calcified microbial reefs in cambrian series 2 north china platform implications for the evolution of cambrian calcified microbes abstract this study focuses on the microbial reefs of the zhushadong formation cambrian series 2 in shandong province china in order to understand the evolution of calcified microbes in the north china platform during the cambrian series 2 and 3 the microbial reefs occur in a thin unit ca 3 m thick over an area of 1 km 2 they consist of three types of thrombolite based on their mesostructures rimmed grainstone patch and dendritic the thrombolites mainly occur in various coarse grained carbonate facies including crudely stratified oolitic grainstone stromatolitic grainstone and disorganized limestone conglomerate calcified microbes in the thrombolites include epiphyton kordephyton a tubiform microbe bija tarthinia renalcis amgaina and razumovskia the zhushadong thrombolites were formed within a grainstone shoal and experienced repeated burial and exposure the rimmed thrombolite and grainstone patch thrombolite experienced abundant input of carbonate grains forming grainstone patches in contrast the dendritic thrombolite formed solely by calcification of microbes that mainly include epiphyton tarthinia and the tubiform microbe the outer crusts of the rimmed thrombolite were formed by amgaina under high energy conditions the diverse calcified microbes of the zhushadong formation form the earliest assemblage of their type in the north china platform their descendants mostly epiphyton subsequently thrived forming a ca 180 m thick microbialite oolite dominated succession during the cambrian series 3 zhangxia formation although the reefs in the zhushadong formation are much smaller than those of the overlying zhangxia formation their calcified microbes are more diverse this most likely reflects changes in depositional environments e g abundant siliciclastic input and tidal effects vs those of a stable carbonate platform and or global changes within reef environments e g end cambrian series 2 extinction of archaeocyaths and calcified microbes a decrease in diversity of calcified microbes in the north china platform where archaeocyaths were absent may help to account for evolutionary trends in calcified microbes that occurred independently of archaeocyath influence

marine oxygenation lithistid sponges and the early history of paleozoic skeletal reefs abstract microbial carbonates were major components of early paleozoic reefs until coral stromatoporoid bryozoan reefs appeared in the mid ordovician microbial reefs were augmented by archaeocyath sponges for 15 myr in the early cambrian by lithistid sponges for the remaining 25 myr of the cambrian and then by lithistid calathiid and pulchrilaminid sponges for the first 25 myr of the ordovician the factors responsible for mid late cambrian microbial lithistid sponge reef dominance remain unclear although oxygen increase appears to have significantly contributed to the early cambrian explosion of marine animal life it was followed by a prolonged period dominated by greenhouse conditions as sea level rose and co2 increased the mid late cambrian was unusually warm and these elevated temperatures can be expected to have lowered oxygen solubility and to have promoted widespread thermal stratification resulting in marine dysoxia and hypoxia greenhouse conditions would also have stimulated carbonate platform development locally further limiting shallow water circulation low marine oxygenation has been linked to episodic extinctions of phytoplankton trilobites and other metazoans during the mid late cambrian we propose that this tendency to dysoxia hypoxia in shallow marine environments also limited many metazoan reef builders in contrast during the mid late cambrian the ability of lithistid sponges to withstand low oxygen levels allowed them to create a benthic association with microbial carbonates that dominated global reefs these conditions ameliorated during the ordovician as temperature decline promoted ocean ventilation the prolonged time gap occupied by low diversity reefs between the cambrian explosion and the great ordovician biodiversification event reflects elevated temperatures and reduced marine oxygenation that limited metazoan diversification in shallow marine environments

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

sulfur isotope evidence for widespread euxinia and a fluctuating oxycline in early to middle ordovician greenhouse oceans article i nfo despite marine geochemical records indicating widespread oxygenation of the biosphere in the terminal neoproterozoic era late cambrian records point to the persistence of deep water anoxia and potential for development of euxinic conditions the late cambrian spice steptoean positive carbon isotope excursion event however is a globally recognized chemostratigraphic marker that likely represents significant organic carbon burial and subsequent liberation of oxygen to the biosphere here we present high resolution carbon and sulfur isotope profiles from early to middle ordovician carbonate rocks from the argentine precordillera and western newfoundland to constrain oceanic redox conditions in the post spice world marine c isotope profiles record relatively stable behavior excursions b3 that is characteristic of greenhouse climates ma rine s isotope profiles record short term b10 6 yr rhythmic variation superimposed over a longer term

high precision dating of the kalkarindji large igneous province australia and synchrony with the early middle cambrian stage 4 5 extinction the voluminous kalkarindji flood basalts erupted in australia during the cambrian and covered 2 x 10 6 km 2 new u pb and ar 40 ar 39 age data from intrusive rocks and lava flows yielded statistically indistinguishable ages at ca 511 ma suggesting a relatively brief emplacement for this province a zircon age of 510 7 0 6 ma shows that this province is temporally indistinguishable at the few hundred thousand year level from the early middle cambrian stage 4 5 boundary age of 510 1 ma which marks the first severe extinction of the phanerozoic and an extended marine anoxia period sulfur concentration measurements ranging from 50 to 1900 mu g g and fractal analysis of extensive explosive volcanic breccias suggest that blasts and phreatomagmatic explosions have contributed to injection of large amounts of sulfur into the stratosphere in addition magma intrusions in oil gas and sulfate deposits may have generated significant emission of ch4 and so2 which along with volcanic gases would have combined to cause an oscillation of the climate and led to the cambrian extinction less

