shallow marine carbon and oxygen isotope and elemental records indicate icehouse greenhouse cycles during the early jurassic 1 for much of the mesozoic record there has been an inconclusive debate on the possible global significance of isotopic proxies for environmental change and of sequence stratigraphic depositional sequences we present a carbon and oxygen isotope and elemental record for part of the early jurassic based on marine benthic and nektobenthic molluscs and brachiopods from the shallow marine succession of the cleveland basin uk the invertebrate isotope record is supplemented with carbon isotope data from fossil wood which samples atmospheric carbon new data elucidate two major global carbon isotope events a negative excursion of 2 at the sinemurian pliensbachian boundary and a positive excursion of 2 in the late pliensbachian the sinemurian pliensbachian boundary event is similar to the slightly younger toarcian oceanic anoxic event and is characterized by deposition of relatively deepwater organic rich shale the late pliensbachian strata by contrast are characterized by shallow marine deposition oxygen isotope data imply cooling locally for both events however because deeper water conditions characterize the sinemurian pliensbachian boundary in the cleveland basin the temperature drop is likely of local significance in contrast a cool late pliensbachian shallow seafloor agrees with previous inference of partial icehouse conditions both the large scale long term and small scale short duration isotopic cycles occurred in concert with relative sea level changes documented previously from sequence stratigraphy isotope events and the sea level cycles are concluded to reflect processes of global significance supporting the idea of an early jurassic in which cyclic swings from icehouse to greenhouse and super greenhouse conditions occurred at timescales from 1 to 10 ma

carbonate platform crisis in the carnian late triassic of hanwang sichuan basin south china insights from conodonts and stable isotope data abstract during the carnian the hanwang area in the northwestern sichuan basin south china was characterized by shallow water carbonate sedimentation that underwent an abrupt demise associated to a sudden input of terrigenous sediments this major facies change was considered to be the expression of the onset of the carnian humid episode a most remarkable environmental crisis in late triassic that is well recognized in northwestern tethys margins and coincides with a major global perturbation of the carbon stable isotope record however the lack of detailed biostratigraphic constraints have so far prevented a precise dating of the carbonate platform demise in western sichuan basin in this work the qingyan gou hwq section cropping out in hanwang was investigated for its facies and microfacies carbonate carbon and oxygen isotopes on brachiopods microbial grains and bulk matrix facies analysis shows a marine transgression from inner ramp oolitic shoal to middle ramp siliceous sponge mound then overlain by shale and calcareous siltstone with interbedded silty mudstones refined biostratigraphic data from hwq and guanyin ya hwg sections imply that the demise of sponge mounds occur in the late tuvalian or later a negative carbon isotope perturbation was found in the bulk matrix immediately below the sponge mounds demise but it was not found on the isotope record from brachiopods this suggests that the negative shift in the bulk carbonate was probably related to diagenesis given the late tuvalian last substage of carnian age attributed to the demise of the sponge mounds and the absence of a carbon isotopic excursion we infer that the carbonate platform crisis and strong terrigenous input in hanwang cannot be related to the onset of the carnian humid episode these the demise of the carbonate platform and the facies deepening trend could be rather due to the interplay between accelerating subsidence rates environmental chants and enhanced siliciclastic input related to the formation of a foreland basin during indosinian orogenesis

paleo seawater ree compositions and microbial signatures preserved in laminae of lower triassic ooids abstract signals indicative of paleo seawater rare earth element ree composition and microbial activity were identified in marine ooids from the lower triassic of south china using in situ laser ablation inductively coupled plasma mass spectroscopy la icp ms together with petrographic and isotope geochemical techniques quantitative trace element profiles were generated across successive growth laminae in the cortices of selected ooids the shale normalized ree and yttrium y data of these layers show 1 light rare earth element depletion mean la sn yb sn 0 36 0 14 2 positive la anomalies mean la la sn 2 02 1 25 and 3 high ratios of y ho mean 53 12 which are similar to modern seawater compositions and bahamian ooids these findings imply that ooids in the study samples faithfully record early triassic paleo seawater chemical signals such as ree y distributions petrographic observations revealed dark colored layers with intense fluorescence containing structures that resemble microbial filaments or extracellular polymeric substances these layers also possess more enriched ree compositions and higher concentrations of nutrient like elements e g zn and ba than adjacent recrystallized light colored laminae most ooid laminae contain negative ce anomalies indicative of a well oxygenated environment of formation but some laminae have minimal negative anomalies suggesting the influence of suboxic porewater conditions the present study provides a new perspective on the role of microbes in ooid genesis and on the utility of ooids as proxies for paleo seawater chemistry

a rise in the carbonate compensation depth of western tethys in the carnian late triassic deep water evidence for the carnian pluvial event the upper triassic of the lagonegro basin southern apennines southern italy is represented by hemipelagic cherty limestones of the calcari con selce formation deposited in an oceanic setting two stratigraphic sections petina chiana and pignola 2 representative of the evolution of the lagonegro basin during the carnian have been studied in detail with a multidisciplinary approach in the pignola 2 section within the calcari con selce formation a unique interval composed of green shales and radiolarites has been identified the absence of carbonate deposition within this interval is interpreted as evidence of a contemporaneous shallowing of the carbonate compensation depth conodont and palynomorph biostratigraphy constrain the age of this interval to the julian tuvalian lower carnian upper carnian boundary the age and characteristics of this interval suggest correlation with a putative climatic event known as the carnian pluvial event which has also been recognized in continental and shallow marine successions from different european localities this event is thus now documented also in a deep marine setting like the continental and shallow water settings it is characterized by a sudden input of siliciclastics petina chiana and pignola 2 integrate current knowledge of the carnian distribution of conodonts paragondolella praelindae kozur to date known only from the lower tuvalian has now been documented from the uppermost julian moreover a drastic turnover was recorded between julian and tuvalian conodont assemblages which is clearly associated with the carnian pluvial event thus a biotic crisis oceanographic changes associated with the rise of the carbonate compensation depth increased rainfall and an anomalous siliciclastic input occur contemporaneously at the time of the carnian pluvial event a similar pattern is associated with perturbations of the carbon cycle that occur during the jurassic and cretaceous e g in the early aptian thus it is hypothesized that the carnian pluvial event may have analogous causes

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

meteoric burial diagenesis of middle pennsylvanian limestones in the orogrande basin new mexico water rock interactions and basin geothermics abstract stable isotopic compositions of cyclic middle pennsylvanian gobbler formation limestones record two stages of alteration early open system meteoric diagenesis during episodic subaerial exposure stabilized cycle top carbonate in the presence of meteoric fluid at high water rock ratios 400 4000 subsequent closed system burial diagenesis stabilized meteoric and residual marine carbonate in the presence of connate pore fluids at elevated temperatures to 150 c and low water rock ratios 1 0 10 present 18o distributions record normal to high geothermal gradients 27 86 c km during burial stabilization high basin center geothermal gradients probably resulted from elevated heat flow due to rapid crustal extens on and subsidence of the orogrande basin during the late pennsylvanian a dike injection lithospheric extension model with 40 oceanization best accounts for subsidence and geothermal patterns of the orogrande basin

sulphate reduction associated with hardgrounds lithification afterburn negative excursions in 13c profiles from platform carbonates that coincide with pyritised hardgrounds are commonly linked to subaerial exposure events but we show here that they can also result from subsurface bacterially mediated early cementation in addition to the precipitation of syndepositional marine cements a non soil derived origin for 13c depleted micrites offers an alternative origin and bathymetric interpretation for these surfaces the lower cretaceous lekhwair formation platform carbonate successions from offshore abu dhabi contain abundant hardgrounds that are important for both regional correlation and control of subsurface flow the micrite from these hardgrounds have average 13c values of 0 7 1 5 lower than non hardground micrites that are similar to contemporary open ocean values hardground 13c values are due to the addition of 13c depleted carbonate generated as a by product of sulphate reduction to the normal marine calcite that caused hardground lithification pyritisation of the hardgrounds occurred before during and after normal calcite precipitation the persistence of sulphate reduction after hardground lithification is shown by the presence of pyrite and low 13c micrite in sediment up to a few mm above the hardgrounds

