climate simulation of the latest permian implications for mass extinction life at the permian triassic boundary ca 251 ma underwent the largest disruption in earth s history paleoclimatic data indicate that earth was significantly warmer than present and that much of the ocean was anoxic or euxinic for an extended period of time we present results from the first fully coupled comprehensive climate model using paleo geography for this time period the coupled climate system model simulates warm high latitude surface air temperatures related to elevated carbon dioxide levels and a stagnate global ocean circulation in concert with paleodata indicating low oxygen levels at ocean depth this is the first climate simulation that captures these observed features of this time period

upper permian main dolomite microbial carbonates as potential source rocks for hydrocarbons w poland abstract various microbialite lithofacies were common in the shallow water environments which flourished under highly saline and arid climate conditions in the polish part of the zechstein upper permian main dolomite ca2 carbonates data came from detailed analysis of 78 cores from wells located at the southern and northern margins of the main dolomite basin in west poland microbialite lithofacies are represented by columnar planar and domal stromatolites clotted thrombolites and biolaminites developed in high to low energy environments within the upper slope lower parts of oolitic barrier shoal restricted lagoon and tidal flat and tidal channel zones in barrier environments ooids were predominant whereas in lagoonal settings microbial oncoids and peloids were common in basinal settings laminated dolomudstones formed which are regarded as hemipelagic and are partly pelagic microbial in origin microbial communities coexisted with algae and developed mainly within shallow marine environments microbialites are built of cyanobacterial filaments and organo mineral coccoidal forms possibly of bacterial origin organic geochemistry data confirm that organic matter was transformed by cyanobacteria and bacteria which may have played a main role in hydrocarbon generation this is confirmed by c29 to c35 hopanes pr ph ratio below 1 0 and the presence of gammacerane as typical for ca2 profiles the role and occurrence of algae as confirmed by c29 steranes in hydrocarbon generation was possibly minor thus it is concluded that the main dolomite microbialites could be the likely source rocks for hydrocarbons with calculated original toc values from 0 8 to ca 2 0 wt these units also form the reservoir rocks with porosities reaching 20

high frequency cyclicity milankovitch and millennial scale in slope apron carbonates zechstein upper permian north east england the upper permian zechstein slope carbonates in the roker formation zechstein 2nd cycle carbonate in north east england consist of turbidites interbedded with laminated lime mudstone studies of turbidite bed thickness and relative proportion of turbidites percentage turbidites in 20 cm of section reveal well developed cyclicities consisting of thinning upward and thickening upward packages of turbidite beds these packages are on four scales from less than a metre up to 50 m in thickness assuming that the laminae of the hemipelagic background sediment are annual allows the durations of the cycles to be estimated in addition counting the number and thickness of turbidite beds in 20 cm of laminated lime mudstone which is approximately equivalent to 1000 years each lamina is 200 m gives the frequencies of the turbidite beds the average thicknesses and the overall sedimentation rates through the succession for 1000 year time slots figures obtained are comparable with modern rates of deposition on carbonate slopes the cyclicity present in the roker formation can be shown to include milankovitch band ca 100 kyr short eccentricity ca 20 kyr precession and ca 10 kyr semi precession cycles and sub milankovitch millennial scale cycles 0 7 to 4 3 kyr eccentricity and precession scale cycles are related to highstand shedding and relative sea level change caused by milankovitch band orbital forcing controlling carbonate productivity the millennial scale cycles which are quasi periodic probably are produced by environmental changes controlled by solar forcing i e variations in solar irradiance or volcanic activity most probable here are fluctuations in carbonate productivity related to aridity humidity and or temperature changes precession and millennial scale cycles are defined most strongly in early transgressive and highstand parts of the larger scale short eccentricity cycles the duration of the roker formation as a whole can be estimated from the thickness of the laminated lithotype as ca 0 3 myr

