organic carbon burial rate and the molybdenum proxy theoretical framework and application to cenomanian turonian oceanic anoxic event 2 1 in this study the controls on organic carbon burial and molybdenum accumulation in ancient strata are investigated through an integration of biogeochemical modeling and data analysis critical aspects of the study are employment of a biogeochemical model for organic matter degradation to explore the controls on pore water sulfide generation and authigenic molybdenum accumulation and use of accumulation rate data for mo oc caco3 fe and ti to reconstruct organic matter remineralization processes the model results form a conceptual framework for the interpretation of primary production estimates and geochemical burial fluxes calculated on the basis of a high resolution orbital timescale for the cenomanian turonian c t oceanic anoxic event 2 interval in the western interior basin the results of this study suggest that the strong correlation between source rock development and intervals of transgression in the geologic record such as the c t could reflect a confluence of biogeochemical processes within sediments that obviates the need for large magnitude changes in primary production levels or oceanographic conditions such as prolonged periods of stable water column stratification

are time and temperature the only constraints to the simulation of organic matter maturation abstract confined pyrolysis hydrous pyrolysis and high pressure hydrous pyrolysis were performed with various samples toarcian shale and kerogen woodford shale and kerogen manakam coal and under different experimental conditions in order to test the effects of pyrolysis variables on the simulation of maturation of organic matter results show that i experimental time and temperature are not exchangeable parameters as suggested by first order kinetic law models ii increasing confining pressure 300 1300 bars in gold cell experiments performed on woodford samples has a limited influence on the reduction rate of the oil potential the tsom total soluble organic matter yield and the structure of the polars iii the presence of excess liquid water 0 100 weight in confined pyrolysis experiments does not significantly influence organic matter maturation however comparisons with classic hydrous pyrolysis 200 weight water could indicate major differences in timing and composition of the tsom bitumen expelled fraction as well as of the solid residue it appears that excess water is not necessary to simulate organic matter maturation when the system is sufficiently confined hydrous pyrolysis conditions low partial pressure of products delay woodford kerogen conversion in addition results concerning the mahakam coal suggest that the structure of the organic matter plays an important role concerning the water effect iv increasing water pressure in hydrous conditions 220 1300 bars drastically lowers and delays woodford kerogen maturation quantitative analysis of the water produced during confined pyrolysis and comparison of the extent of aromatization in hydrous and confined pyrolysis suggests that two competing hydrogen transfer mechanisms occur during organic matter pyrolysis this study shows that additional parameters must be defined when comparing the results of the experimental simulation of organic matter maturation

pt group metal anomalies in the lower mississippian of southern oklahoma four iridium pt group elements abundance anomalies have been found within a stratigraphic span of 3 m in the lower mississippian of oklahoma in ascending order the first anomalies occur at the top of the woodford shale ir 0 25 ppb pt 48 ppb os 7 5 ppb and au 18 ppb the anomalies occur just below a redox boundary and we suspect that the enriched elements were precipitated from sea water that contacted the organic and sulfide rick black shale two more anomalies occur in the welden limestone the lower one weak and the upper one strong ir 0 42 ppb pt 50 ppb os 0 075 ppb and au 0 14 ppb the excess ir and pt also co as and ni might have been enriched from sea water by bacteria at these two horizons a 70 cm thick interval of excess heavy siderophiles occurs in the overlying caney shale the interval contains the following peak concentrations ir 0 56 ppb pt 150 ppb os 0 51 ppb co 725 ppm and ni 1450 ppm these elements vary in proportion to the al clay content and we suspect that they were carried in with detrital material from erosion of ultramafic source rocks we found no evidence of microspherules or shocked mineral grains in any of these anomaly zones

a tale of shales the relative roles of production decomposition and dilution in the accumulation of organic rich strata middle upper devonian appalachian basin abstract a new consensus on the processes responsible for organic carbon burial in ancient epeiric seas has emerged more firmly grounded in the uniformitarian framework of modern oceanography and biogeochemistry this consensus recognizes the interdependent roles of sedimentation primary production and microbial metabolism in favor of earlier end member models e g production vs preservation in this study one of the classic stratigraphic sequences upon which the preservation end member was based is re interpreted in light of this new consensus the study employs an extensive new sedimentological biogeochemical database from cores drilled in western new york the database spans over 500 m and 15 my of devonian deposition in the appalachian basin and provides a framework for comparative study of organic matter burial the major conclusions are 1 few organic rich units were deposited under pervasive anoxic sulfidic water columns 2 establishment and breakdown of seasonal thermoclines on annual or longer timescales were the predominant mode of stratification and 3 under such conditions remineralization of bio limiting nutrients may have played a key role in organic matter burial by creating a eutrophication pump this pump may have augmented an already rising nutrient inventory such that productivity levels exceeded the threshold required for development of suboxic to anoxic conditions in sediments and episodically in bottom waters a final conclusion asserts that the master variable for organic matter accumulation was relative sea level change which exerted influence on clastic dilution preservation and production processes sea level rise events led to sediment starvation and organic carbon concentration in distal basin sediments as well as to decreased effectiveness of seasonal mixing and thus longer build up intervals for remineralized nutrients episodic mixing of nutrient enriched bottom waters led to enhanced production ultimately increased clastic sediment delivery and water column mixing during relative sea level fall diluted surface sediment organic content such that respiratory demand could be met by increased oxygen supply thus terminating deposition of strata enriched in organic carbon

detection of natural weathering of upper mcalester coal and woodford shale oklahoma u s a abstract natural weathering refers to the natural oxidation of organic and inorganic matter in rocks at the surface and in the shallow subsurface the objective of this study is to apply routine geochemical analyses including organic petrography to coal and shale samples extending from the weathered to unaltered zones to illustrate the effects of weathering on organic matter in coal and shale some significant observations from the upper mcalester coal and the woodford shale are 1 a sulfate index si using sulfur form analysis data that reveals the transformation of pyrite to sulfate minerals is a very sensitive weathering indicator it increased in weathered samples 2 rock eval pyrolysis data such as hydrogen index hi and oxygen index oi are very sensitive to weathering oi hi increased in weathered samples 3 vitrinite reflectance decreased in weathered samples and 4 petrographic signs of weathering include microfractures pitted surface dark reaction rims and high relief sulfate index and petrographic signs of weathering should be used on surface and shallow subsurface rock samples as an indication of the extent of weathering the validity of other analyses can then be evaluated accordingly

rhenium and molybdenum enrichments in sediments as indicators of oxic suboxic and sulfidic conditions of deposition abstract the trace elements re and mo both behave conservatively in seawater yet are strongly enriched in reducing sediments their potential for authigenic enrichment above crustal concentrations is greater than for many other elements due to the high ratio of metal sw metal crust we present sedimentary re and mo data from box and multi cores spanning a range of redox conditions from well oxygenated sites to locations with substantial sulfide concentrations at the oxic sites re and mo as expected accumulate at concentrations close to their crustal abundances re shows substantial enrichment in suboxic absence of o 2 and h 2 s sediments of the sea of japan in sediments within the oxygen minimum of the pakistan margin as well as in sediments underlying the sulfide bearing waters of the black sea and saanich inlet re enrichment occurs in these cores just below the depths of fe and u reduction only in the sediments underlying the sulfidic waters of the black sea and saanich inlet is there substantial authigenic mo accumulation absence of re and mo enrichments in sediment trap samples from the sulfide bearing basins suggests that the addition of both metals occurs at or below the sediment water interface the re and mo concentration profiles are modeled to hindcast the removal depth of re and mo in the sediments which along with the re mo ratio determine whether oxic suboxic or sulfidic conditions were present in the water column or in the sediments in the past using this approach historical redox conditions can be inferred even in environments such as continental margins where a substantial lithogenic component can obscure authigenic enrichments of other metals

oxygenation of ediacaran ocean recorded by iron isotopes abstract the increase in atmospheric oxygen during the late neoproterozoic era ca 800 542 ma may have stimulated the oxygenation of the deep oceans and the evolution of macroscopic multicellular organisms however the mechanism and magnitude of neoproterozoic oxygenation remain uncertain we present fe isotopes fe species and other geochemical data for two sections of the doushantuo formation ca 635 551 ma deposited after the nantuo glacial episode in the yangtze gorge area south china it is highlighted that highly positive 56 fe values reflect a lower oxidation rate of fe ii aq under ferruginous conditions and in turn near zero 56 fe values indicate oxidizing conditions our study suggests that during the deposition of the bottom of member ii of the doushantuo formation the shallow seawater was oxic but the deep water was characterized by ferruginous conditions which is consistent with a redox chemical stratification model subsequent anoxic conditions under shallow seawater represented by positive 56 fe and negative 13 c carb excursions should be ascribed to the upwelling of fe ii aq and dissolved organic carbon doc rich anoxic deep seawater the oxidation of fe ii aq and doc rich anoxic deep seawater upon mixing with oxic shallow water provides an innovative explanation for the well known negative 13 c carb excursions enc2 and positive 56 fe excursions in the middle of doushantuo formation meanwhile the upwelling fe ii aq and doc rich anoxic deep seawater could increase photosynthetic activity the balance between oxygen consumption and production was most important criteria for the oxygenation of early ediacaran ocean and diversity of eukaryotic organisms

