formation and spreading of red sea outflow water in the red sea hydrographic data chlorofluorocarbon 12 cfc 12 and sulfur hexafluoride sf6 measurements collected in march 2010 and september october 2011 in the red sea as well as an idealized numerical experiment are used to study the formation and spreading of red sea outflow water rsow in the red sea analysis of inert tracers potential vorticity distributions and model results confirm that rsow is formed through mixed layer deepening caused by sea surface buoyancy loss in winter in the northern red sea and reveal more details on rsow spreading rates pathways and vertical structure the southward spreading of rsow after its formation is identified as a layer with minimum potential vorticity and maximum cfc 12 and sf6 ventilation ages of seawater within the rsow layer calculated from the partial pressure of sf6 psf6 range from 2 years in the northern red sea to 15 years at 17 n the distribution of the tracer ages is in agreement with the model circulation field which shows a rapid transport of rsow from its formation region to the southern red sea where there are longer circulation pathways and hence longer residence time due to basin wide eddies the mean residence time of rsow within the red sea estimated from the psf6 age is 4 7 years this time scale is very close to the mean transit time 4 8 years for particles from the rsow formation region to reach the exit at the strait of bab el mandeb in the numerical experiment

sedimentary dynamics of the kimmeridge clay tempests and earthquakes storms are suggested to be an important influence upon the formation of epicontinental black shales controlling both their distribution and facies types a variety of storm produced event beds are described from the kimmeridge clay of dorset these include horizons of graded rip up clasts silt laminae thin graded mud horizons and shell pavements biostratinomy and population dynamics indicate that the pavements represent brief benthic colonization events in a predominantly anaerobic dysaerobic environment differential near surface lithification has also affected the sediments leading to the formation of flow phenomena these include loop structures microfolding and brecciation earthquake induced fissuring also occurs at a number of horizons the kimmeridge clay shows well developed cyclically alternating organic rich shales and mudstones on a decimetre scale a feedback mechanism of storm induced benthic oxygenation and temperature stratified inhibition of storm mixing may account for the abrupt nature of the cyclicity subsidence and sedimentation rate were probably important factors controlling the thickness and organic richness of the sediments whilst the influence of storms was important in controlling the distribution and facies types of these important source rocks the model proposed for the kimmeridge clay may be of general application to many epicontinental black shales in the geological record

lack of evidence for enhanced preservation of sedimentary organic matter in the oxygen minimum of the gulf of california a test of the hypothesis that hydrogen rich organic matter accumulates preferentially in sediments under oxygen minima has been carried out by examining the composition of laminated and homogeneous diatomaceous sediments of the guaymas basin in the gulf of california the laminated sediments occur where an intense oxygen minimum intersects the slope around the margins of the basin above and below the depth of the oxygen minimum the sediments are homogenized by a burrowing infauna the two sediment types have very similar bulk chemical and mineral compositions and the organic matter is overwhelmingly marine the total organic carbon contents and rock eval parameters hydrogen and oxygen indices of the two sediment types are not significantly different whereas a road organic carbon maximum in the homogeneous sediments is centered at roughly 1200 m depth on the slope of the basin this maximum lies deeper than the core of the oxygen minimum thus both the concentration and the nature of the organic matter in the sediments of this highly productive marginal marine basin are not related to the concentration of dissolved oxygen in the bottom waters

an oceanographic nowcast forecast system for the red sea we describe the application of a nowcast forecast system for three dimensional currents temperature and salinity to the red sea the modeling system is constructed around a high resolution 6 7 km primitive equation numerical circulation model with complete thermodynamics and an imbedded turbulence closure submodel it is coupled to near real time databases containing meteorological forecasts and remotely sensed and in situ temperature and salinity data the temperature and salinity data are ingested into the model daily using a nudged objective analysis technique because the red sea is a relatively narrow basin bounded by typically high and complex orography a single layer atmospheric boundary layer submodel has been used to increase the effective resolution of the original 40 km resolution meteorological fields by taking into account orographic steering of the low level winds in order to validate the modeling system two very complete hydrographic surveys of the red sea were undertaken and their results are described both the surveys and the modeling system nowcasts demonstrate that the circulation pattern of the red sea is variable and often composed of a series of eddies or subgyres mainly anticyclones immediately before one survey the winds tended to be along axis while just before the second they tended to be cross axis the red sea circulation was much more eddy like when the winds were cross axis by forcing the modeling system with and without orographically steered winds we were able to establish that the complex eddy structure is a response to a wind field which can be highly structured and vorticity rich because of interaction with the high and variable adjacent orography when the winds are more along axis there is less interaction with the adjacent orography and consequently there are fewer eddies in the red sea

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

eddies in the red sea a statistical and dynamical study sea level anomaly sla data spanning 1992 2012 were analyzed to study the statistical properties of eddies in the red sea an algorithm that identifies winding angles was employed to detect 4998 eddies propagating along 938 unique eddy tracks statistics suggest that eddies are generated across the entire red sea but that they are prevalent in certain regions a high number of eddies is found in the central basin between 18 n and 24 n more than 87 of the detected eddies have a radius ranging from 50 to 135 km both the intensity and relative vorticity scale of these eddies decrease as the eddy radii increase the averaged eddy lifespan is approximately 6 weeks aes and cyclonic eddies ces have different deformation features and those with stronger intensities are less deformed and more circular analysis of long lived eddies suggests that they are likely to appear in the central basin with aes tending to move northward in addition their eddy kinetic energy eke increases gradually throughout their lifespans the annual cycles of ces and aes differ although both exhibit significant seasonal cycles of intensity with the winter and summer peaks appearing in february and august respectively the seasonal cycle of eke is negatively correlated with stratification but positively correlated with vertical shear of horizontal velocity and eddy growth rate suggesting that the generation of baroclinic instability is responsible for the activities of eddies in the red sea

direct observations of seasonal exchange through the bab el mandab strait the exchange flow between the red sea and the gulf of aden indian ocean through the bab el mandab strait was measured continuously for 10 months june 1995 march 1996 adcp and temperature salinity chain moorings allow an unprecedented look at the magnitude and seasonal evolution of the inflow layer from the gulf of aden and the high salinity outflow layer from the red sea the timing structure and evolution of the summer season mid depth intrusion of cold low salinity water into the red sea from the gulf of aden is measured for the complete intrusion cycle of 1995 we unexpectedly find the deep outflow still strong in june 1995 with speeds of 0 6 m sec and transport of 0 4 sv 1 sv 106 m sec from july to mid september the deep outflow persists but is attenuated to speeds of 0 2 m sec and transport of 0 05 sv the dominant summer feature the cold low salinity intermediate layer intrusion persists for 3 months occupies 70 of the water column in the strait and carries approximately 1 7 1012 m of cold nutrient rich water into the red sea the winter regime begins in mid september is fully developed by early november and continues to the end of our first observation interval in march 1996 speeds in the lower layer are 0 8 1 0 m sec and 0 4 0 6 m sec in the upper layer at maximum exchange in mid february outflow transport reaches 0 7 sv ubiquitous oscillations in current and salinity at synoptic and intraseasonal periods appear closely related to fluctuations in the along channel wind forcing and perhaps to coastally trapped waves

