organic matter accumulation in the upper devonian duvernay formation western canada sedimentary basin from sequence stratigraphic analysis and geochemical proxies abstract we present a model for organic carbon accumulation in the upper devonian duvernay formation of the western canada sedimentary basin relating total organic carbon toc concentrations to a high resolution geochemical and organic petrologic database and comparing these to a core based sequence stratigraphic interpretation many previous source rock studies have suggested that organic matter is enriched in transgressive systems tracts or at maximum flooding surfaces an observation that is commonly attributed to an assumed relationship between water depth and oxygen levels our data set enables us to associate total organic matter content and organic assemblages with particular systems tracts and to examine how the organic assemblages change across the basin tested against proxies for redox conditions and bioproductivity to relate relative sea level to specific mechanisms for organic accumulation the duvernay formation comprises three third order depositional sequences superimposed on a second order late transgressive systems tract and early highstand systems tract sequences are composed almost entirely of transgressive systems tracts and highstand systems tracts with a lowstand systems tract only at the base of the upper cycle that marks the second order sea level turnaround depositional facies generally vary from bioturbated carbonate rich siltstones to siliceous mudstones from the platform margins to basin center organic petrologic analysis records predominantly amorphous organic matter and solid bitumen with much less abundant vitrinite and inertinite organic matter type indicated by rock eval analysis shows that in most cases high total organic carbon toc content is associated with better quality organic matter high hydrogen index and vice versa indicating more reducing conditions or higher bioproductivity were responsibility for organic enrichment however near carbonate reefs hydrogen index is uncorrelated with toc indicating that here dilution by carbonate minerals was the primary control on organic enrichment across most of the basin highest tocs are recorded just above the second order maximum flooding surface secondary peaks in toc are recorded above the maximum flooding surface in the upper third order cycle and in the transgressive systems tract of lower third order cycle low toc values are recorded in the lowstand systems tract and in the middle and upper third order transgressive systems tracts almost up to the maximum flooding surfaces throughout much of the basin proxies for relative sea level restriction of water masses mo toc redox conditions mo al and s fe and bioproductivity biogenic silica coincide these relationships demonstrate that organic carbon accumulation resulted from influxes of nutrient rich upwelled water during high sea level thus toc values are highest in the upper part of transgressive systems tracts and lower highstand systems tracts anoxia typically developed as a result of bioproductivity and enhanced organic matter accumulation but was not itself a trigger for organic sedimentation near carbonate reefs however varying sea level regulated carbonate sedimentation rate and organic matter dilution and bioproductivity had less impact on organic matter concentrations thus toc was high when carbonate deposition was low during transgressions which forced carbonate reefs to backstep limiting carbonate sedimentation in deeper water area

conditions required for oceanic anoxia euxinia constraints from a one dimensional ocean biogeochemical cycle model article i nfo widespread black shale depositional intervals termed oceanic anoxic events oaes occurred repeatedly during the phanerozoic eon here we developed a new vertical one dimensional ocean biogeochemical cycle model that involves several chemical reactions in an oxic anoxic sulfidic water column to explore the theoretical constraints for global oceanic anoxia euxinia quantitatively and systematically we conducted sensitivity analyses of the proposed causal mechanisms including elevated rates of riverine phosphorus p input ocean stagnation and lowered oxygen solubility due to climate warming we gave special attention to the vertical chemical structure of the ocean and also to the characteristic behaviors of the marine p cycle under anoxic conditions because the relationship between the depth of anoxia and the benthic phosphorus flux could be important for the occurrence of oceanic anoxia euxinia steady state simulations indicated that 1 a decrease in ocean stagnation or oxygen solubility is not enough by itself to achieve widespread anoxia with the present reactive p river input rate and 2 shallow water anoxia followed by massive p liberation from surface sediments can lead to widespread eutrophication and anoxia euxinia we conclude that elevated riverine flux of reactive p is the most important factor for triggering global anoxic events via a positive feedback loop among ocean anoxia phosphorus regeneration and surface biological productivity

high resolution facies analyses of mudstones implications for paleoenvironmental and sequence stratigraphic interpretations of offshore ancient mud dominated successions abstract the extent of lithofacies variability in fine grained sedimentary rocks is very poorly known in comparison to that present in coarser grained clastic and carbonate successions the absence of this information means that sediments present on continental shelves are rarely considered as integrated systems because fine grained facies such as shales are mostly excluded from sophisticated regional facies models to shed light upon lithofacies and grain size in shale dominated successions so that they can be incorporated into shelf wide depositional models the blackhawk formation of the mancos shale campanian age exposed in the book cliffs utah was investigated using combined field whole rock geochemical optical and electron optical methods these sediments show systematic grain size variations are intensely bioturbated and composed predominantly of detrital clays mainly dioctahedral micas quartz and feldspar with minor pyrite and organic matter they are organized into very thin 10 mm upward fining genetic beds they exhibit both systematic lateral 103 m scale and vertical 10 2 to 100 m scales lithofacies variability preferentially cemented units occur close to sequence boundaries unconformities these cemented units typically contain a very different detrital assemblage including significant quantities of chlorite from the rest of the succession and are located close to levels where there are marked stacking pattern discontinuities overall lithofacies variability is interpreted in terms of deposition occurring on an oxic continental shelf with the coarser grained facies being deposited in proximal settings offshore transition zone in contrast to the finer grained units that were deposited in more distal environments offshore zone storms are interpreted to have been the dominant mechanism dispersing the sediment once deposited the surface layers of the sediment were intensely reworked by burrowing organisms preferential preservation of ichnogenera from mid and lower tiers suggest that the depositional environment was energetic and erosion commonly removed the surface sediment layers prior to deposition of thin 10 2 m storm beds the larger scale 100 m upward coarsening units that are composed of stacked beds are interpreted to be parasequences preferential cementation at levels where large scale stacking patterns change is interpreted to occur at horizons where there were breaks in sediment accumulation and bacterial metabolic processes were able to supply sufficient solutes to fill uncompacted pore space with cement the presence of a very different detrital assemblage in these units suggests that winnowing occurred despite their relatively innocuous appearance in the field these surfaces are likely to be significant bypass surfaces over which sediment was delivered to the deeper parts of the basin during times of relative lowstand of sea level

organic carbon and sedimentation rate further evidence for anoxic deep water conditions in the cenomanian turonian atlantic ocean abstract the relationship between organic carbon content and sedimentation rate based on data derived from recent to miocene sediments deposited under oxic and anoxic sea water conditions is used to characterize the different depositional environments these data are compared with data of cenomanian turonian dsdp sediments from the atlantic ocean the results may support deposition in anoxic environments due to extremely reduced deep water circulation as the main cause for the formation of cenomanian turonian black shales in the north atlantic rather than increased supply of organic matter due to higher oceanic productivity

lenticular shale fabrics resulting from intermittent erosion of water rich muds interpreting the rock record in the light of recent flume experiments lenticular lamination is a fabric that is known from shales of all ages but its origin and paleoenvironmental significance is poorly understood we have successfully reproduced this fabric in flume experiments beds of water rich mud were eroded in a flume and yielded sub millimeter to centimeter size fragments that can be transported in bedload for distances of ten kilometers or more upon redeposition and compaction these deposits have the same textural qualities as lenticular laminated shales from the rock record although accumulation of fecal pellets or abundant burrow tubes in a shale may produce comparable fabrics upon compaction these can be distinguished from erosion produced lenticular lamination via petrographic criteria lenticular lamination in shales that is due to deposition of water rich mud fragments most likely records intermittent erosion and transport of surficial muds by currents