on the causes of mass extinctions the temporal link between large igneous province lip eruptions and at least half of the major extinctions of the phanerozoic implies that large scale volcanism is the main driver of mass extinction here we review almost twenty biotic crises between the early cambrian and end cretaceous and explore potential causal mechanisms most extinctions are associated with global warming and proximal killers such as marine anoxia including the early middle cambrian the late ordovician the intra silurian intra devonian end permian and early jurassic crises many but not all of these are accompanied by large negative carbon isotope excursions supporting a volcanogenic origin most post silurian biocrises affected both terrestrial and marine biospheres suggesting that atmospheric processes were crucial in driving global extinctions volcanogenic atmospheric kill mechanisms include ocean acidification toxic metal poisoning acid rain and ozone damage and consequent increased uv b radiation volcanic darkness cooling and photosynthetic shutdown each of which has been implicated in numerous events intriguingly some of the most voluminous lips such as the oceanic plateaus of the cretaceous were emplaced with minimal faunal losses and so volume of magma is not the only factor governing lip lethality the missing link might be continental configuration because the best examples of the lip extinction relationship occurred during the time of pangaea many of the proximal kill mechanisms in lip extinction scenarios are also potential effects of bolide impact including cooling warming acidification and ozone destruction however the absence of convincing temporal links between impacts and extinctions other than the chicxulub cretaceous example suggests that impacts are not the main driver of extinctions with numerous competing extinction scenarios and the realisation that some of the purported environmental stresses may once again be driving mass extinction we explore how experimental biology might inform our understanding of ancient extinctions as well as future crises

multiple s isotopic constraints on paleo redox and sulfate concentrations across the ediacaran cambrian transition in south china abstract changes in oceanic chemical conditions are frequently invoked as a primary driver of biodiversification and mass extinction events in earth history during the ediacaran cambrian transition two major biological events including the extinction of the ediacaran biota and the cambrian explosion occurred approximately coincident with perturbations of the carbon and sulfur cycle these dramatic biological changes and coeval geochemical events are commonly thought to be linked but their causal relationships remain controversial here we present multiple s isotopic compositions of pyrite 34spy and 33spy from the xiaotan section spanning the ediacaran cambrian transition interval in south china our isotopic results show that negative 33spy values together with positive 34spy values occurred across the ediacaran cambrian boundary the negative 33spy data suggest mixing of sulfide from deep waters during the upwelling of sulfidic waters into oxygenated shallow waters the coincidence between the negative 33spy and the approximate timing of the extinction of the ediacaran biota implies that paleo redox perturbations may have contributed to the disappearance of the ediacaran biota negative 33spy values coupled with positive 34spy values were also observed in the cambrian zhongyicun member when the phosphorites were deposited suggesting a strong linkage between the upwelling of nutrient rich sulfidic deep waters and the deposition of the phosphorites in oxygenated shelf areas in addition using box models and stoichiometry calculations we quantitatively estimated elevated burial rates of organic matter and pyrite based on the parallel positive 13ccarb 34spy and 33spy excursions observed at xiaotan within cambrian stage 2 our mass balance modelling results provide an independent constraint on sulfate concentrations which were 4 mm or lower in the early cambrian oceans the probable increase in oxygen levels resulting from the enhanced burial of pyrite and organic matter could have provided a more habitable environment for early animals and thus paved the way for the radiation of early cambrian animals

geochemical evidence for widespread euxinia in the later cambrian ocean it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking gill et al present sulphur isotope data from cambrian rocks at six different locations around the world and find a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time a prolonged period of anoxia during the cambrian may explain the previously enigmatic peculiarities seen in the fossil record it has been suggested that the cambrian ocean was oxygen deficient but physical evidence for widespread anoxia has been lacking now sulphur isotope data from cambrian rocks at six different locations around the world is presented with the finding of a positive sulphur isotope excursion in phase with a large excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation at the time with the help of a box model these isotope shifts support the idea of large scale anoxic and sulphidic conditions in the later cambrian ocean widespread anoxia in the ocean is frequently invoked as a primary driver of mass extinction as well as a long term inhibitor of evolutionary radiation on early earth in recent biogeochemical studies it has been hypothesized that oxygen deficiency was widespread in subsurface water masses of later cambrian oceans1 2 possibly influencing evolutionary events during this time1 2 3 physical evidence of widespread anoxia in cambrian oceans has remained elusive and thus its potential relationship to the palaeontological record remains largely unexplored here we present sulphur isotope records from six globally distributed stratigraphic sections of later cambrian marine rocks about 499 million years old we find a positive sulphur isotope excursion in phase with the steptoean positive carbon isotope excursion spice a large and rapid excursion in the marine carbon isotope record which is thought to be indicative of a global carbon cycle perturbation4 5 numerical box modelling of the paired carbon sulphur isotope data indicates that these isotope shifts reflect transient increases in the burial of organic carbon and pyrite sulphur in sediments deposited under large scale anoxic and sulphidic euxinic conditions independently molybdenum abundances in a coeval black shale point convincingly to the transient spread of anoxia these results identify the spice interval as the best characterized ocean anoxic event in the pre mesozoic ocean and an extreme example of oxygen deficiency in the later cambrian ocean thus a redox structure similar to those in proterozoic oceans6 7 8 may have persisted or returned in the oceans of the early phanerozoic eon indeed the environmental challenges presented by widespread anoxia may have been a prevalent if not dominant influence on animal evolution in cambrian oceans

c o and sr isotope stratigraphy across the lower middle cambrian transition of the cantabrian zone spain and the montagne noire france west gondwana c o and sr isotopes have been analysed for three sections of the cantabrian zone northern spain and the southern montagne noire france that cross the lower middle cambrian transition or bilbilian leonian transition in its iberian sense the base of the leonian middle cambrian is regionally defined by the first appearance of the trilobite acadoparadoxides mureroensis which is well constrained in the cantabrian zone but absent in the montagne noire in the bilbilian parts of the three sections nearshore to peritidal strata are capped by erosive unconformities the succeeding leonian relative sea level rise is recorded in similar fashion in both environments leading to the deposition of aggradational bioclastic limestones and or transgressive limestone shale couplets the so called griotte facies overlain by offshore shales which relate to platform drowning and coastal smothering during the leonian caesaraugustan transition bilbilian leonian carbonates show a long term trend to higher 13c values that was punctuated by a succession of positive excursions in cremenes valdore cantabrian zone and ferrals les montagnes montagne noire two bilbilian 13c shifts an older uncertain peak at 0 1 0 01 and a younger certain shift at 0 6 1 7 and two leonian shifts peaking at 1 1 1 2 and 1 3 respectively are apparent at genestosa cantabrian zone a fifth early middle caesaraugustan shift is identified peaking at 2 1 these positive excursions and increasing trend are similar to published trends from the lower middle cambrian transition in siberia and australia although in those areas only two 13c excursions have been reported so far the marked negative 13c excursion reported from the lower middle cambrian boundary of laurentia and china is not recorded in our dataset oxygen isotope and trace element ca mn and sr data indicate that our 13c trends are unlikely to be diagenetic features while the lack of correlation with relative sea level fluctuations facies changes or benthic community dynamics means that they could be of potential for global stratigraphic correlation sr isotope compositions for the cantabrian zone succession exhibit consistent values upsection which suggests that seawater 87sr 86sr remained around 0 7089 0 7090 our more limited dataset for the montagne noire region confirms this value and both are consistent with published constraints from laurentia for seawater 87sr 86sr across the lower middle cambrian boundary the only other 87sr 86sr study to cover the boundary interval reported significantly lower 87sr 86sr values not vert similar0 7087 0 7088 indicating perhaps that the lower middle cambrian boundary in siberia lies stratigraphically below its equivalent levels in europe and laurentia however we consider it more likely that these siberian samples have been diagenetically altered to less radiogenic values

