erosional and climatic effects on long term chemical weathering rates in granitic landscapes spanning diverse climate regimes abstract we used cosmogenic nuclide and geochemical mass balance methods to measure long term rates of chemical weathering and total denudation in granitic landscapes in diverse climatic regimes our 42 study sites encompass widely varying climatic and erosional regimes with mean annual temperatures ranging from 2 to 25 c average precipitation ranging from 22 to 420 cm year 1 and denudation rates ranging from 23 to 755 t km 2 year 1 long term chemical weathering rates range from 0 to 173 t km 2 year 1 in several cases exceeding the highest granitic weathering rates on record from previous work chemical weathering rates are highest at the sites with rapid denudation rates consistent with strong coupling between rates of chemical weathering and mineral supply from breakdown of rock a simple empirical relationship based on temperature precipitation and long term denudation rates explains 89 95 of the variation in long term weathering rates across our network of sites our analysis shows that for a given precipitation and temperature chemical weathering rates increase proportionally with fresh material supply rates we refer to this as supply limited weathering in which fresh material is chemically depleted to roughly the same degree regardless of its rate of supply from breakdown of rock the temperature sensitivity of chemical weathering rates is two to four times smaller than what one would expect from laboratory measurements of activation energies for feldspar weathering and previous inter comparisons of catchment mass balance data from the field our results suggest that climate change feedbacks between temperature and silicate weathering rates may be weaker than previously thought at least in actively eroding unglaciated terrain similar to our study sites to the extent that chemical weathering rates are supply limited in mountainous landscapes factors that regulate rates of mineral supply from erosion such as tectonic uplift may lead to significant fluctuations in global climate over the long term

characterization of stream meanders for stream restoration recently increased emphasis and attention has been given to river management and restoration of modified streams a variety of restoration techniques and objectives exist including asymmetrical cross section construction point bar development two stage channel design floodplain approaches pools and riffles re creation and sinuosity and meander restoration modifications of the planform geometry can induce undesirable morphological and ecological consequences and significant channel adjustments that depending on the energy of the flow can result in failure of the restoration design through either erosion or sedimentation in this study we provide an analysis of the accuracy of empirical relations of meander parameters for use in meander restoration procedures a case study in central maryland is used to demonstrate this analysis it is suggested that the combination of a field reconnaissance and analytical study should be used to determine the appropriateness of using published regression equations

major and trace elemental compositions of the upper carboniferous batamayineishan mudrocks wulungu area junggar basin china implications for controls on the formation of the organic rich source rocks abstract the upper carboniferous batamayineishan mudstones are an important and effective gas source rock in the wulungu area these sediments are rich in organic matter however organic matter accumulation has not been studied before in these mudstones the major and trace elements were used to reconstruct the depositional environments of these sediments and to improve our understanding of the factors controlling organic matter accumulation major and trace elements data indicate that 1 paleoweathering was low to intermediate in the source terrain 2 paleoclimate was hot and arid during late carboniferous in the wulungu area 3 low paleoproductivity may have been induced by the low input of nutrients caused by the hot arid climate 4 the batamayineishan mudstones were deposited under a reducing environment 5 organic matter accumulation in these studied deposits was mainly controlled by the input of higher plants rather than redox conditions and paleoproductivity

graptolite derived organic matter in the wufeng longmaxi formations upper ordovician lower silurian of southeastern chongqing china implications for gas shale evaluation abstract the organic rich shales of the wufeng longmaxi formations ordovician silurian are one of the most important hydrocarbon source rocks and shale gas exploration targets in china graptolites are abundant in these shales but their contribution to the dispersed organic matter om has been overlooked this lack of attention could seriously affect the evaluation of om type om maturity hydrocarbon generation potential reservoir characteristics and gas content of these shales optical microscope and focused ion beam scanning electron microscope fib sem techniques were employed to describe the optical characteristics and micro nanopores of the graptolites to determine the contribution of the graptolites and to evaluate the thermal maturity of the wufeng longmaxi formations non granular graptolites which show a stronger anisotropy and higher reflectance under polarized light than the granular graptolites were primarily observed in these sediments graptolites account for 20 93 of the dispersed om in the wufeng longmaxi formations and the level of their contribution has been attributed to the radiation of graptolites at the late ordovician kaptian and the recovery of graptolites at the early silurian rhuddanian the bireflectance values of the non granular graptolites fall between 2 22 and 4 32 indicating a behavior similar to biaxial anthracitic vitrinite the equivalent vitrinite reflectance eqvro values of the sediments in the wufeng longmaxi formations calculated from the mean maximum reflectance of non granular graptolite fall in the range of 3 08 4 29 and these values have a precision that is greater than in previous studies on the wufeng longmaxi formations abundant organic pores were observed in the non granular graptolites and they are aligned parallel to the fusellar layers of the graptolites this indicates that the fusellar layers of non granular graptolites controlled the development and distribution of organic pores such abundant organic pores played a significant role in the accumulation of shale gas in the wufeng longmaxi formations of the upper yangtze platform

