate of anthropogenic co2 in the pacific ocean based on measurements from the woce jgofs oaces global co2 survey these estimates used a modified version of the c technique modifications include a revised preformed alkalinity term a correction for denitrification and an evaluation of the disequilibrium terms using an optimum multiparameter analysis the total anthropogenic co2 inventory over an area from 120 e to 70 w and 70 s to 65 n excluding the south china sea the yellow sea the japan east sea and the sea of okhotsk was 44 5 5 pg c in 1994 approximately 28 pg c was located in the southern hemisphere and 16 5 pg c was located north of the equator the deepest penetration of anthropogenic co2 is found at about 50 s the shallowest penetration is found just north of the equator very shallow anthropogenic co2 penetration is also generally observed in the high latitude southern ocean one exception to this is found in the far southwestern pacific where there is evidence of anthropogenic co2 in the northward moving bottom waters in the north pacific a strong zonal gradient is observed in the anthropogenic co2 penetration depth with the deepest penetration in the western pacific the pacific has the largest total inventory in all of the southern latitudes despite the fact that it generally has the lowest average inventory when normalized to a unit area the lack of deep and bottom water formation in the north pacific means that the north pacific inventories are smaller than the north atlantic

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

diastasis cracks mechanically generated synaeresis like cracks in upper cambrian shallow water oolite and ribbon carbonates upper cambrian limestones and dolostones of western newfoundland canada display conspicuous synsedimentary mud cracks cracks occur in carbonate mudstone interbedded with ooid and peloid grainstone unwashed oolite and ribbon rock lithofacies the traditional interpretation is that these are desiccation cracks the weight of evidence supports an alternative e explanation cracks resulted from the differential mechanical behaviour under stress of stiff mud interlayered with loose ooid peloid sand the processes envisaged to cause such diastasis cracks may be applicabl e to a wide variety of both carbonate and terrigenous clastic deposits composed of interlayered sediments of contrasting material properties and may be a viable alternative to synaeresis

influence of dissolved oxygen on secular patterns of marine microbial carbonate abundance during the past 490 myr abstract shallow marine benthic microbial carbonate sediments declined episodically during the phanerozoic they were relatively abundant during the cambrian mid ordovician late devonian mississippian mid permian mid late triassic and to a lesser degree in the late jurassic early cretaceous they were least abundant when invertebrate especially reef diversity was relatively high in the mid ordovician late devonian early mid permian late triassic mid late jurassic and early cretaceous to present day these intervals of microbial carbonate abundance and invertebrate diversity generally alternate transitionally with one another but lows and periods of overlap also occur lows when benthic microbial carbonate abundance and invertebrate diversity both declined are apparent during the pennsylvanian and early mid jurassic overlaps when microbial carbonates and invertebrates were both relatively common occur in the early cambrian and late jurassic overall these patterns broadly support suggestions that microbial carbonate abundance declined as calcified invertebrates increased to further explore these relationships we compared microbial carbonate abundance and invertebrate diversity with estimates of changes in sea surface temperature and marine dissolved oxygen for the past 490 myr this analysis suggests that invertebrate diversity varied directly with oxygen availability invertebrate diversity was low when dissolved oxygen was low in the early ordovician late devonian early triassic and early mid jurassic it appears that by reducing invertebrate diversity low oxygen levels favored microbial carbonates at the same time low oxygen levels likely stimulated anaerobic metabolisms favoring carbonate precipitation this study suggests that dissolved oxygen was a major control on secular patterns of marine microbial carbonate abundance during the phanerozoic together with marine temperature and carbonate saturation state

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

molecular records of microbialites following the end permian mass extinction in chongyang hubei province south china abstract by using gas chromatograph gc and gc mass spectrometry a series of biomarkers were identified in the aliphatic fractions of extracts from microbialites following the end permian faunal mass extinction in chongyang section hubei province south china the dominance of lower molecular weight n alkanes in the samples from the section suggests that algae and bacteria were the dominant contributors to the organic fraction preserved in this marine section with bacteria particularly enhanced within the stromatolite the end permian biotic crisis coincided with a short term suppression of autotrophs indicated by the ratio of pristane pr and phytane ph to c 17 and c 18 n alkanes and proliferation of heterotrophs shown by the ratio of branched to normal c 17 alkanes the biotic crisis also may have been associated with a transient oxygenation event in the shallow marine indicated by elevated pr ph ratios and lowered c 27 18 h 22 29 30 trisnorneohopane ts to c 27 17 h 22 29 30 trisnorhopane tm and gammacerane to c 31 homohopane c 31 hp ratios subsequently three short term episodes of intensified anoxia or enhanced salinity at chongyang are recorded by decreases in pr ph ratios in conjunction with lithological boundaries in the section

ordovician cyanobacterial calcification a marine fossil proxy for atmospheric co2 abstract ordovician atmospheric co2 level was an important influence on climate and life however modelled estimates of ordovician co2 differ widely and in contrast to much of the subsequent phanerozoic they lack fossil proxy constraints in vivo cyanobacterial sheath calcification promoted by carbon dioxide concentrating mechanisms ccms creates distinctive microfossils these provide a direct ecophysiological link to ambient concentrations of co2 and to a lesser extent o2 cyanobacteria do not calcify at high co2 concentrations experiments show that ccms can be induced in present day cyanobacteria at co2 levels below 10 times present atmospheric level pal and that this promotes sheath calcification we compiled a global database of cyanobacterial calcification in marine environments throughout the ordovician 485 443 myr ago and compared it with modelled estimates of atmospheric co2 and o2 these data show that many genera of marine calcified cyanobacteria reappeared from cambrian series 2 or first appeared globally during the late middle to late upper ordovician late darriwilian to late katian in carbonate platform facies resulting in a previously unrecognized ten fold increase in global diversity such a large increase in calcification suggests widespread induction of ccm expression in cyanobacteria consistent with sustained decline in external co2 concentrations below 10 pal together with increase in dissolved o2 level during the late darriwilian sandbian and katian stages 460 445 myr ago these cyanobacterial calcification fossil proxy data provide a first order constraint on modelled estimates of atmospheric co2 for the ordovician estimated co2 outputs from copse and recent geocarb based models are broadly consistent with this cyanobacterial calcification proxy for the ordovician in view of the long history of cyanobacteria the calcified cyanobacterial proxy offers potential to assist interpretation of co2 deeper into geological time

submarine spring controlled calcification and growth of large rivularia bioherms late pleistocene mis 5e gulf of corinth greece the cyanobacterium rivularia haematites has calcified to form unusually large up to 10 m high bioherms in the pleistocene gulf of corinth today r haematites calcifies only in freshwater environments but these gulf of corinth bioherms have a brackish affinity limited areal extent and occur within marine deposits field relations and preliminary u series dating suggest a marine isotope stage mis 5e age for the bioherms this age is compatible with published mis 5e ages for corals in the marine sediments above the bioherms and is consistent with their current elevation based on average uplift rates bioherm growth during mis 5e constrains their formation during a time of near sea level highstand when the gulf of corinth was marine growth cavities in the bioherms are encrusted by brackish tolerant coralline algae field mapping of the mis 5e highstand palaeoshoreline shows the bioherms grew in water

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

in situ calcium carbonate dissolution in the pacific ocean over the past several years researchers have been working to synthesize the woce jgofs global co2 survey data to better understand carbon cycling processes in the oceans the pacific ocean data set has over 35 000 sample locations with at least two carbon parameters oxygen nutrients cfc tracers and hydrographic parameters in this paper we estimate the in situ caco3 dissolution rates in the pacific ocean water column calcium carbonate dissolution rates ranging from 0 01 1 1 mmol kg1 yr1 are observed in intermediate and deepwater beginning near the aragonite saturation horizon in the north pacific intermediate water between 400 and 800 m caco3 dissolution rates are more than 7 times faster than observed in middle and deep water depths average 0 051 mmol kg1 yr1 the total amount of caco3 that is dissolved within the pacific is determined by integrating excess alkalinity throughout the water column the total inventory of caco3 added by particle dissolution in the pacific ocean north of 40s is 157 pg c this amounts to an average dissolution rate of approximately 0 31 pg c yr1 this estimate is approximately 74 of the export production of caco3 estimated for the pacific ocean these estimates should be considered tomore be upper limits for in situ carbonate dissolution in the pacific ocean since a portion of the alkalinity increase results from inputs from sediments less

soft sediment deformation structures induced by cyclic stress of storm waves in tempestites miocene guadalquivir basin spain the identification of triggering agents for soft sedimentation structures is an enigmatic geological problem mainly seismic induced soft sediment structures have been recognized in ancient sediments rather than those resulting from storm waves we analyse soft sediment deformation structures in upper miocene calcarenitic tempestites of the guadalquivir basin southern spain the most common structures are load casts which vary in height and width from 10 centimetres to several metres the structures are always restricted to a small part of the stratigraphic sections in exclusive association with tempestites the analysed soft deformation structures are interpreted to be the result of liquidization processes chiefly from their inferred depositional environment and subordinately from the deformation style we have devised basic criteria to identify the trigger mechanism in these soft sediment deformation structures the liquefaction was triggered by pore pressure changes induced by cyclic and residual stress of storm waves

