carbonate factories a conundrum in sedimentary geology abstract describing characterizing and interpreting the nearly infinite variety of carbonate rocks are conundrums intricate and difficult problems having only conjectural answers that have occupied geologists for more than two centuries depositional features including components rock textures lithofacies platform types and architecture all vary in space and time as do the results of diagenetic processes on those primary features approaches to the study of carbonate rocks have become progressively more analytical one focus has evolved from efforts to build reference models for specific phanerozoic windows to scrutinize the effect of climate and long term oscillations of the ocean atmosphere system in influencing the mineralogy of carbonate components this paper adds to the ongoing lively debates by attempting to understand changes in the predominant types of carbonate producing organisms during the mesozoic cenozoic while striving to minimize the uniformitarian bias our approach integrates estimates of changes in ca2 concentration in seawater and atmospheric co2 with biological evolution and ecological requirements of characteristic carbonate producing marine communities the underlying rationale for our approach is the fact that co2 is basic to both carbonates and organic matter and that photosynthesis is a fundamental biological process responsible for both primary production of organic matter and providing chemical environments that promote calcification gross photosynthesis and hypercalcification are dependent largely upon sunlight while net primary production and e g subsequent burial of organic matter typically requires sources of new nutrients n p and trace elements our approach plausibly explains the changing character of carbonate production as an evolving response to changing environmental conditions driven by the geotectonic cycle while identifying uncertainties that deserve further research with metazoan consumer diversity reduced by the end permian extinctions excess photosynthesis by phytoplankton and microbial assemblages in surface waters induced by moderately high co2 and temperature during the early mesozoic supported proliferation of non tissular metazoans e g sponges and heterotrophic bacteria at the sea floor metabolic activity by those microbes especially sulfate reduction resulted in abundant biologically induced geochemical carbonate precipitation on and within the sea floor for example with the opening of tethyan seaways during the triassic massive sponge microbe boundstones the benthic automicrite factory formed steep massive and thick progradational slopes and locally mud mounds as tectonic processes created shallow epicontinental seas photosynthesis drove lime mud precipitation in the illuminated zone of the water column the resulting neritic lime mud component of the shallow water carbonate factory became predominant during the jurassic paralleling the increase in atmospheric pco2 while the decreasing importance of the benthic automicrite factory parallels the diversification of calcifying metazoans phytoplankton and zooplankton with atmospheric pco2 declining through the cretaceous the potential habitats for neritic lime mud precipitation declined at the same time peak oceanic ca2 concentrations promoted biotically controlled calcification by the skeletal factory with changes produced by extinctions and turnovers at the cretaceous tertiary boundary adaptations to decreasing ca2 and pco2 coupled with increasing global temperature gradients i e high latitude and deep water cooling and strategies that efficiently linked photosynthesis and calcification promoted successive changes of the dominant skeletal factory through the cenozoic larger benthic foraminifers protist protist symbiosis during the paleogene red algae during the miocene and modern coral reefs metazoan protist symbiosis since late miocene

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

seismic inversion for organic richness and fracture gradient in unconventional reservoirs eagle ford shale texas abstract a method using eagle ford organic shale from texas predicts key unconventional reservoir properties total organic carbon toc and fracture pressure gradient fg applying petrophysical and rock physics models from previous work to the available well log data generates the required logs for calibration i e shear sonic toc organic porosity and saturation prestack seismic data can be evaluated using synthetic forward modeling and can be conditioned further to improve avo response simultaneous prestack inversion to derive acoustic impedance ai and shear impedance si volumes can be run and toc can be derived from those volumes by linear interpolation fracture gradient which also can be thought of as frackability is related directly to poisson9s ratio and effective stress and can be estimated from elastic properties the fracture gradient is related nonlinearly and inversely to toc i e assuming laterally and vertically homogeneous pore pressure distribution inside the spatially limited block of the eagle ford shale higher toc results in lower fg and hence better frackability

anomalous early triassic sediment fluxes due to elevated weathering rates and their biological consequences analysis of 16 marine permian triassic boundary sections with a near global distribution demonstrates systematic changes in sediment fluxes and lithologies in the aftermath of the end permian crisis sections from continent margin and platform settings exhibit higher bulk accumulation rates bars and more clay rich compositions in the griesbachian earliest triassic relative to the changhsingian latest permian these patterns which largely transcend regional variations in tectonic setting sequence stratigraphic factors and facies are hypothesized to have resulted from a substantial average 7 increase in the flux of eroded material from adjacent land areas owing to accelerated rates of chemical and physical weathering as a function of higher surface temperatures increased acidity of precipitation and changes in landscape stability tied to destruction of terrestrial ecosystems this sediment surge may have been a contributory factor to the latest permian marine biotic crisis as well as to the delayed recovery of early triassic marine ecosystems owing to the harmful effects of siltation and eutrophication contemporaneous deep sea sections show no increases in sediment flux across the permian triassic boundary owing to their remoteness from continental siliciclastic sources and location below the paleo carbonate compensation depth

microbial deposits in the aftermath of the end permian mass extinction a diverging case from the mineral mountains utah usa the lower triassic mineral mountains area utah usa preserves diversified smithian and spathian reefs and bioaccumulations that contain fenestral microbialites and various benthic and pelagic organisms ecological and environmental changes during the early triassic are commonly assumed to be associated with numerous perturbations productivity changes acidifica tion redox changes hypercapnia eustatism and temperature changes post dating the permian triassic mass extinction new data acquired in the mineral mountains sediments provide evidence to decipher the relationships between depositional environments and the growth and distribution of microbial structures these data also help to understand better the controlling factors acting upon sedimentation and community turnovers through the smithian early spathian the studied section records a large scale depositional sequence during the dienerian spathian interval during the transgression depositional environments evolved from a coastal bay with continental deposits to intertidal fenestral microbial limestones shallow subtidal marine sponge microbial reefs to deep subtidal mud dominated limestones storm induced deposits microbialite sponge reefs and shallow subtidal deposits indicate the regression three microbialite associations occur in ascending order i a red beds microbialite association deposited in low energy hypersaline supratidal conditions where microbialites consist of microbial mats and poorly preserved microbially induced sedimentary structure ii a smithian microbialite association formed in moderate to high energy tidal conditions where microbialites include stromatolites and associated carbonate grains oncoids ooids and peloids and iii a spathian microbialite association developed in low energy offshore conditions that is preserved as multiple decimetre thick isolated domes and coalescent domes data indicate that the morphologies of the three microbialite associations are controlled primarily by accommodation hydrodynamics bathymetry and grain supply this study suggests that microbial constructions are controlled by changes between trapping and binding versus precipitation processes in variable hydrodynamic conditions due to the presence of numerous metazoans associated with microbialites throughout the smithian increase in accommodation and spathian decrease in accommodation the commonly assumed anachronistic character of the early triassic microbialites and the traditional view of prolonged deleterious conditions during the early triassic time interval is questioned