migration of the carbonate ramp and sponge buildup driven by the orogenic wedge advance in the early stage carnian of the longmen shan foreland basin china abstract the marine carnian the maantang fm overlies a flexural forebulge unconformity and records the initial establishment drowning and migration of a carbonate ramp and sponge buildup along the forebulge margin of the longmen shan foreland basin the maantang fm is of wedge shaped geometry and is composed of oolitic and bioclastic limestones siliceous sponge reef and shale in an upward fining succession the formation shows the establishment and drowning of a distal margin carbonate ramp and sponge buildup deepening into offshore marine muds followed by progradation of marginal marine siliciclastics the formation also shows the transition from shale cratonward into carbonate rock southeastward the sponge reefs and shoal were deposited on a carbonate ramp on the distal margin of the early foreland basin the growth rate of sponge reefs is 0 04 mm yr equivalent to the rate of relative sea level rise of 0 01 0 05 mm yr the sponge buildup and oolitic shoal are divided into seven zones southeastward on the carbonate ramp along the basal unconformity their migration rate of 18 mm yr from nw to se coincides with the estimated orogenic wedge advance rate 5 15 mm yr li et al 2003 a clear indication that the advancing wedge controlled the migration rate of foreland oolitic shoal siliceous sponge reef we have inferred that the tectonic load of the longmen shan orogenic wedge led to flexural subsidence and rising relative sea level in the foreland basin located at the western margin of the yangtze craton driving the growth and subsequent drowning of the oolitic shoal sponge buildup in the early stage of the foreland basin we propose that the drowning and migration processes were the sedimentary response to the orogenic wedge advance toward the yangtze craton and to the rapid closure of the carnian songpan ganzi remnant ocean basin

marine cements in mid tertiary cool water shelf limestones of new zealand and southern australia large areas of southern australia and new zealand are covered by mid tertiary limestones formed in cool water shelf environments the generally destructive character of sea floor diagenesis in such settings precludes ubiquitous inorganic precipitation of carbonates yet these limestones include occasional units with marine cements 1 within rare in situ biomounds 2 within some stacked cross bedded sand bodies 3 at the top of metre scale subtidal carbonate cycles and 4 most commonly associated with certain unconformities the marine cements are dominated by isopachous rinds of fibrous to bladed spar interstitial homogeneous micrite and interstitial micropeloidal micrite often precipitated sequentially in that order internal sedimentation of microbioclastic micrite may occur at any stage the paradox of marine cemented limestone units in an overall destructive cool water diagenetic regime may be explained by the precipitation of cement as intermediate mg calcite from marine waters undersaturated with respect to aragonite in some of the marine cemented limestones aragonite biomoulds may include marine cement sediment internally suggesting that dissolution of aragonite can at times be wholly marine and not always involve meteoric influences we suggest that marine cementation occurred preferentially but not exclusively during periods of relatively lowered sea level probably glacio eustatically driven in the mid tertiary at times of reduced sea level there was a relative increase in both the temperature and the carbonate saturation state of the shelf waters and the locus of carbonate sedimentation shifted towards formerly deeper shelf sites which now experienced increased swell wave and or tidal energy levels fostering sediment abrasion and reworking reduced sedimentation rates and freer exchange of sediment pore waters energy levels were probably also enhanced by increased upwelling of cold deep waters onto the southern ocean margins of the australasian carbonate platforms where water mass mixing warming and loss of co2 locally maintained critical levels of carbonate saturation for sea floor cement precipitation and promoted the phosphate glauconite mineralization associated with some of the marine cemented limestone units

multi carbonate component reconstruction of mid carboniferous chesterian seawater δ13c abstract this study presents the first stratigraphically continuous 13ccarb record for the chesterian interval developed from antler foreland basin platform successions the bulk carbonate derived 13c curve was constructed using 700 biostratigraphically constrained samples providing a 105 yr resolution a multi component study of 13c and 18o variability in petrographically and geochemically screened abiotic and biogenic calcite components delineates the degree of preservation and 13c heterogeneity in these ancient epicontinental carbonates furthermore it constrains the influence of kinetic and vital effects and local to regional scale c cycling on their 13ccarb values the 13c and 18o values of micrites and bulk carbonates overlap regardless of lithofacies and show minimal intrasample variability overall biogenic calcite 13c and 18o values are higher than the average isotope compositions of bulk carbonates and micrites although 13c values in contemporaneous samples are only minimally 0 3 2 std err of 0 3 different relative to much larger differences in 18o values although brachiopod 13c and 18o values are higher than average bulk carbonate and micrite values their 13c values exhibit considerable isotopic variability by taxa and ultrastructure notably the 13c values of brachiopod secondary shell layers overlap with bulk carbonate micrite and marine cement 13c values conversely 13c values of brachiopod tertiary prismatic layers including composita are on average 2 to 5 higher than the 13c values of contemporaneous bulk carbonates micrites and brachiopod secondary shell layers an observed average 2 decrease in the 13c values of secondary cross bladed laminar layers in productids relative to contemporaneous bulk carbonate micrite and marine cement values suggests a previously unrecognized kinetic and or vital effect on carboniferous productid 13c values given that they have the highest 18o values of all analyzed components the observed higher 13c values in these tertiary prismatic layers are comparable to greater than the 13c enrichment 1 previously documented in pennsylvanian composita the overlap in 13c values of bulk carbonates with diagenetically screened microdrilled matrix marine cements and brachiopod secondary shell layers indicates that the chesterian bulk carbonate derived 13c values may reliably record to within 1 the evolution of ambient seawater 13c in the outer carbonate ramp of the antler basin comparison of the chesterian 13c record to the bulk carbonate c isotope curve derived from the arrow canyon nv carbonate succession further suggests that these bulk carbonate derived 13c records are reliable proxies of the composition and trends in seawater 13c regionally along the equatorial eastern panthalassan margin the newly resolved chesterian stratigraphy documents multiple 13c excursions including previously unrecognized significant c isotope shifts a shift to higher frequency and amplitude shorter term 13c fluctuations in the upper third of the chesterian stage occurred simultaneously with a change in stratigraphic cyclicity from dominantly 3rd order to 4th order carbonate cycles suggesting a mechanistic linkage between ambient seawater 13c and sea level fluctuations in the antler basin this change in the character of the shorter term 13c fluctuations coupled with a subsequent significant 4 positive c isotope excursion across the mid carboniferous boundary previously recognized in all carboniferous curves is interpreted to record the onset of late paleozoic glaciation and glacio eustasy

geochemistry of modern brachiopods applications and implications for oceanography and paleoceanography abstract modern rhynchonellida terebratulida thecideida and a few inarticulated brachiopods were collected live or soon after death at 30 locations from depths of 2 3940 m from the equator to high latitudes covering the atlantic pacific indian caribbean and mediterranean oceans seas well preserved fibers of the secondary layer combined with sr 450 1928 mg kg mn 1 199 mg kg and fe 1 610 mg kg contents confirm with few exceptions the excellent preservation of the modern brachiopod material evaluation of the stable isotope compositions was conducted on 276 specimens and on 374 published samples for a total database of 650 samples from 80 locations it revealed that oxygen isotope incorporation into shell calcite secondary layer of modern articulated brachiopods in most cases occurs in equilibrium with the ambient water and as such reflects surrounding environmental conditions thecideida as a group shallow water and low latitude incorporate oxygen isotopes 3 04 to 0 35 into shell calcite in equilibrium with their ambient water a large majority of genera and species of the terebratulida shallow water and low mid latitude also incorporate oxygen 2 30 to 3 48 into shell calcite in isotopic equilibrium with their surrounding water in contrast equilibrium incorporation of oxygen isotopes into shell calcite by the rhynchonellida is uncertain but a vital effect probably applies to the craniida the question of equilibrium disequilibrium incorporation of carbon isotopes into shell calcite of modern brachiopods remains unresolved at this time isotope compositions range up to 4 5 5 6 and 1 5 for 13 c and up to 5 5 5 9 and 0 3 for 18 o for shallow water low mid and high latitude brachiopods respectively strontium isotopes of modern brachiopods as expected show no significant variation with location latitude water depth temperature salinity and general water conditions once local habitat and ecological influences of fossil brachiopods from similar latitudes are considered their isotopic elemental values should be valuable diagenetic indicators and important oceanographic chemostratigraphic proxies

late triassic and early jurassic palaeogeography of the world abstract a new version of global and regional palaeogeographic maps is presented for two time intervals these maps depict the plate tectonic configuration palaeoenvironment and lithofacies during the late triassic carnian norian and early jurassic hettangian toarcian time the individual maps illustrate the general conditions present during the maximum marine transgressions of higher frequency cyclicity within the absaroka sequence of sloss during triassic time pangaea began to stretch initiating the rifting and future break up of the supercontinent the continued northward drift of the cimmerian continent corresponded with the progressive closure and consumption of palaeotethys oceanic crust and the opening of the neotethys ocean the most significant late triassic convergent event was the indosinian orogeny occurring as a result of the consolidation of south china and north china blocks also indochina and indonesia were sutured to south china at the same time the qiangtang block approached the eurasian margin the consolidation of the north chinese and amurian blocks left open a large embayment of panthalassa between amuria and laurasia the so called mongol okhotsk ocean active subduction existed along the margin of this ocean dipping cratonwards towards east siberia the last collisional events of the uralian orogeny took place during the triassic and early jurassic time the conclusion of the uralian orogeny was accompanied by uplift of the adjacent areas of eastern europe and western siberia during the early jurassic the palaeotethys ocean was finally closed and the cimmerian continent collided with asia causing the cimmerian orogeny the time around the triassic jurassic boundary marked an important biotic extinction event plate tectonic activity caused palaeogeographic and palaeoclimatic change which may have contributed to the mass extinction from the plate tectonic and palaeogeographic point of view the following events could have influenced the extinction 1 the closure of palaeotethys and assembly of the asian part of pangaea 2 the break up of pangaea in the future central atlantic area and transition from rifting to drifting and 3 the very extensive basaltic volcanism of the central atlantic magmatic province