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

depth distributions of alkalinity tco2 and δ13ctco2 at seats time series site in the northern south china sea abstract in this study measurements of titration alkalinity ta total dissolved carbon dioxide tco2 and 13c of tco2 13 c tco 2 throughout the water column at the southeast asian time series study seats site were investigated in order to understand better the fundamental processes controlling their vertical distributions in the south china sea scs the linear correlations between ta and salinity in the shallow waters as identified by the mixing line between the surface water and salinity maximum water suggested the predominant control of physical mixing on the variability of ta in contrast tco2 and 13 c tco 2 showed the non conservative behavior in the respective tco2 and 13 c tco 2 vs salinity plot due to the effect of biological production a stoichiometric model further showed that the depth profile of nta ta salinity 35 largely reflects the increase of preformed nta in the shallow waters whereas carbonate dissolution was responsible for the continuous increase of nta in the deep waters a one dimensional diffusion advection model further revealed that the carbonate dissolution could account for 28 of ntco2 tco2 salinity 35 increase in deep waters and the remaining 72 of ntco2 was from organic decomposition calculation of excess ta further showed that it emerged well above the aragonite and calcite saturation depths at 600 and 2500 m respectively indicating that some biologically chemically and physically mediated processes must be involved to provide excess ta into the shallow waters the decrease in 13 c tco 2 with depth primarily resulted from organic decomposition the influence of anthropogenic co2 throughout the water column was assessed with the carbon chemistry and the isotope based approach in this study both methods obtained nearly the same results in which the signal of anthropogenic co2 decreased exponentially with depth and its penetration depth were found to be at 1000 m the inventory of anthropogenic co2 in the water column was estimated to be 16 6 mol c m 2 which was less than that reported in the northwest pacific at the same latitude presumably due to the enhanced upwelling in the scs such an anthropogenic co2 penetration had led to decreases of the saturation levels of aragonite and calcite by 17 and 14 respectively in the surface water and an upward migration of aragonite saturation depth by 100 m since industrial revolution

paleoenvironmental reconstruction of microbial mud mound derived boulders from gravity flow polymictic megabreccias visean sw spain abstract the upper visean outcrops from the guadiato valley cordoba sw spain provide a well preserved record of the mud mound factory which was developed in a mainly siliciclastic synorogenic foreland basin during the oblique sinistral collision of two terranes ossa morena and central iberian blocks the first onset of mud mound development has been recorded as microbial mud mound derived boulders in polymictic megabreccias as result of strong tectonic activity the upper visean record from the mississippian central band at guadiato valley starts with lower heterolithic units up to 180 m thick and shows two major tectonically controlled cycles a fining upwards interval fu followed by a coarsening upwards interval cu these cycles are linked to two active margins with gravelly fan delta development and different source areas mud mound derived boulders occur in the cu interval and are formed by peloidal primary and secondary reworked automicrites and allomicrites showing a diverse faunal and floral assemblage although never as the main skeletal framebuilders however the observed coeval richness in sponges lyssacinose hexactinellids and non lithistid demosponges and the diverse calcareous algae assemblage in mud mound derived boulders are not common in other visean buildups the growth cavities display changes in the geopetal relationships between fillings and the secondary cavities containing sand to gravel fillings reflecting a complex pre boulder and mud mound derived boulder history detailed mapping sampling stratigraphic and microfacial analyses have allowed the reconstruction of the mud mounds sedimentary environment prior to the collapse transport and emplacement as boulders with polymictic gravels

construction model and paleogeographic distribution of late pennsylvanian phylloid algal microbial reefs a case study in eastern inner mongolia north china abstract the gzhelian late pennsylvanian reefs of the amushan formation in eastern inner mongolia north china were formed by filamentous microbes and phylloid algae loosely accumulated prostrate phylloid algae provided substrates for growth of filamentous microbes to construct a rigid reef framework filamentous microbes grew parallel to the surfaces of phylloid algae forming micritic encrustations subsequent developed stage of the filamentous microbes growing perpendicularly to the phylloid algae surfaces produced the peloid a aggregations concentrated areas of peloids of a type the remaining spaces in the phylloid algal microbial frameworks were filled by microbes that grew perpendicularly to the phylloid algae surfaces generating peloid b aggregations concentrated areas of peloids of b type microbial sediment with various proportions of phylloid algae is a significant character of the gzhelian buildups in the subtropical north china north china buildups have similar reef building organisms to the typical tethyan buildups but have a different construction model as such the subtropical north china buildups are considered as a sub type of the tropical tethyan buildups

a middle late pleistocene palustrine lacustrine travertine system borj edouane unit nw tunisia sedimentology stable isotopes and palaeohydrological implications the carbonate borj edouane unit represents the northernmost documented middle late pleistocene continental carbonate deposits in tunisia the unit consists of two main facies associations asymmetrically distributed 1 calcrete palustrine laminar crust 2 microbialites the first accumulated carbonate formed in the distal zone of alluvial fans calcretes and in shallow lakes subjected to periodic exposure palustrine facies that occupied the westernmost strip of the basin the second association formed in permanent lakes stromatolites oncoids and planar stromatolites located in the central areas of the basin fed by springs associated with a concentration of vertical faults in the eastern area of the basin travertine facies at time of deposition these facies communicated with the lake via a transitional lacustrine travertine environment transitional travertine stromatolite facies all facies show a restricted range of 18o values around 5 8 0 5 suggesting formation from paleoprecipitation largely of atlantic derivation brought about by westerly winds as for the 13c values these show a wide range 6 4 to 11 7 overall relatively high values for all facies with the lower values corresponding to the calcrete palustrine association and the higher ones linked to the microbialite facies the trend in travertines probably mimics an increasing influence of carbon derived from dissolution of carbonate bedrock of the cretaceous substrate while that of palustrine samples records increasing respired c contribution the sedimentological and isotopic characteristics of the borj edouane unit reflect wetter conditions at the time of deposition and point to a humid period at the middle late pleistocene transition

cyclicity and paleoenvironmental dynamics rocknest platform northwest canada the superbly exposed rocknest formation northwest territories canada contains 140 to 160 shallowing upward cycles 1 to 15 m thick that contain distinctive marker beds and can be correlated for 200 km parallel to strike and 120 km perpendicular to strike cycles are grouped according to cycle base lithology which reflects paleogeographic position on the platform shale based cycles of the distal inner shelf pass westward into dolosiltite based cycles then into tufa based cycles of the shoal complex and then into grainstone based cycles of the outer shelf cycles are bounded by erosional surfaces that become less pronounced away from the shoal complex cycles formed in response to small asymmetric rapid rise slow fall eustatic oscillations in sea level 10 m during sea level rise rapid transgression and submergence of tidal flats occurred along the eastern margin of the shoal complex followed by eastward expansion of the shoal complex and slow progradation of tidal flats over lagoonal facies during sea level fall a glacio eustatic model for cyclicity accounts for the data favoring asymmetric eustatic sea level oscillations subaerial exposure and vadose diagenesis of platform during sea level falls arrested progradation and incomplete shoaling of many cycles and cycle periods of 20 000 to 100 000 yr 18 000 to 30 000 yr for rocknest inner shelf slopes ranged from 8 cm km average at high sea level stand to 2 cm km average at low sea level stand tidal flat progradation rates were 7 to 9 km 1 000 yr interaction of inner shelf slope sea level fall rate and sedimentation rate generates complete condensed or expanded cycle profiles one dimensional computer modeling reveals that sedimentation rates of shoal complex facies were 250 cm 1 000 yr that lag times in sedimentation following transgression may have ranged from zero on the shoal complex to 2 000 yr on the distal inner shelf and that subtidal sedimentation rates may have ranged from 80 cm 1 000 yr for the proximal inner shelf to 20 cm 1 000 yr for the distal inner shelf

trilobite associations taphonomy lithofacies and environments of the silurian reefs of north greenland abstract llandovery silurian reefs in north greenland have yielded extensive collections of remarkably well preserved trilobites dominated by scutelluids these collections provide a unique opportunity to analyse the reefs and their trilobite faunas in a palaeoenvironmental context and the study highlights the importance of pre existing collections to which further scientific value can be added counts of trilobite sclerites from thirteen reef localities are analysed using cluster and correspondence analyses to identify trilobite associations and taphonomic signatures lithofacies analysis allows these to be understood in a detailed palaeoenvironmental context seven trilobite associations are identified scutelluid illaenimorph scutelluid scutelluid cheirurid scutelluid harpetid proetid encrinurid and illaenimorph the number of associations highlights the variable distribution of taxa within the reefs which is partly a reflection of intense hydrodynamic sorting in reef environments trilobites are predominantly associated with a cement rich microbial lithofacies it is apparent that microbial processes were the principal contributors to the production of carbonate mud and played a significant role in the development of the greenland reefs the observed associations comprise time averaged event beds in an otherwise low energy and slow sedimentation regime and possibly result from storm activity remobilising sclerites and depositing them within depressions and cavity fills within the reef surface correspondence analysis reveals two distinct taphonomic signatures within the reef and transport distance is the primary influence on these the proetid association is readily separated from the others by its taphonomic attributes representing the least amount of transport and suggesting the taxa involved took advantage of the more sheltered niches within the reef this is the first study of reef dwelling trilobites to take advantage of multivariate techniques to identify associations and describe their taphonomic attributes in particular the effectiveness of correspondence analysis in recognising taphonomic signatures is demonstrated

transformation of aragonite dominated lime muds to microcrystalline limestones scanning electron microscopy of textures in several well lithified pleistocene micrites mixed micrite and microspar from south florida and the bahamas shows significant diagenetic alteration of the lime mud precursors the dominance of aragonite in those precursor muds is supported by the surprising presence of abundant aragonite relics in the neomorphic calcite crystals confirmed by feigl stain x ray and electron diffraction polished very lightly etched surfaces of neomorphic calcite crystals even in the microspar show aragonite relics and pits both absent in coexisting void fill cements similarities between micrite and microspar crystals indicate their common origin through a one step neomorphic process of calcitization that is the mud did not first calcitize to micrite and then alter to microspar by aggrading neomorphism this conclusion has more general implications for the interpretation of the origins of other older microsparitic carbonates both early calcitization and concurrent early meteoric cementation were significant in producing the florida bahamas micrites studied which have low porosities similar to those found in most ancient fine grained limestones these low porosities despite the absence of significant overburden indicate that major porosity reduction without compaction can occur in calcitized aragonite dominated muds

submarine hydrothermal weathering global eustasy and carbonate polymorphism in phanerozoic marine oolites abstract the age and fabric of 347 phanerozoic marine oolites have been compiled in order to evaluate secular variations in the original mineralogy of these physicochemically precipitated sedimentary carbonates variation in the abundance of oolite correlates with positions of global sea level ooids were common during transgressions and regressions but were rare during lowstands and highstands the rarity of oolite during continental emergence early cambrian permo triassic late tertiary quaternary probably relates to a diminished areal extent of shallow carbonate environments causes for a similar paucity during continental submergence silurian devonian late cretaceous are more problematic higher atmospheric co2 and lower hydrospheric co3 concentration during highstands may have inhibited a biotic carbonate precipitation ooids coeval with highstands display a preponderance of fabrics evincing a primary calcite mineralogy ooids formed during lowstands are more diverse but record dominance of aragonite variations in cortical mineralogy relate more closely to flooded continental areas than to sea level elevations supporting the suggestion of mackenzie and pigott 1981 that variations in hydrospheric carbonate concentrations were more important in determining phanerozoic ooid mineralogy than were magnesium calcium concentrations these data on oolite abundance and mineralogy demonstrate that abiotic phanerozoic marine carbonates have been responsive to secular changes in atmospheric hydrospheric chemistry and global eustasy and suggest that these changes are directly related to past rates of submarine weathering and sea floor hydrothermal activity