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

griesbachian earliest triassic palaeoenvironmental changes in the salt range pakistan and southeast china and their bearing on the permo triassic mass extinction abstract facies and faunal analysis from pakistan and china show that the permo triassic mass extinction of marine invertebrate faunas was associated with a spectacularly rapid griesbachian transgression which lead to the widespread establishment of deep water anoxic and dysoxic conditions the extinction event was thus caused by habitat loss due to the extensive development of inhospitable conditions the initial griesbachian transgression in pakistan produced extensive shallow normal marine conditions in which permian holdover taxa were able to survive until the development of dysaerobic facies in the late griesbachian the exceptionally complete sections of china show a three phased deepening and extinction event beginning in the latest permia by the late griesbachian a variety of dysaerobic and anaerobic facies were developed in all the regions studied several of these contain evidence for minimal sulphate reducing activity suggesting that marine productivity and thus organic matter flux to the sediments was very low in early triassic seas

calcium carbonate seafloor precipitates from the outer shelf to slope facies of the lower triassic smithian spathian union wash formation california usa sedimentology and palaeobiologic significance abstract formerly aragonite seafloor fans from the lower triassic smithian spathian union wash formation of east central california were examined to determine the processes active during their growth the seafloor fans were deposited in an outer shelf to slope environment along the western margin of pangaea and are contained within two stratigraphic intervals the lower precipitate bearing interval is 130 m thick comprised of micritic limestone and contains precipitates that fall into 2 end member morphologies 1 laminated precipitate masses that contain distinct hemispheres or fans and 2 precipitate masses that are composed of a complex interlocking mosaic of hemispheres or fans precipitates found in the bedded lower half of the interval are typically 2 3 cm tall and 10 20 cm wide and are commonly undercut disturbed and in the case of the interlocking mosaics of hemispheres show evidence of entrainment and transport by density currents precipitates are larger in the upper massive portion of the lower precipitate bearing interval and occur only as interlocking hemisphere fan mosaics fans and hemispheres attain heights as tall as 30 cm and precipitate bodies made of interlocking mosaics of hemispheres and fans attain thicknesses of up to 50 cm and widths of 1 2 m chaotic bedding broken precipitates and brecciation of precipitate bodies imply an unstable and mobile substrate the upper precipitate bearing interval is 30 m thick comprised of bivalve ammonoid and microgastropod bearing wackestone and is separated from lower precipitate bearing strata by 23 m of interbedded shale and calcareous siltstone much of the upper precipitate bearing unit was deposited by subaqueous debris flows as suggested by multiple breccias contained within the interval seafloor cements are found in undisturbed units and rarely within breccia clasts suggesting that precipitates formed locally as well as higher on the shelf precipitate growth was likely the result of an increase in the saturation state of calcium carbonate in early triassic oceans related to widespread oceanic anoxia the presence of unusual carbonates during the period and their correlation with depauperate faunas in the equivalent shallow facies of the virgin limestone suggest that the remarkable oceanographic conditions associated with precipitate growth likely dampened the biotic recovery in the region until those conditions disappeared in the middle triassic

tempestite facies models for the epicontinental triassic carbonates of the betic cordillera southern spain this study focuses on storm deposits in the muschelkalk facies of the betic cordillera southern spain and interprets their deposition mechanisms three types of storm deposit are distinguished i pot gutter casts ii tempestite beds and iii storm winnowed deposits each deposit provides information about the carbonate platform environment in which it was deposited the tempestite models proposed are i the bypass zone tempestite model occurring in a muddy ramp at the epicontinental basin margin this model is characterized by potholes and gutters that form in a shoreline bypass zone during storms ii the gradient current tempestite model in which frequent tempestite beds are related to storm gradient currents thickness and grain size decrease towards the deep distal ramp and iii the winnowed deposit tempestite model whereby storm deposits are winnowed and deposited in the same environment with only short lateral transport having occurred this model evokes more restricted and shallower conditions lagoons or inland seas the distribution of all these deposits in the stratigraphic sections studied corroborate the eustatic third order cycle identified although the different features of the storm deposits and their positions in each section indicate a subsidence varying in time and space in the transgressive stage the margins of the epicontinental basin were a well developed ramp with potholes and gutters in contrast during the high sea level stage storm deposits generated tempestite beds or storm winnowed deposits in the different areas the epicontinental carbonate platform with ramp edges evolved into a complex depositional system of coastal and shallow marine environments with lagoons and restricted inland seas thus the epicontinental platform underwent substantial change from the late anisian to the late ladinian and this is reflected in its storm deposits

earliest triassic microbialites in curuk dag southern turkey composition sequences and controls on formation the permian triassic boundary sequence at curuk dag near antalya turkey begins with a major erosion surface interpreted as being the late permian lowstand on which lies ca 0 4 m of grainstone packstone composed of ooids peloids and bioclasts most ooids are superficial coats on fragments of calcite crystals presumed to be eroded from crystal fans which are no longer present the erosion surface is smooth and shows no evidence of dissolution the grainstone packstone contains intraclasts of the underlying wackestone proving erosion next are 15 m of microbialite comprised of interbedded stromatolites thrombolites plus beds of planar limestones with small scale erosion the latter comprise a complex interlayering of stromatolitic thrombolitic and peloidal fabrics and precipitated crystal fans which form a hybrid of microbialite and inorganic carbonate together with bioclastic debris and micrite the curuk dag microbialite sequence is repetitious the lower part is more complex with abundant stromatolites and hybrid microbialites some of the stromatolites are themselves hybrids composed of peloids and crystal fans in the upper part of the sequence stromatolites are missing and the rock is composed mostly of recrystallized thrombolites that develop upwards from tabular to domal form the domes form directly below small breaks in microbialite growth where very thin shelly micrites and grainstones packstones are deposited repetition of facies may be controlled by sea level change a deepening up model is consistent with the evidence stromatolites with abundant crystal fans dominate in shallower water deepening through hybrid microbialite and interlayered sediments to thrombolite probably no more than a few tens of metres deep followed by breaks and renewal of microbialite growth an interpretation of open marine fully oxygenated waters for microbialite growth is consistent with ongoing parallel work that has identified bairdioid ostracods in the microbialite a group known to be open marine however other researchers have proposed low oxygen conditions for permian triassic boundary facies globally so work continues to confirm whether the curuk dag microbialite grew in dysoxic or normally oxygenated conditions the principal stimulus for post extinction microbialites is likely to be carbonate supersaturation of the oceans the microbialite sequence is overlain by a further 25 m of grainstone packstone without microbialite followed by early triassic shales overall microbialites form a thin aggradational sequence during an overall relative sea level rise consistent with global eustatic rise following the late permian lowstand