black shale deposition and faunal overturn in the devonian appalachian basin clastic starvation seasonal water column mixing and efficient biolimiting nutrient recycling integrated geochemical data suggest that black shale deposition in the devonian geneseo formation of western new york was initiated by the coincidence of siliciclastic starvation and the intensification of seasonal water column stratification and mixing once established however black shale deposition was maintained through efficient recycling of biolimiting nutrients which enhanced primary productivity recycling efficiency was achieved through a positive feedback loop of oscillating benthic redox conditions that enhanced n and p regeneration from sediments sustained high primary productivity by returning nutrients to the photic zone during mixing and ensured a downward flux of organic matter that drove or enhanced the episodic development of benthic anoxia during stratification this feedback was ultimately disrupted by rising siliciclastic influx which diluted organic matter and restored benthic redox stability the abrupt overturn of diverse long standing appalachian basin marine communities may have been the result of trophic resource destabilization during geneseo deposition

eutrophication by decoupling of the marine biogeochemical cycles of c n and p a mechanism for the late devonian mass extinction the late devonian mass extinction was unusually protracted and ecologically selective with preferential diversity losses among reefbuilding organisms and tropical shallow water faunas in general we have investigated the link between the extinction s unique characteristics and changes in biogeochemical cycling through analyses of the 13 c and c n p atomic ratios of organic matter buried across the kellwasser horizons in western new york state each horizon is characterized by 1 a long term 4 5 excursion in 13 c 3 of which occurs within the horizon and 2 a dramatic increase in the burial ratios of c n p from values of 100 15 1 to an average of 5000 170 1 on the basis of these results we propose that 1 increased efficiency of biolimiting nutrient recycling resulting from cyclic water column stratification and mixing promoted eutrophication during kellwasser deposition in new york and 2 the isotope excursions represent the composite effect of long term global organic c burial and local changes in photosynthetic c isotope fractionation related to nutrient availability this eutrophication model forges a mechanistic link between proposed late devonian climatic cooling and the selective demise of taxa likely to have been narrowly adapted to oligotrophic conditions

paleosalinity determination in ancient epicontinental seas a case study of the t oae in the cleveland basin uk abstract the early jurassic toarcian oceanic anoxic event t oae was marked by deposition of organic rich sediments and a pronounced negative carbon isotope excursion across the northwest european sea nwes representing a signal that was stronger regionally than globally various models for the t oae have been proposed some focusing on general atmospheric oceanic controls to reflect its global character and others emphasizing local or regional factors to account for its strong expression in the nwes in this study we evaluate watermass dynamics of the early jurassic cleveland basin uk during the t oae using a combination of paleosalinity proxies b ga sr ba and s toc these proxies suggest that brackish conditions existed prior to onset of the t oae with a shift to nearly freshwater conditions during the t oae reflecting a large increase in terrestrial runoff due to a stronger hydrological cycle possibly combined with shallowing of the marginal sill of the cleveland basin through sea level fall following the t oae basinal salinity conditions first returned to brackish and then gradually shifted to fully marine this hydrographic history accounts for low mo concentrations in t oae sediments of the cleveland basin demonstrating control by watermass restriction and local rather than global aqueous mo drawdown these findings demonstrate the importance of local hydrographic controls on the sedimentary expression of the t oae the more general significance of this study is that it highlights the need for application of paired salinity and redox proxies in order to correctly interpret paleoenvironmental variations in marginal marine basins

tracing bottom water redox conditions during deposition of lower and upper jurassic organic rich sedimentary rocks in the lusitanian basin portugal insights from inorganic geochemistry abstract the lower jurassic agua de madeiros am fm and vale das fontes vf fm formations and the upper jurassic cabacos formation cab fm are considered the most important units with petroleum source rock potential in the lusitanian basin and the likely sources for its widespread hydrocarbon occurrences nonetheless the bottom water redox conditions during their deposition remain debatable to resolve this controversy we investigated whole rock inorganic geochemical data of the most significant organic rich levels of the am vf and cab fms cropping out at basin scale significant variations in toc ts and redox sensitive elements contents and their ratios are evident within and between the organic rich levels of the studied units a positive covariation between primary productivity proxies toc enrichment and paleo redox proxies for the lower jurassic units clearly suggest an interdependence between enhanced primary productivity organic matter accumulation and bottom water redox conditions for the am fm the paleo redox proxies indicate that the black shales deposition took place beneath bottom waters that ranged from suboxic to strongly euxinic conditions with a clear predominance of the latter a toc threshold of 6 7 wt clearly separates samples deposited under suboxic to anoxic conditions from those deposited under true euxinic conditions and is interpreted as the minimum amount of organic matter om accumulation within sediments required to sustain h2s production at rates that outpaced its consumption through precipitation of sulphides and or om sulphurization allowing the diffusion of h2s to the bottom waters for the vale das fontes fm the paleo redox proxies suggest a prevalence of suboxic to anoxic bottom waters despite all black shales displaying toc contents greater than the above threshold the less reducing conditions relative to the am fm euxinic black shales are attributed to i a larger proportion of continental om ii lower reactivity of the om reaching the sediment water interface decreasing oxygen consumption and iii higher availability of reactive iron increasing the buffer effect to h2s produced through om remineralization by sulphate reducing bacteria both units display mo ef vs u ef covariation patterns that deviate from the field of sediments deposited under unrestricted open marine conditions towards higher mo enrichment relative to that of u indicating an accelerated transport of aqueous mo to the sediments consistent with the operation of a metal oxyhydroxide particulate shuttle linked to mn and fe redox cycling within the water column in a weakly restricted basin the mo cot regression line slope indicates a moderate degree of bottom water mass restriction with mo aq concentration of 60 70 of the present day seawater value and bottom water renewal times of 10 20 years akin to the present day cariaco basin the redox conditions of the cab fm organic rich levels are dependent on the location of the depositional environment in the basin with deposition taking place beneath oxygenated bottom waters at cabo mondego and under suboxic conditions at vale de ventos and pedrogao the latter denoting a larger degree of oxygen depletion than the former in this context the overall potential for om preservation should increase from cabo mondego to vale de ventos and pedrogao

global events of the late paleozoic early devonian to middle permian a review abstract the late paleozoic early devonian to middle permian was an interval of profound changes in earth surface systems reflected in dynamic interplay among the biosphere hydrosphere atmosphere and geosphere major events transpired including the colonization of landmasses by vascular plants the assembly of the supercontinent pangea two first order mass extinctions the frasnian famennian and devonian carboniferous boundary events and the most severe icehouse climate mode of the phanerozoic the late paleozoic ice age lpia the goals of the present review are 1 to summarize major global developments in climate oceanography and paleobiology during the late paleozoic 2 to examine the roles of land plant evolution global tectonics and large igneous province magmatism in driving these developments and 3 to serve as an introduction to the 23 contributions to this special issue of palaeogeography palaeoclimatology palaeoecology indicating how they advance our knowledge of various scientific issues related to these developments

ragged edge of the herrin no 11 coal western kentucky abstract the herrin no 11 coal in western kentucky is normally a bright banded high vitrinite high sulfur coal three sites have been found where the coal deviates from the expected appearance in union county a site known only from a literature description the upper two thirds of the coal was described as a cannel in ohio county a thin truncated section of the herrin coal has a greater abundance of liptinite and inertinite rich microlithotypes towards the top of the seam the various microlithotypes were frequently found in brecciated assemblages in hopkins county the herrin coal was found to be largely a coarse breccia of oxidized macerals cemented by calcite a marine limestone was present as a parting within the coal each occurrence represents the edge of the coal the sites varied in the energy of the environment and perhaps also in proximity to marine waters

molybdenum accumulation in cariaco basin sediment over the past 24 k y a record of water column anoxia and climate molybdenum mo concentrations in a sediment core from the cariaco basin on the venezuelan continental shelf can be partitioned between a marine fraction and a terrigenous fraction the accumulation rate of the marine fraction of mo increased abruptly 15 000 calendar years ago 15 ka from 2 yr 1 to 4 g cm 2 yr 1 and then decreased abruptly at 9 ka the accumulation rate remained high throughout this 6 k y period but exhibited maxima at 15 14 and 12 5 ka corresponding in time to meltwater pulse ia into the gulf of mexico and the onset of the younger dryas cold event respectively the marine fraction of mo is interpreted in terms of redox conditions of bottom water as dictated by both the flux of settling organic matter and bottom water residence time correspondence between geochemical extremes in this core with changes in sea level and global climate demonstrates the high degree to which this ocean margin basin has responded to the paleoceanographic regime throughout the past 24 k y