violent volcanism stagnant oceans and some inferences regarding petroleum strata bound ores and mass extinctions past changes from a well mixed aerated ocean to a stratified stagnant ocean are indicated by decreasing 13c of limestone opposite to prior conclusions as well as by increasing 34s of marine sulfates the proposed stagnant ocean model includes a warm co2 enriched atmosphere and a bathyal to abyssal marine system dominated by bacterial components in the food web and by consequent light carbon in organic material and biogenic carbonates culminations of prolonged stagnant episodes correspond with marine faunal extinctions of late permian and late cretaceous time and the protracted changes and correlations provide evidence against any hypothesis of mass extinction by sudden worldwide catastrophe including the asteroid impact hypothesis the cretaceous stagnant ocean taken as the prime example is attributed to climatic warming triggered by volcanic co2 greenhouse effect and several feedbacks including decreased earth albedo and increased sinking of warm evaporite brines instead of aerated polar waters marine extinctions are attributed to upward expansion of the oxygen minimum zone and to catastrophic mixing of surface waters with poisonous sulfidic waters of the deeps the stagnant ocean provided a counterbalance between deep reduction and shallow oxidation conditions that favored maximal formation of black sulfidic shales protopetroleum and sedimentary sulfide ores and shallow to mid depth barite phosphorite iron ore cherty iron formation and sulfate bearing red beds trace elements concentrated in stagnant ocean sediments include chalcophile and pt group metals negating claims that ir provides a unique fingerprint of meteorite impact and cosmic accretion

evaluating the relationship between the carbon and sulfur cycles in the later cambrian ocean an example from the port au port group western newfoundland canada abstract we present a high resolution 34 s sulfate and pyrite and 13 c carbonate record from the middle upper cambrian port au port group a mixed carbonate siliciclastic succession exposed in western newfoundland canada the results illustrate systematic 34 s sulfate shifts of 15 over relatively short stratigraphic intervals 10 m likely 34 s sulfate pyrite ca 23 and a generally positive coupling between changes in 13 c carbonate and 34 s sulfate together these results indicate that middle to late cambrian sulfate concentrations were low and that the sulfate reservoir was more sensitive to change than it was in either terminal neoproterozoic or cenozoic oceans however a simple carbon c and sulfur s isotope box model of the late cambrian ocean illustrates that low sulfate concentrations alone fail to account for the 15 34 s sulfate shifts recognized in port au port strata such large shifts can be generated only if fluctuating oceanic redox is invoked marine anoxia forces reduced c s burial and elevated 34 s driving larger 34 s changes per mole of organic carbon buried the conclusion that later cambrian oceans featured both low sulfate levels and widespread subsurface anoxia supports hypotheses that link fluctuating marine redox conditions in the delayed recovery of skeletal animals and metazoan reefs from late early cambrian extinction

sulfur isotopic trends and pathways of iron sulfide formation in upper holocene sediments of the anoxic black sea down core trends for extents of iron sulfidation in upper holocene microlaminated deposits of the black sea abyssal plain imply that most of the pyrite in these sediments is formed in the sulfidic water column and or very close to the sediment water interface sulfur isotopic data for pyrite within microlaminated muds from two localities in the deep basin show striking uniformity between sites and down core with a mean 34scdt value of 37 2 0 9 1 n 18 these isotopic trends support the hypothesis of early pyrite formation isotopic compositions of pyrite sulfur in the microlaminated bottom sediments are similar to those reported for particulate reduced sulfur collected in middepth sediment traps and to 34s values for water column dissolved sulfide within a narrow zone immediately below the o2 h2s interface these three sulfur reservoirs are distinctly different from the isotopic composition of ambient dissolved sulfide of the deep water column 175 m with 34s values for the deep dissolved sulfide reservoir being consistently lower by 2 to 4 these isotopic relationships suggest that iron sulfidation is occurring dominantly within a narrow shallow region at the top of the sulfidic water mass isotopic data from a fine grained turbidite collected in the deep basin and from rapidly accumulating iron monosulfide rich muds on the anoxic upper slope are enriched in34s relative to the microlaminated deposits the enrichments on the basin margin reflect a large component of iron sulfide formed during rapid burial a broad suite of geochemical data including sulfur isotopic results are consistent with an upper slope sediment source for the ubiquitous muddy turbidites of the deep basin the collective effects of reworking transport and redeposition result in a complete conversion of avs to pyrite with little additional iron sulfidation this conclusion is supported by a detailed isotopic mass balance the present isotopic study also highlights fundamental differences in the reactivities of the iron reservoirs distributed throughout the anoxic basin sediments of the upper slope and the genetically linked turbidites of the deep basin show similar extents of iron sulfidation that are significantly lower than those of the microlaminated deposits of the deep basin floor suggesting dramatically shorter timescales of iron reactivity for the microlaminated sediments of the deep basin importantly isotopic patterns from the modern black sea should assist greatly in the recognition and interpretation of ancient anoxia in the stratigraphic record

