sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

early diagenesis in deep sea turbidites the imprint of paleo oxidation zones sediment cores up to 35 m long have been recovered from turbidite sequences in the madiera abyssal plain and the southern nares abyssal plain detailed geochemical analyses of these sediments si al fe mn ca organic and inorganic carbon and associate pore waters nitrate ammonia silicate fe2 mn2 and alkalinity provide representative profiles of both steady state and nonsteady state diagenetic reactions initiated by oxidation and reduction processes models demonstrate that chemical transport in the pore water system is diffusion dominated over periods of a few thousands of years to several hundreds of thousands of years mn and fe mobilized in the subsurface mildly reducing sediments are precipitated as easily reducible oxyhydroxides in the near surface oxidized sediments nonsteady state profiles show the influence of episodic and rapid turbidite deposition and the imprint of oxidation zones that developed as the result of oxygen diffusion into the upper portions of turbidites during intervals of slow pelagic deposition the time required for development of oxidation zones between turbidites ranges from 2 0 to 15 ka in the madeira abyssal plain and from 0 2 to 2 4 ka in the southern nares abyssal plain paleo oxidation zones can be recognized in old turbidites by distinct changes in color between lower and upper portions of the deposit in the basal unoxidized portion of the turbidite the sediments are characteristically dark green gray or brown in the paleo oxidized zone the sediments are pale green blue or yellowish brown these zones in both the madeira and southern nares abyssal plains contain distinctly less organic c and carbonate in the paleo oxidized zone as compared with the unoxidized sediments depletion of carbonate content in the oxidized zones in the southern nares abyssal plain is particularly significant in that as much as 80 of the initial carbonates have been lost also the relative amounts of weak acid soluble fe and mn are generally less in the paleo oxidized zones due to the initial oxidation of metal carbonate and metal hydroxide forms to easily reducible oxide forms which are then subsequently solubilized under the mildly reducing conditions at depth in the sediment column

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

anoxic vs dysoxic events reflected in sediment geochemistry during the cenomanian turonian boundary event cretaceous in the umbria marche basin of central italy abstract one of the most spectacular expressions of global oceanic anoxic events oaes of the cretaceous is the livello bonarelli of central italy deposited during the cenomanian turonian boundary event ctbe or oae2 at around 93 5 ma at furlo in the umbria marche basin in italy the bonarelli consists of approximately 1 m of c org rich shales interbedded with radiolarian rich layers and contrasts sharply with the extensive over and underlying siliceous limestones several minor c org rich intervals herein termed black levels average thickness 4 5 cm are interbedded within the scaglia bianca beneath the bonarelli x ray fluorescence and icp ms analyses show that these sediments consist of different mixing systems with three end members 1 sio 2 caco 3 scaglia bianca 2 average shale caco 3 black levels and 3 average shale sio 2 bonarelli given the sharp lithologic contacts and the little geochemical mixing between the groups these are thought to represent rapid switching events between sedimentary modes major element concentrations are generally low except for si and p owing to dilution by silica up to 96 and carbonates as al normalised ratios for elements such as ti or zr taken as proxies for higher energy environments are close to average shale values excess sio 2 is most likely linked to biogenic processes rather than quartz element al ratios of ti mg k rb and zr are fairly constant pointing to a mostly homogeneous source area the black levels and bonarelli are characterised by lower mg al ratios compared to the scaglia bianca sediments suggesting variability in chlorite input which could be linked with short term sea level drops indicated by ti al ratios the bonarelli sediments are severely depleted in mn which is indicative of oxygen depleted bottom water conditions and an open marine environment while the black levels appear to have been deposited in a much more restricted setting a model involving partial physical isolation of the furlo site by a sill coupled to omz variations by extra basinal forcing mechanisms is proposed to account for these conflicting data based on re mo ratios the bonarelli sediments were deposited under varying oxygen depletion levels from suboxic to anoxic while re mo ratios in the black levels show deposition under less oxygen deficient conditions most minor elements many of them redox sensitive or sulphide residing are strongly enriched in the c org rich sediments further documenting the absence of oxygen and potential availability of hydrogen sulphide in the water column at times while high zn concentrations suggest elevated submarine hydrothermal activity during this time interval ba is also present in very high concentrations up to 1 4 with an average weighed concentration of 0 6 for the entire bonarelli and is probably indicative of high paleoproductivity in this area this is further supported by high p concentrations hinting at nutrient availability at this site

organic rich layers in the metochia section gavdos greece evidence for a single mechanism of sapropel formation during the past 10 my abstract three well developed 10 ma old sapropels from the island of gavdos greece were selected for a detailed geochemical micropaleontological and sedimentological study the sapropels are characterized by a high organic carbon and a low carbonate content productivity was higher during sapropel formation as indicated by increased ba contents and higher percentages of the planktonic foraminiferal species neogloboquadrina acostaensis enrichment of mo and v in the sapropels indicates less oxygenated bottom water conditions which is supported by the flourishing of low oxygen tolerant benthic foraminifera variation in grainsize and the ti al ratio point to an alternating dominance of fluvial sapropels and eolian derived homogeneous intervals terrigenous clastics evidence for a local origin of the enhanced fluvial input comes from the gradual replacement of the sapropels by cyclic turbidite sequences which were fed by bed load type rivers the increased fluvial input during sapropel formation increased the sedimentation rate and caused the observed carbonate depletion the results obtained for the gavdos sapropels are consistent with those of previous studies of younger sapropels and related caco 3 cycles in the mediterranean the consistency in most of the geochemical and micropaleontological characteristics indicates that all sapropels and related layers are the result of a single mechanism for at least the past 10 my namely precession induced dry wet oscillations in the mediterranean climate still the effect of this mechanism on the intensity of surface water productivity dilution and diagenetic signals may differ from site to site depending on location depositional environment and intensity of the astronomical forcing