climate variability during the carnian pluvial phase a quantitative palynological study of the carnian sedimentary succession at lunz am see northern calcareous alps austria abstract the middle and upper triassic prevailing dry climate was interrupted by a global phase of increased humidity during the early carnian the carnian pluvial phase cpp it started at the julian 1 2 boundary and lasted approximately until the latest julian or early tuvalian in the tethys this is reflected by a change from limestone deposits to first organic rich mudstones and then to siliciclastics the cpp occurred along the northern rim of the tethys and is reported from many locations within and surrounding europe in this study samples from lunz am see in austria were analyzed for palynology and for bulk carbon isotope values covering a 450 m thick succession a known 3 bulk organic carbon isotope excursion possibly as a result of the eruption of large amounts of volcanogenic material in the gostling member and the basal reingraben formation has been confirmed a total of five distinctive palynology assemblages were recognized and correlated regionally while the under and overlying formations yield terrestrial and subordinate also marine palynomorphs the palynoflora of the lunz formation is near wholly terrestrial in origin climate trends were inferred from multivariate statistical analysis pca of the palynofloral record palynomorphs show a general trend from a dry climate during the julian 1 to wetter conditions during the julian 2 the wetter conditions were periodically interrupted by shorter periods of dryer climate in terms of temperature trends the climate was warmer during the early julian 2 which corresponds with the deposition of the reingraben formation temperature decreased again and remained fairly stable during most of later part of the julian 2 which corresponds to the deposition of the lunz formation this study correlates with similar observations from other locations from the western tethys region that support the theory of a wide ranging to global carnian pluvial phase

sequence stratigraphy after the demise of a high relief carbonate platform carnian of the dolomites sea level and climate disentangled abstract sedimentary facies analysis aided by quantitative 3d georeferenced field data is applied to constrain the sequence stratigraphy of a complex stratigraphic interval in the late triassic of the dolomites this multidisciplinary approach was the key to disentangle the timing of climatic change vs sea level fluctuation and their effects on shallow water carbonate depositional systems the carnian pluvial event a global episode of climate change worldwide documented at low latitudes involved increased rainfall and possibly global warming this climatic event begins before a drop of sea level and caused the demise of microbial dominated high relief carbonate platforms that dominated the dolomites region and was followed by a period of coexistence of small microbial carbonate mounds and arenaceous skeletal oolitic grainstones a subsequent sea level fall brought to the definitive disappearance of microbialites and shallow water carbonates switched to ramps dominated by oolitic bioclastic grainstones the crisis of early carnian shallow water carbonate systems of the dolomites generated a geological surface similar to a drowning unconformity although no transgression occurred as the high relief microbial carbonate systems characterized by steep slopes switched to gently inclined oolitic skeletal siliciclastic ramps basins were rapidly filled the change of carbonate depositional systems was associated with an increase in siliciclastic input in turn triggered by the onset of a humid climatic event and only later to a sea level drop this evolution of carbonate systems cannot be interpreted in the light of sea level changes only climate change and consequent ecological changes in the main carbonate producing biotas induced significant modifications in depositional geometries this case study may serve as a conceptual model for the sedimentary evolution of carbonate systems subject to ecological crisis that do not evolve in platform drowning because despite a drop in shallow water carbonate production a combination of low subsidence and or sea level drop maintains the platform top at shallow depth

ooid microfabrics the origin and distribution of high intra ooid porosity mid jurassic reservoirs s england abstract the bathonian great oolite of southern england which forms a hydrocarbon reservoir in the subsurface adjacent to the weald basin consists of oolitic grainstones to wackestones within the great oolite three main types of ooid cortex fabric are recognised pristine radial micritised radial and completely micritised the type of ooid fabric controls the distribution and amount of intragranular porosity detailed stable isotope analysis of ooids suggests that in addition to microinfestation meteoric exposure is an important factor controlling the distribution of ooid fabric types micritised ooids and high intragranular porosity occurs where meteoric influence has been greatest

discovery of a major negative δ13c spike in the carnian late triassic linked to the eruption of wrangellia flood basalts major climate changes and mass extinctions are associated with carbon isotope anomalies in the atmosphere ocean system and have been shown to coincide with the onset of large igneous provinces lips and by association their emissions of greenhouse gases and aerosols however climatic and biological consequences of some known lip eruptions have not yet been explored during the carnian late triassic large volumes of flood basalts were erupted to form the so called wrangellia lip western north america this huge volcanic province is similar in age to a major climatic and biotic change the carnian pluvial event cpe but no evidence of a causal relationship exists other than timing here we report a sharp negative 13 c excursion at the onset of the cpe recorded in organic matter an abrupt carbon isotope excursion of 4 occurs in terrestrial and marine fossil molecules whereas total organic carbon records an 2 shift we propose that this carbon isotope negative shift was caused by an injection of light carbon into the atmosphere ocean system linked to the eruption of wrangellia flood basalts this carbon cycle perturbation occurs slightly before two major evolutionary innovations the origin of dinosaurs and calcareous nannoplankton

carbonate ramp depositional systems abstract the classification tectonic settings stratigraphy and early diagenesis of carbonate ramp systems are reviewed carbonate ramps are common in all geological periods but were dominant at times when reef constructing organisms were absent or inhibited ramps can be subdivided into inner mid and outer ramp environments the mid ramp zone extends from fair weather wave base to normal storm wave base although the water depths which these boundaries represent vary an additional outer slope environment occurs on distally steepened ramps as with siliciclastic shelves a range of wave storm and tide dominated ramps can be recognised and this forms the most convenient basis for ramp classification the carbonate productivity profile of ramps differs from that of rimmed shelves with the inner ramp showing lower production rates than comparable shallow water facies on rimmed shelves the zone of greatest organic carbonate sediment production appears to have shifted from the mid ramp to the inner ramp since the late jurassic carbonate ramps occur in most types of sedimentary basin but are best developed where subsidence is flexural and gradients are slight over large areas as in foreland and cratonic interior basins and along passive margins the featureless depositional profiles of many ramps means that sequence geometries are best observed on regional seismic lines some show low angle sigmoidal or shingled clinoforms suggesting that ramps may seldom be homoclinal but possess subtle slope geometries which reflect depositional environments because of their low angle slopes ramps respond differently to rimmed shelves during relative sea level changes although results seem to be strongly dependent on the rate of relative sea level change during a minor fall shallow ramp facies belts will simply shift basinwards in a forced regression in contrast the whole surface of a steep sloped flat topped rimmed shelf may be exposed so that sediment production ceases or is drastically reduced during a major fall shallow ramp bounded basins may empty completely conversely ramps also flood gradually whereas rimmed shelves do so more rapidly homoclinal ramps develop no resedimented lowstand deposits rimmed shelves and distally steepened ramps in contrast may develop lowstand talus or turbiditic wedges distally steepened ramps may behave more like homoclinal ramps during minor base level falls and like rimmed shelves during major base level falls many ramps consist of layered successions of several ramp sequences stacked one upon the other ramp stacks of this sort may show gross vertical accretion but individual ramp sequences seldom appear to develop in a keep up style apart from minor organic buildups as with many rimmed shelves steepening of the outer ramp margin due to tectonism slope inheritance or differential sedimentation may promote the development of a distally steepened ramp or rimmed shelf a wide variety of organisms have constructed buildups in mid and outer ramp environments isolated buildups may seed early in ramp development accrete to wave base or sea level and continue growth by stacking through successive ramp sequences so that depositional and diagenetic features within them are in concert with those of the shallow ramp the location of isolated buildups on ramps is governed by tectonism halokinesis antecedent topography or by the subtle slope geometry of the previous ramp sequence diagenesis on ramps shows some major variations compared with diagenesis on steep sloped flat topped carbonate platforms ramp bounded basins may form prolific petroleum sourcing and reservoiring systems and offer a range of subtle stratigraphic play types and lateral facies variations which determine reservoir quality and distribution isolated buildups in the mid and outer ramp environments represent one of the commonest petroleum reservoirs in ramp systems and tend to have their foundations in transgressive systems tracts grainstone and packstone reservoirs are widespread and range from shoreline carbonate sandbodies to major detached shoal complexes or shoals over offshore highs grainstone sandbodies occur in both highstand systems tracts and in prograding lowstand wedges