tectonic climatic supercycle in the billion year plate tectonic eon permian pangean icehouse alternates with cretaceous dispersed continents greenhouse abstract the earth alternates in a supercycle 400 m y long from a single continent pangea and ocean panthalassa with an icehouse climate to many continents and oceans with a greenhouse climate the supercycle is driven by the heat that accumulates beneath the insulator of pangea and the greenhouse is made by the excess co2 vented from the mantle during the faster rate of plate activity in the current supercycle a since the mid carboniferous 320 ma the growth and decay of pangean heat is observed in globally synchronous cratonic sedimentary sequences that represent in ascending order 1 a stratigraphic gap 2 sagging 3 rifting 4 fast and 5 slow seafloor spreading stages 4 and 5 of the previous supercycle b are observed back to the start of the phanerozoic in the proterozoic earlier stages of b are postulated back to 720 ma and a third supercycle c to 1100 ma the big glaciations of the latest proterozoic 700 600 ma and late palaeozoic 320 260 ma are confined to the icehouse state during stages 1 3 the sturtian 800 ma latest ordovician 440 ma and quaternary 2 0 ma glaciations fall within greenhouse states during stage 5 of slow seafloor spreading the next icehouse glaciation is expected 80 ma hence the problem of long term past and future climate change is soluble by global studies urgently needed are 1 global stock takes of a the rate of granite emplacement which serves as a proxy via plate activity for the mantle source of atmospheric co2 and b carbonate sinks and other sedimentary indicators of co2 and 2 the extension of the sea level curve back past 570 ma to the start of the plate tectonic eon 1100 ma ago from such studies environmental baselines for past climatic states can be drawn for gauging present and future background variations

cyanobacterial tufa calcification in two freshwater streams ambient environment chemical thresholds and biological processes abstract calcareous freshwater streams near bad urach southwest germany were studied to determine the environmental limits to cyanobacterial calcification daily variations in temperature ph calcium concentration and alkalinity were measured at seasonal intervals from september 1993 to january 1995 in two small woodland streams with lengths of 1 0 and 1 5 km the principal cause of supersaturation in these fast flowing streams is inorganic carbon dioxide outgassing from resurging groundwater locally enhanced by turbulence at waterfalls and cascades photosynthetic uptake of carbon dioxide and temperature effects are negligible nonetheless organic substrates particularly cyanobacteria dominated microbial mats and biofilm significantly localize precipitation by providing suitable nucleation sites precipitation rates on artificial substrates up to 2 2 mm yr on limestone correlate with high saturation index values copper substrates inhibited microbial colonization and received negligible encrustation tufa formation and external calcium carbonate encrustation of cyanobacteria are conspicuous where the annual wateq4f saturation index exceeds 0 8 and are slightly below 0 7 calcium carbonate impregnation of cyanobacterial sheaths has not been observed we infer that in these fast flowing streams cyanobacteria utilize co2 in photosynthesis whereas elsewhere in sluggish freshwater cyanobacteria utilize hco3 leading to sheath impregnation by calcium carbonate even where saturation index is only 0 2 0 3 thus photosynthetic influence on cyanobacterial calcification appears to be negligible in fast flowing co2 rich streams and cyanobacterial calcification takes the form of external encrustation in slow flowing co2 poor streams and lakes cyanobacteria preferentially utilize bicarbonate and sheath impregnation can result modern tropical marine carbonate shelves have saturation indices commonly in the range 0 62 0 82 and cyanobacterial calcification is negligible extrapolation suggests that cyanobacterial calcification could occur in present day seas if saturation index exceeded 0 8 this level corresponding with heavy calcification in the freshwater streams studied may have been widespread in marine environments in the geological past at times when calcified cyanobacteria and environmentally influenced non skeletal calcium carbonate precipitates were abundant

the influence of air sea exchange on the isotopic composition of oceanic carbon observations and modeling although the carbon isotropic composition of ocean waters after they leave the surface ocean is determined by biological cycling air sea exchange affects the carbon isotopic composition of surface waters in two ways the equilibrium fractionation between oceanic and atmospheric carbon increases with decreasing temperature in southern ocean surface waters this isotopic equilibrium enriches delta sup 13 c relative to the delta sup 13 c expected from uptake and release of carbon by biological processes alone similarly surface waters in the subtropical gyres are depleted in delta sup 13 c due to extensive air sea exchange at warm temperatures countering the tendency toward isotopic equilibration with the atmosphere a relatively slow process are the effects of the equilibration of co sub 2 itself a much faster process in regions where there is a net transfer of isotopically light co sub 2 from the ocean to the atmosphere e g the equator surface waters become enriched in sup 13 c whereas in regions where isotopically light co sub 2 is entering the ocean e g the north atlantic surface waters become depleted in sup 13 c a compilation of high quality oceanic delta sup 13 c measurements along with experiments performed using a zonally averaged three basin dynamic ocean model are used to explore these processes 40 refs 14more figs 1 tab less

diurnal and seasonal variations of carbonate system parameters on luhuitou fringing reef sanya bay hainan island south china sea the 3 day diurnal dynamics of carbonate system and related parameters on luhuitou fringing reef of sanya bay adjacent to the south china sea scs were observed in december of 2009 early winter april spring july summer and november late autumn of 2010 the luhuitou fringing reef ecosystem was generally dominated by macro and planktonic algae throughout the year except by coralline algae in winter the system parameters showed distinct diurnal trends in the four seasons averaged ranges of diurnal variation for dissolved oxygen and partial pressure of co2 pco 2 were higher in the autumn 4 67 mg l 1 and 218 2 mu atm respectively than other seasons averaged ranges of diurnal variation for normalized total alkalinity nta was higher in the winter 61 3 mu mol kg 1 and lower in the spring 16 0 mu nol kg 1 the diurnal variations are mainly controlled by biological activities especially by the processes of photosynthesis and respiration in the reef ecosystem in winter however calcification and dissolution contributed more to the diurnal variations compared with the other three seasons total alkalinity was largely related to seasonal changes in river inflow rates dissolved oxygen ph total co2 and aragonite saturation also showed seasonal variations these variations were mainly controlled by the seasonal changes of photosynthesis and respiration which were mainly affected by changes in benthic community structure temperature and river inflow rates the oversaturated pco 2 in the reef ecosystem with respect to the atmosphere in the winter and summer resulted in co2 discharge from the reef ecosystem to the scs the whole system served as net source of co2 to the atmosphere and the adjacent south china sea on an annual time scale c 2013 elsevier ltd all rights reserved

kinetic control of morphology composition and mineralogy of abiotic sedimentary carbonates abstract conventional thinking has long held that the abiotic precipitation of calcium carbonate occurs with a causal relationship between fluid my ca ratios and crystal morphology crystal composition and carbonate mineralogy resulting in the formation of meteoric equant low magnesium calcite and marine acicular high magnesium calcite and aragonite problematically calcites with varying amounts of incorporated magnesium occur either as equant or acicular crystals and aragonite may coexist with calcite in either environment commonly however a systematic relation exists between crystal morphology composition mineralogy and rates of reactant supply to growing crystal surfaces for example equant rather than acicular crystals of calcite form in modern deep and or cold marine meteoric phreatic and deep burial settings where the degree of carbonate saturation and or rates of fluid flow are low in areas of higher saturation and or fluid flow such as in warm shallow marine and meteoric vadose environments acicular calcite may predominate this relation is also seen in systems in which aragonite and calcite form in intimate association aragonite precipitation is favored when rates of reactant supply are high calcite forms when rates are low such relations suggest that crystal morphology composition and mineralogy are controlled by the kinetics of surface nucleation and the amount of reactants principally carbonate ions at growth sites precipitating phases are the ones which can best accommodate such excess reactants ambient mg ca ratios only indirectly control the nature of inorganically precipitated carbonate phases

megablocks of calcified algae in the cow head breccia western newfoundland vestiges of a cambro ordovician platform margin slope and basin deposits in the cow head group of early paleozoic age contain a wide variety of carbonate clasts among the most common largest and most persistent middle middle cambrian to lower middle ordovician are blocks of fine grained white limestone the origin of these clasts is unknown as no limestones of similar lithology have been found in contemporaneous shallow water carbonate deposits anywhere in the northern appalachians petrographic study of these enigmatic limestones reveals that no matter what their age they are of similar composition calcified algae cement and fine grained sediment the predominant algae are epiphyton spp occurring as numerous masses of tiny shrublike and clumplike growths and girvanella spp developed as numerous thin strands and arcuate sheets renalcis spp and stromatolitic algae although locally common are not persistent the algae are surrounded by fibrous calcite cement interpreted to be synsedimentary while the numerous small cavities between algae are partly filled with geopetal marine sediment these blocks are interpreted to be redeposited fragments of reef mounds and buildups which grew along the shallow submerged margin of the north american craton during early paleozoic time these buildups are now probably buried beneath the allochthonous cow head strata the mounds were composed of calcareous algae because there were no large reef building metazoans during this time in geologic history recognition of similar clasts in analogous settings in the quebec and southern appalachians as well as in the cordillera suggests that this facies was both widespread and persistent for more than 70 m y

reconstructing the oceanic 13c suess effect the anthropogenic 13c change for the time period 1968 to 1991 was determined based on calculations of the preformed 13c 12c of dissolved inorganic carbon dic distributions on isopycnal surfaces in the main thermocline of the pacific north atlantic and south indian oceans the time rate of change of preformed 13c the 13c suess effect along isopycnals was calculated using cfc derived water ages and yields a time history of the surface water 13c change at the isopycnal outcrop location the surface ocean suess effect recorded on isopycnals decreased with increasing outcrop latitude from approximately 0 2 decade 1 within the subtropics to around 0 1 decade 1 in the subpolar oceans in the pacific ocean these surface 13c change rate reconstructions agree both in magnitude and meridional trend with direct observations of surface ocean 13c changes reported from time series measurements and from comparisons of surface water 13c of dic measurements in 1970 and 1993 a global ocean average surface 13c rate of change of 0 15 0 04 decade 1 is determined which is slightly smaller than a previous time series data and model based estimate 0 171 decade 1 bacastow etal 1996 depth integrations of the 13c reconstructions in the pacific indian and atlantic oceans when combined with these previous individual depth profile comparisons and geochemical ocean sections study bomb 14c inventories quay et al 1992 imply a global depth integrated 13c change rate of 9 7 2 4 m yr 1 over the time period 1970 1990 these results imply a net oceanic co2 uptake rate of 1 9 0 9 gt c yr 1 over the time period 1970 1990 when applied to an atmospheric 13co2 and 12co2 budget