spatial productivity variations during formation of sapropels s5 and s6 in the mediterranean sea evidence from ba contents abstract we investigated five time equivalent core sections 180 110 kyr bp from the balearic sea menorca rise the easternmost levantine basin and southwest south and southeast of crete to reconstruct spatial patterns of productivity during deposition of sapropels s5 and s6 in the mediterranean sea our indicators are ba total organic carbon and carbonate contents we found no indications of ba remobilization within the investigated core intervals and used the accumulation rate of biogenic ba to compute paleoproductivity maximum surface water productivity up to 350 g c m2 yr was found during deposition of s5 isotope stage 5e but pronounced spatial variability is evident coeval sediment intervals in the balearic sea show very little productivity change suggesting that chemical and biological environments in the eastern and western mediterranean basins were decoupled in this interval we interpret the spatial variability as the result of two different modes of nutrient delivery to the photic zone river derived nutrient input and shoaling of the pycnocline nutricline to the photic zone the productivity increase during the formation of s6 was moderate compared to s5 and had a less marked spatial variability within the study area of the eastern mediterranean sea given that s6 formed during a glacial interval glacial boundary conditions such as high wind stress and or cooler surface water temperatures apparently favored lateral and vertical mixing and prevented the development of the spatial gradients within the eastern mediterranean sea ems observed for s5 a non sapropel sediment interval with elevated ba content and depleted 18o 16o ratios in planktonic foraminifer calcite was detected between s6 and s5 that corresponds to the weak northern hemisphere insolation maximum at 150 kyr at this time productivity apparently increased up to five times over surrounding intervals but abundant benthic fauna show that the deep water remained oxic following our interpretation the interval denotes a failed sapropel when a weaker monsoon did not force the ems into permanent stratification the comparison of interglacial and glacial sapropels illustrates the relevance of climatic boundary conditions in the northern catchment in determining the facies and spatial variability of sapropels within the ems

lack of organic matter accumulation on the upwelling influenced somalia margin in a glacial interglacial transition abstract monsoon induced upwelling has been operating off somalia for at least the last 160 000 years making the nw indian ocean one of the most productive oceanic areas in the world we have studied the sediments recovered during the indusom cruise of the r v marion dufresne from three different environments off this margin a core from the highly productive surface waters core md85 674 a core where the oxygen minimum intersects the slope core md85 664 and a reference core from the deep basin with normal bottom oxygen levels and moderate primary production core md85 668 though the first two environments are a priori favourable to organic matter om accumulation no marine om enrichment can be observed in the cores to understand this anomaly emphasis is placed upon the transition from isotopic stage 6 to stage 5 because the end of the glacial stage 6 is characterised by intensified upwelling and primary productivity in this region whereas stage 5 experienced a marked decrease in productivity various palaeoenvironmental markers such as om v ni cu zn ba and p have been used to identify periods of high productivity and or bottom water oxygen depletion the results suggest that 1 the lack of marine om in two settings favourable to organic carbon storage may be due to the nature of primary productivity coccolithophorid production would not be prone to om accumulation in contrast to the contribution of om by diatoms or particularly naked phytoplankton dinoflagellates or other peridinians 2 ba is not an accurate palaeoproductivity marker in this region although the oceanic environment would have been a priori suitable for the use of ba as a proxy indicator 3 the period of intensified upwelling in stage 6 as well as the stage 6 5 transition left no geochemical imprint on the sediments this means that some upwelling systems may not be accompanied by marked enrichments in marine organic matter within the underlying sediments in other words the somalia upwelling does not participate to the so called biological pump and has no positive effect upon long term carbon storage

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

burial of organic carbon and pyrite sulfur in sediments over phanerozoic time a new theory in present day marine sediments almost all of which are deposited in normal oxygenated seawater rates of burial of organic carbon c and pyrite sulfur s correlate positively and bear a constant ratio to one another c s 3 on a weight basis by contrast calculations based on the isotopic model of garrels and lerman 1981 indicate that at various times during the phanerozoic the worldwide burial ratio must have been considerably different than the present day value this ratio change is caused by the requirement that increases in the worldwide mass of organic carbon must be accompanied by equivalent decreases in the mass of sedimentary pyrite sulfur in order to maintain a roughly constant level of o2 in the atmosphere such apparently contradictory behavior can be explained if the locus of major organic carbon burial has shifted over time from normal marine environments as at present to non marine freshwater or to euxinic environments in the geologic past a shift to predominantly freshwater burial can help explain predicted high c s ratios in permo carboniferous sediments and a shift to euxinic environments can help explain predicted low c s ratios during the early paleozoic it is demonstrated that the three environments today exhibit distinguishably different average c s ratios

early diagenetic reactions in interbedded pelagic and turbiditic sediments in the nares abyssal plain western north atlantic consequences for the composition of sediment and interstitial water abstract measured pore water concentrations of iron in interbedded pelagic and turbiditic sediments from the nares abyssal plain are in excellent agreement with sediment colour and measured redox potential the organic carbon content of these sediments appears to define the redox conditions and consequently the porewater and solid phase concentration of constituents that are involved in early diagenetic reactions in the turbiditic sediments the concentration of no 3 generally goes to zero within a sediment depth of 1 m whereas at 8 m in a pelagic core from the same area the concentration of no 3 is still higher than it is in the bottom water the pore water concentration of mn 2 in the turbiditic sediments increases sharply down to a depth of approximately 3 m and from thereon remains nearly constant due to saturation with respect to mn ca co 3 the pore water of the turbiditic sediments is also saturated with respect to calcite the few diagenetic spikes in the pore water concentration of no 3 and mn 2 and the concentration depth profile of dissolved iron h 4 sio 4 and phosphate all clearly demonstrate the inhomogeneous nature of interbedded pelagic and turbiditic sediments the simultaneous occurrence of peaks of dissolved iron silica and of sediment intervals with a relatively high organic carbon content is attributed to enhanced early diagenetic reactions associated with the decomposition of organic matter in these specific intervals linked with these reactions is the irregular pore water concentration of phosphate which is shown to originate partly from the oxidation of organic matter but mainly from the desorption of phosphate from iron oxide potential concentrations of phosphate are calculated from the stoichiometric early diagenetic reactions and compared with measured concentrations due to the unique combination of low porosity and relatively high sedimentation rates the sediments from the nares abyssal plain are an ideal basis for the study of such interbedded sequences of pelagic and turbiditic deposits