late triassic compositional changes of aeolian dusts in the pelagic panthalassa response to the continental climatic change abstract the carnian pluvial event cpe is considered as the drastic environmental change that occurred in the western tethys during the carnian late triassic although some studies have suggested that the cpe was a global event no studies have referred to pelagic environment related to the cpe to reveal the pelagic environment during the carnian x ray absorption fine structure xafs analysis was used to determine the iron fe species in chert samples collected from the ladinian carnian strata in the tamba mino ashio belt japan the x ray absorption near edge structure xanes analysis shows that all the red cherts contain hematite with a combination of clay minerals such as illite chlorite and smectite the existence of these minerals is identified using extended xafs exafs the xanes analysis of the green and the white cherts does not show any hematite signatures while the exafs analysis indicated increasing amounts of chlorite the stratigraphic change in the fe bearing compositions observed in this study can be divided into three stages i a stage where a relatively stable mineral composition chlorite illite hematite is observed in cherts deposited during the early carnian julian ii the abrupt change in mineral composition lack of chlorite and appearance of smectite observed in the middle area in the studied section and corresponding to the middle part of carnian late julian early tuvalian and iii the recovery of the previous stable mineral composition during the late carnian tuvalian these variations in the mineralogical composition of pelagic cherts can be interpreted to mean that the continental climate conditions changed during the carnian and different clay fractions were delivered to the pelagic region these data combined with the results of previous studies performed around the continental realm can be interpreted as follows i there was a relatively stable dry climate before the cpe ii there were increasing amounts of precipitation owing to the cpe and iii the climate returned to dry conditions similar to those prior to the cpe

the middle carnian wet intermezzo of the stuttgart formation schilfsandstein germanic basin abstract the middle carnian wet intermezzo mcwi of the stuttgart formation schilfsandstein and age equivalent strata of the northwestern tethys occurred entirely within equivalents of the upper subzone of the austrotrachyceras austriacum ammonoid zone of the late julian its duration is estimated to be only about 0 7 0 8 myr in both the germanic basin and the northwestern tethys the warm climate during the mcwi was characterized by a rate of precipitation that exceeded somewhat the evaporation but was not so great as to be pluvial the mcwi was related to the atmospheric circulation of a megamonsoonal system that was characterized by strong moisture laden northwesterly flowing trade winds that rose as they reached the estimated 2000 3000 m high eastern shoulder uplift of a huge rift causing them to drop an extraordinary amount of rain this eastern shoulder uplift lay within the caledonides of modern day western scandinavia this region only between 30 and 50 n palaeolatitude had a truly pluvial climate and the huge amounts of fresh water dropped there transported large amounts of siliciclastics from this rift shoulder uplift southward into the germanic basin before deposition of the siliciclastics an early julian eustatic sea level fall caused widespread erosion in the germanic basin in the later part of late julian a transgression from the eastern gates with the concurrent strong fresh water influx from the north flooded the centre of the northern germanic basin with a shallow brackish sea in which the osterhagen horizon basisschichten of the lower stuttgart formation was deposited in the upper osterhagen horizon the salinity rapidly decreased from mesohaline through mio and oligohaline to fresh water levels in southern germany the basisschichten formed entirely within fresh water or very low salinity brackish environments later a slight subsidence of the southwestern germanic basin shifted the main outflow of fresh water toward the southwestern end of the basin creating local brackish conditions in the northern marginal part of the northwestern tethys e g in the lunz beds during this time interval tidal influence also can be found in the stuttgart formation deposited in palaeoestuaries of the southwestern germanic basin adjacent to the tethys the very strong fresh water influx from the north however prevented these estuaries from developing a strongly elevated salt content so that only fresh water to oligohaline brackish faunas are found there such as the eberstadt bivalve conchostracan fauna at the base of the tuvalian the megamonsoonal system either disintegrated or else the trade winds shifted their principal flow direction this caused the climate within the germanic basin and in the nearby northwestern tethys sea to become arid again as it had been before the deposition of the stuttgart formation these changes in the atmospheric circulation patterns also terminated the pluvial climatic regime to the north along the scandinavian eastern rift shoulder uplift this in turn ended the transport of huge amounts of siliciclastics from this region southward into the germanic basin and ended the deposition of the schilfsandstein after this the hypersaline sabkha and playa sedimentation of the weser formation began which was accompanied by some minor marine ingressions in the southwestern germanic basin

δ13c and δ18o values of triassic brachiopods and carbonate rocks as proxies for coeval seawater and palaeotemperature abstract a dataset of 160 isotope 13c and 18o values from anisian ladinian carnian and rhaetian articulate brachiopod shells complemented by 158 carbon and oxygen isotope values from whole rock carbonates define the first continuous stable isotope baseline trends for the triassic seawater the carbon isotope data suggest the existence of several short term high amplitude excursions in the early triassic followed by a predominance of values around 0 5 1 during the middle triassic a rise to 3 5 during the carnian plateau at this level during the late carnian to early norian and a 1 5 decline in the middle norian to values around 2 during the late norian rhaetian interval the causation scenarios for these rapid oscillations are at present equivocal but may in part reflect a biological instability of the carbon cycle following the recovery from the end permian extinction event and or an input of mantle derived co2 from enhanced volcanic activity the 18o values from well preserved brachiopods from the tethyan realm range from 3 9 to 0 6 v pdb these values require open marine triassic seawater 18o values close to 0 v smow for the calculated temperatures to be within the range of tolerance of the coexisting reef building corals a 2 18o increase within the uppermost cordevolian and early julian suggests either a distinct temperature decline in the southern alps during that time interval an increase in seawater salinity or their combination oxygen isotope values for the muschelkalk brachiopods range between 6 2 and 2 0 and likely reflect a strong influx of meteoric waters into the germanic basin that shifted the oxygen isotopes to more negative values

controls on the 87sr 86sr ratio of carbonates in the garhwal himalaya headwaters of the ganges abstract the episodic variation of the seawater 87sr 86sr ratio has been attributed to either variations in the sr flux or the sr isotopic composition of the riverine dissolved load derived from weathering of the continental crust the discovery that himalayan rivers are characterized by high concentrations of dissolved sr concentrations with high 87sr 86sr ratios has raised the possibility that collisional orogens play a critical role in moderating the variations in seawater 87sr 86sr ratios here we describe himalayan carbonates and calc silicates from garhwal the headwaters of the ganges with extreme 87sr 86sr ratios 1 0 elevated sr isotope ratios result from exchange with rb rich silicate material during both himalayan and pre himalayan metamorphic episodes and the carbonates contribute a significant fraction to the ganges 87sr flux particularly elevated 87sr 86sr ratios are found in calc silicates from the deoban formation of the lesser himalaya a detailed traverse of shales and calc silicat

diagenetic origins of the calcite microcrystals that host microporosity in limestone reservoirs abstract micron size pores are common in limestones and they host significant hydrocarbon reserves in conventional and unconventional plays worldwide previous studies have shown that the vast majority of micropores in limestones occur in the interstices between micron size calcite crystals that are present in nearly all depositional environments and burial depths throughout the phanerozoic in an effort to elucidate the genetic history of these calcite microcrystals a geochemical study was undertaken to investigate a global dataset collected from seven new subsurface microporous reservoirs as well as data from 21 previous studies bulk elemental analyses indicate that the vast majority of microcrystals are composed of low mg calcite average 14 mmol mol range 1 6 90 mg ca microcrystal sr mg ratios are consistent with abiotic calcite cements though overall mg ca and sr ca are lower than modern abiotic calcite cements reported in the literature higher sr ca observed in depositional chalks implies a biotic though probably not aragonitic precursor most calcite microcrystals have oxygen isotope compositions that are 0 to 4 more negative and carbon isotope compositions just slightly more negative 1 than contemporaneous abiotic marine calcite most stable oxygen and carbon isotopic data plot either along a burial trend anchored at its most positive end in the age equivalent marine calcite composition or parallel to that trend with an offset in 13c assuming that 13c offsets are due to marine carbon isotopic excursions the isotopic data are consistent with shallow burial diagenesis as the dominant diagenetic pathway for most calcite microcrystals for samples with information on porosity and depth more negative 18o ca 1 4 is associated with increased depth and reduced porosity implying that progressive overgrowth of calcite microcrystals is modifying bulk chemistry and rock properties of the reservoir during burial diagenesis a meteoric calcite line was evident only in two datasets this demonstrates that evidence of meteoric diagenesis can be preserved in the chemistry of calcite microcrystals but that its occurrence is rare in comparison with evidence for diagenesis during shallow burial geochemical data from calcite microcrystals are bulk samples i e measurements averaged over many many calcite microcrystals which themselves may have zoned chemistries as such microcrystal data require additional interpretation compared to samples from calcite macrocrystals where superposition puts samples into clear chronological order and produces diagenetic trends on for example 18o 13c plots bulk samples of calcite microcrystals should show mixing between phases on diagenetic trends with this model in mind the assembled database suggests that most samples are mixes of primary marine and burial calcite