the behavior of molybdenum and its isotopes across the chemocline and in the sediments of sulfidic lake cadagno switzerland abstract molybdenum mo isotope studies in black shales can provide information about the redox evolution of the earth s oceans provided the isotopic consequences of mo burial into its major sinks are well understood previous applications of the mo isotope paleo ocean redox proxy assumed quantitative scavenging of mo when buried into sulfidic sediments this paper contains the first complete suite of mo isotope fractionation observations in a sulfidic water column and sediment system the meromictic lake cadagno switzerland a small alpine lake with a pronounced oxygen sulfide transition reaching up to h 2 s 200 m in the bottom waters or about 300 m total sulfide s 2 h 2 s hs s 2 we find that mo behaves conservatively in the oxic zone and non conservatively in the sulfidic zone where dissolved mo concentrations decrease from 14 nm to 2 8 nm across this transition dissolved mo in the upper oxic waters has a 98 mo oxic 0 9 0 1 which matches that of the riverine input 98 mo river 0 9 0 1 in the deeper sulfidic waters a subaquatic source delivers mo at 1 55 0 1 but the dissolved mo is even heavier at 98 mo sulfidic 1 8 sediment traps in the sulfidic zone of the lake collect particles increasingly enriched in mo with depth with 98 mo values significantly fractionated at 0 8 to 1 2 both near the chemocline and in the deepest trap suspended particulates in the sulfidic waters carry lighter mo than the ambient dissolved mo pool by 0 3 1 5 sedimentary mo concentrations correlate with total organic carbon and yield mo levels which are two orders of magnitude higher than typical crustal values found in rocks from the catchment area solid phase mo in the sediment shows a slightly positive 98 mo trend with depth from 98 mo 1 2 to 1 4 while the pore waters show dramatic enrichments of mo 2000 nm with a relatively light isotope signature of 98 mo 0 9 1 0 these data are explained if mo is converted to particle reactive oxythiomolybdates in the sulfidic waters and is fractionated during removal from solution onto particles isotope fractionation is expressed in the water column despite the high sulfide concentrations because the rate of mo removal is fast compared to the slow reaction kinetics of thiomolybdate formation however elemental and isotopic mass balances show that mo is indeed quantitatively removed to the lake sediments and thus the isotopic composition of the sediments reflects sources to the sulfidic water this efficient mo drawdown is expected to occur in settings where h 2 s is very much in excess over mo or in a restricted setting where the water renewal rate is slow compared to the mo burial rate we present a model for the mo isotope fractionation in sulfidic systems associated with the slow reaction kinetics and conclude that quantitative removal will occur in highly sulfidic and restricted marine systems

from greenhouse to icehouse nitrogen biogeochemistry of an epeiric sea in the context of the oxygenation of the late devonian atmosphere ocean system abstract the late devonian emergence of extensive arborescent terrestrial ecosystems produced changes in the earth s atmosphere and climate that resulted in substantial changes to the biogeochemistry of marine ecosystems the biogeochemistry of nitrogen in epeiric seas was particularly susceptible to alteration because of its dependence upon the series of redox mediated reactions that comprise the marine n cycle in order to explore the impact of climate change on n biogeochemistry in a late devonian epeiric sea we sampled a core from the appalachian basin that spans the interval from the greenhouse climate at the base of the famennian period to glacial conditions near its conclusion based upon stable isotope analysis of n c and s as well as elemental analysis of n c p s and fe we contend that two distinct biogeochemical regimes obtained during the contrasting climates the greenhouse regime featured low seawater o2 and ph that served to significantly curtail the oxidation of ammonia i e nitrification resulting in an ammonium dominated water column and low sediment 15n values the greenhouse also featured more extensive recycling of c n and p in contrast the higher seawater o2 and ph of the icehouse regime permitted nitrification in the water column resulting in a nitrate dominated system and higher sediment 15n values we conclude that nitrification was the key component of the n cycle that differentiated the two climate biogeochemical regimes

ichnofabrics and chemostratigraphy argue against persistent anoxia during the upper kellwasser event in new york state abstract organic rich strata coeval with bioevents of varying magnitudes characterize global devonian sedimentary successions the upper kellwasser ukw black shale depositional event is coincident with the largest pulse of diversity loss within the marine late devonian mass extinction and has been shown to be an ecologically critical turnover for shallow water species marine anoxia euxinia is widely thought to be an important and ubiquitous driver of this biotic crisis though the duration intensity and global extent of these environmental conditions during the ukw event are not well constrained we characterized redox conditions during deposition of the ukw in the northern appalachian basin to constrain local variability and relative magnitude of dissolved oxygen fluctuations we used a combination of proxies relating to the bottom waters water column and photic zone to compile an integrated picture of basinal oxygen dynamics our multi faceted approach combines trace fossil evidence for faunal activity at the sediment water interface with inorganic and organic geochemical proxies for redox conditions within the water column minor biological disruptions to laminated sedimentary fabric indicate at least intermittent oxygenation of the bottom waters during deposition of the ukw albeit in a low dissolved oxygen seafloor setting trace metal proxies mo mn u and v and fe mineral speciation provide compelling evidence for a water column experiencing intermittent rather than persistent anoxic euxinic conditions lipid biomarkers reinforce the interpretation of variable dissolved oxygen conditions with very low concentrations of chlorobi carotenoid biomarkers pointing to seasonal rare episodes of photic zone euxinia this integrated dataset provides evidence for local redox variability in ukw deposition and supports the likelihood that marine anoxia and euxinia were not globally persistent at the frasnian famennian boundary

palaeoenvironmental and palaeoceanographic controls on black laminated mudrock deposition example from devonian carboniferous strata alberta canada abstract sedimentological palaeontological and ichnological analyses indicate that heightened episodes of equatorial upwelling in tandem with an expanded and intensified oxygen minimum zone promoted deposition of upper famennian to lower tournaisian laminated organic rich mud rocks of the exshaw formation on the alberta cratonic platform exshaw mud rocks represent the culmination of an upper devonian transgression that commenced with deposition of open marine carbonates of the big valley formation the transgression was abruptly halted at the devonian carboniferous boundary by a rapid eustatic sea level fall and the consequent deposition of near shore marine to shelfal bioturbated siltstones and sandstones of the exshaw formation the siltstones grade into laminated organic lean mud rocks to the north in more distal offshore shelf settings these mudrocks reflect a period of low primary production but continued anoxia of bottom waters continuation of anoxic conditions resulted from development of restricted circulation in the epicontinental sea due to the establishment of a westward located physical barrier following this event was a relative sea level rise that led to deposition of black laminated mudrocks of the banff formation

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

assessing bottom water anoxia within the late devonian woodford shale in the arkoma basin southern oklahoma abstract comparing the concentration of molybdenum mo ppm and total organic carbon toc wt within sediments allows interpretation of the relative degrees of bottom water restriction within the geologic record the woodford shale is interpreted as transgressive systems tract tst grading into highstand systems tract hst the lowermost woodford preserves a mo toc signal that is consistent with a restricted basin that periodically received influxes of water consistent with rising sea levels flowing into restricted sub basins that became isolated by localized conditions the middle woodford preserves a signal that indicates an increased ventilation at the sediment water interface persisting until the maximum flooding surface the presence of phosphate nodules in the uppermost woodford suggests sufficient oxygen to retain the mo in solution and indicates active upwelling and circulation with the paleotethys it is also possible to document changing ventilation patterns non destructively within a basin by utilizing changing trends in redox sensitive trace metals mo ni and cu and an approximation of the degree of pyritization adop based on an idealized formula for pyrite fes2 this chemofacies approach produces a qualitatively similar interpretation to the changing mo toc signal and can evaluate lateral trends in bottom water ventilation where destructive sampling is not permitted distal regions preserve the greatest degree of bottom water ventilation proximal regions preserve highly variable conditions with more restricted conditions being common in the lowermost woodford shale and ventilation improving upsection interpreting changing levels of bottom water anoxia enable greater degrees of precision in targeting potential hydrocarbon resources furthermore this information improves our understanding of the changing environmental conditions of the woodford shale the framvaren fjord is a reasonable modern analog for bottom water restriction in the lowermost portion of the woodford shale the cariaco basin is a good modern analog for bottom water restriction in the middle and uppermost woodford shale

effect of sedimentary environment on the formation of organic rich marine shale insights from major trace elements and shale composition abstract sedimentary environment and redox conditions play a significant role in the formation of organic rich shale the vertical variations of major trace elements toc total organic carbon and mineral compositions were investigated for the lower silurian longmaxi typical marine shale in the upper yangtze platform south china to decipher sedimentary environment redox conditions detrital input sedimentation rate sr paleoproductivity and watermass restriction this gives insight to the effects of variations in sedimentary environment on the formation of organic rich shale the results show that the lower longmaxi formation is composed of three systems tracts tst transgressive systems tract ehst early highstand systems tract and lhst late highstand systems tract from tst to lhst the contents of toc quartz and pyrite decline steadily whereas clay minerals and carbonate show an increasing trend thus organic rich siliceous orss organic moderate mixed omms and organic lean argillaceous olas shales are dominant for tst ehst and lhst respectively due to a continues fall of the relative sea level a deep water shelf environment with anoxic condition high paleoproductivity and low detrital input in tst gradually evolves into a semi deep water environment with dysoxic oxic conditions moderate paleoproductivity and moderate detrital influx in ehst further to an environment of oxic condition low paleoproductivity and high detrital flux in lhst as evidenced by mo toc and mo u patterns orss was deposited in a moderately restricted watermass weaker than black sea which progressively evolved into an enhanced restriction degree during the deposition of omms and olas due to a fall of relative sea level major trace elements and excess silica ex sio2 concentrations illustrate that origins of quartz in the lower longmaxi shale are primarily terrigenous biogenic and authigenic smectite illitization the average proportions of ex sio2 biogenic and authigenic quartz are 52 34 24 86 and 6 57 for orss omms and olas respectively biogenic quartz is the dominant contributor to ex sio2 while the contribution of authigenic quartz is limited and the formation of the former is earlier than the latter according to the diagenetic transformation temperature as both biogenic quartz and organic matter are firmly related to the abundance and preservation of paleoorganisms anoxic condition high paleoproductivity low detrital flux and moderate restriction collectively control the high enrichment and preservation of organic matter and biogenic quartz while oxic condition low paleoproductivity high detrital flux and stronger watermass restriction are unfavorable for the enrichment of biogenic quartz and organic matter