geochemical and paleomagnetic evidence for the occurrence of missing sapropels in eastern mediterranean sediments the cyclic occurrence of sapropels appears to be associated with maxima in the 65 n summer insolation target curve studies of the most recent sapropel have revealed extensive oxidation of organic matter or even the complete removal of this unit geochemical and magnetic signals allow for the detection of such a missing sapropel in older sediments these signals are altered by ongoing diagenetic processes an important parameter to reveal missing sapropels is ba elevated concentrations of ba are always found in visible sapropels and even after oxidation of part of the sapropel the initial ba profile remains visible we use this tool to trace down missing sapropels in kc01b a 37 m kullenberg core from the calabrian ridge eastern mediterranean at least 8 of 11 sampled intervals around insolation maxima contain evidence of a completely oxidized sapropel ba trace metal distributions and magnetic parameters are similar to those observed around visible sapropels

post depositional migration of elements during diagenesis in brown clay and turbidite sequences in the north east atlantic abstract two cores from a ne atlantic pelagic clay area of low accumulation rate each contain a single turbidite with different age thickness and composition diagenesis following introduction of exotic turbidite material into the pelagic clay sequence has resulted in distinctive colour changes the diagenetic process is thought to be driven by bacterially mediated organic oxidation and compositional differences in the turbidites and clays allow examination of the effects on metal concentrations of this process in one core a long turbidite section emplaced 330 000 years ago is overlain by clay organic oxidation has apparently proceeded from the turbidite top downwards and has maintained a u concentration peak below the oxidation front marked by a colour change the u source is believed to be u initially associated with the organic matter in the oxidised section of the turbidite vanadium and cu behave similarly but upward migration of the redox sensitive metals mn and ni is also seen in the second core an 8 cm turbidite section was emplaced about 170 000 years ago in a clay column in this case organic consumption now appears complete but evidence for diagenetic effects is found in a 16 cm compositional alteration halo of the underlying pelagic clay fe ii has been enriched and the hydrogenous component of mn co ni and cu removed from the pelagic clay to form the halo

middle and late quaternary depositional sequences and cycles in the eastern mediterranean although most of the quaternary sediments of the eastern mediterranean appear reworked extensive areas of hemipelagic sediments occur mainly in the central part of the basin mediterranean ridge the most obvious character of these muddy sediments is the numerous changes in colour they result from the organic carbon content as well as from concentration and chemical form of metallic elements mn fe cu zn the succession of coloured layers is arranged into sequences developed between two sharp contacts a complete sequence involves five lithofacies from an oxidized layer at the base to a reduced sapropel at the top and displays progressive internal changes of colour from ochre beige greyish beige grey and black layers several sequence variants top truncated base truncated recurrent are identified these sequences are a consequence of changes in oceanographic conditions i e from oxidizing to reduced environments resulting in different organic and mineral contents based on detailed studies of quaternary sediments collected by coring a synthesized standard succession representative of the ordered sequences in the eastern mediterranean is proposed from about 650 000 yr as deduced from the calculated rate of sedimentation of 1 7 mm 1000yr 1 this succession appears modulated by cyclic events large scale periods 200 000 yr of reduced and oxidized sequences correlate with major alternate phases of flooding and reduced flow of the nile river during the quaternary subsequent sequences of shorter time scale 20 000 50 000 yr results from two factors heaviest monsoons leading to an increase of the influx of the nile river and global climatic changes eurasian ice sheet meltwater these two factors act synchronously or independently along the studied time span these interplaying factors result in periodic stages of increasingly restricted conditions in the basin and explain the complexity of the eastern mediterranean succession at least since 650 000 yr ago

diagenetic magnetic enhancement of sapropels from the eastern mediterranean sea diagenetic dissolution of magnetic minerals has been widely observed in organic rich sediments from many environments organic rich sediments from the eastern mediterranean sea sapropels recovered during leg 160 of the ocean drilling program reveal a surprising catalogue of magnetic properties sapropels from all sites studied across the eastern mediterranean sea are strongly magnetic and the magnetization is directly proportional to the organic carbon content the magnetization of the sapropels is dominated by a low coercivity probably single domain magnetic mineral with an inverse magnetic fabric that exhibits a clear decay in magnetic properties when exposed to air during heating the magnetic particles irreversibly break down between 360 and 400 c the contrast between the magnetic properties of sapropels and surrounding sediments is marked with remanence intensities of sapropels often being more than three orders of magnitude higher than those of underlying sediments the contrast between the magnetic properties of sapropels and the surrounding sediments is apparently controlled by non steady state diagenesis sulphate reducing conditions dominated during sapropel deposition while overlying sediments were deposited under oxic conditions the mineral responsible for the magnetic properties of sapropels is most likely to have formed under sulphate reducing conditions that existed during times of sapropel formation attempts to identify this mineral have been unsuccessful but several lines of evidence point toward an unknown ferrimagnetic iron sulphide phase the influence of diagenesis on the magnetic properties of cyclically deposited eastern mediterranean sedimentary sequences suggests that magnetic parameters may be a useful proxy for diagenesis in these sediments