was phanerozoic reef history controlled by the distribution of non enzymatically secreted reef carbonates microbial carbonate and biologically induced cement throughout most of the phanerozoic reef rigidity resulted as much or more from early lithification by microbial carbonates and biologically induced cements non enzymatic carbonates than from biological encrustation of or by large enzymatically secreted metazoan skeletons reef framework is divided into four categories 1 skeletal metazoan 2 non skeletal microbialite stromatolite and thrombolite 3 calcimicrobe and 4 biocementstone in which small or delicate organisms serve as scaffolds for rigid cement crusts the last three categories are dominated by non enzymatic carbonates skeletal framework and non skeletal microbialite framework were the most abundant framework types through the phanerozoic the composition and abundance of skeletal framework was controlled largely by mass extinction events but most reefs consisted of both microbialite and skeletal organisms in a mutually beneficial relationship microbialite framework was abundant throughout the palaeozoic and early mesozoic but declined after the jurassic calcimicrobe framework was important during the cambrian early ordovician and devonian and biocementstone framework was important from the late mississippian to the late triassic the phanerozoic history of reefs does not correlate well with the stratigraphic distribution of large skeletal reef builders or with a variety of physicochemical parameters including sea level history wilson cycle or global climate cycles because non enzymatic carbonates result from induction by non obligate calcifiers and not enzymatic precipitation by obligate calcifiers the distribution of these carbonates was controlled to a larger extent by temporal changes in physicochemical parameters affecting the saturation state of sea water with respect to carbonate minerals changes in pco ca mg ratios cation concentrations and temperature may have affected the abundance of non enzymatic carbonates and hence reefs independently from the effects of these same parameters and mass extinction events on skeletal reef biota the decline in abundance of reefal microbialite and absence of calcimicrobe and biocementstone reef framework after the jurassic may be a result of relatively low saturation states of sea water owing to increased removal and sequestration of finite marine carbonate resources by calcareous plankton since the jurassic reef history is difficult to correlate with temporal changes in specific global parameters because these parameters affect skeletal biota and biologically induced carbonate precipitation independently hence reef history was regulated not just by skeletal reef biota but by parameters governing non enzymatic carbonates

secular variation in abiotic marine carbonates constraints on phanerozoic atmospheric carbon dioxide contents and oceanic mg ca ratios abiotic marine carbonates have been precipitated as ooids and synsedimentary cement within shallow marine carbonate sequences throughout the phanerozoic these components exhibit variable abundances and compositions that temporally correlate with estimates of global eustasy with rising sea level aragonite and acicular magnesium calcite precipitation gave way to the formation of equant calcite and possibly dolomite similarly the abundance of ooids was limited by positions of global sea level and associated changes in ocean chemistry modern abiotic marine carbonates also exhibit variable abundances and compositions as a function of changing fluid chemistry with latitude and depth chemical data on ambient marine waters suggest that carbonate ion concentrations and rates of precipitation presently control the nature of marine cement and ooids using data from modern oceans to calculate the requisite atmospheric pco 2 levels necessary to form this range of phases in ancient seas suggests that atmos

global and regional variations in tropical marine environments of gondwana as revealed by a multi stable isotope study middle triassic anisian israel levant basin abstract the world during the early middle triassic anisian was characterized by a distinct recovery of the carbonate factory after the permian triassic crisis this recovery seems to have passed over the anisian environment on the tropical northern margin of gondwana israel levant basin and to have resulted in the low diversity of barren horizons of carbonate secreting organisms four anisian successions the ramon 1 hameishar 1 nafha 1 and david 1 boreholes were studied to decode the factors preventing regional recovery a multi proxy analysis was performed on these boreholes including the carbonate siliciclastic ratio total organic carbon toc carbon nitrogen c n ratio and inorganic carbon 13ccarb oxygen 18ocarb and nitrogen 15n isotopic compositions the aim of assessing the combination of these proxies was to characterize the geochemical conditions in the regional basins these successions record two c cycle perturbation events characterized by negative shifts in 13ccarb values and recognized in most successions indicating the land marine teleconnection effect on the c cycle perturbation the 18ocarb excursions revealed similar oscillation trends with global warming evidenced by increasing circumtropical precipitation and terrestrial influxes whereas global cooling was reflected by increased carbonate factory production the low 15n values in all of the studied successions indicated the presence and flourishing of n fixers the absence or scarcity of carbonate secreting organisms suggests that these n fixers were the source of the carbonate fraction in the sediments episodic events with high 15n values suggest an accumulation of terrestrial organic matter om or oxygenation events allowing short term colonization by benthic fauna at the marine sites

calcium carbonate budget in the atlantic ocean based on water column inorganic carbon chemistry 1 recent independent lines of evidence suggest that the dissolution of calcium carbonate caco3 particles is substantial in the upper ocean above the calcite 100 saturation horizon this shallow water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic caco3 at shallow water depths here we use more than 20 000 sets of carbon measurements in conjunction with cfc and 14c data from the woce jgofs oaces global co2 survey to estimate in situ dissolution rates of caco3 in the atlantic ocean a dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface the in situ caco3 dissolution increases rapidly at the aragonite 100 saturation horizon estimated dissolution rates north of 40on are generally higher than the rates to the south which is partly attributable to the production of exported caco3 being higher in the north atlantic than in the south atlantic as more caco3 particles move down the water column more particles are available for in situ dissolution the total water column caco3 dissolution rate in the atlantic ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5 6 1012 mol c yr 1 from caco3 rich sediments the resulting water column dissolution rate of caco3 for the atlantic ocean is approximately 11 1 1012 mol c yr 1 this corresponds to about 31 of a recent estimate 35 8 1012 mol c yr 1 of net caco3 production by lee 2001 for the same area our calculation using a large amount of high quality water column alkalinity data provides the first basin scale estimate of the caco3 budget for the atlantic ocean

inorganic carbon in the indian ocean distribution and dissolution processes 1 this study uses nearly 25 000 carbon measurements from the woce jgofs global co2 survey to examine the distribution of dissolved inorganic carbon dic and total alkalinity ta in the indian ocean shallow and intermediate distributions of inorganic carbon do not strictly follow temperature and salinity because of differing surface gradients and vertical biological processes that work to modify the circulation derived features anthropogenic co2 has increased the shallow dic by as much as 3 decreasing the vertical dic gradient deep ocean dic and ta increase toward the north because of the decomposition and dissolution of organic and inorganic particles calcite saturation depths range from 2900 3900 m with the deepest saturation depth in the central indian ocean variations of aragonite saturation depth 200 1400 m are similar to calcite but the deepest saturations are in the southwestern indian ocean the shallowest aragonite saturation depths are found in the bay of bengal in the northern arabian sea and bay of bengal the current aragonite saturations are 100 and 200 m shallower respectively than in preindustrial times estimates of carbonate dissolution rates on isopycnal surfaces range from 0 017 to 0 083 mol kg 1 yr 1 in deep waters upper water column dissolution rates range from 0 to 0 73 mol kg 1 yr 1 with a local maximum occurring in intermediate waters just below the aragonite saturation horizon dissolution is also generally higher north of the chemical front at 10 20 s there is some evidence for significant sedimentary sources in the northern indian ocean

carbonate dissolution in the guts of benthic deposit feeders a numerical model abstract we present a numerical model to quantify calcite dissolution in the guts of deposit feeding invertebrates deposit feeder guts were modeled as constantly stirred reactors cstrs following terminology from digestion theory saturation state and dissolution of calcium carbonate were calculated from changes in total dissolved carbon dioxide and alkalinity resulting from sediment passage through the digestive tract while accounting for dissolution of calcite and respiration of organic carbon typical dissolution rates for a gut volume of 1 ml ranged between 0 5 4 mg calcite d 1 sensitivity analysis revealed gut ph sediment organic matter om content and om reactivity to be the critical parameters determining calcite dissolution rate carbonate dissolution rate was inversely related to gut ph however calcite dissolution was found to be possible even at alkaline gut ph due to respiration by intestinal microbes the kinetics of calcite dissolution had only marginal influence on daily calcite dissolution rates varying the calcite dissolution rate constant by six orders of magnitude affected calcite dissolution rates by less than a factor of 10 calcite dissolution rates were calculated for 4 different hydrographic regimes that differed in their content of sedimentary calcite and om and furthermore in their om reactivity highest dissolution rates were calculated for the shallow water setting where relatively high om content facilitated high microbial respiration rates depressing gut ph however dissolution rates for the deep sea setting were only slightly lower due to greatly elevated ingestion rates resulting from low om content as a consequence of much higher faunal abundances shallow water benthos is likely to contribute the vast majority of gut mediated carbonate dissolution nevertheless the fraction of sedimentary calcite that dissolves during one gut passage is probably too small to be observable by simple gravimetric analysis this may explain the notable scarcity of evidence for gut mediated carbonate dissolution in the literature to date assuming depth dependent calcite dissolution rates and deposit feeder abundances we estimate gut mediated carbonate dissolution to contribute approximately 5 of the annual global sedimentary carbonate dissolution rate which corresponds to an average calcite dissolution rate of approximately 0 5 mg m 2 d 1 for the entire ocean floor

stable isotopic compositions of recent freshwater cyanobacterial carbonates from the british isles local and regional environmental controls recent 50 years old freshwater cyanobacterial carbonates from diverse environments streams lakes waterfalls throughout britain and ireland were analysed for their stable carbon and oxygen isotope compositions the mean 18o value of 5 9 pdb for river and stream data represents calcite precipitation in equilibrium with the mean oxygen isotopic composition of precipitation in central britain 7 5 smow assuming a mean water temperature of 9 c the mean 18o of lake data 4 5 pdb is statistically different reflecting the effects of residence time and or variations in the oxygen isotopic composition of rainfall carbon isotopes have wide variations in both fluviatile and lake data sets 3 to 12 pdb these variations are principally controlled in the fluviatile samples by contribution of isotopically light soil zone carbon relative to isotopically heavier carbon from limestone aquifer rock dissolution lake samples have the heaviest carbon isotope values reflecting a trend toward isotopic equilibrium between atmospheric co2 and aqueous hco 3 we infer that isotopic compositions of ancient cyanobacterial carbonates should also record environmental information although the effects of stabilization and diagenesis on primary 18o values will need careful consideration primary carbon isotope compositions should be well preserved although in marine samples values will be buffered by the isotopic composition of aqueous marine bicarbonate