evolution of a terminal neoproterozoic carbonate ramp system buah formation sultanate of oman effects of basement paleotopography the buah formation is a carbonate unit of late neoproterozoic age exposed in the jabal akhdar of northern oman and the huqf region of central oman the buah formation is interpreted as a distally steepened storm dominated ramp containing inner ramp tidally influenced oolitic shoal and back shoal lagoon fades and storm dominated mid ramp facies a slope break separates mid ramp facies from outer ramp facies characterized by accumulation of redeposited carbonates on gently inclined slopes 1 2 degrees combined facies stacking patterns and outcrop correlation via 1 3 c profiles suggest that buah carbonates formed as a highstand systems tract characterized by a general upward shallowing of facies and strong lateral progradation on a regional scale buah facies distributions across oman were controlled by the presence of basement highs defining areas of reduced subsidence which promoted lateral progradation of the buah carbonate ramp for tens of kilometers while the faster subsiding areas became sites of deep water deposition

carbonate lithofacies as paleolatitude indicators problems and limitations abstract detailed study of miocene carbonates in the mediterranean region and their analogues on modern carbonate shelves in the mediterranean sea brazil and other areas reveals at least three major types of carbonate platform lithofacies in addition to the classic tropical coral reef chlorozoan lithofacies a chloralgal lithofacies similar to the chlorozoan but without hermatypic corals b rhodalgal lithofacies characterized by abundant encrusting coralline algae and c molechfor lithofacies consisting of benthic foraminifers molluscs echinoids bryozoans and barnacles these carbonate lithofacies present complex distribution patterns seemingly related primarily to latitude and depth that control water temperature although other factors e g water circulation river discharge suspended sediment controlling water salinity and temperature nutrient content light penetration etc also play important roles chloralgal and rhodalgal lithofacies can be considered two transitional terms between the two end members the chlorozoan lithofacies which characterizes shallow tropical shelves and the molechfor lithofacies which characterizes colder and or deeper areas detailed textural and sequential analysis are required for satisfactory interpretation of these lithofacies in ancient rocks

development of organic porosity in the woodford shale with increasing thermal maturity abstract using a combination of focused ion beam milling and scanning electron microscopy we describe the evolution of secondary organic porosity in eight woodford shale late devonian early mississippian samples with mean random vitrinite reflectance values ranging from 0 51 ro to 6 36 ro organic porosity was observed to be absent in samples with vitrinite reflectance values of up to 0 90 ro with the first appearance of secondary pores starting with the 1 23 ro sample porosity in the organic matter was unexpectedly absent in a sample with a vitrinite reflectance of 2 00 ro however organic pores were again found in samples with higher thermal maturities porosity when present did not appear to be uniformly distributed among the organic matter that was within less than a micron of each other suggesting important differences in composition of the organic matter thin regions of organic matter were observed between grains raising the possibility that small amounts of the deposited organic matter were compacted between grains to form thin layers and or the structures are part of the secondary organic matter interpreted to be post oil bitumen which was left behind as a residue during oil migration through the shale some regions of porous organic matter appeared to be grain protected whereas others did not which indicates that these non protected porous organic regions may be stress supporting with porosity intact under in situ reservoir conditions these observations suggest that thermal maturity alone is insufficient to predict porosity development in organic shales and other factors such as organic matter composition complicate porosity development

seafloor precipitated carbonate fans in the neoproterozoic rainstorm member johnnie formation death valley region usa cm sized carbonate seafloor fans occur in the neoproterozoic rainstorm member of the johnnie formation death valley usa the fans formed in a mixed carbonate clastic succession near storm wave base at the base of parasequences on a storm dominated ramp petrographic observations indicate that the fans were originally precipitated as aragonite and later inverted to calcite during diagenesis although not directly dated the rainstorm member preserves a large magnitude negative carbon isotopic anomaly down to 11 pdb tentatively correlated to the largest known carbon isotope excursion found in many stratigraphic successions around the world between 585 ma and 550 ma thus the age distribution of seafloor aragonite fans in neoproterozoic strata appears more widespread than previously thought occurring in strata significantly younger than the last widespread neoproterozoic glaciation rainstorm member carbonate fans and oolitic units representing time correlative shallower environments record similar carbon isotope ratios during the negative carbon isotopic anomaly the carbon isotopic homogeneity displayed between fans and other carbonate sediments implies that waters across the shelf were well mixed rather than stratified during the late neoproterozoic isotopic anomaly in addition the similarity of carbon isotope ratios shared among fans along a stratigraphic horizon on a m to cm scales suggests that the local source of alkalinity required for fan growth was derived from a well mixed reservoir likely seawater rather than local diagenetic fluids increased alkalinity and the presence of inhibitors to carbonate nucleation perhaps fe2 under anoxic conditions likely fostered precipitation of aragonite crystal fans on the seafloor

lower triassic deep sea carbonate precipitates from south tibet china abstract sea floor carbonate precipitates scps commonly seen in pre cambrian strata were widely developed during the permian triassic mass extinction and the early triassic recovery interval most scps are found in shallow water facies with few scps reported from deep sea settings here we document lower triassic deep sea scps from turbidite deposits exposed at the xiukang section south tibet china the scps only occur within thin bedded silty limestones that are embedded in dark grey shale parallel aligned mud cobbles rounded micritic intraclasts and micro erosional surfaces are commonly seen in these planar laminated limestones that contain abundant radiolarians and thin shelled bivalves indicating deposition in a deep basin via turbidity currents the deep sea scps which are comprised of bladed calcite crystals display a weak vertical 13c variation with the overlying matrix and a uniform element distribution and consequently have a homogenous cathodoluminescence pattern suggesting rapid precipitation in the open ocean followed by a quick burial which led to minimal diagenetic effects on the scps we propose a new hypothesis that rapid carbonate precipitation resulted from mixing driven by the turbidity current that introduced shallow seawater to the deep seawaters with a high alkalinity based on this model the turbidity currents during the early triassic might serve as a potential role in the connection between the oxic surface oceans and the euxinic deep oceans

the permo triassic extinction the end permian mass extinction brought the palaeozoic great experiment in marine life to a close during an interval of intense climatic tectonic and geochemical change improved knowledge of latest permian faunas coupled with recent advances in isotopic studies and biostratigraphy have greatly enhanced our understanding of the events of 250 million years ago and have begun to provide answers to many questions about the causes of extinction

a biogeographically mixed late guadalupian late middle permian brachiopod fauna from an exotic limestone block at xiukang in lhaze county tibet a total of 17 brachiopod species belonging to 15 genera are recorded from a limestone block of about 3 4 km2 in the indus tsangbo suture zone at xiukang in lhaze county of tibet the brachiopod fauna generally indicates a late guadalupian age late wordian capitanian late middle permian based on its association with the timorites bearing ammonoid fauna and the presence of the brachiopod urushtenoidea crenulata palaeobiogeographically the fauna exhibits transitional mixed characters between the warm water cathaysian and cold to temperate gondwanan faunas and may have developed on a carbonate build up or seamount on the oceanic crust

