control actions of sedimentary environments and sedimentation rates on lacustrine oil shale distribution an example of the oil shale in the upper triassic yanchang formation southeastern ordos basin nw china abstract oil shale is an important form of unconventional resources it is significant to determine the control factors on oil shale distribution abundant oil shale resources are hosted in the member chang 7 3 ch7 3 triassic yanchang formation in southeastern ordos basin nw china this study was conducted to investigate the sedimentary environment distribution and organic matter source of the ch7 3 oil shale by a combined study of outcrops core data organic and element geochemical indices the controlling factors of the oil shale distribution were determined by an analysis of sedimentary environments and geochemical features of the oil shale sedimentary facies analysis based on outcrops and core data indicated that the ch7 3 oil shale was deposited in lacustrine delta environments warm and moist climates and reducing conditions indicated by major and trace elements were favorable to organic matter production and preservation rock eval pyrolysis showed that the organic matter of the ch7 3 oil shale is from both lacustrine phytoplankton and terrigenous higher plants the organic matter from terrigenous higher plants was probably transported into the deep lake by gravity flows sedimentary facies and la yb n values show that the spatial distribution of oil shale was controlled by sedimentary environments and sedimentation rates in the deep lake area near to delta turbidite fan deposition systems terrestial organic matter input was bounteous and sedimentation rates were moderate which were beneficial to organic matter accumulation and preservation providing favorable conditions for oil shale formation in delta turbidite fan deposition systems high sedimentation rates led to organic matter dilution in the deep lake area far from delta turbidite fan deposition systems sedimentation rates were relatively low and organic matter was easily degraded in addition only lacustrine organic matter input with no terrestial organic matter input inhibited organic matter enrichment

origins and maturity of organic matter in mid cretaceous black shales from odp site 1138 on the kerguelen plateau abstract we have conducted elemental isotopic and rock eval analyses of cenomanian santonian sediment samples from odp site 1138 in the southern indian ocean to assess the origin and thermal maturity of organic matter in mid cretaceous black shales found at this high latitude location total organic carbon toc concentrations range between 1 and 20 wt in black to medium gray sediments deposited around the cenomanian turonian boundary results of rock eval pyrolysis indicate that the organic matter is algal type ii material that has experienced modest alteration important contributions of nitrogen fixing bacteria to the amplified production of organic matter implied by the high toc concentrations is recorded in 15n values between 5 and 1 and the existence of a near surface intensified oxygen minimum zone that favored organic carbon preservation is implied by toc tn ratios between 20 and 40 in contrast to the marine nature of the organic matter in the cenomanian turonian boundary section deeper sediments at site 1138 contain evidence of contributions land derived organic matter that implies the former presence of forests on the kerguelen plateau until the earliest cenomanian

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

the problems in esr dating of tooth enamel of early pleistocene and the age of longgupo hominid wushan china abstract quite often esr dating of tooth enamel provides underestimated ages the factors which may account for the age suppression are studied for dating of the samples of early pleistocene thermal fading of the g 2 0018 signal during the burial time may also lead toage underestimation isothermal annealing of the g 2 0018 line was studied in this work and a mixed first and second order kinetics was observed its implication to the practical dating purpose is discussed it is suggested that if no uranium leakage is detected esr eu ages of early pleistocene enamel samples should be considered only as the lower limits of the true ages combined esr and magnetic dating of the longgupo profile wushan china assigns the olduvai subchron to the fossil hominid bearing layers of 7 8 of this profile

redox reactions and carbonate preservation in deep sea sediments abstract geochemical analyses of long sediment cores in turbidite sequences from two abyssal plains in the north atlantic have provided evidence for a relationship between post depositional oxic decay of organic matter and the dissolution of carbonates palaeo oxidation zones in the upper part of individual turbidites were initially identified by distinct colour changes in the sediments these zones were found to have distinctly lower amounts of organic carbon carbonate minerals and labile metals such as fe mn ni and zn as compared with the underlying unoxidized parts of the same turbidite it appears that the initial oxidation of organic matter by oxygen results in an undersaturation of the pore water with respect to carbonates while at the same time some metals are precipitated as easily reducible and soluble oxyhydroxides after burial under suboxic conditions the palaeo oxidation zones are subjected to mildly reducing pore waters that leach the oxyhydroxides resulting in a depletion in labile metal contents in the palaeo oxidized zones it is important that these characteristics be identified in the sedimentary record as the result of diagenetic processes and not as a reflection of primary production in palaeo oceans

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

dissolved organic carbon doc fluxes of deep sea sediments from the arabian sea and ne atlantic abstract diffusive flux of dissolved organic carbon doc from deep sea sediments is a poorly constrained component of the global marine carbon cycle but may play an important role for doc concentrations in the oceans during six cruises between the years 1995 and 2000 we measured doc concentrations in pore waters of surface sediments and the ambient bottom waters at five stations in the deep arabian sea water depths 3190 4420 m and at two sites in the ne atlantic 4500 4800 m pore water doc concentrations were usually one order of magnitude greater than in bottom waters with maximum doc contents between 509 and 1526 mol l in the uppermost sediment interval 0 0 5 cm doc values generally decrease towards 3 cm core depth with slightly increasing concentrations in deeper layers under sub oxic to anoxic conditions calculated benthic doc effluxes into the bottom water caused by concentration gradients ranged between 59 8 and 223 9 mol m 2 d 1 in the arabian sea and 47 2 and 121 2 mol m 2 d 1 in the ne atlantic doc efflux rates were highly correlated with the annual vertical particle flux rates at the sites and thus appear to be a function of the regional productivity taking an average global oceanic doc efflux rate between 50 5 and 78 1 mol m 2 d 1 we calculated that the doc release is in the order of 70 103 1012 g c yr 1 from sediments below 2000 m water depth thus deep sea sediments have the potential to represent a significant source of doc in the oceans

ecologic interpretation of deep sea trace fossil communities abstract trace fossil types and their vertical arrangement tiering are closely related to the biotope and hence can provide information on ecological conditions especially on oxygenation benthic food content sedimentation rate and substrate consistency however to use the full potential of trace fossils for environmental analyses various ichnologic criteria are necessary in addition to trace fossil taxonomy based on a taxonomically oriented ichnologic evaluation of modern deep sea environments six ichnologic aspects to ecologic changes have been found to be of major importance 1 1 penetration depth of burrows is influenced by oxygenation benthic food availability and substrate consistency 2 2 the number and vertical extension of tiers varies due to environmental changes a decrease in the vertical extension of tiers telescoping indicates a decrease in oxygenation benthic food content and or sedimentation rate if shallow penetrating traces disappear oxygen may be depleted and if the deepest tiers disappear the benthic food content may be lowered 3 3 the size diameter of specific trace fossils can indicate oxygen and benthic food availability 4 4 degree of bioturbation is related to sedimentation rate and benthic food content and the diversity of the whole ichnocoenoses or within a specific tier is affected by oxygenation benthic food content sedimentation rate and substrate consistency 5 5 the type of burrow wall unlined mucus lined pellet lined mainly refers to substrate consistency and subordinately to pore water oxygenation 6 6 the type of sediment displacement by body appendages used for excavation ingestion sideward pressing or outside pumping is related to substrate consistency and grain size

physical properties and rock physics models of sediment containing natural and laboratory formed methane gas hydrate this paper presents results of shear strength and acoustic velocity p wave measurements performed on 1 samples containing natural gas hydrate from the mallik 2l 38 well mackenzie delta northwest territories 2 reconstituted ottawa sand samples containing methane gas hydrate formed in the laboratory and 3 ice bearing sands these measurements show that hydrate increases shear strength and p wave velocity in natural and reconstituted samples the proportion of this increase depends on 1 the amount and distribution of hydrate present 2 differences in sediment properties and 3 differences in test conditions stress strain curves from the mallik samples suggest that natural gas hydrate does not cement sediment grains however stress strain curves from the ottawa sand containing laboratory formed gas hydrate do imply cementation is present acoustically rock physics modeling shows that gas hydrate does not cement grains of natural mackenzie delta sediment natural gas hydrates are best modeled as part of the sediment frame this finding is in contrast with direct observations and results of ottawa sand containing laboratory formed hydrate which was found to cement grains waite et al 2004 it therefore appears that the microscopic distribution of gas hydrates in sediment and hence the effect of gas hydrate on sediment physical properties differs between natural deposits and laboratory formed samples this difference may possibly be caused by the location of water molecules that are available to form hydrate models that use laboratory derived properties to predict behavior of natural gas hydrate must account for these differences