the carnian humid episode of the late triassic a review from 1989 to 1994 a series of papers outlined evidence for a brief episode of climate change from arid to humid and then back to arid during the carnian stage of the late triassic epoch this time of climate change was compared to marine and terrestrial biotic changes mainly extinction and then radiation of flora and fauna subsequently termed albeit incorrectly the carnian pluvial event cpe by successive authors interest in this episode of climatic change has increased steadily with new evidence being published as well as several challenges to the theory the exact nature of this humid episode whether reflecting widespread precipitation or more local effects as well as its ultimate cause remains equivocal bed by bed sampling of the carnian in the southern alps dolomites shows the episode began with a negative carbon isotope excursion that lasted for only part of one ammonoid zone a austriacum however that the carnian humid episode represents a significantly longer period both environmentally and biotically is irrefutable the evidence is strongest in the european middle eastern himalayan north american and japanese successions but not always so clear in south america antarctica and australia the eruption of the wrangellia large igneous province and global warming causing increased evaporation in the tethyan and panthalassic oceans are suggested as causes for the humid episode

early marine lithification and hardground development on a miocene ramp maiella italy key surfaces to track changes in trophic resources in nontropical carbonate settings abstract phosphatic and carbonate hardgrounds occur in a lower miocene nontropical carbonate succession in the maiella carbonate platform margin located in the central apennines multiple diagenetic events occurred at or near the sea floor before the deposition of the overlying sediment and included precipitation of inclusion rich calcite micrite iron oxides and phosphates later diagenetic features are limited to chemical compaction and precipitation of clear calcite cement we relate the development of these features to a two step model involving progressive intensification of upwelling on this carbonate margin which was triggered by regional changes in water circulation and modulated by sea level changes leading initially to precipitation of inclusion rich calcite with an increase in trophic resources related to the paleoceanographic conditions on the ramp increased flux of organic matter to the sea floor led to temporary formation of microbial biofilms these conditions were associated with extensive precipitation of micrite and phosphate microspherules in the uppermost sediment the lack of sedimentation provides the precondition to accumulate and preserve evidence for organic matter utilization in the uppermost sediment layer our study suggests that hardgrounds in nontropical carbonates might be used as indicators of circulation changes and can provide a useful link to major environmental changes in the ocean margin environment the occurrence of microbial micrite and phosphate microspherules precipitated in the absence of sedimentation near the sea floor as a response to higher nutrient supply provides a new and important criterion to differentiate nontropical carbonate facies deposited under the influence of higher nutrient supplies rather than temperature alone furthermore our study shows that local depletion in 13c at a key stratigraphic surface does not necessarily reflect meteoric exposure but may be related to microbial activity at the sea floor

carbon sulfur oxygen and strontium isotope records organic geochemistry and biostratigraphy across the permian triassic boundary in abadeh iran pelagic deposits at abadeh represent a complete biostratigraphic record across the permian triassic boundary ptb the presumed water depth during deposition of these sediments was between 60 and 90 m similar to other permian triassic boundary sections the succession at abadeh is characterised by a negative carbon isotope shift of approximately 4 the values start to decrease in the lower c changxingensis c deflecta s l zone reach 0 12 v pdb in the uppermost permian just below the ptb remain low to the early i isarcica zone 0 32 and increase subsequently in the upper i isarcica zone for the time interval of the ptb negative carbon isotope excursion between the c iranica and the i isarcica zones no correlation exists between the 13ccarb and the 18ocarb the above observations argue against the conclusion of heydari et al 2001 that the carbon isotope event at the p t transition is an alteration artefact and not a global signal the decrease in 13ccarb is accompanied by a 5 and potentially up to 10 increase in 34ssss together these features are thought to reflect a complex global event notably the development of widespread anoxic oceans with anoxic bottom layers rising onto the shelves for the carbon isotope drop other factors such as the collapse of ocean primary productivity may also have played a role the 87sr 86sr ratios of dzhulfian seawater show only a minor increase from 0 70705 to 0 70710 reaching 0 70720 in the dorashamian the increase becomes steeper in the early triassic reaching 0 70754 in the n dieneri zone the rise of the strontium isotope values is thought to be related to enhanced continental weathering under humid climatic conditions in the uppermost permian c meishanensis h praeparvus zone and the lack of a dense land vegetation in the early triassic prior to the spathian upper olenekian

brachiopods recording seawater temperature a matter of class or maturation calcite fibres of the innermost secondary layer of low magnesium calcite brachiopod shells are in oxygen isotope equilibrium with ambient seawater previous work on terebratalia transversa indicates that the first formed calcite fibres of the secondary layer are not in isotopic equilibrium while the later fibres of mature valves are in oxygen isotope equilibrium with seawater here secondary ion mass spectrometry sims analyses reveal that this trend of oxygen isotope equilibrium being attained towards the innermost shell rather than being a feature throughout the secondary layer occurs in brachiopods from two orders and two sub orders this suggests a general pattern among brachiopods with low magnesium calcite shells and leads to the recommendation that only the innermost fibres of mature valves be included in proxy calculations of seawater temperature although the trend is common in the three species studied here the extent of the isotopic range is much less marked in the species that lacks punctae

petrography and environmental controls on the formation of phanerozoic marine carbonate hardgrounds early marine seafloor lithification of carbonate sediments leads to the formation of hardgrounds and is known from rocks as old as the proterozoic hardground surfaces however are more commonly recorded in the phanerozoic sedimentological archive while ecological studies of hardground biota abound the environmental and physico chemical parameters leading to the development of seafloor lithification remain in many cases poorly understood and documented this paper reviews published evidence on the petrography mineralogy and geochemistry of phanerozoic carbonate hardgrounds within a process oriented context of their environmental controls hardgrounds typically develop in warm and shallow agitated tropical waters that are saturated with respect to caco3 but are also reported from hemi pelagic to bathyal realms and from cool water temperate settings a range of early marine cement types are documented from present day hardgrounds whereas preserved cement fabrics and related mineralogies are less diverse in early phanerozoic hardgrounds carbonate hardgrounds are widespread during calcite sea periods e g ordovician and cretaceous as opposed to some preservation bias ancient aragonite seas e g permian and triassic obviously the relation between seawater chemistry and hardground abundance and attributes is not an easy one here the concept of aragonite versus calcite seas serves as a first order template for the sake of a structured discussion whereas modern aragonite mode oceans document a significant diversity in spatial and bathymetric seawater properties this spatio temporal complexity is perhaps reflected in the scarce record of calcite sea hardgrounds from the devonian or paleogene rock record contrasted by the abundance in aragonite holocene and recent seas holocene hardgrounds allow for the direct assessment of rates of and reasons for early subaquatic lithification and in most cases escaped subsequent non marine diagenetic overprint conversely studies of ancient hardgrounds are often biased by early biological and mechanical erosion the degree of diagenetic overprint and tectonic to orogenic processes the formation distribution and physical properties of hardgrounds depend on the global climatic context greenhouse icehouse modes on sea level changes on ocean stratification on the spatial extent of epicontinental seas and carbonate depositional environments and on the spatially different mineralogies and rates of carbonate production the fabrics and mineralogies of early hardgrounds cement seem to substantially hinge on variations in atmospheric co2 thus the application of lessons from modern to ancient hardground case examples is not straightforward a holistic model explaining the full variability of controls on submarine hardground formation and their cement petrography throughout the phanerozoic is as yet lacking a more critical view on secular changes in hardground formation patterns is clearly needed future work should rely on the combination of sedimentological stratigraphic palaeoecological petrographic and geochemical approaches specific emphasis should be given to time intervals triassic carboniferous cambrian etc where the bulk of reported case studies is at best scarce

integrated stratigraphy and palaeoclimate history of the carnian pluvial event in the boreal realm new data from the upper triassic kapp toscana group in central spitsbergen norway the late triassic climate is characterized by arid conditions interrupted by a humid phase known as the carnian pluvial event cpe this wet phase is well documented in the tethyan realm but evidence from the boreal realm is scarce here we present evidence from quantitative palynology for the cpe from the kapp toscana group on central spitsbergen integrated with organic carbon isotope data linked to the geomagnetic polarity time scale our data reveal an early to mid julian 1 age for the tschermakfjellet formation the transition to the julian 2 is located in the de geerdalen formation and the isfjorden member is confirmed as mostly tuvalian 3 in age the aulisporites astigmosus pollen assemblage zone that marks the base of the cpe in the tethys realm at the base of the julian 2 is assigned to the julian 1 in the boreal region palaeoclimate proxy data inferred from principal component analysis indicate wetter conditions from the julian 2 onwards which is in agreement with the establishment of local swamp vegetation on top of a delta plain the palaeotemperature curve indicates a period of cooler climate during the early julian 1 followed by warming during the late julian 1 supplementary materials a list of all identified morphotaxa of pollen spores and aquatic palynomorphs is available at http www geolsoc org uk sup18879