the paleoenvironmental evolution of the cambrian longwangmiao formation stage 4 toyonian on the yangtze platform south china petrographic and geochemical constrains abstract during the cambrian period stage 4 biodiversity and biomass declined rapidly and globally in an event known as the botomian toyonian crisis to gain a better understanding of the paleoenvironment in south china during this stage we present and interpret complex multi parameter carbonate analyses petrography carbon and oxygen isotopic composition and major trace and rare earth elements from the toyonian longwangmiao formation in the bandenggou section the longwangmiao formation comprises primarily carbonate deposits with massive detrital mineral occurrences in its lower middle sequence principal component analysis of the minerals and oxides leads to the definition of two intervals i and ii interval i is composed mainly of dolostones interbedded with sandstones and contains exceedingly high amounts of terrestrial original minerals and oxides as well as high ree y th and sc concentrations interval ii which is composed primarily of limestones has trace amounts of terrestrial original minerals and oxides and low ree y th and sc concentrations the 13c and 18o values show a significant positive shift from interval i to interval ii after eliminating the effects of diagenesis contributions through the analyses of diagenesis sensitive indexes 18o values mgo cao mn sr and fe sr ratios and the correlations of 13c 18o 18o eu eu eu eu ce ce and eu eu feo the sr and na concentrations of calcites in interval i are extremely high exceeding even the corresponding ranges of marine aragonites while calcites from interval ii have low sr and na concentrations that are within the range of marine low mg calcite however both show strong positive correlations between ca sr ca na and sr na the different calcite elemental behaviors in intervals i and ii suggest different carbonate precursors associated with seawater temperature and climate furthermore the sr ca ratios are negatively correlated with 13c and 18o values and the 13c values also negatively correlated with sio2 content these features indicate a significant change in the depositional environment during the cambrian toyonian stage from an early restricted marine environment under a warm and arid climate with massive terrestrial influxes to a later relatively open marine environment under a cool and humid climate with negligible terrestrial influxes this shift likely resulted in the observed changes in biomass and biodiversity

geochemistry and tectonic environment of basaltic rocks from the misis ophiolitic melange south turkey abstract the miocene misis tectonosedimentary melange was formed during the closing stages of the neotethys in what is now the adana basin of southern turkey a major part is characterized by large disorientated limestone blocks set in a predominantly volcanogenic matrix of bedded and chaotic units comprising basaltic pillow lavas associated hyaloclastites serpentinites and various acidic tuffs all the basaltic rocks are mildly metamorphosed zeolite facies variably vesicular and differentially altered to smectite chlorite fe oxides zeolites and carbonate petrographic and chemical data on the least altered pillow lavas indicate they were originally sparsely olivine plagioclase clinopyroxene phyric tholeiites and minor amphibole phyric basaltic andesites the basaltic clasts in the melange matrix are genetically related to the pillow lava sequences with the observed variation throughout the suite being governed by low pressure fractional crystallization as a group the basalts are characterized by low zr y 2 4 relatively high th yb 0 5 0 7 and la nb 1 5 2 5 ratios and moderate chondrite normalized light ree enrichment la yb n 3 patterns the basalts have a mildly enriched subduction related chemistry and were possibly formed initially in a back arc basin setting the supra subduction zone characteristics of the misis basaltic units are similar to other tethyan basalts in eastern mediterranean ophiolites

a molecular and isotopic study of palaeoenvironmental conditions through the middle cambrian in the georgina basin central australia abstract the cambrian period marks an important point in earth s history with profound changes in the ocean s biogeochemistry and the occurrence of the most significant evolutionary event in the history of life the cambrian explosion the cambrian explosion is described as a succession of complex cycles of extinctions and radiations this study integrates biomarkers and their compound specific stable carbon isotopes to investigate the palaeoenvironmental depositional conditions in middle cambrian series 3 sedimentary rocks thorntonia limestone inca formation and currant bush limestone from two drillholes in the undilla sub basin in the eastern georgina basin central australia the occurrence of photic zone euxinia pze was detected throughout these three formations by the identification of green sulfur bacteria chlorobiaceae derived biomarkers including a series of 2 3 6 aryl isoprenoids and the intact biomarker isorenieratane pulses of enhanced pze conditions were detected in two core intervals 90 110 mkb currant bush limestone and 170 200 mkb inca formation by an increase in the 2 3 6 aryl isoprenoids and c19 biphenyl concentrations these enhanced pze conditions were followed by blooms of phytoplankton as demonstrated by the increase in algal derived biomarker i e pristane phytane and the c19 n alkane concentrations and compound specific isotopes these observations confirm that palaeoenvironmental conditions were similar to those reported for the permian triassic and triassic jurassic mass extinction events the sterane distributions varied across the three formations reflecting possible changes in the phytoplanktonic communities through time although a rise in atmospheric oxygen during the cambrian has been previously associated with the rapid evolution of metazoans the ecological challenges related to widespread anoxia must have had a major influence on the evolution of life in cambrian oceans

a negative carbon isotope excursion defines the boundary from cambrian series 2 to cambrian series 3 on the yangtze platform south china a globally recorded negative carbon isotope excursion characterizes the transition from cambrian series 2 to cambrian series 3 this transition is also well exposed in sedimentary successions on the yangtze platform and the wuliu zengjiayan section guizhou province south china has been proposed as a potential global stratotype section and point gssp for this boundary here we report delta 13 c carb values for the jianshan and the wuliu zengjiayan sections both sections display a progressive decrease in delta 13 c from values around 3 parts per thousand upwards in stratigraphy to a pronounced delta 13 c minimum with values as low as 6 9 parts per thousand at the proposed boundary level and a return to delta 13 c values between 0 and 1 parts per thousand in the upper part of the sections the delta 13 c minimum is thought to be caused by a transgressive event flooding the shelf area with 13 c depleted basinal anoxic bottom water our delta 13 c data are in good agreement with carbon isotope profiles recorded elsewhere these define the so called roece event redlichiid oleneliid extinction carbon isotope excursion cf zhu et al 2006 2007 and may reflect the perturbation of the global carbon cycle during the cambrian series 2 to cambrian series 3 transition c 2009 elsevier b v all rights reserved