an integrated assessment of a type euxinic deposit evidence for multiple controls on black shale deposition in the middle devonian oatka creek formation an integrated lithologic paleontologic and multi proxy geochemical study of the middle devonian oatka creek formation a black shale in the northern appalachian basin indicates that a number of different factors contributed to organic carbon rich black shale deposition conditions leading to this organic rich sedimentary deposit were ultimately controlled by a relative sealevel rise dominantly eustatic but with possible contributions from local tectonics which cut off the supply of carbonate to the basin geochemical proxy evidence such as mo ti fe ti corg spy and 34spy suggests that as sealevel continued to rise after the carbonate supply was cut off a threshold was crossed at which point conditions in the basin shifted from dominantly anoxic to dominantly euxinic anoxic sulfidic bottom waters concurrent with the shift to dominantly euxinic conditions the supply of siliciclastic sediments was cut off resulting in a condensed horizon as evidenced by the elemental ratios of si al and k fe mg and the relative concentration of eolian silt as determined petrographically and from scanning electron microscopy sediment starvation in the basin appears to have facilitated the biogeochemical re cycling of c n and p specifically the elemental ratios of c n and p and the stable carbon isotope composition of organic matter suggest that the preferential regeneration of p under anoxic conditions and of n during the oxic phase of oxic anoxic oscillation led to enhanced primary production in surface waters thereby maintaining euxinic conditions in the bottom waters through respiration of settling organic matter finally it is observed that though conditions in the basin seem to have remained consistently anoxic sulfidic for some time after the initial shift to euxinic conditions a progressive increase in siliciclastic sedimentation led to a corresponding decrease in the enrichment of various redox related elements illustrating the overriding control that sedimentation can have on geochemical proxy records

mo total organic carbon covariation in modern anoxic marine environments implications for analysis of paleoredox and paleohydrographic conditions 1 sedimentary molybdenum mo s has been widely used as a proxy for benthic redox potential owing to its generally strong enrichment in organic rich marine facies deposited under oxygen depleted conditions a detailed analysis of mo s total organic carbon toc covariation in modern anoxic marine environments and its relationship to ambient water chemistry suggests that 1 mo s while useful in distinguishing oxic from anoxic facies is not related in a simple manner to dissolved sulfide concentrations within euxinic environments and 2 patterns of mo s toc covariation can provide information about paleohydrographic conditions especially the degree of restriction of the subchemoclinal water mass and temporal changes thereof related to deepwater renewal these inferences are based on data from four anoxic silled basins the black sea framvaren fjord cariaco basin and saanich inlet and one upwelling zone the namibian shelf representing a spectrum of aqueous chemical conditions related to water mass restriction in the silled basin environments increasing restriction is correlated with a systematic decrease in mo s toc ratios from 45 5 for saanich inlet to 4 5 1 for the black sea this variation reflects control of mo s by mo aq which becomes depleted in stagnant basins through removal to the sediment without adequate resupply by deepwater renewal the basin reservoir effect the temporal dynamics of this process are revealed by high resolution chemostratigraphic data from framvaren fjord and cariaco basin sediment cores which exhibit long term trends toward lower mo s toc ratios following development of water column stratification and deepwater anoxia mo burial fluxes peak in weakly sulfidic environments such as saanich inlet owing to a combination of greater mo aq availability and enhanced mo transport to the sediment water interface via fe mn redox cycling and are lower in strongly sulfidic environments such as the black sea and framvaren fjord these observations demonstrate that at timescales associated with deepwater renewal in anoxic silled basins decreased sedimentary mo concentrations and burial fluxes are associated with lower benthic redox potentials i e more sulfidic conditions these conclusions apply only to anoxic marine environments exhibiting some degree of water mass restriction e g silled basins and are not valid for low oxygen facies in open marine settings such as continent margin upwelling systems

inorganic geochemical indicators of glacial interglacial changes in productivity and anoxia on the california continental margin abstract evidence from sediments in cores collected from within the present oxygen minimum zone omz 600 1200 m on the central and northern california margins record several episodes during the last interstadial ois 3 ca 60 24 ka of deposition of laminated sediments containing elevated concentrations of several trace elements indicative of anoxic conditions e g mo ni zn and cu the presence of abundant well preserved organic matter as well as lack of bioturbation and the presence of elevated concentrations of mo and other trace elements all support the theory that the omz in the northeastern pacific ocean was more intense possibly anoxic at several times during the late pleistocene sediments of all ages in cores from the southern california margin contain elevated concentrations of mo suggesting that this area has always had higher rates of sulfate reduction than either the central or northern california areas most of the ba in sediments in all cores collected on the upper continental slope 200 2700 m off california and southern oregon is derived from detrital clastic material and this source did not change much in time however the amount of biogenic ba did vary with time and these variations closely follow the temporal variations in organic c corg mass accumulation rate using ba and corg mass accumulation rates as proxy variables for productivity all cores show that organic productivity under the california current upwelling system was highest during ois 3 and the holocene and lowest during the last glacial interval lgi ca 24 10 ka all paleoproductivity proxy variables indicate that the southern california area has always experienced higher productivity than other areas under the california current at least over the last 50 ky

organic rich transitional facies in silled basins response to sea level change high resolution profiles of organic carbon delta sup 13 c sub org sulfur delta sup 38 s and some trace elements in cores from two silled basins kau bay indonesia and the black sea allow division of the sedimentary record into three distinct units representing a pleistocene fresh water brackish water facies unit 3 a holocene transitional facies unit 2 and a modern fully marine facies unit 1 the geochemical characteristics of these units are strikingly similar for both basins the sediments form unit 3 are characterized by the predominance of terrestrial organic matter mo and u concentrations at crustal abundance and positive delta sup 34 s values the transitional sediments unit 2 are strongly enriched in marine organic matter and mo v and u and have intermediate delta sup 34 s values sediments from the modern marine facies unit 1 are moderately organic carbon rich and slightly enriched in mo and u and have negative delta sup 34 s values the organic carbon rich sediments from unit 2 were formed by increased production during the transition from the pleistocene isolated fresh water brackish water environment to the modern open marine facies this temporarily higher productivity was caused by displacement of nutrients from the deep water into the euphotic zone owing to the gradual infilling by marine waters

erosion on an anaerobic seafloor significance of reworked pyrite deposits from the devonian of new york state abstract several devonian black shale units in new york state display conspicuous basal discontinuities marked by accumulations of exhumed and reworked pyrite nodules tubes and fossil steinkerns this coarse debris is overlain by and or interlayered with black laminated shale the most important level is the leicester pyrite member which occurs along a regional unconformity flooring black shale deposits of the basal genesee formation the detrital pyrite occurs in discontinuous lenses both on and slightly above this surface basal genesee beds geneseo shale member record westward overlap of basinal anoxic muds during a major marine transgression taghanic onlap the reworked pyrite deposit is regionally diachronous as indicated by conodont data and shingling of lenses with basal genesee beds which are successively younger from east to west pyrite chemically unstable in aerobic bottom settings was exhumed and concentrated on the sea floor during brief erosion episodes in a normally anaerobic environment lenses contain istinctive diagenetic pyrite structures e g fossil steinkerns burrow tubes derived from muds underlying the discontinuities erosional reworking of pyrite on the sea floor is shown by mechanical breakage of pyrite grains reorientation of geopetal stalactitic pyrite and compactional features plus alignment of pyritic tubes by bottom currents general absence of carbonate allochems in lenses is believed to reflect dissolution of carbonate following its exhumation episodic deep storm generated turbulence was probably important in exhuming and transporting pyrite however shoaling internal waves impinging the sediment starved basin margin slope may also have been important in scouring the bottom a model of internal wave erosion during the taghanic transgression is presented herein we feel that such erosion concentrated at or near the base of the pycnocline during a period of relative sea level rise offers a particularly good explanation for the observed juxtaposition of geneseo and other similar black shale deposits on erosional discontinuities the diachronous character of leicester lenses and associated black genesee muds above the unconformity suggests a transient rather than fixed basin axis allowing for progressive westward burial of the unconformity and assiciated remanie deposits by onlapping black muds older and younger occurrences of resedimented pyrite are briefly described from other devonian basinal units and are shown to have formed in about the same manner as the leicester reworked pyrite is believed to be common although seldom recognized in phanerozoic sediment starved basinal settings moreover detrital pyrite analogous to that described herein probably awaits discovery in certain modern marine basins

seawater as the source of minor elements in black shales phosphorites and other sedimentary rocks many of the minor elements in seawater today have a concentration depth profile similar to that of the biologically essential nutrients no 3 and po3 4 they show a relative depletion in the photic zone and enrichment in the deep ocean the difference between their surface and deep ocean values normalized to the change in po3 4 approaches the average of measured minor element p ratios in marine plankton although individual analyses of the latter show extreme scatter for a variety of reasons despite this scatter in the minor element analyses of plankton agreement between the two sets of data shows unequivocally that an important marine flux of many minor elements through the ocean is in the form of biogenic matter with a composition approaching that of plankton this interpretation is further supported by sediment studies particularly of sediments which accumulate in shelf slope environments where biological productivity in the photic zone is exceptionally high and organic carbon contents of the underlying sediment elevated the interelement relations observed for some of these sediments approach the average values of plankton these same interelement relations are observed in many marine sedimentary rocks such as metalliferous black shales and phosphorites rocks which have a high content of marine fractions e g organic matter apatite biogenic silica and carbonates many previous studies of the geochemistry of these rocks have concluded that local hydrothermal activity and or seawater with an elemental content different from that of the modern ocean was required to account for their minor element contents however the similarity in several of the minor element ratios in many of these formations to minor element ratios in modern plankton demonstrates that these sedimentary rocks accumulated in environments whose marine chemistry was virtually identical to that seen on continental shelf slopes or in marginal seas of the ocean today the accumulation of the marine fraction of minor elements on these ancient sea floors was determined largely by the accumulation of organic matter settling from the photic zone and with a composition of average plankton a second marine fraction of minor elements in these rocks accumulated through precipitation and adsorption from seawater the suite of elements in this fraction reflects redox conditions in the bottom water as determined by bacterial respiration for example high mn high cr v and high mo concentrations above those which can be attributed to the accumulation of planktonic matter characterize accumulation under bottom water oxidizing denitrifying and sulfate reducing conditions respectively