the effect of terrace geology on ground water movement and on the interaction of ground water and surface water on a mountainside near mirror lake new hampshire usa the west watershed of mirror lake in the white mountains of new hampshire contains several terraces that are at different altitudes and have different geologic compositions the lowest terrace fse has 5 m of sand overlying 9 m of till the two next successively higher terraces fs2 and fs1 consist entirely of sand and have maximum thicknesses of about 7 m a fourth and highest terrace fs3 lies in the north west watershed directly adjacent to the west watershed this highest terrace has 2 m of sand overlying 8 m of till all terraces overlie fractured crystalline bedrock numerical models of hypothetical settings simulating ground water flow in a mountainside indicated that the presence of a terrace can cause local ground water flow cells to develop and that the flow patterns differ based on the geologic composition of the terrace for example more ground water moves from the bedrock to the glacial deposits beneath terraces consisting completely of sand than beneath terraces that have sand underlain by till field data from mirror lake watersheds corroborate the numerical experiments the geology of the terraces also affects how the stream draining the west watershed interacts with ground water the stream turns part way down the mountainside and passes between the two sand terraces essentially transecting the movement of ground water down the valley side transects of water table wells were installed across the stream s riparian zone above between and below the sand terraces head data from these wells indicated that the stream gains ground water on both sides above and below the sand terraces however where it flows between the sand terraces the stream gains ground water on its uphill side and loses water on its downhill side biogeochemical processes in the riparian zone of the flow through reach have resulted in anoxic ground water beneath the lower sand terrace results of this study indicate that it is useful to understand patterns of ground water flow in order to fully understand the flow and chemical characteristics of both ground water and surface water in mountainous terrain copyright 2007 john wiley sons ltd

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

active diagenetic formation of metal rich layers in n e atlantic sediments sediment cores from the porcupine abyssal plain exhibit an indurated layer 0 5 3 cm thick at depths of approximately 50 cm this is some 15 20 cm below the glacial holocene transition as interpreted by radiocarbon dating and the palaeontological criteria of ruddiman and mcintyre 1981 the layer is forming currently at the oxic post oxic boundary in the sediments as revealed by pore water data o2 and no 3 are present in solution above the layer while fe2 mn2 po3 4 and nh 4 are present in solution below and all these species show concentration gradients indicating fluxes into the layer these data are consistent with the hypothesis for the initiation and sustained formation of such layers proposed by wilsonet al 1986a b the elements mn ni co fe p v cu zn and u are all enriched to varying degrees in the vicinity of the layer some differential stratification of these elements in the vertical consistent with a redox control is observed at one site with a 0 5 cm layer with mn ni and co above fe p v and cu in the layer and u below at another site the metal rich layer has higher fe and p concentrations and is more indurated here all enrichments except co are contained within a single layer sample 3 cm thick

the marker bed of the mediterranean ridge diapiric belt geochemical characteristics abstract a prominent marker bed jet black in colour with a sharp basal contact and a few centimetres in thickness is ubiquitous in the mediterranean ridge crestal area where collision between the european plate and the african plate occurs and where mud diapirism is a common phenomenon the market bed is consistently recorded in the upper part of the sediment cores within the holocene pteropod foraminiferal oozes above sapropel s 1 which documents the last youngest postglacial sapropelic episode recorded in the eastern mediterranean the marker bed consists of numerous mn micronodules of bacterial origin and presents an abnormal concentration of metals especially of manganese of the 25 cores recovered during the r v gelendzhik 1993 cruise ttr 3 leg2 12 contained the marker bed but 13 did not the large majority of the latter 10 consisted of extruded mud breccia up to the core top and one consisted of pre holocene sediment eight cores of the 12 containing the marker bed had a pelagic make up the remaining ones contained the diapiric mud breccia of deep provenance seven cores were investigated geochemically for their elemental composition the new results confirm and support the previous ones and record percentages of mn within the marker bed ranging from 2 98 to 16 12 values that exceed by at least one order of magnitude those of the adjacent layers suggesting an origin independent from the local environment and dependent on an episode probably linked to the santorini bronze age eruption

trace element indicators of increased primary production and decreased water column ventilation during deposition of latest pliocene sapropels at five locations across the mediterranean sea abstract compositions of productivity and redox sensitive trace metals in two upper pliocene sapropel sequences from western mediterranean odp sites 974 and 975 and eastern mediterranean sites 964 969 and 967 provide information about the conditions leading to sapropel deposition except at site 975 closest to the atlantic ocean all sapropels display elevated element al ratios for ba re cd mo u cr cu v and zn high total organic carbon toc concentrations and ba al ratios point to increased primary productivity during sapropel deposition enrichments of redox sensitive trace elements and elevated re mo ratios indicate water column oxygen depletion during sapropel formation anoxia likely was caused by increased fluxes of organic matter to the seafloor that would have enhanced oxygen demand at depth one of the sapropel sequences investigated in this study insolation cycle 178 contains a zone having low toc low ba al ratios and low trace metal contents these features identify this interval as an interruption of the increased productivity associated with sapropels and of the sub oxic anoxic conditions that are fully developed in the upper half of this sapropel layer significant differences in trace metal enrichments between the eastern and western mediterranean indicate that the eastern basin was a focal point for sapropel initiation in contrast site 975 appears to have been heavily influenced by the atlantic ocean during i cycles 178 and 180 and was not strongly influenced by the paleoceanographic changes affecting the rest of the mediterranean