reappraisal of anoxia and organic richness with emphasis on cretaceous of north atlantic accumulation of anoxic sediments in the north atlantic during barremian through turonian time early to middle cretaceous was controlled mainly by local conditions although global climatic and oceanographic factors played a supporting role evidence does not support the popular hypothesis developed over the past few years of global or oceanwide anoxia data which contradict this hypothesis are based on 1 a reevaluation of criteria for identifying sediments that accumulated in anoxic water 2 a critical reappraisal of reported worldwide occurrences of anoxic sediments of these ages and 3 an examination of the spatial and temporal distribution of anoxic sediments in the north atlantic and elsewhere a model is proposed in which the earliest anoxic sediments of cretaceous age in the north atlantic were deposited in deep restricted basins by middle cenomanian time about 97 m y ago sluggish circulation had led to a gradual expansion of the oxygen minimum layer permitting deposition of anoxic sediment in nonbasinal settings as well expansion of the oxygen minimum layer caused the calcite compensation depth to rise promoting oxidation of organic carbon and causing contraction of the oxygen minimum layer development of anoxia was thus self damping anoxia effectively disappeared by early senonian time 88 m y ago when improved circulation created oceans more like those of the present some evidence indicates that enhanced biologic productivity and upwelling may have been local factors in fostering anoxia but the early and middle cretaceous were generally not highly productive times

organic rich sedimentation at the cenomanian turonian boundary in oceanic and coastal basins in the north atlantic and tethys one of the most striking results of the deep sea drilling project is the proof that organic rich sediments have a widespread geographical distribution during the period from upper cenomanian to middle turonian such sediments were drilled at north atlantic dsdp sites 105 135 137 138 367 398 551 603 they are also present from outcrops or oil wells on the shelf of the african continental margin senegal tarfaya and agadir basins in the tethys former alboran block southern spain algeria tunisia and umbrian apennines italy and in the north sea although these sediments have different lithologies and depositional environments from shelf areas to the deep sea their study mainly based on organic geochemistry with additional data on sedimentology biostratigraphy and palaeo bathymetry suggests that a unique pulse of organogenic accumulation characterizes the cenomanian turonian boundary event ctbe the content and type of organic matter are related to the depositional environment and organic preservation the organogenic accumulation is distributed according to various trends off the african continental margin the organic content increases from onshore areas to the shelf casamance area and moreover increases also in deep sea areas with a gradual transition from terrestrial type iii to marine type ii the best preservation of the organic matter being in the deepest areas i e site 367 off the american continental margin site 603 shows the same toc and type of organic matter as at site 105 the ctbe is also well recorded in the northern part of the atlantic celtic margin north sea by a drastic lithological change black shales within chalks but the type of organic matter is mainly terrestrial in the tethyan area the organic matter is of marine origin and well preserved results are compared with those of pratt 1984 from the western interior basin of the usa different hypotheses to explain this synchronous widespread accumulation of organic matter are discussed 1986 the geological society

sources and deposition of organic matter in cretaceous passive margin deep sea sediments a synthesis of organic geochemical studies from deep sea drilling project site 603 outer hatteras rise abstract the results of organic geochemical studies of rock samples from cretaceous strata at site 603 on the outer hatteras rise are reviewed and integrated with their lithostratigraphic information although most of the strata contain little organic carbon black shales enriched in organic matter were found in two settings these rocks exist as claystones in the aptian to turonian hatteras formation and as marlstones in the neocomian blake bahama formation terrigenous organic matter predominates in these deposits except in cenomanian and valanginian rocks where marine material becomes dominant organic carbon concentrations in cenomanian black claystones are higher than any previously reported from the western north atlantic but lower than the concentrations found in the eastern north atlantic black shales at site 603 appear to result from downslope transport and rapid reburial of coastal and ocean margin sediments by turbidity flows deep basin anoxia is not a major factor except during the cenomanian turonian when the entire atlantic ocean may have briefly become anoxic organic matter in the sediments from all locations is thermally immature

methane oxidation following submarine permafrost degradation measurements from a central laptev sea shelf borehole submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the east siberian shelf sediment drilled 52 m down from the sea ice in buor khaya bay central laptev sea revealed unfrozen sediment overlying ice bonded permafrost methane concentrations in the overlying unfrozen sediment were low mean 20 m but higher in the underlying ice bonded submarine permafrost mean 380 m in contrast sulfate concentrations were substantially higher in the unfrozen sediment mean 2 5 mm than in the underlying submarine permafrost mean 0 1 mm using deduced permafrost degradation rates we calculate potential mean methane efflux from degrading permafrost of 120 mg m 2 yr 1 at this site however a drop of methane concentrations from 190 m to 19 m and a concomitant increase of methane 13c from 63 to 35 directly above the ice bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column high rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice bonded permafrost as their source

taliks in relict submarine permafrost and methane hydrate deposits pathways for gas escape under present and future conditions we investigate the response of relict arctic submarine permafrost and gas hydrate deposits to warming and make predictions of methane gas flux to the water column using a 2 d multiphase fluid flow model exposure of the arctic shelf during the last glacial cycle formed a thick layer of permafrost protecting hydrate deposits below however talik formation below paleo river channels creates permeable pathways for gas migration from depth an estimate of the maximum gas flux at the present time for conditions at the east siberian arctic seas is 0 2047 kg yr 1 m 2 which produces a methane concentration of 142 nm in the overlying water column consistent with several field observations for conditions at the north american beaufort sea the maximum gas flux at the present time is 0 1885 kg yr 1 m 2 which produces a methane concentration of 78 nm in the overlying water column shallow sediments are charged with residual methane gas after venting events sustained submergence into the future should increase gas venting rate roughly exponentially as sediments continue to warm studying permafrost associated gas hydrate reservoirs will allow us to better understand the arctic s contribution to the global methane budget and global warming

sapropelic deposits in a sediment from the guinea basin south atlantic until recently it has been generally thought that a stagnant water column is a prerequisite to the formation of organic rich deposits in deep water marine sediments a belief best exemplified by studies on the eastern mediterranean sapropels many workers have assumed that following the hydrological isolation of the deep waters stagnation of the eastern mediterranean basins and the concomitant development of anoxic conditions occurred before the deposition of the sapropelic layers1 10 opposing arguments suggesting a role for increased marine productivity have however been put forward both specifically with respect to the eastern mediterranean sapropels11 12 and more generally regarding deep water organic rich deposits13 15 we report here the discovery of sapropelic layers 0 5 organic carbon 16 in a recent sediment core from a deep water site in the guinea basin it is thought most unlikely that stagnant conditions could prevail in the water column at this site and preliminary analyses of the sediments suggest that the organic rich deposits have been a direct result of increased productivity in the overlying water column the most recent occurring about 18 000 yr ago and coinciding with the last glacial maximum

geochemistry and organic petrography of cretaceous sediments of the calabar flank southeastern nigeria abstract detailed bulk geochemistry and organo petrography of outcrop cretaceous sediments with no significant effects of weathering from the calabar flank southeast nigeria were performed to understand the organic carbon source accumulation and degradation and paleo climatic paleoceanographic and paleoenvironmental conditions in west africa during early cretaceous aptian to maastrichtian times this study was based on microscopic elemental analyses organic carbon nitrogen iron and sulphur rock eval pyrolysis and carbon isotope analyses in general the calabar flank shales are characterised by highly variable total organic carbon toc contents which range between 0 1 in aptian albian mfamosing limestone and 9 9 in the awi formation sediments the organic matter om is a mixture of immature to early mature marine and terrigenous om of types iii and iv this is indicated by low hydrogen indices hi value 10 190 mg hc g toc tmax 417 460 c vitrinite reflectance ro 0 39 0 62 ro low to high c n ratios 3 4 1158 0 and high amounts of terrigenous macerals vitrinite inertinite based on carbon isotope c n ratios and sulphate reduction index sri om degradation up to 70 sri 2 5 is most pronounced for shales deposited in a marine environment the geochemical and petrographic data indicate that local factors such as low bioproductivity down slope transport and redeposition of sediments from a fluvial deltaic basin to nearshore facies shallower oxic and mildly oxygen deficient environments humid arid paleogeographic conditions specifically controlled the amount and quality of the om during aptian mastrichtian stages where marine sediments have been assumed to be deposited during the global anoxic events therefore the order of the main factors controlling om content in sediments are input of terrigenous material transported from the land low om productivity by marine photoautotrophs low preservation

stereochemical studies of acyclic isoprenoids xii lipids of methanogenic bacteria and possible contributions to sediments abstract abundant volatile lipids of methanobacterium thermoautotrophicum and methanosarcina barkeri include isoprenoid hydrocarbons c30 and c15 c20 and c25 isoprenoid alcohols m barkeri contains 2 6 10 15 19 pentamethyleicosane whose relative stereochemistry is the same as found in marine sediments indicating that it is a marker of methanogenic activity the c20 c30 and c25 alkenes in m thermoautotrophicum also have a preferred sterochemistry the latter have the 2 6 10 14 18 pentamethyleicosanyl skeleton suggesting that the alkane in marine sediments may derive from methanogens the stereochemistry of squalane in a marine sediment is also compatible with an origin in methanogens in contrast the stereochemistry of pristane in m thermoautotrophicum indicates a fossil fuel contaminant origin suggesting that this and certain other alkanes reported in archaebacteria might also be of contaminant origin there is therefore little evidence at present that the pristane in immature marine sediments originates in methanogens the c15 and c20 saturated alcohols in m thermoautotrophicum have mainly the all r configuration if this is generally true for methanogens the c20 alcohol in the messel shale may originate mainly from methanogens whereas that in the green river shale may originate mainly from photosynthetic organisms