sedimentary history of the tethyan basin in the tibetan himalayas after an epicontinental phase the sedimentary rocks in the tibetan himalayas document a complete wilson cycle of the neo tethyan tethys ill evolution between the gondwana supercontinent and its northward drifting margin lhasa block from the late permian to the eocene during the triassic rift stage the basin was filled with a huge clastic dominated sediment wedge with up to 5 000 m of flysch in the northern zone widespread deltaic clastics and shallow water carbonates of late norian to earliest jurassic age in the southern zone mark in conjunction with decreasing tectonic subsidence the transition to the drift stage some 4 500 m of jurassic and early cretaceous shallow water carbonates and siliciclastics accumulated on the tethyan indian passive margin deepening upward sequences with condensed beds at their tops alternate with repeated progradational packages of shelf sediments extensive abyssal sediments with basaltic volcanics in the northern deep water zone reflect continued ocean spreading and thermal subsidence paleomagnetic data gained separately for the northern indian plate and the lhasa block indicate that the neo tethys reached its maximum width about 110 ma ago with a spreading rate of 4 8 cm year before it commenced to close again during the remnant basin stage in the late cretaceous and paleogene a shallowing upward megasequence capped by a carbonate platform developed in the southern inner shelf realm in the northern slope basin plain zone turbidites and chaotic sediments derived from both the acretionary wedge and the steepening slope of the passive margin accumulated the depositional center of the remnant basin shifted southward as a result of flexural subsidence and southward overthrusting the sediments from the triassic to the paleogene are tentatively subdivided into five mega sequences which are controlled mainly by regional tectonics climatic influence e g carbonate deposition due to northward plate motion is partially subdued by terrigenous input and or increased water depth during the oligocene and miocene crustal shortening led to rapid uplift and the deposition of fluvial molasse in limited basins

biogeochemical formation of calyx shaped carbonate crystal fans in the subsurface of the early triassic seafloor abstract the kuh e dena sedimentary section in iran developed on the southwestern margin of the neotethys ocean the fossil and bioturbation lean early triassic section late dienerian to early smithian is typified by finely laminated calcareous shales that are interbedded with laterally extending carbonate beds which are mostly composed of calyx shaped carbonate crystal fans the calyxes consist of fibrous crystals that apparently formed within the subseafloor in soft water saturated sediment by displacive growth rare earth element and yttrium patterns indicate that calyx shaped crystals precipitated from anoxic pore waters biomarker patterns of the carbonate beds reveal major input of lipids from prokaryotes that typically occur within layered benthic microbial mats i e cyanobacteria anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea along their length the fibrous crystals of the calyxes reveal a trend of increasing 13 c carb values from 2 7 to 3 3 suggesting that archaeal methanogenesis affected the carbonate pool apart from the putative benthic prokaryotes molecular fossils of halophilic most likely planktic archaea were detected in the carbonate beds low pristane to phytane ratios 0 8 and the presence of halophilic archaea are in accord with the lack of bioclasts and bioturbation which likely reflects increased salinities the former presence of a benthic microbial mat with cyanobacteria underlain by anoxygenic phototrophic bacteria sulphate reducing bacteria and methanogenic archaea is in accordance with studies on living microbial mats in hypersaline low oxygen marine environments the early triassic subseafloor seems to have been a sink for carbon driven by biologically induced formation of secondary diagenetic carbonate

sedimentology and sequence stratigraphy of a tithonian valanginian carbonate ramp vaca muerta formation a misunderstood exceptional source rock in the southern mendoza area of the neuquen basin argentina abstract the vaca muerta formation early tithonian early valanginian is a rhythmic succession of marls and limestones cropping out in the neuquen basin west central argentina this lithostratigraphic unit was traditionally interpreted as basinal to slope deposits detailed facies analysis allows to differentiate seven facies associations representing basinal to middle ramp facies of a homoclinal ramp system prograding westward from the eastern margin and slope facies attributed to a distally steepened ramp system that progrades eastward from the andean volcanic arc in the west two sequence hierarchies are recognized five third order depositional sequences and fifteen fourth order high frequency sequences fluctuations in organic matter content within the vaca muerta formation suggest relationship with depositional sequences finding the highest values associated with transgressive system tracts this work represents an important advance in the understanding of the sedimentary and stratigraphic evolution of this exceptional unconventional reservoir our sequence stratigraphic approach contributes to the understanding of the relationship between organic matter facies and sea level changes

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

sedimentation rates and growth potential of tropical cool water and mud mound carbonate systems carbonate fixation in the ocean proceeds in three basic modes abiotically biotically induced with organic trigger and biotically controlled where organisms determine timing location and composition of the product the three modes combine in a variety of ways to produce carbonate sediment when viewed on the scale of formations and global facies belts three benthic carbonate production systems or factories emerge 1 the tropical shallow water system dominated by biotically controlled mainly photoautotrophic and abiotic precipitates 2 the cool water system dominated by biotically controlled mainly heterotrophic precipitates and 3 the mud mound system dominated by abiotic and biotically induced mainly microbial precipitates the sedimentation rates of all three factories decrease as the time span of observation increases this scaling trend is not just an artifact of ratio correlation it is almost certainly related to the episodic pulsating nature of sedimentation the growth potential of the three systems can be estimated by drawing the envelope of the maximum observed rates of aggradation the tropical system shows the highest rates 10

lower triassic storm dominated ramp sequence in northern hungary an example of evolution from homoclinal through distally steepened ramp to middle triassic flat topped platform

proximal distal facies relationships and sedimentary processes in a storm dominated carbonate ramp kimmeridgian northwest of the iberian ranges spain abstract facies analysis of the upper kimmeridgian rocks in the outcrops located near ricla zaragoza province northeast spain and the integration of the resultant data in a broader context the northern part of the iberian basin has produced two general models showing the facies distribution and the processes that controlled the sedimentation in the kimmeridgian carbonate ramp using these two models the transition from shallow to relatively deep environments of the carbonate ramp is examined in detail model 1 corresponds to the development of a mixed carbonate siliciclastic ramp during a slow rise and stillstand of sea level sequence 1 hst whereas model 2 represents the growth of a pure carbonate ramp during a rapid rise of sea level sequence 2 tst carbonate production was higher in the shallow ramp domains coral reefs and oolitic shoals in model 1 and reefs in model 2 than in deeper domains where there is no indication of significant pelagic or benthic production the activity of unidirectional return flows induced by winter storms and hurricanes played an important role in the redistribution of the sediment across the ramp generating different coarse grained deposits in the inner and mid ramp settings dunes lower scale bedforms and tempestites occur in model 1 and storm lobes bars and tempestites in model 2 moreover a significant bulk of the carbonate mud produced in shallow areas would eventually be resedimented in the outer ramp as suspended load in the density currents stillstand of sea level in model 1 involved a rapid progradation of the inner and proximal mid ramp carbonate and siliciclastic facies the rapid relative sea level rise of model 2 is determined by the dominance of the carbonate facies and by the presence of aggradational geometries in the transitional area between shallow and deep ramp domains the presence of relatively thick sections in the outer ramp settings instead of condensed sections as observed in model 1 during times of sea level rise model 2 can mainly be explained by the increase of the shallow production in the reef dominated areas