effective stress response of a plane sea bed under wave loading this note describes the determination for a wide class of wave pressure forms of the response to waveloading of an infinite half space consisting of a porous elastic soil skeleton under such loading no volumetric strains occur in the soil mass and there is no coupling between the pore water and the skeleton also an analytical relationship has been established between stresses and pore pressures so that the computation of the pore pressures is sufficient to solve the complete effective stress problem the paper gives an integral formulation for the pore pressure as a function of the wave pressure

biogeochemistry and dynamics of particulate organic matter in a shallow water hydrothermal field kueishantao islet ne taiwan abstract the particulate organic matter pom of shallow water hydrothermal fields has been studied in the context of food web reconstruction but the processes governing its biogeochemistry and dynamics are poorly explored here we investigate the pom in the kueishantao hydrothermal field using chemical and hydrodynamic approaches the depletion of total suspended matter lower c n ratios and higher carbon isotopic values of particulate organic carbon 13cpoc in the vertical plumes relative to values derived from si based models were attributed to the hydraulic sorting of the vented particles which tend to have more n and 13c in the fine fraction the particulate organic carbon poc unlike the total suspended matter was enriched in the vertical plumes and explained by physicochemical processes rather than biological addition the poc enriched plume top water was found to be a better endmember than the vent fluids to explain particle mixing in the lateral plume physical mixing played a steering role in shaping the particle chemistry of the lateral plumes but markedly 13c enriched poc was still observable in several near vent low to intermediate si plume waters implying locally enhanced primary production of at least 0 1 0 4 mg c m3 h the presence of eddies confirmed by flow field measurements should have contributed to the detection of biogeochemical anomalies via extending the retention time of plume water to 1 2 h the dominating mixing process resulted in decoupling between the 13cpoc signatures and carbonate chemistry in this shallow water hydrothermal plume

chemistry and stromatolites of the sea linked satonda crater lake indonesia a recent model for the precambrian sea abstract the abundance of in situ calcified stromatolites in the precambrian paleontological record and their absence from modern seas is still an enigma we report on the discovery of the first recent in situ calcified stromatolites growing in a sea linked environment the stromatolites are produced by coccoid cyanobacteria and started to grow 4000 yr ago in the crater lake of satonda island indonesia compared to seawater the lake has gained alkalinity and lost ca its ph 8 45 as well as its saturation with respect to calcite is significantly higher than in seawater the additional alkalinity is provided by biogenic co2 and subsequent weathering of volcanic silicates satonda crater lake may provide an analogue to the stromatolite sustaining precambrian marine environments which therefore may have been more alkaline than present day seawater this conclusion is congruent with the recently advanced hypothesis of an early soda ocean

the late jurassic tithonian a greenhouse phase in the middle jurassic early cretaceous cool mode evidence from the cyclic adriatic platform croatia well exposed mesozoic sections of the bahama like adriatic platform along the dalmatian coast southern croatia reveal the detailed stacking patterns of cyclic facies within the rapidly subsiding late jurassic tithonian shallow platform interior over 750 m thick ca 5 6 myr duration facies within parasequences include dasyclad oncoid mudstone wackestone floatstone and skeletal peloid wackestone packstone shallow lagoon intraclast peloid packstone and grainstone shoal radial ooid grainstone hypersaline shallow subtidal intertidal shoals and ponds lime mudstone restricted lagoon fenestral carbonates and microbial laminites tidal flat parasequences in the overall transgressive lower tithonian sections are 1 4ae5 m thick and dominated by subtidal facies some of which are capped by very shallow water grainstone packstone or restricted lime mudstone laminated tidal caps become common only towards the interior of the platform parasequences in the regressive upper tithonian are dominated by peritidal facies with distinctive basal oolite units and well developed laminate caps maximum water depths of facies within parasequences estimated from stratigraphic distance of the facies to the base of the tidal flat units capping parasequences were generally 4 m and facies show strongly overlapping depth ranges suggesting facies mosaics parasequences were formed by precessional 20 kyr orbital forcing and form parasequence sets of 100 and 400 kyr eccentricity bundles parasequences are arranged in third order sequences that lack significant bounding disconformities and are evident on accommodation fischer plots of cumulative departure from average cycle thickness plotted against cycle number or stratigraphic position modelling suggests that precessional sea level changes were small several metres as were eccentricity sea level changes or precessional sea level changes modulated by eccentricity supporting a global hot greenhouse climate for the late jurassic tithonian within the overall cool mode of the middle jurassic to early cretaceous

evolution pattern of early permian carbonate buildups with reference to the carbonate mounds in eastern inner mongolia north china abstract the sakmarian kungurian early permian carbonate mounds of the amushan formation of the deyanqimiao section in eastern inner mongolia north china comprise phylloid algae echinoderm mound fusulinid echinoderm mound and echinoderm mound they were constructed by repeating the following steps in the mid ramp and outer ramp environments 1 skeletal grains accumulated in situ or after short distance transportation 2 tubiform microbes eroded skeletal grains induced the formation of caco3 crystallites near the cell surface and trapped and bound suspended lime mud from ambient water 3 some positive topographies slightly higher than adjacent sediments were formed data from north china as well as the tropical tethyan domain and the subtropical pangean domain show a three phase development pattern of early permian carbonate buildups the first phase asselian sakmarian is marked by carbonate buildups rich in organisms such as phylloid algae palaeoaplysina shamovella sponges and bryozoans the second phase artinskian is represented by the disappearance of phylloid algae and palaeoaplysina from carbonate buildups resulted from the paleoclimatic change from an icehouse to a greenhouse the third phase kungurian is characterized by the sharp contrast between drastic decline of carbonate buildups in the subtropical pangean domain and their successful development in north china and the tropical tethyan domain

proterozoic ministromatolites with radial fibrous fabric small digitate stromatolites with diameters in the range of 0 2 20 mm ministromatolites are common in early and middle proterozoic carbonate sequences and extend stratigraphically from the archaean to the holocene an occurrence of columnar and stratiform types exhibiting a primary or early diagenetic radial fibrous fabric and microscopically crinkled microcrenate lamination is described from the 1 9 gyr old belcher supergroup mcleary formation in southeastern hudson bay canada the structures which can be considered to be a variety of tufa are unusually well preserved because of early diagenetic silicification columnar types are referable to pseudogymnosolen asperia and are morphologically similar to other occurrences of these taxa in coeval dolostones in northwestern and eastern canada where the fabric is normally preserved by a secondary mosaic of dolomite the textural evidence of angulate cross sections and rectilinear divergent patterns indicates that the radial fibrous fabric represents primary or very early diagenetic precipitation and that pseudogymnosolenids with mosaic dolomite originally also had radial fibrous structure the precipitation may have been within or on microbial mats

high energy coralgal stromatolite frameworks from holocene reefs tahiti french polynesia drill cores from holocene reefs on tahiti french polynesia reveal a framework composed of massive branching acroporids encrusted by coralline algae associated with sessile vermetid gastropods and arborescent foraminifers laminated micritic crusts form coatings over coral branches or more commonly over related encrusting organisms throughout the cored reef sections these crusts appear as a major structural and volumetric component of the reef framework the microbial nature of these micritic crusts is inferred from their typical organic growth forms and geometry the occurrence of microbial remains and stable isotope measurements the reef communities accumulated at depths less than 5 m below mean sea level in a high energy environment throughout vertical growth from 7140 170 yr bp to the present the nature of the involved benthic communities stable isotope data and high calcification rates of microbially encrusted corals strongly suggest that local environmental conditions have been optimal for reef development for the last 7000 years the causes of the predominance of microbial communities over actual encrusters red algae foraminifers remain problematic and could be related to short term fluctuations in ecological parameters microbial micritic crusts seemingly played a prominent role in protecting the coralgal colonies from bioeroders and grazers and possibly in strengthening the framework due to rapid lithification the record of similar microbial crusts in other quaternary reef tracts suggests that microbial communities may have played a more prominent role in quaternary reefs than presently recognized

an early soda ocean in analogy to modern soda lakes commonly associated with volcanic regions it is postulated that the ancient sea had a high alkalinity a high ph and low ca and mg concentrations the change towards nacl dominance as observed in the present day ocean can best be explained by a series of mineral equilibria crustal differentiation and life processes in principle hydrothermal leaching of chlorine from the oceanic crust caused this ion to accumulate in the sea while at the same time dissolved carbonates became gradually removed by organisms and carbonates the switch from a soda to a halite ocean was accomplished 1 ga ago critical biochemical events marking the chemical evolution of the precambrian sea and their implications for the pco2 in air will be discussed

secular variation of calcium carbonate mineralogy an evaluation of ooid and micrite chemistries three ooid types are recognized from the lower tournaisian kohlenkalk shelf facies at velbert germany ooids from this unit have a predominantly concentric laminae fabric radial concentric and small radial fibrous ooids are minor components to this oolite the diagenetic response of kohlenkalk ooid chemistry is significantly different from that observed in contemporaneous crinoid and brachiopod material fabric evidence suggests that radial concentric and radial fibrous ooids were probably originally aragonite high mg calcite and high mg calcite respectively fabric and trace elemental chemistries of the concentric fabric ooids suggests that they were originally precipitated as aragonite and subsequently altered to low mg calcite

assemblages of calcareous algae near the precambrian cambrian boundary in siberia and mongolia calcareous algae make their first appearance near the base of the tommotian the oldest confirmed occurrences are of gemma obruchevella and renalcis in the nemakit daldyn horizon and late yudomian of siberia a little higher in the sequence in the aldanocyathus sunnaginicus zone of the earliest tommotian angulocellularia bajanophyton batenevia botomaella girvanella hedstroemia korilophyton proaulopora subtifloria and tarthinia appear immediately above this in the dokidocyathus regularis zone of the middle tommotian chabakovia appears with the epiphytacean genera epiphyton gordonophyton and tubomorphophyton kordephyton appears in the dokidocyathus lenaicus zone of the late tommotian and razumovskia in the early atdabanian these fossils constitute three calcareous algae assemblages caa 1 2 3 characteristic of the nemakit daldyn horizon late yudomian early tommotian and middle tommotian atdabanian respectively most of the genera are long ranging but their rapid appearance and diversification near the base of the tommotian represents an important event in the history of calcareous algae and augments faunal data concerning evolution and biostratigraphy near the precambrian cambrian boundary modified journal abstract