tree ring dating of pre 1980 volcanic flowage deposits at mount st helens washington tree ring dating ring width pattern matching was used to determine emplacement dates for eight subfossil tree bearing pre 1980 pyroclastic flow and lahar deposits in stream valleys draining mount st helens washington limiting dates were also established for nine other pre 1980 flowage deposits from the ages of trees rooted on or near them or from exhumed trees the 17 new dates improve understanding of the chronology of events during and after mount st helens9s kalama eruptive period which extended from a d 1479 to the mid 1700s we assign bracketing dates to the three phases of the kalama eruptive period 1479 1510 to the early kalama during which mount st helens erupted explosive dacitic tephras pyroclastic flows and one or more domes 1489 1566 to the middle kalama during which mount st helens produced andesitic tephras pyroclastic flows and lava flows and 1489 1750 to the late kalama during which mount st helens again erupted dacite overlap of the brackets reflects the limits of our dating resolution the revised chronology confirms that little time perhaps 50 yr elapsed between the end of mount st helens9s kalama eruptive period and the start of the succeeding goat rocks eruptive period a d 1800 1857 eruptions apparently occurred sporadically during the entire 1479 1857 interval the record also indicates that a large pyroclastic flow occurred 7 10 yr after the explosive eruptions that began the kalama eruptive period the dates further imply that extrusion of the pre 1980 summit dome continued intermittently for 100 yr and limit the ages of two tephras these findings demonstrate the usefulness of relict tree bearing deposits to volcanic history studies

sequence stratigraphy of carbonate evaporite basins models and application to the upper permian zechstein of northeast england and adjoining north sea the successions of carbonate evaporite basins which are periodically cut off from the world ocean are considered in terms of their sequence stratigraphy two basin types are distinguished those where incomplete drawdown takes place and those showing complete drawdown and wholesale basin desiccation it is argued that following relative sea level falls sequences begin with the evaporites precipitated as marginal lowstand gypsum wedges in the first basin type and as lowstand basin centre halite fills in the second the evaporites pass up into carbonate sediments which are mainly deposited on shallow water platforms around the basin during transgressive and highstand systems tracts the concepts and models developed are applied to the zechstein upper permian strata of northeast england and adjoining north sea seven sequences are proposed with some containing thin parasequences the sequence approach to carbonate evaporite basins which considers both basin margin and basin centre facies gives a more encompassing perspective of sedimentation than the traditional cycle concept with its emphasis on the basin centre

association of oil seeps and chemosynthetic communities with oil discoveries upper continental slope gulf of mexico abstract geochemical fingerprinting of many upper gulf slope oils indicates an origin from deeply buried mesozoic carbonate source rocks substantial vertical migration 6 km 19 680 ft along salt and fault migration conduits must be invoked to explain the emplacement of mesozoic sourced oils in shallow miocene to pleistocene reservoirs gulf slope seeps provide evidence of oil and gas charge in a rapidly subsiding salt basin where oil and gas migration is a geologically recent or ongoing event sea floor oil and gas seeps gas hydrates chemosynthetic communities authigenic carbonate derived from hydrocarbon oxidation and natural oil slicks are diagnostic indicators of charge there is a regional association between seeps and the upper gulf slope oil province offshore louisiana and texas there is also a subregional relationship between seeps and the localized charge systems that give rise to individual oil accumulations key case histories include marquette field jolliet field and the gc 228 discovery in northwest green canyon as well as the cooper and auger discoveries in northeast garden banks

microbially induced sedimentary structures a new category within the classification of primary sedimentary structures abstract cyanobacterial films and mats syndepositonally influence erosion deposition and deformation of sediments the biomass levels surface morphologies and microbial mats stabilize depositional surfaces and shelter the sediment against erosion or degassing growing microbial mats dredge grains from their substrate upwards whereas cyanobacterial filaments that are oriented perpendicular to the mat surface reach into the supernatant water and baffle trap and bind suspended particles these and similar biotic physical interactions are reflected in syndepositional formation of microbially induced sedimentary structures we distinguish structures on bedding planes leveled bedding surfaces wrinkle structures microbial mat chips erosional remnants and pockets multidirectional ripple marks and mat curls and internal bedding structures sponge pore fabrics gas domes fenestrae structures sinoidal laminae oriented grains benthic ooids biolaminites mat layer bound grain sizes we propose to place this group of microbially mediated structures as a fifth category bedding modified by microbial mats and biofilms in pettijohn and potter s 1964 existing classification of primary sedimentary structures