palynology and vegetation dynamics across the permian triassic boundary in southern tibet abstract the end permian mass extinction epme is regarded as the most severe biotic crisis in earth history which is particularly well documented in the marine fossil record despite compelling evidence that dramatic global environmental changes probably drove this extinction event its effects on terrestrial plants are still highly controversial here we present changhsingian latest permian to late smithian latest early triassic composite palynological successions from the lagoonal to open marine qubu and tulong sections in southern tibet quantitative analyses of palynomorph distributions range charts and relative abundance data allow us to differentiate five distinct informal palynofloral assemblages in ascending order the scheuringipollenites ovatus vitreisporites pallidus op assemblages the reduviasporonites catenulatus assemblage the endosporites papillatus pinuspollenites thoracatus pt assemblages the lundbladispora brevicula densoisporites nejburgii bn assemblages and the falcisporites nuthallensis alisporites landianus nl assemblages these palynological assemblage intervals and the associated ammonoid and conodont biostratigraphy resolve vegetation changes across the permian triassic boundary ptb on the northern tethyan margin of gondwanaland in great detail and high resolution principal component analysis pca of palynological data indicates that the op assemblages which are dominated by non taeniate bisaccate pollen represent a vegetation in a cool and dry climate during the changhsingian in the qubu section the palynological turnover from the op assemblages to the c assemblage 0 81 m below the ptb coincides with abrupt sea level fluctuations in the latest permian as this turnover further coincides with an extreme negative 13corg shift a great abundance of amorphous organic matter aom and marine acritarchs as well as the frequent occurrence of reduviasporonites catenulatus the c assemblage is tentatively interpreted to represent the fungal spike reported worldwide at the onset of the epme in southern tibet the epme appears to result only in a short term disturbance and range contraction of land plant communities surprisingly the early dienerian pt assemblages postdating the epme by about 500kyrs closely resemble the late changhsingian op assemblages suggesting a resurgence of those land plant groups that were dominant during the late changhsingian this recovery was disrupted with the onset of the late dienerian bn assemblages in the qubu section which is represented by a peak abundance of cavate trilete spores reflecting large scale deforestation for nearly one million years the regional vegetation appears to have been dominated by pioneer communities of quillworts and spike mosses only towards the end of the smithian bisaccate gymnosperm pollen regained dominance with the onset of the nl assemblages in the tulong section integrating the results of the principal component analysis on our new palynological data and conodont apatite oxygen isotope data from neighbouring sections in pakistan the contraction of gymnosperm forests during the early dienerian smithian in southern tibet is interpreted to be accompanied by an abrupt change to an episode with a warmer and more humid climate this observation supports the hypothesis that the secondary eruptions of the siberian large igneous province during the induan led to long term global warming and as a side effect to more humid conditions in the southern temperate zone as a result of altered precipitation and evaporation patterns

a microbialite carbonate crust at the permian triassic boundary in south china and its palaeoenvironmental significance a 1 m thick carbonate crust layered and commonly domal caps crinoidal limestones on reef complexes of the top permian changxing formation in the huaying mountains eastern sichuan china the crust s stratigraphic level lies at a sharp change in facies and is overlain by poorly fossiliferous laminated micrites and shales of the lower triassic feixianguan formation the crust therefore appears to coincide with the end permian extinction event although the dating of the strata is currently imprecise the crust is composed mostly of digitate carbonate locally thrombolitic with remnant lobate fabric and resembles microbialites but is mostly recrystallised and a microbial origin is unconfirmed it is enclosed in micrite with pyrite crystals ostracode and other shell debris the crust is absent from interreef areas previous interpretations of karstification and calcrete formation are not upheld and the facies were deposited under water overlying sediments are low energy with abundant ferroan calcite and pyrite reflecting anoxia associated with rising sea level various interpretations of the crust are possible 1 it was organic and microbia grew preferentially on topographic highs of reef tops 2 microbia were a disaster biota in the absence of grazers 3 microbia took advantage of favourable conditions for calcification associated with a rapidly rising environmental co2 content during the late permian 4 the crust was an inorganic precipitate associated with co2 rich water microbial crusts are rare after the cambrian but whether this crust is organic or not its presence in these strata reinforces the view that oceanic atmospheric conditions in the permian triassic boundary interval were unusual

the late paleoproterozoic orogeny in the north china craton abstract granulite ttg and khondalite formations are the two typical types of precambrian metamorphic basement in the north china craton the former belongs to the basement of the archean craton while the latter is a paleoproterozoic metasedimentary rock series the formation of the ttg rock series took place during the period of 2500 to 2450 ma near the end of the archean and it has undergone multiple times of metamorphism the cooling rate of the ttg lower crust is quite low less than 0 3 ma developed during slow crustal cooling in a rather stable tectonic environment the khondalite rock series underwent amphibolite to granulite facies metamorphism that is isotopically constrained to 2000 to 1800 ma followed by fast crustal cooling from 2 4 to 3 4 ma based on the thermal and dynamic features of different types of metamorphic rocks the tectonic state of the crust and the obvious change of crustal cooling rate from neo archean to paleoproterozoic it is clear that continental orogeny existed in the north china craton between 2000 ma and 1800 ma

a dolomitization event at the oceanic chemocline during the permian triassic transition the permian triassic boundary ptb crisis caused major shortterm perturbations in ocean chemistry as recorded by the precipitation of anachronistic carbonates here we document for the first time a global dolomitization event during the permian triassic transition based on mg mg ca data from 22 sections with a global distribution representing shallow to deep marine environments ten of these sections show high mg mg ca ratios bracketing the ptb recording a short term spike in dolomite formation the dolomite consists mainly of micron scale anhedral to subhedral crystals that are associated with abundant fossilized bacterial bodies and extracellular polymeric substances suggesting that dolomite precipitation was induced by microbial metabolic activity sections showing a dolomite spike at the ptb are widely distributed geographically but mostly encountered in mid shelf to upper slope settings because the dolomitization event coincided with a rapid expansion of oceanic anoxia and high rates of sulfate reduction we hypothesize that it was triggered by enhanced microbial sulfate reduction within the oceanic chemocline