middle late cambrian rankenella girvanella reefs of the mila formation northern iran following the collapse of the early cambrian archaeocyathan calcimicrobial reef consortium the middle late cambrian furongian was an interval dominated by purely microbial dendrolite and stromatolite reefs however among these latter a few exceptional occurrences of metazoan reefs are known one such reef complex occurs in the late middle early late cambrian furongian portion of the mila formation of northern iran in the otherwise low energy interval of this formation the anthaspidellid demosponge rankenella hamdii sp nov is associated with encrusting girvanella eocrinoid plates rhynchonelliformean brachiopod valves and subordinate hyoliths and trilobites in tempestite shell beds these beds underwent synsedimentary cementation on the seafloor to form hardgrounds in the succeeding higher energy interval a complex of metre scale bioherms and or taphoherms incorporates toppled or transported rankenella hamdii in association with brachiopods echinoderm plates trilobites and some red arg

constraints on the late ediacaran sulfur cycle from carbonate associated sulfate we report new sulfur isotope compositions 34s in carbonate associated sulfate cas and pyrite from the lower nama group namibia 550 to 35 is highly unusual in earth history and in the terminal ediacaran is best explained by a high pyrite burial flux pyrite in the nama group is close in isotopic composition to coeval sulfate but the sulfur isotope fractionation between sulfate and pyrite varies widely among different studied basins suggesting highly heterogeneous redox and depositional conditions

transports of nordic seas water masses and excess sf6 through fram strait to the arctic ocean to determine the exchanges between the nordic seas and the arctic ocean through fram strait is one of the most important aspects and one of the major challenges in describing the circulation in the arctic mediterranean sea especially the northward transport of arctic intermediate water aiw from the nordic seas into the arctic ocean is little known in the two ship study of the circulation in the nordic seas arctic ocean 2002 the swedish icebreaker oden operated in the ice covered areas in and north of fram strait and in the western margins of greenland and iceland seas while rv knorr of woods hole worked in the ice free part of the nordic seas here two hydrographic sections obtained by oden augmented by tracer and velocity measurements with lowered acoustic doppler current profiler ladcp are examined the first section reaching from the svalbard shelf across the yermak plateau covers the region north of svalbard where inflow to the arctic ocean takes place the second western section spans the outflow area extending from west of the yermak plateau onto the greenland shelf geostrophic and ladcp derived velocities are both used to estimate the exchanges of water masses between the nordic seas and the arctic ocean the geostrophic computations indicate a total flow of 3 6 sv entering the arctic on the eastern section the southward flow on the western section is found to be 5 1 sv the total inflow to the arctic ocean obtained using the ladcp derived velocities is much larger 13 6 sv and the southward transport on the western section is 13 7 sv equal to the northward transport north of svalbard sulphur hexafluoride sf6 originating from a tracer release experiment in the greenland sea in 1996 has become a marker for the circulation of aiw from the geostrophic velocities we obtain 0 5 sv and from the ladcp derived velocities 2 8 sv of aiw flowing into the arctic the annual transport of sf6 into the arctic ocean derived from geostrophy is 5 kg year which is of the same magnitude as the observed total annual transport into the north atlantic while the ladcp measurements 19 kg year imply that it is substantially larger little sf6 was found on the western section confirming the dominance of the arctic ocean water masses and indicating that the major recirculation in fram strait takes place farther to the south

seawater carbon and strontium isotope variations through the late ediacaran to late cambrian in the tarim basin abstract the radiation of early animals during the cambrian explosion was accompanied by widespread perturbations in oceanic and atmospheric conditions however the cause effect relationships between evolutionary innovations carbon c cycling and continental weathering are still a matter of debate further paleoenvironmental reconstructions of poorly studied paleo continents covering the precambrian cambrian pc c transition may improve the correlation of the events and their impact on the earth system on a global scale the tarim basin was presumably located proximal to the well studied south china craton during the ediacaran cambrian boundary and is expected to contribute equally to our paleoenvironmental reconstructions here we apply carbon and strontium sr isotope records 13c and 87sr 86sr obtained from well preserved marine carbonates spanning the late ediacaran to the late cambrian from the keping region in the northwestern tarim basin nw china by comparison to other carbonate successions from various paleo continents our obtained seawater 87sr 86sr curve in this study shows a stepwise first order increase to more radiogenic values superimposed by second order presumably regional variations our obtained 13c variations exhibit four prominent negative and three positive excursions identical to the global 13c record based on existing paleontological evidence and our new tarim 13c and 87sr 86sr curves we propose a stratigraphic correlation from the late ediacaran to the late cambrian between the tarim basin and other paleo continents besides our paleoenvironmental reconstruction reveals both regional and global sea level changes that may have controlled the influx of radiogenic sr and presumably the influx of nutrients controlling primary production and the rate of organic carbon burial in the tarim basin at the time of deposition these feedbacks may have ultimately influenced the rapid diversification of metazoans and the oxygenation of the cambrian ocean and atmosphere approaching present po2 levels

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

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

the late early cambrian microbial reefs immediately after the demise of archaeocyathan reefs hunan province south china abstract the archaeocyath bearing reefs that first appeared in south china in the atdabanian were last seen in the lower toyonian e g in the tianheban and jindingshan formations the upper toyonian lower amgan qingxudong formation of hunan province examined in this study includes large sized reefs formed solely by calcimicrobes of epiphyton kordephyton girvanella hedstroemia and renalcis during the middle and upper cambrian small scale stromatolite reefs were formed the qingxudong reefs are therefore interpreted to be the most well developed microbial reefs of the post archaeocyath bearing reefs in the late early cambrian the transition from archaeocyath bearing to purely microbial reefs was caused by a decline in the diversity of metazoans and was accompanied by a reduction in the abundance of reefs possibly related in part to late early cambrian regression the late early cambrian reefs of south china contain a well preserved record of reef succession and provide important insights into the factors that led to the demise of archaeocyath bearing reefs and the subsequent long lasting hindrances to the development of skeletal dominated reefs during the middle and late cambrian