a note on the iugs reclassification of the high mg and picritic volcanic rocks the purpose of this short note is to offer some comments and observations on the new iugs classification of high mg rocks le bas 2000 particularly its use of the terms komatiite and picrite with no reference to texture or the original usage of these terms at the outset of this discussion we would like to place on record that we are in agreement with the need to redefine the nomenclature of high mg rocks there are however important issues relating to both the use of the term komatiite for all extrusive volcanic rocks with 18 wt mgo and the definition and use of the term picrite neither of which are discussed by le bas

controls on phosphorus regeneration and burial during formation of eastern mediterranean sapropels the carbon c and phosphorus p geochemistry of sapropels from four sites in the eastern mediterranean sea was determined to obtain more insight into the role of differences in sediment accumulation rates and bottom water anoxia on p regeneration and burial in sediments sediment corg porg with org organic ratios above redfield indicate enhanced regeneration of p relative to c from organic matter during formation of the most recent sapropel s1 and a pliocene sapropel odp site 969e i 282c release of p from fe oxides was relatively unimportant increased burial of ca p authigenic carbonate fluorapatite and or biogenic hydroxyapatite occurred but was of minor importance compared to the enhanced p release from organic matter for sapropel s1 corg porg and corg preac with reac reactive defined as the sum of organic fe bound authigenic and biogenic ca p ratios decreased with increasing sedimentation rate and oxygen exposure and decreasing water depth whether the water column in the deep basin was dysoxic semi euxinic s1 or euxinic pliocene does not appear to affect the estimated burial efficiencies of porg and preac enhanced corg burial under the euxinic water column explains the much higher corg porg and corg preac ratios in the pliocene sapropel on average 2860 and 760 respectively compared to sapropel s1 on average 530 and 160 respectively

the organic petrology of graptolites and maturity assessment of the wufeng longmaxi formations from chongqing china insights from reflectance cross plot analysis abstract the wufeng longmaxi formations ordovician silurian contain abundant graptolite bearing shales which have proven to be one of the most successful shale gas exploration targets in china and can provide an opportunity to study the organic petrology of graptolites organic petrology analysis has been conducted on these organic rich shales in order to depict the shape of graptolite reflectance indicating surface gris and their organic maturity granular and non granular graptolites have been observed in the studied sediments and non granular graptolites were the major graptolite species the strong positive correlation between the maximum reflectance rmax and bireflectance of graptolites indicates that the graptolites display stronger anisotropy with maturation a linear coalification path of graptolite fragments was observed in the studied sediments a remarkable decrease in the minimum reflectance rmin values of graptolites was observed when rmax exceeds 6 the samples with lower thermal maturity rmax 2 tend to be biaxial neutral whereas higher rank samples display biaxial negative characteristics the gris shape becomes more oblate with maturation the wufeng longmaxi shales from the southeastern chongqing and wuxi areas of the chongqing municipality china are post mature and in the dry gas zone whereas samples from the chengkou area of the chongqing municipality china are still in the oil window their different burial and thermal histories controlled their thermal maturity