palaeoceanography of organic rich rocks of the loma chumico formation of costa rica late cretaceous eastern pacific the late cretaceous late cenomanian campanian loma chumico formation consists of laminated to massive bedded siliceous shales cherts ash fall tuffs volcanic glass beds and volcaniclastic sandstones the loma chumico formation is at least 630 m thick core data in the tempisque basin and can be subdivided in the subsurface into organic rich and organic lean total organic carbon 1 facies rock eval total organic carbon toc data show that toc in the organic rich facies averages 15 5 with values as high as 33 inorganic geochemical petrological and sedimentological analyses indicate that all the lithologies of the loma chumico formation were deposited in middle shelf to outer slope environments adjacent to an active subaerial island arc the organic geochemistry and palaeontology of the loma chumico formation help constrain the factors that controlled biological productivity in the region during the late cretaceous biomarkers identified in organic rich facies by gas chromatography mass spectrometry gc ms show a high abundance of total steranes relative to hopanes in the morote 1 core indicating algal dominated organic input the hopane to sterane ratio of the extract from the manzanillo 1 core indicates a relatively high bacterial component to the organic matter upwelling and extrusive volcanism were the most important factors that controlled nutrient supply including silica flux and biological productivity within the loma chumico formation depositional system episodic radiolarian dinoflagellate or diatom blooms instigated by rapid infusions of volcanogenic silica may have resulted in expansion of the oxygen minimum zone omz enhancing the preservation of organic matter productivity appears to have been uniform even during deposition of the organic lean facies the findings of this study suggest that ocean wide anoxia in the eastern pacific was unlikely during the late cretaceous high toc contents of organic rich radiolarites from central caribbean deep sea drilling project dsdp sites may be related to upwelling produced in the eastern pacific by convergence of the easterly trade winds eastern pacific equatorial upwelling zone or may be part of a more complex pacific atlantic ocean interaction the end of deposition of organic rich rocks began near the end of the latest santonian earliest campanian in the central caribbean and costa rica palaeoceanographic models suggest that improved circulation and ventilation of bottom waters due to early opening of the north atlantic south atlantic seaway may explain this observation this may represent the influx of a previously unrecognized source of colder oxygenated intermediate bottom water proto antarctic intermediate water into the late cretaceous central atlantic and eastern pacific oceans

geochemical dynamics of the gas hydrate system in the qilian mountain permafrost qinghai northwest china abstract the gas hydrate system in the qilian mountain permafrost region exists as an epigenetic hydrocarbon reservoir situated over a deep seated potential hydrocarbon reservoir this system is characterized by a particular series of geochemical processes and elemental behaviors which control the origin of the gases associated mineralization processes and the geochemical migration and enrichment of different elements in this study we discuss these processes based on compositional analyses of the hydrate bound gases associated minerals fracture fluid and major trace and rare earth element behaviors most of the hydrate bound gases are thermogenic in origin with minor additional mixed microbial and thermogenic methane that is sourced from sapropelic kerogens in the underlying hydrocarbon reservoir episodes of mineralization that formed pyrite alstonite and ankerite along rock fractures were likely caused by decomposition of nearby gas hydrate due to shrinkage of the gas hydrate stability zone major element concentration anomalies partly result from ion precipitation that occurred in the pore and fracture fluid during hydrate formation and decomposition most of the anomalies in the measured trace element concentrations are interpreted to demarcate the base of the gas hydrate layer as low temperature hydrate has a strong sealing ability some of these enriched elements are shown to have migrated into the pyrite crystals causing their anomalously high concentrations in addition the pyrite ree pattern varies with depth and for pyrites with the same origin the presence of a hydrate reservoir may be the major cause of fractionation of ree into pyrite this study provides a new description of the geochemical dynamics of a gas hydrate system operating in a region of permafrost

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

thermoluminescence dating of le moustier dordogne france the chronology of the neanderthal cultures commonly called mousterian which flourished between 100 000 and 40 000 yr ago has not been well established the lower rock shelter of le moustier provides one of the most important stratigraphic sequences incorporating ten main mousterian layers originally identified by peyrony1 and two early upper palaeolithic layers the stratigraphy of which is mainly defined in terms of the regional climatic chronostratigraphy derived from the alpine glacial sequence1 4 a correlation has recently been proposed between the chronostratigraphy of dordogne and the past 125 000 yr of the well established stratigraphy based on oceanic oxygen isotope ratios5 6 but the lack of absolute datings of mousterian settlements makes this correlation uncertain between 100 000 and 40 000 yr bp we now report dates obtained by thermoluminescence measurements of 34 specimens of burnt flint recovered from the upper 3 m of the mousterian deposits and from the superimposed upper palaeolithic layer the dates which range from 56 000 to 40 000 yr bp allow us to correlate the cold sediment deposits of le moustier with cold intervals of the oxygen isotopic record of the mediterranean sea during isotopic stage 3

simulating the biogeochemical effects of volcanic co2 degassing on the oxygen state of the deep ocean during the cenomanian turonian anoxic event oae2 cretaceous anoxic events may have been triggered by massive volcanic co2 degassing as large igneous provinces lips were emplaced on the seafloor here we present a comprehensive modeling study to decipher the marine biogeochemical consequences of enhanced volcanic co2 emissions a biogeochemical box model has been developed for transient model runs with time dependent volcanic co2 forcing the box model considers continental weathering processes marine export production degradation processes in the water column the rain of particles to the seafloor benthic fluxes of dissolved species across the seabed and burial of particulates in marine sediments the ocean is represented by twenty seven boxes to estimate horizontal and vertical fluxes between boxes a coupled ocean atmosphere general circulation model aogcm is run to derive the circulation patterns of the global ocean under late cretaceous boundary conditions the aogcm modeling predicts a strong thermohaline circulation and intense ventilation in the late cretaceous oceans under high pco2 values with an appropriate choice of parameter values such as the continental input of phosphorus the model produces ocean anoxia at low to mid latitudes and changes in marine 13c that are consistent with geological data such as the well established 13c curve the spread of anoxia is supported by an increase in riverine phosphorus fluxes under high pco2 and a decrease in phosphorus burial efficiency in marine sediments under low oxygen conditions in ambient bottom waters here we suggest that an additional mechanism might contribute to anoxia an increase in the c p ratio of marine plankton which is induced by high pco2 values according to our aogcm model results an intensively ventilated cretaceous ocean turns anoxic only if the c p ratio of marine organic particles exported into the deep ocean is allowed to increase under high pco2 conditions being aware of the uncertainties such as diagenesis this modeling study implies that potential changes in redfield ratios might be a strong feedback mechanism to attain ocean anoxia via enhanced co2 emissions the formation of c enriched marine organic matter may also explain the frequent occurrence of global anoxia during other geological periods characterized by high pco2 values

origins and accumulation of organic matter in expanded albian to santonian black shale sequences on the demerara rise south american margin ocean drilling program leg 207 recovered thick sequences of albian to santonian organic carbon rich claystones at five drill sites on the demerara rise in the western equatorial atlantic ocean dark colored finely laminated cenomanian santonian black shale sequences contain between 2 and 15 organic carbon and encompass oceanic anoxic events 2 and 3 high rock eval hydrogen indices signify that the bulk of the organic matter in these sequences is marine in origin however d 13 corg values lie mostly between 30 and 27 and toc tn ratios range from 15 to 42 which both mimic the source signatures of modern c3 land plants the contradictions in organic matter source indicators provide important implications about the depositional conditions leading to the black shale accumulations the low d 13 corg values which are actually common in mid cretaceous marine organic matter are consequences of the greenhouse climate prevailing at that time and an associated accelerated hydrologic cycle the elevated c n ratios which are also typical of black shales indicate depressed organic matter degradation associated with low oxygen conditions in the water column that favored preservation of carbon rich forms of marine organic matter over nitrogen rich components underlying the laminated cenomanian santonian sequences are homogeneous dark colored lower to middle albian siltstones that contain between 0 2 and 9 organic carbon the organic matter in these rocks is mostly marine in origin but it occasionally

the aeromagnetic method as a tool to identify cenozoic magmatism in the west antarctic rift system beneath the west antarctic ice sheet a review thiel subglacial volcano as possible source of the ash layer in the waiscore abstract the west antarctic ice sheet wais flows through the volcanically active west antarctic rift system wars the aeromagnetic method has been the most useful geophysical tool for identification of subglacial volcanic rocks since 1959 64 surveys particularly combined with 1978 radar ice sounding the unique 1991 97 central west antarctica cwa aerogeophysical survey covering 354 000 km 2 over the wais 5 km line spaced orthogonal lines of aeromagnetic radar ice sounding and aerogravity measurements still provides invaluable information on subglacial volcanic rocks particularly combined with the older aeromagnetic profiles these data indicate numerous 100 1000 nt 5 50 km width shallow source magnetic anomalies over an area greater than 1 2 10 6 km 2 mostly from subglacial volcanic sources i interpreted the cwa anomalies as defining about 1000 volcanic centers requiring high remanent normal magnetizations in the present field direction about 400 anomaly sources correlate with bed topography at least 80 of these sources have less than 200 m relief at the wais bed they appear modified by moving ice requiring a younger age than the wais about 25 ma exposed volcanoes in the wars are the present rapid changes resulting from global warming could be accelerated by subglacial volcanism