calcisponge microbialite reef facies middle permian lower guadalupian northwest shelf margin of permian basin new mexico exceptional mimetic preservation of reef fabrics in a dolostone subsurface core from vacuum field lea county new mexico along the northwest shelf margin of the permian basin reveals the significant microbialite role in a calcisponge microbialite reef of the upper san andres formation lower guadalupian middle permian the shelf margin reef facies which comprises more than 85 of the 175 ft 53 34 m cored section is bordered shelfward by crestal shelf margin shoal facies and seaward by basinal sandstones of the delaware mountain group the thick shelf margin reef located within 500 ft 152 4 m of basinal sandstone facies indicates a relatively steep reefal shelf margin microbialite encrustations are the most important binding agent in the reef and their major contribution to the cohesion and volume of the reef has significant implications for the growth and character of other middle permian shelf margin reefs the reef facies is composed of 1 a calcisponge dominated reef framework guadalupia lemonea amblysiphonella discosiphonella cystaulete and cystothalamia 2 a binding biota of ubiquitous micritic laminated and thrombolitic microbialite moderately common tubiphytes shamovella and sparse archaeolithoporella and bryozoans 3 sparse botryoids of syndepositional radial fibrous cements 4 sparse reef dweller biota of gastropods brachiopods and crinoids and 5 reef cavities lined by banded isopachous layers of marine phreatic radiaxial cements partly filled by geopetal sediments and finally filled by anhydrite the paragenetic sequence is 1 reef growth 2 framework cavities lined by marine phreatic radiaxial cements and partially filled by geopetal sediments 3 partial aragonite dissolution and karsting 4 rapid reflux dolomitization 5 localized fracturing and spalling of cavity walls before and during emplacement of anhydrite and 6 burial and pressure solution patchy intraskeletal skelmoldic porosity is mostly within calcisponges karstic fractures and cavities in the upper reef are filled with breccia clasts fusulinid packstone grainstones dark argillaceous dolomudstones and massive anhydrite

late palaeoproterozoic 1800 1600ma stromatolites cuddapah basin southern india cyanobacterial or other bacterial microfabrics abstract late palaeoproterozoic stromatolites from the vempalle formation of the cuddapah supergroup south eastern india contain well preserved microfabrics these exhibit a range of complex clotted to bush like micritic fabrics set in microsparite and sparite cements no calcified microfossils confidently referable to calcified cyanobacteria have been recognized although micritic masses crudely resembling the phanerozoic calcified cyanobacterium angusticellularia are present it is suggested that these vempalle stromatolitic microfabrics compare more closely with modern calcified non cyanobacterial biofilms this interpretation questions the widespread assumption that cyanobacteria were important components of stromatolite building microbiotas during the proterozoic and instead emphasizes the possibility that examples similar to those studied were dominated by non cyanobacterial bacteria it is generally thought likely that cyanobacteria were important components of stromatolite building microbiotas during the proterozoic and that early lithification by carbonate precipitation was widespread and intense if these assumptions are correct then the apparent absence of diverse calcified cyanobacteria suggests that these organisms which are conspicuous in the early palaeozoic underwent evolutionary radiation close to the neoproterozoic cambrian boundary

seasonal variability of the effect of coral reefs on seawater co2 and air sea co2 exchange there are complex physical and biological processes controlling the exchange of carbon dioxide co2 between the ocean and atmosphere in coral reef ecosystems the balance of biological processes such as calcium carbonate caco3 formation and organic carbon production can either lead to co2 being retained in the oceanic environment i e oceanic sink of co2 or returned to the atmosphere through gas exchange oceanic source of co2 what remains uncertain is the fate of co2 in reefs subject to seasonal change and the annual balance of air sea co2 flux in such systems here it is shown that the bermuda coral reef acts as a source of co2 to seawater overlying the reef the magnitude of this source of co2 varies seasonally in response to changes in the reef community between coral and macroalga dominated states reflecting changes in the net balance between calcification and organic carbon production with knowledge of the calcification rate 5 6 to 10 6 g caco3 m 22 d 21 and observed modification in seawater f co2 by reef metabolism rates 20 6 to 3 3 g c m 22 d 21 and seasonal patterns of macroalgal productivity were estimated whether the bermuda coral reef system acts as an oceanic sink or source of co2 to the atmosphere not only depends on this seasonal variation but more importantly depends on the pre existing air sea co2 disequilibrium of open ocean waters surrounding the reef system the bermuda coral reef system serves as a useful model for understanding the fate of co2 in other reefs particularly those reefs changing because of environmental stress

microbial mounds prior to the frasnian famennian mass extinctions hantang guilin south china late frasnian mounds of the yunghsien formation guilin south china developed as part of the guilin platform mostly in reef flat and platform margin settings microbial mounds in platform margin settings at hantang about 10 km west of guilin contain frasnian biota such as stachyodes and kuangxiastraea and thus occur below the frasnian famennian mass extinction boundary platform margin facies were dominated by microbes algae and receptaculitids massive corals and stromatoporoids are not common and rarely show reef building functions as they did in givetian time the margin mounds are composed of brachiopod receptaculitid cementstone and a variety of boundstones that contain rothpletzella renalcis thrombolite and stromatolite other microbial communities include girvanella izhella ortonella and wetheredella solenoporoid algae are abundant locally zebra structures and neptunian dykes are well developed at some intervals pervasive early cementation played an important role in lithification of the microbial boundstones and rudstones frasnian reefs of many regions of the world were constructed by stromatoporoids and corals although a shift to calcimicrobe dominated frameworks occurred before the famennian however the exact ages of many frasnian margin outcrops are poorly constrained owing to difficulties dating shallow carbonate facies the hantang mounds represent a microbe dominated reef building community with rare skeletal reef builders consistent with major late devonian changes in reef composition diversity and guild structure occurring before the end of the frasnian a similar transition occurred in the canning basin of western australia but coeval successions in north america western europe and the northern urals are either less well known or represent different bathymetric settings the transition in reef building style below the frasnian famennian boundary is documented here in the two best exposed successions on two continents which may have been global set in the larger context of late devonian and mississippian microbial reef building the hantang mounds help to demonstrate that controls on microbial reef communities differed from those on larger skeletal reef biota calcimicrobes replaced stromatoporoids as major reef builders before the frasnian famennian extinction event and increasing stromatoporoid diversity towards the end of the famennian did not result in a resurgence of skeletal reef frameworks calcimicrobes dominated margin facies through the famennian but declined near the devonian carboniferous boundary stromatolite and thrombolite facies which occurred behind the mound margin at hantang rose to dominate mississippian shallow water reef frameworks with only a minor resurgence of the important frasnian calcimicrobe renalcis in the visean when well skeletonized organisms corals also became volumetrically significant frame builders again

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

carbonate ramp to deeper shale shelf transitions of an upper cambrian intrashelf basin nolichucky formation southwest virginia appalachians the nolichucky formation 0 300 m thick formed on the cambrian pericratonic shelf in a shallow intrashelf basin bordered along strike and toward the regional shelf edge by shallow water carbonates and by nearshore clastics toward the craton lateral facies changes from shallow basinal rocks to peritidal carbonates suggest that the intrashelf basin was bordered by a gently sloping carbonate ramp peritidal facies of the regional shelf are cyclic upward shallowing stromatolitic carbonates these grade toward the intrashelf basin into shallow ramp cross bedded ooid and oncolitic intraclast grain stones that pass downslope into deeper ramp subwave base ribbon carbonates and thin limestone conglomerate ribbon limestones are layers and lenses of trilobite packstone parallel and wave ripple laminated quartzose calcisiltite and lime mudstone arranged in storm generated fining upward sequences 1 5 cm thick that may be burrowed shallow basin facies are storm generated upward coarsening and upward fining sequences of green calcareous shale with open marine biota parallel to hummocky laminated calcareous siltstone and intraformational flat pebble conglomerate there are also rare debris flow paraconglomerate 10 60 cm thick and shaly packstone wackestone with trace fossils glauconite horizons and erosional surfaces hardgrounds a 15 m thick tongue of cyclic carbonates within the shale package contains subtidal digitate algal bioherms which developed during a period of shoaling in the basin understanding the nolichucky facies within a ramp to intrashelf basin model provides a framework for understanding similar facies which are widely distributed in the lower palaeozoic elsewhere the study demonstrates the widespread effects of storm processes on pericratonic shelf sedimentation finally recognition of shallow basins located on pericratonic shelves is important because such basins influence the distribution of facies and reservoir rocks whose trends may be unrelated to regional shelf edge trends

microbial carbonate abundance compared with fluctuations in metazoan diversity over geological time abstract secular variation in microbial carbonate abundance may be reflected by stromatolite morphotype diversity and reefal microbial carbonate abundance these datasets reveal long term changes over the past 3000 myr that include a peak of abundance 1250 myr ago late proterozoic decline cambrian resurgence and fluctuating decline during the remainder of the phanerozoic it is conceivable that proterozoic metazoan diversification coincided with inception of stromatolite decline 1250 myr ago but microbial carbonate increase during cambrian metazoan radiation together with failure of microbial carbonates to increase in the aftermaths of the end ordovician end triassic and end cretaceous mass extinctions suggest that factors in addition to metazoan competition significantly influenced long term changes in microbial carbonate abundance