characterization of lacustrine mixed fine grained sedimentary rocks using coupled chemostratigraphic petrographic analysis a case study from a tight oil reservoir in the jimusar sag junggar basin abstract mixed deposits are sediments consisting of external clastic epiclastic or terrigenous intrabasinal components and pyroclastic components the mixture comprising variable amounts of the three components is defined as mixed sedimentary rocks the permian lucaogou formation p2l in the jimusar sag of the junggar basin is a promising tight oil target in western china the fine grained mixed sedimentary rocks of which are rich in organic matter om and two sweet spot intervals with relatively high porosity however the sediment composition provenance and deposition environmental settings have not been studied in detail in this study coupled chemostratigraphic petrographic analysis were used to reconstruct their depositional environments the results show that the fine grained sedimentary rocks have three major sediment sources external clastic input terrigenous clastics intrabasinal autochthonous to parautochthonous components carbonates siliceous skeletal debris and om and pyroclastic input main lithofacies include siltstone fine sandstone mudstone dolomite and tuffite the silt sandstones were mainly sourced from rocks with calc alkaline composition while the tuffaceous sedimentary rocks were sourced from high k calc alkaline rocks elemental proxies suggest that the carbonate rocks were generally deposited under warm and arid conditions whereas the fine grained clastic sediments were deposited under relatively humid conditions the muddy or silty tuffaceous mixed rocks were deposited under relatively reducing conditions compared with carbonates and sandstones variations of lithofacies and om accumulation of different intervals reflect changing deposition environmental settings and the frequently altered high toc content rocks and good reservoirs are benefit for tight oil formation the work may provide some useful insights and serve as a reference for studying other mixed fine grained sedimentary rocks and tight oil plays in similar lacustrine basins elsewhere

a model for lateral hyporheic flow based on valley slope and channel sinuosity 1 the meandering of rivers results in head gradients across point bar deposits leading to hyporheic exchange the flow of groundwater from and back to the stream two models for predicting horizontal fluid flux through the hyporheic zone one based solely on valley slope and another that uses both valley slope and channel sinuosity are presented in this article both models require knowledge of aquifer hydraulic conductivity the models are developed via a suite of groundwater flow simulations with boundary conditions taking a variety of channel geometries idealized as sinusoidal and valley slopes that we assume are similar to that of the water table functional predictive models are developed by fitting a line or surface to discrete model output which covers the spectrum of most natural meandering rivers since the fitted models only require channel slope and or sinuosity plus hydraulic conductivity they are amenable for regional estimation of hyporheic flux using digital terrain data

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

phosphorus burial as a function of paleoproductivity and redox conditions in arabian sea sediments in this study the response of sedimentary phosphorus p burial to changes in primary productivity and bottom water oxygen concentrations during the late quaternary is investigated using two sediment cores from the arabian sea one recovered from the continental slope and the other from the deep basin the average solid phase p speciation in both cores is similar authigenic and biogenic fish debris apatite make up the bulk of the p inventory ca 70 whereas p adsorbed to iron oxides organic p and detrital apatite constitute minor fractions postdepositional redistribution has not significantly altered the downcore distribution of total solid phase p phosphorus burial efficiencies are generally lower during periods of increased paleoproductivity this is caused by a partial decoupling of the p export flux consisting primarily of particulate organic p and the p burial flux consisting primarily of biogenic and authigenic apatite and b the lack of increased rates of authigenic cfa formation during periods of higher p deposition in addition fluctuations in bottom water oxygen concentrations may have affected p burial in continental slope sediments the results of this study indicate that higher primary productivity induces more efficient p cycling on time scales exceeding the oceanic p residence time this process may induce higher surface water productivity thus creating a positive feedback loop in the arabian sea this feedback mechanism may have contributed to changes in sea surface productivity on sub milankovitch time scales because p regenerated on the continental slopes of the oman and somalian coastal upwelling zones is reintroduced into the photic zone relatively fast

geochemical characterisation of early cretaceous lacustrine sediments of bima formation yola sub basin northern benue trough ne nigeria organic matter input preservation paleoenvironment and palaeoclimatic conditions the bima formation is the oldest lithogenetic unit occupying the base of the cretaceous successions in the yola sub basin of the northern benue trough it is differentiated into lower b1 middle b2 and upper b3 bima members integrated organic and inorganic geochemical studies were applied on the lacustrine sediments of the bima formation with the aim of reconstructing the palaeodepositional environment and organic matter input in response to climate and tectonism the analysed sediments were deposited in a freshwater lacustrine environment with a low salinity stratified water column and suboxic to relatively anoxic conditions as indicated by the bulk geochemical parameters the biomarkers provide evidence for a contribution of aquatic algae and microorganisms with a significant amount of terrigenous organic matter input the preservation of the organic matter is possibly attributed to the stratified water column with low salinity and suboxic to relatively anoxic conditions based on the geochemistry of major and trace elements the sediments were deposited during semi arid climatic conditions within passive continental margin setting this agrees with the tectonic events in the west and central african rift system wcars during the early cretaceous period