model for prediction of organic carbon content in possible source rocks abstract a quantitative model has been developed to improve the prediction of the occurrence of marine siliciclastic source rocks and their likely organic carbon content the input parameters of this quantitative model are organic matter supply in the surface layer of the ocean photic zone water depth calculation of the carbon flux sedimentation rate and preservation conditions presence or absence of oxygen at the sediment water interface to handle the difficulties in the quantification of input parameters a probabilistic approach is applied depending on the available data or the interpretation of the kind of environment different risk distribution functions are used to describe the possible range of each input parameter the calculation is then carried out using the monte carlo simulation technique resulting in a probability distribution of the total organic carbon content which forms the basis of the analysis different scenarios currently under debate e g high primary productivity or the possible effects of enhanced preservation under anoxic bottom water conditions and the influence of varying water depth and sedimentation rate can be tested very quickly using examples of recent peru continental margin and ancient lower toarcian shale germany organic rich marine shales the potential of this tool is demonstrated firstly to quantify souce rock quality in this case total organic carbon content only secondly to assess quantitatively the uncertainties in source rock prediction e g evaluation of organic matter supply water depth and sedimentation rates and thirdly to determine source quality risk values to be used in the appraisal of sedimentary basins and prospects

depletion of 13c in cretaceous marine organic matter source diagenetic or environmental sigal geochemical studies of cretaceous strata rich in organic carbon oc from deep sea drilling project dsdp sites and several land sections reveal several consistent relationships among amount of oc hydrocarbon generating potential of kerogen measured by pyrolysis as the hydrogen index hi and the isotopic composition of the oc first there is a positive correlation between hi and oc in strata that contain more than about 1 oc second percent oc and hi often are negatively correlated with carbon isotopic composition 13c of kerogen the relationship between hi and oc indicates that as the amount of organic matter increases this organic matter tends to be more lipid rich reflecting the marine source of the organic matter cretaceous samples that contain predominantly marine organic matter tend to be isotopically lighter than those that contain predominantly terrestrial organic matter average 13c values for organic matter from most cretaceous sites are between 26 and 28 and values heavier than about 25 occur at very few sites most of the 13c values of miocene to holocene oc rich strata and modern marine plankton are between 16 to 23 values of 13c of modern terrestrial organic matter are mostly between 23 and 33 the depletion of terrestial oc in 13c relative to marine planktonic oc is the basis for numerous statements in the literature that isotopically light cretaceous organic matter is of terrestrial origin even though other organic geochemical and or optical indicators show that the organic matter is mainly of marine origin a difference of about 5 in 13c between modern and cretaceous oc rich marine strata suggests either that cretaceous marine planktonic organic matter had the same isotopic signature as modern marine plankton and that signature has been changed by diagenesis or that oc derived from cretaceous marine plankton was isotopically lighter by about 5 relative to modern plankton oc diagenesis does not produce a significant shift in 13c in miocene to holocene sediments and therefore probably did not produce the isotopically light cretaceous oc this means that cretaceous marine plankton must have had 13c values that were about 5 lighter than modern marine plankton and at least several per mil lighter than cretaceous terrestrial vegetation the reason for these lighter values however is not obvious it has been proposed that concentrations of co2 were higher during the middle cretaceous and this more available co2 may be responsible for the lighter 13c values of cretaceous marine organic matter

minimum distribution of subsea ice bearing permafrost on the u s beaufort sea continental shelf 1 starting in late pleistocene time 19 ka sea level rise inundated coastal zones worldwide on some parts of the present day circum arctic continental shelf this led to flooding and thawing of formerly subaerial permafrost and probable dissociation of associated gas hydrates relict permafrost has never been systematically mapped along the 700 km long u s beaufort sea continental shelf and is often assumed to extend to 120 m water depth the approximate amount of sea level rise since the late pleistocene here 5 000 km of multichannel seismic mcs data acquired between 1977 and 1992 were examined for high velocity 2 3 km s 1 refractions consistent with ice bearing coarse grained sediments permafrost refractions were identified along 5 of the tracklines at depths of 5 to 470 m below the seafloor the resulting map reveals the minimum extent of subsea ice bearing permafrost which does not extend seaward of 30 km offshore or beyond the 20 m isobath

ocean wide stagnation episode in the late cretaceous in this paper we report that marine sediment locations spread over a wide area contain evidence of an anoxic interval during the mid cretaceous here called the cenomanian turonian black shale horizon ctbsh the occurrence of laminated carbonaceous shales with marine organic matter in an unoxidized state implies deposition and early diagenesis in anaerobic environments the stratigraphic record above and below the ctbsh in environments as different as the deep north atlantic ocean and marginal and epicontinental seas over enormous areas in north america north africa and northwestern europe is characterized by a stratigraphic gap a disconformity or a continuous but strongly condensed stratigraphic section the anoxic layer coincides in time with the maximum extension of a worldwide marine transgression of eustatic origin recorded on continental margins1 as well as on various cratons2 no simple model has yet been found to explain the occurrence of the ctbsh in such a wide range of depth and palaeoenvironmental conditions

late quaternary environments of the waco mammoth site texas usa abstract the waco mammoth site wms in central texas contains the remains of the largest mammoth herd mammuthus columbi in north america that died in a single catastrophic event most mammoths at the site died on a gravel bar of the ancient bosque river adjacent to a collapsing tributary wall however the timing and cause of death of the 26 mammoths documented to date are controversial the objectives of this research are to describe and interpret the alluvial stratigraphy and infer the cause of death employ optically stimulated luminescence osl dating to determine the timing of death and analyze stable c isotopes of pedogenic carbonate to infer local plant communities dietary habits and summer temperatures dating of quartz from seven sediment samples by osl places the death event to a weighted mean of 66 8 5 0 ka the site is coeval with marine oxygen isotope stage 4 consistent with our reconstructed mean july temperatures 4 c cooler than today based on a buried soil isotopic transfer function our buried soil isotopic interpretation of a dominance of c3 plants is contrary to previous studies of mammoth tooth enamel at the site suggesting a dietary preference for warm season grasses c4

petroleum systems modeling on gas hydrate of the first experimental exploitation region in the shenhu area northern south china sea abstract two dimensional gas hydrate petroleum system modeling was conducted to understand gas hydrate accumulation mechanisms and spatial distribution related to geologic and geochemical processes in the first experimental gas hydrate exploitation region in the shenhu area of the south china sea based on the gas production in core samples a new biogenic methane generation model was created and incorporated into a kinetic model with the results of a rock pyrolysis experiment a thermogenic gas kinetic model for deep formations in the study area was also developed the entire dynamic evolution process from gas generation to migration and gas hydrate formation and accumulation in the perspective area was simulated with the petroleum system modeling method the results showed that the gas hydrate stability zone ghsz began to form after 3 88 ma and its thickness was greatest when the paleowater depth peaked at 3 66 ma the mass of thermogenic gas generation in deep formations is large and that of biogenic gas in shallow formations is relatively small formations that overlap the gas hydrate bearing layers act as cap rocks that prevent the gas from migrating vertically to shallow layers there was a geological time gap between thermogenic gas generation migration and ghsz formation however the timing of biogenic gas generation which is typically of recent generation in the shallow layer matched well with the formation of the ghsz finally coupling of the age and space of gas migration and ghsz formation has allowed gas hydrate accumulation at structural highs in the shenhu area the evaluation technique of petroleum system modeling is of great significance for the improvement of gas hydrate exploration in frontier areas in the future particularly where survey data are limited

origin and stability of a permafrost methane hydrate occurrence in the canadian shield abstract relatively little attention has been given to the stability of methane hydrates formed during periods of past climate change currently in areas of continuous permafrost although a large portion of the canadian arctic is underlain by crystalline rocks the occurrence phase and origin of alkanes in crystalline rocks under thick permafrost conditions 500 m have not been reported for the first time composition and isotopic data for gases from a crystalline shield environment currently under permafrost conditions are presented gas and water samples were collected from exploration boreholes and seeps between 890 and 1130 m depths in the lupin gold mine nunavut canada gases were methane dominate 64 87 with nitrogen 10 37 the next largest component and smaller amounts of ethane propane and carbon dioxide pressure and temperature measurements indicated gas hydrates were stable at the site prior to mining operations a conclusion supported by noble gas and salinity determinations gas hydrate stability over the last 120 kyr glacial cycle was demonstrated by calculating transient subsurface pressure and temperature conditions utilizing the memorial university university of toronto glacial systems model mun uoft gsm and the hydrogeosphere groundwater flow model model results also indicated glacial loading increased subsurface pressures resulting in increased hydrate stability fields during glacial periods subglacial groundwater recharge would be limited by any significant formation of gas hydrates gas composition combined with carbon and hydrogen isotopic determinations on methane 56 to 42 vpdb and 349 to 181 vsmow carbon dioxide 55 to 15 vpdb ethane 37 to 27 vpdb and 330 to 228 vsmow and propane 34 to 27 vpdb and 196 to 172 vsmow indicated formation of natural gases by thermogenic processes mixed with bacteriogenic gas reasonable given site geologic history methane hydrate formation affected gas composition and gas 2 h values complicating the interpretation gas production is not a modern process at this location and the overall contribution to the global carbon budget is small glacial groundwater recharge models need to account for methane hydrate formation and dissipation due to changes in subsurface stability fields during glaciation and the effect of methane hydrate on hydraulic conductivity