synchroneity of climatic change and extinctions in the late triassic although the late triassic was a time of widespread aridity evidence exists for a significant increase in rainfall during the middle to late carnian upper triassic playa lake sediments were interrupted by late carnian fluviatile sandstones with erosive bases and high kao linite illite ratios there was also an increase in the clastic component of marine sequences during this interval middle and upper carnian marine carbonates show an extreme depletion in 13 c values consistent with increased fresh water influx large scale karstic phenomena in limestone areas subaerially exposed during the late triassic are a further indication of increased rainfall important faunal and floral changes occurred during the carnian norian interval marine invertebrate turnover was greatest at the lower middle carnian boundary and terrestrial extinctions were concentrated at the carnian norian boundary the cause of this carnian pluvial episode may have been related to the rifting of pangea through disruption of atmospheric and oceanic circulation patterns eustatic changes or the effects of volcanism associated with rifting a change in surface ocean temperature salinity or ph or habitat loss may have caused the decline of many shallow marine invertebrates at the start of the middle carnian a return to arid conditions at the carnian norian boundary would account for the turnover among terrestrial vertebrates and plants

climate warming euxinia and carbon isotope perturbations during the carnian triassic crisis in south china abstract the carnian humid episode che also known as the carnian pluvial event and associated biotic changes are major enigmas of the mesozoic record in western tethys we show that the che also occurred in eastern tethys south china suggestive of a much more widespread and probably global climate perturbation oxygen isotope records from conodont apatite indicate a double pulse warming event the che coincided with an initial warming of 4 c this was followed by a transient cooling period and then a prolonged 7 c warming in the later carnian tuvalian 2 carbon isotope perturbations associated with the che of western tethys occurred contemporaneously in south china and mark the start of a prolonged period of carbon cycle instability that persisted until the late carnian the dry wet transition during the che coincides with the negative carbon isotope excursion and the temperature rise pointing to an intensification of hydrologic cycle activities due to climatic warming while carbonate platform shutdown in western tethys is associated with an influx of siliciclastic sediment the eastern tethyan carbonate platforms are overlain by deep water anoxic facies the transition from oxygenated to euxinic facies was via a condensed manganiferous carbonate mno content up to 15 1 wt that records an intense mn shuttle operating in the basin significant siliciclastic influx in south china only occurred after the che climatic changes and was probably due to foreland basin development at the onset of the indosinian orogeny the mid carnian biotic crisis thus coincided with several phenomena associated with major extinction events a carbonate production crisis climate warming 13 c oscillations marine anoxia biotic turnover and flood basalt eruptions of the wrangellia large igneous province

cycle calibrated magnetostratigraphy of middle carnian from south china implications for late triassic time scale and termination of the yangtze platform abstract thick successions from the margins of the triassic yangtze platform of the south china block record a transition from carbonate rich facies zhuganpo formation and equivalents to clastic rich facies xiaowa formation and equivalents during the carnian early late triassic that mark the final phase of termination of this long lived platform cyclostratigraphy derived from spectral gamma ray sgr intensity curves was combined with magnetostratigraphy of two sections in guizhou province wayao transect and its upward extension into the geopark wayao in guanling county and the laishike section in zhenfeng county and one location in sichuan province hanwang section the cyclostratigraphy from all the guizhou sections indicates a persistent suite of ca 34 m 9 m and 1 8 m cycles which are consistent with the ratios of orbital climate oscillations caused by long eccentricity 405 kyr short eccentricity 100 kyr and precession 20 kyr the magnetostratigraphy of all sections is consistent with the cyclicity and characteristic sgr features thereby enabling a cycle tuned magnetic polarity scale spanning 2 4 myr the main feature is a 1 3 myr interval of reversed polarity containing brief normal polarity subchrons and this reversed polarity chron appears to correspond to the significant reversed polarity dominated interval spanning the upper half of the trachyceras aonoides through the lower half of the austrotrachyceras austriacum ammonoid zones of the upper julian the lower substage of carnian this magnetostratigraphic correlation implies that the termination of the yangtze platform is coeval with the beginning of the mid carnian episode of climatic disruption in europe which is locally called the carnian pluvial event or wet intermezzo and with the temporary cessation of the platform carbonates in the dolomites the cycle scaled magnetic polarity time scale supports the short tuvalian long norian age model of the late triassic in which the base of the cycle tuned polarity pattern from the newark group of eastern north america is younger than the end of the julian substage

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

deep water hexactinellid sponge mounds from the upper triassic of northern sichuan china a belt of upper triassic carnian sponge mounds was discovered in northern sichuan in the transition zone between a shallow shelf sea in the se chuan dian shelf and a deeper marine trough ganzi aba trough in the nw individual sponge mounds are up to 60 m high and 150 m wide and interfinger laterally with dark shales main frame builders of the mounds are lychniscosa and lyssacinosa accompanied by much rarer hexactinosa lithistida annelid worms occasional crinoids and bryozoa the reef dwelling fauna consists of brachiopods ostracods foraminifera pelecypods gastropods and ammonites typical shallow water reef builders scleractinian corals and calcareous algae are lacking or extremely rare coralline sponges this supports the interpretation of the mounds as buildups in deeper water of several tens up to one hundred meters the sponge mounds of northern sichuan are thus an equivalent of similar buildups of late jurassic age in central and western europe they provide the first well established record of lychniscosa in the triassic and their first reported pre tertiary occurrence outside of europe

chemical variation in pennsylvanian brachiopod shells diagenetic taxonomic microstructural and seasonal effects abstract to improve our ability to use minor and trace element mte variation in biotic carbonates as diagenetic and paleoenvironmental indicators we performed electron probe microanalysis on more than 100 late pennsylvanian brachiopod shells from texas kansas missouri and new mexico texturally preserved specimens of the genera crurithyris composita and neospirifer from all three regions were analyzed as were eridmatus specimens from texas twenty measurements were made in two transects across each shell shell microstructure and cathodoluminescence were described for each spot analyzed three modern shells were analyzed for comparison diagenesis as indicated by cathodoluminescence and or absence of microstructure tends to enrich shells in fe and mn x ca 0 7 mmol mol and deplete shells in na and s mg content shows no consistent trend with diagenesis in fabric retentive nonluminescent shell areas mg na and s contents vary twofold to sevenfold depending on taxonomy microstructure and season overall taxonomy is the dominant factor controlling mte composition na and s concentrations are consistently highest in crurithyris and eridmatus intermediate in neospirifer and lowest in composita in taxa with mixed microstructure composita neospirifer secondary fibrous layer calcite contains 1 5 to 2 times more na than does interlayer prismatic calcite thus whole shell na contents of these taxa depend on the proportion of fibrous and prismatic shell seasonal cycles are revealed in mte transects across growth lines mg na and s contents commonly vary by more than a factor of two between maxima presumably summer and minima winter within the same shell retention of taxonomic microstructural and seasonal effects in shell chemistry argues for preservation of original chemistry in fabric retentive nonluminescent paleozoic brachiopod shells

impact of diagenetic alteration on brachiopod shell magnesium isotope δ26mg signatures experimental versus field data due to their thermodynamically stable low mg calcite mineralogy the shells of brachiopods are often counted among the most reliable archives of the physicochemical conditions that occurred during the phanerozoic in marine waters consequently traditional and non traditional isotope and elemental proxy data from brachiopod valves have been analyzed in numerous studies and results obtained have been placed in context with ancient seawater properties this paper tests the sensitivity of brachiopod shell magnesium isotope 26mg data to diagenetic alteration we apply a dual approach by i performing hydrothermal alteration experiments using meteoric marine and burial reactive fluids and ii comparing these data to naturally altered ancient brachiopod shells the degree of alteration of individual shells is assessed by a combination of fluorescence and cathodoluminescence microscopy the absence of luminescence might indicate both well preserved shell material but also the secondary enrichment of quenching elements such as iron along diagenetic pathways complementary oxygen isotope data provide insight into the question of open versus closed system behavior of brachiopod shells brachiopod shell magnesium isotope values respond to differential fluid temperature chemistry and experiment durations the patterns observed are complicated by the interplay of kinetic and thermodynamic patterns and the presence of variable amounts of water soluble and water insoluble organic matter within these biominerals generally the range in bulk 26mg from experimentally altered 1 52 and that of bulk samples from ancient diagenetically altered brachiopod valves 1 53 exceed the geochemical variability of 26mgbrachiopod bulk values of most recent specimens 1 26 in the lower and upper range more 26mg enriched 0 8 and more 26mg depleted 0 7 values respectively are found in altered shells in comparison to unaltered ones the data shown here are considered significant for those aiming to reconstruct palaeoenvironmental parameters based on brachiopod archives consequently we propose tentative guidelines for magnesium isotope research applied to ancient carbonates