palaeoenvironmental changes at the frasnian famennian boundary in key european sections chemostratigraphic constraints abstract the study aims to put constraints on global environmental changes which took place during the frasnian famennian f f transition by using a geochemical multiproxy approach for this several key european f f boundary sections deposited in different palaeogeographic settings were selected including in addition to the stratotype and parastratotype sections of coumiac montagne noire france and steinbruch schmidt branau germany respectively also some other sections thoroughly characterized by other authors the drilling budesheimer bach prumer mulde germany kowala section holy cross mountains poland la serre france changes in the detrital flux along the sections were evaluated on the basis of both variations in mineral composition and in some diagnostic element ratios like ti al the biogenic flux was assessed as a function of the corg content the input of nutrients or the palaeoproductivity was determined by the p2o5 and ba in excess the degree of anoxia during deposition was constrained by determining the concentration of redox sensitive metals e g fe mn in the bulk sediment of specific element ratios e g v cr as well as the size of pyrite grains together with the degree of pyritization dop in the budesheimer bach core the hydrothermal and volcanic influence in the sedimentary record was detected using e g the al al fe mn and zr al2o3 ratios the kellwasser horizons are characterized by a general decrease in the detrital input together with the increase of al normalized concentration of some of the transition metals these changes are interpreted as reflecting a relative sea level rise and a higher hydrothermal influence in contrast to these the establishment of dysoxic anoxic conditions in the depositional environment as well as the increase of organic matter burial are not always restricted to the kellwasser horizons kwh moreover the hydrothermal influence can lead to misinterpretation with respect to redox conditions and productivity due to the additional input of some specific elements our results indicate the coincidence of sea level rise with hydrothermalism and volcanism during the deposition of the kwh in the area of south laurussia and north gondwana the resulting enrichment in metals and nutrients is coupled in several f f boundary sections with a higher microbial activity as already observed by some authors these effects coupled with a general lowering of the degree of oxygenation of the water bodies could have played a significant role in the demise of the biota

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

hyporheic exchange in gravel bed rivers with pool riffle morphology laboratory experiments and three dimensional modeling received 7 june 2005 revised 30 june 2006 accepted 25 august 2006 published 31 january 2007 1 we report the first laboratory simulations of hyporheic exchange in gravel pool riffle channels which are characterized by coarse sediment steep slopes and three dimensional bed forms that strongly influence surface flow these channels are particularly important habitat for salmonids many of which are currently at risk worldwide and which incubate their offspring within the hyporheic zone here we perform a set of laboratory experiments examining the effects of discharge and bed form amplitude on hyporheic exchange with surface subsurface mixing measured directly from the concentration decay of a conservative tracer fluorescein injected into the surface flow near bed pressure measurements were also used to predict hyporheic exchange from a three dimensional pumping transport model comparison of the predicted and observed hyporheic exchange shows good agreement indicating that the major mechanism for exchange is bed form induced advection however the effect of bed forms is modulated by discharge and the degree of topographic submergence we also tested the performance of the hydrostatic pressure as a proxy for the observed near bed pressure in driving hyporheic exchange which would facilitate field measurement and analysis of hyporheic flow in natural rivers we found agreement with measured hyporheic exchange only for low bed form amplitudes and high flows

weathering and global denudation a negative correlation between sediment yield and weathering history as measured by the chemical alteration cia of the suspended sediment is observed for many of the world s major rivers and other regions of denudation the weathering history is a first order control on the sediment yield of such areas termed equilibrium denudation regions for other areas data scatter with either apparent increases or decreases of sediment yield for given cia values these areas are termed nonequilibrium denudation regions low sediment yields can be attributed to moderated erosion either natural or human induced and or the incorporation of unweathered glacial debris accelerated erosion resulting in high sediment yield is primarily human induced and results from cultivation and other land use each of these effects has a profound influence on global sediment discharge from the continents pre human suspended sediment discharge from the continents is estimated to be 12 6 times 10 15 g yr or about 0 6 the