biotic and abiotic processes in the formation and diagenesis of permian dolomitic stromatolites zechstein group ne england abstract the crinkly bed of the upper permian zechstein group succession roker formation hauptdolomit z2c in northeast england is a distinctive 1 4 meter thick unit that has been interpreted as a stromatolite of microbial origin or alternatively as the result of purely abiotic precipitation close examination of this stratigraphically significant unit shows that it is the result of both physical and microbial processes and was deposited in hypersaline shallow water immediately following lowstand evaporite deposition within the zechstein basin the internal structure of the crinkly bed consists of fine millimeter scale laminae of alternating clotted peloidal or aphanitic micritic layers and granular laminae composed of silt size peloids with rare hollow spheroids the lamination is extremely regular in thickness and laterally persistent for up to 4 meters a microbial community composed of coccoid and filamentous microorganisms inferred from fossil evidence colonized the original sediment surface it is suggested that this biofilm was responsible for the precipitation of both the micrite laminae and most of the peloids of the granular laminae the peloids are consequently interpreted as autochthonous this interpretation of a microbial origin is consistent with the microstructure and geochemical signatures of the micritic dolomite which constitutes both the continuous micritic laminae and the peloids themselves primary dolomite precipitation is hypothesized to have taken place from marine to slightly hypersaline waters mediated by bacterial metabolism similar to the process that operates in modern intertidal microbial mats the crinkly bed shows macro structures that vary along a continuum from symmetrical to asymmetrical centimeter scale ripple like structures some showing interference patterns through to domical and conical structures more typical of stromatolites the more ripple like structures have a lamination of microbial origin identical to that within the domal conical stromatolites there is no internal cross lamination their origin is equivocal they could be the result of physical current or wave induced deformation of a surficial biofilm or their form could be inherited from true mechanically deposited ripples not observed that provided a template for biofilm growth changes in the nature and strength of the wave and or current regime and possibly in the community structure of the microbial mat produced this array of microbially induced macrostructures miss the latter plus the absence of desiccation features indicative of intertidal to supratidal deposition suggest subtidal sedimentation at a depth of several meters intergranular gypsum cement precipitated during early diagenesis and ferroan sparry dolomite precipitated during burial tertiary uplift and the consequent exposure to meteoric waters resulted in the precipitation of calcite cements that replaced gypsum and pre existing dolomite probably via the biological mediation of heterotrophic bacteria the interpretation of this distinctive stratigraphic unit illustrates the difficulty in distinguishing between biotic and abiotic processes in the sedimentary record

growth morphologies of modern marine stromatolites a case study from highborne cay bahamas abstract stromatolites are a uniquely coupled geo biosphere system which potentially records important paleoenvironmental and biological information characterizing and distinguishing between the biological and physical factors that control stromatolite morphogenesis therefore has important implications for the understanding of modern stromatolites and the interpretation of ancient systems this paper documents the occurrence and distribution of stromatolites with distinct growth morphologies in the highborne cay reef system and other locations in exuma cays bahamas and explores the relative contributions of physical and biological environmental factors controlling stromatolite shape our observations suggest that macro scale growth morphologies of exuma stromatolites are primarily controlled by accommodation space hydrodynamics and sedimentation patterns the latter are critical for the stromatolite ecosystem in that the suspended sediment provides grains for trapping and binding and thus stromatolite accretion furthermore sediment burial removes macroalgae allowing the prokaryotic community to dominate changes in sedimentation patterns and frequency allow for the colonization of stromatolites by macroalgae and boring macrofauna which in time destroy and degrade the stromatolite structure