pitfalls of normalization of marine geochemical data using a common divisor abstract normalization of trace element contents of sediment through division by the content of an immobile element usually aluminum is common practice in marine geochemical studies this might appear to be a simple way of correcting for dilution by sedimentary phases barren of a particular trace element for instance carbonates or silica and for comparison with its content in a standard clay or shale the purpose of this paper is to revive the awareness of the pitfalls of this practice by giving numerical examples of the often unexpected results of normalization taking a statistical perspective it is first shown that uncorrelated variables acquire spurious correlations when normalized but normalization can also increase decrease change sign of or even blur the correlations between unmodified variables next a number of realistic scenarios are worked out to show that the correlations between normalized element contents still suffer from the closure effect only in a few simple cases it is possible to extract from the normalized data realistic estimates of trace element contents in distinct sedimentary phases such as organic matter this is ascertained from data on copper contents in sediment from the black sea and arabian sea when the coefficient of variation i e standard deviation divided by the mean of the aluminum data is relatively low and much lower than for the original values of the trace elements comparisons of correlations can equally well or even better be made on the basis of the unmodified values then the comparison of trace element data with their values for standard shales is discussed the inherent problem is that the composition of the commonly used standard shale and consequently the reference values of normalized elements are not necessarily representative of the local or regional sediments in the study area also this method falls short of identifying the processes responsible for enrichment or diminution in trace element contents finally consideration is given to some aspects of a proper use of al normalization

pelagic molybdenum concentration anomalies and the impact of sediment resuspension on the molybdenum budget in two tidal systems of the north sea the seasonal dynamics of molybdenum mo were studied in the water column of two tidal basins of the german wadden sea sylt romo and spiekeroog between 2007 and 2011 in contrast to its conservative behaviour in the open ocean both losses of more than 50 of the usual concentration level of mo in seawater and enrichments up to 20 were observed repeatedly in the water column of the study areas during early summer mo removal by adsorption on algae derived organic matter e g after phaeocystis blooms is postulated to be a possible mechanism mo bound to organic aggregates is likely transferred to the surface sediment where microbial decomposition enriches mo in the pore water first 98 95mo data of the study area disclose residual mo in the open water column being isotopically heavier than momo mean ocean molybdenum during a negative mo concentration anomaly whereas suspended particulate matter shows distinctly lighter values based on field observations a mo isotope enrichment factor of e 0 3 has been determined which was used to argue against sorption on metal oxide surfaces it is suggested here that isotope fractionation is caused by biological activity and association to organic matter pelagic mo concentration anomalies exceeding the theoretical salinity based concentration level on the other hand cannot be explained by replenishment via north sea waters alone and require a supply of excess mo laboratory experiments with natural anoxic tidal flat sediments and modelled sediment displacement during storm events suggest fast and effective mo release during the resuspension of anoxic sediments in oxic seawater as an important process for a recycling of sedimentary sulphide bound mo into the water column

multiple controls on the preservation of organic matter in devonian mississippian marine black shales geochemical and petrographic evidence geochemical and petrographic analysis of an interval of black shales between the huron shale member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian suggests that multiple controls influenced the accumulation of organic matter stratigraphic trends were determined following detailed analysis of a core from the central appalachian basin d6 montgomery county ky specifically c s fe relationships mo v v ni ni co and v cr were used to assess paleo redox conditions during sediment accumulation the role of clastic input was evaluated using ti al k al and si al and c p was used as a proxy for paleoproductivity the terrestrial to marine maceral ratio t m vitrinite plus inertinite alginite plus bituminite was used to evaluate changes in om source c s fe relationships and trace element ratios suggest anoxic conditions prevailed during deposition of much of the upper part of this interval however bottom water conditions were intermittently dysoxic during accumulation of the huron shale member and possibly dysoxic to marginally oxic during accumulation of the lowermost huron shale member productivity appears to have been an important factor in the accumulation of corg and high c p ratios are consistent with a productivity anoxia feedback mechanism in addition nutrients from increased terrestrial weathering may have contributed to enhanced productivity variations in sediment influx may also have influenced corg concentrations through sediment starvation one of the more significant observations in this work is an increase in terrestrial om inertinite and vitrinite up section which may reflect vegetative changes occurring on land during this time interval most of this increase is due to inertinite much of which appears to be fusinitic in origin and hence may be fossil charcoal this latter observation has implications for the expansion of land plants into drier niches and for late devonian atmospheric oxygen levels introduction of more resistant terrestrial om to anoxic basins may have been an important factor in the preservation of high carbon 10 intervals especially in the cleveland member of the new albany shale upper devonian famennian and the sunbury shale lower mississippian tournaisian

tectonic and eustatic signals in the sequence stratigraphy of the upper devonian canadaway group new york state we have refined the late frasnian to early famennian relative sea level curve based on detailed stratigraphic data from more than 1200 outcrops in the appalachian basin of western new york this curve is constructed from considerations of lithologies bedforms and ichnofacies we document 3 sequences and 48 parasequences in the canadaway group part of the marine component of the catskill delta complex several apparent lowstands and one transgression are localized along the syndepositionally active clarendon linden fault system we infer that these systems tracts are forced and result from interaction between fault block motion and eustatic sea level changes this detailed study thus demonstrates that sea level curves inferred from local foreland basins may have a stronger tectonic signal than formerly perceived

inverse correlation between the molybdenum and uranium isotope compositions of upper devonian black shales caused by changes in local depositional conditions rather than global ocean redox variations abstract coupled mo u isotope data from the upper devonian kettle point formation ontario canada provide a cautionary tale regarding interpretation of global ocean redox conditions using data from euxinic black shales in the gore of chatham core the kettle point black shales have high mo concentrations 48 473 g g and consistently high mo u ratios 3 times the mo u ratio of modern seawater suggesting a euxinic depositional environment these shales yield an inverse correlation r 0 89 p

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

molybdenum isotope evidence for widespread anoxia in mid proterozoic oceans how much dissolved oxygen was present in the mid proterozoic oceans between 1 8 and 1 0 billion years ago is debated vigorously one model argues for oxygenation of the oceans soon after the initial rise of atmospheric oxygen 2 3 billion years ago recent evidence for h 2 s in some mid proterozoic marine basins suggests however that the deep ocean remained anoxic until much later new molybdenum isotope data from modern and ancient sediments indicate expanded anoxia during the mid proterozoic compared to the present day ocean consequently oxygenation of the deep oceans may have lagged that of the atmosphere by over a billion years

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

pyrite and organic matter in phanerozoic normal marine shales data have been obtained from our own chemical analyses and from the literature for the concentrations of organic carbon c and pyrite sulfur s in over 600 samples of cambrian to recent normal marine shales normal marine refers to deposition in oxygenated bottom water as evidenced by the presence of benthic fossils and or indicators of bioturbation all samples were selected to minimize 1 1 loss of c and or s due to weathering at the outcrop by emphasizing the use of drill core material 2 2 analytical errors and non diagenetic effects by avoiding sediments low in c or s content such as sandstones 3 3 fe limitation of pyrite formation by avoiding limestones cherts and euxinic shales 4 4 metamorphic loss of c relative to s by avoiding rocks obviously subjected to even low grade metamorphism our results indicate that 1 there is generally a good positive linear correlation between organic c and pyrite s for normal marine shales of all ages and 2 the mean cs ratio for normal marine shales has varied over time devonian to tertiary shales exhibit mean cs weight ratios 1 8 0 5 somewhat lower than quaternary sediments meancs 2 8 this we believe is due to preferential c loss relative to s during biogenic methanogenesis plus diagenetic heating distinctly lower mean c s values for the cambrian and ordovician 0 5 0 1 cannot be explained solely in terms of diagenetic c loss and instead must represent low original ratios the low original ratios we suggest were due mainly to the absence of bacterially refractory organic matter added to the marine environment by rivers at that time because the major source of such material vascular land plants had not yet evolved this along with a possibly lower degree of bioturbation contributed to enhanced pyrite formation and preservation and thus lower early paleozoic cs ratios