catastrophic environmental transition at the permian triassic neo tethyan margin of gondwanaland geochemical isotopic and sedimentological evidence in the spiti valley india abstract interpreting global consequences of the permian triassic p tr extinction requires examination across paleogeographic realms of pangaea the spiti valley in india remnant of the peri gondwanan shelf preserved trails of this environmental catastrophe in the neo tethys ocean we document new sedimentological observations and high resolution trace element concentrations and carbon oxygen lead isotope data across the p tr boundary in spiti framboidal pyrites fossils and laminated lithology of the late permian shales indicate deeper anoxic depositional environment while 13 c org excursions of 2 4 and 3 1 in atargu and guling outcrops respectively identify the p tr transition across a clayey partly gypsiferous ferruginous layer sedimentological similarities of this layer to other neo tethyan sections from transcaucasia and iran indicate subaqueous oxidation of shallow marine sediments on a regional scale light rare earth element enriched late permian shales with conspicuous ce eu anomalies reflect their source from the adjacent panjal trap basalts ca 289 ma of kashmir continental crustal nb ta and zr hf anomalies appear at the p tr boundary sediments and prevail through the overlying early triassic carbonates original pb isotope ratios along with an increasing pb abundance closer to the p tr boundary distinguish the volcanic source of the late permian shales from the continental crustal siliciclastic signature of the early triassic carbonates our 13 c org trace element and pb isotope record from spiti indicate catastrophic changes in sediment sources and facies with effects on carbon cycle and are consistent with an abrupt episode of marine regression and erosional forcing also observed elsewhere along northern gondwanaland simultaneous eruption of siberian volcanics and bolide impacts in parana basin of brazil and elsewhere implicating impact triggered volcanism left catastrophic regional global imprints on sea level climate marine anoxia and tectonic stability that connected the p tr crisis across terrestrial and marine realms worlwide

the lower triassic sedimentary and carbon isotope records from tulong south tibet and their significance for tethyan palaeoceanography abstract the lower triassic sedimentary and carbonate organic carbon isotope records from the tulong area south tibet are documented in their integrality for the first time new age control is provided by ammonoid and conodont biostratigraphy the basal triassic series consists of griesbachian dolomitic limestones similar to the kathwai member in the salt range pakistan and to the otoceras beds in spiti india the overlying thin bedded limestones of dienerian age strongly resemble the lower ceratite limestone of the salt range they are followed by a thick series of dark green silty shales of dienerian early smithian age without fauna that strikingly resemble the ceratite marls of the salt range this interval is overlain by thin bedded light grey fossil rich limestones of middle to late smithian age resembling the upper ceratite limestone of the salt range these are followed by a shale interval of early spathian age that has no direct counterpart in other tethyan sections carbonate production resumes during the late early and middle spathian with the deposition of red bioclastic nodular limestone ammonitico rosso type facies apart from its colour this facies is similar to the one of the niti limestone in spiti and of the spathian nodular limestone in guangxi south china as in other tethyan localities such as spiti the early middle anisian part of the tulong section is strongly condensed and is characterized by grey thin bedded limestones with phosphatized ammonoids as for many other tethyan localities the carbon isotope record from tulong is characterized by a late griesbachian dienerian positive 13ccarb excursion 2 and a very prominent positive excursion 5 at the smithian spathian boundary thus confirming the well documented perturbations of the global carbon cycle following the permian triassic mass extinction event

the effect of kerogen on the elastic anisotropy of organic rich shales abstractthe elastic properties of reservoir rocks are important for geomechanics applications the most important of which are analysis of stress changes due to production analysis of rock deformation and failure wellbore trajectory optimization and the design of hydraulic fractures organic rich shales are often observed to be strongly anisotropic due to the partial alignment of anisotropic clay minerals and the bedding parallel lamination of organic material within the shale neglecting shale anisotropy may lead to incorrect estimates of the in situ stress or stress changes resulting from production as a result isotropic models may fail to describe geomechanical behavior correctly the distribution of the organic phase plays an important role in determining the elastic properties of organic rich shales and this has a significant effect on production induced stress changes the presence of kerogen leads to a decrease in all of the elastic moduli and has a significant effect on the geomechanical b

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

rock physics of organic shales several publications over the last 20 years have established that black organic shales are generally characterized by strong velocity anisotropy low velocity in the bedding normal direction and relatively low density and porosity e g vernik and nur 1992 vernik and liu 1997 these rock properties are of interest in seismic attribute studies but even more so in geomechanical applications related to reservoir characterization and hydraulic fracture stimulation organic shales typically but not necessarily express strong vertical transverse isotropy vti with axis of symmetry perpendicular to the bedding parallel lamination and clay particle preferred orientation high resolution sem imaging figure 1 immediately reveals all these textural features in addition to silt grains and the lenticular distribution of the solid organic matter kerogen which in turn is characterized by significant intraparticle porosity in mature shales any ti medium is described by the five independent elastic consta

early triassic calcimicrobial mounds and biostromes of the nanpanjiang basin south china stanley s model 1988 proposed that a permiantype reef fauna survived the early triassic reefless period in yet undiscovered refuges in the ancestral pacific ocean and then reappeared as the builders of middle triassic reefs flugel 1994 in contrast suggested that the middle triassic reefbuilding fauna are not holdovers from the permian but bear only a superficial resemblance to permian fossils recent publications reflect a consensus that the early triassic lacked reefs and reef mounds although some authors acknowledged the possibility that reef like structures may have existed in poorly explored areas such as south china and russia senowbari daryan et al 1993 flugel 1994 it is shown herein that calcimicrobial framework mounds and biostromes existed in the early triassic in the nanpanjiang basin of south china organic framework in this paper refers to a three dimensional biologically constructed network of calcified fossils that forms a rigid mass and supports an interconnected network of internal cavities that were open during accumulation although the calcimicrobial frameworks discussed herein are much smaller than frameworks of modern metazoan reefs the term framestone is more appropriate for these fabrics than other reef rock terms such as bindstone or bafflestone embry and klovan 1971 these calcimicrobial mounds and biostromes are important as the first organic framestones documented from the early triassic

a triassic homoclinal ramp from the western tethyan realm western balkanides bulgaria integrated insight with special emphasis on the anisian outer to inner ramp facies transition abstract the triassic carbonate succession exposed in the western balkanides is analyzed in terms of depositional evolution sequence stratigraphy sedimentation rate environmental constraints and biota distribution deposition took place on a storm dominated ramp which existed at the nw end of the tethys ocean from late olenekian to early carnian time subtidal intertidal and supratidal sediments were accumulated in three zones of the ramp profile inner ramp mid ramp and outer ramp the calculated average sedimentation rate is typical for other ancient marine shallow water carbonates including those deposited on ramps newly accomplished sedimentological study on part of the anisian interval reveals a homoclinal ramp model with episodic initial distal steepening two main phases of the ramp evolution are distinguished on the basis of changing relative paleobathymetry transgressive e g retrogradational depositional trend and regressive e g progradational depositional trend the maximum flooding zone is marked by the terebratula beds having late pelsonian age the inferred environmental constraints of the ramp system comprise normal marine to hypersalinity warm well illuminated water aerobic and rarely dysaerobic bottom conditions dominantly soft lime mud substrate intensive storm activity temporal seismic influence presumably related to early triassic rifting the vertical distribution of marine fauna indicates shifting from germanic peri tethyan affinity to alpine tethyan affinity in anisian time the sedimentation was not characterized by formation of large buildups because of the paucity or lack of metazoan and other reef builders the studied rocks are well correlated with the triassic ramp succession outcropping in the tizsa meagunit of southern hungary similarities to the german polish and spanish muschelkalk are also clearly outlined and some parallel can be drawn with other platform carbonates from the nw tethys shelf area and peri tethys basins