sedimentation distribution and diagenesis of organic matter in a recent carbonate environment abu dhabi u a e abstract in the modern hypersaline carbonate lagoon and sabkha sedimentary environments of abu dhabi united arab emirates three types of organic matter originate respectively from microbial mat avicennia mangrove and halodule lagoonal seagrass the study of recent sedimentary processes and cross sections through the sabkha sediments lead to the definition of organo sedimentary facies based on geochemical and sedimentological criteria this permits the construction of an organo sedimentary sequence which expresses the holocene sedimentary record involving a transgressive and a regressive sequence the various organic facies occur in both sequences heterogeneity within the individual organic facies reflects several factors including sedimentation dynamics mineral matrix oxidation and reduction and selective organic and mineral diagenesis these parameters are discussed in terms of depositional environment and location within the organo sedimentary sequence changes in distribution quantity and preservation potential of the buried organic matter are discussed in terms of sea level changes and sedimentary accretion rates

palaeoclimatic imprint distribution and genesis of zechstein main dolomite upper permian petroleum source rocks in poland sedimentological and geochemical rationales

upper permian zechstein supergroup carbonate evaporite platform palaeomorphology in the uk southern north sea abstract seismic interpretation geological mapping and depth conversion of the zechstein supergroup z2 cycle using high quality well calibrated three dimensional 3 d seismic has revealed the complex palaeomorphology of a deeply buried ancient carbonate shelf margin on the southwestern margin of the southern permian basin the new mapping shows that the margin comprises a series of corrugated embayments and promontories which extend up to 5 km 3 mi into the basin and locally have a palaeobathymetric relief of 200 m 650 ft well calibration across the margin demonstrates a strongly bipartite lateral thickness distribution between a high velocity anhydrite dominated shelf and a lower velocity halite dominated basin strong lateral and vertical velocity variations in the upper permian zechstein supergroup are known to have major impacts upon seismic imaging and depth conversion in the spb the resulting uncertainty remains one of the major challenges when interpreting and assessing the prospectivity of the underlying upper permian rotliegend group leman sandstone formation reservoirs in the uk southern north sea an understanding of the zechstein shelf edge s 3 d physiography and its velocity variation has implications for the delineation of traps containing the prospective reservoirs that lie below recognition of the complexity and effects of this shelf margin contributed to the recent juliet discovery whose position outside of the presently defined rotliegend group play fairway suggests that prospectivity is more extensive along the basin margin than previously thought as such the work provides a means by which to identify and delineate new structures and extend the life of this mature yet prolific gas province

introduction aapg hedberg research conference on microbial carbonate reservoir characterization conference summary and selected papers with the recent discovery of hydrocarbons in microbial carbonate reservoir facies along the south atlantic margins industry is keen to further the understanding of the origin and development of nonmarine lacustrine to marine microbial carbonates the nature of the depositional and diagenetic characteristics of microbialite and associated facies and the sedimentary and petrophysical properties of microbial carbonate petroleum reservoirs in this regard the authors of aapg getting started series 19 microbial carbonate reservoirs mancini et al 2010 found that a vast literature on microbes and their functions in geological processes and products ranging from biogeochemistry to geomicrobiology sedimentary petrology and stratigraphy was available however only a small part of this literature deals with microbial carbonates as petroleum reservoirs further these authors reported that sparse available literature exists on microbial carbonate reservoirs formed in lacustrine and continental settings and on carbonate reservoirs of abiotic origin in general to help address these shortcomings an aapg hedberg research conference was proposed to focus on microbial carbonate reservoir characterization with an emphasis on depositional settings of microbial and abiotic carbonate reservoirs especially in lacustrine settings associated with rift basins the proposal was accepted august 21 2010 and the hedberg conference was held in houston texas last june 3 8 2012 with 85 attendees from 10 countries the conference was dedicated to wayne m ahr who passed away in november 2011 he was one of the conference organizers one of the intended field trip leaders and a friend to many at the conference the following overview of microbial carbonates is modified from sections 1 and 2 of aapg getting started series 19 microbial carbonate reservoirs mancini et al 2010 microbes are defined as microorganisms visible only under a microscope some examples are bacteria fungi molds algae and protozoa unlike the older classification of living organisms