formation processes of framboidal pyrite abstract pyrite framboid formation may be the result of four consecutive processes 1 nucleation and growth of initial iron monosulfide microcrystals 2 reaction of the microcrystals to greigite fe 3 s 4 3 aggregation of uniformly sized greigite microcrystals i e framboid growth and 4 replacement of greigite framboids by pyrite the uniform morphology uniform size range and ordering of the microcrystals in individual framboids as well as the range of observed framboid structures from irregular aggregates to densely packed spherical aggregates and polyframboids are consequences of these processes using dlvo theory derjaguin landau verwey and overbeek we have evaluated the stability of colloidal iron monosulfide suspensions with ionic strengths typical of marine and lacustrine waters in addition to van der waals attractive and double layer repulsive forces a term is included to account for the ferrimagnetic properties of greigite numerical models predict that magnetically saturated greigite particles 0 1 m in diameter will rapidly aggregate in either marine or fresh water the aggregation model is in agreement with the sequence of greigite formation followed by pyrite framboid formation established in a previous experimental study sweeney and kaplan 1973 and is consistent with the occurrence of framboids composed of other magnetic minerals e g greigite magnetite and magnesioferrite based on the temperature dependent magnetic properties of greigite and aging experiments in hydrothermal solutions this mechanism for framboid formation via precursor greigite could operate to temperatures of 200 c consistent with the occasional occurrence of pyrite framboids in the paragenesis of metalliferous ore deposits

integrated workflows for shale gas and case study results for the horn river basin british columbia canada the variation in well performance observed between various shale gas plays and indeed within individual basins and on individual pads has gone some way to dispelling myths regarding the perceived homogeneity of shale gas targets with increased quantities of data and more determined analysis we show that understanding the micro and mesoscale heterogeneity can be advanced through interdisciplinary studies that incorporate traditional and advanced geophysical data and methods with geological understanding and engineering measurements this understanding is critical in optimizing well placement the spacing and length of horizontal wells and hydraulic fracturing effort to maximize recovery specifically we illustrate that in the muskwa formation and the otter park klua and evie members of the horn river formation reservoir quality can be predicted using lambda rho and mu rho data extracted from avo inversion studies from log data we show that the most prospective reservoir intervals are characterized by decreasing lambda increasing mu and or a lambda mu ratio less than one

variations in pyrite texture sulfur isotope composition and iron systematics in the black sea evidence for late pleistocene to holocene excursions of the o2 h2s redox transition time dependent variations in the physicochemical properties of pyrite were investigated in four sediment cores from the black sea in the laminated deep basin sediments of unit i and unit ii 86 of pyrite particles are present as fine grained framboidal aggregates in these sediments the dominance of pyrite framboids with a narrow size distribution and maximum size 18 m is evidence of syngenetic water column pyrite formation subjacent to the o2 h2s boundary sediments from the basin margin collected below the impingement of the o2 h2s boundary contain an increased proportion of fine grained euhedral grains of pyrite relative to framboidal aggregates suggesting increased additions of diagenetic pyrite below the sediment water interface the more efficient reduction and sulfidation of iron in the water column of the central region of the basin implies a more reactive source of iron there compared to the basin margins and is tied to increasing pyrite as framboids and greater degrees of pyritization dop in the basin center relative to the basin margins an evaluation of fe s c relations indicates that pyrite formation was limited by sulfate availability during deposition of the oldest lacustrine sediments of unit iii c limited for upper unit iii due to the input of sulfate rich mediterranean seawater and fe limited in the laminated organic carbon rich sediments of units i and ii these changes in pyrite limiting factors occurred within 4 m of compacted burial representing 15 ka sediment fabric and framboid size distributions at a shallow basin margin site suggest that during two extended periods of unit ii deposition the o2 h2s transition retreated to depths below 200 m however during these same intervals the 34s of pyrite remains uniform compared to overlying and underlying laminated sediments implying that this chemical signature may not be uniquely tied to the position of the o2 h2s boundary relative to the sediment water interface but rather is likely related to biogeochemical processes

the gas bearing devonian presqu ile dolomite of the cordova embayment region of british columbia canada dolomitization and the stratigraphic template white dolospar of the presqu ile dolomite forms the reservoir for many gas fields of northeastern british columbia within the keg river sulphur point and slave point formations along the shelf margin of the cordova embayment the embayment fill succession of the organic rich klua shale the otter park shale and marlstones equivalent to the sulphur point and slave point formations are aquicludes that blocked the upward and lateral flow of dolomitizing brines presqu ile dolomitization along the slave point shelf edge is interrupted in places where the klua shale extends shelfward underneath the slave point formation the watt mountain shale was also a regional aquiclude that prevented upward circulation of dolomitizing fluids in areas behind the slave point shelf edge flow of dolomitizing nacl cacl2 mgcl2 h2o brine solutions began in the shallow subsurface and precipitated dolomite cements type 1 at temperatures less than 50 degreesc possibly even during slave point deposition as northwestward directed shallow subsurface brine reflux from the elk point basin began this was followed by upward directed subsurface convective flow of nacl cacl2 mgcl2 h2o and nacl mgcl2 h2o brines and precipitation of dolomite cements at temperatures of about 130 degreesc during the late devonian carboniferous lower salinity brines that precipitated calcite cements and some dolomite type 2 may have interacted with connate fluids of marine origin or less likely with meteoric fluids modeling of organic maturation indicates that the muskwa shales above the slave point formation passed through the oil generation window in the permian and the onset of dry gas generation in the middle mesozoic postdolomitization calcite cements precipitated during these times contain abundant liquid hydrocarbon filled and methane filled inclusions high temperatures of close to 200 degreesc experienced by slave point strata in the mesozoic caused stretching but no leakage or refilling of fluid inclusions in all dolomite cements

a depositional model for organic rich duvernay formation mudstones abstract the upper devonian duvernay formation of western canada is an organic rich shale formation now targeted as a hydrocarbon reservoir we present a detailed sedimentological analysis of the duvernay formation in order to better understand organic rich mudstone depositional processes and conditions and to characterize the vertical and lateral heterogeneity of mudstone lithofacies that affect petrophysical and geomechanical rock properties organic rich mudstone facies of the duvernay formation were deposited in a dynamic depositional environment by a variety of sediment transport mechanisms including suspension settling turbidity currents and bottom water currents in variably oxygenated bottom waters suspension settling dominated in distal relatively deep areas of the basin but evidence for weak turbidity currents and bottom water currents was observed in the form of graded beds and thin grain supported siltstone laminae organic enrichment primarily occurred in distal areas as a result of bottom water anoxia and low depositional rates of inorganic sediment in deep water locations near platform margins alternating silty sandy contourite beds and organic rich mudstone beds are present the former interpreted to have been deposited and reworked by bottom water currents flowing parallel to slope in shallower more oxygenated settings mudstone lithologies vary from calcareous to argillaceous these sediments were deposited from suspension settling turbidity currents and bottom water currents although primary sedimentary structures are often obscured by extensive bioturbation locally organic enrichment in dysoxic rather than anoxic bottom waters was driven by a slightly increased sedimentation rate and possibly also by aggregation of sedimentary particles in the water column due to interaction between organic matter and clay minerals large variations observed in sediment composition from siliceous to calcareous to argillaceous reflect multiple biogenic carbonate and clastic sediment sources sediment composition is influenced by basin morphology circulation patterns sea level variation and proximity to sediment sources