the end permian regression in south china and its implication on mass extinction abstract records of more than 20 permian triassic boundary ptb sections from south china show that widespread end permian regression took place in whole south china timing of the low ebb of this regression was pinpointed to the clarkina meishanensis and hindeodus changxingensis zones biostratigraphic and paleogeographic studies at conodont zonation level reveal that the yangtze carbonate platform and isolated small carbonate platforms in the hunan guizhou guangxi hgg basin experienced sedimentary hiatus during these two zones which lasted about 50 100 kya meanwhile the basinal areas namely the northern marginal basin of yangtze platform and the hunan guizhou guangxi basin have continuous conodont zonation with silicious and ashbed deposits the basinal areas show two negative 13c shifts during the ptb interval from clarkina yini zone to isarcicella isarcica zone while on the platforms there is usually only one negative shift because the early shift at c meishanensis zone was lost during hiatus the end permian regression and successive rapid transgression taking place at the ptb casted important effects to the pattern and process of the ptb mass extinction the depositional hiatus hitherto underestimated will necessitate reassessment of some interpretations on the causes and results of that extinction

permo triassic boundary and lower to middle triassic in south tibet abstract the abundance of conodonts increases sharply across the permian triassic boundary in south tibet and as a consequence griesbachian assemblages are much better defined than changxingian ones the otoceras latilobatum bed representing the base of the triassic at selong is a condensed biocalcirudite including abundant macrofossils crinoids corals bryozoans brachiopods of permian aspect associated with a varied conodont assemblage including hindeodus parvus of early griesbachian age condensation and reworking at the p t boundary is interpreted as related to starvation and subaqueous erosion redeposition during rapid transgression at the base of the triassic rather than to subaerial exposure during a first order sea level drop all of the lower triassic is strongly condensed particularly in the west gyirong and selong where total thickness is 6 5 m at most to 8 5 m thickness is more comparable with other himalayan localities at tulong where the dienerian to spathian section reaches 20 m as in central nepal carbonate intervals dated as early griesbachian to dienerian early to mid smithian and latest smithian to earliest aegean are separated by two mudrock intervals locally reduced to millimetric interbeds dated as late dienerian or earliest smithian and late smithian condensed wackestone packstone intervals were deposited during transgressive stages on the outermost shelf to continental slope during highstand stages mudrock intervals slowly accumulated on the outer shelf whereas only a thin veneer of mud was deposited close to the shelf break oceanic currents intruding onto the outermost shelf during peak transgressions are inferred to be the main causes of winnowing and resuspension of mud during the spathian when oxidized packstones in ammonitico rosso facies were deposited at tulong grey limestones locally with bacterial mats or containing agglutinated foraminifers and intercalated black mudrocks indicate instead dysoxic conditions which were widespread from griesbachian to smithian times the middle triassic is mostly represented by marls and marly wackestones with crinoids pelagic bivalves and benthic foraminifers a notable increase in silty to sandy quartzo feldspathic detritus is recorded at mid aegean times and very fine grained subarkoses characterize the mid anisian section at tulong terrigenous supply was renewed probably in the early carnian but accumulation rates sharply increased only in the latest carnian and norian

new permian triassic conodont data from selong tibet and the youngest occurrence of vjalovognathus the controversial biostratigraphy of the well known permo triassic p t boundary section at selong south tibet is reinvestigated based on large conodont samples the conodont data in this study confirm that the upper part of selong formation and the waagenites bed in the lower part of kangshare formation as changshingian age just above the waagenites bed the otoceras latilobatum bed is assigned to the basal triassic due to the presence of h parvus zone the discovery of vjalovognathus a cool temperature tolerant form in changshingian strata allows the youngest vjalovognathus species v carinatus sp nov to be described and a possible permian vjalovognathus evolutionary trend proposed in ascending order this is v australis late sakmarian early artinskian v shindyensis early kungurian v nicolli late kugurian early roadian and ultimately v carinatus sp nov changshingian the last species v carinatus sp nov is also found in the pre mass extinction beds at guryul ravine kashmir allowing correlation with south tibet

stromatolites in precambrian carbonates evolutionary mileposts or environmental dipsticks stromatolites are attached lithified sedimentary growth structures accretionary away from a point or limited surface of initiation though the accretion process is commonly regarded to result from the sediment trapping or precipitation inducing activities of microbial mats little evidence of this process is preserved in most precambrian stromatolites the successful study and interpretation of stromatolites requires a process based approach oriented toward deconvolving the replacement textures of ancient stromatolites the effects of diagenetic recrystallization first must be accounted for followed by analysis of lamination textures and deduction of possible accretion mechanisms accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during archean and older proterozoic times but that younger proterozoic stromatolites grew largely through the accretion of carbonate sediments most likely through the physical process of microbial trapping and binding this trend most likely reflects long term evolution of the earth s environment rather than microbial communities

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

two pulses of extinction during the permian triassic crisis over 90 of marine species were lost during the end permian extinction fossil data show that the crisis in china was marked by two distinct phases of marine extinction separated by a 180 000 year recovery period

a depositional and sequence stratigraphic model for cold water spiculitic strata based on the kapp starostin formation permian of spitsbergen and equivalent deposits from the barents sea this article summarizes the lithostratigraphy of two sections through the kapp starostin formation on spitsbergen having contrasting distal and proximal depositional settings these outcrop sections are compared with an approximately age equivalent spiculitic unit penetrated in two exploration wells 800 km to the southeast on the finnmark platform eight main facies associations comprise these strata including limestones matrix rich matrix poor and mudstone siliciclastics shale and sandstone spiculite dark tight and light colored porous and phosphatized surfaces a sequence stratigraphic model is proposed wherein siliciclastic limestone intervals represent lowstands of relative sea level and the spiculites are mainly highstand deposits based on this model seven depositional cycles sequences are recognized in the distal high accommodation locality on spitsbergen akseloya four in the proximal locality dickson land and two on the finnmark platform a speculative model for correlation between these localities is presented wherein lateral amalgamation of sequences due to landward pinch out of some lowstand intervals results in recognition of fewer sequences in areas of lower accommodation on both dickson land and the finnmark platform an upward change in spiculite lithology from dark tight to light porous is shown and dickson land also shows an upward change in siliciclastic lithology from shale to glauconitic sandstone these changes record a long term shoaling trend approaching the permian triassic boundary this model provides a basis for interpreting the basin scale begin page 2062 distribution of lithofacies and predicting the occurrence of porous zones representing potential hydrocarbon reservoirs