the effect of global warming and global cooling on the distribution of the latest permian climate zones abstract the end permian biotic crisis is commonly associated with rapid and severe climatic changes these climatic changes are commonly suggested to have originated from solid earth carbon degassing leading to global warming but aerosol and ash induced cooling induced by lava degassing has been suggested as well the application of an earth system model of intermediate complexity has enabled a visualisation of the major climatic shifts on the supercontinent pangaea caused by rapid temperature changes due to changed radiative properties from greenhouse gases the reconstructed reference climate was validated by latest permian climate indicative sediments to investigate the possible climatic shifts from a set of 22 reconstructions which varied with temperature a minimum global annual mean temperature of 18 2 c for the late permian climate prior to the climatic perturbation event was determined starting from this pre event setup global warming and global cooling scenarios were simulated the response of the end permian climate system to temperature increase and decrease show marked differences while global cooling is followed by major climatic changes in the high latitudes and replacement of boreal biomes by tundra and polar frost the changes during global warming are less pronounced with only locally increasing aridity compensated by humidisation in other regions the different behaviour of the climatic belts under warm and cold conditions is accompanied by different climate sensitivities caused by different strength of the snow cover albedo feedback thus changes in the energy balance of the latest permian surface troposphere system have a 30 higher perturbation potential during cold climate conditions than during warmhouse conditions therefore substantial global cooling resulting in coldhouse climate conditions and an annual global mean temperature below 18 c is more efficient in perturbing the earth palaeoclimate during the end permian warmhouse the results suggest that global cooling mechanisms as injection of sulphur aerosols and ash particles from the siberian traps large igneous province into the late permian palaeoatmosphere have a higher climate perturbation potential than a warming due to carbon greenhouse gases with a similar magnitude of radiative forcing

sensitivity of biomarker properties to depositional environment and or source input in the lower toarcian of sw germany abstract a sequence of lower toarcian sediments which are highly contrasting in their depositional environment over a 5 m depth interval has been investigated in detail for the variability of geochemical properties which are used for source characterization and oil to source correlation lower liassic marls are representative of a well aerated shallow water environment in contrast to the immediately overlying bituminous shales which are deposited under extremely reducing conditions various properties have been found to vary considerably within these two units amongst the most important are carbon isotopic composition of the kerogen the pristane phytane ratios nickel as opposed to vanadyl porphyrins and the c27 dia regular steranes although maturation within the profile does not change some of the maturation dependent biomarker properties such as the monoaromatic steroid side chain cracking and the tm ts ratio exhibit large changes which can be assigned to diagenetic processes another maturation dependent property the 20s 20r epimerization of c29 steranes exhibits smaller changes which could also be due to early diagenetic processes the study suggests that reducing and oxidizing conditions i e eh and ph in the sediment exert an influence on several biomarker precursor product pathways in maturation studies initial variations due to depositional conditions have therefore to be taken into account

upper permian zechstein microbialites supratidal through deep subtidal deposition source rock and reservoir potential zechstein 2 z2 carbonate microbialites flourished under arid paleoclimatic conditions in the late permian microbial carbonates from the roker formation outcrop in northeast england with its subsurface equivalent being the main dolomite from northwest central poland the z2 carbonate deposits developed in supratidal through deep subtidal zones and consist of various stromatolites and thrombolites planar stromatolites and thrombolites characterize intertidal and supratidal facies and biohermal stromatolites with oolitic grainstone and crinkled stromatolites typify shallow subtidal facies the z2 subtidal and or intertidal microbialites with oolites form complexes more than 10 m 33 ft thick and are important reservoir facies for hydrocarbons subtidal slope and intertidal lagoonal microbial mudstone and wackestone have poor reservoir properties but contain total organic carbon as much as 2 wt and are considered as potential source rocks the thermal maturity assessed from c27 17 trisnorhopane tm and c27 18 trisnorhopane ts as the ts ts tm ratio c30 moretane hopane ratio sterane ratio expressed as 20s 20s 20r and ratio shows to indicates a mature character of organic matter with respect to oil generation