impact of heterogeneity bed forms and stream curvature on subchannel hyporheic exchange 1 advection through hyporheic zones hz consisting of heterogeneous channel bend streambed deposits and their equivalent homogenous medium was investigated using finite difference groundwater flow and transport simulations and forward particle tracking the top prescribed head boundary was varied in order to mimic various stream channel head distributions resulting from the presence of bed forms and channel curvature flux calculations show that heterogeneity causes significant additional hz flux compared to an equivalent homogenous medium however the major cause of hz flux is a spatially periodic sinusoidal head distribution along the boundary representing the effect of bed forms the additional influence of heterogeneity on the total channel bed exchange and the overall hz geometry are increased when boundary head sinusoidal fluctuation is more subdued we present dimensionless numbers that summarize these relationships heterogeneity s influence is further magnified by considering the effect of channel curvature on boundary heads the simulations illustrate the dynamic influence of heterogeneity on the hyporheic zone since the various head boundaries employed in our modeling efforts are a proxy for different surface water conditions and bed form states that may occur during a single flood furthermore we show that residence times total tracking times of particles originating from the streambed follow a lognormal distribution in the presence of heterogeneity residence times can decrease or they can increase compared to residence times for homogeneous conditions depending on the relative positions of the heterogeneities and the bed forms hence streambed heterogeneity and stream curvature factors often neglected in previous modeling efforts combine with bed form configuration to dynamically determine hz geometry fluxes and residence time distributions

alluvial sandstone composition and paleoclimate i framework mineralogy abstract systematic variations in compositional maturity of first cycle fluvial sandstones are found in the cutler formation permian and fountain formation permian pennsylvanian in colorado and in the gondwana supergroup permian triassic of peninsular india these variations reflect changing climate during deposition climate is considered to be the critical factor affecting maturity because source rocks granite granite gneiss and tectono environmental setting alluvial systems associated with basement cored block uplifts were similar and remained relatively unchanged throughout deposition of all three of the units the roughly 3 200 m thick gondwana succession consisting of five sandstone petrofacies is characterized by the following sequence of change oldest to youngest in compositional maturity expressed in q f r percentages 54 42 4 88 10 2 62 34 4 82 16 2 99 1 0 this sequence is a function of the changing paleoclimate glacial arid temperate humid warm semiarid warm semihumid warm humid associated with the overall global limatic change and the changing latitudinal location of india as it moved from a location close to the south pole northward during the interval of time represented by gondwana deposition lithologic and fossil evidence indicates that during deposition of the fountain formation climate gradually changed from relatively wet and warm to at least semiarid and warm this climatic change is the main factor responsible for the difference in compositional maturity of the older fountain sandstone q f r 65 26 9 relative to the younger q f r 54 36 10 cutler sandstone was deposited in an arid climate and has maximum compositional immaturity q f r 49 44 7 a log log plot of the ratio of total quartz to total feldspar plus rock fragments against the ratio of total polycrystalline quartz to to al feldspar plus rock fragments is a sensitive discriminator of first cycle sandstones with differing climatic heritage bulk chemical composition data support interpretation of climate from framework mineralogy but by themselves are not sensitive enough to be unequivocal indicators the same is true for the ztr index and observations of degree and abundance of solution pits embayments on detrital quartz results of this study support the conclusion of earlier empirical and theoretical analyses which suggest that the optimum conditions for the production and preservation of a distinctive climatic signature on sand composition are met in extensional plate tectonic settings such settings are characterized by coarse grained crystalline parent rocks short transport distances in low order streams deposition in nonroutine environments and shallow burial diagenesis however even in such optimum settings only rarely will climate be a more important determinant of sandstone composition than the tectonic setting itself

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

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

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

moderate chemical weathering of subtropical taiwan constraints from solid phase geochemistry of sediments and sedimentary rocks abstract the well known earthquake and storm triggered extremely high physical weathering rate in taiwan is consistent with present geochemical studies of sediments from different subenvironments offshore coastal river and lake and sedimentary rocks of different geological ages indicating a moderate chemical weathering condition major and trace element concentrations normalized to the average upper crust of yangtze craton show that the sediments and the average composition of sedimentary rocks of taiwan are depleted in ca mg na and sr enriched in rb and zr and unchanged with respect to k indicating their moderately altered nature the mean chemical index of alteration cia 71 75 and plagioclase index of alteration pia 81 86 values of coastal and offshore sediments reveal the sediments derivation from sedimentary rocks by moderate silicate chemical weathering processes the mean cia value 62 of sedimentary rocks of taiwan is similar to that for chinese sediment 61 further confirming