genetic stratigraphy and depositional systems of the upper devonian lower mississippian price rockwell deltaic complex in the central appalachians u s a abstract rocks of the price and rockwell formations comprise the uppermost devonian lower mississippian deltaic complex in the central appalachians the price formation is dominantly marine and refers to all uppermost devonian lower mississippian rocks above either hampshire group red beds or the marine greenland gap formation and below either the greenbrier limestone group or maccrady formation red beds in the central appalachians the rockwell formation is dominantly non marine and refers to equivalent rocks in south central pennsylvania and the maryland west virginia panhandle region members of the price formation are generally equivalent to discrete genetic events price deposition was initiated in latest devonian time when a regional transgression covered delta and alluvial plain facies of the catskill deltaic complex with protected bay and strandline facies of the oswayo member in west virginia pennsylvania and western maryland farther south these transgressive facies overlie the cloyd conglomerate member a thin regressive transgressive sedimentary wedge and occur in the lower part of the sunbury shale member subsurface berea sandstone deposition corresponded to regional exposure and erosion in the outcrop belt this unconformable surface was overstepped in earliest mississippian time by a major transgression that deposited a variably thick but persistent basal transgressive sandstone during shoreface retreat sandstones that have been referred to the cussewago sandstone in northern west virginia and southwest pennsylvania are part of this basal sandstone eastward these sandstones thicken coarsen and interbed with a polymictic diamictite at the base of the rockwell formation shaly facies of the earliest mississippian transgression overlie the basal sandstone the riddlesburg shale preserves offshore and open bay facies in west virginia that grade eastward to estuarine and restricted back bar lagoon and marsh facies of a barred bay complex in south central pennsylvania and the maryland west virginia panhandle from central west virginia riddlesburg facies grade southward into basinal facies of the sunbury shale member syndepositionally active basement features the west virginia dome and tri state block were structurally positive areas in the foreland basin the tri state block caused truncation of lower mississippian marine facies in western maryland and large scale westward erosional overlap of channel fill sandstones in the upper rockwell formation the west virginia dome was also structurally positive and the basal transgressive sandstone contains phosphatic omission surfaces on the dome crest lack of subsidence caused scour and incision of riddlesburg facies by overlying deltaic facies progradation ensued with fluvial dominant shallow water deltaic systems price rockwell member in northern west virginia and marine dominant deep water deltaic facies farther south a 150 m minimum paleodepth estimate in the foreland basin is based on stratigraphic thickness in southern west virginia following a transgression near the kinderhookian osagean boundary price marine deltaic facies form a coarsening upward sequence to delta plain coals and coastal alluvial plain red beds a 35 m estimate for average storm wave base utilized tempestite proximal distal trends

the frasnian famennian boundary in central and eastern united states abstract the frasnian famennian f f boundary in the northern appalachian basin is found in the hanover shale and equivalent strata where it is locally associated with a black shale interval equivalent to the upper kellwasser interval in europe the boundary is immediately below the dunkirk huron black shale that represents the iie t r cycle transgression in the southern appalachian basin the southern edge of the cincinnati arch and the southeastern illinois basin the f f boundary is at or near the base of the gassaway member of the chattanooga shale or the morgan trail member of the new albany shale or was eroded during the iie t r cycle beginning in the middle triangularis zone in the western illinois basin grassy creek shale michigan basin lachine member of antrim shale and southern continental margin woodford shale the f f boundary is within black shale strata indicative of an earlier development of the iie t r transgression inboard of the appalachian basin or the juxtaposition of the iie t r transgression over the upper kellwasser black shale interval without significant or recognizable lithologic change

trace element behavior and redox facies in core shales of upper pennsylvanian kansas type cyclothems the black shale submember of core shales of pennsylvanian kansas type cyclothems is highly enriched in redox sensitive trace elements tes relative to the overlying gray shale submember as well as to many other modern and ancient organic rich deposits controls on trace element behavior in the black shale can be inferred from trace element enrichment factors efs relative to gray shale and the relationship of tes to total organic carbon toc most tes conformed to one of two patterns 1 mo u v zn and pb exhibited moderate efs and strong covariation with toc in samples having 10 wt toc and 2 cu ni cr and co exhibited low efs and moderate to strong covariation with toc in all samples these patterns are inferred to represent different responses to benthic redox conditions the first pattern is characteristic of tes of strong euxinic affinity i e those taken up in solid solution by fe sulfide or involved in other reactions catalyzed by free h2s and resident mainly in authigenic phases whereas the second pattern is characteristic of tes of weak euxinic affinity i e those not strongly influenced by the presence of free h2s and resident mainly in the organic carbon or detrital fractions of the sediment these inferences allowed development of a multiproxy technique for assessing redox facies in black shale samples euxinic conditions were considered to have existed if at least two of four redox indicator trace elements mo u v zn showed euxinic levels of enrichment and nonsulfidic anoxic conditions were inferred otherwise the validity of the procedure is indicated by 1 agreement among all four redox indicators for a large majority of samples 69 of 185 2 among samples yielding a mixed redox signal a systematic sequence of te enrichment v zn mo u and 3 for tes of weak euxinic affinity reduced variance among samples representing each redox facies sequential enrichment may be a response to differential redox thresholds for accumulation e g v or postdepositional remobilization of trace elements e g u and may provide a basis for finer assessment of redox conditions in low oxygen paleoenvironments than permitted by simple classification schemes the multiproxy procedure for redox facies analysis developed in this study is likely to be more reliable than widely used single proxy indicators based on trace elements e g mo authigenic u or v v ni or c s fe systematics e g s toc or dop d 2004 elsevier b v all rights reserved

ichnology of a late devonian early carboniferous low energy seaway the bakken formation of subsurface saskatchewan canada assessing paleoenvironmental controls and biotic responses abstract in spite of the high interest on the late devonian early carboniferous bakken formation as one of the most important oil plays in north america and the numerous studies carried out in this unit no ichnologic analysis has been presented yet based on conventional sedimentologic data previous studies of the bakken interpreted the unit as formed entirely under open marine conditions however integration of ichnology has been key to the identification of not only open marine but also brackish water marginal marine conditions based on the geometry of the sedimentary bodies and the sequence stratigraphic framework the brackish water interval is interpreted as an embayment with limited or intermittent connection to the open sea salinity oxygen content and storms are regarded as the most important environmental parameters that controlled the distribution and nature of the trace fossils in the bakken formation sparse bioturbation relatively low ichnodiversity and the impoverished cruziana ichnofacies characterize the marginal marine deposits suggesting stressful brackish water conditions marine deposits from the middle member in contrast are highly bioturbated with a moderate ichnodiversity and the distal cruziana ichnofacies that flourished during fully marine well oxygenated conditions there is only a slight difference between the total ichnodiversity of the open marine interval ten ichnogenera and that of the brackish water interval seven ichnogenera ichnodiversity should not be considered at face value and isolated from other aspects when evaluating stress levels in order to detect a brackish water signal lack of bioturbation in the black shale of the lower and upper members resulted from anoxic conditions the passage from anoxic lower member to well oxygenated conditions middle member was gradational as is revealed by the occurrence of oxygen deficient trace fossils at the top of the lower member finally the contrasting styles in tempestite preservation in upper offshore deposits from the lower and upper open marine intervals is attributed to variations in the intensity and frequency of storm during deposition of the highstand and transgressive deposits

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

contrasting sulfur geochemistry and fe al and mo al ratios across the last oxic to anoxic transition in the cariaco basin venezuela an abrupt transition from oxic to anoxic sulfidic euxinic marine bottom waters occurred in the cariaco basin in response to increasing productivity resulting from the late pleistocene post glacial rise in sea level and corresponding increase in surface water nutrient availability the microlaminated sediments of the euxinic interval which span the last f14 5 ky suggest a predominance of water column syngenetic pyrite formation based on 1 high pyrite sulfur spy concentrations in the surficial sediment layers 2 values for degree of pyritization dop that generally do not increase appreciably with increasing burial 3 ratios of total iron fet to al that are elevated above the continental baseline recorded in the underlying oxic sediments and 4 spy isotope trends that largely mimic the d 34 shsof the modern water column intermediate dop values in the microlaminated deposits and fet al ratios that are slightly above continental levels indicate an iron reservoir controlled by scavenging during syngenetic pyrite formation in combination with intermediate rates of fe bearing siliciclastic accumulation as predicted from the relative rates of siliciclastic delivery fet al and dop data lie between end member values observed in the modern black sea as viewed broadly fet al and dop relationships in euxinic sediments reflect the balance between syngenetic fe scavenging and temporal and spatial gradients in siliciclastic input pyrite concentrations are generally low in the underlying oxic marine deposits because of limitations in the supply of organic carbon corg however the upper 80 cm of the fe rich corg poor bioturbated sediment show evidence for a strong diffusional hsoverprint from the overlying fe limited euxinic marine environment this post glacial transition manifests in pyrite overprints that are strongly 34 s depleted relative to those in restricted presently euxinic marine settings elsewhere in the world such as the black sea where the sedimentary sequence spanning the last glacial interglacial transition begins with a shift from freshwater to corg poor oxic marine deposition and thus dominantly sulfate diffusion trends for mo al ratios in the microlaminated sediments suggest that mo is enriched by roughly two orders of magnitude above the continental levels recorded in the oxic deposits organic matter plays a role by enhancing hsproduction and or by providing a substrate for mo scavenging significant mo enrichment via diffusion into the upper portion of the bioturbated zone was not observed despite hs rich pore waters as recorded in the heavy iron sulfide overprint we have

contrasting depositional models for pennsylvanian black shale discerned from molybdenum abundances some black shales contain 1 000 ppm mo comparable to conventional ores these include mo rich pennsylvanian black shales that were deposited rapidly near shore as epeiric seas inundated peat swamps while coeval beds less enriched in mo accumulated slowly offshore concentration of mo probably resulted from retention of the metal by organic matter in acidic pore fluids characteristic of nearshore deposits thus in pennsylvanian shales where organic productivity is significant mo variations may be used to distinguish nearshore from offshore conditions enrichments in mo occur in black shales of other ages therefore a high mo content may be useful as a general criterion for nearshore environments and other conditions with strong ph gradients