cyanobacterial blooms tied to volcanism during the 5 m y permo triassic biotic crisis widespread but episodic deposition of cyanobacterial mats occurred during the 5 m y permo triassic biotic crisis providing a critical record to decipher the long term stressful environmental conditions and thus a linkage with the killer here we document the timing and duration of these blooms indicated by lipid biomarkers and microbialites throughout south china and compare them to the timing of volcanic activity the initial cyanobacterial bloom has the longest duration and is associated with a prominent eu anomaly in southwestern china where the most intensive volcanism has been proposed to occur suggesting a causal relationship subsequent cyanobacterial blooms in the early triassic are associated with known volcanic events in south china and also with the most voluminous siberian flood basalts and with the largest negative carbon isotope excursions thus it appears that volcanic activity has had a significant impact on microbial development in south china south china volcanism around the permian triassic boundary ptb could have played a much larger role in biotic changes of both bacterial and calcified faunal ecosystems than previously thought the well known siberian volcanism is proposed herein on the basis of the current compilation of dating data to protract the early triassic faunal recovery rather than to cause the end permian extinction

high resolution biochronology and diversity dynamics of the early triassic ammonoid recovery the smithian faunas of the northern indian margin a new high resolution biozonation based on the unitary association ua method is constructed for the dienerian ammonoid succession of the northern indian margin it includes 12 ua zones and leads to the subdivision of the dienerian into three parts early middle and late the corresponding diversity analyses coupled with results previously obtained for the early smithian ammonoids of the same regions highlight the four following phases 1 a first modest peak of diversity in the early dienerian 2 a very low diversity persisting throughout the middle dienerian 3 a slow increase of diversity during the late dienerian and 4 a marked diversification in the early smithian turnover rates are very high during this entire time interval and the boundaries between early middle and middle late dienerian are emphasised by complete renewals of the ammonoid faunas the low diversity values in the middle and early late dienerian are concomitant with an anoxic event on outer continental shelves and coincide with warmer temperatures than those of the early dienerian and early smithian this diversity pattern stands in strong contrast with the credo of a protracted or stepwise recovery following the end permian mass extinction together with the end smithian extinction the middle and early late dienerian diversity crises were likely both radical setbacks in the recovery of early triassic ammonoids however these two diversity crises do not necessarily imply identical environmental triggers that ultimately led to anoxic bottom waters on outer continental platforms in both cases

the timing and pattern of biotic recovery following the end permian mass extinction the aftermath of the great end permian period mass extinction 252 myr ago shows how life can recover from the loss of 90 species globally the crisis was triggered by a number of physical environmental shocks global warming acid rain ocean acidification and ocean anoxia and some of these were repeated over the next 5 6 myr ammonoids and some other groups diversified rapidly within 1 3 myr but extinctions continued through the early triassic period triassic ecosystems were rebuilt stepwise from low to high trophic levels through the early to middle triassic and a stable complex ecosystem did not re emerge until the beginning of the middle triassic 8 9 myr after the crisis a positive aspect of the recovery was the emergence of entirely new groups such as marine reptiles and decapod crustaceans as well as new tetrapods on land including eventually dinosaurs the stepwise recovery of life in the triassic could have been delayed either by biotic drivers complex multispecies interactions or physical perturbations or a combination of both this is an example of the wider debate about the relative roles of intrinsic and extrinsic drivers of large scale evolution from a much more devastated planet and biota than the others with only some 10 of species surviving the epme was much harsher than the other mass extinctions during which global species diversity reduced to only about 50 of the pre extinction total 1 2 24 26 this means that the triassic recovery has two profound implications first it may show qualitative as well as quantitative differences from the other post extinction recoveries and second it can act as an exemplar of what to expect at its most extreme when global biodiversity is pushed to the brink there are obvious implications for current concerns about biodiversity loss and recovery resulting from human impacts 27 28 in the past ten years attention has focused on the sedimentary successions in south china these are enormously laterally extensive with some formations extending more than 2 000 km from the zhejiang to yunnan provinces the huge exposures length of the sections and improving dating open up the opportunity to explore physical environmental and biotic changes through the extinction and recovery times in varied marine habitats and compare these with patterns elsewhere in the world fig 1 a fine scale forensic analysis of this extraordinary time in earth s history now becomes possible the end permian mass extinction the epme killed 80 96 of marine animal species and 70 of terrestrial vertebrate species

assessing early triassic paleoceanographic conditions via unusual sedimentary fabrics and features article i nfo analysis of the lower triassic sedimentary rock record has revealed a variety of unusual sedimentary fabrics and features many of which were more common in the proterozoic than the phanerozoic these so called anachro nistic facies developed across lower triassic carbonate platforms from shallow subtidal environments to deep basinal environments and include features associated with the enhanced precipitation of calcium carbonate e g synsedimentary seafloor cements microbialites and fabrics that formed due to a reduction in the intensity and depth of bioturbation e g vermicular limestones three interacting factors controlled the development of anachronistic facies during the early triassic including 1 environmental conditions i e the unusual chemistry of early triassic oceans 2 biotic factors e g bioturbation and grazing pressures and 3 actualistic sedimen tologic processes e g waves and currents sedimentation because these three factors typically acted in concert with each other it is important to consider the role of each when using anachronistic facies to reconstruct early triassic paleoceanographic conditions overall anachronistic facies are indicative of enhanced calcium carbonate precipitation during the early triassic but do not necessarily indicate the former presence of anoxic or suboxic conditions where they were deposited the influence of seawater chemistry on the deposition of anachronistic facies was most pronounced in deeper water environments where anomalous paleoceanographic conditions heightened calcium carbonate precipitation and caused a decrease in bioturbation and grazing pressures via the upwelling of anoxic alkaline waters the degree of environmental influence lessened shorewards where biotic factors and actualistic processes were more important and slight modification of seawater by microbial activity shallow burial or co2 degassing was necessary for calcium carbonate precipitation to occur anachronistic facies are a useful tool for reconstructing paleoceanographic conditions and examining shifts in the distribution of environmental stress during the recovery from the permian triassic mass extinction but only when the biologic sedimentologic and geochemical factors that led to their growth are carefully considered

lower triassic large sea floor carbonate cements their origin and a mechanism for the prolonged biotic recovery from the end permian mass extinction precipitation of inorganic calcium carbonate is a common occurrence in both modern and ancient marine environments however synsedimentary growth of large 5 10 cm crystalline carbonate cements directly onto the sea floor has been thought to be limited to the proterozoic when seawaters were highly oversaturated with calcium carbonate compared to average phanerozoic values outer shelf to slope deposits of the lower triassic union wash formation in east central california deposited in oxygen restricted settings contain crystalline calcium carbonate cements that appear to have grown directly on the sea floor paleoenvironmental analyses indicate that these large calcium carbonate cements grew under conditions that were similar to those proposed for the precipitation of inorganic calcite in the black sea sulfate reduction of organic matter led to an increase in the amount of bicarbonate ion in deep waters and a concomitant increase in co 2 and alkalinity mixing with surface waters led to co 2 degassing and precipitation of cements from waters supersaturated with calcium carbonate the presence of these cements and associated facies thus provides evidence of harsh environmental conditions in the early triassic at the regional level which may have acted in concert with biotic effects of the end permian mass extinction as well as similar deleterious conditions e g shelf anoxia in other regions to produce a prolonged as well as temporally and geographically variable biotic recovery from this mass extinction