preservation of early and middle cambrian soft bodied arthropods from the pioche shale nevada usa abstract the early middle cambrian pioche shale of lincoln county nevada preserves a diverse array of soft bodied ecdysozoans that are well known from the burgess shale soft bodied fauna of british columbia canada at pioche certain genera occur both above and below the middle cambrian boundary allowing a comparison of the nature of their preservation across this interval in order to investigate the mineralization of this fauna sem analysis of mineral textures and element mapping of anomalocaris tuzoia and canadaspis specimens using energy dispersive x ray spectroscopy eds was undertaken results of these analyses show that early cambrian specimens are generally preserved in botryoidal hematite which is dark red in hand specimen while specimens from the middle cambrian are preserved as kerogenized carbon films with associated oxidized pyrite crystals and framboids comparison with other cambrian soft bodied biotas reveals that the nature of preservation of the middle cambrian biota at pioche is remarkably similar to that described for the chengjiang soft bodied fauna china there does not seem to be an adequate analogue for the early cambrian preservation of soft bodied organisms at pioche the preservation of the fauna is discussed in relation to changing environmental conditions at the early middle cambrian boundary

redox fluctuations in the early ordovician oceans an insight from chromium stable isotopes abstract chromium cr stable isotopes are a useful tracer of changes in redox conditions because changes in its oxidation state are accompanied by an isotopic fractionation recent co precipitation experiments have shown that cr vi is incorporated into the calcite lattice suggesting that carbonates are a potential sink for dissolved cr in the ocean and could effectively capture the cr isotope composition of ambient seawater thus the cr isotopic composition 53cr of carbonates has the potential to record changes in the oxygenation state of ancient oceans to test the potential of this system we measured 53cr values of limestones and dolostones from an early ordovician marine carbonate platform cerro la silla section of the precordillera san juan argentina an increasing number of studies support the hypothesis that the early ordovician oceans were stratified with respect to oxygen and that the global ocean experienced multiple episodes of anoxic expansion and contraction making this time period ideal for testing the usefulness of the cr isotope system the most prominent feature of the cerro la silla cr isotope profile is a positive excursion of 0 5 during the late tremadocian accompanied by exceptionally low cr concentrations

global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events rea d k zachos j c owen r m and gingerich p d 1990 global change at the paleocene eocene boundary climatic and evolutionary consequences of tectonic events palaeogeogr palaeoclimatol palaeoecol 79 117 128 events of the paleocene eocene boundary provide the clearest example to date of how a tectonic event may have global climatic consequences recent advances permit well constrained stratigraphic determination of several events that occurred at that boundary in chron c24r a many fold increase in sea floor hydrothermal activity a global warming a reduction in the intensity of atmospheric circulation a conversion to salinity driven deep ocean circulation a marked lightening of oceanic 313c values extinction and evolution of both benthic foraminifera and land mammals and important plate boundary reorganizations including the outpouring of the east greenland volcanics and the initiation of the oceanic rift between norway and greenland we hypothesize that enhanced sea floor hydrothermal activity occasioned by global tectonism resulted in a flooding of the atmosphere with coz causing a reduced pole to equator temperature gradient and increased evaporation at low latitudes increased formation of warm salty probably low nutrient waters coupled with the warm temperatures at high latitudes occasioned a salinity driven rather than temperature driven deep water circulation this newly evolved ocean circulation pattern changed the apportionment of global heat transport from the atmosphere to the ocean with concomitant changes in the circulation intensity of both reduced intensity of atmospheric circulation resulted in lower oceanic biological productivity and enhanced seasonality of climate on the continents a major extinction event among benthic foraminifera was probably a response to the new low nutrient and chemically changed bottom waters and endemism following rapid evolution and dispersal of mammalian orders may have been in response to the new continental climate regime

paired δ34s data from carbonate associated sulfate and chromium reducible sulfur across the traditional lower middle cambrian boundary of w gondwana abstract in this study we present the first high resolution data from coupled 34 s analyses of carbonate associated sulfate cas and chromium reducible sulfur crs from three lower middle cambrian sections in western gondwana cas and crs were extracted and analyzed from marine dolostone limestone and nodular limestone from spanish and french successions in parallel carbonate samples were also analyzed for 13 c carb 18 o carb and major trace element concentrations ca fe mg mn sr 34 s cas values vary between 17 6 and 33 2 with a maximum cas concentration of ca 900 ppm 34 s crs data show a similar broad range between 5 1 and 29 7 with maximal crs contents up to ca 3700 ppm notably there is little stratigraphic variation in the 34 s cas data in each of the sections confounding inter basinal chemostratigraphic correlations nonetheless the absolute differences in 34 s cas between sections as well as variations in cas and crs concentrations are attributed to paleoenvironmental differences between proximal and distal parts of the carbonate ramp as well as effects of subaerial exposure and riverine input thus the generated 34 s cas data deliver not only valuable paleoecological and paleoenvironmental information they also illustrate a heterogeneity in the seawater sulfate sulfur isotopic composition of the western gondwanan ocean consequently the lack of correlation between our gondwanan 34 s cas data and time equivalent sections of laurentia and siberia is probably not only caused by the absence of an internationally accepted biostratigraphic correlation but rather supports the view that sulfate was non conservative anion in seawater during the cambrian period

the earliest phanerozoic carbonate hardground cambrian stage 5 series 3 implications to the paleoseawater chemistry and early adaptation of hardground fauna abstract carbonate hardgrounds are lithified seafloors formed by synsedimentary cementation of carbonate sediments which dominantly occur during the period of calcite seas the earliest typical phanerozoic hardground known until now was reported from the furongian of usa which was suggested to indicate onset of the early paleozoic calcite sea period in this study we report hardgrounds from the early and middle parts of the cambrian series 3 stage 5 and drumian of the north china platform which predate previously reported hardgrounds the hardground surfaces developed on oolitic grainstone oncolitic wackestone and microbialite thrombolite and dendrolite which sharply truncate the underlying deposits the radial fibrous calcite cements between the carbonate grains below the hardground surfaces indicate that the cements formed by early marine cementation epma analysis reveals that the fibrous cements typically consist of low mg calcite the hardgrounds are sometimes encrusted by microbialites and coated by hematite suggesting long exposure to the open seawater after formation of the surface in addition detailed review on the sedimentological studies of cambrian series 3 to furongian deposits throughout the world reveals that there may be several other hardgrounds during these times which could have been overlooked the abundant occurrence of hardgrounds in cambrian series 3 deposits suggests that the general paleoseawater chemistry was suitable to induce synsedimentary cementation of low mg calcite implying that seawater chemistry would have changed from the aragonite to calcite seas during the cambrian series 3 or even earlier period metazoan encrustors and macroborers possibly could not have adapted to the newly appeared substrate condition yet until the latest cambrian series 3