enhanced regeneration of phosphorus during formation of the most recent eastern mediterranean sapropel s1 phosphorus regeneration and burial fluxes during and after formation of the most recent sapropel s1 were determined for two deep basin low sedimentation sites in the eastern mediterranean sea organic c p ratios and burial fluxes indicate enhanced regeneration of p relative to c during deposition of sapropel s1 this is largely due to the enhanced release of p from organic matter during sulfate reduction release of p from fe bound p also increased but this was only a relatively minor source of dissolved p pore water hpo4 concentrations remained too low for carbonate fluorapatite formation an increased burial of biogenic ca p i e fish debris was observed for one site estimated benthic fluxes of p during sapropel formation were elevated relative to the present day 900 to 2800 vs 70 to 120 mol m 2 yr 1 the present day sedimentary p cycle in the deep basin sediments is characterized by two major zones of reaction 1 the zone near the sediment water interface where substantial release of hpo4 from organic matter takes place and 2 the oxidation front at the top of the s1 where upward diffusing hpo4 from below the sapropel is sorbed to fe oxides the efficiency of aerobic organisms in retaining p is reflected in the low organic c p ratios in the oxidized part of the sapropel burial efficiencies for reactive p were significantly lower during s1 times compared with the present day 7 to 15 vs 64 to 77 budget calculations for the eastern mediterranean sea demonstrate that the weakening of the antiestuarine circulation and the enhanced regeneration of p both contributed to a significant increase in deep water hpo 4 concentrations during sapropel s1 times provided that sufficient vertical mixing occurred enhanced regeneration of p at the seafloor may have played a key role in maintaining increased productivity during sapropel s1 formation copyright 2002 elsevier science ltd

channel reach morphology in mountain drainage basins a classification of channel reach morphology in mountain drainage basins synthesizes stream morphologies into seven distinct reach types colluvial bedrock and five alluvial channel types cascade step pool plane bed pool rime and dune ripple coupling reach level channel processes with the spatial arrangement of reach morphologies their links to hillslope processes and external forcing by confinement ripar ian vegetation and woody debris defines a process based framework within which to assess channel condition and response potential in mountain drainage basins field investigations demonstrate character istic slope grain size shear stress and roughness ranges for different reach types observations consistent with our hypothesis that alluvial channel morphologies reflect specific roughness configurations ad justed to the relative magnitudes of sediment supply and transport ca pacity steep alluvial channels cascade and step pool have high ratios of transport capacity to sediment supply and are resilient to changes in discharge and sediment supply whereas low gradient alluvial channels pool rime and dune ripple have lower transport capacity to supply ra tios and thus exhibit significant and prolonged response to changes in sediment supply and discharge general differences in the ratio of transport capacity to supply between channel types allow aggregation of reaches into source transport and response segments the spatial distribution of which provides a watershed level conceptual model linking reach morphology and channel processes these two scales of channel network classification define a framework within which to in vestigate spatial and temporal patterns of channel response in moun tain drainage basins

transfer of nonsorbing solutes to a streambed with bed forms theory a theoretical analysis of the exchange of nonsorbing solutes between a permeable streambed and the overlying water of a stream or river is presented in this paper in a companion paper elliott and brooks this issue the results of experimental studies of such exchange are presented the analysis focuses on water movements into within and out of the bed which result from the presence of bed forms ripples and dunes and highlights the mechanisms of pumping and turnover pumping is the movement of fluid through the bed induced by steady dynamic pressure variations over bed forms turnover occurs as moving bed forms trap and release interstitial fluid the detailed analysis was used to generate the distribution of the residence time of solute within the bed which can be used to calculate the net mass exchange due to pumping and turnover