a geochemical investigation of reduction haloes developed under turbidites in brown clay abstract the sediments of the nares abyssal plain contain olive or grey silt clay turbidites interbedded within brown pelagic clays three examples of a pale brown orange horizon located immediately under turbidite units have been investigated these horizons which are up to 22 cm thick have sharp colour changes at their upper and lower boundaries they are interpreted as reduction haloes within pelagic clay units developed as a result of the nearcomplete removal of mn iv oxyhydroxides from these regions following the deposition of the overlying turbidites this has resulted in bleaching of the dark brown pelagic sediment this is believed to be caused by bacterially mediated oxidation of the labile organic carbon of the pelagic surface buried beneath the turbidite by mn and fe oxyhydroxides in post oxic conditions in addition a further displacement of mn iv by fe ii occurs in this region as a concomitant of the contemporaneous oxidation of the organic carbon of the overlying turbidite unit by a progressive oxidation front much of the mn ii remobilised from the halo has been concentrated in the lower reaches of this unit by reprecipitation with oxygen clear associations are evident of co and ni with mn and of p and as with fe copper and pb have also been affected but the controls on these elements are uncertain the current distributions of the redox sensitive elements are therefore much changed since deposition because of this early diagenetic effect and exhibit subtle detail of distribution in contrast the haloes themselves appear featureless because evidence of bioturbation detail has been largely destroyed by bleaching

the impact of gravel extraction on groundwater dependent wetlands and lakes in the boreal plains canada the impact of gravel excavation on a groundwater dependent ecosystem gde in a glacial outwash plain was determined using a combination of time series stable isotopic measurements 2h and 18o and a numerical flow model of lake groundwater interaction isotopic analyses of the lake and groundwater indicated a shift from a dominance of evaporative enrichment to more meteoric conditions confirming the hypothesis of increased recharge following forest clearing and gravel extraction from an esker on the outwash plain the effect of these land use changes on source water for the gde was quantified by simulating the lake water budget seepage and groundwater conditions for a period spanning pre and post mining activity enhanced cycling of shallow groundwater driven by increased recharge in the gravel excavation area was predicted to cause annual groundwater discharge pulses greater than baseline conditions for the groundwater fed lake the additional groundwater discharge represents approximately 4 of the annual lake budget increasing the flushing rate of the lake the influence of regional groundwater conditions represented by variation of water table gradient and outwash hydraulic conductivity and an alternative excavation location were investigated in a sensitivity analysis simulation results illustrate that a simple groundwater capture zone analysis for the gde could be used to determine a location for gravel excavation that would reduce impact on gde water source

distribution and chemical composition of tephra layers from eastern mediterranean abyssal sediments abstract most cores of late quaternary sediments from the eastern mediterranean sea contain many ash layers glass shards from discrete layers have been analysed chemically for major elements the layers from different cores have been correlated and unambiguously related to known volcanic events on the basis of the chemical data most of the layers are derived from explosive eruptions of the santorini volcanic complex other layers have their source in other volcanoes of the hellenic arc yali nisyros kos one layer originated from the campanian area italy

late quaternary changes in mediterranean intermediate water density and formation rate three recently acquired eastern mediterranean cores containing late quaternary sediments display a marked faunal contrast between the holocene and older sapropels it is suggested that the absence of neogloboquadrinids in the holocene sapropel and their abundance in older sapropels reflect differences in food availability related to the extent of development of a deep chlorophyll maximum layer dcm and the intensity of new primary production associated with this layer the depth of such a layer which consists of phytoplankton with a characteristic taxonomic composition is determined by the vertical hydrodynamical structure during deposition of the older sapropels the pycnocline was apparently positioned well above the base of the euphotic layer a situation that favors a pronounced dcm and an associated relatively high rate of new production shallowing of the pycnocline implies a relatively low density of the mediterranean intermediate water miw on the other hand during deposition of the holocene sapropel the pycnocline had apparently vanished due to termination of miw formation

geochemical studies of the recent sapropel and associated sediment from the hellenic outer ridge eastern mediterranean sea i mineralogy and chemical composition abstract the mineralogy major and minor element geochemistry and the accumulation rate of a single kastenlot core from the eastern mediterranean is reported the sapropel is similar mineralogically and in its major element composition to the associated marl ooze and calcareous clay it differs from these sediments in having higher concentrations of ba cr cu mo ni sr and zn and lower concentrations of mn the enrichments are explained by increased fertility ba organic matter or sulphide association cr cu mo ni and zn and the presence of aragonitic pteropods sr the organic material has a marine origin based on the carbon isotopic value 13 c 20 and c n ratio 10 the sapropel accumulated 3 to 5 times faster than the associated sediments in this particular core the evidence is consistent with the formation of this sapropel by an increased flux of carbon to the sea floor this would have been caused by increased marine primary production in the eastern mediterranean during periods of reversed circulation brought about by high post glacial runoff primarily from northern africa the additional carbon flux would have lowered the oxygen levels of the bottom waters but it is not known whether anoxic conditions ensued or whether they would have been necessary to preserve the deposited carbon

magnetic iron nickel sulphides in the pliocene and pleistocene marine marls from the vrica section calabria italy abstract the rock magnetic properties of the late pliocene and early pleistocene open marine marls from the vrica section in calabria italy point to magnetic sulphide as the main magnetic mineral and remanence carrier the maximum blocking temperatures however are between 340 and 360 c which is too high for stoichiometric monoclinic pyrrhotite magnetic concentrates of the sediment are rich in iron sulphide grains and iron nickel sulphide grains microprobe observations show that most of the grains are of the order of 1 m in size and attached to iron bearing clay flakes microprobe analyses of the sulphides yield a large range of compositions ranging from pyrite through greigite pyrrhotite to sulphur deficient monosulphides and with ni contents varying from zero to a few atom percent in the pyrite grains and from zero to as much as 35 atm in the monosulphides the high ni content of many of the grains is extraordinary and has not been reported before in marine sediments most of the compositions cannot be directly connected with a known mineral phase the marine depositional environment of the marls imposes an authigenic origin for the sulphides and this is supported by several observations the great number of sulphide grains in the magnetic concentrates suggests that at least one of the sulphide compositions must have a ferrimagnetic structure possibly the sulphides with a metal to sulphur ratio close to that of monoclinic pyrrhotite and between 25 and 35 of the fe replaced by ni the ni substitution could possibly be the cause of the high blocking temperatures