eve of biomineralization controls on skeletal mineralogy carbonate mineralogies have oscillated between aragonite and calcite seas through geological time proposed to be due mainly to secular variation in the magnesium calcium ratio driven by changing rates of ocean crust production a quantitative compilation of inorganic and biominerals from the onset of biomineralization late ediacaran middle ordovician reveals a correspondence between seawater chemistry and the first adopted mineralogy of skeletal clades ediacaran tommotian skeletons and inorganic precipitates were composed exclusively of aragonite or high mg calcite but these were replaced by low mg calcite mineralogies during the early atdabanian implying the onset of a calcite sea this transition is empirically constrained by fluid inclusion data late atbadanian botoman inorganic precipitates returned to aragonite with high mg calcite echinoderms and solitary tabulaconids and massive aragonitic tabulaconids originating during this interval middle cambrian ordovician inorganic precipitates were low mg calcite and the ordovician radiation in skeletal expression was due mostly to groups with low mg calcite mineralogies these short lived transitions can be most parsimoniously explained by minor oscillations of mmg ca around 2 during this period possibly combined with the progressive onset of greenhouse conditions during the mid late cambrian

marine biogeochemical cycling during the early cambrian constrained by a nitrogen and organic carbon isotope study of the xiaotan section south china the precambrian cambrian boundary is claimed as one of the most crucial biological breakthroughs on our planet when changes in chemical and physical conditions together with key biological innovations helped to trigger a biodiversity explosion the yangtze platform south china mainly characterized by continuous and unaltered successions of this age is ideally suited to high resolution palaeomarine investigations of this event in this study 15n and 13corg records from xiaotan section yunnan sw china were investigated in order to provide insight into variations in primary productivity ecological developments and marine environment the ediacaran early cambrian xiaotan section is characterized by relatively high sedimentation rates and variable lithologies carbonates cherts phosphorites sandstones and siltstones that alternate through nearly 600 meters thickness organic carbon isotope values vary between 36 and 21 tightly following and helping to complete published 13ccarb trends the base of the cambrian is characterized in this section by a significant drop from 25 to 35 mirroring the 13ccarb fall observed at this and other sections worldwide higher in the section in the dahai member values increase to 20 again demonstrating communication between doc and dic pools during the early cambrian on 105 106 year time scales from the base of the overlying shiyantou formation 13corg values remain around 30 until the end of the section testifying to an interval of more modest change in dic 13c that would be consistent with biostratigraphic correlations nitrogen isotope values vary independently from carbon isotope trends exhibiting several major 15n cycles with values fluctuating between 9 and 1 robust trends in 15n within the dahai member testify to changes in the ratio between nitrogen fixation and denitrification possibly reflecting fluctuations in the water column chemocline as 13c values reached their global acme up section nitrogen isotope values show dampened cyclicity with values remaining between 0 and 5 indicating establishment of an equilibrium state in marine biogeochemistry and nutrient cycles the overall variability in 15n closely resembles that of recent marine sediments while the observed cyclicity is defined by several samples in all cases these observations argue for good preservation of original isotopic signatures which bodes well for future n isotope studies of the precambrian cambrian boundary

increasing global ocean oxygenation and the ordovician radiation insights from th u of carbonates from the ordovician of western utah abstract the cambrian and ordovician radiations were the most important biodiversification events in the history of animal life yet they were separated by intervals of recurrent anoxic sedimentation and regional biomere extinction events in the late cambrian and early ordovician recent work linked biomere extinction events to positive carbon isotopic excursions interpreted to represent enhanced organic matter burial under anoxic conditions this led to the hypothesis that an increase in oceanic oxygenation following the last of the biomere extinctions paved the way for the rapid diversification of the ordovician radiation here we test the hypothesis of increasing ocean oxygenation using th u preserved in carbonate rocks from the lower middle ordovician succession near ibex utah usa the global seawater uranium inventory is expected to vary inversely with the amount of deep water anoxic deposition due to uranium sequestration in black shales therefore in shallow water carbonates higher th u ratios may reflect increased global ocean anoxia our data show that the highest th u values are coincident with the heaviest carbon isotopic values reported from the base of this succession which is latest tremadocian in age th u then decreases and remains low through the floian up through the contact with the kanosh formation a shale dominated unit with interspersed limestone units the geochemistry of the carbonates within the kanosh formation likely represents local rather than global conditions in the marine environment we interpret the overall decrease in th u ratios throughout the tremadocian to floian interval to represent an increase in global seawater uranium concentration these data are consistent with the hypothesis that an increase in ocean oxygenation occurred prior to the major pulses of diversification associated with the ordovician radiation