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

does carbon 13 track anthropogenic co2 in the southern ocean a multiparametric linear regression technique was used for waters in the southern ocean to estimate the change in both 13 c dic 13 c dic and dissolved inorganic carbon dic dic between 1978 and 1998 due to the accumulation of anthropogenic co 2 the observed decrease in 13 c dic at the surface the suess effect was 0 015 0 003 yr 1 in the sub antarctic zone and 0 005 0 003 yr 1 in the antarctic zone similar to values reported for the southern indian ocean gruber et al 1999 sonnerup et al 2000 to compare the 13 c dic with adic we used the ratio of these two anomalies rc 13 c dic dic mol kg 1 1 along the section arc ranged from 0 015 0 005 at 42 s to 0 007 0 005 mol kg 1 1 at 54 s the spatial variability in arc in the southern ocean reflects different timescales for processes controlling the uptake of 13 c from those controlling the uptake of 12 c and indicates that 13 c dic decouples from adic poleward of the sub antarctic zone the variations of arc along the section suggest that the 13 c dic anomaly is not a good predictor of the anthropogenic co 2 inventory in the southern ocean some methods for determining anthropogenic co 2 uptake both on the global and regional scale assume the penetration depths of 13 c dic to be the same as adic which implies a constant value for arc in the ocean at 0 016 mol kg 1 1 heimann and maier reimer 1996 ortiz et al 2000 bauch et al 2000 the use of a constant arc and the observed 13 c dic to estimate anthropogenic co 2 could lead to an underestimate in the inventory of anthropogenic co 2 for the southern ocean by 50

in situ calibration of mg ca ratio in planktonic foraminiferal shell using time series sediment trap a case study of intense dissolution artifact in the south china sea this study examines mg ca temperature equations through the use of planktonic foraminifers collected from continuous time series sediment traps at four water depths in the south china sea this deployment provides an opportunity to refine partial dissolution artifacts and to identify responses of shell chemistry to changes in ambient seawater conditions paired mg ca and 18o measurements on shells are strongly correlated with seasonal variability in terms of temperature at specific habitat depths however partial dissolution can significantly alter mg ca ratios even at depths well above the calcite lysocline or carbonate compensation depth of the three species studied neogloboquadrina dutertrei is the most sensitive species to dissolution relative to the other surface dwelling species globigerinoides ruber and globigerinoides sacculifer differences between the mg derived temperature equation here and those from previously established core top or sediment trap calibrations can be attributed to various degrees of dissolution and lateral advection thus highlighting the need for in situ empirical calibration for different ocean basins

marine red staining of a pennsylvanian carbonate slope environmental and oceanographic significance abstract red stained platform facies are a common feature of many carbonate settings throughout the geological record although the mechanisms involved in red staining of subaerially exposed or argillaceous peri platform limestones are reasonably well understood the environmental and oceanographic significance of red carbonates often remains uncertain here sedimentological sequence stratigraphic geochemical paleontological and quantitative bathymetric data from pennsylvanian red intervals across a well exposed carbonate platform top and slope are documented and interpreted in a process oriented context on the upper slope 80 350 meters below the shelf break red intervals alternate with gray mainly microbial algal boundstones on the lower slope 350 600 meters below the shelf break redeposited red stained mud builds matrix supported breccia tongues interbedded with predominantly redeposited clast supported carbonate debris the presence of large volumes of fibrous calcite biocementstones as well as firmgrounds point to low sedimentation rates or omission in terms of sequence stratigraphy red intervals occur within maximum flooding intervals and reflect near platform drowning elevated 18o values 2 3 and an essentially cool water heterotrophic biotic association in red intervals on platform top and slope suggest deposition during sea level highs associated with colder water masses and high nutrient levels the most likely drivers are an elevated thermocline and upwelling the red staining is the result of iron oxidation which occurred during early diagenesis likely by iron bacteria these red intervals provide an important bathymetric benchmark against which other mainly paleozoic red facies can be tested and calibrated

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

paleoclimatic significance of phanerozoic reefs a database of pre quaternary phanerozoic reefs is used to test the significance of ancient reefs as paleoclimatic tracers the compilation of reef paleolatitudes through time and comparison with published paleoclimate curves shows that neither the width of the tropical reef zone nor the total latitudinal range of reefs is correlated with published estimates of paleotemperature however reefs trace paleoclimate indirectly algal reefs tend to prevail during icehouse climatic intervals and distinct high latitude reefs are only developed in cold intervals whereas during greenhouse episodes the reef zone usually ended abruptly at a particular latitudinal boundary in the subtropics additionally different biotic reef types tended to be concentrated in different latitudes the lowest latitudes have usually been occupied by coralline sponge or microbial reefs coral reefs tended to grow in intermediate latitudes and bryozoan reefs constantly occupied the highest latitudinal position

carbon isotope records from extant caribbean and south pacific sponges evolution of δ13c in surface water dic stable isotope records of demosponges from the caribbean and coral sea are described for the purpose of studying the influence of fossil fuel co2 on the carbon isotopic composition of dissolved inorganic carbon dic in surface water the slow growing sponges precipitate calcium carbonate in isotopic equilibrium with ambient sea water and are used to detect changes in 13cdic from pre industrial times early 19th century to the present we observed similar shapes and ranges in 13c curves measured on caribbean specimens collected from water depths of 25 84 and 91 m as well as a specimen collected in shallow waters off new caledonia the records reveal a highly significant correlation with atmospheric 13cco2 13cdic values for caribbean and coral sea surface waters were calculated using the 13c sponge records while 13c of atmospheric co2 decreased by about 1 4 from the early 19th century to 1990 13cdic of caribbean and coral sea surface waters decreased by 0 9 0 2 and 0 7 0 3 respectively no isotopic equilibrium between surface water dic and atmospheric co2 was observed either during the pre industrial steady state or during the last 100 years the lower amount of depletion in the surface water 13cdic with respect to the atmospheric anthropogenic signal is explained by the dilution of the surface waters by biologically altered subsurface water dic the lower 13c decrease in the coral sea points to a stronger influence of the subsurface water source compared to the caribbean

the mechanism of production enhancement in coral reef carbonate systems model and empirical results coral reefs are characterized by enormous carbonate production of the organisms it is known that rapid calcification is linked to photosynthesis under control of the carbonate equilibrium in seawater we have established a model simulating the coexisting states of photosynthesis and calcification in order to examine the effects of photosynthesis and calcification on the carbonate system in seawater supposing that the rates of photosynthesis and calcification are proportional to concentrations of their inorganic carbon source the model calculations indicate that three kinds of unique interactions of the organic and inorganic carbon productions are expected these are photosynthetic enhancement of calcification calcification which benefits photosynthesis and carbonate dissolution induced by respiration the first effect appears when the photosynthetic rate is more than approximately 1 2 larger than that of calcification this effect is caused by the increase of co32 content and carbonate saturation degree in seawater if photosynthesis use molecular carbon dioxide the second effect occurs when the calcification rate is more than approximately 1 6 times larger than that of photosynthesis time series model experiments indicate that photosynthesis and calcification potentially enhance each other and that organic and inorganic carbon is produced more efficiently in the coexisting system than in the isolated reactions these coexisting effects on production enhancement of photosynthesis and calcification are expected to appear not only in the internal pool of organisms but also in a reef environment which is isolated from the outer ocean during low tide according to the measurements on the fringing type shiraho reef in the ryukyu islands the diurnal change of water properties ph total alkalinity total carbon dioxide and carbonate saturation degree were conspicuous this environment offers an appropriate condition for the appearance of these coexisting effects the photosynthetic enhancement of calcification and the respiratory inducement of decalcification were observed during day time and night time slack water periods respectively these coexisting effects especially the photosynthetic enhancement of calcification appear to play important roles for fluorishing coral reef communities

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

transgressive oversized radial ooid facies in the late jurassic adriatic platform interior low energy precipitates from highly supersaturated hypersaline waters dark gray oolitic units characterized by oversized ooids with primary radial calcite fabrics occur in the interior of the late jurassic late tithonian adriatic platform a large mesozoic tethyan isolated platform in croatia they differ from open marine platform margin ooid grainstones in their dark color cerebroid outlines broken and recoated grains abundant inclusions highly restricted biota and lack of cross stratifithey have been interpreted as being of vadose origin vadoids at tops of upward shallowing parasequences however detailed sections show that most oolitic units occur at bases of precessional parasequences overlying erosional surfaces on fenestral carbonates the oolitic units are similar to quiet water ooids that form today in low energy settings they developed in an arid climate during initial transgression of supratidal fl ats along lowenergy shores seaward of tidal fl ats and along the margins of restricted lagoons and intertidal ponds superimposed fenestral fabrics meniscus micrite cements and grain breakage occurred as they aggraded to high tide level and were subjected to wetting and drying thermal expansion and contraction and wind transport they migrated landward with transgression forming extensive sheets and were overlain by subtidal lagoonal facies that shallow up into fenestral carbonates these distinctive facies may have been overlooked in the geological record or their geological distribution requires juxtaposition of calcite seas high calcite supersaturation states arid climate and presence of fl at topped carbonate platforms in a greenhouse world

the nature of fossil bacteria a guide to the search for extraterrestrial life in an attempt to establish reliable criteria for the identification of potential fossil life in extraterrestrial materials the fossilizable characteristics of bacteria namely size shape cell wall texture association and colony formation are described and an overview is given of the ways in which fossil bacteria are preserved as compressions in fine grained sediments preservation in amber permineralized by silica replacement by minerals such as silica pyrite fe mn oxides calcite phosphate and siderite or as molds in minerals the problem of confounding minerally replaced bacteria with non biological structures having a bacterial morphology is addressed examples of fossilized bacteria from the early archaean through to the recent are used to illustrate the various modes of preservation and the morphology of fossil bacteria

tectonic controls of phanerozoic sedimentary rock cycling the cyclic nature of the phanerozoic sedimentary rock distribution carbon sulphur coupling and material transfer among sedimentary reservoirs appears to be controlled by tectonic factors the distribution of preserved sedimentary mass in terms of rock mass remaining u geologic age shows a minimum c 300 350 ma ago which separates two subcycles of erosion and deposition of sedimentary rocks the older subcycle was interrupted because of the major continental collisions of the devonian and late carboniferous these collisions resulted in a reduction of outcrop areas of rocks of the older cycle relative to their masses leading to a decline in the probability of destruction and an increase in half life of these older sediments a strong correlation exists between the long term cyclicity in the phanerozoic global sea level curve and the distribution of carbon and sulphur among their major exogenic reservoirs this correlation is related to two principal tectonic modes of the phanerozoic oscillatory and submergent it is postulated that the submergent mode of active plate convergence obduction and subduction of sediments large ridge volume and high sea level gave rise to low erosion and sedimentation rates less restricted environments of carbonate deposition and relatively high atmospheric co 2 levels high temperatures resulting from an increased rate of production of co 2 from diagenetic and metamorphic reactions at subduction zones as sea level rose carbon was transferred from the sedimentary reservoir of reduced organic carbon to that of oxidized inorganic carbon in limestones whereas sulphur moved from the oxidized sulphate reservoir to the reduced sulphide reservoir as sea level fell reservoir transfers were opposite to those above culminating in the oscillatory mode of generally elevated continental interiors these reservoir transfers are consistent with secular changes observed in the distribution of 13 c and 34 s in sedimentary materials during the phanerozoic petrographic examination of phanerozoic oolite formations shows that ooids with preserved calcitic relict textures are characteristic of pre carboniferous carbonate rocks whereas ooids with relict textures indicative of initial aragonite mineralogy are dominant in rocks of younger age these changes in ooid mineralogy may be interpreted as reflecting changes in co 2 levels of the ocean atmosphere system consistent with the above tectonic considerations atmospheric co 2 levels were higher prior to carboniferous time favouring formation of calcitic ooids and skeletal parts after the carboniferous co 2 levels fell and aragonite and mg calcites of greater than 8 mol mg increased in abundance as precipitates