10be in a deep sea core implications regarding10be production changes over the past 420 ka abstract the influx of 10 be into a globigerinid ooze core ch72 02 from the eastern north atlantic has been studied this core contains a depositional record of the first 11 18 o stages covering the last 423 ka it is shown that the marine deposition of 10 be is strongly influenced by the sedimentation of clays clay particles appear 10 times more efficient than the carbonate component as a carrier in bringing 10 be to the bottom sediments in core ch72 02 the deposition rates of 10 be averaged over each oxygen isotope stage for the past 11 stages show a scatter of 40 about the mean value of 6 6 10 8 atoms cm 2 ka 1 however after correction for changes in lithology the data show that the production rate of 10 be over the same period has varied no more than 25 and the variations are not systematic in that high or low 10 be production appear to be associated with either cold or warm climates on the time scale of this investigation intervals of ca 50 ka over the last 420 ka with resolutions as fine as 10 ka for portions of the record it is unlikely that the shielding effect of the solar wind has deviated by more than 25 or the geomagnetic field intensity has deviated by more than a factor of 1 6 from their long term averages

anoxic events in the mediterranean sea in relation to the evolution of late neogene climates stable isotopic and micropaleontological studies were made of selected sapropels organic rich sediments deposited in the mediterranean sea during the last 5 0 m y to determine the processes responsible for their formation distinct isotopic and faunal changes occur across sapropels of late pleistocene early pleistocene and latest pliocene age while smaller isotopic changes and more stable faunal assemblages are associated with the early and mid late pliocene sapropels the large 18o depletions and euryhaline fauna associated with latest pliocene pleistocene sapropels supports a density stratification model with a low salinity surface layer in contrast early pliocene and mid late pliocene sapropels appear to have been formed as the result of sluggish circulation and low oxygen contents in bottom waters of the eastern mediterranean due to the stable warm climatic conditions of that time period

ams 14c analysis of teeth from archaeological sites showing anomalous esr dating results abstract we have carried out ams radiocarbon analysis on two groups of samples the first one gave reasonable esr age estimates and the second one yielded serious age underestinations all samples were supposedly older than 35 ka the oldest being around 160 ka two pretreatment techniques were used for radiocarbon dating acid evolution and thermal release heating to 600 750 and 900 c combined with total de gassing at these temperatures was chosen to obtain age estimates on the organic fraction secondary carbonates and original carbonate present in the hydroxyapatite mineral phase respectively all radiocarbon results present serious age underestimations the secondary carbonate fraction gives almost modern results indicating an extremely rapid exchange of this component owing to this very rapid carbonate exchange it is not likely that the esr signals used for dating are associated with the secondary carbonates one tooth from tabun with independent age estimates of 150 ka was further investigated by the oxford ams laboratory yielding an age estimate of 1930 100 bp on the residual collagen from dentine and 18 000 160 bp on the carbonate component of the enamel bioapatite we did not however find an explanation of why some samples give serious esr underestimatioils whilst many others provide reasonable results

chronology of the later stone age and food production in east africa abstract evidence from several archaeological sites in sub saharan africa suggests that the transition to modern human technology marked by the change from the middle to the later stone age lsa occurred first in east africa enkapune ya muto rockshelter in the central rift valley of kenya contains the oldest known archaeological horizons spanning this transition radiocarbon and obsidian hydration dates from this 5 6 m deep cultural sequence show that the later stone age began substantially earlier than 46 000 years ago ostrich eggshell beads were made 40 000 years ago early dates for the lsa and beads may have implications for the origin and dispersal of modern human behaviour and modern humans out of africa this site also contains the only known occurrences dating to the middle holocene dry phase in highland kenya and tanzania as well as occurrences that span the transition from hunting and gathering to food production and from the neolithic to the iron age the adoption of domestic animals by indigenous eburran hunter gatherers in highland east africa occurred gradually between 4900 and 3300 uncorrected radiocarbon years bp and the neolithic later iron age transition occurred around 1300 bp

detailed mass spectrometric u series analyses of two teeth from the archaeological site of pech de l aze ii implications for uranium migration and dating abstract we report th u ages obtained by thermal ionization mass spectrometry of cross sections of two teeth from the archaeological site of pech de l aze ii the aim of this study is to reconstruct the pathways and time dependency of uranium uptake into different constituents of the two teeth a previous esr dating study of the two teeth yielded age estimates in the range of about 130 000 to 200 000 years which was in agreement with the geological assignment of riss for layers from which the specimens were recovered the closed system u series ages of all analyses range from 48 to 137 ka thus yielding age estimates which are between 30 and 90 ka too young the apparent closed system u series ages of the dentine and cement fractions at the top of the teeth are the oldest becoming gradually younger towards the interior of the two teeth the difference between apparent u series ages of dentine at the outer and inner parts of the two teeth is about 35 ka the enamel sections show the same patterns in u concentration and progression of apparent th u ages as the adjacent dentine samples but with generally younger ages our results indicate that uranium migrates both from the top and the base into the dentine of the teeth and from there into the adjacent enamel depending on the position of the sample significant uranium uptake appears to have taken place over many tens of thousands of years modelling the u uptake histories using a parametric model shows that for the cement and dentine components uptake is intermediate between linear uptake lu and early uptake eu closed system the enamel although often assumed to approximate more closely a closed system shows evidence of more recent u uptake these results also imply that it is not possible to use a simple single parameter u uptake model for all components of a given tooth either for u series or esr dating

tests for diagenesis in tooth enamel esr dating signals and carbonate contents abstract we have tested whether tooth enamel might be altered during burial by focusing on the carbonate content and electron spin resonance esr signals used for dating since oxidized carbon atoms co 2 or co 3 moieties in the apatite lattice give rise to the esr dating signal as a function of absorbed radiation dose inward or outward carbonate mobility would induce changes in the radiation sensitivity of the esr dating signal we used manometry and fourier transform infra red spectroscopy to study carbonate in 11 fossil and five modern tooth enamels from horse cow hippopotamus rhinoceros and mammoth we have shown that ungulate tooth enamel exhibits a narrow range of both carbonate content 4 5 to 5 1 wt and esr signal intensity at 300 gy radiation dose these characteristics are true both for modern and most fossil samples ranging in age up to several hundred thousand years old evidence for possible diagenesis was found only for two samples consisting of fragments of enamel which exhibited anomalous high and low carbonate contents and esr signal sizes

dynamics of anoxia abstract a simple steady state one dimensional advective diffusive model of the ocean s coupled carbon oxygen and phosphorous system is developed the model is an extension of wyrtki s 1962 model of the oxygen distribution the occurrence of anoxia requires two conditions 1 sufficiently high productivity and 2 sufficiently low oxygen concentration in the bottom water it is shown that anoxic layers are most likely to occur fairly high in the water column anoxic events may be associated with timesof vigorous thermohaline circulation in contrast to stagnation arguments often invoked the model results are used to interpret both modern and ancient oceanic anoxic events

multidating studies of batadomba cave sri lanka abstract in order to explore the reliability of dating techniques and to determine which materials are most useful for the establishment of precise chronologies 14 c esr tl and osl analyses were carried out on charcoal bones shells and sediments from the archaeological site of batadomba cave sri lanka the dating techniques were complemented by fourier transform infra red ftir spectrometry x ray diffraction analysis as well as scanning electron microscopy sem compared with the new and existing charcoal 14 c chronology radiocarbon dating of shells luminescence dating of sediments as well as esr dating of shells provided reasonable agreement outliers could be explained by diagenetic alteration of the samples esr dating of bones seems to he fraught with many complications but also provided some reasonable age estimates

organic carbon accumulation in bannock basin evaluating the role of productivity in the formation of eastern mediterranean sapropels abstract three sediment cores from bannock basin a hypersaline anoxic basin in the eastern mediterranean have been studied to evaluate the importance of productivity on organic carbon accumulation and sapropel formation in this region organic carbon accumulation rates were determined for two cores from within the anoxic hypersaline zone and for one core from the oxygenated portion of this basin organic carbon accumulation rates are higher by an order of magnitude in the surficial sediments of the anoxic zone due to better preservation an empirically derived preservation factor which allows calculation of paleoproductivity during the deposition of the most recent sapropel si indicates that productivity increased by an order of magnitude during the formation of si we conclude that increased productivity was coupled with a density stratification and a circulation reversal in the eastern mediterranean which together led to sapropel formation

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

intrapermafrost gas hydrates from a deep core hole in the mackenzie delta northwest territories canada visible gas hydrate and possible pore space hydrate samples have been recovered for the first time in north america from within ice bonded permafrost in a 451 m deep core hole in the mackenzie delta northwest territories canada the visible hydrate was found as thin icelike layers that released methane gas initially upon retrieval but stabilized for up to 4 h at atmospheric pressure conditions and subfreezing temperatures the temporary stabilization of hydrate samples is attributed to the self preservation phenomenon described by others on the basis of laboratory studies high methane concentrations in well ice bonded sediments and gas releases suggest that pore space hydrate may be found at depths as shallow as 119 m geochemical and isotopic determinations suggest that the methane hydrate observed in the core hole is biogenic microbial in origin

hydrocarbon gases associated with permafrost in the mackenzie delta northwest territories canada abstract molecular and isotopic analyses of core gas samples from 3 permafrost research core holes 92gsctaglu 92gsckumak 92gscunipkat sample core depths ranging from 0 36 to 413 82 m in the mackenzie delta of the northwest territories of canada reveal the presence of hydrocarbon gases from both microbial and thermogenic sources analyses of most headspace and blended gas samples from the ice bonded permafrost portion of the core holes yielded c 1 c 2 c 3 hydrocarbon gas ratios and ch 4 c isotopic compositions 13 c ch 4 indicative of microbially sourced ch 4 gas however near the base of ice bonded permafrost and into the underlying non frozen stratigraphic section an increase in ethane c 2 concentrations decreases in c 1 c 2 c 3 hydrocarbon gas ratios and ch 4 c isotopic 13 c ch 4 data indicate the presence of hydrocarbon gases derived from a thermogenic source the thermogenic gas below permafrost in the mackenzie delta likely migrated from deeper hydrocarbon accumulations and or directly from thermally mature hydrocarbon source rocks

electron spin resonance esr dating abstract esr dating has been systematically applied in earth sciences and archaeology since 1975 when ikeya dated a stalactite from the akiyoshi cave in japan in the meantime this new technique has been successfully applied to the dating of materials such as speleothems spring deposited travertines mollusc shells corals and tooth enamel the present research focuses on the dating of quartz which allows the age assessment of heated ceramics volcanic rocks intrafault material or windblown sediments esr dating is based on the measurement of the number of paramagnetic centers in a mineral these centers are generated by alpha beta and gamma radiation of the matural radioelements such as u th and k and have accumulated over time two parameters have to be determined the accumulated dose ad and the dose rate d to which the sample was exposed this review comprises three major parts a introduction into esr dating b application of the method and c appendices giving detailed description of dose rate calculation physical basis of electron spin resonance the esr spectrometer and esr lines the major emphasis lies on the outline of the application of esr dating this includes the discussion of the esr signals of the various materials sampling sample preparation and measurement techniques

origin of pingo like features on the beaufort sea shelf and their possible relationship to decomposing methane gas hydrates 1 the arctic shelf is currently undergoing dramatic thermal changes caused by the continued warming associated with holocene sea level rise during this transgression comparatively warm waters have flooded over cold permafrost areas of the arctic shelf a thermal pulse of more than 10 c is still propagating down into the submerged sediment and may be decomposing gas hydrate as well as permafrost a search for gas venting on the arctic seafloor focused on pingo like features plfs on the beaufort sea shelf because they may be a direct consequence of gas hydrate decomposition at depth vibracores collected from eight plfs had systematically elevated methane concentrations rov observations revealed streams of methane rich gas bubbles coming from the crests of plfs we offer a scenario of how plfs may be growing offshore as a result of gas pressure associated with gas hydrate decomposition

organic geochemistry of cretaceous black shales from the galicia margin ocean drilling program leg 103 organic carbon rich black shales from three different cretaceous episodes sampled during ocean drilling program leg 103 have been studied by organic geochemical methods rock eval analysis carbon isotope data and lipid biomarkers show organic matter to contain varying proportions of marine and continental materials in hauterivian barremian organic carbon rich turbiditic marlstones major amounts of land derived organic matter are found aptian albian black colored shales are interspersed within green claystones from which they differ by containing more marine organic matter an abbreviated layer of black shale from the cenomanian turonian boundary is dominated by well preserved marine organic matter downslope transport and rapid reburial within a predominantly oxygenated dcepwater setting created most of these examples of black shales except for the cenomanian turonian deposits in which decpwater anoxia may have been involved

paleoceanographic and paleoclimatic similarities between mediterranean sapropels and cretaceous black shales pliocene quaternary sapropels of the mediterranean sea and mid cretaceous black shales share many distinctive properties organic carbon concentrations that often exceed 5 in both types of sequences record episodes of exceptional accumulation of organic matter although both are rich in marine organic matter they have high c n ratios that mimic those of land plant organic matter which suggests less efficient organic matter recycling than in the modern ocean the coupled presence of isorenieratene derivatives and low 15n values that result from microbial primary productivity indicates that photic zone anoxia existed during their formation and implies strong stratification of the surface ocean enrichments of redox sensitive metals and sediment laminations indicate that anoxia existed deeper in the water column and at the seafloor multiple proxies indicate freshening of surface waters of the mediterranean and imply periods of wetter climate during times of sapropel deposition episodes of black shale deposition similarly coincide with times of wetter climate these comparisons suggest that the wetter climate created similar conditions of surface salinity stratification that enhanced microbial primary production and magnified organic matter export during deposition of both the mediterranean sapropels and mid cretaceous black shales

sediments with gas hydrates internal structure from seismic avo we interpret amplitude variation with offset avo data from a bottom simulating reflector bsr offshore florida by using rock physics based synthetic seismic models a previously conducted velocity and avo analysis of the in situ seismic data showed that the bsr separates hydrate bearing sediments from sediments containing free methane the amplitudes at the bsr are increasingly negative with increasing offset this behavior was explained by p wave velocity above the bsr being larger than that below the bsr and s wave velocity above the bsr being smaller than that below the bsr we use these avo and velocity results to infer the internal structure of the hydrated sediment to do so we examine two micromechanical models that correspond to the two extreme cases of hydrate deposition in the pore space 1 the hydrate cements grain contacts and strongly reinforces the sediment and 2 the hydrate is located away from grain contacts and does not affect the stiffness of the sediment frame only the second model can qualitatively reproduce the observed avo response thus inferred internal structure of the hydrate bearing sediment means that 1 the sediment above the bsr is uncemented and thereby mechanically weak and 2 its permeability is very low because the hydrate clogs large pore space conduits the latter explains why free gas is trapped underneath the bsr the seismic data also indicate the absence of strong reflections at the top of the hydrate layer this fact suggests that the high concentration of hydrates in the sediment just above the bsr gradually decreases with decreasing depth this effect is consistent with the fact that the low permeability hydrated sediments above the bsr prevent free methane from migrating upwards

molecular and stable isotope compositions of natural gas hydrates a revised global dataset and basic interpretations in the context of geological settings abstract a global dataset of molecular and stable isotope compositions of gases released from 209 different specimens of natural gas hydrate is presented and discussed the 26 hydrate bearing areas from 21 geographic regions are grouped into high gas flux hgf settings low gas flux lgf settings and hydrated gas accumulations hga methane ch4 is the most abundant hydrate bound gas while co2 and c2 hydrocarbon gases are frequently present in small amounts non hydrocarbon gases such as h2s are uncommon the stable isotope composition of hydrate bound gases varies significantly e g 13c of ch4 from 74 7 to 39 6 suggesting that gases of both microbial and thermogenic origin form gas hydrates hydrate bound gases are derived from autochthonous located predominantly within the gas hydrate stability zone ghsz and allochthonous located in deep sediments sources the occurrence and concentration of gas hydrates in sediments are controlled not by the origin of gases but rather by their sources which in turn strongly depend on geological setting allochthonous gases microbial and or thermogenic dominate in hgf and hga settings where they are focused in the shallow ghsz along faults within mud volcanoes in permeable carrier beds and other geological features from underlying petroleum systems relatively high concentrations of gas hydrate average 5 15 of pores and locally up to 100 of volume occurring over small areas are typical of hgf and hga settings in contrast autochthonous and diffuse allochthonous gases mostly microbial occur in stratigraphically and structurally simple lgf settings and result in relatively low concentrations of gas hydrate average 2 of pores in the ghsz spread over large areas the major implication of this finding is that successful prediction of resource and geohazard potential of gas hydrates is possible only if regional petroleum systems extending well below the ghsz are properly evaluated in addition to the diagnosis of origins and sources of hydrate bound gases molecular and isotopic data help to better identify hydrate bearing intervals and provide valuable insights into the dynamics of hydrate bearing sites