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

euxinia linked to the cambrian drumian carbon isotope excursion dice in australia geochemical and chemostratigraphic evidence abstract the cambrian drumian carbon isotope excursion dice event is a negative carbon isotope 13 c excursion it is associated with the first appearance datum fad of the agnostoid arthropod ptychagnostus atavus whose first appearance in the global boundary stratotype section and point gssp defines the base of the cambrian series 3 drumian stage although this isotopic event has been clearly identified in the great basin usa it has not been consistently reported in other areas of the world here we report a study integrating isotopic and geochemical data from middle cambrian series 3 sections from the northeastern georgina basin australia to investigate the occurrence of the dice event in australia and the paleoenvironmental conditions associated with this event the similarity between the isotopic excursions observed in the georgina basin 2 to 3 2 13 c excursion and that observed in the great basin 2 to 3 6 13 c excursion highlighted the presence of the dice in australia and emphasized the potential use of this event for refining global isotopic correlations the multi proxy correlation used in this study also showed a pulse of euxinia in association with the dice suggesting strongly euxinic conditions near the base of the drumian stage

a paired carbonate organic δ13c approach to understanding the cambrian drumian carbon isotope excursion dice abstract the middle cambrian cambrian series 3 drumian carbon isotope excursion dice represents a pronounced negative carbon isotopic excursion and has been proposed as a key chemostratigraphic marker for identifying the base of cambrian drumian stage and global correlation however the precise interbasinal correlation of the dice to the south china remains unsolved and the driving mechanism of the dice is to be further understood in this study we report new paired 13ccarb and 13corg data from the wangcun section in south china both 13ccarb and 13corg profiles capture a large negative excursion dice near the fad of p atavus we suggest that the parallel 13ccarb and 13corg negative excursions during the dice may have resulted from the shoaling of anoxic deep waters associated with the transgressive event shoreward and upward incursion of deep anoxic waters into oxygenated shallower water column during transgression could lead to the enhanced oxidation of dissolved organic carbon doc and introduce additional 13c depleted carbon to the surface water resulting in the parallel 13ccarb and 13corg negative excursions more importantly we use a box model to quantify the flux of doc oxidation needed to produce a carbon isotope excursion of the magnitude and duration of the dice we observed the model results indicate that oxidation of doc during the dice may require massive amounts of oxidants i e sulfate and oxygen probably causing further expansion of anoxia in the shallow marine environment we suggest that shoaling of anoxic water during the dice could have delayed the recovery of metazoan reef systems from the early middle cambrian mass extinctions

contrasting long term global and short term local redox proxies during the great ordovician biodiversification event a case study from fossil mountain utah usa abstract the great ordovician biodiversification event gobe was a time of pronounced radiation within the paleozoic and modern evolutionary faunas despite increases in metazoan diversity during both the cambrian and the ordovician recent geochemical evidence suggests that the early paleozoic may have experienced recurring deep ocean euxinia the dynamic connections between deep ocean redox and fossil rich shelf environments remain unclear but one way to elucidate these relationships is to study rocks formed during the gobe using both long term global and short term local redox proxies here we report geochemical results from the middle ordovician juab formation and kanosh formation at fossil mountain utah the kanosh formation has been interpreted by different workers either as an anoxic restricted basin or as a well oxygenated normal marine basin based on sedimentological and paleontological characteristics here we employ the sulfur isotopic composition of carbonate associated sulfate cas as a proxy for long term whole ocean redox changes during the middle ordovician we use the abundances of organic carbon and total sulfur as proxies for short term localized changes in redox during the deposition of the fossil mountain sediments organic carbon abundances are low overall average 0 7 wt maximum 1 2 wt using the most conservative estimate although some units may have had considerably higher organic content before burial total sulfur is uniformly low with an average value of 0 02 wt and a maximum value of 0 07 wt the total sulfur and organic carbon abundance results suggest that anoxia was not prevalent in the depositional environment of the juab and kanosh formations similarly the sulfur isotopic results correlate well with those reported from time equivalent strata in newfoundland suggesting that the fossil mountain sediments were not deposited in a restricted basin even though the total sulfur and organic carbon data suggest that the local environment was not anoxic our sulfur isotopic results support the hypothesis that the global ocean was likely euxinic during the middle ordovician

a major sulphur isotope event at c 510 ma a possible anoxia extinction volcanism connection during the early middle cambrian transition a new approach to constraining seawater 34s and sulphate concentration using francolite bound sulphate reveals an abrupt increase in 34s to 50 around the early middle cambrian boundary such high 34s values are best explained by increased rates of pyrite burial due to ocean anoxia coupled with an increased sensitivity of the ocean sulphate reservoir to perturbations due to low sulphate concentrations of 500 700 gl 1 we argue that the spread of anoxic waters at this time was partly the result of greenhouse warming related to the eruption of the kalkarindji large igneous province of northern australia and that it triggered the collapse of early metazoan reef ecosystems during the latest early cambrian mass extinctions of the last 260 myr have all coincided with enhanced volcanic activity while several are also associated with positive shifts in seawater 34s extending this correlation back in time further implicates volcanically induced climate change as a major determining factor in biosphere evolution

middle late ordovician darriwilian sandbian decoupling of global sulfur and carbon cycles isotopic evidence from eastern and southern laurentia abstract middle late ordovician sequences from the appalachian basin and arbuckle mountain regions of north america were analyzed for carbonate associated sulfate 34 s cas and pyrite 34 s pyr paired with carbonate 13 c carb and organic matter 13 c org chemostratigraphy two major negative drops in 34 s cas 12 excursions are recognized the older decline in 34 s cas occurs within the histiodella holodentata phragmodus polonicus conodont zones and the younger drop is within the cahabagnathus sweeti amorphognathus tvaerensis baltoniodus gerdae subzone zones these overall these negative shifts in 34 s cas have an antithetical relationship with positive shifts in 34 s pyr 10 and 13 c carb 2 recorded in the same successions the older negative 34 s cas shift is coincident with the widely documented mid darriwilian 13 c excursion mdice and the younger negative 34 s cas shift is coincident with another positive 13 c carb shift in the early sandbian geochemical modeling of these sulfur isotope shifts suggests that a decrease in the global rate of pyrite burial or isotope fractionation between seawater sulfate and sedimentary pyrite could account for these negative 34 s cas trends additionally a substantial increase in the weathering flux of pyrite to the global oceans could also explain these secular sulfur isotope trends while increased crustal weathering is broadly consistent with a sea level lowstand and the seawater 87 sr 86 sr isotope record of change in continental weathering in the late darriwilian stage of the ordovician geologic and geochemical proxy evidence do not support distinct pulses of continental weathering required to generate two separate negative shifts in 34 s cas these antithetical isotope trends may be best explained by changes in the marine redox state that significantly reduced microbially mediated pyrite burial and organic matter remineralization rates pulses of oceanic ventilation would have expanded habitable environments for marine organisms and thus is broadly consistent with major increases in biodiversification during this period of the ordovician