geochemistry of brachiopods oxygen and carbon isotopic records of paleozoic oceans abstract combined trace element and isotope studies of 319 brachiopods covering the ordovician to permian time span show that 13c and 18o in well preserved specimens varied during the paleozoic the overall 13c secular trend is in accord with the previously published observations but its details are obscured by vital isotopic fractionation effects at generic level nonetheless the results suggest that the negative correlation between marine 13ccarbonate and 34ssulphate deteriorates at time scales of 106 years due to the long residence time and thus slow response of so42 in the ocean for oxygen isotopes all devonian and older specimens have 18o of 4 while the well preserved permian samples have near present day 18o of about 1 pdb this isotopic dichotomy is probably not due to post depositional phenomena salinity or biogenic fractionation effects this leaves open the perennial arguments for a change in 18 o 16 o of sea water versus warmer ancient oceans the present data are difficult to explain solely by the temperature alternative the coincidence of the proposed shift in 18o with the large late paleozoic changes in marine 87 sr 86 sr 13 c 12 c 34 s 32 s and sea level stands argues for a tectonic cause and for a change in 18 o 16 o of sea water although such explanation is difficult to reconcile with global balance considerations and with isotopic patterns observed in alteration products of ancient basalts and ophiolites whatever the precise cause or combination of causes the implications for tectonism and or paleoclimatology are of first order significance

climatic and oceanographic isotopic signals from the carbonate rock record and their preservation stable isotopic data from marine limestones and their constituent fossils and marine cements can provide quantitative evidence for changes in global climate and ocean circulation oxygen isotopic data can indicate changes in temperature and ocean composition whereas stratigraphic variation in carbon isotope ratios may reflect changes in the carbon cycle that can be linked to changes in oceanic productivity and atmospheric greenhouse gases terrestrial carbonates meteoric cements calcretes and speleothems similarly offer significant potential for understanding the evolution of terrestrial climates by providing evidence for the composition of rainwater and the nature of vegetative cover primary environmental isotopic signals may be obscured by the effects of post depositional diagenetic alteration cementation and replacement reactions can take place in a wide range of diagenetic environments the diagenetic history of an individual limestone is determined by a combination of its mineralogical diagenetic potential and depositional setting together with subsequent changes in relative sea level and burial history carbon isotopic values are less prone to alteration during diagenesis than oxygen values but shifts can be significant where organogenic carbon is incorporated linear covariation of carbon and oxygen values is not a reliable indicator of diagenetic alteration water rock interaction and fluid mixing may produce non linear distributions attempts to determine long term changes in climatic and oceanographie conditions through isotope stratigraphy of shallow water limestones must include an assessment of the diagenetic history of the materials analysed petrographic examination using conventional microscopy backed up where appropriate by cathodoluminescence and scanning electron microscopy together with elemental and strontium isotopic analysis can help to identify the effects of diagenetic alteration where material with a range of different degrees of alteration is preserved in the same sediment it may be possible to compare patterns of isotopic and elemental variation and to attempt to unravel the effects of diagenesis in order to determine primary environmental isotopic signals recent research has shown that these techniques can be successfully employed in both phanerozoic and precambrian sediments

magnetostratigraphy of the mayerling section austria and erenkolu mezarlik turkey section improvement of the carnian late triassic magnetic polarity time scale abstract we present a magnetostratigraphic study of two carnian late triassic pelagic limestone sections from the northern calcareous alps mayerling section and southwestern turkey erenkolu mezarlik section biostratigraphic control is based on conodont zonation for the mayerling section and both on conodonts and ammonoids for the erenkolu mezarlik section in both sections the characteristic magnetization is essentially carried by a mineral of the magnetite family eight magnetic intervals are obtained from the mayerling section and fourteen from erenkolu mezarlik when these results are compared to the carnian magnetostratigraphic sequence obtained from the bolucektasi tepe section satisfactory correlations are observed and a composite carnian magnetic polarity time scale containing 24 intervals can be proposed by combining all these results the lower part of the upper carnian is however missing tuvalian 1 zone and lower part of the tuvalian 2 zone no clear correlation is observed between our composite sequence and the other published magnetostratigraphic data of carnian age the satisfactory correlation observed between the mayerling and the bolucektasi tepe sections indicates that both sections were deposited in the northern hemisphere thus providing constraints on the origin of the antalya nappes

the geochemistry of carbonate diagenesis the past present and future stable carbon and oxygen isotopes 18o and 13c values and trace elements have been applied to the study of diagenesis of carbonate rocks for over 50 years as valuable as these insights have been many problems regarding the interpretation of geochemical signals within mature rocks remain for example while the 18o values of carbonate rocks are dependent both upon the temperature and the 18o value of the fluid and additional information including trace element composition aids in interpreting such signals direct evidence of either the temperature or the composition of the fluids is required such information can be obtained by analysing the 18o value of any fluid inclusions or by measuring the temperature using a method such as the clumped isotope technique such data speak directly to a large number of problems in interpreting the oxygen isotope record including the well known tendency for 18o values of carbonate rocks to decrease with increasing age unlike the 18o 13c values of carbonates are considered to be less influenced by diagenesis and more a reflection of primary changes in the global carbon cycle through time however many studies have not sufficiently emphasized the effects of diagenesis and other post depositional influences on the eventual carbon isotopic composition of the rock with the classic paradigm that the present is the key to the past being frequently ignored finally many additional proxies are poised to contribute to the interpretation of carbonate diagenesis although the study of carbonate diagenesis is at an exciting point with an explosion of new proxies and methods care should be taken to understand both old and new proxies before applying them to the ancient record

diagenetic evaluation of a pennsylvanian carbonate succession bird spring formation arrow canyon nevada u s a 1 brachiopod and whole rock comparison abstract diagenetic evaluation of the pennsylvanian bird spring formation arrow canyon nevada u s a involved the detailed petrographic and geochemical examination of its brachiopod and whole rock components 13 c 18 o and 87 sr 86 sr of whole rock wr statistically p 0 0001 do not agree with isotope values of coeval brachiopod low mg calcite lmc more importantly a detailed investigation of the best preserved fine grained whole rock material demonstrates that it does not universally preserve its carbon isotope values in contrast with hypothetical predictions furthermore lumped trace chemistry or stable isotope tests do not unequivocally identify brachiopod or whole rock fine to coarse grained samples that carry an original seawater signal instead diagenetic evaluation involving as many screening tests as possible on a horizon by horizon level to compensate for spatial and temporal variations is necessary to identify the sample s that carries an original seawater signature many brachiopods from the bird spring formation are blue to non luminescent and carry microstructures and trace element contents similar to those of their modern tropical counterparts concurrence of chemical results between well preserved brachiopods and whole rock if originally low mg calcite is achieved in 22 of coeval samples for 13 c blmc wr with natural limits of 0 25 in 20 of samples for 18 o blmc wr with natural limits of 0 25 and in 9 of samples for 87 sr blmc wr with global limits of 0 000025 after an adjustment for mineralogical fractionation if whole rock is considered originally aragonite the concurrence of 13 c blmc wr drops to 0 and for 18 o blmc wr it drops to 6 furthermore comparison of stable isotopes of our well preserved brachiopods with those of preserved whole rock from the literature suggests that they are significantly different p 0 0001 with results of the latter dataset being more negative by about 0 77 2 57 with mineralogical adjustment for 13 c pdb and 1 31 2 11 for 18 o pdb thus our integrated screening and comparative tests indicate that 1 an overwhelming number of the whole rock samples from the bird spring formation carry a diagenetic instead of a primary signal for both carbon and oxygen isotopes and 2 many of the biogenic low mg calcite brachiopods in this succession carry an original chemical signal suitable for the reconstruction of high resolution seawater isotope curves representative of the pennsylvanian north american epeiric sea and potentially of the global oceans