organic carbon variations of the eastern mediterranean holocene sapropel a key for understanding formation processes abstract this work reports on the organic carbon content of the s1 holocene sapropel the youngest and most extensively researched of the eastern mediterranean sapropels the peak organic carbon percentage of the s1 sapropel varies between 1 2 and 3 4 at varying locations these variations could not be correlated with sapropel thickness or with spatial location in contrast there was a close linear correlation with water depth the deeper samples containing the highest values of organic carbon within the s1 layer the highest values were found in the top of the sapropel even if primary productivity increased during the s1 sapropelic period the main factors responsible for sapropel deposition were changes in the degradation and preservation of organic matter in the water column and at the sediment water interface water column stratification created an oxygenated surficial layer 0 350 400 m thick and a stagnant deep water layer the majority of the organic material escaping the surficial layer was remineralised either at the sediment water interface or just below it organic matter preserved in sapropelic sediments can be assumed to have remained for a significantly longer time 1000 years within the benthic boundary layer than in the water column organic flux decreased with depth through the stagnant deep water layer when stagnation was established water exchanges either did not exist or were limited vertical oxidant transport depended on eddy diffusion while oxidant fluxes at the sediment water interface decreased with depth the organic matter mineralisation rate also decreased and the burial efficiency increased the linear relationship between sapropel organic content and depth was reflected in a linear decrease in oxidant flux regardless of location the same organic carbon percentage was preserved at the same depth in contrast in the same area but at different depths organic carbon content ranges between 1 2 and 3 4 this observation suggests that primary productivity was of the same order of magnitude basinwide the organic carbon concentration of sediment should be used with caution as a quantitative record of palaeoproductivity

source and depositional controls on heavy metal distribution in marine sediments of the gulf of iskenderun eastern mediterranean the concentrations of major al mg fe and mn and trace zn cr ni co cu and pb elements as well as carbonate organic carbon and grain size distributions have been determined in surface sediments collected at 73 stations from the gulf of iskenderun the shelf sediments of the gulf of iskenderun are largely muds but sediments with higher contents of sand and gravel also occur due to the presence of high biogenic caco3 contents up to 80 in the samples the abundance and regional distributions of elements in the surface sediments of the gulf are largely controlled by differences in grain size and in the level of dilution by skeletal shell remains and by the variation in composition of source materials mg ni cr co and to a lesser extent zn and pb are significantly enriched relative to their average crustal abundances these metal enrichments are found especially in the eastern part along the sw ne trending areas of the gulf and are mostly consistent with the chemical and mineralogical compositions of the major basic and ultrabasic source rocks present on the adjacent coast and hinterland there is strong evidence that suggest that aluminosilicates fe and mn compounds possibly oxyhydroxides and organic matter act as the most effective carriers for transfer of available metals zn cr ni co and cu to the sediments

seasonal variation in surface subsurface water exchange and lateral hyporheic area of two stream aquifer systems abstract we used two dimensional unconfined transient groundwater flow models to investigate the interface between stream and groundwater flow systems or hyporheic zone of two first order streams that drain catchments with distinctly different alluvial sediments and bedrock lithology particle tracking showed that lateral hyporheic area planimetric area of flow paths lateral to the stream that are recharged by and return to the stream with travel times of 10 days or less differed between the two study streams and varied with discharge within each system at the rio calaveras welded tuff lateral hyporheic area ranged from 1 7 to 4 m 2 over the annual cycle in the aspen creek system sandstone lateral hyporheic area 1 1 5 m 2 was restricted to roughly half of that observed at rio calaveras the size of the hyporheic zone lateral to the streams at both sites decreased by approximately 50 during high flows sensitivity analyses indicated that changes in the hydraulic conductivity of alluvial and streambed sediments and variation in recharge rates have greatest impact on the magnitude direction and spatial distribution of stream groundwater exchange

paleoclimatic and paleoceanographic conditions leading to development of sapropel layer s1 in the aegean sea abstract sapropel s1 occurs as 25 35 cm thick black weakly laminated muds in aegean sea cores s1 was deposited between 9600 and 6400 yr b p during a period of isotopically depleted and relatively cool surface waters micro faunal and floral data indicate a major reduction in surface waters salinity during the deposition of s1 and oxygen isotopic data show a northerly fresh water source relatively light 13 c org and high pollen spore concentrations in s1 suggest increased influx of terrestrial organic carbon probably supplied by major rivers draining into the northern aegean sea benthic foraminifera indicate high nutrient low oxygen bottom waters for s1 and together with silt sized hematite and manganese coatings suggest that during the deposition of s1 surface sediments were oxic visual and xrd evidence of pyrite in s1 together with enrichments in s cu zn as ni cr and fe suggest that subsurface conditions were sufficiently reducing for so 4 2 reduction to occur probably by diffusion from surface oxic into subsurface anoxic sediments palynomorphs in s1 show large increases in terrestrial pollen and spores with the floral assemblage indicating significant influx from northern european rivers and minor african components associated with increased summer monsoonal rain abundance of dinoflagellates and amorphogen suggests some increase in primary productivity in response to increased influx of humic compounds however there is no evidence of upwelling the clay fraction in s1 shows notable decreases in smectite and kaolinite and reciprocal increases in illite and chlorite the combined data suggested that the evolution of s1 in the aegean sea largely resulted from stagnation of the surface waters during the final disintegration of the continental ice sheets rather than an increase in primary productivity and higher preservation of organic carbon on the sea floor