enhanced trapping of molybdenum by sulfurized marine organic matter of marine origin in mesozoic limestones and shales there have been many studies devoted to trace metals and their value in assessing the paleoredox conditions of ancient marine deposition among them molybdenum mo is frequently cited as an effective proxy for sediments and sedimentary rocks recently helz et al helz g r miller c v charnock j m mosselmans j l w pattrick r a d garner c d vaughan d j 1996 mechanisms of molybdenum removal from the sea and its concentration in black shales exafs evidences geochim cosmochim acta 60 3631 3642 and adelson et al adelson j m helz g r miller c v 2001 reconstructing the rise of recent coastal anoxia molybdenum in chesapeake bay sediments geochim cosmochim acta 65 237 252 suggested that mo does not behave conservatively in the water column when h2s reaches a threshold concentration above this concentration a switch operates and mo is scavenged by forming bonds with metal rich notably iron particles sulfur rich organic molecules and pyrite in this paper mo trapping by sulfur rich organic matter om in ancient marine deposits is emphasized the following mesozoic geological formations were selected for study because of their relatively high concentration of sulfurized om the akkuyu formation turkey the calcaires d orbagnoux france and kimmeridge clay uk and its timeequivalent in boulonnais france the kashpir oil shales russia and the la luna formation venezuela the sulfur rich om is identified by either measured organic s abundance or kerogen microscope observation our results show that mo is systematically more enriched relative to the other redox sensitive sulfide forming elements studied u v ni cu zn cr and mo enrichment is positively correlated with the amount of sulfurized om but not with pyrite abundance these results illuminate the role played by sulfurized om in geologic scale mo capture and retention but they also underline the role played by reactive iron significant om sulfurization is only possible when reactive iron is limited nevertheless pyrite formation though limited could act as an initial mo trap prior to mo uptake by om that is sulfurized after the pyritization step in future paleoenvironmental reconstructions attention must be paid to this enhanced mo enrichment in the presence of sulfurized organic matter in such cases the use of mo could lead to overestimation of the reducing conditions of the depositional environment

geochemical study of organic matter rich cycles from the kimmeridge clay formation of yorkshire uk productivity versus anoxia abstract in this contribution we study two meter scale cycles from the kimmeridge clay formation cored near marton yorkshire which shows cyclic organic matter om distribution our aim is to try to understand the factors responsile for om accumulation the first cycle called lower cycle shows a total organic carbon toc content between 1 and 10 whereas the second called upper cycle shows a toc content varying between 5 and 35 the geochemical composition major elements and trace elements the organic geochemistry toc hi palynofacies and mineralogy of the sediments have been determined in both cycles the cyclicity is expressed through variations in the nature and in the relative abundance of the various types of organic matter constituents furthermore dilution effects by inorganic components of the sediment cannot account for the toc cyclicity for lower cycle the mo v and u content is low and little variable as is the intensity of the oxidation which om suffered from this indicates that variations in phytoplanktonic productivity may be held responsible for the cyclicity in steady and mildly reducing redox conditions in the upper cycle cyclicity also appears to depend on productivity but variations in the concentration of mo v and u and in the oxidation state of the om suggest the environment was temporarily more reducing it is proposed that larger amounts of h 2 s were released into marine bottom waters as a result of initial om decomposition forced the oxic anoxic boundary to rise in the water column and thus favoured om storage the main driving force for variations in the om concentration was the productivity of organic matter walled phytoplankton redox conditions of the depositional environment could have had a positive action but only by acting as a positive feedback effect

geochemical paleoredox indicators in devonian mississippian black shales central appalachian basin usa the degree of anoxia that existed during accumulation of devonian mississippian black shales in central kentucky has been debated widely in this study geochemical data were used to elucidate paleodepositional environments for these units using analyses from ten cores collected from the outcrop belt in central kentucky sulfur carbon and selected trace element relationships were compared the sunbury shale tournasian lower mississippian and the cleveland and huron members of the ohio new albany shale fammenian upper devonian show different relationships between carbon sulfur and trace elements c s fe relationships for the sunbury suggest anoxic possibly even euxinic conditions prevailed during sediment accumulation analysis of c s fe data suggests that the cleveland may have accumulated under anoxic conditions with intermittent dysoxia whereas the huron member may have accumulated under a relatively wide range of conditions from anoxic to dysoxic to possibly oxic these three units exhibit different degrees of trace element enrichment with the approximate order of enrichment relative to an average shale being mo pb zn v ni cu cr co the sunbury shows the highest levels of enrichment followed by the cleveland with the huron showing only slight enrichment for most of these trace elements differing degrees of enrichment may reflect differences in depositional environment during accumulation high mo concentrations in the sunbury generally 200 550 ppm may infer euxinic conditions prevailed during sediment accumulation the cleveland and the huron both show considerably lower mo contents averaging around 100 ppm geochemical ratios including ni co v cr and v v ni also indicate variable paleoredox conditions for these shales based on previously established thresholds v cr and ni co ratios infer at least anoxic conditions during accumulation of the sunbury anoxic to dysoxic conditions during cleveland accumulation and dysoxic to oxic conditions for the huron v v ni ratios tend to indicate consistently lower oxygen regimes than do other paleoredox indicators and this discrepancy is greatest for the huron member it is suggested that thresholds established for paleoredox indicators in previous studies should not be applied strictly but that relative differences in these indicators collectively can infer variations in the degree of anoxia in addition relationships between corg and redox elements may help elucidate the role of anoxia in om accumulation it may be concluded from this study that the devonian mississippian black shales of central kentucky accumulated under variable bottom water conditions at least anoxic conditions prevailed during accumulation of much of the sunbury shale and the upper part of the cleveland member and possibly euxinic conditions for the sunbury bottom water conditions may have been intermittently anoxic and dysoxic during deposition of the lower cleveland during accumulation of the huron member it is likely that conditions ranged from anoxic to dysoxic to marginally oxic possibly being close to normal marine conditions at times during accumulation of the lowermost huron sediments

chemical and mineralogical analysis of devonian black shale samples from martin county kentucky carroll and washington counties ohio wise county virginia and overton county tennessee u s a abstract core samples of devonian shales from five localities in the appalachian basin have been analyzed chemically and mineralogically the amounts of major elements are similar however the minor constituents organic c s phosphate and carbonate show ten fold variations in amounts trace elements mo ni cu v co u zn hg as and mn show variations in amounts that can be related to the minor constituents all samples contain major amounts of quartz illite two types of mixed layer clays and chlorite in differing quantities pyrite calcite feldspar and kaolinite are also present in many samples in minor amounts dolomite apatite gypsum barite biotite and marcasite are present in a few samples in trace amounts trace elements listed above are strongly controlled by organic c with the exception of mn which is associated with carbonate minerals amounts of organic c generally range from 3 to 6 and s is in the range of 2 5 amounts of trace elements show the following general ranges in ppm parts per million co 20 40 cu 40 70 u 10 40 as 20 40 v 150 300 ni 80 150 high values are as much as twice these values the organic c was probably the concentrating agent and the organic c and sulfide s together created an environment that immobilized and preserved these trace elements closely spaced samples showing an abrupt transition in color also show changes in organic c s and trace element contents several associations exist between mineral and chemical content pyrite and marcasite are the only minerals found to contain sulfide s in general the illite chlorite mixed layer clay mineral shows covariation with organic c if calcite is not present the enriched trace elements are not related to the clay types although the clay and organic matter are intimately associated as the bulk fabric of the rock

sequences cycles and basin dynamics in the silurian of the appalachian foreland basin abstract field stratigraphic analysis of the early and medial silurian strata of ontario new york and pennsylvania permits recognition of six major sequences reflecting 3rd order cycles in the niagaran llandoverian ludlovian of new york and adjacent regions these sequences correspond approximately to the medina lower clinton middle clinton upper clinton two sequences and lockport groups each is bounded by widespread unconformities produced by the interplay of eustatic sea level drop and local tectonic uplift in general erosional sequence boundaries and transgressive surfaces are merged with no record of the lowstand wedge each sequence is subdivisible into two to five sub sequences that are marked by sharp though generally non erosional basal discontinuities investigation of the clinton and lockport groups corroborates earlier suggestions that carbonate and siliciclassic tongues extended basinward from opposite margins synchronously in response to sea level drops analysis of the thickness and basinward extent of the progradational tongues reveals the existence of multi scale sedimentary cycles sequences and component sub sequences are correlative basinwide and are synchronous within the resolution of bio and event stratigraphy major drops in relative sea level are represented by the sequence bounding discontinutiies these surfaces are overlain by siliciclastic wedges near terrigenous source areas or winnowed carbonate pack and grainstones on the tectonically passive margin overlying highstand deposits typically shales calcareous mudstones and limestones are separated from lowstand or transgressive deposits by thin condensed intervals commonly marked by phosphatic or glauconitic material and or surfaces of maximum sediment starvation the relative highstand deposits of sequences and sub sequences are developed in relatively deep water facies and are at most slightly progradational hence most sequences and sub sequences are sharply bounded roughly upward deepening to slightly shallowing successions of strata in turn sub sequences are further divisible into widespread minor parasequences and parasequence sets probably corresponding to 6th and 5th order cycles respectively the smaller scale units 0 2 5 mthick commonly display an upward shallowing motif the nested relationship of these cycles supports the hierarchical model of transgressive regressive allocycles proposed by busch and rollins 1984 niagaran cycles discussed herein are equivalent to third fourth and fifth order cycles and are traceable circumbasinally depocenters of successive sequences and sub sequences display a pattern of eastward westward eastward basin axis migration through the silurian during early llandoverian the taconic queenston deltaic complex began to subside and the basin axis depocenter and eastern shoreline shifted eastward approximately 200 km over a 6 million year period as the basin axis migrated eastward the western basin ramp forebulge was repeatedly upwarded and eroded resulting in the generation of regionally angular unconformities at the bases of sequences ii iv and vi the pattern of unconformity greatest to the west suggests rise of the algonquin arch concomitant with eastward basin axis migration during the late llandoverian to early wenlockian the algonquin arch subsided slightly concurrently with a reversal in direction of basin axis migration during deposition of upper clinton and lockport vernon strata sequences v vi the basin axis shifted approximately 300 km back to the west eastward migration of the basin axis corresponds with a time of tectonic quiescence and probable thrust load relaxation the abrupt reversal of migration in the late llandoverian may be a signal of renewed thrusting in the hinterland at the onset of the salinic disturbance