mobility of arsenic and trace element inventories in sediment cores from masuda city southwestern japan the vertical distribution of arsenic and other trace and major elements has been studied in four sediment cores from masuda city nagashima and okite in the shimane prefecture of southwestern japan the sediment cores were also subjected to leaching techniques and 14c dating the stratigraphic sequences in the cores consist of silt and sandy silt at top passing downward into gray to black clays elevated values of as pb zn cu ni cr and v are present in several horizons while abundances of these elements tend to be higher in the black and gray clays probably due to adsorption onto clay sediments higher concentrations of fe and total sulfur ts occur in black clays the correlations of the trace metals with iron suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur in some cores indicate that they were precipitated as fe sulfides age determinations suggest that clay horizons at 5 m depth were deposited at around 5 000 and 6 000 years bp 14c ages during the transgressive phase of sea level change the results of the leaching techniques in the core samples show that higher amounts of as were extracted with deionized water even at neutral ph as can be released from sediments to groundwater and therefore groundwater pollution is a concern in masuda city and the surrounding area

influence of paleoenvironmental factors on preservation of organic matter in middle cretaceous greenhorn formation pueblo colorado sedimentological and geochemical studies of the upper cretaceous hartland shale and overlying bridge creek limestone members of the greenhorn formation reveal close associations between abundance of current induced sedimentary structures extent of bioturbation and type of preserved organic matter abundant hydrogen rich organic matter 4 5 wt and low sulfur to organic carbon ratios are characteristic of the laminated facies which lack current induced sedimentary structures sparse hydrogen poor organic matter 0 1 0 5 wt and relatively high sulfur to organic carbon ratios are characteristic of the bioturbated facies which contain numerous sedimentary structures indicative of currents the concentration of oxygen in the benthic environment and the degree of bio urbation of the sediment apparently were determined principally by the rate that oxygen was supplied advectively by currents rather than by the rate of oxygen consumption by decomposition thus paleoclimatic and paleo oceanographic factors that influenced mixing and current strength in the water column profoundly affected the amount and type of organic matter preserved in these units it is proposed that episodes of high river discharge lead to density stratification of the water column and in turn to quiescent oxygen depleted bottom water and high preservation of organic matter thus accounting for the intermittent widespread deposition of organic rich strata during maximum transgression and depth of the greenhorn sea the lateral association of voluminous deltaic deposits with dee water black shales in other elongate or restricted marine basins may have causes similar to those envisioned for the hartland shale and bridge creek limestone members

process modeling studies of physical mechanisms of the formation of an anticyclonic eddy in the central red sea surface drifters released in the central red sea during april 2010 detected a well defined anticyclonic eddy around 23 n this eddy was 45 60 km in radius with a swirl speed up to 0 5 m s the eddy feature was also evident in monthly averaged sea surface height fields and in current profiles measured on a cross isobath shipboard ctd adcp survey around that region the unstructured grid finite volume community ocean model fvcom was configured for the red sea and process studies were conducted to establish the conditions necessary for the eddy to form and to establish its robustness the model was capable of reproducing the observed anticyclonic eddy with the same location and size diagnosis of model results suggests that the eddy can be formed in a red sea that is subject to seasonally varying buoyancy forcing with no wind but that its location and structure are significantly altered by wind forcing initial distribution of water stratification and southward coastal flow from the upstream area momentum analysis indicates that the flow field of the eddy was in geostrophic balance with the baroclinic pressure gradient forcing about the same order of magnitude as the surface pressure gradient forcing

the inorganic geochemistry of cretaceous black shales dsdp leg 41 in comparison to modern upwelling sediments from the gulf of california

occurrence and origin of ultralaminar structures in amorphous kerogens of various source rocks and oil shales abstract forty low maturity type i ii kerogens from source rocks and oil shales ranging in age from infra cambrian to miocene were examined by transmission electron microscopy tem when previously observed by light microscopy and or uv fluorescence microscopy the above samples like a very large number of kerogens seemed homogeneous and amorphous in fact tem revealed the presence of ultralaminar structures in 22 of these amorphous kerogens the abundance of ultralaminae depends on the considered sample and some of the tested kerogens are nearly exclusively composed of ultralamina accumulations based on thickness three main groups of ultralaminae can be identified parallel studies on extant algae indicated that some of the above ultralaminae likely derived from the resistant outer walls of microalgae the fossilization of such outer walls should occur via the selective preservation pathway and result in the formation of highly aliphatic ultralaminar kerogens the lack of ultralaminae in infra cambrian kerogens is consistent with a cyanobacterial origin

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

an oceanic general circulation model ogcm investigation of the red sea circulation 2 three dimensional circulation in the red sea 1 the three dimensional circulation of the red sea is studied using a set of miami isopycnic coordinate ocean model micom simulations the model performance is tested against the few available observations in the basin and shows generally good agreement with the main observed features of the circulation the main findings of this analysis include an intensification of the along axis flow toward the coasts with a transition from western intensified boundary flow in the south to eastern intensified flow in the north and a series of strong seasonal or permanent eddy like features model experiments conducted with different forcing fields wind stress forcing only surface buoyancy forcing only or both forcings combined showed that the circulation produced by the buoyancy forcing is stronger overall and dominates the wind driven part of the circulation the main circulation pattern is related to the seasonal buoyancy flux mostly due to the evaporation which causes the density to increase northward in the basin and produces a northward surface pressure gradient associated with the downward sloping of the sea surface the response of the eastern boundary to the associated mean crossbasin geostrophic current depends on the stratification and b effect in the northern part of the basin this results in an eastward intensification of the northward surface flow associated with the presence of kelvin waves while in the south the traditional westward intensification due to rossby waves takes place the most prominent gyre circulation pattern occurs in the north where a permanent cyclonic gyre is present that is involved in the formation of red sea outflow water rsow beneath the surface boundary currents are similarly intensified southward undercurrents that carry the rsow to the sill to flow out of the basin into the indian ocean index terms 4243 oceanography general marginal and semienclosed seas 4255 oceanography general numerical modeling 4532 oceanography physical general circulation keywords red sea marginal sea oceanic general circulation model water mass formation

comprehensive evolution of a petroleum system in absolute time the example of brynhild norwegian north sea abstract petroleum systems are inherently complex comprising multiple components and processes which variably interact in space and time to form petroleum accumulations improved understanding of these complex systems requires a holistic approach of integrating diverse geological geophysical and organic and inorganic geochemical data here we present an applied and comprehensive re os geochronological and geochemical study on the brynhild petroleum system from the norwegian north sea essential components of this system include shale source rocks of the mandal and farsund formations reservoir sandstones of the ula formation and their bitumen extracts and produced brynhild crude oil rock eval trace metal and re os data reveal the excellent oil generation potential of the shaley source rocks high contents of organic matter containing large amounts of type i kerogens and constrain their depositional conditions anoxic bottom waters in a high productivity regime driven by enhanced supply of land derived nutrients seven re os shale ages between 146 and 134 ma are consistent with existing volgian ryazanian age estimates and constrain the initial 187os 188os of the shales to 0 52 in the lowermost farsund formation and 0 75 in the uppermost mandal formation solvent extracted reservoir rocks of the ula formation contain insoluble organic matter with type iii type iv kerogens likely supplied by erosion of older a precise 179 ma re os age with unrealistically low initial 187os 188os coal bearing sediments or organic rich shales the brynhild crude oil has relatively low 187os 188os and a generation age of 44 ma based on an asphaltene only re os isochron maltenes from the brynhild crude oil are isotopically affected by interaction with organic rich source rocks that represent the seal for the brynhild oil field compared with the crude oil bitumen from ula formation sandstones have contrasting re os properties high 187os 188os ratios and young generation ages between 8 and 0 ma based on asphaltene bitumen maltene re os triplets asphaltene only re os regressions and re os model ages for components with extremely high 187re 188os the 44 ma and 8 0 ma re os ages agree well with regional burial models that indicate oil generation from 44 ma to present day a genetic link between crude oil and bitumen is indicated by their similar alkane patterns v and ni contents and v ni and pristane phytane ratios modeling of 187os 188os for individual organic components through time shows that shales of the mandal formation developed 187os 188os ratios that match those of the crude oil and bitumen at 44 ma and 8 ma respectively and therefore confirm the source for both hydrocarbon phases we suggest that bitumen formed during in reservoir mixing of a 44 ma old early mature asphaltene poor oil brynhild crude oil with an 8 ma old asphaltene rich oil

wind wave source functions in opposing seas the red sea is a challenge for wave modeling because of its unique two opposed wave systems forced by opposite winds and converging at its center we investigate the different physical aspects of wave evolution and propagation in the convergence zone the two opposing wave systems have similar amplitude and frequency each driven by the action of its own wind wave patterns at the centre of the red sea as derived from extensive tests and intercomparison between model and measured data suggest that the currently available wave model source functions may not properly represent the evolution of the local fields that appear to be characterized by a less effective wind input and an enhanced white capping we propose and test a possible simple solution to improve the wave model simulation under opposing winds and waves condition this article is protected by copyright all rights reserved

proliferation of shallow water radiolarians coinciding with enhanced oceanic productivity in reducing conditions during the middle permian south china evidence from the gufeng formation of western hubei province the middle permian is a critical period when a possible cooling regime prevailed and massive deep water cherty sediments were deposited in the south china craton an integration of radiolarian paleoecologic and geochemical studies from the middle permian gufeng cherty succession of western hubei province south china tests the relationships among oceanic productivity redox conditions and radiolarian responses as well as origin of the cherts a total of 21 species and six undetermined species in 10 radiolarian genera are identified from the gufeng formation in the northern margin basin of the yangtze platform of the south china craton three radiolarian pseudoalbaillella globosa follicucullus monacanthus and follicucullus scholasticus zones were established and constrained the gufeng formation as roadian to middle capitanian in age the gufeng cherts embrace a biologic and hydrothermal origin in the northern marginal basin and southern margin basin the nanpanjiang basin of the south china craton respectively the high oceanic primary productivity in surface oceans resulted in the widespread reducing conditions in the bottom water column such high oceanic productivity event slightly predated the middle permian kamura cooling event of the panthalassian ocean both the elevated continent weathering due to pre eruptive crustal uplift of the emeishan flood volcanism and active oceanic upwelling may have stimulated high oceanic productivity and facilitated the deposition of the gufeng cherts all radiolarians bloomed in relatively oxic conditions only shallow water radiolarians mainly spherical forms proliferated in the reducing conditions which also coincided with an enhanced oceanic productivity the abundance of spherical radiolarians therefore is an ideal proxy indicating oceanic primary productivity

physical and biological characteristics of the winter summer transition in the central red sea the central red sea crs lies between two distinct hydrographic and atmospheric regimes in the southern red sea seasonal monsoon reversal regulates the exchange of water between the red sea and the indian ocean in the northern red sea intermediate and occasionally deep water are formed during winter to sustain the basin s overturning circulation highly variable mesoscale eddies and the northward flowing eastern boundary current ebc determine the physical and biogeochemical characteristics of the crs ship based and glider observations in the crs between march and june 2013 capture key features of the transition from winter to summer and depict the impact of the eddy activity on the ebc flow less saline and relatively warmer water of indian ocean origin reaches the crs via the ebc initially an anticyclonic eddy with diameter of 140km penetrating to 150m depth with maximum velocities up to 30 35 cm s 1 prevails in the crs this anticyclonic eddy appears to block or at least redirect the northward flow of the ebc dissipation of the eddy permits the near coastal northward flow of the ebc and gives place to a smaller cyclonic eddy with a diameter of about 50km penetrating to 200m depth by the end of may as the northerly winds become stronger and persistent throughout the basin characteristic of the summer southwest monsoon wind regime the ebc and its associated lower salinity water became less evident replaced by the saltier surface water that characterizes the onset of the summer stratification in the crs

organic rich biolaminated facies from a kimmeridgian lagoonal environment in the french southern jura mountains a way of estimating accumulation rate variations abstract during kimmeridgian times the present day southern jura was a carbonate platform in the palaeolagoon at the village of orbagnoux organic matter was deposited giving birth to calcareous laminites with organic carbon reaching 12 three facies may be distinguished two types of laminites are encountered one made of parallel laminae and the other made of undulating laminae the laminites alternate with massive limestone beds in which no internal structure may be seen the lithology sedimentology and the faunal floral and organic content of laminites and of massive limestones was thoroughly investigated at different scales using various methods field observation transmitted light and scanning electron microscopy rock eval pyrolysis biomarkers infrared study of kerogen palynofacies observation it is suggested that the different types of laminites parallel or undulating may reflect variations in the accumulation rates linked with the carbonate and organic matter productions undulating laminae would correspond to periods of lack of sedimentation whereas parallel laminae would reflect alternations of periods of sedimentation and periods of non sedimentation these variations might in turn reflect climatic changes affecting the emerged lands supplying the lagoon with detrital products organic or inorganic the accumulation and preservation of organic matter were made possible by the development of microbial mats building oxygen tight barriers at the water sediment interface these barriers separated overlying oxygenated water from anaerobic sediments these phenomena may explain one way in which potential hydrocarbon source rocks can form under a poorly oxygenated water column

vanadium accumulation in carbonaceous rocks a review of geochemical controls during deposition and diagenesis abstract published data relevant to the geochemistry of vanadium were used to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks reduction adsorption and complexation of dissolved vanadium favor addition of vanadium to sediments rich in organic carbon dissolved vanadate v v species predominate in oxic seawater and are reduced to vanadyl ion v iv by organic compounds or h 2 s vanadyl ion readily adsorbs to particle surfaces and is added to the sediment as the particles settle the large vanadium concentrations of rocks deposited in marine as compared to lacustrine environments are the result of the relatively large amount of vanadium provided by circulating ocean water compared to terrestrial runoff vanadium rich carbonaceous rocks typically have high contents of organically bound sulfur and are stratigraphically associated with phosphate rich units a correspondence between vanadium content and organically bound sulfur is consistent with high activities of h 2 s during sediment deposition excess h 2 s exited the sediment into bottom waters and favored reduction of dissolved v v to v iv or possibly v iii the stratigraphic association of vanadiferous and phosphatic rocks reflects temporal and spatial shifts in bottom water chemistry from suboxic phosphate concentrated to more reducing euxinic conditions that favor vanadium accumulation during diagenesis some vanadium organic complexes migrate with petroleum out of carbonaceous rocks but significant amounts of vanadium are retained in refractory organic matter or clay minerals as carbon in the rock evolves toward graphite during metamorphism vanadium is incorporated into silicate minerals

sensitivity of red sea circulation to monsoonal variability during the holocene an integrated data and modeling study received 20 october 2009 revised 6 march 2010 accepted 30 june 2010 published 4 november 2010 1 we used an oceanic general circulation model to evaluate the sensitivity of the hydrography and circulation of the red sea in response to reduced sea level and modified atmospheric conditions during the holocene with holocene sea level close to the modern level the red sea was sensitive to changes in atmospheric conditions and it only shows a relatively mild response to sea level change changes in the monsoon system influence the exchange flow through the strait of bab el mandab the meridional overturning circulation of the red sea and its hydrography forced by humid conditions the modeled red sea temperature increased by 1 5 c while when arid conditions were imposed the temperature decreased by 2 5 c similar heating and cooling events during the early and late holocene are seen in a sea surface temperature record from the northern red sea derived from the temperature sensitive tex86 molecular biomarker which suggests that humid conditions prevailed during the early holocene and more arid conditions prevailed during the late holocene the gradual decline in red sea temperature between these two time periods suggests a gradual decline in the summer monsoon strength this monsoon trend and the resulting changes in the red sea circulation are supported by the distribution of crenarchaea fossil lipids in red sea sediments from this period monsoon driven changes in the exchange flow through the strait of bab el mandab affected the crenarchaea population structure and therefore their molecular fossil distribution in the sediments of the red sea potentially provides an index for the summer monsoon strength during the holocene

a paleoceanographic approach to the kimmeridge clay formation the upper jurassic lower cretaceous kimmeridge clay formation kcf is northern europe s premier source rock and can be understood using a new but relatively simple oceanographic model this explains or accommodates most current observations about the kcf and its depositional environment and draws upon paleogeographic paleoclimatic geochemical sedimentological and paleontological evidence

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

relationship between inferred redox potential of the depositional environment and geochemistry of the upper pennsylvanian missourian stark shale member of the dennis limestone wabaunsee county kansas u s a analyses of 21 samples collected from a core of the 52 8 cm thick stark shale member of the dennis limestone in wabaunsee county kansas demonstrate four cycles with two orders of magnitude variations in contents of cd mo p v and zn and order of magnitude variations in contents of organic carbon cr ni se and u the observed variability in amounts and or ratios of many metals and amounts and compositions of the organic matter appear related to the cause and degree of water column stratification and the resulting absence presence of dissolved o2 or h2s high cd mo u v zn and s contents a high degree of pyritization dop 0 75 0 88 and high high v v ni 0 84 0 89 indicate the presence of h2s in a strongly stratified water column intermediate contents of metals and s intermediate dop 0 67 0 75 and intermediate v v ni 054 0 82 indicate a less strongly stratified anoxic water column whereas low metal contents and low v v ni 0 46 0 60 indicate a weakly stratified dysoxic water column high p contents at the top of the organic matter rich intervals within the stark shale member indicate that phosphate precipitation was enhanced near the boundary between anoxic and dysoxic water compositions relatively abundant terrestrial organic matter in intervals deposited from the more strongly stratified h2s bearing water column indicates a combined halocline thermocline with the fresher near surface water the transport mode for the terrestrial organic matter the predominance of algal organic matter in intervals deposited from a less strongly stratified water column indicates the absence of the halocline and the presence of the more generally established thermocline relatively low amounts of degraded hydrogen poor organic matter characterize intervals deposited in a weakly stratified dysoxic water column the inferred variability in chemistry of the depositional environments may be related to climate variations and or minor changes in sea level during the general phase of deeper water deposition responsible for this widespread shale member

timing and tectonic setting of the sijiaying banded iron deposit in the eastern hebei province north china craton constraints from geochemistry and sims zircon u pb dating the north china craton ncc one of the oldest continental blocks in asia has a complicated evolutionary history with the age of the old crust up to 3 8 ga and records the important geological events of the earth the sijiaying bif the largest banded iron formation located in eastern hebei province in the east part of ncc records an important thermo tectonic event previous studies focused on the geological description but the timing and tectonic setting have been unclear so far the sijiaying bif is hosted in neoarchean metamorphic rocks which includes biotite leptynite hornblende plagioclase gneiss and biotite plagioclase gneiss using major element contents and ratios of the host rocks the protoliths of the hornblende plagioclase gneiss and biotite plagioclase gneiss are shown to be dacite whereas those of the biotite leptynites are sedimentary rocks based on geology and geochemistry of the host rocks we infer that the sijiaying bif is an algoma type deposit sims zircon u pb dating shows igneous zircons from the biotite plagioclase gneiss and hornblende plagioclase gneiss have u pb ages of 2535 8 ma and 2543 14 ma respectively zircons from the biotite leptynite have an age of 2537 13 ma we infer that the ages of 2543 2535 ma represent the time of the sijiaying bif paas normalized rey profiles of the ore samples are characterized by lree depletion and hree enrichment positive la and eu anomalies and an average y ho weight ratio of 32 indicating a mixture of submarine hydrothermal fluids and deep seawater ree data was combined with the 18o analyzed by previous researcher of the ore from individual magnetite bands to infer that the sijiaying bif precipitated from hydrothermal fluids discharging on the sea floor the hornblende plagioclase gneiss and biotite plagioclase gneiss that are enriched in lile and lree and depleted in high field strength elements hfse nb ta and ti have geochemical signatures that are similar to those of island arc volcanic rocks the biotite leptynite shows the characteristics of continental island arc based on the geology and geochemistry of associated wall rocks and ore samples we suggest that the sijiaying bif formed in a back arc basin in neoarchean

physical mechanisms routing nutrients in the central red sea mesoscale eddies and boundary currents play a key role in the upper layer circulation of the red sea this study assesses the physical and biochemical characteristics of an eastern boundary current ebc and recurrent eddies in the central red sea crs using a combination of in situ and satellite observations hydrographic surveys in november 2013 autumn and in april 2014 spring in the crs 22 15 24 1 n included a total of 39 and 27 ctd stations respectively in addition high resolution hydrographic data were acquired in spring 2014 with a towed undulating vehicle scanfish in situ measurements of salinity temperature chlorophyll fluorescence colored dissolved organic matter cdom and dissolved nitrate phosphorous ratios reveal distinct water mass characteristics for the two periods an ebc observed in the upper 150 m of the water column during autumn transported low salinity and warm water from the south toward the crs patches of the low salinity water of southern origin tended to contain relatively high concentrations of chlorophyll and cdom the prominent dynamic feature observed in spring was a cyclonic anticyclonic eddy pair the cyclonic eddy was responsible for an upward nutrient flux into the euphotic zone higher chlorophyll and cdom concentrations and concomitant lower nitrate phosphorous ratios indicate the influence of the ebc in the crs at the end of the stratified summer period

seasonal overturning circulation in the red sea 1 model validation and summer circulation the overturning circulation in the red sea exhibits a distinct seasonally reversing pattern and is studied using high resolution mit general circulation model simulations in the first part of this study the vertical and horizontal structure of the summer overturning circulation and its dynamical mechanisms are presented from the model results the seasonal water exchange in the strait of bab el mandeb is successfully simulated and the structures of the intruding subsurface gulf of aden intermediate water are in good agreement with summer observations in 2011 the model results suggest that the summer overturning circulation is driven by the combined effect of the shoaling of the thermocline in the gulf of aden resulting from remote winds in the arabian sea and an upward surface slope from the red sea to the gulf of aden set up by local surface winds in the red sea in addition during late summer two processes associated respectively with latitudinally differential heating and increased salinity in the southern red sea act together to cause the reversal of the contrast of the vertical density structure and the cessation of the summer overturning circulation dynamically the subsurface northward pressure gradient force is mainly balanced by vertical viscosity resulting from the vertical shear and boundary friction in the strait of bab el mandeb unlike some previous studies the three layer summer exchange flows in the strait of bab el mandeb do not appear to be hydraulically controlled

kimmeridge clay sedimentation a new cyclic model abstract the kimmeridgian upper jurassic fine clastic sequences of the boulonnais northern france and dorset southern england represent oxygen controlled environments five facies types with increasingly deteriorating living conditions ranging from normal shelf environments to submarine lifeless desert have been distinguished the widespread occurrence of this facies in the late jurassic north atlantic shelf sea and the palaeogeographic situation require a large scale model to explain the kimmeridge clay sedimentation anoxic conditions are generally explained by one of three models none of which applies directly to the kimmeridge clay a new model derived from the overall palaeogeographic and palaeoclimatic situation is therefore proposed in this model water mass stratification and anoxic bottom conditions refer to a high latitude monsoonal type wind circulation causing a water current and counter current system in the north atlantic shelf sea and the arctic ocean variations in the amount of oxygen in the bottom waters allow recognition of four different cycles with periods ranging from seasonal to 3 107 years they influenced the counter current system and the resulting anoxic conditions

observations of the summer red sea circulation 1 aiming at exploring and understanding the summer circulation in the red sea a cruise was conducted in the basin during the summer of 2001 involving hydrographic meteorological and direct current observations the most prominent feature characteristic of the summer circulation and exchange with the indian ocean is a temperature salinity and oxygen minimum located around a depth of 75 m at the southern end of the basin associated with gulf of aden intermediate water inflowing from the gulf of aden during the summer season as an intruding subsurface layer stirring and mixing with ambient waters lead to marked increases in temperature from 16 5 to almost 33 c and salinity from 35 7 to more than 38 psu in this layer by the time it reaches midbasin the observed circulation presents a very vigorous pattern with strong variability and intense features that extend the width of the basin a permanent cyclone detected in the northern red sea verifies previous observations and modeling studies while in the central sector of the basin a series of very strong anticyclones were observed with maximum velocities exceeding 1 m s the three layer flow pattern representative of the summer exchange between the red sea and the gulf of aden is observed in the strait of bab el mandeb in the southern part of the basin the layer flow is characterized by strong banking of the inflows and outflows against the coasts both surface and intermediate water masses involved in the summer red sea circulation present prominent spatial variability in their characteristics indicating that the eddy field and mixing processes play an important role in the summer red sea circulation

pyritization of trace metals in anoxic marine sediments the pyritization of reactive trace elements in different anoxic marine sediments was investigated to determine the importance of factors such as h2s reactive fe pyrite content and salinity in controlling this process the areas studied included anoxic sulfidic sediments baffin bay a hypersaline coastal lagoon from texas and green canyon a hemipelagic oil seepage area anoxic nonsulfidic sediments with high sedimentation rates atchafalaya bay mississippi delta system hemipelagic anoxic nonsulfidic sediments with low sedimentation rates gulf of mexico shelf and slope and orca basin an euxinic hypersaline basin and organic rich marsh sediments atchafalaya bay results indicate that the degree of trace metal pyritization dtmp of all trace metals except cd increased with increasing degree of pyritization dop irrespective of the type of sedimentary environment involved however for as hg and mo the dtmpdop values were generally above the 1 1 ratio line whereas the transition metals co cu mn and ni displayed a close to linear increase in dtmp with dop and moderate incorporation into pyrite chromium and the class b metals pb and zn were also gradually incorporated into the pyrite phase but without reaching the dtmp levels exhibited by the transition metals cadmium was not incorporated to a significant extent these results are consistent with the chemical attributes of these different classes of trace elements availability of dissolved trace metals and organic matter content are apparently important factors controlling the incorporation of co cr cu and ni into pyrite in anoxicsulfidic fe poor and h2s rich environments

anoxia and fluctuating climate recorded from the devonian carboniferous black shales tethys himalaya india a multi proxy approach due to inaccessibility and tough conditions high altitude low oxygen region very less information is available about the indian tethys himalayan sequences particularly geochemical data are scarce an attempt is made in the present study to evaluate the sediment geochemistry and paleo redox conditions of devonian carboniferous black shales from the spiti region tethys himalaya using multi proxy approach besides black shales this paper also provides the first in depth study of the geochemistry of phosphatic nodules hosted by the black shales that will allow primary and secondary processes to be understood geochemical investigations particularly redox sensitive trace element ratios for e g v v ni 0 5 ni co 4 3 7 2 v cr 2 and positive ce anomalies suggest deposition of these black shales under sub oxic to anoxic marine conditions thus recording an ocean anoxic event in the region these ocean anoxic events of devonian carboniferous spiti black shales which possess distinctive geochemical signatures can very well be correlated with global events such as hangenberg events and the lower alum shale event the span of the chemical index of alteration cia values 54 78 variation of 4si parameter 82 3 and c values 0 1 0 6 recorded in the black shales strongly indicate varying degrees of weathering conditions in the source area which in turn reflect fluctuating climatic conditions prevailing during the deposition of these sediments in devonian carboniferous period in the spiti region the distinct geochemical characteristics such as y sr and rare earth element ree enrichments particularly middle ree enrichments with a hat shaped pattern with high p2o5 contents up to 14 wt distinguish the nodules from the host rocks black shales sem scanning electron microscope results supplemented by xrd x ray diffraction studies of the nodules show the dominance of calcium silica and phosphatic phases the diversity of clay minerals significant variations in mineralogical composition and lack of any continuous vertical trend in the nodules suggest a relatively low impact on the primary environmental signal by burial diagenesis

major elements trace hydrocarbon sources in over mature petroleum systems insights from the sinian sichuan basin china abstract identifying hydrocarbon sources in over mature petroleum systems is important and challenging here we present a pilot study using inorganic geochemistry to trace hydrocarbon sources in the giant natural gas accumulations within the sinian neoproterozoic dengying formation in the sichuan basin sw china we investigated the major elements ti al fe mn mg ca na k and p as tracers of hydrocarbon sources for the first time our results show that the over mature solid bitumen in the reservoirs contains parts per million amounts of major elements in addition to carbon i e organic matter na and k in the bitumen occur mainly in the v ni porphyrin form al fe and mn are present in the fe porphyrin form the behavior of p is relatively complex and it may reside mainly in a non porphyrin organic form the other elements ti mg and ca may be present as emulsified invisible nano minerals the mn fe ratio and ternary 10mn fe p diagram can be used for hydrocarbon source rock correlations based on the proxies it is suggested that the lower cambrian qiongzhusi formation was the main source of hydrocarbons in the dengying formation our data suggest that inorganic geochemistry is an effective method for the study of over mature hydrocarbons and complements traditional organic geochemical approaches

distribution of arsenic and other trace elements in the holocene sediments of the meghna river delta bangladesh geochemical study of the holocene sediments of the meghna river delta chandpur bangladesh was conducted to investigate the distribution of arsenic and related trace and major elements the work carried out includes analyses of core sediments and provenance study by rare earth element ree analysis results showed that the cores pass downward from silty clays and clays into fine to medium sands the uppermost 3 m of the core sediments are oxidized average oxidation reduction potential orp 230 mv and the orp values gradually become negative with depths 45 to 170 mv indicating anoxic conditions prevail in the meghna sediments the ree patterns of all lithotypes in the study areas are similar and are comparable to the average upper continental crust arsenic and other trace elements pb zn cu ni and cr have greater concentrations in the silts and clays compared to those in the sands positive correlation between as and fe was found in the sediments indicating as may be adsorbed on fe oxides in aquifer sediments

chemical evidence of kerogen formation in source rocks and oil shales via selective preservation of thin resistant outer walls of microalgae origin of ultralaminae abstract new structures termed ultralaminae were recently observed by transmission electron microscopy usually in high amounts in a number of kerogens from oil shales and source rocks morphological similarities were noted between ultralaminae and the thin ca 15 nm resistant outer walls composed of non hydrolyzable macromolecules algaenans commonly occurring in extant chlorophyceae especially in the cosmopolitan genus scenedesmus identification of the pyrolysis products of s quadricauda algaenan showed i a highly aliphatic structure based on a macromolecular network of long up to c32 polymethylenic chains probably cross linked by ether bridges and ii a close correlation based on the formation of n alkylnitriles between this algaenan and two ultralaminar kerogens the rundle oil shale mainly composed of ultralamina accumulations and the green river shale ultralaminae dispersed within an amorphous matrix these fossil ultralaminae therefore likely originated from the selective preservation of the thin algaenan containing outer walls of scenedesmus and or of other chlorophyceae containing outer walls of a similar morphology and composition relative distributions of n alkylnitriles and of n alkanoic acids in the pyrolysates of s quadricauda algaenan and of the rundle oil shale indicated that nitriles are not derived from secondary reactions of carboxylic acids but originate from preexisting nitrogen functions likely amides previous evidence of kerogen formation via selective preservation of algaenans was restricted to rather uncommon kerogens the present results added to ultralamina common occurrence and abundance point to a wide involvement and to a large contribution of the selective preservation of algaenan containing thin outer walls of chlorophyceae in the formation of kerogens in a number of lacustrine source rocks and oil shales all the available information suggest that the three way correlation selective preservation of algaenans from thin resistant chlorophycean outer walls formation of fossil ultralaminae presence of n alkylnitriles with a typical distribution in the pyrolysates of ultralaminar kerogens observed in this study might be of a general character

carbon sulfur iron systematics of the uppermost deep water sediments of the black sea box cores recovered during leg 4 of the 1988 r v knorr black sea oceanographic expedition from deep water regions of the basin were dominated by coccolith rich microlaminated unit 1 sediment and muddy gray turbidite layers both organic carbon oc and pyrite sulfur values for unit 1 display narrow ranges with mean concentrations of 5 3 1 1 1 wt and 1 3 0 3 wt respectively unit 1 is not enriched in pyrite s relative to sediments deposited under oxygenated bottom waters normal marine sediments with comparable oc concentrations carbon sulfur relationships evaluated on a calcium carbonate free basis to avoid spurious correlations resulting from dilution effects demonstrate that oc and pyrite s are essentially decoupled these observations combined with the persistence of elevated pore water sulfide to depth and a strong correlation between pyrite s and the detrital fe component argue strongly for limitation of pyrite formation in unit 1 by the availability of reactive fe unit 1 fe limitation is further indicated by degree of pyritization dop studies a measure of the extent to which the original potentially reactive fe has been transformed to pyrite these studies show sulfidation of reactive fe ranging from 57 to 78 with dop values independent of oc concentration unit 1 dop profiles suggest that the majority of the pyrite is formed in the sulfidic water column and or very close to the sediment water interface pyrite s concentrations of unit 1 when compared with the particulate reduced sulfur fluxes measured in time series sediment traps are compatible with predominantly water column pyrite formation because of the limitations in the supply of reactive fe associated with the comparatively high supply of oc the microlaminated sediment is characterized by c s ratios greater than those typical of holocene oxically deposited sediments the turbidite muds of the deep basin display high reduced s values relative to holocene normal marine sediments in samples with low oc concentrations low c s ratios this reflects pyrite formation under anoxic sulfidic bottom water conditions in a probable upper slope source region as well as during transport and final deposition intermediate dop values for the turbidites in part a product of their rapid rate of deposition reveal that fe limitation is ultimately not a factor and that further pyrite should form during burial however the very rapid rate at which unit 1 pyrite forms suggests fundamental differences between the overall reactivities of the fe phases associated with the microlaminated and turbiditic sediments the signature of water column anoxia with regard to sedimentary pyrite formation is clearly indicated by the high dop values of unit 1 and the comparatively high levels of s associated with the low concentrations of oc of the turbidite muds this agrees with similar conclusions based on studies of ancient sedimentary rocks

on the crossover of boundary currents in an idealized model of the red sea the west to east crossover ofboundarycurrents has been seen in mean circulationschemes fromseveral past models of the red sea this study investigates the mechanisms that produce and control the crossover in an idealized eddy resolving numerical model of the red sea the authors also review the observational evidence and derive an analytical estimate for the crossover latitude the surface buoyancy loss increases northward in the idealized model and the resultant mean circulation consists of an anticyclonic gyre in the south and a cyclonicgyreinthenorth in themidbasin thenorthwardsurfaceflow crossesfromthewestern boundarytothe eastern boundary numerical experiments with different parameters indicate that the crossover latitude of the boundary currents changes with f0 b and the meridional gradient of surface buoyancy forcing in the analytical estimate which is based on quasigeostrophic b plane dynamics the crossover is predicted to lie at the latitude where the net potential vorticity advection including an eddy component is zero various terms in the potential vorticity budget can be estimated using a buoyancy budget a thermal wind balance and a parameterization of baroclinic instability

present environment of dam lake sambe southwestern japan a geochemical study of bottom sediments geochemical analyses of lakebed and core sediments from lake sambe on the outskirts of oda city in shimane prefecture in southwestern japan were carried out in order to assess the water quality and the concentration and distribution patterns of sixteen elements the lake water showed a stratified condition with respect to dissolved o2 and as fe and mn concentrations in the bottom layers which increased in the summer the chemical composition of the sediments as measured by x ray fluorescence included major and trace elements p ca sc ti v cr fe ni cu zn as sr zr pb and th and total sulfur ts elevated values of as zn v fe p and ts were present in several layers of the upper cores from 0 to 5 cm and other surface sediments increases in the abundances of these metals in lake sediments are probably related to the reducing condition of the sediments fine grained organic rich sediments and post depositional diagenetic remobilization moreover correlations between the concentrations of trace metals and iron in the sediments suggest their adsorption onto fe oxy hydroxides whereas correlations with sulfur indicate that they were precipitated as fe sulfides the average abundances of as pb zn and cu exceeded the lowest effect level and interim sediment quality guideline values that the new york state department of environmental conservation and the canadian council of ministers of the environment determined to have moderate impact on aquatic organisms in addition concentrations of as and zn exceeded the coastal ocean sediment database threshold value indicating potentially toxic levels therefore the presence of trace metals in the lake sediments may result in adverse effects on biota health

climatological coastal jet collision intermediate water formation and the general circulation of the red sea the authors present climatologies of a numerical model of the red sea focusing on the dynamics of winter intermediate water formation northward flowing boundary currents are identified as the major dynamical elements at the northern boundary the eastern current follows the geometry eventually turning back to the south at 268n and the western wall the two boundary currents collide at the collision site the denser eastern current subducts under the western boundary current the subduction forces the western boundary current eastward into the interior convection communicates the surface fluxes to the downwelled plume and intermediate water forms the estimated rate 0 11 sv sv 106 m3 s21 agrees with previous estimates the authors identify basin scale sea surface tilt to the north due to variable thermohaline forcings as the key dynamical variable the resultant geostrophic eastward cross channel flow interacts with the boundaries and creates upwelling and surface topography spatial patterns that drive the coastal jets upwelling induced vortex stretching dominates the vorticity balance and governs the separation of the western boundary current from the western wall the process ceases in the summer

the geochemistry of dsdp sediments from site 223 indian ocean abstract detailed major and trace element chemistry is presented for 41 sediment samples from dsdp site 223 borehole cores a marked change in chemical and mineralogical character is shown at the end of the early miocene epoch which relates to tectonic events and associated changes in sedimentary regime enrichment in the contents of such elements as mg cr and ni compared with average values for fine grained sediments occurs throughout the sequence and is particularly marked in the upper group of samples a basic ultrabasic provenance is suggested the oman ophiolites leaching with combined acid reducing agent indicated typical lithogenous character ordering for the elements and emphasised the enrichment of mg cr ni and li cu zn pb fe and ti over values for near shore muds and terrigenous material factor analysis on the bulk chemical data identifies the main lithogenous and biogenous components subdividing the latter it separates the upper and lower group of chemically dissimilar sediments and delineates a mn hydroxide phase it also shows the essentially independent roles of na ba and p

anoxia vs productivity what controls the formation of organic carbon rich sediments and sedimentary rocks discussion the prevailing explanation for the origin of organic rich sediments and rocks invokes deposition under conditions of anoxia however recent research suggests that high primary production and not water column anoxia provides the first order control on the accumulation of organic rich facies in the modern oceans oxygen minima do not appear to have any direct effect on carbon accumulation in continental margin or marginal sea environments sediments accumulating in the modern black sea the type euxinic basin are not particularly enriched in organic matter despite the presence of an anoxic water column although a sapropel containing extremely high carbon concentrations was deposited during the holocene at a time when the basin was oxic results of a recently published co pled ocean atmosphere model indicate that during the cretaceous thermohaline and surface circulation in the oceans was similar to or more intense than modern conditions despite the overall equable climate such conditions confound the idea that circulation in the cretaceous atlantic for example was punctuated by oceanic anoxic events brought about by more sluggish circulation sporadic temporal and spatial increases in primary production reflecting changes in the behavior and or state of the ocean atmosphere system constitute a more tenable explanation for the occurrence of modern and quaternary carbon rich sediments and cretaceous black shales consequently the fundamental control on the accumulation of carbon rich facies in the oceans and marginal seas is not the presence or absence of anoxia

paleoseismic inferences from a high resolution marine sedimentary record in northern chile 23 s abstract the active margin of northern chile is characterized by strong seismic events which induce gravity instability for sedimentary sequences located along the outer forearc of the andean range even though the narrow continental platform of this area limits the accumulation of marine sediments a detailed paleoceanographic reconstruction using high resolution sedimentological and geochronological techniques of a holocene sedimentary sequence in mejillones bay 23 s provides important tools to infer the occurrence of past great subduction earthquakes and or associated tsunamis from the analyses of short cores retrieved in this shallow marine basin we infer the occurrence of two strong seismic events during historical times the first one dated between the years 1409 and 1449 ad produced an angular unconformity and associated lenticular coarse grained deposits generated after local reworking of shallower material the second one dated between the years 1754 and 1789 ad caused slumping erosive processes and local reworking of material the analysis of seismic profile data acquired in this bay allowed the recognition of a major slump deposit within the upper sedimentary sequence tentatively dated as of middle holocene age this event might record the greatest earthquake and tsunami affecting the basin within the last few thousand years we interpret that destabilization of sediments occurs most probably in response to local reactivation of faults within the mejillones peninsula during strong earthquakes especially the mejillones fault

formation of intrathermocline lenses by eddy wind interaction abstractmesoscale intrathermocline lenses are observed throughout the world ocean and are commonly attributed to water mass anomalies advected from a distant origin an alternative mechanism of local generation is offered herein in which eddy wind interaction can create lens shaped disturbances in the thermocline numerical simulations illustrate how eddy wind driven upwelling in anticyclones can yield a convex lens reminiscent of a mode water eddy whereas eddy wind driven downwelling in cyclones produces a concave lens that thins the mode water layer a cyclonic thinny such transformations should be observable with long term time series in the interiors of mesoscale eddies

geochemistry of eastern mediterranean sediments primary sediment composition and diagenetic alterations abstract two cores recovered in the eastern mediterranean were analysed for major minor and trace elements the primary chemical composition of the sediment is different at each location probably because the lithological sources and the relative biogenic contributions differ carbonates are important for the concentration of ca mg and sr whereas aluminosilicates determine the concentration of si al k li y and be and to a lesser extent that of fe cr ti mg zn and zr in sapropels organic carbon and sulphur seem to be closely related bromine mo p fe v cu zn co ni and cr are closely associated with organic and sulphidic compounds the concentration versus depth profile for organic carbon in two sapropels points to a rapid establishment of conditions that gave rise to sapropel formation followed by a gradual transition back to normal conditions the primary composition is overprinted by diagenetic processes sulphate reducing conditions occurred during and just after sapropel deposition a progressive oxidation front mechanism which became active after sapropel deposition is responsible for additional major geochemical changes this diagenetic phenomenon has strong implications for the chemistry of fe mn ni co zn cu cr v u as and sb

diagenesis of the kimmeridge clay formation onshore uk study of sedimentology carbonate geochemistry and clay mineralogy of four laterally continuous beds from the outcrop of the kimmeridge clay formation indicates strong lateral variations in the depositional and early diagenetic processes reflecting the basin and swell topography of the depositional basin the mudstones from the swell environment with low sedimentation and subsidence rates are shelly and carbonate rich with thin poorly developed oil shales they were deposited under dysaerobic conditions with consequent poor organic matter preservation early diagenetic processes were limited to the sulphate reduction and methanogenesis zones with the formation of discrete horizons of concretions the shallow burial depths attained are reflected by the immaturity of the organic matter in the mudstones although ordered illite smectites are present sediments from other locations comprise black organic rich mudstones the thick beds and good organic matter preservation indicating deposition under high sedimentation and subsidence rates with anoxic bottom waters in a basinal environment these indurated mudstones contain a few shell fragments and much pyrite indicating intense reaction in the sulphate reduction zone carbonates were precipitated in the methanogenesis and decarboxylation zones as ferroan calcites and dolomites the much greater burial depths are indicated by the higher maturity of the organic matter and by the ordered nature of the illite smectites and the loss of kaolinite

seasonal overturning circulation in the red sea 2 winter circulation author posting 0american geophysical union 2014 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 119 2014 2263 2289 doi 10 1002 2013jc009331

comparative study by infrared spectroscopy of the organic matter of phosphate rich oulad abdoun basin and black shale timahdit basin series morocco abstract fourier transform infrared spectroscopy has been used to get quantitative information on the oxidation state of the organic matter of stable residues extracted from strata of the phosphate rich basin of oulad abdoun and from oil shales of the timahdit basin morocco throughout the respective filling of both basins the redox conditions have been more oxidizing in the top part of the sediments in oulad abdoun basin than in the timahdit basin this is interpreted as the result of the sedictural evolution of the basin oulad abdoun basin having evolved in stable platform conditions while the timahdit basin evolved in subsiding ones the phosphate rich beds contain the more oxidized organic stable residues sedimentological evidence shows that the oxidation was associated reworking processes these processes are responsible for the progressive concentration of the phosphatic grains and prove to be necessary for the p 2 o 5 content to become higher than 10 this value being the highest encountered in the sediment within which the phosphatic grains form

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

interplay between sedimentary organic matter and dissolved oxygen availability in a coastal zone of the humboldt current system mejillones bay northern chile abstract geochemical and petrographical analyses were done in 26 surficial sediment samples from mejillones bay northern chile to investigate the processes that participate in the preservation of sedimentary organic matter annual variability of chlorophyll a and dic 13 c measured in surface waters of three different parts of mejillones bay did not show any significant spatial variability in biological productivity on the other hand bottom dissolved oxygen showed strong changes associated with water depth and season surface sediment composition was statistically analyzed displaying organic facies which are in agreement with the principal zones of bottom oxygenation annual mean condition identified in this bay in the oxic coastal zone 1 ml l 1 the total carbon tc total nitrogen tn total organic carbon toc hydrogen index hi and oxygen index oi were 1 3 0 1 0 4 355 8 mg hc g toc and 237 6 mg co 2 g toc respectively these results and the presence of almost exclusively dispersed amorphous organic matter suggest an environment where most metabolizable organic matter is degraded within the water column and or in the sediment water interface in the microxic hemipelagic zone 1 located deeper than 65 m the tc tn toc hi and oi were 10 5 1 0 6 6 529 7 mg hc g toc and 103 1 mg co 2 g toc respectively these values and the presence of abundant agglomerated amorphous organic matter suggest a better preservation of metabolizable and non metabolizable compounds we can conclude that biological productivity and dissolved oxygen exert a similar influence on the sedimentary organic matter but the characteristics and quantity of organic material preserved in bottom sediments of this bay are controlled principally by the availability of dissolved oxygen at the sediment water interface according to this conclusion we suggest that the sedimentary record of mejillones bay must be interpreted in paleoceanographic terms primarily in relation to the temporal variability of dissolved oxygen more than biological productivity the oi seems to be a good proxy of paleoxygenation in this coastal system

hydraulic control of three layer exchange flows application to the bab al mandab two layer hydraulic models have proven to be extremely useful in understanding a number of exchange flows through straits for example the strait of gibraltar there are though some strait flows that cannot be represented by a two layer model a very striking example is the bab al mandab in the exchange between the red sea and the gulf of aden three distinct water masses are observed in the strait during summer the wintertime flow is though very different with only two layers observed in the strait in this paper a three layer model of hydraulically controlled exchange flows is described the model can represent exchange flows that are controlled with respect to either the first or second or both internal modes a number of different examples are discussed the model is able to explain the qualitative features of the seasonal variation of the flow in the bab al mandab in particular the reversal of the direction of flow of the surface layer and the intrusion into the red sea of cold intermediate water from the gulf of aden during the summer months can be explained by upwelling in the gulf of aden forced by the southwest monsoon

globally enhanced mercury deposition during the end pliensbachian extinction and toarcian oae a link to the karoo ferrar large igneous province the mesozoic era featured emplacement of a number of large igneous provinces lips formed by the outpouring of millions of cubic kilometres of basaltic magma the radiometric ages of several mesozoic lips coincide with the dates of oceanic anoxic events oaes as a result of these coincidences a causal link has been suggested but never conclusively proven this study explores the use of mercury as a possible direct link between the karoo ferrar lip and the coeval toarcian oae t oae mercury is emitted to the atmosphere as a trace constituent of volcanic gas and may be distributed globally before being deposited in sediments modern marine deposits show a strong linear correlation between mercury and organic matter content results presented here indicate departures from such a simple linear relationship in sediments deposited during the t oae and also during the pliensbachian toarcian transition an event that saw elevated benthic extinctions and carbon cycle perturbations prior to the t oae a number of depositional settings illustrate an increased mercury concentration in sediments that record one or both events suggesting a rise in the depositional flux of this element complications to this relationship may arise from very organic rich sediments potentially overprinting any hg toc signal whereas environments preserving negligible organic matter may leave no record of mercury deposition however the global distribution of coevally elevated hg rich levels suggests enhanced atmospheric mercury availability during the early toarcian potentially aided by the apparent affinity of hg for terrestrial organic matter although the relative importance of aquatic vs terrestrial fixation of hg in governing these enrichments remains uncertain a perturbation in atmospheric hg is most easily explained by enhanced volcanic output it is suggested that extrusive igneous activity caused increased mercury flux to the early toarcian sedimentary realm supporting the potential of this element as a proxy for ancient volcanism this interpretation is consistent with a relationship between lip formation and a perturbed carbon cycle during the pliensbachian toarcian transition and t oae the recording of these two distinct hg excursions may also indicate that the karoo ferrar lip released volatiles in temporally distinct episodes due either to multiple phases of magmatic emplacement or sporadic release of thermogenic gaseous products from intrusion of igneous material into volatile rich lithologies

a review on the huoqiu banded iron formation bif southeast margin of the north china craton genesis of iron deposits and implications for exploration abstract the huoqiu iron ore field in northwest anhui province is located in the north china craton ncc as a large banded iron formation bif iron ore field ore bodies occur in a middle high grade of neoarchean metamorphic formation forming a banded silicon iron series from north to south the main ore bodies can be divided into two sub belts from bottom to upper layers i e the a b ore belt consisting of leptynite schist magnetite quartz formation and the d ore belt consisting of schist marble hematite quartz formation based on a dataset from geological settings geophysical and geochemical exploration ore forming conditions and structural analysis of the iron deposit we discuss structural types sedimentary environments deep tectonic and ore controlling factors as well as characteristics and distribution of this colossal bif ore field in the huoqiu region using la icp ms techniques we obtained the oldest u pb age of ca 2 7 ga for plagioclase amphibolite as its original rock and 1 8 ga for magmatic granite in the huoqiu group the hf isotopes of zircon were also determined resulting in the oldest hf model age of 3 5 ga geochemical data indicate that the protolithes of amphibolites belong to a series of subalkaline rocks with enrichments of large ion lithophile elements and depletions of high field strength elements which are typical volcanic arc rocks the amphibolites have low k 2 o concentrations with low ratios of ti v 22 7 to 25 9 averaging 24 5 similar to island arc tholeiite this suggests that the iron deposit and bif are of the superior type in the huoqiu region

basinal restriction black shales re os dating and the early toarcian jurassic oceanic anoxic event 1 profiles of mo total organic carbon toc through the lower toarcian black shales of the cleveland basin yorkshire united kingdom and the posidonia shale of germany and switzerland reveal water mass restriction during the interval from late tenuicostatum zone times to early bifrons zone times times which include that of the putative early toarcian oceanic anoxic event the degree of restriction is revealed by crossplots of mo and toc concentrations for the cleveland basin which define two linear arrays with regression slopes ppm of 0 5 and 17 the slope of 0 5 applies to sediment from the upper semicelatum and exaratum subzones this value which is one tenth of that for modern sediments from the black sea mo toc regression slope 4 5 reveals that water mass restriction during this interval was around 10 times more severe than in the modern black sea the renewal frequency of the water mass was between 4 and 40 ka the mo toc regression slope of 17 applies to the overlying falciferum and commune subzones the value shows that restriction in this interval was less severe and that the renewal frequency of the water mass was between 10 and 130 years the more restricted of the two intervals has been termed the early toarcian oceanic anoxic event but is shown to be an event caused by basin restriction local to nw europe crossplots of re os and mo against toc show similar trends of increasing element concentration with increase in toc but with differing slopes together with modeling of 187 os 188 os and d 98 mo the element toc trends show that drawdown of re os and mo was essentially complete during upper semicelatum and exaratum subzone times mo toc regression slope of 0 5 drawdown sensitized the restricted water mass to isotopic change forced by freshwater mixing so that continental inputs of re os and mo via a low salinity surface layer created isotopic excursions of up to 1 3 in d 98 mo and up to 0 6 for 187 os 188 os restriction thereby compromises attempts to date toarcian black shales and possibly all black shales using re os chronology and introduces a confounding influence in the attempts to use d 98 mo and initial 187 os 188 os for palaeo oceanographic interpretation