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

on the relationship between river basin geomorphology aquifer hydraulics and ground water flow direction in alluvial aquifers the delineation of ground water flow in alluvial valley stream aquifer systems is important in studies of water availability environmental impact and aquifer remediation and is required by some states water laws published potentiometric surfaces and head data however are not always available when data are absent it is commonly assumed that ground water and dissolved solutes flow toward the river analysis of published geomorphologic and hydraulic data in 24 alluvial systems and the results of digital simulations indicate that in some cases this assumption is only valid immediately adjacent to an effluent river ground water flow in the remaining portions of an alluvial valley aquifer may be dominated by downstream or underflow components this paper investigates the nature of ground water flow in alluvial valleys and presents a new classification scheme for alluvial aquifers the geomorphologic conditions that may allow underflow to be the predominant regional ground water flow component are described in order to classify alluvial aquifers two darcy flux end member components are defined the baseflow component is that portion of the ground water flux that moves perpendicular to the river the baseflow component may flow toward the river or away from the river depending on whether the river is effluent or influent respectively the underflow component of the darcy flux moves parallel to the river and in the same direction as the stream flow the alluvial stream aquifer systems are classified based on the predominant regional ground water flow component as underflow component dominated baseflow component dominated or mixed on the basis of the results of this study we conclude that the dominant regional ground water flow component base flow or underflow can be inferred in an alluvial valley aquifer from geomorphologic data these data include the channel slope the river sinuosity the degree of penetration incision through the alluvium of the river the width to depth ratio and the fluvial depositional system the underflow component is demonstrably predominant when the following conditions exist 1 the channel gradient exceeds 0008 2 the sinuosity is less than 1 3 3 the river penetration is less than 20 4 the width to depth ratio is greater than 60 and 5 the fluvial depositional system is either valley fill or mixed load to bed load the underflow component can also be dominant on flood plains where the lateral valley slope is negligible

precession related sapropelites of the messinian sorbas basin south spain paleoenvironmental significance abstract the sorbas basin southern spain is a narrow and elongated basin located in the betic corridor that formed the northern connection between the atlantic and the paleomediterranean during the late miocene in the centre of the basin about 120 m of well preserved cyclic marine sediments crop out ranging in age from 7 2 to 6 myr these cycles make up the abad member and are an excellent example of precession control over sedimentation in the upper part of the sequence upper abad member the cycles include organic rich laminated brown marls sapropelites alternating with homogeneous marls displaying diatomite layers the om rich laminated marls are the westernmost sapropelites of the mediterranean this paper is a geochemical mineralogical sedimentological and micropaleontological analysis of three cycles with sapropelites the data enable us to distinguish two main climatic scenarios the climate which dominated each of these scenarios regulated the sedimentology and the physico chemistry of the water column resulting in the sapropelite homogeneous marl cyclic alternations the sapropelites developed during a climate characterised by a long period of temperate and humid conditions that occur at times of precession minima these climatic conditions changed progressively to a subarid and drier weather during which homogeneous sediments were deposited the changes between these scenarios were gradual as expected from precession dynamics our data suggest that the change from the subarid to the humid climate transition from homogeneous marls to laminated sapropelites took place at a faster rate or at least was recorded more rapidly by the sediments than the transition from the humid interval to the sub arid period

geology and eruptive history of unzen volcano shimabara peninsula kyushu sw japan abstract during the past 500 thousand years unzen volcano an active composite volcano in the southwest japan arc has erupted lavas and pyroclastic materials of andesite to dacite composition and has developed a volcanotectonic graben the volcano can be divided into the older and the younger unzen volcanoes the exposed rocks of the older unzen volcano are composed of thick lava flows and pyroclastic deposits dated around 200 300 ka drill cores recovered from the basal part of the older unzen volcano are dated at 400 500 ka the volcanic rocks of the older unzen exceed 120 km3 in volume the younger unzen volcano is composed of lava domes and pyroclastic deposits mostly younger than 100 ka this younger volcanic edifice comprises nodake myokendake fugendake and mayuyama volcanoes nodake myokendake and fugendake volcanoes are 100 70 ka 30 20 ka and

redistribution and geochemical behaviour of redox sensitive elements around s1 the most recent eastern mediterranean sapropel the youngest eastern mediterranean sapropel s1 is generally believed to have formed 7 9 14c ky b p the distribution of redox sensitive elements above in and below the sharply defined organic rich unit reveal that s 1 has already suffered heavy diagenetic alteration its present thickness based on its dark colour is only a fraction of its original thickness in one core visual evidence of s1 with an inferred initial thickness of 6 cm has been destroyed and a similar thickness appears to have been lost from the tops of another two examples this is caused by oxidation of the upper reaches of s 1 by a progressive oxidation front which commenced 5 2 5 4 14c ky ago and still appears to be active in the three cores studied diagenetic relocation of many redox sensitive elements has occurred most elements expected to be enriched in sapropels or sulphide rich sediments already have maximum concentrations above or below rather than in the present s 1 layers similarities are observed in the geochemical behaviour of as fe and p of co cu mn ni and zn and of cd mo sb ti u and v the behaviour of ba is distinctive and its immobility as barite makes it an indicator for palaeoproductivity and the original high s1 corg content the elements se and i exhibit particularly large sharp concentration peaks and together are proposed as useful indicators of the present boundary between oxic and post oxic conditions