tracing paleoredox conditions across the devonian carboniferous boundary event a case study from carbonate dominated settings of belgium the czech republic and northern france the devonian carboniferous boundary was coeval with the hangenberg crisis which is regarded as a first order mass extinction event related with large sea level changes and widespread anoxia this study aims to trace the geochemical paleoproductivity and paleoredox proxies across the devonian carboniferous carbonate dominated successions of the namur dinant basin belgium northern france and the moravo silesian basin czech republic located in the variscan rhenohercynian zone the research was focused on the distribution of oxides sio2 al2o3 fe2o3 cao na2o k2o tio2 mno and trace elements th u v zr mo zn pb ni cu measured by icp oes and icp ms respectively the enrichment factors of mo and u and their ratios were used as the main paleoredox proxies whereas the enrichment factors of zn cu pb and ni were employed to trace the paleoproductivity changes high values of zr al2o3 0 001 tio2 al2o3 0 06 and fe ti 20 and low values of al al fe mn 035 coinciding with an increase of paleoredox proxies suggest a possible volcanic and hydrothermal source of nutrients related to late devonian and early carboniferous extensional magmatism in the rhenohercynian domain although a relationship between higher paleoproductivity and enhanced continental runoff of volcanic material cannot be excluded the studied devonian carboniferous boundary sections from the namur dinant basin gendron celles ardennes quarry reveal three levels with similar vectors of mo and u enrichments the pre crisis famennian pattern is typical for weakly restricted basins with fe mn redox cycling accompanying vertical fluctuations of the oxic anoxic chemocline close to the sediment water interface with the influence of particulate shuttle the mo ef and u ef patterns corresponding to the unrestricted or weakly restricted basin with alternating suboxic to anoxic conditions are considered to represent the transgressive hangenberg black shale event the lower tournaisian mo ef and u ef patterns fall along a vector in the direction of the strongly restricted marine conditions with prevailing suboxic conditions in the moravo silesian basin lesni lom section the pre crisis famennian mo ef and u ef vector indicates an unrestricted marine trend which converges with that of restricted systems redox conditions range from suboxic to euxinic in the tournaisian mo ef and u ef oscillate between oxic and anoxic conditions and fall along a vector of strongly restricted marine conditions increased isolation of both studied basins in the early tournaisian is regarded as a reflection of a significant eustatic fall during the hangenberg crisis linked to a severe episode of the gondwana glaciation these paleohydrographic patterns have correlative potential that should be considered for a revised devonian carboniferous boundary definition

high resolution geochemistry and sequence stratigraphy of the hushpuckney shale swope formation eastern kansas implications for climato environmental dynamics of the late pennsylvanian midcontinent seaway abstract the hushpuckney shale member of the swope formation missourian stage eastern kansas is the core shale of a kansas type cyclothem formed during the late transgressive to early regressive phases of a late pennsylvanian glacio eustatic cycle coeval high frequency climato environmental dynamics of the midcontinent seaway are preserved in the kgs orville edmonds no 1a study core as centimeter scale variation in major components organic carbon authigenic sulfides and phosphate detrital siliciclastics organic macerals trace element redox proxies mo u v zn and ichnofabric features benthic o 2 levels declined sharply from the base of the black shale 0 cm went sulfidic at 4 cm and reached a redox minimum at 21 cm above this level redox potential gradually rose fluctuating between sulfidic and nonsulfidic conditions from 35 cm to the black shale gray shale contact at 52 cm onset of dysoxic conditions at that contact allowed establishment of a benthic community of soft bodied organisms comprised of deep tiered tracemakers tolerant of low o 2 conditions trichichnus and shallow tiered tracemakers favoring soupground helminthopsis or firmground substrates the zoophycos phycosiphon schaubcylindrichnus planolites association most geochemical records exhibit a low order cycle spanning the full 52 cm thickness of the black shale submember reflecting a dominant glacio eustatic control the base and top of the black shale submember record lateral migration of the pycnocline across the midcontinent shelf during the transgressive and regressive phases respectively the maximum flooding surface mfs is at 17 23 cm an interval containing the euxinic peak and characterized by high concentrations of illite representing a cratonic siliciclastic flux and terrestrial organic macerals the product of transient increases in humidity weathering rates and the export of coal swamp vegetation associated with the interglacial highstand of the swope cyclothem although a transgressive surface of maximum starvation sms cannot be confidently identified a phosphate rich regressive condensation surface at 28 34 cm records pycnoclinal weakening due to increased aridity associated with renewed southern hemisphere icesheet growth a correlative shift in dominance from terrestrial to marine derived organic macerals reflects increased upwelling of nutrient rich deepwaters and enhanced primary productivity penecontemporaneous paleogeographic and climatic factors e g semirestricted circulation monsoonal precipitation predisposed the midcontinent seaway toward sensitivity to high frequency climato environmental fluctuations which are preserved as 2 to 7 cm thick cycles in the study core the 52 cm thick black shale submember contains 12 such high order cycles which have an estimated average duration of 2 to 9 kyr implying a sub milankovitch band i e millennial scale climatic control the results of this study are relevant to the sequence stratigraphic interpretation of kansas type cyclothems the dynamics of gondwanan ice age glacio eustatic cycles and the development of boundary conditions for late pennsylvanian paleoclimate models

geochemical study of potential source rocks and crude oils in the anadarko basin oklahoma paleozoic source rocks and crude oils from the anadarko basin oklahoma have been characterized by means of a variety of organic geochemical techniques the potential source rocks investigated include the viola group sylvan shale lower mississippian limestone chester group springer formation and morrow group the woodford shale which is an important source rock in the basin and has been discussed extensively in the literature was used as a laboratory standard in this study the crude oils examined in this study were obtained from reservoir formations of various ages from throughout the basin the source rock screening analysis indicates that the lower and middle subfacies of the viola especially from the southeastern part of the basin have substantial oil generation potential the sylvan is not a source rock although the black shales in the springer and morrow have substantial oil and especially gas generation potential the results of this study support the proposal for multiple sources of oil and gas generation in the anadarko basin selected source rock and oil samples were characterized in more detail and the distributions and concentrations both relative and absolute concentrations of biomarkers in different source rocks and oils were determined the biomarker characteristics were combined with other geochemical and geological data to interpret the sources depositional environments diagenesis and catagenesis processes migration and weathering oil source rock correlations were made between source rocks and a number of crude oils based on quantitative and qualitative biomarker distributions petrographic descriptions and graptolite reflectance measurements were used to evaluate copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received november 1 1995 revised manuscript received april 8 1996 final acceptance september 13 1996 2arco international oil and gas company 2300 w plano parkway plano texas 75057 3school of geology and geophysics university of oklahoma norman oklahoma 73019

defining the nature and location of a late devonian early mississippian pycnocline in eastern kentucky the pycnocline the intermediate layer in a tripartite density stratified water column is an important element in recent explanations of the origin of anaerobic sediments dysaerobic sediments deposited where the pycnocline intersects the bottom are distinct from overlying aerobic and underlying anaerobic sediments and were used to define the position of the paleopycnocline on a late devonian early mississippian sea bottom in eastern kentucky surface and subsurface mapping of the bedford berea sequence and equivalent parts of the new albany and chattanooga shales reveals approximately coeval aerobic dysaerobic and anaerobic facies that permitted mapping of the paleopycnocline apparently the first time the actual sea bottom position of a paleopycnocline has been defined the bedford berea devonian mississippian sequence is situated between the black ohio shale devonian below and the black sunbury shale mississippian above the black shales reflect deposition in a deepening transgressive sea where anaerobic conditions were easily established and maintained the intervening bedford berea sequence however represents deposition in aerobic and dysaerobic environments during a shallowing regressive episode as deltas prograded to the south and west in eastern kentucky the gray sandstones siltstones and shales of the bedford berea sequence have been interpreted as pinching out between the black shales above and below in east central kentucky each of the above units however has a distinctive signature on gamma ray logs comparison of gamma ray logs and radioactivity profiles with corresponding cores drillers9 logs and exposures indicates that black shale equivalents are present beyond the point where the gray bedford shale pinches out this also is supported by limited biostratigraphic data this transition from gray bedford shales to black shale equivalents marks the approximate position of the ancient pycnocline and has been mapped in the subsurface and on the outcrop in eastern kentucky the ancient pycnocline closely parallels the bedford berea delta front suggesting major control by the delta the continued influx of oxygen rich sediment laden waters from the delta apparently prevented the northward and eastward migration of the pycnocline up the delta front the introduced oxygen and sediment however were effective only in breaking up the pycnocline over a distance of 25 to 40 km from the active delta fronts stratigraphic paleontologic and geographic constraints indicate that the paleopycnocline was not horizontal but sloped northeastward from shallower waters near the cincinnati arch to deeper waters off the delta fronts