traces in the dark sedimentary processes and facies gradients in the upper devonian lower mississippian upper shale member of the bakken formation williston basin north dakota u s a reply we welcome the opportunity to respond to schieber s 2014 discussion of egenhoff and fishman 2013 because it enables us to further elaborate on the structures we interpreted as fecal strings attributable to phycosiphon incertum that are visible in mudstone samples collected from the upper shale member of the bakken formation schieber 2014 in his discussion raised four points that can be summarized as 1 the structures interpreted as phycosiphon incertum by egenhoff and fishman 2013 are artifacts introduced during the thin section manufacturing process 2 the structures egenhoff and fishman 2013 interpreted as burrows may instead have formed through depositional processes rather than by bioturbation siltstone laminae could represent the toe portion remaining from a migrating current ripple the siltstone laminae would therefore reflect the original composition of silt rich ripple foresets where they were in contact with the seafloor whereas locations where mud rich forests were in contact with the muddy seafloor would produce the holes seen in the siltstone laminae alternatively currents flowing over previously deposited silt laminae could have scoured and plucked individual silt grains out of the laminae and thereby produced sites that were later filled with mud 3 near surface burrows presumably like those that egenhoff and fishman 2013 observed in the upper shale member would have to be produced in soupgrounds burrows in these freshly deposited muds can be maintained only when stabilized by mucus observations from the recent suggest that these types of burrows are likely produced by nematodes that are only detected using the color differences between the fill and the surrounding rock 4 the amount of compaction can be very high in mudstones therefore the compaction in the upper shale member should have strongly affected original sedimentary features including the burrows the burrows shown by egenhoff and fishman 2013

historical variability in atlantic meridional baroclinic transport at 26 5 n from boundary dynamic height observations the strength of the atlantic meridional overturning circulation moc at 26 5 n may be inferred from the combination of florida straits transport derived from cable measurements ekman transport estimated from wind stress climatologies and mid ocean geostrophic shear traditionally obtained from hydrographic sections with application of mass balance to the section to yield the mid ocean barotropic flow the recent rapid monitoring project has provided time series information for the mid ocean geostrophic shear since 2004 this work presents methods to assemble a comparable dataset from ctd end stations and boundary mooring temperature and pressure time series to estimate the past variability from 1980 to 2005 variability in the end station derived transport anomalies suggests that the moc has fluctuated by more than 10 sv encompassing all moc estimates reported in the literature interannual changes in moc transport are masked by this variability and calculated trends in layer transports are not statistically significant more extensive datasets of ctd casts and moored temperature records at the western boundary do show significant changes with warming in the thermocline and long term freshening of the deep waters between the 1980s and 2005 these changes are associated with stronger southward flow in the upper waters and weaker southward flow in the deep waters and suggest a decrease in the moc strength of 2 4 sv any such decrease however is masked by the scale of variability in layer transports derived from the historical database of ctd end stations

a silurian devonian marine platform deltaic system in the san rafael block argentine precordillera cuyania terrane lithofacies and provenance fil manassero marcelo jorge consejo nacional de investigaciones cientificas y tecnicas centro cientifico tecnologico conicet la plata centro de investigaciones geologicas universidad nacional de la plata facultad de ciencias naturales y museo centro de investigaciones geologicas argentina

organic accumulation in the lower chihsia formation middle permian of south china constraints from pyrite morphology and multiple geochemical proxies article i nfo the organic rich chihsia formation middle permian on the yangtze platform western hubei south china is considered to be the major hydrocarbon source rock in south china the lower part of the chihsia formation reported here was deposited in an intrashelf basin and is characterised by black laminated marlstones shales intercalated with dark grey limestones dolomites in which metre scale shallowing or cleaning upward cycles are ubiquitous each cycle is composed of basal marlstone shale and upper lime stone the organic matter is concentrated exclusively in the shaley bases of these cycles and shows system atic cyclic variations in abundance up through the succession an integrated approach of pyrite morphology and multiple geochemical proxies was used to determine the mechanism of organic accumulation in the organic rich sediments many redox proxies including pyrite framboid size distribution c s fe relation ships iron speciation and 34 s values of pyrite suggest deposition beneath the dysoxic bottom water which evolved into a more oxic water body when the organic poor limestones were deposited however the coincidence of increased abundance of total organic carbon toc with increased ba and mo contents in dicates that organic matter accumulation was controlled mainly by primary productivity these data indicate that increased organic accumulation resulted mainly from higher organic carbon export with increased nutri ent flux during superimposed sea level rises of different orders this in turn could have increased the oxygen consumption by respiration of microorganisms and organic matter decay leading to the depletion of oxygen in the water columns furthermore the rapid sedimentation rate further limited bioturbation and organic matter decomposition facilitating the preservation of buried organic matter

deep marine tidal bottom currents and their reworked sands in modern and ancient submarine canyons abstract submarine canyons provide a unique setting for tidal processes to operate from shallow marine to deep marine environments in modern canyons current meter measurements at varying water depths 46 4200 m show a close correlation between the timing of up and down canyon currents and the timing of semi diurnal tides these tidal bottom currents in submarine canyons commonly attain maximum velocities of 25 50 cm s based on core and outcrop studies of modern and ancient deep marine deposits it is proposed here that sand mud rhythmites double mud layers climbing ripples mud draped ripples alternation of parallel and cross laminae sigmoidal cross bedding with mud drapes internal erosional surfaces lenticular bedding and flaser bedding can be used to interpret deposits of deep marine tidal currents this approach is an alternative to the conventional approach in which most deep water traction structures e g climbing ripples and cross bedding would be attributed to deposition from turbidity currents underwater photographs show active mass flows i e slides slumps grain flows and debris flows in modern canyons box cores taken from modern submarine canyons e g la jolla california and conventional cores and outcrops of ancient canyon fill facies oua iboe pliocene nigeria and the annot sandstone eocene oligocene se france contain deposits of both tidal processes and mass flows this facies association in the rock record can be used as a criterion for recognizing submarine canyon settings in a channel mouth environment deep marine tidal deposits are likely to develop elongate bars that are aligned parallel to the channel axis within the channel whereas turbidites are more likely to develop depositional lobes that are aligned perpendicular to channel axis turbidite depositional lobes are much larger than the channel width whereas tidal sand bars are much smaller than the channel width therefore the wrong use of a turbidite lobe model with sheet geometry in lieu of a tidal bar model with bar geometry will result in an unrealistic overestimation of sandstone reservoirs in deep water exploration

maximizing information from fine grained sedimentary rocks an inclusive nomenclature for mudstones abstract a simple nomenclature for fine grained sedimentary rocks is proposed based on sedimentary structures present and abundance of all materials forming more than 10 of rock volume irrespective of their origin allochthonous autochthonous and diagenetic a mudstone sedimentary rock that comprises 50 grains 90 clay silt and sand bearing clay rich mudstone 50 to 90 clay 10 to 50 sand 10 to 50 silt and calcite ce ment calcareous nannoplankton and clay bearing mudstone all components 10 to 50 textural information can and should be incorporated into this scheme by prefixing the rock name with descriptions such as bioturbated and thin bedded such a nomenclature is necessary to fully describe variability within fine grained sedimentary rocks that hitherto have typically been described using selected constituents of varying significance such as total organic carbon fissility parting spacing ray signature and lamination using the inclusive nomenclature proposed here will improve opportunities to compare all fine grained sediments aid interpretation of depositional and diagenetic controls of variability and enable these rocks to be more easily integrated into basin scale facies models

depositional controls on mudstone lithofacies in a basinal setting implications for the delivery of sedimentary organic matter deep water mudstones from ancient epicontinental settings are significant repositories for organic matter but the detailed temporal variations of and controls on the abundance and type of organic matter om is little studied using micro petrographic and geochemical data from late mississippian mudstones of the widmerpool gulf uk the processes that delivered fine grained sediment to this basin during a glacioeustatic sea level cycle are interpreted from detailed lithofacies analysis seven primary lithofacies are identified from core which show specific and systematic variations in total organic carbon toc content and bulk carbon isotope composition of organic material 13corg during sea level highstands thin bedded carbonate bearing mudstones are the dominant facies deposited contain up to 6 6 toc average 4 6 1 3 and have mean 13corg of 28 5 0 9 during phases of lower sea level thin bedded silt bearing clay rich mudstones with up to 4 1 toc average 2 3 0 8 mean 13corg 28 2 1 0 were interbedded with more organic lean graded silt bearing mudstones and sand bearing silt rich mudstones average toc 1 7 0 6 derived from turbidity currents the latter mean 13corg 26 2 0 7 are closely linked to significant proportions of terrestrial plant material while some rare plant debris and sand bearing mudstones produced from debris flows have more than 7 0 toc and 13corg 26 0 the 13c values of wood fragments ranged from 27 1 to 24 0 and therefore the 13corg is interpreted as a function of the ratio of marine and terrestrial organic matter more negative values in the carbonate bearing and the clay rich mudstones indicate marine planktonic algae whereas the least negative values reflect greater contribution of terrestrial plant material the data suggest that the marine conditions prevailed and supported marine planktonic algae throughout different sea level stages marine om was delivered to the sea floor by continuous hemipelagic settling whereas terrestrial om was delivered by sediment density flows variations in bioproductivity and dilution by siliciclastics influenced the burial rate of marine om organic rich mudstones preserved in these marine basins are potential hydrocarbon source rocks especially as unconventional shale gas reservoirs detailed microtextural and compositional analysis coupled with rigorous geochemical parameters as used in this study are important for the understanding of the source rock potential of basinal mudstones and of fine grained organic rich sediments in general

hydrographic conditions of the devono carboniferous north american seaway inferred from sedimentary mo toc relationships abstract deepwater anoxia developed widely within a series of silled intracratonic basins in north america during the middle devonian to early carboniferous but the hydrographic factors contributing to this development are virtually unknown the present study demonstrates that the degree of enrichment of strongly hydrogenous elements such as molybdenum mo in the organic rich shales that accumulated in these basins has the potential to provide information about paleohydrographic conditions most of the study units 49 of 55 exhibit significant positive covariation between elemental mo and toc concentrations yet there is substantial variation in the statistical parameters that define these relationships specifically the regression lines characterizing mo toc covariation have slopes m ranging from 2 to 65 10 4 although a majority of the study units yield m values between 10 and 25 10 4 the parameter m exhibits systematic stratigraphic variation within individual basins and geographic variation among basins suggesting that mo toc relationships were controlled by slowly evolving watermass characteristics of the devono carboniferous north american seaway a recent study of modern anoxic silled basins algeo t j lyons t w 2006 mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions paleoceanography 21 pa1016 doi 10 1029 2004pa001112 demonstrated that m is closely linked to the degree of restriction of the subpycnoclinal watermass as reflected in aqueous mo concentrations mo aq and deepwater renewal times dw these relationships reflect control of sedimentary mo enrichment by both the amount of sedimentary organic matter i e host phase availability and the concentration of aqueous mo i e source ion availability when applied to black shales of the devono carboniferous north american seaway these relationships permit both qualitative and quantitative inferences regarding the degree of restriction of deepwaters in cratonic basins and the evolution of hydrographic conditions through time black shales associated with early stages of sea level rise commonly exhibit low m values 1000 yr higher sea level stands resulted in more open marine conditions and enhanced deepwater renewal leading to deposition of black shales with m values up to 65 equivalent to mo aq 70 of the normal seawater concentration and dw

analysis of a longitudinal ripple from the nova scotian continental rise abstract a longitudinal ripple was obtained in a box core taken from the nova scotian continental rise in july 1982 soft brown mud comprising 1 5 10 sand 60 silt and 35 of m clay forms the 5 cm high and 40 cm wide ripple a maximum thickness of 8 cm of this mud under the crest thinning to 2 cm on the ripple s flank overlies stiff muddy foram ooze the vane shear strength of the brown mud is 0 4 kpa whereas that of the ooze is 4 kpa x radiographs show the mud to contain many fine burrows and a few larger ones as well as winnowed horizons rich in foraminifera of both benthonic and planktonic origin gentle wet sieving of the sand fraction on board ship showed the sand fraction to contain very few faecal pellets thus it appears unlikely that bedload movement played a large part in formation of the ripple rapid initial deposition from a concentrated suspension is suggested to have formed the structure but this was followed by periods of erosion to yield winnowed horizons and further rebuilding with material deposited from suspension radiochemical data 234 th and 210 pb and x radiographs suggest intense particle mixing d b 90 cm 2 yr 1 and rapid sediment deposition 1 5 cm month 1 thus it is possible that the bedform and associated structures are destroyed and recreated on a time scale of a few months

lithofacies and sequence stratigraphy of the barnett shale in east central fort worth basin texas ten barnett shale lithofacies have been recognized in a 223 ft 68 m long core from johnson county texas eight of these lithofacies match those previously identified in the main producing area of the newark east barnett shale field in the northern part of the fort worth basin but two new lithofacies have been identified in this core resedimented spiculitic mudstone lithofacies and lag deposits both of which are indicative of a relatively higher energy environment and downslope resedimentation of shallower water deposits the recognition of cyclical stacking patterns of the lithofacies condensed sections css and transgressive surfaces of erosion were the keys to establishing the sequence stratigraphic framework in these fine grained rocks which consists of seven stratigraphic intervals in the lower barnett shale and nine stratigraphic intervals in the upper barnett shale spectral gamma ray uranium and thorium logs aided in this objective and are recommended for future sequence stratigraphic studies of these and other shales the sequence stratigraphic framework reveals that the lower barnett shale in this area was deposited mainly in a low energy relatively deep water environment somewhat far from a terrigenous source area which probably lies to the northwest by contrast the upper barnett shale was deposited in an oxygenated shallower water environment which had a source area from the west and southwest sides of the basin the higher frequency of sea level fluctuation during development of the upper barnett shale most probably indicates periodic tectonic activity perhaps associated with a structural high that was susceptible to sea level fluctuations alternatively it could have resulted from the onset of glaciations in gondwanaland during this time this higher frequency may indicate that the upper barnett is chesterian in age because cyclicity was higher than during the osagean and meramecian stages if so there may be more high frequency cycles than recognized in this core siliceous sponge spicules are more common in this core than in more northerly cores so more brittle facies might prevail in the southern part of the fort worth basin high gamma ray log responses which are caused by a high total organic carbon and or in situ phosphate minerals are commonly found in css and can be used for regional correlations however high gamma ray phosphatic deposits that have been resedimented to downslope positions by sediment gravity flows are an exception to the previous statement correlation of the barnett stratigraphic intervals now provides a north to southeast stratigraphic framework along the fort worth basin relative hydrocarbon potential rhp is an organic geochemical parameter applied to this core and found to provide an indicator of marine transgressions and regressions we recommend continued testing and use of the rhp parameter for high frequency sequence stratigraphic analysis of unconventional gas shales

fossil contourites a critical review abstract despite three decades of study there is still great controversy over the recognition and interpretation of fossil contourites exposed in ancient series on land in order to best examine this problem we briefly review the evidence from modern systems including the many examples of cenozoic contourites that have been recovered from dsdp odp drilling on major drifts in the present day oceans the range of contourite facies described from both deep water 2000 m and mid water 300 2000 m drifts are mostly fine grained bioturbated and homogeneous often with a distinct bedding cyclicity and with some coarser grained sandy contourites developed under higher energy bottom currents there are also a number of current controlled sediment bodies that have formed in outer shelf upper slope settings 50 300 m under the influence of counter currents underflows and major surface currents these are not considered contourites sensu stricto but may be mistaken as such in ancient examples the most commonly described fossil contourites in the literature have been interpreted by the authors concerned as bottom current reworked turbidites however a critical review suggests that these are the facies most subject to misinterpretation and many of the sediments claimed as fossil contourites are almost certainly fine grained turbidites whereas others were more likely formed under outer shelf upper slope current systems there remain very few ancient examples that are more closely comparable to modern contourites these include the cretaceous talme yafe formation in israel the ordovician jiuxi drift in china and parts of the paleogene lefkara formation cyprus and the neogene misaki formation in japan we present a set of possible criteria for the recognition of fossil contourites and bottom current reworked turbidites

submarine transitional flow deposits in the paleogene gulf of mexico gravity driven flows on the seafloor are the largest yet least well understood sediment transport agents on earth recent exploration wells in ultradeep basins have revealed the presence of large sandy submarine fan systems of enigmatic facies types many hundreds of kilometers from paleocoastlines these sedimentary deposits often defy conventional turbidite or debrite interpretations having a character suggestive of deposition from flows with transient turbulent laminar rheologies in the wilcox formation gulf of mexico inferred transitional flow deposits have distinctive stratigraphic stacking patterns from fine grained debrites to coarser grained turbidites the vertical sequence of beds is here inferred to reflect the longitudinal bed distribution in response to lobe progradation and demonstrates a transition from well mixed turbulent flow to progressively more rheologically stratified flow and eventually to fully laminar flow the progressive development of internal rheological boundaries resulted in a high concentration but fluidal basal layer and an upper quasi laminar layer with an overriding sheared dilute turbidity current the long runout of the flows is linked to their high silt and clay content it is most likely flow expansion at the channel lobe transition that drives flow transformation this process based model may be applicable to many deep water settings and provides a framework within which to interpret the stratigraphic and spatial distribution of these complex deposits

changes in marine productivity and redox conditions during the late ordovician hirnantian glaciation abstract changes in marine productivity and redox conditions during the end ordovician hirnantian glaciation and ordovician silurian transition were investigated through mo isotope and major and trace element analyses of the wangjiawan hubei province and nanbazi guizhou province sections from the yangtze platform of south china katian shales of the wufeng formation which yield the graptolites dicellograptus complanatus dicellograptus complexus and paraorthograptus pacificus were deposited under euxinic conditions at both localities as shown by high mo ef u ef and 98 mo values a major sea level regression during the hirnantian glaciation resulted in shallowing and a shift toward better oxygenated conditions within the yangtze sea as well as deposition of thin bedded siliceous sediments calcirudite debris flows and limestone turbidites of the kuanyinchiao formation the base of which correlates with the first phase of the end ordovician mass extinction the termination of the hirnantian glaciation at the top of the kuanyinchiao formation was associated with a major sea level transgression a rapid expansion of euxinia in the yangtze sea as documented by a return of high mo ef u ef and 98 mo values and the second phase of the mass extinction during which the cool adapted hirnantian fauna went extinct the long term cooling trend of the middle and late ordovician which culminated in the hirnantian glaciation was driven by enhanced burial of organic carbon as documented by 13 c carb 13 c org and 34 s py records increased organic carbon burial was linked to high rates of marine productivity as shown by high toc and biogenic ba concentrations especially at the deeper less restricted wangjiawan locale producing the hice hirnantian isotopic curve excursion 13 c carb excursion the locus of organic carbon burial during the hirnantian crisis shifted to deeper water environments that were located outside the study region the relatively rapid onset and termination of the hirnantian glaciation were probably due to crossing of tipping points in the late ordovician climatic oceanic system

mudstone lithofacies in the kimmeridge clay formation wessex basin southern england implications for the origin and controls of the distribution of mudstones abstract lithofacies analysis has been undertaken on a suite of apparently monotonous organic rich mudstones from the upper jurassic kimmeridge clay formation kcf in the wessex basin southern england using a combination of hand specimen description whole rock geochemistry optical petrography and electron optical petrography five lithofacies have been identified these are clay rich mudstones silt rich mudstones nannoplankton rich mudstones laminated mudstones and concretionary carbonates these facies can be distinguished from one another on the basis of physical sedimentary structures and the relative proportions of allochthonous autochthonous and diagenetic components in each all five of the kcf lithofacies studied were deposited in a marine shelf environment below fair weather wave base but in relatively shallow water close to storm wave base deposition occurred in regions where sand and other coarse clastic allochthonous debris were not being supplied and the bottom waters varied from oxic to anoxic the main factors influencing the development of the five facies were distance from source area primary productivity bottom water anoxia absolute bathymetry clastic dilution and local sediment accumulation rates specifically the clay rich mudstones were deposited in regions farthest down the sediment transport paths commonly in areas by passed by the main sediment supply and beneath surface waters of relatively low primary productivity in contrast the silt rich mudstones were deposited in more proximal areas closer to the source of the sediment in regions where surface productivity and sediment accumulation rates were much higher the nannoplankton rich mudstones accumulated beneath regions where productivity in the surface water layers was fairly high dominated by coccolithophoroid production and the supply of clastic sediment was insufficient to significantly dilute the autochthonous fraction of the sediment unlike the other facies laminated mudstones were deposited in areas where the bottom waters were anoxic surface productivity was enhanced and local sediment accumulation rates were high the concretionary carbonates were precipitated by diagenetic processes in areas where sediment accumulation rates were very low these facies descriptions have enabled a detailed sedimentological study of the kimmeridge clay formation to relate depositional and diagenetic processes directly to the facies present thereby allowing classical facies analyses to be undertaken on apparently homogeneous mudstone successions

origin of longitudinal triangular ripples on the nova scotian continental rise since the recognition of current produced bedforms in the deep ocean attempts have been made to predict direction intensity and variability of abyssal flow from the nature of sea floor irregularities see refs 1 3 longitudinal triangular ripples ltrs are inter mediate scale bedforms 20 cm high metres long that are becoming recognized as important and geographically widespread predictors of bottom current flow i describe here recent sea floor photographs of ltr fields on the lower continental rise off nova scotia which show that the bedforms develop in fine grained cohesive sediment with an alignment parallel to the regional contours and to mean current direction an observational model for ltr formation is proposed wherein ltrs are deposited initially as tails behind large sea floor biological mounds and are subsequently constructed and propagate in the direction of mean current by sediment transport oblique to the bedform axis this transport is induced by short term currents that deviate from mean current direction and cause formation of a separation bubble on one side or the other of the ltr crest

a sequence stratigraphic framework for the upper devonian woodford shale permian basin west texas criteria for recognizing stratigraphic sequences are well established on continental margins but more challenging to apply in basinal settings we report an investigation of the upper devonian woodford shale permian basin west texas based on a set of four long cores identifying sea level cycles and stratigraphic sequences in an organic rich shale the woodford shale is dominated by organic rich mudstone sharply overlain by a bioturbated organic poor mudstone that is consistent with a second order eustatic sea level fall interbedded with the organic rich mudstone are carbonate beds chert beds and radiolarian laminae all interpreted as sediment gravity flow deposits bundles of interbedded mudstone and carbonate beds alternate with intervals of organic rich mudstone and thin radiolaria rich laminae defining a 5 10 m 16 33 ft thick third order cyclicity the former are interpreted to represent highstand systems tracts whereas the latter are interpreted as representing falling stage lowstand and transgressive systems tracts carbonate beds predominate in the lower woodford section associated with highstand shedding at a second order scale chert beds predominate in the upper woodford section responding to the second order lowstand additional variability is introduced by geographic position wells nearest the western margin of the basin have the greatest concentration of carbonate beds caused by proximity to a carbonate platform a well near the southern margin has the greatest concentration of chert beds resulting from shedding of biogenic silica from a southern source a well in the basin center has little chert and carbonate here third order sea level cycles were primarily reflected in the stratigraphic distribution of radiolarian rich laminae

characteristic trace fossil associations in oxygen poor sedimentary environments the sedimentologic record of oxygen poor depositional environments typically includes trace fossils produced by deposit feeding organisms we propose an oxygen controlled trace fossil model in which increasing oxygen concentration of interstitial water in sediment parallels a transition from fodinichnia dominated through pascichnia dominated to domichnia dominated trace fossil associations in certain places such as parts of the late paleozoic oquirrh basin in utah this model provides a reasonable alternative to the more traditional depth controlled model of trace fossil distribution

evidence for high energy events and shallow water deposition in the chattanooga shale devonian central tennessee usa abstract the upper devonian chattanooga shale of central tennessee a classical black shale was deposited in an epicontinental setting west of the appalachian foredeep its finely laminated and highly carbonaceous nature is commonly interpreted to indicate deposition in comparatively deep and stagnant water interbeds of bioturbated greenish gray shale indicating oxygenated bottom waters are commonly ascribed to pycnocline fluctuations however laminated fine sand and silt and hummocky cross stratification hcs at the base of some of these beds indicates interaction of storm waves with the seabed and suggests that greenish gray shale beds are post storm mud drapes other interesting features are inclined undulose erosion surfaces that are conformably overlain by shale beds sets of inclined shale beds that suggest low angle cross bedding and clearly and uniformly developed alignment of clay particles magnetic fabric studies these observations show that the seabed was at times subject to prolonged erosion by bottom currents erosion surfaces agitation and reworking by storm waves hcs and greenish gray shale beds and sediment transport by long lived bottom currents particle alignment the epicontinental sea setting and the presence of hcs and other storm produced features suggest a relatively shallow water depth possibly only a few tens of meters together with abundant evidence of variably strong bottom currents and bioturbation of black and gray shale beds this suggests that abundant planktonic organic matter production rather than stagnant bottom waters are the primary cause for black shale formation

sedimentological and ichnological characterization of the middle to upper devonian horn river group british columbia canada insights into mudstone depositional conditions and processes below storm wave base abstract the middle and upper devonian horn river group in northeastern british columbia canada consists predominantly of organic rich mudstones that are typically described as black shales this stratigraphic unit has seen substantial exploration and development for natural gas during the last decade although black shales such as the horn river group have historically been interpreted as deposited in anoxic deep water basins detailed sedimentological and ichnological analyses of eleven horn river group cores indicate that the depositional conditions varied significantly with respect to paleoenvironments redox conditions and physical processes resulting in distinctive sedimentary facies this study integrates data on lithology and physical and biogenic sedimentary structures from detailed core descriptions combined with total organic carbon content to better understand depositional processes and conditions ten mudstone lithofacies and three lithofacies associations are identified massive mudstones and pyrite rich mudstones display very rare planar lamination and graded beds and scarce bioturbation bi 0 1 and are interpreted to represent anoxic waters below storm wave base swb with conditions of relatively low to moderate energy heterolithic laminated and more bioturbated lithofacies are interpreted to represent oxygenated waters below swb with relatively high energy conditions overall bioturbation intensity varies between moderate to intense bi 3 6 where these lithofacies are not intensely bioturbated oxygenated lithofacies show combinations of well preserved physical sedimentary structures including horizontal parallel lamination soft sediment deformation double mud drapes graded beds and current ripples a third lithofacies association represents conditions intermediate between anoxic and oxygenated lithofacies associations mainly based on local changes in the ichnological characteristics these lithofacies show either intense or sparse bioturbation bi 4 6 or bi 0 1 respectively depending on the core location possibly indicating local changes in the depositional conditions and processes e g variations in the oxygen content and or sedimentation rate they can also be found in thick anoxic and oxygenated deposits these lithofacies display intervals of faint lamination amalgamated current ripples and normally graded bedding the cores collectively display significant spatial and stratigraphic heterogeneity in lithology sedimentary structures and bioturbation that are related to relative water depth oxygen content sediment input and deep water currents we interpreted bioturbation intensity to vary mainly as a function of oxygen content related to proximity to the basin margin and sea level fluctuations although secondary stress conditions e g nutrient content and sedimentation rate may also be important unbioturbated and massive fabrics represent anoxic to dysoxic conditions current generated structures are present mainly in the central and distal parts of the basin and are interpreted to represent the presence of contour currents in the proximal parts of the basin laminated and heterolithic units are more common and more bioturbated than in the central and distal basin this study thus can provide significant insights into other shale basins that show similar lateral and vertical variations integration of multidisciplinary studies particularly sedimentology ichnology and total organic carbon aids in understanding and modeling the complexity of these systems

monitoring the atlantic meridional overturning circulation the rapid climate change programme rapid has established a prototype system to continuously observe the strength and structure of the atlantic meridional overturning circulation moc at 26 5 n here we provide a detailed description of the rapid moc monitoring array and how it has evolved during the first four deployment years as well as an overview of the main findings so far the rapid moc monitoring array measures 1 gulf stream transport through florida strait by cable and repeat direct velocity measurements 2 ekman transports by satellite scatterometer measurements 3 deep western boundary currents by direct velocity measurements 4 the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the mid atlantic ridge and 5 barotropic fluctuations using bottom pressure recorders the array became operational in late march 2004 and is expected to continue until at least 2014 the first 4 years of observations april 2004 april 2008 have provided an unprecedented insight into the moc structure and variability we show that the zonally integrated meridional flow tends to conserve mass with the fluctuations of the different transport components largely compensating at periods longer than 10 days we take this as experimental confirmation of the monitoring strategy which was initially tested in numerical models the moc at 26 5 n is characterised by a large variability even on timescales as short as weeks to months the mean maximum moc transport for the first 4 years of observations is 18 7 sv with a standard deviation of 4 8 sv the mechanisms causing the moc variability are not yet fully understood part of the observed moc variability consists of a seasonal cycle which can be linked to the seasonal variability of the wind stress curl close to the african coast close to the western boundary fluctuations in the gulf stream and in the north atlantic deep water nadw coincide with bottom pressure variations at the western margin thus suggesting a barotropic compensation ongoing and future research will put these local transport variations into a wider spatial and climatic context

minor and trace element and re os chemistry of the upper devonian woodford shale permian basin west texas insights into metal abundance and basin processes the trace and minor element and re os geochemistry of the upper devonian woodford shale are analyzed in order to characterize elemental abundances to identify associations among trace elements and to constrain paleoceanographic conditions and depositional processes this organic carbon rich mudstone in the permian basin west texas is a major source of hydrocarbons in the basin and is coeval with many other upper devonian shales in north america the woodford lacks enrichment in many trace metals only mo u s and se are significantly enriched other redox sensitive elements are depleted or similar to average shale composition including pb bi cr ti cu zn co and v elements associated with granitic sources such as rare earths th ce and tio2 are also depleted relative to average shale this appears to be related to be a source control a strong basin reservoir effect is noted among several redox sensitive elements including mo cu and ni which largely accounts for the depletion dilution by biogenic silica had an additional effect on metal concentrations multivariate factors analysis identified associations between elements including groupings of rare earth elements elements enriched in granitic crust silica varying antithetically with elements in carbonate minerals organic carbon mo and u v phosphate fe and s noteworthy among the results are the different behavior of redox sensitive elements suggesting different precipitation mechanisms or varying dependence on reservoir effects a strong redox effect is noted in the toc ptot ratio at approximately the frasnian famennian boundary indicating an abrupt transition to an anoxic column boundary that coincides with a short term significant fall in sea level this suggests that anoxia was induced by isolation of the basin from the global ocean however with the exception of the uppermost famennian initial 187os 188os values determined from re os geochronology for the permian basin are similar to correlative sections of the appalachian and peace river basins of north american and the rhenohercynian basin of europe this indicates that although the permian basin became restricted during the upper devonian and early mississippian ocean connectivity remained between regional and global basins

shelf slope exchanges associated with a steep submarine canyon off calvi corsica nw mediterranean sea a modeling approach a three dimensional unsteady nonlinear high resolution model is used to investigate the impact of the calvi canyon nw corsica steep topography on the shelf slope exchanges as well as on the circulation in the calvi bay in homogeneous winter and early spring conditions a double coordinate system is considered in order to represent adequately the high depth gradients within the canyon the studied region is under the influence of the west corsica current flowing northeastward along the nw corsican coast right bounded flow model results show that the circulation in the calvi bay is determined by flow modifications in the canyon area the mean horizontal flow is deviated southwestward upstream of the canyon to form an anticyclonic gyre in the western part of the calvi bay within the canyon the circulation is cyclonic leading to an offshore flow downstream of the canyon around the canyon rim the cross shelf currents become important indicating that this region acts as a transition zone of high exchange between nearshore and offshore areas furthermore the canyon topography generates high downwelling upwelling and downsloping upsloping velocities responsible for an intense vertical transport of material in the area numerical runs are performed for typical prevailing wind conditions the wind is responsible for a drastic increase of cross shore transports between the bay and the canyon area 3 4 times larger than in the no wind case sw winds induce a further enhancement of cross shelf exchanges whereas the effect of n ne winds is to reduce exchange at the shelf break apart from the canyon head where an intense offshore flow occurs within the canyon high vertical velocities are shown to be associated with high cyclonic vorticity which is enhanced reduced by the n ne sw wind event a comparison between model results and measured distributions of nitrate and chlorophyll a concentrations in the area shows the role played by this specific hydrodynamics as a strong constraint on the coastal pelagic ecosystem

a new estimate of the global 3d geostrophic ocean circulation based on satellite data and in situ measurements abstract a new estimate of the global ocean 3d geostrophic circulation from the surface down to 1500 m depth surcouf3d has been computed for the 1993 2008 period using an observation based approach that combines altimetry with temperature and salinity through the thermal wind equation the validity of this simple approach was tested using a consistent dataset from a model reanalysis away from the boundary layers errors are less than 10 in most places which indicate that the thermal wind equation is a robust approximation to reconstruct the 3d oceanic circulation in the ocean interior the surcouf3d current field was validated in the atlantic ocean against in situ observations we considered the andro current velocities deduced at 1000 m depth from argo float displacements as well as velocity measurements at 26 5 n from the rapid mocha current meter array the surcouf3d currents show similar skill to the 3d velocities from the glorys mercator ocean reanalysis in reproducing the amplitude and variability of the andro currents in the upper 1000 m high correlations are also found with in situ velocities measured by the rapid mocha current meters the surcouf3d current field was then used to compute estimates of the atlantic meridional overturning circulation amoc through the 25 n section showing good comparisons with hydrographic sections from 1998 and 2004 monthly averaged amoc time series are also consistent with the rapid mocha array and with the glorys mercator ocean reanalysis over the april 2004 september 2007 period finally a 15 years long time series of monthly estimates of the amoc was computed the amoc strength has a mean value of 16 sv with an annual resp monthly standard deviation of 2 4 sv resp 7 1 sv over the 1993 2008 period the time series characterized by a strong variability shows no significant trend

unburrowed mudstones may record only slightly lowered oxygen conditions in warm shallow basins unbioturbated mudstones and highly bioturbated silty and sandy mudstones from the late albian of alberta canada are characterized by their ichnological foraminiferal and geochemical signatures a comparison of these data sets is undertaken to isolate the dissolved oxygen do conditions that led to the preservation of unbioturbated mudstones versus highly bioturbated silty and sandy mudstones highly diverse and abundant benthic foraminiferal assemblages coupled with conclusive geochemical signatures indicate that unbioturbated mudstones were deposited under oxic bottom waters the paucity of bioturbation in these rocks is attributed to the persistence of low oxic conditions 5 do 2 mg l 1 at the seafloor comparable to the present day gulf of mexico we assert that unbioturbated mudstone should not automatically be attributed to oxygen deficiency 2 mg l 1 instead it may reflect oxygenation sufficient to support benthic microfauna foraminifera but insufficient to sustain a diverse ecosystem of macrofauna burrowing fauna moreover we propose that the distribution of unburrowed mudstones deposited below low oxic waters is predictable a paucity of bioturbation is normal in shallow marine below fair weather wave base to 200 m water depth deposits of subtropical to tropical ocean basins and or semienclosed seaways

episodic euxinia in the changhsingian late permian of south china evidence from framboidal pyrite and geochemical data abstract a multiproxy study of a new upper permian lower triassic section xiaojiaba in sichuan province china documents large changes in marine productivity redox conditions and detrital input prior to the latest permian mass extinction marine productivity as proxied by total organic carbon content toc biogenic sio 2 and excess barium displays a long term decline through most of the changhsingian stage late late permian culminating in very low values around the permian triassic boundary concurrently redox proxies including pyrite framboid 34 s py mo auth and u auth and c org p document a shift from suboxic to dysoxic oxic conditions that was interrupted by several episodes of benthic euxinia and detrital siliciclastic proxies al hf nb and rees suggest an increased flux of weathered material from land areas the long term changes in productivity redox conditions and terrigenous detrital fluxes were probably caused by a regional sea level fall across the south china craton on the other hand the brief euxinic episodes occurring during the late permian had oceanographic causes probably related to the transient upward expansion of the chemocline at the top of the oceanic oxygen minimum zone these euxinic episodes may have been harbingers of the more widespread anoxia that developed concurrently with the latest permian mass extinction and that may have played a major role in triggering the largest biotic crisis of the phanerozoic

pyrite framboid study of marine permian triassic boundary sections a complex anoxic event and its relationship to contemporaneous mass extinction size analysis of pyrite framboids has been undertaken on epicontinental permian triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia mid paleolatitude sections from the margins of the boreal spitsbergen greenland and neotethyan oceans western australia reveal intense anoxia throughout the permian triassic boundary interval with euxinic conditions frequently developing and dysoxia encountered even in relatively shallow water settings above storm wave base at equatorial paleolatitudes weakly oxygenated dysoxic conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition although euxinia was rare western and eastern tethyan locations re veal a complex and unstable redox history anoxia in the hindeodus praeparvus zone was replaced by oxygenated facies in the permian triassic boundary interval h changxingensis to h parvus zones oxygen poor deposition returned during the succeeding isarcicella isarcica zone the more persistent and intense development of oxygen restriction in cooler water mid paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of permian triassic bound ary anoxia in higher paleolatitudes the ben thic invertebrate extinctions occurred during a prolonged phase of oxygen poor deposition while in equatorial tethyan locations benthic losses occurred at the end of the fi rst anoxic phase in the late h praeparvus zone

bedform velocity matrix the estimation of bottom current velocity from bedform observations a wide variety of bedforms both depositional and erosional in origin has been recognized on the deep seafloor and attributed to the influence of bottom currents these range in scale from those visible in bottom photographs centimeter to decimeter to those recorded with seafloor bathymetric imaging meter to kilometer in many cases it has been possible to provide some quantification of substrate grain size and flow velocity responsible for each bedform type we have synthesized both our own and published data in order to present a bedform velocity matrix which facilitates the estimation of bottom current velocity based on bedform type despite imperfections we believe this to be a valuable model for assessing strength and variability of bottom currents that can have a significant influence on the siting of submarine cables pipelines and other seafloor installations

discovery of agglutinated benthic foraminifera in devonian black shales and their relevance for the redox state of ancient seas abstract agglutinated foraminifera are benthic organisms that occur in marginal marine to bathyal environments though some taxa can live in oxygen deficient environments they require at least some oxygen in order to persist at the seafloor the discovery that they occur widely in late devonian black shales has a bearing on the boundary conditions required for episodes of extensive carbon sequestration in marine sediments and their connection to atmospheric composition and global climate devonian black shales of the eastern us have been studied extensively to determine the fundamental controls on carbon burial and a range of mechanisms has been proposed finding agglutinated benthic foraminifera in these black shales refocuses the debate about their origin and points to limitations of earlier models

porosity characteristics of the devonian horn river shale canada insights from lithofacies classification and shale composition abstract this study evaluates pore systems of the horn river shale in western canada sedimentary basin from lithofacies classification of core samples to micro scale pore structure investigation samples from the middle and upper devonian horn river shale sequence were examined by core description porosity measurement sem and tem imaging of ion milled samples and nitrogen adsorption analysis in order to develop a better understanding of the controls of organic and inorganic rock constituents on porosity development and pore microstructure five primary shale lithofacies were identified by hand core and thin section analyses massive mudstones massive mudstones with pyrite streaks laminated mudstones bioturbated mudstones and carbonates porosity ranges from 0 62 to 12 04 and shows wide variation between different lithofacies massive mudstones and pyritic mudstones with high total organic carbon toc content have the highest porosity whereas bioturbated mudstones and carbonates with low toc content have the lowest porosity sem and tem images suggest that several kinds of sites for porosity development are present including organic matter pyrite framboids clay platelets quartz rims carbonate grains and microfractures a general positive relationship between toc and porosity indicates that a large proportion of pores are developed in organic matter results from the nitrogen adsorption analysis suggest that samples with more organic matter tend to develop smaller pores thus while porosity development is a combined function of organic matter mineral components fabric and fractures it is most affected by organic matter concentration the muskwa formation and the evie member have more gas storage capacity as they primarily consist of massive mudstones and pyrite rich mudstones showing the best porosity the otter park member has lower porosity which may relate to the fact that its lithofacies mainly consists of laminated mudstones and bioturbated mudstones

algal blooms and marine snow mechanisms that enhance preservation of organic carbon in ancient fine grained sediments abstract combined petrographic and geochemical methods are used to investigate the microfabrics present in thin sections prepared from representative organic carbon rich mudstones collected from three successions the kimmeridge clay formation the jet rock member of the whitby mudstone formation and the pebble shale and hue shale this study was initiated to determine how organic carbon rich materials were being delivered to the sediment water interface and what happened to them after deposition prior to deep burial analyses of the fabrics present shows that they exhibit many common attributes in particular they are all 1 highly heterogeneous on the scale of a thin section 2 organized into thin beds the organomineralic aggregates present in these mudstones are interpreted to be ancient examples of marine snow this marine snow likely formed in the water column particularly during phytoplankton blooms and was then transported rapidly to the seafloor the existence of the thin beds with homogenized tops and an in situ infauna indicates that between blooms there was sufficient oxygen and time for a mixed layer to develop as a result of sediment colonization by diminutive organisms using either aerobic or dysaerobic metabolic pathways these textures suggest that the constituents of these mudstones were delivered neither as a continuous rain of sediment nor were the bottom waters persistently anoxic in addition the presence of thin lags and sharp based beds suggests that the seafloor was being episodically reworked during deposition these fabrics indicate that conditions in the water columns and at the seafloors while these rocks were being deposited were very dynamic and episodic fluxes of high concentrations of organic carbon to the seafloor during phytoplankton blooms likely enhanced preservation of organic carbon

an overview of canadian shale gas production and environmental concerns abstract production of hydrocarbons from canadian shales started slowly in 2005 and has significantly increased since natural gas is mainly being produced from devonian shales in the horn river basin and from the triassic montney shales and siltstones both located in northeastern british columbia and to a lesser extent in the devonian duvernay formation in alberta western canada other shales with natural gas potential are currently being evaluated including the upper ordovician utica shale in southern quebec and the mississippian frederick brook shale in new brunswick eastern canada this paper describes the status of shale gas exploration and production in canada including discussions on geological contexts of the main shale formations containing natural gas water use for hydraulic fracturing the types of hydraulic fracturing public concerns and on going research efforts as the environmental debate concerning the shale gas industry is rather intense in quebec the utica shale context is presented in more detail

a near uniform fluctuation of ocean bottom pressure and sea level across the deep ocean basins of the arctic ocean and the nordic seas across the arctic ocean and the nordic seas a basin wide mode of ocean bottom pressure and sea level fluctuation is identified using satellite and in situ observations in conjunction with a global ocean circulation model and its adjoint the variation extends across the interconnected deep ocean basins of these semi enclosed arctic seas collectively called the arctic mediterranean with spatially near uniform amplitude and phase the basin wide fluctuation is barotropic and dominates the region s large scale variability from sub monthly to interannual timescales the fluctuation results from bifurcating coastally trapped waves generated by winds along the continental slopes of the arctic mediterranean and its neighboring seas including the north atlantic ocean the winds drive ekman transport across the large bathymetric gradients forcing mass divergence between the shallow coastal area and the deep ocean basins and creating ocean bottom pressure anomalies of opposite signs in the two regions the anomalies rapidly propagate away as barotropic coastally trapped waves with the coast and continental slope as respective boundaries the waves subsequently bifurcate at the shallow straits connecting the arctic mediterranean with the rest of the globe the straits transmit the shallow anomalies but not the deep variations thereby inhibiting the anomalies mutual cancelation by geographically separating the two anomalies that enter the deep arctic basins equilibrate uniformly across the domain characterized by a homogeneous depth integrated planetary potential vorticity distribution the potential vorticity s steep gradient that borders the basins shields the region from neighboring shallow variations giving rise to the observed spatially confined fluctuation compensating anomalies outside the arctic adjust similarly across the rest of the globe but are comparatively negligible in amplitude because of the global ocean s larger area relative to that of the deep arctic mediterranean the study from a technical perspective illustrates the utility of a model s adjoint in identifying causal mechanisms underlying a complex system