early organic diagenesis the significance of progressive subsurface oxidation fronts in pelagic sediments abstract porewater and solid phase geochemical data at two contrasting ne atlantic stations are reported station 10552 on the cape verde abyssal plain is a site of slow pelagic accumulation ca 0 4 cm kyr 1 molecular oxygen is present in the sediment column to at least 2 m and probably much deeper labile organic carbon is almost totally consumed in the upper few centimetres of the sediment by contrast at station 10554 on the madeira abyssal plain the pelagic sequence has been interrupted by the occasional deposition of organic rich turbidites porewater oxygen and nitrate profiles show that subsurface organic metabolism of the organic carbon associated with the uppermost turbidite layer is a significant fraction of the overall metabolism in the sediment column this metabolism occurs at a relatively thin reaction front which progresses deeper into the turbidite with time this phenomenon exerts a controlling influence on the present nutrient profile and redox succession in a less extreme form substrate distributions of this latter type are not uncommon in atlantic sediments a model has been developed which is controlled by both oxygen and nitrate data this model permits a vertical profile of metabolic activity to be derived and also gives estimates of the reaction rate constants and solid phase mixing rates at these two contrasting stations about 30 of the total activity at station 10554 is located within the turbidite at the deepening reaction front this is a non steady state condition in fact it is found that the integrated metabolic activity at the two stations is not dissimilar ca 1 2 10 13 moles cm 2 sec 1 the striking differences in redox profile are therefore primarily attributable to differences in the distribution of metabolic activity within the column

combined organic and inorganic geochemical reconstruction of paleodepositional conditions of a pliocene sapropel from the eastern mediterranean sea layers of organic carbon rich sapropels in the sediment record of the mediterranean sea give evidence of repetitive changes in regional plio pleistocene climate results from biomarker molecule and major and trace element analyses of closely spaced samples are used to reconstruct the conditions leading to deposition of a pliocene sapropel at ocean drilling program odp site 969 on the mediterranean ridge organic carbon concentrations increase from 0 2 outside the sapropel and peak to more than 30 within it major and trace elemental composition and biomarker derived parameters indicate elevated productivity depletion of water column dissolved oxygen content and changes in sediment provenance in response to climatic changes budgets of rhenium thallium and other trace metals indicate that deep water exchange between the mediterranean subbasins and the atlantic ocean was not completely interrupted during sapropel formation enrichment factors of redox sensitive and sulfide forming trace metals as well as the presence of isorenieratene derivatives and high stanol sterol ratios point to an extended zone of anoxic water masses depth profiles of biomarker compositions sterols long chain alkenones alkandiols and ketols fatty acids indicate great floral diversity during deposition of a single sapropel and highlight the sensitive response of the marine community to variable environmental conditions changes in water mass circulation and eolian transport can be reconstructed by use of both lithogenic elements and average chain lengths of n alkanes acl index

the diagenetic formation of metal rich layers in sapropel containing sediments in the eastern mediterranean two cores recovered from different locations in the eastern mediterranean contain intercalations of organic rich sapropels in organic poor hemipelagic sediments in both cores enrichments of mn and fe were found in the oxidised section of the sediment above the sapropel s1 the sediments followed a diagenetic cycle which began after the sapropel formation finished about 7000 years ago first during a non steady state diagenetic phase metal rich layers were formed at a downward moving oxidation front the front decelerated at the top of the sapropel as a consequence of increasing amounts of corg and sulphides that had to be oxidised during the second part of this non steady state phase the oxidation front starts moving upwards with respect to the sapropel manganese is remobilised in preference to iron due to thermodynamics reinforced by kinetics when the upward movement of the oxidation front becomes equal to the sedimentation rate steady state is established with respect to the new organic poor sedimentary circumstances at location 31g1 the system is at or close to steady state at location 9g1 however this steady state phase has never been reached between 1900 and 1350 years bp the organic carbon accumulation rate probably increased suddenly inducing a retreat of the oxidation front and the non steady state formation of double peaks

iridium and other platinum group elements as geochemical markers in sedimentary environments iridium anomalies are commonly used as indicators of extraterrestrial processes which caused global extinctions however platinum group element pge anomalies may result from several different processes both syn and postdepositional acting separately or jointly the sources and processes of enrichment involved are extraterrestrial asteroid comet cosmic dust impact ejecta volcanogenic pge rich condensates precipitation from seawater low sedimentation rate anoxic conditions microbial concentration dissolution reprecipitation exhalative hydrothermal leaching transport and precipitation at a redox boundary geochemical characteristics of pge and accompanying elements in sediments can be used to identify the contributions of some specific sources and processes 1 extraterrestrial chondritic ru ir and os ir ratios low 187os 186os ratio high ir compared to pt pd and au 2 volcanogenic high iridium and se as sb and in contents 3 exhalative hydrothermal high au pd and pt relatively low ir contents 4 precipitation from seawater high pt and low pd contents also high cd and ag contents under anoxic conditions and 5 reduction from intermediate and low temperature solutions high pge and cu or mo u ni contents

geochemistry of an exotic sediment layer above sapropel s 1 mud expulsion from the urania basin eastern mediterranean in a gravity core from the eastern mediterranean sea a chemically and mineralogically distinct 5 5 cm thick layer is present above sapropel s 1 and overlain by hemipelagic marls calcite is completely absent in this exotic layer dolomite is present only in small amounts and the cr concentrations are significantly enhanced the layer was deposited primarily under reducing conditions but the distributions of redox sensitive elements show that a large part of the exotic layer is now oxidised by a downward progressing oxidation front sediments from within the nearby anoxic hypersaline urania basin are similar to those from the exotic layer in particular in s c and o isotope distributions of pyrite and dolomite as well as increased cr concentrations mud expulsion due to expansion of gas rich mud is proposed to explain the presence of the exotic layer outside the urania basin the deposition of an anoxic layer above s 1 shielded the sapropel from oxidation which resulted in the rare occurrence of a complete preservation of s 1 and provides the first minimum age for the start of anoxic mud accumulation in the urania basin