the world s most spectacular carbonate mud mounds middle devonian algerian sahara abstract in the southern ahnet basin of algeria a unique middle devonian underwater scenery is revealed which consists of 191 mud mounds 15 mud ridges and 2 mud atolls distributed over nine discrete areas of a shallow pelagic carbonate shelf all the buildups are totally exhumed thus perfectly exhibiting their original morphologies slope angles elevations and the pattern of the onlapping strata as well as their relationship to the surrounding off buildup sequences types of buildups include 1 small mud mounds 1 5 m high 10 20 m diameter 2 large mud mounds up to 40 m high up to 200 m diameter 3 lens shaped mounds 1 30 m thick 10 15 slopes 4 mud ridges up to 100 m high 150 8500 m long and 5 semicircular mud atolls 2500 2800 m long 20 30 m high the buil ups were constructed during a short time span in the early givetian part of the lower varcus zone probably not exceeding a few hundred thousand years sedimentation rates in coeval off buildup areas were at least 3 10 times lower the lithology of the buildups is a massive boundstone with a high proportion of irregular spar filled cavities stromatactis but only very scattered potential frame builders the carbonate mud is considered to be an in situ cyanobacterial precipitate although evidence of such is poor organic components of the buildups are not significantly different from those of the off buildup lithologies and include numerous crinoid ossicles some tabulate and solitary rugose corals brachiopods mollusc debris trilobites and very rare sponge spicule and bryozoans the total absence of stromatoporoids large tabulate and colonial rugose corals green algae and micritic envelopes around grains suggests growth of the buildups in the lower part of the photic zone 100 200 m they are onlapped by a discontinuous sequence a few meters thick of skeletal packstones and grainstones and locally orthoceratid floatstones that were deposited later in the givetian a widespread rise of sea level in the early frasnian buried both buildups and adjacent areas under shales and siltstones postdepositional alteration of the mud buildups includes 1 formation of stromatactis cavities probably by dewatering and internal erosion 2 cementation of stromatactis cavities and interparticle pore spaces by early high mg calcite and late blocky low mg calcite 3 neomorphic transformation of mg calcitic mud and aragonitic skeletal debris 4 occasional formation of neptunian dikes 5 slight erosion of buildup surfaces 6 compaction and slumping of onlapping capping beds and 7 local dolomitization the formation and growth of the mud build ups is envisaged as a sequence of stages starting with patchy coral thickets evolving into small mud mounds that coalesced into larger mounds by continuous vertical and lateral growth closely spaced mounds amalgamated into mud ridges and mud atolls regular nw se and n s patterns of some mound rows and ridges show a relationship of buildup formation to rejuvenated late precambrian tectonic lineaments which reappear in the hercynian orogeny the isotopic signature of matrix and early ements of mound rocks however does not support the idea of fluid migration and hydrothermal co2 supply during buildup growth

demise of late triassic sponge mounds along the northwestern margin of the yangtze block south china related to the carnian pluvial phase upper triassic carnian marine successions in the northwestern margin of upper yangtze region sichuan basin china show a lithological change from grey oolitic into a sponge mound limestone units 1 and 2 of the lower member of the ma antang formation then overlain by greyish black to dark grey sandy shale and siltstone units 3 and 4 of the upper member of the ma antang formation siliceous sponge mounds were built by hexactinellida and this succession was examined in three localities jushui section in anxian js and guanyinya hwg and qingyangou sections hwq in hanwang mianzhu the conodont quadralella polygnathiformis confirms a carnian age for the biolithite and oolitic limestone of the lower ma antang formation abundant ammonoids identified as belonging to the discotropitid and juvavitid families suggest a tuvalian 1 early late carnian age for the lowermost part of the greyish black sandy shale that overlies the sponge mound at the jushui section field investigations and microfacies analysis suggest that sponge mounds had two stages of growth in relatively deeper water with low energy the first sponge growth mound stage ended in a regional karstified omission surface and was followed by a sudden increase of siliciclastic input greyish black shales containing plant fossils cover a second upper carnian sponge mound stage which is mainly recorded in hwg the onset of these shales may be related to the carnian pluvial phase cpp documented in the western tethys region e g in italy austria and hungary the demise of the sponge mounds at all three sections may have been triggered by the joint effect of climatic changes associated with the fresh water input caused by cpp and with a relative sea level change caused by local tectonic movements in the course of the indosinian orogeny

mars paleomagnetic field as the result of a single hemisphere dynamo mars crustal magnetic field was most likely generated by dynamo action in the planet s early history unexplained characteristics of the field include its strength concentration in the southern hemisphere and lack of correlation with any surface features except for the hemispheric crustal dichotomy we used numerical dynamo modeling to demonstrate that the mechanisms proposed to explain crustal dichotomy formation can result in a single hemisphere dynamo this dynamo produces strong magnetic fields in only the southern hemisphere this magnetic field morphology can explain why mars crustal magnetic field intensities are substantially stronger in the southern hemisphere without relying on any postdynamo mechanisms

a tethys wide mid carnian upper triassic carbonate productivity crisis evidence for the alpine reingraben event from spiti indian himalaya abstract a significant mid carnian lithological change from carbonatic to siliciclastic sedimentation is described from the spiti himalaya n india the recorded sudden increase of terrigenous influx occurs at the boundary from the chomule to the rama formation it is dated within the late lower carnian uppermost aonoides zone and isochronous all over the tethys himalaya bio and chemostratigraphic data point to a synchrony with changes in carbonate productivity known from on area of wide extent along the nw tethys the reingraben event of the northern calcareous alps austria defines a regional decline in carbonate productivity related to both a platform demise and enhanced siliciclastic input laminated shales found in a distal part of the spiti basin document the onset of anoxic conditions within the deeper shelf synchronous to the reingraben event in austria high resolution biostratigraphy and identical 13ccarb curves are therefore in support of a direct link between the change in spiti and the reingraben event our data combined with a comprehensive review of previously postulated scenarios regarding the reingraben event suggest linking of climatic change with siliciclastic input and a carbonate productivity crisis initiated by onset of a relatively humid megamonsoonal late lower carnian atmospheric system that affected both the southern and northwestern tethys and point to a supra regional trigger of the alpine reingraben event

the aftermath of the carnian carbonate platform demise a basinal perspective dolomites southern alps in the dolomites of northernmost italy the carbonate platform growth came to a standstill late in the early carnian late triassic the response to this shutdown of shallow water carbonate production in the interplatform basins is largely unknown because erosion has removed most of the soft basinal sediments giving rise to today s scenic landscape of the dolomites mapping in the central part of the dolomites and newly available core material has recently revealed a wellpreserved succession of basinal rocks within the heiligkreuz hospiz basin ital ospizio di santa croce basin in this paper the regional depositional nature of arrested carbonate platform production is reconstructed by tracing its sedimentological record across the slope and into the basin the uppermost st cassian formation the time equivalent basinal rocks to the prograding carbonate platforms is overlain by the heiligkreuz formation whose basal succession was deposited in a restricted and oxygen depleted environment immediately post dating the platform demise the succession consists mainly of mudrocks marlstones and peloidal packstones with abundant low diversity ostracod and pelecypod fauna and early diagenetic dolomite c and o isotope values of the basal heiligkreuz formation post dating platform demise average 2 ae4 and 2ae4 respectively and largely overlap the isotopic composition of st cassian carbonates a shift toward slightly lower d 13 c values in the heiligkreuz formation may reflect incorporation of isotopically depleted c released during bacterial sulphate reduction in the heiligkreuz sediments sedimentological palaeobiological and geochemical indices suggest that nearnormal marine conditions persisted long after the shutdown of shallow water carbonate platform growth although there are clear indications of severely reduced oxygen levels in the restricted heiligkreuz hospiz interplatform basin the early carnian platform demise induced a distinct switch in the locus of carbonate production from the shallow water platform and slope to the basin floor and a decrease in the availability of dissolved oxygen in the basinal waters it is inferred that anoxia extended at least temporarily to the top of the carbonate slope as indicated by the onlap of normal marine mounds by dark marlstones of the basal heiligkreuz formation

18o16o and 13c12c in lower paleozoic articulate brachiopods implications for the isotopic composition of seawater three hundred and eleven articulate brachiopods with extensive geographic coverage spanning the cambrian to silurian stratigraphic interval were analyzed for oxygen and carbon isotopic composition cambrian samples have 18o 7 ordovician samples 2 4 and silurian samples 1 9 confirming the previously established trend towards lighter isotopic compositions with increasing age throughout the lower paleozoic forty nine best preserved ordovician and silurian samples were identified based on scanning electron microscopy and trace element analysis they were found to bracket the isotopic compositions of over 85 of specimens from these stratigraphic intervals supporting widespread preservation of the isotopic signal some latest ordovician and lower ludlovian samples associated with shale sequences are apparently enriched in 18o these are interpreted as an environmental phenomenon perhaps related to water temperature and glaciation a number of silurian samples of varying genera and stratigraphic levels are highly enriched in 13c up to 6 some are shale related but some are associated with carbonate bearing basins these are also thought to represent near original compositions but a single environmental cause is unknown the present data show that luminescence is not a decisive criterion for evaluating the degree of brachiopod preservation whole shell values were isotopically similar to their nonluminescent portions for both oxygen and carbon

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects