the concentration of uranium in freshwater vadose and phreatic cements in a holocene ooid cay a method of identifying ancient water tables abstract the concentration of uranium has been measured using the fission track technique in vadose and freshwater phreatic cements from south joulters cay in the bahamas these analyses reveal dramatic differences in the u concentration of vadose 0 28 0 11 ppm and freshwater phreatic 1 80 75 ppm cements this distinctive change in concentration is proposed to result from 1 variations in the co2 of the waters of the phreatic and vadose environments and 2 selective exclusion of u during the precipitation of calcite the pco2 is important because it controls the ph and hence the concentration of co32 ions in the pore fluids as well as the amount of dissolution of the u rich aragonitic precursors for example an increas in pco2 will lower the ph and decrease the concentration of co32 present in the porewaters as the u present as the uranyl ion uo22 is mainly complexed with co32 a decrease in the concentration of co32 will not only alter the speciation of u but also increase the uo2 co3 22 co32 ratio of the fluid and hence the concentration of u in the precipitated carbonate cements the second mechanism for explaining the increase of u in phreatic cements relies on the low distribution coefficient for the incorporation of u into low mg calcite lmc the precipitation of lmc therefore leads to an increase in the concentration of u in the residual solution as fluids do not remain in the vadose zone but rather accumulate in the freshwater phreatic portion of the lens phreatic waters become relatively enriched in u compared to vadose fluids the clear difference in the u concentrations of cements in these two zones may enable the u concentration of cements to be used as an indicator of paleo water tables in ancient rocks even where other geochemical and petrographic evidences are equivocal

trace element signatures of chilean upwelling sediments at 36 s abstract with this contribution we continue the discussion on trace element te cycling in chilean upwelling sediments from within and below the oxygen minimum zone omz boning et al 2005 marine geology 220 1 21 low authigenic i e non lithogenic contents of te ag cd mo re and se were interpreted to result from the distinct seasonality in productivity induced organic flux bottom water oxygenation as well as dilution by terrigenous matter while all sediments were reducing enough to become depleted in mn highest enrichments in mo cd and re occur in sediments in contact with the omz here for a meaningful discussion total contents of as bi co cr cu ni pb sb tl v u and zn were corrected for the lithogenic background by determining te al ratios from local river samples the latter showed significantly lower te al ratios than average shale crust or andesite which are classically used for background correction hence the precise assessment of the lithogenic te contribution for the calculation of authigenic te contents allows to examine the source sink relationship of individual authigenic te for chilean sediments four te groups may be distinguished i mo re u and sb likely originate from sea water and accumulate via diffusive supply across the swi ii cd cr cu ni and zn require biologically induced pre concentration within biogenic material iii ag as se tl and v show an intermediate behaviour and iv bi and pb are contributed by anthropogenic activity highest enrichments in ni cu u as and v occur in sediments in contact with the omz the distinct depletion in co along with mn indicates the overall reducing but non sulfidic character of the chilean omz the degree of sedimentary sulfate reduction seems to be the most important control on chilean and peruvian near coastal enrichment of cd mo and u

inherent anisotropic stiffness of weathered geomaterial and its influence on ground deformations around deep excavations the shear modulus g0 at very small strain 0 001 or less is an important parameter for predicting ground movements of many geotechnical structures recent advances in laboratory testing enable th

geochemistry of peruvian near surface sediments sixteen short sediment cores were recovered from the upper edge ueo within wo and below bo the oxygen minimum zone omz off peru during cruise 147 of r v sonne solids were analyzed for major trace elements total organic carbon total inorganic carbon total sulfur the stable sulfur isotope composition 34 s of pyrite and sulfate reduction rates srr pore waters were analyzed for dissolved sulfate sulfide and 34 s of sulfate in all cores highest srr were observed in the top 5 cm where pore water sulfate concentrations varied little due to resupply of sulfate by sulfide oxidation and or diffusion of sulfate from bottom water 34 s of dissolved sulfate showed only minor downcore increases strong 32 s enrichments in sedimentary pyrite to 48 vs v cdt are due to processes in the oxidative part of the sulfur cycle in addition to sulfate reduction manganese and co are significantly depleted in peruvian upwelling sediments most likely due to mobilization from particles settling through the omz whereas release of both elements from reducing sediments only seems to occur in near coastal sites cadmium mo and re are exceptionally enriched in wo sediments 600 m water depth high re and moderate cd and mo enrichments are seen in bo sediments 600 m water depth re mo ratios indicate anoxic and suboxic conditions for wo and bo sediments respectively cadmium and mo downcore profiles suggest considerable contribution to ueo wo sediments by a biodetrital phase whereas re presumably accumulates via diffusion across the sediment water interface to precipitation depth uranium is distinctly enriched in wo sediments due to sulfidic conditions and in some bo sediments due to phosphorites silver transfer to suboxic bo sediments is likely governed by diatomaceous matter input whereas in anoxic wo sediments ag is presumably trapped due to sulfide precipitation cadmium cu zn ni cr ag and t1 predominantly accumulate via biogenic pre concentration in plankton remains rhenium sb as v u and mo are enriched in accordance with seawater te availability lead and bi enrichment in ueo surface sediments is likely contributed by anthropogenic activity mining accumulation rates of toc cd mo u and v from peruvian and namibian sediments exceed those from the oman margin and gulf of california due to enhanced preservation off peru and namibia copyright 2004 elsevier ltd

zone of metal driven anaerobic oxidation of methane is an important sink for phosphorus in the taixinan basin south china sea abstract phosphorus p is an important nutrient and has an important impact on global primary productivity presently the dynamics of the p cycle in low sulfate anoxic settings are largely unknown in this study the adsorption desorption behavior of fe bound p organic p loosely bund p detrital apatite p and refractory p was described in the sulfate and methane transition zone smtz at site 973 4 in the cold seep area of the taixinan basin south china sea results showed that the fe bound p and organic p were influenced by sulfate driven anaerobic oxidation of methane sd aom and metal driven anaerobic oxidation of methane md aom and subsequently the fe bound p and organic p were released as hpo42 into the pore water meanwhile significant increases were detected in authigenic carbonate fluorapatite pcfa and vivianite within the md aom zone which indicate that this zone is an important p sink area the md aom plays an important role in the formation of pcfa and vivianite because md aom provide the necessary hpo42 and fe2 for the formation of these minerals our findings have major implications for understanding the p cycle in low sulfate anoxic settings and are important for understanding the influence of md aom on the phosphate cycle

mobility of mo u as and sb within modern turbidites modern turbidites uranium molybdenum arsenic antimony we present and discuss porewaters and sediment data of mn fe mo u as and sb within four recent turbidites from the capbreton canyon sw france the deposition of turbidites on continental margins exerts strong influence on the fate of trace metals causing trace metal migration and or immobilization the down core distribution of the elements here depends entirely of ongoing diagenetic processes rather than the diffusion of o2 the persistence of fe mn oxides under anoxic conditions led to anoxic reoxidation of numerous species as nh4 reduced s compounds and trace metals metal oxides thus control the immobilization of mo and as in the solid phase and the remobilization of u and sb to the porewaters although the low sulphide production prevents anoxic authigenesis of mo and as reducing conditions below each horizon rich in mn fe oxides resulted in u and sb accumulation the exact mechanisms of sb immobilization are not known but it is most certainly different from that of as the profile shapes of mn and u were used to estimate the age of the turbidite deposits which cannot be determined by conventional radionuclide methods our interpretations however depend on calculations of diffusion coefficient particularly for u a simple diffusive model applied to mn suggested that the age of the latest deposit noted t1 was 22 months this date is close to the time elapsed between the core sampling and the last known turbiditic event in the capbreton canyon i e martin storm 18 months using the u data set and depending on diffusion coefficients used the estimated ages of the deeper layers were 4 7 yr for t2 and 7 5 14 yr for t3 the reliability and precision of this new approach to date sediments at short timescales is limited by the ignorance of a precise value for u diffusion coefficient reducing uncertainty on u diffusion coefficient will greatly support application of the proposed approach

trace metal signatures of eastern mediterranean sapropels abstract sapropel samples of pliocene to pleistocene age recovered during odp leg 160 from sites 964 ionian basin 969 mediterranean ridge 966 967 top and northern slope of the eratosthenes seamount south of cyprus and 968 cyprus margin were analysed for major and trace elements eastern mediterranean sapropels are characterized by high organic carbon and sulphur contents and by significant enrichments in several redox sensitive and or sulphide forming trace metals bi cd co cr cu mo ni re sb tl u v enrichment factors relative to average shale are comparable to those found in ctbe black shales the re content is extremely high in the sapropels studied with maximum values up to 1000 ng g re mo ratios averaging 2 7 10 3 are close to the seawater value high trace metal enrichments and re mo ratios close to the seawater value point to an anoxic water column during sapropel formation additionally enhanced ba concentrations in the sapropels support the assumption that bioproductivity was also high during these episodes trace metal signatures of sapropels originating from different drill sites on a transect across the eastern mediterranean are not only influenced by water depth but also by their location in the eastern mediterranean metal enrichments seem to be higher at the western sites compared with the eastern sites this probably reflects a change in the circulation pattern during periods of sapropel formation pliocene sapropels exhibit elevated trace metal contents in comparison with pleistocene examples therefore different palaeoceanographic conditions may have developed during the pleistocene compared with the pliocene altering palaeoceanography was probably controlled by climatic change which may be related to the onset of glaciation of the northern hemisphere decreasing summer precipitation throughout the late pliocene and the pleistocene may also have influenced sapropel deposition

rapid flooding of the sunda shelf a late glacial sea level record the increase in sea level from the last glacial maximum has been derived from a siliciclastic system on the tectonically stable sunda shelf in southeast asia the time from 21 to 14 thousand calendar years before the present has been poorly covered in other records the record generally confirms sea level reconstructions from coral reefs the rise of sea level during meltwater pulse 1a was as much as 16 meters within 300 years 14 6 to 14 3 thousand years ago

carbon and oxygen isotope composition of carbonate in bulk sediment in the southwest taiwan basin south china sea methane hydrate decomposition history and its link to mud volcano eruption abstract anaerobic oxidation of methane aom coupled with sulfate reduction sr generates authigenic carbonate which has the unique carbon and oxygen isotope composition in sulfate methane transition zone smtz the carbon and oxygen isotope composition of carbonate in sediments which can be used to revel the variable methane flux is affected by the percentage of aom driven carbonate in sediments to investigate the methane hydrate decomposition history in the southwest taiwan basin we analyzed a 13 m long sediment core for grain size carbonate and elemental carbon contents and stable carbon and oxygen isotopes composition of carbonate 13ccarb and 18ocarb the ams 14c dating results and carbonate content reveal that a turbidity current occurred at around 14 ka b p which reversed sediment accumulation between 455 and 885 cm in depth combining the chronological framework and 13ccarb values we identified that the methane hydrate decomposition scale began to decrease at 14 ka b p moreover we discovered that three transiently enhanced methane hydrate decomposition events occurred from then on although the 13ccarb and 18ocarb variability are as expected the low 18ocarb values are inconsistent with the previous theory which favors 18o enriched in aom driven authigenic carbonate thus we suggest that a large amount of 18o depleted water which originally migrated from southwest taiwan island was injected into surface sediment along with the eruption of mud volcanos as the terminal electron accepter of aom sr reaction the exogenous 18o depleted water leads its special oxygen isotope to be inherited by the authigenic aom driven carbonate the proposed theory provides new insights on the authigenic carbonate in methane hydrate area and the association between methane hydrates and mud volcanoes

the accumulation of silver in marine sediments a link to biogenic ba and marine productivity 1 the concentrations of ag and a suite of redox sensitive trace metals re cd and mo were measured in surface sediments from the western canadian mexican peruvian and chilean continental margins in all regions ag content increases from 80 ng g 1 i e lithogenic values on the shelf up to as high as 1483 ng g 1 on the lower slope however the trend of increasing ag with increasing water depth breaks down at deepwater sites 2500 m where only lithogenic concentrations are documented silver content does not correlate with the distributions of redox sensitive trace metals suggesting that sedimentary redox conditions are not the primary control on ag accumulation instead a positive correlation between ag and ba in surface and near surface sediments suggests that ag is scavenged by and delivered to the sediment with the organic particle flux scavenging probably results from the precipitation of ag2s within the organic particles due to the development of anoxia and sulfate reduction if this hypothesis is correct then ag has the potential to be a paleoproductivity proxy

upward flow of north pacific deep water in the northern south china sea as deduced from the occurrence of drift sediments 1 reflection seismic profiles show that drift sediments occur in the depth range of 1200 2800 m on the continental margin off southeast china these drift deposits were generated by upward flow near the dongsha islands of the north pacific deep water npdw which enters the south china sea via the bashi channel sill depth 2500 m this flow results in deposition of slope sediments resuspended off east and south taiwan on the slope southeast of the dongsha islands at 1200 m water depth this upward flow probably terminates and the npdw mixes with the surface water sediment ages from odp site 1144 southeast of the dongsha islands show that this process started at least 1 1 m y ago indications for mass wasting in the area of upslope water flow document the simultaneous occurrence of current and gravity controlled sedimentation processes however bottom current related drift sedimentation dominates

increased contribution of terrigenous supply from taiwan to the northern south china sea since 3 ma seismic profiles provide evidence that there has been strong transport by deep water bottom currents and drift deposition on the northern slope of the south china sea earlier geochemical studies suggest that the drift sediments originated primarily from taiwan however the transport process history and origin of the deep water bottom deposition in the northern south china sea on both glacial interglacial and tectonic time scales remain unclear here we show new high resolution records of clay minerals grain size and mass accumulation rate mar of terrigenous materials from ocean drilling program odp site 1144 together with trace element concentrations in siliciclastic sediments from odp site 1146 combined with other published data we find that the primary source for sediments at odp sites 1144 1148 since 3 ma is from taiwan and not from pearl river as previously thought before 3 ma however sediment source to odp sites 1146 and 1148 was mainly from the pearl river increased contribution of terrigenous supply from taiwan to the northern south china sea since similar to 3 ma may be related to the formation of the taiwan orogen and strengthening of deep water bottom current transport in the northern south china sea variations in clay mineralogy and sedimentology at odp site 1144 located on a sediment drift shows strong glacial interglacial cyclicity this suggests that bottom current deposition is highly dependent on sea level fluctuations which control the terrigenous supply to the deep sea c 2010 elsevier b v all rights reserved

the effects of diagenetic processes and fluid migration on rare earth element and organic matter distribution in seep related sediments a case study from the south china sea abstract methane seepage is an important factor governing microbial activity in marine sediments although its impact on the distribution of rare earth elements rees and organic matter in sediments is unclear here we report isotope signatures of organic 13ctoc and inorganic 13ctic carbon as well as total rees contents of core sediments collected from a well characterized seep area on the northern south china sea previous studies have identified sediments corresponding to three methane release events mres in the studied core mre i at 4 0 5 5 m mre ii at 7 4 8 2 m and mre iii at 10 0 11 5 m depth intervals increased methane flux and reducing bottom waters during mre i resulted in a higher accumulation of marine sourced organic matter as indicated by lower c n ratios and higher 13ctoc values compared with those of mres ii and iii sediments deposited during mre i have relatively low total ree contents which may be related to reduced ree adsorption on mn oxyhydroxides however the absence of ce anomaly at mre i is more likely due to the detrital input that obscures the original ce anomaly in the mre iii sediments a weak negative eu anomaly relative to that in the mre i and ii may be attributed to the reduction of eu3 to eu2 under strongly reducing conditions that caused by intense methane seepage these observations demonstrate that fluid flow may have an important effect on the distribution of both organic matter and rees in methane rich marine sediments

geochemical records of taiwan sourced sediments in the south china sea linked to holocene climate changes we present a multi proxy geochemical analysis of core kng5 retrieved from the northern south china sea slope spanning the last 13 0 ka bp to assess the response of weathering and erosion processes in the southwestern taiwan river basin to climate change a provenance analysis indicates that the core sediments were primarily derived from the southwestern taiwan river and can be used to reconstruct the erosion and or weathering history of this river basin the chemical index of alteration the plagioclase index of alteration rb sr al ti principle component 1 and k al combined with terrigenous mass accumulation rates and the proportion of clay exhibit sharp excursions from 12 0 to 5 5 ka peaking at 10 0 ka which suggests strong chemical weathering and physical erosion during the early mid holocene the period of the maximum summer monsoon abrupt falling weathering trends during 5 2 and 3 5 ka bp correlate with a weaker monsoon after 3 5 ka bp a stable lower weathering trend to the present day was evident indicating the deposition of less weathered sediments in the slope when the monsoon rainfall was weakening a good correlation between our proxy records of chemical weathering and variations of the monsoon intensity in south china emphasizes that variation in monsoon intensity is most likely the primary drive of the intensity of weathering and erosion in southwestern taiwan river sediments over the last 13 0 ka bp finally we concluded that geochemical parameters can be used as reliable proxies for climate variation on a millennial centennial time scale in such areas as taiwan where weathering limited regimes exist c 2015 elsevier b v all rights reserved

redox zonation of elements at an oxic post oxic boundary in deep sea sediments abstract deep sea sediments generally provide limited evidence of redox control on the post depositional redistributions of elements this is because only a fraction of any element is reactive and observed elemental distributions are the result of a number of competing processes which are simultaneously active so that redox effects are not dominant a detailed investigation is reported of a core which is unusual in showing unequivocal evidence of direct redox control operating in a homogeneous environment that is relatively free from competing processes a progressive oxidation front has migrated slowly downwards into a uniform turbidite over a long period ca 250 ky the reactive fractions of several redox sensitive elements now show a remarkable degree of organisation around the redox boundary of this front with the different elements exhibiting individual responses solid phase enrichments are not coincident but are arranged in a clear succession of concentration peaks along the redox gradient from oxic to postoxic conditions the succession is mn i fe se and pt cu and pb v zn and sb and u the movement directions of most elements can be inferred from the peak shapes against the homogeneous turbidite background composition the system seems to have been essentially isolated within the sediment for most elements so that no loss or gain can be ascribed to redox processes exceptions are u and v which have been augmented by uptake from ocean bottom waters into the sediments by an efficient redox trap mechanism

trace metal evidence for changes in the redox environment associated with the transition from terrigenous clay to diatomaceous sediment saanich inlet bc abstract we measured the concentrations of redox sensitive trace metals mn v mo u cd and re in sediments from odp leg 169s hole 1033b in saanich inlet british columbia to determine changes in redox conditions associated with the onset of laminated sediments at 12 5 kyr the most striking result is a large peak in authigenic re along with detrital levels of mo at the glacial terrigenous clay diatomaceous sediment transition in contrast the underlying glacial terrigenous clay which extends throughout the bottom section of the core is chemically similar to detrital concentrations either cowichan river particulates or average shale values these data suggest a period of oxic bottom waters but reducing pore waters this could be due to the dramatic transformation of saanich inlet during the late deglaciation from an open bay to an inlet which restricted circulation and slowed bottom water oxygen renewal a peak and gradual increase in authigenic mn in younger sediments subsequent to the re peak suggests that increasingly oxic conditions followed the authigenic enrichment in re these conditions could be connected to the younger dryas cooling period which was coincident with an increase in well oxygenated upwelled waters on the west coast of north america that form the bottom waters of saanich inlet metal concentrations in a gray clay bed 11 kyr are similar to their concentrations in the glacial terrigenous clay implying that they have a common source authigenic enrichments of re with little authigenic mo and cd suggest that before the deposition of this bed bottom waters were oxic and pore water oxygen was consumed in the top centimeter or less laminations above the clay layer suggest anoxic conditions which are also indicated by higher authigenic mo and cd and slightly lower re mo ratios in these sediments the basin remained mostly anoxic after the gray clay was emplaced as seen by continuous authigenic enrichment of the redox sensitive trace metals these results are consistent with increased stratification of the water column brought about by an influx of fresh water to the basin by a large flood

geochemical response to pulsed sedimentation implications for the use of mo as a paleo proxy abstract deglacial sediments in piston core jt96 02 from the continental slope off western canada contain numerous centimeter thick iron sulfide rich layers major and minor element chemistry as well as c and n isotopic data suggest that these layers represent background hemipelagic sedimentation intervening gray silty clay layers each of which exhibits a fining upward trend are distal turbidites the iron sulfides precipitated in response to the emplacement of each turbidite which slowed oxygen diffusion into the sediment allowing anoxic conditions to develop in the underlying relatively organic rich deposits resulting sulfate reduction and precipitation of fe sulfide fostered mo enrichment 2 g g it may also explain ni cr v and co enrichments although differences in detrital mineralogy cannot be ruled out particularly for ni and cr rhenium is also enriched albeit slightly within the sulfide layers but low re mo ratios 0 78 ng g g g suggest that anoxic conditions developed very rapidly metals with high lithogenic concentrations cd and u are not obviously enriched in the sulfide layers because there was insufficient time for noticeable authigenic accumulation before deposition of the next turbidite which severed diffusive communication with overlying seawater the primary source of metals silver is also slightly higher in the sulfide layers possibly linked to higher marine organic matter content in summary the pulsed character of sedimentation during the deglaciation led to episodic enrichment of mo and occurred independently of changes in bottom water oxygen or organic carbon content this observation potentially complicates the use of mo as a paleo proxy in some continental margin environments

carbonate rich sequences in the deep sea of the eastern south china sea subbasin iodp hole u1431d during the last 600 kyr abstract here we examined changes in carbonate preservation in a deep sea record hole u1431d 4240 m water depth retrieved from the south china sea scs during the international ocean discovery program iodp expedition 349 to evaluate these changes we applied a micropaleontological and geochemical multiproxy approach including planktonic foraminifera pf total abundance fragmentation fi and dissolution fdx indexes and total organic carbon toc the results of this study showed that during the last 600 kyr hole u1431d site has been under the effect of carbonate dissolution associated with the deepening of the lysocline and the calcite compensation depth nonetheless during mis 8 and mis 7 there was a significant increase in pf total abundance and toc content the low pf total abundance found in some intervals resulted in an underestimation of the fi and fdx indexes although high pf total abundance events occur at hole u1431d turbidite sequences these are also interpreted in the context of higher primary productivity pp in the central scs high toc contents from mis 10 to mis 6 were associated with the effects of enhanced pp during the mid brunhes dissolution interval as well as the dynamics of the east asian monsoon eam during mis 8 and 7 increased abundances of pf and toc contents may have been related to enhanced pp promoted by the seasonal eam our data suggest that enhanced pp associated with the occurrence of turbidite currents at the east scs subbasin allowed the preservation of pf at hole u1431d

deep water bottom current evolution in the northern south china sea during the last 150 kyr evidence from sortable silt grain size and sedimentary magnetic fabric abstract deep water bottom current dwbc plays a central role in global climate relative to the atlantic due to poor preservation of marine carbonate in the pacific sediments the evolution of pacific deepwater circulation is still unclear the south china sea scs connection to the pacific through luzon strait at a depth of about 2400 m offers a unique opportunity to monitor the changes of western pacific deep water circulation we present a magnetic and grain size analysis of two sediment cores pc111 and pc83 located in xisha trough northern scs in order to reconstruct past changes of dwbc during the last 150 kyrs variations in the mean size of sortable silt are interpreted to indicate past changes of dwbc which suggest abrupt millennial scale increasing dwbc strength during heinrich stadials hs1 hs2 hs3 hs4 hs5 hs6 hs7 hs8 hs9 hs10 hs11 for past 150 kyr the flow orientation of dwbc revealed by the anisotropy of magnetic susceptibility ams are mostly nw se direction in core pc111 and core pc83 which are both parallel to the local topography combined with the published studies we suggest the increase bottom current in northern scs during the heinrich stadials hs1 to hs11 times of weak north atlantic deep water formation demonstrating the tight coupling between the atlantic and pacific oceans

undrained anisotropy of k0 consolidated silt direct measurements of the initial shear strength and yielding anisotropy of a dense k0 consolidated silt are described and interpreted within a bounding surface framework the experiments were performed using the imperial college large hollow cylinder apparatus in which samples were sheared undrained with a range of orientations of the major principal stress 1 following initial k0 consolidation the interpretation is aided by data from oedometer and triaxial stress path tests strongly anisotropic stiffness yielding undrained strength and mobilized angle of shearing resistance characteristics are revealed the effects of drained and undrained stress changes applied to the samples after k0 consolidation are also described key words anisotropy hollow cylinder k0 consolidation silt bounding surface

early diagenetic processes in coastal marine sediments disturbed by a catastrophic sedimentation event abstract following a catastrophic flash flood in july 1996 as much as 50 cm of post glacial clays were deposited in less than 2 days in the upper reaches of the saguenay fjord quebec canada disrupting the normal sedimentation and diagenetic regimes we report detailed geochemical analyses of sediments porosity eh organic and inorganic carbon fe and mn reactive solid phases and acid volatile sulfide and porewaters salinity dissolved organic carbon doc fe ii mn ii nitrate ammonium and sulfate for seven stations located in the saguenay fjord three of these sag 05 sag 09 and sag 30 were visited in 1996 and once per year thereafter to document the chemical evolution of the sediment toward a new steady state the flood deposits contain less organic carbon and more inorganic carbon than the indigenous fjord sediments the flood deposit modified the distribution patterns of reactive mn and fe as a result of the reduction of mn and fe oxides delivered with the deposit and those concentrated at the now buried former sediment water interface most of the mn ii migrated to the new sediment water interface where a mn rich layer was formed in contrast much of the fe ii was precipitated as sulfides and remained trapped at or close to the old interface a nitrate peak developed in the porewater at the old sediment water interface possibly because of the oxidation of ammonia by mn oxides the distributions of porewater doc within the flood deposit correlate with the distributions of dissolved mn ii and fe ii suggesting that adsorbed doc was released when metal oxides were reduced

sedimentary responses to the east asian monsoon and sea level variations recorded in the northern south china sea over the past 36 kyr abstract sediment grain size is an important proxy to detect sedimentary process and record paleoenvironmental variations in continental slopes grain size measurements were performed for 298 samples of the 5 96 m long core pc338 spanning the past 36 kyr recovered from the northern south china sea scs results show that sea level and climatic influences on grain size distributions are crucial a turbidite formed during the last glacial maximum lgm is ascribed to the favorable topography close to the red river estuary induced by the low sea level four end member em components for the normal sediment layers were unmixed using a lognormal parametric end member modeling emm with the sea level decreasing more em4 15 100 m and less em1 0 2 m supplied the scs slope because em2 2 10 m consisted of fluvial suspension is dominated by the east asian summer monsoon easm precipitation it has the potential to substitute for the easm intensity em2 varied in phase with many south china paleoclimate records and the 30 n july insolation over the past 36 kyr and cooling climate events including the lgm heinrich events h1 and h3 younger dryas 8 2 ka and 10 3 ka lowered the em2 content our results further confirm the synchronous easm evolution in the south china continent mainly forced by the northern hemisphere summer insolation

the trace metal content of recent organic carbon rich sediments implications for cretaceous black shale formation organic carbon rich sediments are enriched in several redox sensitive and stable sulfide forming trace metals tm and form an important sink in global tm cycles in today s ocean such sediments are deposited in coastal upwelling areas like those in the gulf of california off peru or off the namibian coast and euxinic basins like the black sea in an attempt to distinguish both environments by their specific tm patterns some important conclusions may be drawn 1 the tm enrichment seen in both environments broadly is rather similar 2 upwelling sediments are often enriched in cd and p and depleted in co and mn 3 sapropels have a tendency towards higher enrichments in ba and mo s re as cu ni sb and fe reflecting the strong sulfidation in an anoxic water column 4 upwelling systems cover a broad range of environmental settings where the steepness of the slope the proximity of h2s to the sediment seawater interface and the intensity of bio accumulation and regeneration play an important role for tm accumulation 5 the tm content of anoxic basins is mainly controlled by tm availability in the water column and sedimentation rate 6 enhanced bio productivity is the main switch turning an oxygenated into an anoxic environment cretaceous black shales oae 2 exhibit tm signatures of both coastal upwelling areas and sapropels the strong enrichments in cd mo tl v cu ni bi and sb demonstrate that bio accumulation and presence of h2s in the water column and associated sulfidation processes persisted during this time interval in large parts of the proto atlantic the usefulness of ba as a paleoproductivity proxy is obscured by diagenesis the extreme accumulation in ag and zn requires either an additional tm source for instance hydrothermal input or a different tm seawater composition during the cretaceous the geochemical data suggest that the major driving force for the widespread occurrence of c t black shales seems to be the increase in volcanic activity and associated co2 input throughout the cretaceous the ocean atmosphere system operated in a mode different from today during this time interval after conversion of the nutrient co2 into organic matter the system switched back into the normal operational mode

controls on trace metal authigenic enrichment in reducing sediments insights from modern oxygen deficient settings any effort to reconstruct earth history using variations in authigenic enrichments of redox sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry further unravelling the multiple controls on sedimentary enrichments requires a multi element approach of the range of metals studied most is known about the behavior of fe mn and mo in this study we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined cd cu zn and ni in three oxygen poor settings the black sea the cariaco basin venezuela and the peru margin these three settings span a range of biogeochemical environments allowing us to isolate the different controls on sedimentary enrichment our approach relying on the covariation of elemental enrichment factors ef defined for element x as efx x al sample x al lithogenic has previously been applied to mo and u to elucidate paleoenvironmental information on for example benthic redox conditions the particulate shuttle and the evolution of water mass chemistry we find two key controls on trace metal enrichment first the concentration of an element in the lithogenic background sediment used in calculating efx controls the magnitude of potential enrichment maximum enrichment factors of 376 and 800 are calculated for mo 1 ppm in detrital sediments and cd 0 3 ppm respectively compared to values not greater than 17 in any setting for the other five metals 45 ppm to 4 5 wt in detrital sediments second there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment we further identify four important processes for delivery of trace metals to the sediment these are 1 cellular uptake especially important for zn and cd 2 interaction co precipitation with sulfide mo cu and cd 3 passive scavenging via the traditional particulate shuttle mo ni and cu and 4 an association with the benthic fe redox shuttle mn ni finally we summarize the oceanic mass balance of cd and mo and place the first constraints on the contribution of reducing sediments to the oceanic mass balance of cu zn and ni we show that reducing sediments are the ultimate repository for up to half the total output flux of these elements from the oceanic dissolved pool

depositional characteristics and processes of alongslope currents related to a seamount on the northwestern margin of the northwest sub basin south china sea this study infers from 2d seismic data the presence of a seamount related deep water contourite depositional system located on the northwestern margin of the northwest sub basin of the south china sea alongslope aligned erosive features and contourite drifts developed in water depths between 1000 and 1500 m on the present seafloor a moat formed north of the seamount as a result of bottom current intensification after being deflected by an obstacle morphology indicating a major eastward flowing current due to the coriolis deflection an elongated mounded drift developed to the north of the moat and a modest plastered drift to the south onlapping the north side of the seamount bottom currents away from the seamount are less or minimally intensified generating contourite channels and furrows over the drift to the north of the moat combined with the known oceanographic setting the bottom currents could belong to the anticyclonic south china sea intermediate water circulation from the seismic data the architecture of contourite deposits during progressive burial of the seamount is documented the first appearance of contourite channels in seismic unit 1 is inferred to be the onset of the contourite depositional system which could be traced back to the early late miocene the following aggradational pattern of this system from the base of seismic unit 2 onwards indicates relatively enhanced and stable south china sea intermediate water circulation occurring on the northwestern margin of the northern south china sea subsequently the behaviour and depositional processes of bottom currents upstream and downstream the seamount are discussed the depositional model suggests that a complex contourite channel system will replace the former moat drift system once the seamount is buried finally our findings may provide new challenges for investigating the south china sea cenozoic palaeoceanography which are helpful to understand the sedimentary dynamic processes related to the south china sea deepwater circulation c 2014 elsevier b v all rights reserved

comparative behavior of authigenic re u and mo during reoxidation and subsequent long term burial in marine sediments the trace element re is enriched in mildly reducing suboxic sediments close to or slightly later in the redox sequence than u and before reduction of mo in more reducing sulfidic sediments this work investigates the behavior of authigenic re during oxidation and long term burial in the sediments of several turbidites from the madeira abyssal plain exposure to bottom water o2 clearly remobilizes authigenic re as found in previous work but reimmobilization occurs in reducing sediments below the oxidation front over a depth range of 0 5 3 m the large spread of the re burndown peak must be kinetically controlled perhaps influenced by the corg content once reimmobilized however the authigenic re signal remains immobile for at least 3 4 myr authigenic u in contrast consistently forms peaks 0 5 m broad whereas authigenic mo is lost on oxidation and does not appear to be refixed unless authigenic pyrite is formed these results imply that any paleoenvironmental significance of authigenic re will be compromised in low sedimentation rate environments 10 cm kyr where there is significant exposure of authigenic re to bottom water o2 however authigenic re records from rapidly accumulating continental margin sediments with much less exposure to bottom water o2 still offer considerable potential as high fidelity recorders of past reducing conditions

coupled c s fe geochemistry in a rapidly accumulating marine sedimentary system diagenetic and depositional implications in the present study we have investigated the c s fe systematics in a sediment core md161 13 from the krishna godavari k g basin bay of bengal the core covers the late holocene period with high overall sedimentation rate of 573 cm kyr 1 pore fluid chemical analyses indicate that the depth of the present sulfate methane transition zone smtz is at 6 mbsf the ta ca mg so42 ratios suggest that both organoclastic degradation and anaerobic oxidation of methane aom drive sulfate reduction at the study site the positive correlation between total organic carbon content toc and chromium reducible sulfur crs content indicates marked influence of organoclastic sulfate reduction on sulfidization coupled occurrence of 34s enriched iron sulfide pyrite with 12c enriched authigenic carbonate zones is the possible records of paleo sulfate methane transition zones where aom driven focused sulfate reduction was likely fueled by sustained high methane flux from underlying gas rich zone aluminum normalized poorly reactive iron fepr al and la yb ratios suggest increasing contribution from deccan basalts relative to that of archean proterozoic granitic complex in sediment flux of krishna godavari basin during the last 4 kyr

manganese rich brown layers in arctic ocean sediments composition formation mechanisms and diagenetic overprint we present inorganic geochemical analyses of pore waters and sediments of two late quaternary sediment cores from the western arctic ocean southern mendeleev ridge rv polarstern expedition ark xxiii 3 focussing on the composition and origin of distinct brown colored mn rich sediment layers carbonate enrichments occur in association with these layers as peaks in ca al mg al sr al and sr mg suggesting enhanced input of both ice rafted and biogenic carbonate for the first time we show that the mn rich layers layers are also consistently enriched in the scavenged trace metals co cu mo and ni distinct bioturbation patterns specifically well defined brown burrows into the underlying sediments suggest these metal enrichments formed close to the sediment water interface the geochemical signature of these metal and carbonate rich layers most probably documents formation under warmer climate conditions with an intensified continental hydrological cycle and only seasonal sea ice cover both rivers and sea ice delivered trace metals to the arctic ocean while enhanced seasonal productivity exported reactive organic matter to the sea floor the coeval deposition of organic matter mn oxyhydr oxides and trace metals triggered intense diagenetic mn cycling at the sediment water interface these processes resulted in the formation of mn and trace metal enrichments and the degradation of labile organic matter with the onset of cooler conditions reduced riverine runoff and or a solid sea ice cover terminated the input of riverine trace metal and fresh organic matter resulting in deposition of grayish yellowish metal poor sediments oxygen depletion of arctic bottom waters under these cooler conditions is not supported by our data and did not cause the sedimentary mn distribution while the original composition and texture of the brown layers resulted from specific climatic conditions and corresponding diagenetic processes pore water data show that diagenetic mn redistribution is still affecting the organic poor deeper sediments given persistent steady state conditions purely authigenic mn rich brown layers may form while others may be partly or completely dissolved the degree of diagenetic mn redistribution largely depends on the depositional environment the mn and organic matter availability and apparently affected the co mo ratios of mn rich layers thus brown arctic layers are not necessarily synchronous features and should not be correlated across the arctic ocean without additional age control

external controls on turbidite sedimentation on the glacially influenced armorican margin bay of biscay western european margin abstract sequence stratigraphic models predict increased sediment delivery to deep water areas during sea level lowstand the armorican margin bay of biscay western european margin is an interesting area to test this hypothesis because the margin has a wide continental shelf still partly flooded during sea level lowstand and the armorican turbidite system has experienced fluctuating sediment fluxes since the last glacial period the stratigraphic response of the armorican turbidite system to sea level oscillations and climate changes was assessed for the last 35 000 years through the study of the guilcher crozon and audierne levees millennial timescale resolution chronostratigraphy allowed us to reconstruct the sediment accumulation and turbidite frequency thickness and grain size over this period of time we found that the armorican turbidite system was sediment starved during highstand conditions ca 8 0 ka and that glacial conditions favoured sediment delivery to the deep bay of biscay however contrary to what would be expected from sequence stratigraphic models the turbidite flux did not reach a maximum during the lgm lowstand ca 26 20 ka but at the onset of termination i between ca 20 and 17 ka this makes the armorican turbidite system a transgression dominated one this sediment pulse can be interpreted as a huge increase in the meltwater discharge of the fleuve manche palaeoriver in response to the decay of the british and fennoscandian ice sheets at that time despite the rising sea level a large deltaic system had to have developed on the outer shelf leading to the delivery of the fleuve manche sediment load into the canyon heads on the other hand our dataset suggest that the delivery of sediment into canyons was mainly forced by the winnowing and reworking of the sediment stored on the wide drowned shelf during the last glacial period between ca 35 and 20 ka and between 17 and 8 ka these findings illustrate the competing influences of accommodation and sediment supply on the armorican margin over the last 35 000 years with a shelf acting as a buffer for the sediment supply signal for most of the period except during the last deglaciation at that time the western european sediment routing system was reactive the climatic signal rapidly propagated from the southern limb of the european ice sheet to the armorican turbidite system finally our study demonstrates that precise reconstruction of turbidite flux in deep water areas added to knowledge about the morphology of the margin and the palaeoenvironmental changes fluvial system shoreline position etc are crucial for determining the response of turbidite systems to external forcing

in situ observation of contour currents in the northern south china sea applications for deepwater sediment transport deepwater currents and related suspended sediment concentration were obtained by an acoustic doppler current profiler adcp mooring system in the northern south china sea from september 2011 to may 2013 to characterize the occurrence of contour currents and to evaluate their sediment transport capacity magnitude of the current velocity generally varied in the range of 0 2 cm s with a dominant flow direction of 250 southwestward the observed contour current defined as the along slope component of the deepwater currents has a tunnel like vertical structure with the largest velocity occurring in the middle of the tunnel and decreasing outwards both the magnitude and the depth range of the maximum velocity display evident inter seasonal variations with the strongest velocity in summer and the weakest in spring while the thickness of the contour currents was the highest in winter and the lowest in spring we also found that passing through of the deep reaching mesoscale eddies significantly affected the magnitude and direction of the contour currents the suspended sediment concentration ssc estimated from echo intensities of the adcp is the highest at the near bottom 400 g l and decreases upwards to 10 g l at water depth shallower than 1750 m high ssc is mostly observed during periods of low magnitude of the contour currents suggesting resuspension of sediment from the seafloor is not the major controlling factor of these high ssc events our observation also suggests that the major role that contour currents play is to transport sediment from the sources through keeping sediment suspended above the lower continental slope of the south china sea

sediment waves on the south china sea slope off southwestern taiwan implications for the intrusion of the northern pacific deep water into the south china sea abstract using an integrated multi beam bathymetry high resolution seismic profile piston core and ams 14 c dating data set the current study identified two sediment wave fields fields 1 and 2 on the south china sea slope off southwestern taiwan field 1 is located in the lower slope and sediment waves within it are overall oriented perpendicular to the direction of down slope gravity flows and canyon axis geometries morphology and internal seismic reflection configurations suggest that the sediment waves in field 1 underwent significant up slope migration field 2 in contrast is located more basinward on the continental rise instead of having asymmetrical morphology and discontinuous reflections as observed in field 1 the sediment waves in field 2 show more symmetrical morphology and continuous reflections that can be traced from one wave to another suggesting that vertical aggradation is more active and predominant than up slope migration three sediment wave evolution stages stage 1 through stage 3 are identified in both field 1 and field 2 during stage 1 the sediment waves are built upon a regional unconformity that separates the underlying mass transport complexes from the overlying sediment waves in both of these two fields there is progressive development of the sediment waves and increase in wave dimensions from the oldest stage 1 to the youngest stage 3 even though up slope migration is dominant in field 1 whereas vertical aggradation is predominant in field 2 throughout these three stages the integrated data and the depositional model show that the upper slope of the study area is strongly dissected and eroded by down slope gravity flows the net result of strong erosion is that significant amounts of sediment are transported further basinward into the lower slope by gravity flows and or turbidity currents the interactions of these currents with bottom contour currents induced by the intrusion of the northern pacific deep water into the south china sea and preexisting wavy topography in the lower slope result in the up slope migrating sediment waves in field 1 and the contourites as observed from cores ts01 and ts02 further basinward on the continental rise turbidity currents are waned and diluted whereas along slope bottom contour currents are vigorous and most likely dominate over the diluted turbidity currents resulting in the vertically aggraded sediment waves in field 2 the results from this study also provide the further evidence for the intrusion of the northern pacific deep water into the south china sea and suggest that this intrusion has probably existed and been capable of affecting sedimentation in south china sea at least since quaternary

source to sink transport processes of fluvial sediments in the south china sea the south china sea offers an excellent case for studying source to sink transport processes of fluvial sediments among the global marginal seas this study synthesizes existing clay mineralogical and geochemical data from similar to 1500 samples from the seafloor and surrounding rivers deepwater mooring observation results and high resolution glacial cyclic clay mineralogy records from six high quality sediment cores source to sink sediment transport from the river mouth to the continental shelf and then to the abyssal basin is investigated at two time scales modern process and late quaternary glacial cycles the results firstly show the high diversity of clay mineralogical and geochemical compositions in riverbed surface sediments surrounding the south china sea e g dominant illite and chlorite in taiwan overwhelming majority of smectite in luzon dominant kaolinite in south china and similar amounts of the four clay mineral species in red and mekong river systems the formation of these fluvial sediments through chemical weathering in surrounding drainage systems is controlled principally by the east asian monsoon climate with warm temperature and high precipitation and subordinately by tectonic activity and specific lithological character the basin wide distribution of clay mineral assemblages combined with neodymium and strontium isotopic compositions reflects strong provenance control and differential settling effects the differential settling of kaolinite in slightly saline and proximal regions relative to smectite in more saline and distal regions is well demonstrated in the south china sea through combining clay mineralogical distributions on the seafloor with observed oceanic current systems the modern transport pathways can be well established e g in the northern south china sea illite and chlorite from taiwan are mainly carried by contour currents with the strong influence of mesoscale eddies high resolution sediment dynamic analysis for the late quaternary reveals different sediment transport patterns in the northern western and southern south china sea when the land sea configuration dramatically changed during glacial conditions in the north the terrigenous dispersal is mainly controlled by provenance supply and oceanic current transport in the west the clay mineral assemblage reflects variations of the prevailing surface current influenced by monsoon winds in the south the clay mineral input indicates intensive chemical weathering during interglacial periods and strengthened physical erosion during glacial periods the transport of terrigenous sediments since the last glaciation is quantitatively reconstructed through studying two deepwater sediment cores located in the northern south china sea the relative contributions from three provenances south china luzon and taiwan highlight their distinct variability over the last 28 ka implying that the southward shift of the inter tropical convergence zone itcz at 16 ka bp caused an increased sediment contribution from south china the intensified influence of the kuroshio current intrusion controls more efficient westward transport of luzon sediments and the stronger deepwater current transports taiwan sourced sediments further westward from the last glaciation to the holocene c 2015 elsevier b v all rights reserved

environmental analysis of paleoceanographic systems based on molybdenum uranium covariation abstract modern low oxygen marine systems exhibit patterns of molybdenum uranium covariation that can be linked to specific attributes and processes of the depositional system including 1 variation in benthic redox conditions 2 the operation of particulate shuttles within the water column and 3 the evolution of watermass chemistry the importance of these factors in each depositional system can be assessed both from the degree of enrichment of authigenic molybdenum mo auth and uranium u auth and from the mo u auth ratio of the sediment relative to the seawater mo u molar ratio of 7 5 7 9 in open ocean systems with suboxic bottomwaters u auth enrichment tends to exceed that of mo auth owing to onset of u auth accumulation at the fe ii fe iii redox boundary resulting in sediment mo u auth ratios less than that of seawater as bottomwaters become increasingly reducing and at least occasionally sulfidic the rate of accumulation of mo auth increases relative to that of u auth and sediment mo u auth ratios equal or exceed that of seawater in restricted marine systems with permanently sulfidic deepwaters the relative enrichment of mo auth and u auth depends on additional factors in the cariaco basin which has an aqueous mo u ratio similar to that of seawater the operation of a particulate mn fe oxyhydroxide shuttle serves to accelerate the transfer of mo to the seafloor leading to strong enrichments in mo auth relative to u auth in the black sea the chemistry of the deep watermass has evolved to the point where its aqueous mo u ratio is only 0 04 that of seawater as a consequence of which sediments deposited under deepwater influence are depleted in mo auth relative to u auth these mo u covariation patterns can be used to gain a better understanding of the watermass attributes and processes of ancient low oxygen marine systems analysis of anoxic facies from two north american paleomarine systems the late pennsylvanian midcontinent sea lpms and the late devonian seaway lds reveals authigenic mo u relationships similar to those of the modern marine environments above implying similar redox and hydrographic controls the observed patterns are consistent with laterally unconfined circulation and strong watermass exchange within the lpms and with markedly restricted deepwater circulation in silled basins of the lds patterns of authigenic mo u covariation may prove useful in analysis of other paleoceanographic systems to reveal aspects of watermass composition and environmental dynamics

deconstructing the last glacial termination the role of millennial and orbital scale forcings using an earth system model of intermediate complexity forced by continuously varying boundary conditions and a hypothetical profile of freshwater forcing the model simulates heinrich event 1 h1 the bolling warm period the older dryas the antarctic cold reversal acr and the younger dryas in close agreement with paleo proxy data from different regions worldwide the acr can be simulated as the bipolar seesaw response to the amoc recovery during the termination of h1 however this study also demonstrates that the amplitude of the acr can be further amplified by a rapid deglacial retreat of the antarctic ice sheets we suggest that melting from both the laurentide and the antarctic ice sheets contributed to the sea level rise associated with meltwater pulse 1 a mwp 1a it is hypothesized that the northern hemispheric source of mwp 1a caused the older dryas cooling in the northern hemisphere whereas the southern hemispheric source contributed to the acr the study also documents that for the majority of paleo climate proxies considered here the relative timing can be qualitatively reproduced by the transient modeling experiments the climate model solution presented here may provide a means to further constrain dating uncertainties of some of paleo climate proxies during the last glacial termination

wave velocity and stiffness measurements of the crag and lower london tertiaries at sizewell this paper describes an investigation into the body wave velocity and stiffness characteristics of the foundation soils at the site formerly considered for sizewell c nuclear power station results from both in situ and laboratory tests are presented in situ measurements comprised shear and compression wave velocities using cross hole and down hole techniques including the velocity of horizontally propagating horizontally polarized shear waves laboratory tests included torsional shear tests on hollow cylindrical samples triaxial compression and extension tests with local measurements of strain and resonant column tests sample quality and the effects of destructuring are evaluated the anisotropy of the wave velocity and of the stiffness characteristics is highlighted l article decrit des recherches sur la vitesse de propagation des ondes de volume et les caracteristiques de rigidite des sols d assise de l emplacement propose de la centrale nucleaire sizewell c il presente les resultats des essais

opal and organic carbon in laminated diatomaceous sediments saanich inlet santa barbara basin and the miocene monterey formation abstract laminated biosiliceous sediments from saanich inlet british columbia si the monterey formation california mf and santa barbara basin california sbb are organic rich and were studied to assess the suitability of si and sbb as modern analogs of the miocene mf and to explore the controls on distributions of opal and organic carbon to this end individual laminae and groups of laminae extracted from odp cores and outcrop samples were analyzed using a multi tracer geochemical approach total organic carbon opal c n ratios 13 c of organic matter om kerogen type and major and minor element abundances were measured si sediments are 52 84 detrital 15 45 opal and 1 2 organic carbon 13 c and c n ratios indicate a marine source of the om present in the sediments samples from the upper siliceous member of the mf are 6 41 detritus 28 87 opal and 1 5 organic carbon kerogen types c n ratios and 13 c data are suggest mixed but predominantly marine om sbb samples are 59 90 detritus 6 34 opal 3 22 calcite and 1 5 percent organic carbon si and sbb have similar bulk compositions with the exception of the presence of calcite in sbb samples mf sediments have significantly lower detrital and higher opal contents than si and sbb samples these large differences suggest that si and sbb are not appropriate modern analogs for the mf in si sediments organic carbon is concentrated in opal rich detritus lean laminae and intervals this distribution suggests that the coupling of opal and om created in the surface ocean by diatom productivity is preserved in the sediment record in the mf opal and toc are negatively correlated implying that the coupling of opal and organic carbon did not survive the processes of settling sedimentation diagenesis and or weathering this decoupling of organic carbon and opal in the mf is attributed to dilution of om by high opal flux rates and or the respiration and or redistribution of om during diagenesis and or weathering

climate controlled variability of iron deposition in the central arctic ocean southern mendeleev ridge over the last 130 000 years abstract distinct brown coloured mn rich layers are common features in quaternary sediments of the central arctic ocean but their paleoenvironmental significance is disputed glacial interglacial changes in bottom water ventilation variable riverine input and diagenetic processes have all been suggested to cause the cyclicity in optical and geochemical parameters in these deposits to better assess the nature and origin of these sediment intervals and their implications for nutrient cycles we applied bulk geochemical analyses and a sequential fe extraction scheme to a sediment record covering the last 130 ka on the southern mendeleev ridge all brown layers in this core are enriched in mn but also in fe oxyhydr oxides e g ferrihydrite lepidocrocite goethite that contribute to the characteristic sediment colour phosphorus and several trace metals as co cu mo ni are also enriched indicating that both mn and fe oxyhydr oxides adsorbed p and trace metals from the water column the metal enrichments are most probably caused by a combination of enhanced mn and fe input from arctic rivers and or the erosion of shelf deposits coupled with early diagenetic processes leading to precipitation of authigenic mn and fe oxyhydr oxides close to the sediment water interface both primary supply and diagenetic recycling of metals should have been enhanced by a more intense hydrological cycle under warmer climate conditions combined with seasonal increases in productivity and reactive organic matter export during ice free conditions in the central arctic ocean consequently the studied metal oxyhydr oxide rich layers were formed under interglacial interstadial climatic conditions in contrast sheet silicate bound fe e g chlorite a second major fe pool in these sediments 15 35 of total fe is enriched between the oxide rich layers thus the delivery of fe rich sheet silicates from the east siberian hinterland or the bering sea and subsequent deposition on the mendeleev ridge was enhanced by more intense physical weathering during glacial stadial periods these contrasts in fe speciation between the brown layers and the adjacent sediments document the direct response of biogeochemical element cycles to glacial interglacial variations in river input weathering regime and sea level in the arctic ocean

iron availability as a dominant control on the primary composition and diagenetic overprint of organic matter rich rocks iron is known to stimulate surface ocean productivity as well as intervene with bacterially mediated processes of organic matter remineralization during early diagenesis in this paper we examine the influence of iron supply on the geochemistry trace metals 34s organic matter of sedimentary rocks deposited in a clastic dominated marine ramp environment to this end we studied two late jurassic formations of the boulonnais area north france both formations were deposited under quite similar conditions but they differ in the reactive iron supply they received only one of the two formations was affected by the particulate iron shuttle process our results indicate that 1 the iron shuttle may be recorded through concomitant enrichments in p mo as and sb 2 a limited reactive iron supply will allow the sulfurization of organic matter even in a context of moderate productivity thus sulfurization can be a factor favoring a noticeable accumulation of organic matter iron may thus be an important agent in the c cycle

geochemical and geological constraints on the composition of marine sediment pore fluid possible link to gas hydrate deposits abstract pore water sulfate consumption in marine sediments is controlled by microbially driven sulfate reduction via organo clastic and methane oxidation processes in this work we present sediment pore fluid compositions of 10 long sediment cores and high resolution seismic data from the krishna godavari k g basin bay of bengal our results show occurrence of transient s and kink types and steady state quasi linear sulfate concentration profiles which are attributed partly to the anaerobic oxidation of methane 13 c ch 4 84 8 to 100 1 vpdb and organo clastic sulfate reduction influence of aom on alkalinity is evident from the presence of authigenic carbonate layers with highly depleted carbon isotope ratios in core md161 8 the authigenic carbonates represent the paleo smtzs and suggest marked fluctuation in vertical methane flux our geophysical data show the acoustic signatures of upward fluid migration from shallow sub surface whereas coring during nghp expedition 01 confirms the presence of sub surface gas hydrate deposits in k g basin which can be linked to deep methane sources the geochemical analysis suggests that shallow methane source can be attributed to high burial flux of labile organic matter due to high sedimentation rate sampling sites with high methane flux from the shallow gas source are characterized by quasi linear sulfate concentration profile and a shallow sulfate methane transition zone smtz and may not be necessarily linked to deeper gas hydrate deposits in contrast the deep methane source results in a transient kink type sulfate profile and a deeper smtz we have observed a close link between the occurrence of gas hydrate and the s kink type sulfate profile we interpret the short lived kink in the sulfate profiles as a result of recent enhancement in vertical methane flux possibly driven by reactivation of fault fractures systems which provide the conduits for fluid flow

rare earth elements in cold seep carbonates from the niger delta abstract the circulation of methane rich fluids at cold seeps often leads to precipitation of authigenic carbonates mediated by microbial activity which can be used as archives of fluid seepage on continental margins in this study we have investigated the potential of using rare earth element ree concentrations in authigenic carbonates for tracing fluid sources and providing information on associated biogeochemical processes at cold seeps we have examined various chemical procedures for the analysis of ree in authigenic carbonates and present a robust method using dilute acetic acid solution that allows the extraction of ree from carbonate phases with reduced contamination from fe mn oxides and detrital minerals using this method we analysed a series of carbonate samples collected at various deep sea sites of active fluid seepage on the niger delta for their ree and trace element concentrations 13c and 18o values and 87sr 86sr isotope compositions we show that the ree composition of cold seep carbonates is controlled primarily by that of the fluid from which they have precipitated our results also suggest that significant ree fractionation can occur during carbonate precipitation which can be related to various degrees of ree complexation by organic versus carbonate ligands in response to changing pore water chemical composition for parameters such as carbonate alkalinity

evidence of paleo cold seep activity from the bay of bengal offshore india 1 we report evidence of paleo cold seep associated activities preserved in methane derived carbonates in association with chemosynthetic clams calyptogena sp from a sediment core in the krishna godavari basin bay of bengal visual observations and calculations based on high resolution wet bulk density profile of a core collected on board r v marion dufresne may 2007 show zones of sharp increase in carbonate content 10 55 vol within 16 20 meters below seafloor mbsf the presence of calyptogena clam shells chimneys shell breccias with high mg calcite cement and pyrite within this zone suggest seepage of methane and sulfide bearing fluid to the seafloor in the past highly depleted carbon isotopic values 13c ranges from 41 to 52 vpdb from these carbonates indicate carbon derived via anaerobic oxidation of methane extrapolated mean calendar age 58 7 ka b p of the clastic sediments at a depth of 16 mbsf is close to the upper limit of the u th based depositional age 46 2 3 7 and 53 0 1 6 ka of authigenic carbonates sampled from this level thereby constraining the younger age limit of the carbonate deposition methane expulsion events the observed carbonate deposition might have resulted from the flow of methane enriched fluids through the fracture network formed because of shale diapirism

sr nd isotopic constraints on detrital sediment provenance and paleoenvironmental change in the northern okinawa trough during the late quaternary for this study elemental and sr nd isotopic compositions of ams c 14 age dated core sediments from the northern okinawa trough were investigated to reconstruct sediment provenance and transport processes over the last 22 3 ka and further to trace the forcing mechanisms behind the provenance changes the results clearly showed that large compositional variations of these elements and isotopes occur in deposition suggesting three phases of changes in sediment source paleo huanghe unit 3 223 14 8 ka east china sea shelf derived unit 2 14 8 7 3 ka and taiwan derived detritus stages unit 1 7 3 ka such provenance changes since the last glacial maximum may be closely correlated to sea level fluctuation the evolution of tsushima warm current as well as east asian monsoonal climatic variation at 22 3 14 8 ka the paleo huanghe mouth was situated close to the study area thus dominating sedimentation therein especially during stronger winter monsoon periods at the beginning of unit 2 14 8 12 8 ka rapid sea level rise and significant retreat of the river mouth overwhelmed enhanced continental weathering leading to less detrital sediment supply from the paleo huanghe to the study area subsequently the east china sea shelf derived matter dominated detrital deposition therein from 12 8 to 73 ka since 73 ka the fully evolved tsushima warm current has transported some detrital particles from taiwan to the study area especially during the strengthening period at 7 3 5 1 ka a prominent decline in taiwan sourced matter supply at 5 1 2 8 ka may have been caused by suppression of the tsushima warm current possibly associated with the pulleniatina minimum event c 2015 elsevier b v all rights reserved

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

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

benthic foraminiferal paleoceanography of the south china sea over the last 40 000 years benthic foraminifera in gravity and piston cores from two sites of the northern and southern slopes of the south china sea scs were analyzed to evaluate changes in surface productivity and deep water mass characteristics over the last 40 000 years our observations suggest that changes in organic carbon flux that is food supply and chemical and or physical properties of the ambient water mass may be the two primary and intercorrelated factors controlling the distribution patterns of benthic foraminifera when organic carbon flux increased above 3 5 g c m 2 yr 1 in the southern scs during the last glacial maximum and in the northern scs during the first part of the holocene around 10 ka b p a group of detritus feeders including bulimina aculeata and uvigerina peregrina dominated the benthic foraminiferal assemblage as shown by relative abundance and accumulation rates this may reflect episodes of increased surface productivity possibly induced by increased input of nutrients from nearby river runoff suspension feeders such as cibicidoides wuellerstorfiand a group of opportunistic species including oridorsalis umbonatus melonis barleeanum and chilostomella ovoidea gradually became more abundant than detritus feeders as soon as the organic carbon flux decreased to 2 5 3 5 g c m 2 yr 1 similar glacial to interglacial changes in relative abundance and accumulation rates were observed in both cores for a number of species including eggerella bradyi globocassidulina subglobosa astrononion novozealandicum sphaeroidina bulloidesand cibicidoides robertsonianus these changes were not correlated to the distribution patterns of organic carbon in both cores and may have been related to yet unspecified changes in chemical and or physical properties of the ambient water mass independent of changes in organic carbon flux 1999 elsevier science b v all rights reserved

deep water circulation in the luzon strait deep water circulation in the luzon strait which connects the pacific deep circulation with the south china sea throughflow is investigated using a set of oceanographic observations combined with results from three numerical experiments both the in situ observations and the model show a deep water overflow in the luzon strait their results suggest that the deep pacific water first flows into the luzon strait through the bashi channel 1 2 sv 1 sv 1 106 m3 s 1 and the taltung canyon 0 4 sv then turns southward along the luzon trough and finally enters the south china sea primarily through two gaps in the heng chun ridge overall the mean transport of the luzon strait overflow is about 1 5 sv results from numerical experiments suggest that strong diapycnal mixing in the south china sea and luzon strait which sustains the baroclinic pressure gradient across the luzon strait is the primary driving mechanism of the deep circulation in the luzon strait

analysis of marine environmental conditions based onmolybdenum uranium covariation applications to mesozoic paleoceanography article i nfo article history accepted 13 september 2011 available online 17 september 2011 patterns of uranium molybdenum covariation in marine sediments have the potential to provide insights re garding depositional conditions and processes in paleoceanographic systems specifically such patterns can be used to assess bottom water redox conditions the operation of metal oxyhydroxide particulate shuttles in the water column and the degree of water mass restriction the utility of this paleoenvironmental proxy is due to the differential geochemical behavior of u and mo 1 uptake of authigenic u by marine sediments begins at the fe ii fe iii redox boundary i e suboxic conditions whereas authigenic mo enrichment re quires the presence of h2s i e euxinic conditions and 2 transfer of aqueous mo to the sediment may be enhanced through particulate shuttles whereas aqueous u is unaffected by this process in the present study we examine u mo covariation in organic rich sediments deposited mostly in the western tethyan region during oceanic anoxic events oaes of early jurassic to late cretaceous age our analysis generally confirms existing interpretations of redox conditions in these formations but provides significant new insights regard ing water mass restriction and the operation of particulate shuttles in depositional systems these insights will help to address contentious issues pertaining to the character and origin of mesozoic oaes such as the degree to which regional paleoceanographic factors controlled the development of the oaes

the variation of upper ocean structure and paleoproductivity in the kuroshio source region during the last 200 kyr a core from the source region of the kuroshio warm current east of the luzon island was analyzed using several proxies in order to study the variability of the western pacific warm pool wpwp during the last two glacial interglacial cycles primary productivity pp variations were deduced from variations in the coccolith flora primary productivity was higher during glacial periods the end of marine isotope stage mis 3 some periods in mis 2 and 6 and decreased during interglacial periods mis 7 mis se and probably mis 5c 5d with the lowest pp in mis 5e variations in the delta 13 c difference in benthic and bulk carbonate thus in the vertical gradient of delta 13 c in dissolved inorganic carbon delta delta 13 c c wuellerstorfi n dutertrei and delta delta 13 c c wuellerstorfi coccolith coincided with the pp changes showing that export productivity was low during interglacial periods mis 7 mis 5e and holocene and high during glacial periods mis 6 probably mis 5c 5d late mis 4 and late mis 3 comparison of foraminiferal carbonate dissolution indicators and pp changes reveals that nannofossil assemblage in core ph05 5 is not sensitive to carbonate dissolution intensity the depth of the thermocline dot was estimated from planktonic forminiferal assemblages and was relatively greater during interglacial periods mis 7 mis 5e probably mis 5c and holocene than during glacials middle mis 6 probably mis 5b and 5d some periods in mis 4 mis 3 and mis 2 good coherence between the paleoproductivity records and the dot suggests that the dot changes could be the primary control factor in changes of paleoproductivity and the glacial high productivity in the kuroshio source region could be associated with a global increase of nutrient concentration in the intermediate waters that upwelled into the photic zone the low co 2 values derived for intervals of high productivity and a relatively shallow dot suggest that the changes in biological productivity and dot in the equatorial pacific could have modified atmospheric co 2 concentrations high sea surface temperatures ssts during the warm mis 5e in combination with intensified monsoonal rain fall could have resulted in a more intense stratification of the upper waters resulting in low nutrient supply to the surface waters and a resulting decrease in productivity c 2010 elsevier b v all rights reserved

bioavailability of zinc in marine systems through time zinc is a marine nutrient that may have been limited in the early oceans estimates of marine zinc availability through time suggest that values were instead near modern during the proterozoic eon

redox sensitivity of p cycling during marine black shale formation dynamics of sulfidic and anoxic non sulfidic bottom waters abstract a high resolution geochemical record of a 120 cm black shale interval deposited during the coniacian santonian oceanic anoxic event 3 odp leg 207 site 1261 demerara rise has been constructed to provide detailed insight into rapid changes in deep ocean and sediment paleo redox conditions high contents of organic matter sulfur and redox sensitive trace metals cd mo v zn as well as continuous lamination point to deposition under consistently oxygen free and largely sulfidic bottom water conditions however rapid and cyclic changes in deep ocean redox are documented by short term 15 20 ka intervals with decreased total organic carbon toc s and redox sensitive trace metal contents and in particular pronounced phosphorus peaks up to 2 5 wt p associated with elevated fe oxide contents sequential iron and phosphate extractions confirm that p is dominantly bound to iron oxides and incorporated into authigenic apatite preservation of this fe p coupling in an otherwise sulfidic depositional environment as indicated by fe speciation and high amounts of sulfurized organic matter may be unexpected and provides evidence for temporarily non sulfidic bottom waters however there is no evidence for deposition under oxic conditions instead sulfidic conditions were punctuated by periods of anoxic non sulfidic bottom waters during these periods phosphate was effectively scavenged during precipitation of iron oxyhydr oxides in the upper water column and was subsequently deposited and largely preserved at the sea floor after 15 25 ka sulfidic bottom water conditions were re established leading to the initial precipitation of cds zns and pyrite subsequently increasing concentrations of h2s in the water column led to extensive formation of sulfurized organic matter which effectively scavenged particle reactive mo complexes thiomolybdates at site 1261 sulfidic bottom waters lasted for 90 100 ka followed by another period of anoxic non sulfidic conditions lasting for 15 20 ka the observed cyclicity at the lower end of the redox scale may have been triggered by repeated incursions of more oxygenated surface to mid waters from the south atlantic resulting in a lowering of the oxic anoxic chemocline in the water column alternatively sea water sulfate might have been stripped by long lasting high rates of sulfate reduction removing the ultimate source for hs production

impact origin of the newporte structure williston basin north dakota the newporte field is located just south of the united states canada border in renville county north dakota in the north central portion of the williston basin integration of seismic well log and core data supports the interpretation of an impact origin for the newporte structure the structure involves both precambrian basement and lower paleozoic sedimentary units oil and gas production began in 1977 from brecciated basement rocks along the rim of the 3 2 km diameter circular structure both well logs and seismic data were used to determine thickness changes of sedimentary units overlying the structure resulting isopach maps reveal a circular bowl shaped feature with a recognizable rim microscopic shock metamorphic features in quartz and feldspar are visible in basement clasts that form a mixed breccia with cambrian deadwood sandstone within the western rim of the structure a late cambrian early ordovician age is suggested for the structure because of the presence of flat lying deadwood sandstone overlying mixed basement sandstone breccia along portions of the rim identification of the newporte structure as an impact crater adds to the gro ing base of evidence revealing the relevance of impact craters to petroleum exploration

deepwater overflow through luzon strait 1 this study examines water property distributions in the deep south china sea and adjoining pacific ocean using all available hydrographic data our analysis reveals that below about 1500 m there is a persistent baroclinic pressure gradient driving flow from the pacific into the south china sea through luzon strait applying hydraulic theory with assumptions of zero potential vorticity and flat bottom to the luzon strait yields a transport estimate of 2 5 sv 1 sv 106 m3 s 1 some implications of this result include 1 a residence time of less than 30 years in the deep south china sea 2 a mean diapycnal diffusivity as large as 10 3 m2 s 1 and 3 an abyssal upwelling rate of about 3 10 6 m s 1 these quantities are consistent with residence times based on oxygen consumption rates the fact that all of the inflowing water must warm up before leaving the basin implies that this marginal sea contributes to the water mass transformations that drive the meridional overturning circulation in the north pacific density distributions within the south china sea basin suggest a cyclonic deep boundary current system as might be expected for an overflow driven abyssal circulation

deep water exchanges between the south china sea and the pacific since the last glacial period deep ocean circulation is widely considered as one of the important factors for increasing co2 concentration and decreasing radiocarbon activity 14c of the atmosphere during the last deglaciation the ams 14c ages of benthic and planktonic foraminifers from 18 samples of core md05 2904 water depth of 2066 m in the northern south china sea scs and 15 samples of core md05 2896 water depth of 1657 m in the southern scs were analyzed in this study for reconstructing the intrabasin deep oceanic processes and hence exploring the deep water exchanges between the scs and the pacific since the last glacial period the results show that during the holocene the average apparent ventilation age of deep water was younger in the southern scs 1350 years than in the northern scs 1850 years due to relatively strong vertical mixing and advection consistent with modern observations however during the last glacial period and deglaciation the deep water was older in the southern scs 2050 years and 1800 to 1200 years respectively than in the northern scs 1600 years and 670 years respectively indicating reduced deep mixing and advection moreover the northern scs deep water was significantly younger during the last deglaciation than during the holocene and the last glacial period implying the existence of northern sourced newly formed and relatively young north pacific deep water our records do not support the intrusion of anomalously 14c depleted deep water to the middepth of the low latitude western pacific and the scs during the mystery interval 17 5 14 5 kyr b p

paleoproductivity and paleoredox conditions during late pleistocene accumulation of laminated diatom mats in the tropical west pacific paleoproductivity and paleoredox conditions were reconstructed in a sediment core in the parece vela basin of the eastern philippine sea the core consists of three units from youngest to oldest 1 laminated diatom mats ldm formed by ethmodiscus rex during the last glacial maximum similar to 18 28 kyr b p 2 diatomaceous clay dc and 3 pelagic clay pc elevated levels of export productivity during ldm deposition are indicated by high values for excess ba opal content and toc ti ratios estimated rates of organic carbon degradation ca 98 opal mass accumulation average 1322 g m 2 yr 1 and corrected organic carbon flux average 248 g m 2 yr 1 are comparable to high productivity regions of the modem ocean the ldm is also characterized by moderate enrichment of redox sensitive elements such as u mo cd and zn highly s 34 depleted pyrite sulfur isotopic compositions indicating bacterial sulfate reduction in a sulfate unlimited system and c s fe systematics reflecting limitation of pyrite formation by organic matter rather than reactive fe availability these features suggest mainly suboxic conditions in bottom waters but development of sulfidic anoxic conditions at or close to the sediment water interface association of intensified anoxia with productivity maxima indicates that export production was a more important control on bottom water redox conditions than lateral ventilation the dc and pc accumulated under oxic to suboxic conditions our observations suggest that redox environments during deposition of laminated marine sediments are more complicated and varied than previously thought and thus the use of sediment lamination as an indicator of anoxic bottom water conditions must be approached cautiously c 2012 elsevier b v all rights reserved

palaeoproductivity evolution in the centre of the western pacific warm pool during the last 250 ka to reconstruct the palaeoproductivity evolution history of the centre of the western pacific warm pool wpwp over the last 250 ka multi proxies were analysed in sediment core wp7 recovered from the ontong java plateau palaeoproductivity evolution at the centre of the wpwp during the last 250 ka is closely related to glacial interglacial cycles and the insolation controlled by precession the glacial higher primary productivity relative to the interglacial conditions could have resulted from both thermocline shoaling associated with persistent el nino like conditions and the increased influx of dust resulting from intensified winter monsoon together with important changes in the thermocline the minimum primary productivity values during the last three terminations could be resulted from deglacial thermocline deepening and intensified stratification associated with persistent la nina like conditions and the concurrent neogloboquadrina dutertrei delta c 13 minimum events probably reflect the chemical signatures of subantarctic mode water and antarctic intermediate water in addition primary productivity values are also controlled by the thermocline variations resulting from el nino la nina southern oscillation processes responding to precession forcing and lead the delta o 18 by about 4 ka the 33 1 ka 19 ka and half precession periods are prominent in the palaeoproductivity records copyright c 2011 john wiley sons ltd

impact origin of the avak structure arctic alaska and genesis of the barrow gas fields geophysical and subsurface geologic data suggest that the avak structure which underlies the arctic coastal plain 12 km southeast of barrow alaska is a hypervelocity meteorite or comet impact structure the structure is a roughly circular area of uplifted chaotically deformed upper triassic to lower cretaceous sedimentary rocks 8 km in diameter that is bounded by a ring of anastomosing inwardly dipping listric normal faults 12 km in diameter a zone of gently outward dipping sedimentary country rocks forms a discontinuous ring of rim anticlines within the peripheral ring of normal faults beyond these anticlines the sedimentary rocks are almost flat lying basement consists of strongly deformed ordovician and silurian argillite density and acoustic impedance con rasts between the argillite and the overlying strata produce gravity and seismic reflection signatures that define a ring of anticlines around the disturbed zone and a structural high surrounded by an annular structural low at its center in the adjacent barrow gas fields the tops of the informally named neocomian pebble shale unit and the gas producing lower jurassic barrow sand local usage lie at average subsea depths of 488 m and 670 m respectively in the avak 1 well drilled on the central high the pebble shale and the barrow sand lie near the surface documenting more than 500 m of relative uplift at the high the cores in this well have steep dips 30 90 degrees mixed breccia with franklinian argillite clasts 10 and 90 m above basement quartz grains with shock mosaicism and multiple sets of shock lamellae oriented concussion fractures in sand size quartz grains and shatter cones resembling those found in the peripheral zones of well documented impact structures in addition above background levels o fractured quartz grains in barrow sand were found as far as 19 km beyond the rim of the avak structure data concerning the age of the avak structure are not definitive if submarine landslide deposits in the upper part of the aptian and albian torok formation in the subsurface 200 km to the east were triggered by the avak event then the avak meteorite struck a submerged marine shelf about 100 or 5 ma however the impact features found at avak shatter cones concussion fractures shock lamellae and shock mosaicism in quartz grains and widespread cataclasis characterize the distal zones of meteorite impact structures fused rocks plastic deformation and shock metamorphic minerals found in more proximal zones of impact structures are apparently missing these observations and the lack of avak ejecta in cuttings and cores from the torok formation and nanushuk group albian to middle cenomanian in surrounding test wells indicate that the impact event postdated these beds in this case the avak meteorite struck a late cretaceous or tertiary marine shelf or coastal plain between the cenomanian ca 95 ma and deposition of the basal beds of the overlying late pliocene and quaternary gubik formation ca 3 ma

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

geochemical environment of the coniacian santonian western tropical atlantic at demerara rise abstract organic carbon rich shales deposited during the coniacian santonian oceanic anoxic event 3 were drilled during odp leg 207 at demerara rise we present integrated high resolution geochemical records of core intervals from odp sites 1259 and 1261 both from nannofossil biozone cc14 our results reveal systematic variations in marine and detrital sediment contribution depositional processes and bottom water redox conditions during black shale formation at two locations on demerara rise in different paleo water depths a combination of redox proxies fe s p al c p redox sensitive sulfide forming trace metals mn cd mo ni v zn and other analytical approaches bulk sediment composition p speciation electron microscopy x ray diffraction evidence anoxic to sulfidic bottom water and sediment conditions throughout the deposition of black shale these extreme redox conditions persisted and were periodically punctuated by short termed periods with less reducing bottom waters irrespective of paleo water depth sediment supply at both sites was generally dominated by marine material carbonate organic matter opal although relationships of detrital proxies as well as glauconitic horizons support some influence of turbidites winnowing bottom currents and or variable detritus sources along with less reducing bottom water at the proposed shallower location odp site 1259 at site 1261 located at greater paleo depth redox fluctuations were more regular and steady hemipelagic sedimentation sustained the development of mostly undisturbed lamination in the sedimentary record strong similarities of the studied deposits exist with the stratigraphic older cenomanian turonian oae2 black shale sections at demerara rise suggesting that the primary mechanisms controlling continental supply and ocean redox state were time invariant and kept the western equatorial atlantic margin widely anoxic over millions of years

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

deciphering bottom current velocity and paleoclimate signals from contourite deposits in the gulf of cadiz during the last 140 kyr an inorganic geochemical approach contourites in the gulf of cadiz gc preserve a unique archive of mediterranean outflow water mow variability over the past 5 3 ma in our study we investigate the potential of geochemical data obtained by xrf scanning to decipher bottom current processes and paleoclimatic evolution at two different sites drilled during iodp expedition 339 through contourites in the northern gc site u1387 which is bathed by the upper mow core and site u1389 located more proximal to the strait of gibraltar the lack of major downslope transport during the pleistocene makes both locations ideally suited for our study the results indicate that the zr al ratio representing the relative enrichment of heavy minerals zircon over less dense alumnosilicates under fast bottom current flow is the most useful indicator for a semiquantitative assessment of current velocity although most elements are biased by current related processes the bromine br record representing organic content preserves the most pristine climate signal rather independent of grain size changes hence br can be used for chronostratigraphy and site to site correlation in addition to stable isotope stratigraphy based on these findings we reconstructed mow variability for marine isotope stages mis 1 5 using the zr al ratio from site u1387 the results reveal abrupt millennial scale variations of mow strength during greenland stadials gs and interstadials gi with strong mow during gs and glacial terminations and a complex behavior during heinrich stadials millennial scale variability persisting during periods of poorly expressed gs gi cyclicities implies a strong internal oscillation of the mediterranean north atlantic climate system

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

compositions of foraminifera rich turbidite sediments from the shenhu area on the northern slope of the south china sea implication for the presence of deep water bottom currents abstract the sediments in gravity core dh 1 collected from shenhu area on the northern slope of the south china sea are composed of two dark grey clay silt layers a1 and a3 and two foraminifera rich layers a2 and a4 a1 is the top layer and a4 is the bottom layer major and trace metal contents along with grain size and mineralogic data suggest that these silt layers represent background hemipelagic sedimentation unlike silt layers the intervening foraminifera rich layera4 exhibits a fining upward trend is distal turbidite grain size cm diagram and the sharp contacts between the foraminifera rich layer a2 and the upper and lower layers suggest layer a2 is the result of depositional interaction between turbidite and bottom currents ams 14c dating of planktonic foraminifera indicate the age of the turbidite in a2 is between15 3 ka and 22 6 ka we hypothesize that turbidite formation in this period was related to the increase supply of terrigenous matter since the last glacial maximum the rapid deposition of each turbidite led to reduced rates of oxygen diffusion into the sediment allowing anoxic conditions develop in sediments and fostering u enrichment 3 1 g g in foraminifera rich layer a4b in contrast decrease concentration of u and u mo ratios in foraminifera rich layera2 which is possibly due to u remobilization as a consequence of downward penetration of the oxidation front from the oxygen rich bottom currents these new data suggest that authigenic u was quite sensitive to the inflow of bottom currents and u mo ratios may indicate the depositional environmental change in relation to the bottom current action on the turbidite

tracking euxinia in the ancient ocean a multiproxy perspective and proterozoic case study the evolution and extinction of life are tied intimately to the oxygen state of the ocean and particularly to the presence of anoxic and h2s containing euxinic water on a global scale anoxia and euxinia were more common in the past relative to today s 0 5 euxinic seafloor we are able to constrain the distributions of these conditions through a combination of indirect numerical modeling methods and more direct geochemical proxies with particular emphasis on fe s mo analysis of fine grained siliciclastic rocks for the latter establishing the spatiotemporal pattern of oceanic redox is more difficult with very old rocks because of the limited availability of well dated well preserved materials that span shallow and deep environments across time lines despite these difficulties the multiple approaches synthesized in our case study point to global oxygen deficiency in the deep ocean and perhaps euxinia during most if not all of the proterozoic and likely extending into the early paleozoic

cooling of the south china sea by the toba eruption and correlation with other climate proxies 71 000 years ago the toba tephra layer has been identified in core md972151 in the southern south china sea scs northeast of the indonesia toba caldera this affords us an opportunity to directly determine a 1 c cooling for ca 1 kyr on the scs following the toba eruption 71 ka during the marine isotope stage 5a 4 transition using century scale sea surface temperature records this cooling event in the scs is well correlated with several coeval proxies such as increased east asia winter monsoon intensity increased ice rafted detritus in the north pacific ocean sediments and decreased 18 o in greenland ice core such correlation suggests a climate change where cold climate signals originated in the northern hemisphere ice sheets transferred southward by the winter monsoon and cooled the scs

the behavior of redox sensitive metals across a laminated massive laminated transition in saanich inlet british columbia abstract holocene laminated sediments in saanich inlet british columbia are interrupted by frequent non laminated massive layers these layers may be debris flows released by earthquakes or bioturbated sediments deposited during periods of relatively high bottom water oxygen concentration and or low surface productivity or both we determined the organic carbon content and the concentration of a suite of redox sensitive metals in bulk sediments at approximately 1 cm resolution across a laminated massive laminated interval odp leg 169s site 1033 hole b 4h4 54 74 cm to determine the redox conditions under which the massive layer was deposited our results indicate that this massive interval was deposited under anoxic bottom waters manganese al ratios are consistently low throughout the massive section while mo al cd al re al and u al ratios are enriched relative to their metal al ratios in detrital material represented by cowichan river suspended sediments the concentration of organic carbon in the lower portion of the massive layer is higher than in the upper portion which has a concentration similar to that in the overlying and underlying laminated sediments well defined peaks in mo al cd al and re al and a broad peak in u al occur in the lower portion of the massive layer the positions of the cd al re al and mo al peaks as well as the increase in organic carbon content with depth in the massive layer are best explained by a process of diagenetic redistribution of metals that occurred after the massive layer was emplaced

phosphorus burial and diagenesis in the central bering sea bowers ridge iodp site u1341 perspectives on the marine p cycle abstract to reconstruct the cycling of reactive phosphorus p in the bering sea a p speciation record covering the last 4 ma was generated from sediments recovered during integrated ocean drilling program iodp expedition 323 at site u1341 bowers ridge a chemical extraction procedure distinguishing between different operationally defined p fractions provides new insight into reactive p input burial and diagenetic transformations reactive p mass accumulation rates mars are 20 110 mol cm2 ka which is comparable to other open ocean locations but orders of magnitude lower than most upwelling settings we find that authigenic carbonate fluorapatite cfa and opal bound p are the dominant p fractions at site u1341 an overall increasing contribution of cfa to total p with sediment depth is consistent with a gradual sink switching from more labile p fractions fish remains fe oxides organic matter to stable authigenic cfa however the positive correlation of cfa with al content implies that a significant portion of the supposedly reactive cfa is non reactive detrital contamination by eolian and or riverine cfa in contrast to cfa opal bound p has rarely been studied in marine sediments we find for the first time that opal bound p directly correlates with excess silica contents this p fraction was apparently available to biosiliceous phytoplankton at the time of sediment deposition and is a long term sink for reactive p in the ocean despite the likelihood for diagenetic re mobilisation of this p at depth indicated by increasing ratios of excess silica to opal bound p average reactive p mars at site u1341 increase by 25 if opal bound p is accounted for but decrease by 25 if 50 of the extracted cfa fraction based on the lowest cfa value at site u1341 is assumed to be detrital combining our results with literature data we present a qualitative perspective of terrestrial cfa and opal bound p deposition in the modern ocean riverine cfa input has mostly been reported from continental shelves and margins draining p rich lithologies while eolian cfa input is found across wide ocean regions underlying the northern hemispheric dust belt opal bound p burial is important in the southern ocean north pacific and likely in upwelling areas shifts in detrital cfa and opal bound p deposition across ocean basins likely occurred over time responding to changing weathering patterns sea level and biogenic opal deposition

on the dynamics of the south china sea deep circulation 1 in the south china sea scs the deep water is confined to a bowel type trench and the maximum depth is approximately 4700 m the luzon strait is the only deep connection between the scs and the pacific ocean with the deepest sill at about 2400 m in the bashi channel using the hybrid coordinate ocean model this study gives a good description of the scs deep circulation the most obvious features are basin scale cyclonic gyre and western intensification the gyre is elliptical shaped and its major axis is northeast southwest a numerical experiment is designed to investigate what could be possibly responsible for the scs deep circulation the results reveal that the deepwater overflow through the luzon strait controls over the basin scale circulation structure in the deep scs basin the driving mechanism is elucidated based on the potential vorticity pv integral constraint which means the pv inflow across the boundary is balanced by the net pv dissipation along the boundary

tracing the paleo sulfate methane transition zones and h2s seepage events in marine sediments an application of c s mo systematics 1 microbially mediated anaebic oxidation of methane aom coupled with sulfate consumption within the sulfate methane transition zone smtz in marine sediments is a widely recorded biogeochemical reaction and has profound influence on the atmospheric ch4budget marine carbon cycle and composition of sediment pore fluids recognizing the paleo smtzs in the marine sediments rock records can throw light on the variation of paleo methane fluxes and occurrences of cold seep h2s ch4 events through geologic time here we present results from carbonate carbon pyrite sulfur and molybdenum analyses for two sediment cores overlying the methane hydrate deposits in the bay of bengal the results show intimate association of isotopically depleted carbonate carbon and enriched pyrite sulfur constraining the paleo smtz within the sediment column in addition anomalous enrichments of mo concentrations indicate hydrogen sulfide seepage events here we propose a geochemical tool using c s mo sytematics to decipher the paleo smtzs in marine sediments and rocks

significance of indigenous eocene larger foraminifera discocyclina dispansa in western foothills central taiwan a paleogene marine rift basin in chinese continental margin the western foothills of taiwan was known to be composed of late oligocene to pleistocene shallow marine strata continuously deposited on the stable passive chinese continental margin without significant stratigraphic break here we present multiple micropaleontological evidences including occurrence of larger foraminifera discocyclina dispansa ex interc sella dispansa and calcareous nannoplanktons to show that there are middle eocene marine strata first named as the chungliao formation exposed in the tsukeng anticline of the western foothills central taiwan occurrences of intact tests with thin delicate outer rims and well preserved embryonic chambers suggest that the discocyclina dispansa ex interc sella dispansa lutetian to bartonian in the tethys region are buried indigenously on shallow inner shelf during an episodic transgression in the early middle eocene the conclusion is consistent with a biostratigraphy study of calcareous nannoplanktons zones np14 15 in the shale sandstone alternations overlying the discocyclina bearing bed of the chungliao formation and calcareous nannofossils of zone np16 integrated with an age dating of 38 8 1 ma late middle eocene on zircon grains of the overlying pinglin tuff the middle eocene syn rift sequences chungliao formation and pinglin tuff exposed along the tsukeng anticline are unconformably covered by the latest oligocene miocene post rift sequence a scenario similar to what have been drilled in the east china sea taiwan strait south china sea this rift basin named as the nantou basin is sitting on the peikang basement high margin which further extends southwestward to the central uplift of the pearl river mouth basin in the northern slope of the south china sea the present work documents a hitherto unknown occurrence of the exposed early tertiary marine rift basin sequence in the western foothills of taiwan the study extends our knowledge of the western foothills geohistory from the late oligocene downward to the early middle eocene the occurrence of the paleogene nantou rift basin in the western foothills may also suggest that there could have similar paleogene rift sequences exposed in other parts of the taiwan mountain belt like the hsuehshan range and the central range east of the western foothills