low productivity and slow deep water circulation in mid cretaceous oceans paleofertility estimates are derived from organic carbon accumulation rates determined in nonbioturbated mid cretaceous deep sea deposits using organic carbon preservation factors observed in laminated sediments from anoxic holocene environments the estimated mid cretaceous primary production rates are as much as an order of magnitude lower than those measured in today s oceans an evaluation of dissolved oxygen budgets using a simple oceanic circulation model indicates very low deep water renewal rates in mid cretaceous oceans 28 references 2 tables 4 figures

organic facies of middle cretaceous black shales in deep north atlantic the middle cretaceous black shales of the deep north atlantic consist of alternating layers of sediment rich in total organic carbon toc that contains abundant amorphous types of organic matter and sediment poor in toc that contains mostly woody and coaly types of organic matter the amorphous materials are derived mostly from marine organisms in the eastern north atlantic off africa in the caribbean and on the demerara rise off surinam and from higher land plants in the western north atlantic and off europe marine amorphous material is important off africa because this was an area of upwelling and highly productive surface water amorphous marine organic matter was deposited across the entire north atlantic basin in the cenomanian in response to an ocean wide upwell ng event connected with the opening of the equatorial atlantic the difference between the toc rich and background toc layers reflects deposition of the former under reducing conditions which allowed the preservation of labile amorphous materials of marine and terrestrial orgin and of the latter under oxidizing conditions when nearly all that was preserved was refractory organic material

determination of organic degradation rates in 100 my old sediments application to cretaceous black shale intervals from demerara rise odp leg 207 abstract thick organic rich albian to santonian black shale sequences were recovered from ocean drilling program sites 1261 and 1257 on the demerara rise offshore surinam at depths of 564 and 174 m below seafloor bsf respectively total organic carbon toc concentration varies between 3 9 and 17 3 wt rock eval pyrolysis parameters and elemental analysis indicate that the kerogen samples are of type ii thermally immature and with well preserved organic matter the hydrogen index hi values fluctuate between 608 and 765 mg hydrocarbon hc g toc and correlate well with c n and the sorg c atomic ratios indicating varying early diagenesis conditions between samples higher c n and sorg c values for kerogen from site 1261 suggest more reducing depositional conditions than at site 1257 long term organic diagenesis is marked by a linear decrease in the oxygen index oi at site 1261 from 34 to 22 mg co2 g toc ester and carboxyl functional groups are the main target of the degradation as inferred from the decrease in c o and o c c fourier transform infrared spectroscopy ftir bands as well as in the ch oh and the o ch3 chx n bands in 13c nuclear magnetic resonance nmr spectra degradation rate at site 1261 determined combining quantitative nmr spectra and bulk elemental characterization is between 1 7 and 12 1 mol m3 yr per 1 toc at the lower end of reported rates in a similar context kerogen samples from site 1257 do not show any decrease in oxygen content with depth indicating significantly lower degradation rate we propose that the long term exposure to moderate temperature 30 c at site 1261 activated the organic matter thereby sustaining microbial diagenesis

geochemical and tight reservoir characteristics of sedimentary organic matter bearing tuff from the permian tiaohu formation in the santanghu basin northwest china abstract tuff reservoirs have been found in petroliferous basins but have not been sufficiently studied the discovery of the permian tiaohu formation reservoir in the santanghu basin in northwest china has offered an excellent opportunity to further enhance our knowledge of the tuff s geochemical and reservoir characteristics the tuff reservoir has the peculiar property of being a sedimentary organic matter bearing tuff in this study an integrated analysis of the organic geochemistry elemental and mineral compositions quartz crystallinity pore types and tight reservoir characteristics was conducted based on samples from the 20 30 m thick tuffs the extracted tuff samples have total organic carbon toc values of 0 5 1 0 wt total hydrocarbon yield values of 2 6 mg g and hydrogen index values of 20 336 mg hc g toc the organic matter consists predominantly of type iii and ii 2 kerogens and the temperature of the maximum yield of pyrolysate varies from 420 to 450 c which reflects the oil generating capacity of the rock the physical properties of the tuff are characterised by high porosity varying from 10 to 25 and low permeability the air permeability mainly ranges from 0 01 to 0 50 md the devitrification of vitreous textures within the tuff primarily dictates the reservoir s characteristics i e the greater the degree of devitrification the higher the porosity of the reservoir vitric tuffs have reservoirs with higher porosity than crystal vitric tuffs and the degree of devitrification is generally controlled by the burial depth temperature and organic matter organic acid content vitric tuffs with high porosity and permeability are usually located far from the crater and within the central lower part of the reservoir this research may influence geologists to pay more attention to the exploration value of this special type of reservoir in other regions

20 my of nitrogen fixation during deposition of mid cretaceous black shales on the demerara rise equatorial atlantic ocean abstract thick sequences of dark colored organic carbon rich finely laminated santonian cenomanian claystones and homogeneous albian siltstones were recovered from ocean drilling program sites 1257 1258 and 1260 on the demerara rise in the western equatorial atlantic ocean total organic carbon toc concentrations vary from 2 to over 20 wt in the sequences of black shales that were deposited over a period of 20 million years similarly long periods of elevated marine productivity implied by the high toc concentrations are uncommon in the geological record and must have required unusual paleoceanographic conditions the importance of nitrogen fixing bacteria to sustaining the amplified export production of organic matter is indicated by 15n values that remain between 4 and 0 a range that is notably less positive than the average of 5 for modern ocean sediments although containing mostly marine organic matter the black shales have toc tn molar ratios between 20 and 40 that mimic those of land plant organic matter the anomalously large toc tn ratios suggest selective organic matter degradation probably associated with low oxygen conditions in the water column that favored preservation of nitrogen poor forms of organic matter relative to nitrogen rich components deposition of black shales on the demerara rise was likely a consequence of the mid cretaceous warm and wet greenhouse climate that strengthened thermohaline stratification of this part of the atlantic ocean which in turn encouraged bacterial nitrogen fixation enhanced primary production magnified organic matter export and ultimately established anoxic conditions at the seafloor that improved preservation of organic matter for much of the 20 my period represented by these thick sequences

late quaternary paleoceanography as recorded by benthonic foraminifera in strait of sicily sediment sequences at specific times during the late quaternary a widespread low salinity surface water layer was produced over the eastern mediterranean which created stagnant conditions and associated deposition of sapropelic muds in the deep basins the strait of sicily has been positioned above the anoxic deeper water masses and is therefore devoid of sapropel deposits sediment sequences in the region contain a valuable record of upper bathyal 200 1000 m benthonic foraminiferal change during times of deep basin stagnation quantitative examiniation of benthonic foraminiferal assemblages in strait of sicily quaternary cores generally reveals changes coeval with sapropels s1 s2 s4 s5 and s6 the benthonic foraminiferal expression is seen as increases in frequency ofglobobulimina affinis globobulimina pseudospinescens chilostomella mediterranensis bolivina dilatata and otherbolivina species during intervals corresponding to the episodic abyssal stagnation events some cores also display a decrease incassidulina carinata and an increase inarticulina tubulosa similar assemblage changes have been previously documented to be closely associated with the sapropel layers in the deep basins of the eastern mediterranean the actual sapropel layers usually do not contain benthonic foraminifera however in the strait of sicily area the species exhibit less drastic changes than in the deep eastern basins because of the less severe anoxic conditions in the deep eastern basins benthonic foraminifera almost totally disappeared in sapropel layers at the same time there was a general reduction in foraminiferal numbers in the shallower strait area

accumulation of organic carbon rich sediments in the late jurassic and cretaceous atlantic ocean a synthesis abstract organic carbon rich sediments black shales were deposited at some 40 deep sea drilling project dsdp sites in the atlantic ocean during late jurassic and cretaceous times in order to reconstruct the depositional environments of black shale formation we have studied in detail changes in the occurrence of black shales as well as the type and amount of organic matter in relation to changes in paleogeography paleooceanic circulation and paleoclimate we have calculated accumulation rates of marine and terrigenous organic carbon and combined these with organic carbon content sedimentation rate relationships to obtain information about paleoenvironments main factors causing the preservation and accumulation of organic carbon are 1 the supply of terrestrial organic matter 2 the supply of marine organic matter 3 the oxygenation of the deep water and 4 the bulk sedimentation rate changes in the importance of these different factors and changes in the interrelationships among them determine the complex system of black shale formation and their cyclic variations increased supply of terrestrial organic matter due to increased river discharge and humid climate in northeast america southwest europe and south africa were important in the hauterivian albian northwest and northern northeast atlantic and in the late jurassic aptian south atlantic in the latter anoxic deep water conditions due to restricted circulation in the nascent largely isolated basin as well as higher oceanic productivity may have reinforced the high preservation rates of marine organic matter during that time off northwest africa higher flux rates of marine organic matter were recorded in areas of higher productivity which may have been caused by fluvial nutrient supply during the hauterivian and by intensified upwelling during albian turonian times in general the depositional environment was oxygenated and the content of marine organic matter was a function of the sedimentation rate furthermore at some places redeposition by turbidity currents or slumps may have been important for the accumulation of organic matter in the deep sea basins the only episode of widespread anoxia in the western and eastern basins of the north atlantic may have occurred in the cenomanian turonian when high amounts of marine organic matter were also preserved in areas of low productivity and low sedimentation rates

states of preservation of bones from prehistoric sites in the near east a survey abstract a survey of the states of preservation of organic material in 30 fossil bones from 16 different prehistoric sites in the near east shows that whereas almost all the bones have little or no collagen preserved they do with few exceptions contain non collagenous proteins these macromolecules therefore represent an important reservoir of indigenous fossil bone constituents

enhanced preservation of marine derived organic matter in cenomanian black shales from the southern angola basin black shales possessing high concentrations of organic carbon1 were deposited in many parts of the proto south atlantic ocean during the cretaceous period2 the way such sediments accumulated is not fully understood but is likely to have occurred through a combination of low oxygen availability and abundant supply of organic matter thin centimetre thick layers of black shales are commonly interbedded with thicker layers of organic carbon deficient green claystones as found in strata of aptian to coniacian age at deep sea drilling project dsdp site 530 in the southern angola basin3 and elsewhere these differences in carbon content and colour reflect the conditions of deposition and possibly variations in the supply of organic matter4 5 we have compared using organic geochemical methods the compositions of organic matter in three pairs of closely bedded black and green cenomanian claystones obtained from site 530 kerogen analyses and distributions of biological markers show that the organic matter of the black shales is more marine and better preserved than that of the green claystones

models for the deposition of mesozoic cenozoic fine grained organic carbon rich sediment in the deep sea the widespread occurrence of organic carbon rich strata black shales in certain portions of jurassic cretaceous and cenozoic sequences has been well documented from deep sea drilling project sites in the atlantic and pacific oceans and from sequences now exposed on land originally deposited in the tethyan ocean these ancient black shales usually have been explained by analogy with examples of modern deep sea sediments in which organic matter locally is preserved by 1 increasing the supply of organic matter 2 increasing the rate of sedimentation and or 3 decreasing the oxygen content of the bottom water however detailed examination of many black shales reveals characteristics that cannot be explained by simple local models including their approximate coincidence in time globally their occurrence in a variety of different environments including open oxygenated oceans restricted basins deep and shallow water their interbedding with organic carbonpoor strata which often dominate a so called black shale sequence their deposition by pelagic hemipelagic turbiditic and other processes and the variations in type and amount of organic matter that occur even within the same sequence a more complex model for the origin of black shales therefore appears most appropriate in which the cyclic preservation of organic matter depends on the interplay of the three main variables namely supply of organic matter sedimentation rate and deep water oxygenation each of which varies independently to some extent the variation and relative importance of these parameters in individual basins and widespread black shale deposition in general are linked globally and temporally by changes in global sea level climate and related changes in oceanic circulation an important and often overlooked factor for the supply of organic matter to deep basin sediments is the frequency and magnitude of redepositional processes the interplay of these variables is discussed in relation to the middle cretaceous and cenozoic organic carbon rich strata in particular which show marked differences in the relative importance of the different variables

effects of submarine groundwater discharge on the present day extent of relict submarine permafrost and gas hydrate stability on the beaufort sea continental shelf we investigate the role of submarine groundwater discharge on the offshore temperature and salinity field and its effect on the present day extent of submarine permafrost and gas hydrate stability on the north american beaufort shelf with a two dimensional numerical model based on the finite volume method this study finds that submarine groundwater discharge can play a large role in submarine permafrost evolution and gas hydrate stability suggesting that local hydrology may control the evolution of submarine permafrost as strongly as does sea level or paleoclimatic conditions submarine permafrost evolution shows transient behavior over potentially long time scales e g several glacial cycles before a balance of density and pressure driven flows is established with the permeability variations imposed by the overlying permafrost layer the detectable offshore permafrost extent is related to the quasi stationary location of the saltwater freshwater transition larger values of submarine groundwater discharge allow permafrost to extend farther offshore because fresh pore water preserves relict ice therefore differences in the permafrost extent at locations that share similar paleoclimatic history may be explained in part by differences in the local hydrology gas hydrate stability on the north american beaufort shelf may be more widespread than currently thought because low ice saturation highly degraded submarine permafrost likely exists beyond the boundary detectable by common geophysical methods

bedding rhythms and cyclic sequences as documented in organic carbon carbonate patterns upper cretaceous western interior u s abstract a three component sedimentation model is introduced for estimating the relative effects of major changes in sediment flux coupled organic carbon carbonate changes reflecting different dilution concentration styles are utilized to detect the changing flux between the carbonate siliciclastic and organic matter components the three component model is then applied to upper cretaceous rhythmically bedded units of the greenhorn and niobrara cycles of the western interior seaway the cycles are related to third order sea level changes the western interior seaway was sensitive to small scale climatic cycles only during periods of maximum flooding due to combined variations in carbonate productivity redox conditions and siliciclastic supply from continental sources rhythmic deposition is different for different parts within the periods of maximum flooding for each of the two investigated third order sea level cycles section intervals reflecting peak flooding show variations in carbonate productivity and variations in redox conditions slightly more regressive intervals show variations in calcareous productivity and siliciclastic dilution with stagnant dysaerobic bottom waters for most of the investigated bedding rhythms persistent dysaerobic bottom waters are largely uninfluenced by variations in pelagic carbonate productivity except for section intervals representing peak flooding this suggests the existence of a circulation pattern in which a mixed surface water zone was underlain by more stratified oxygen depleted water masses with slow circulation

sedimentary and geochemical indicators of productivity and oxygen contents in modern and ancient basins the holocene black sea as the type anoxic basin data on the accumulation rates of organic carbon total phosphorus and reduced sulfur over the past 7000 yr from modern abyssal black sea sediments are examined as geochemical monitors of variations in biologic productivity and the development of deep water masses variations in organic carbon accumulation rates at both intermediate and deep water sites are believed to be controlled by the combined effects of enhanced preservation of organic matter under anoxic bottom conditions and the regulation of primary productivity in surface waters by nutrient availability estimates of variations in water column and pore water organic carbon consumption by sulfate reducing bacteria can be made using average carbon and sulfur accumulation rates for various depositional episodes and are examined in the light of changes in the thickness of the h2s zone in the water column the amount of available sulfate within this zone and the reactiveness of particulate organic matter sulfur and phosphorus accumulation rates are used to estimate the maximum amount of phosphorus regenerated from organic matter during bacterial sulfate reduction processes total phosphorus accumulation rates are found to markedly increase over the part 1000 yr and are not proportionally paralled by organic carbon accumulation rates these accelerated phosphorus accumulation rates appear to stem from organic matter degradation adsorption on surfaces of caco3 and perhaps diffusion into sediments from bottom waters and authigenic precipitation of phosphate minerals accumulation rates of organic carbon and phosphorus in black sea sediments are low in comparison to those typical of modern highly productive upwelling zones peru south west africa namibia accumulation rates of reduced sulfur and the ratios of reduced sulfur to organic carbon burial may be higher in anoxic basins than in oxic ones knowledge of accumulation rates therefore rather than concentrations alone may help to differentiate black shales which resulted from enhanced organic matter preservation under anoxic conditions from those resulting from high biologic productivity with or without accompanying oxygen deficiencies

defining the updip extent of the gas hydrate stability zone on continental margins with low geothermal gradients 1 the distribution of gas hydrate on a continental slope is often characterized as a wedge that pinches out on the seafloor this part of the hydrate stability zone is particularly relevant for studies of the dynamics of hydrate accumulations such as processes related to slope stability or hydrate dissociation leading to methane release into the overlying ocean for regions with very low geothermal gradients we have produced a series of thermobaric models of the shallow hydrate stability zone that contain an unexpected geometrical distribution of hydrated sediments in these models the shallowest part of the stability field thickens and bulges landward such a feature is more likely to happen in regions where low geothermal gradients are further lowered by high sedimentation rates also the effect is greater beneath colder oceans although a hydrate stability zone bulge would be difficult to image with conventional seismic methods there are numerous locations around the world where such a system could develop

changes in paleoenvironments in the atlantic ocean during cretaceous times results from black shales studies large parts of the cretaceous atlantic ocean are characterized by the wide spread deposition of organic carbon rich sediments black shales with a maximum occurrence during aptian albian and cenomanian turonian times in order to explain the origin of these black shales changes in the amount and type of organic matter in relation to changes in paleogeography paleoceanic circulation and paleoclimate have been investigated in detail the study is mainly based on calculation of accumulation rates of marine and terrigenous organic carbon organic carbon sedimentation rate relationships and estimates of paleoproductivity