biosedimentology of a silurian thrombolite reef with meter scale growth framework cavities a completely dolomitized silurian reef at maumee ohio u s a is uncommon among early paleozoic reefs in that its framework consists of about 95 thrombolite boundstone and 5 corals the reef lithified syndepositonally as evidenced by centimeter to meter scale growth framework cavities within it that are completely filled with internal sediment the largest cavities 2 3 5 m in diameter are prob ably the largest ever recorded in a thrombolite reef four main types of components are distinguished in the reef frame work 1 dense bushy mesoclots 2 dense rounded to subrounded mesoclots 3 saccate microstructures and 4 crusts mostly struc tureless but also containing dense bushy mesoclots the dense bushy components are abundant rounded to sub rounded mesoclots less so and the remaining components are rare the dense bushy and rounded to subrounded mesoclots are interpreted to represent the calcified re mains of what were initially either aggregates of the probable filamen tous cyanobacterum angulocellularia or aggregates of renalcid calci microbes or both and the saccate mesoclots as the calcimicrobe ren alcis sensu stricto it is speculated that syndepositonal lithification of the reef framework was accomplished by impregnation of unlithified protomesoclots by micrite to create mesoclots along with the formation of micritic cement around and between mesoclots that served to fuse together successive generations of mesoclots the direction of branching of bushy mesoclots in the reef indicates that unlithified protomesoclots were able to grow upward laterally and downward this ability along with syndepositional lithification to create mesoclots and to cement them together enabled the protome soclots and mesoclots to create reef knobs and eventually to roof over spaces that were centimeters to three or more meters in width and height to create growth framework cavities features indicative of rap id deposition including graded bedding poor sorting of bioclasts and textural inversion are common in internal sediment in meter size cav ities these features suggest that storms possibly hurricanes were at least as important and probably more so than everyday wave en ergy in transporting sediment into all cavities in the reef regardless of size

impact of long term climate change and sea level fluctuation on mississippian to permian mid oceanic atoll sedimentation akiyoshi limestone group japan abstract to understand the impacts of long term climatic episodes and sea level changes on mid oceanic atoll sedimentation the stratigraphic changes of litho and bio facies and stratigraphic levels of freshwater diagenetic alteration and biostratigraphic discontinuity of the akiyoshi limestone group upper visean to upper capitanian were reviewed this group records approximately 70 million years of atoll sedimentation in a mid oceanic realm of the panthalassa ocean which developed nearly synchronously with the late paleozoic gondwana glaciation the entire succession of the akiyoshi limestone group was divided into four facies associations skeletal oolitic grainstone muddy limestone muddy limestone skeletal grainstone and reefal limestone associations skeletal oolitic grainstone and reefal limestone associations upper visean to bashkirian are characterized by an abundance of oolite and crinoidal grainstone and reef facies of warm adapted metazoan reef builders corals chaetetes and bryozoans respectively characteristics of skeletal oolitic grainstone and reefal limestone associations indicate their deposition in a warm climate with elevated sea level muddy limestone association moscovian to kasimovian records the demise of the warm adapted metazoan reef builders and frequent emergence events of the buildup many geochemical data support the significant drop in temperature during moscovian through kasimovian time these depositional and biotic events of muddy limestone association indicate that its sedimentation was strongly affected by cool climate and generally low sea level muddy limestone skeletal grainstone association is characterized by an upward increasing significance of calcimicrobes calcareous algae and calcisponges the succession records less frequent emergence events than that of muddy limestone association ii these characters reflect a warming climate and sea level rise in gzhelian to capitanian time the climate episodes and sea level changes interpreted from the akiyoshi limestone group generally correspond to the global trend of mississippian to permian long term climatic change and sea level fluctuation related to the major glacial events of gondwana glaciation the late visean to bashkirian warm climate and elevated sea levels moscovian to kasimovian cooling and sea level lowering and gzhelian to capitanian warming and sea level rise recorded in the akiyoshi buildup are comparable to the global climate model and sea level fluctuation which contain early to middle mississippian pre glacial warm climate and highstands middle to late pennsylvanian cooling and related glacio eustatic sea level fluctuation at the culmination of gondwana glaciation and early to middle permian global warming and sea level rise due to the retreat of gondwana ice sheets akiyoshi atoll sedimentation was most significantly affected pennsylvanian global cooling and related sea level lowering but their impact was short lived the onset of the cooling and frequent emergence events in the akiyoshi buildup occurred delayed approximately 10 millions years later than that of comparable episodes on the pangean shelves the post glacial warming in the akiyoshi buildup started at least several millions of years earlier than in epicontinental seas of the pangea this phenomenon may be due to the palaeoposition of the akiyoshi buildup in a mid oceanic realm of the panthalassa ocean

decadal variability in seawater ph in the west pacific evidence from coral δ11b records long term seawater ph records are essential for evaluating the rates of ocean acidification oa driven by anthropogenic emissions widespread natural decadal variability in seawater ph superimposes on the long term anthropogenic variations likely influencing the oa rates estimated from the ph records here we report a record of annual seawater ph estimated using the b proxy over the past 159 years reconstructed from a porites coral collected to the east of hainan island in the northern south china sea scs by coupling this time series with previously reported long term seawater ph records in the west pacific the decadal variability in seawater ph records and its possible driving mechanisms were investigated the results indicate that large decadal variability in seawater ph has occurred off eastern hainan island over the past 159 years in agreement with previous records the qiongdong upwelling system which controls nutrient supplies regulates surface water productivity and is driven by the east asian summer monsoon is the primary control of this decadal variability while terrestrial inputs appear not influence significantly meanwhile the impacts of the pacific decadal oscillation pdo and the el nino and southern oscillation enso systems on seawater ph off eastern hainan island is likely limited in contrast the pdo is the main factor to influence the decadal seawater ph variability offshore the east australia while the mechanism controlling the decadal seawater ph variability in guam is not clear yet meanwhile the rate of decrease in seawater ph estimated from coral records are significantly different in different regions and over different time spans which may reflect a combination of natural decadal variability in seawater ph and long term variations therefore understanding the mechanisms driving natural variability in seawater ph is important for improving estimates of ocean acidification rates driven by anthropogenic emissions

petrogenesis of early cambrian reef limestones labrador canada through petrography cathodoluminescence and microprobe analysis three styles of particle preservation can be differentiated 1 skeletons with excellent fabric retention as nonferroan calcite trilobites and salterella or both ferroan and nonferroan calcite echinoids and sponge spicules 2 skeletal molds completely filled by nonferroan calcite spar or occasionally a second stage of equant ferroan calcite and dolomite as well archaeogastropods hyolithids brachipods coelenterates and chancelloria 3 fibrous to microcrystalline components which are now either well preserved as nonferroan calcite or are molds filled by equant ferroan calcite and dolomite or both ooids archaeocyathans and the alga renalcis synsedimentary cements localized to reefs are 1 rays or botryoids in which each acicular crystal is a spar filled mold or 2 rinds of fibrous calcite commonly with fascicular optic properties or a partially dissolved fabric in which the solution voids are now filled with iron rich equant calcite cement those cambrian particles and cements which are now only spar filled molds were originally aragonite those without a void stage and retaining original fabric were calcite or mg calcite those with a fibrous to microcrystalline habit in some instances and spar filled molds in other cases were probably mg calcite alteration to calcite occurred as the sediments reacted with meteoric and marine groundwaters in a phreatic lens and then with percolating meteoric waters in a vadose diagenetic environment either conditions of carbonate precipitation have been similar since the earliest paleozoic or that the ocean atmosphere system in early cambrian time was coincidentally similar to that of today but may have been quite different at other times during the phanerozoic modified journal abstract

stromatolitic bioherms and microphytolites from the late proterozoic draken conglomerate formation spitsbergen abstract the late proterozoic draken conglomerate formation akademikerbreen group in eastern spitsbergen displays several prominent stromatolitic bioherms in its lowermost beds the dolomitic bioherms are comprised principally of columnar stromatolites cf gymnosolenoides but include cross bedded microphytolitic grainstones the excellent exposures of the bioherms and microphytolitic grainstones along the margin of petrovbreen glacier and the exquisite preservation of structural and microscopic details permit the documentation and interpretation of these sedimentary and biological associations locally favorable ecologic circumstance or chance colonization initiated stromatolitic mat development which then became self perpetuating to form bioherms until rapid siliciclastic influx overwhelmed the mat building populations intermediate energy conditions in concert with microbial activity and inorganic processes generated the microphytolitic grainstones the interpretation of the biological and sedimentological interactions within these biohermal carbonates microphytolitic grainstones and siliciclastic rocks affords new insights into proterozoic paleoenvironments

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

control of triassic seawater chemistry and temperature on the evolution of post paleozoic aragonite secreting faunas the terminal permian extinction event ended the dominance of calcite secreting benthic faunas that had prevailed during the paleozoic most of those calcite secretors especially brachiopods and corals were replaced during the early and middle triassic by aragonite secreting faunas especially bivalves and scleractinian corals geochemical evidence suggests that a unique combination of elevated sulfate concentrations elevated temperatures and possibly elevated mg ca ratios characterized early and middle triassic seawater these triassic geochemical conditions may have favored evolution of the aragonitic faunas that arose in the aftermath of the permian extinctions and that have subsequently dominated the mesozoic and cenozoic

nonhomogeneous seawater sr isotopic composition in the coastal oceans a novel tool for tracing water masses and submarine groundwater discharge here we present high precision 2 3 ppm 87sr 86sr measurements in coastal waters together with salinity to evaluate water mass mixing and the influence of submarine groundwater discharge sgd in coastal waters and marginal seas nonhomogeneous sr isotopic variations in water columns were documented in the southern okinawa trough sot south china sea and kao ping canyon kpc where seawater 87sr 86sr varied up to 70 ppm seawater sr isotopic composition changes only slightly in the upper 200 m of the sot but was detectable and highly correlated with salinity indicating a mixing between radiogenic north pacific tropical water high 87sr 86sr and high salinity at 100 150 m and a less radiogenic component with low 87sr 86sr and low salinity at 200 m vertical profiles of seawater 87sr 86sr along the kpc show significant variations suggesting dynamic mixing affected by continental inputs i e river runoff and sgd in this region these results highlight the potential use of seawater sr isotopes as a powerful tracer for determining mixing ratios and the dynamic mixing of oceanic water masses especially in coastal and marginal seas