dolomite formation within microbial mats in the coastal sabkha of abu dhabi united arab emirates microbial mediation is the only demonstrated mechanism to precipitate dolomite under earth surface conditions a link between microbial activity and dolomite formation in the sabkha of abu dhabi has until now not been evaluated even though this environment is cited frequently as the type analogue for many ancient evaporitic sequences such an evaluation is the purpose of this study which is based on a geochemical and petrographic investigation of three sites located on the coastal sabkha of abu dhabi along a transect from the intertidal to the supratidal zone this investigation revealed a close association between microbial mats and dolomite suggesting that microbes are involved in the mineralization process observations using scanning electron microscopy equipped with a cryotransfer system indicate that authigenic dolomite precipitates within the exopolymeric substances constituting the microbial mats in current models microbial dolomite precipitation is linked to an active microbial activity that sustains high ph and alkalinity and decreased sulphate concentrations in pore waters such models can be applied to the sabkha environment to explain dolomite formation within microbial mats present at the surface of the intertidal zone by contrast these models cannot be applied to the supratidal zone where abundant dolomite is present within buried mats that no longer show signs of intensive microbial activity as no abiotic mechanism is known to form dolomite at earth surface conditions two different hypotheses can reconcile this result in a first scenario all of the dolomite present in the supratidal zone formed in the past when the mats were active at the surface in a second scenario dolomite formation continues within the buried and inactive mats in order to explain dolomite formation in the absence of active microbial metabolisms a revised microbial model is proposed in which the mineral template properties of exopolymeric substances play a crucial role

source rock potential of evaporitic environment examination of modern saline lakes solar evaporation ponds and lagoons shows that the evaporitic environment can be very productive of organic matter few species survive in the brines but those that do commonly exist in great profusion in a marine evaporitic embayment the flow of surface currents is persistently toward regions of highest salinity so that there is a continual supply and concentration of nutrients prolific growth of phytoplankton may be similar to that in areas of upwelling in modern oceans only carbonates precipitate in the mesosaline part 4 to 12 salinity of such an evaporitic environment and no great dilution of organic matter by clastic or biogenic sediments occurs because stratification of brine may occur and reducing conditions may be a sociated with the bottom waters much of the organic matter produced can be preserved upon maturation the result may be a rich carbonate source rock frequently unrecognized in the geologic column in the middle east mesosaline conditions are known to have occurred many times from the triassic to cretaceous and may be responsible for the vast reserves of petroleum in the area evaporitic conditions may also have played a part in the petroleum productivity of many other areas including the michigan and paradox basins

late jurassic biogeochemical microenvironments associated with microbialite coated unionids bivalvia asturias n spain abstract the vega formation upper jurassic asturias spain contains two kimmeridgian outcrops the abeu and huerres sections with bivalves coated with carbonate microbialites oncoids the bivalve shells in the abeu section were replaced early by calcite while those of the huerres section were dissolved and the moulds filled by late diagenetic cements for the abeu shells there was a loss of sr and a gain of mg fe and mn during the replacement process but much of the original organic matter was retained part of the s present can be linked to this organic matter and part to the sulphate that replaced the carbonate groups in the calcite the thin microbialites inside the shells of some of the huerres bivalves have allowed us to estimate the influence of the growth rate on the incorporation of trace elements in calcite with an approximately six times lower growth rate the internal microbialite incorporates less mg and s and more fe and mn than the external one while maintaining the sr content the trace element content mg s sr fe and mn of the huerres and abeu microbialites are similar these coatings may therefore have been formed in the same type of freshwater but in different microenvironments given the substantial sulphate content of the microbialites from both sections this freshwater probably came from hot springs however the high fe mn ratio of the abeu microbialites suggests a reducing environment during their formation indeed 18o and 13c data confirm that the abeu and huerres microbialites were formed in different microenvironments the positive covariance for 18o and 13c of the abeu microbialites and replaced shells r2 0 83 and the wide range of variation for 18o 2 80 together suggest that the microbialite crusts grew in isolated ponds where evaporation was dominant in the huerres microbialites the positive covariance for 18o and 13c r2 0 59 and the narrow range of variation for 18o 0 74 indicate that the huerres section was formed in a more open environmental system where degassing predominated over evaporation