effects of stream discharge alluvial depth and bar amplitude on hyporheic flow in pool riffle channels 1 hyporheic flow results from the interaction between streamflow and channel morphology and is an important component of stream ecosystems because it enhances water and solute exchange between the river and its bed hyporheic flow in pool riffle channels is particularly complex because of three dimensional topography that spans a range of partially to fully submerged conditions inducing both static and dynamic head variations hence these channels exhibit transitional conditions of streambed pressure and hyporheic flow compared to previous studies of fully submerged two dimensional bed forms here we conduct a series of three dimensional simulations to investigate the effects of bed topography depth of alluvium and stream discharge on hyporheic flow in pool riffle reaches with variable bed form submergence and we propose three empirical formulae to predict the mean depth of hyporheic exchange and characteristic values of the residence time distribution mean and standard deviation hyporheic exchange is predicted with a three dimensional pumping model and hyporheic flow is modeled as a darcy flow we find that the hyporheic residence time is well approximated by a lognormal distribution for both partially and entirely submerged pool riffle topography with the parameters of the distribution defined by the mean and variance of the log transformed residence time depth of alluvium has a substantial effect on hyporheic flow when alluvial depth is less than a third of the bed form wavelength for the conditions examined

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

the cenomanian turonian oceanic anoxic event ii palaeoceanographic controls on organic matter production and preservation correlation of the 13c spike with the well dated occurrences of strata rich in organic carbon detailed in schlanger et al this volume indicates that a global episode of intense organic carbon orgc burial took place during the latest cenomanian earliest turonian oceanic anoxic event oae a plenus through i labiatus macrofossil zones and upper r cushmani trz through w archecretacea prz foraminiferal zones over a period of no more than 1 million years m y the shape of the 13c curve indicates that rates of orgc burial gradually increased in the early part of the late cenomanian increased more rapidly in the later cenomanian and levelled off at peak values in latest cenomanian early turonian time during the maximum rate of orgc burial the 13c values decreased nearly to pre late cenomanian levels in the early to middle turonian the decrease in 13c reflects decreasing rates of orgc burial following the cenomanian turonian oceanic anoxic event as well as the probable oxidation and return of significant amounts of orgc to the oceans following regression and re oxygenation of much of the deeper water masses in contact with the seafloor

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

phosphorus distribution c n p ratios and δ13coc in arctic temperate and tropical coastal sediments tools for characterizing bulk sedimentary organic matter abstract onshore offshore trends in phosphorus p organic carbon oc and total nitrogen tn concentration p distribution elemental organic c n p ratios and stable carbon isotopic composition of oc 13 c oc of surficial sediments are presented from three river dominated coastal regimes the mackenzie river beaufort shelf in the canadian arctic the mississippi delta and louisiana shelf in the temperate gulf of mexico and the tropical amazon shelf these parameters measured in surficial sediments from the three sites are used to assess changes in the importance of terrestrial and marine organic matter sources to sediments as a function of distance from the locus of riverine discharge trends in elemental ratio data from the arctic transect and a portion of the gulf of mexico transects can be explained in terms of a two end member mixture of terrestrial and marine phytodetritus in the arctic transect covariation of organic c p ratios with 13 c oc is consistent with a two end member mixture of terrestrial and marine organic matter a similar relationship between c p ratios and 13 c oc is not evident in gulf of mexico or amazon shelf sediments at these sites the two end member model fails to explain the data adequately the most striking feature of the onshore offshore trends in elemental oc op and oc tn ratios is the occurrence of low ratios in sediments from deep water stations in the gulf of mexico and all stations on the amazon shelf resulting from p and n enrichments exceeding the redfield ratio for marine plankton three explanations are discussed to account for these low ratios 1 the dominance of refractory op and on compounds in the residuum of degraded organic matter 2 differential sorption of op and n compounds regardless of lability on the surfaces of the fine grained sediments characteristic of these sites and 3 a dominance of bacterial biomass or components derived from bacterial biomass elemental ratios and 13 c oc signatures indicate that differential sorption may be most important in the deep water gulf of mexico sites in contrast elemental ratios and 13 c oc on the amazon shelf are most consistent with a sedimentary organic matter pool dominated by bacterial biomass or derivative substances

redox conditions associated with organic carbon accumulation in the late devonian new albany shale west central kentucky illinois basin abstract factors affecting organic carbon accumulation in marine basins may include surface water productivity enhanced preservation due to bottom water anoxia protection by and adsorption onto clays and variations in sediment supply in this study geochemical proxies for the new albany shale of the illinois basin were examined for ten cores from the outcrop belt in west central kentucky in an attempt to evaluate redox conditions associated with organic carbon enrichment in these cores the late devonian new albany shale is represented by the clegg creek camp run morgan trail and the blocher members specifically c s relationships degree of pyritization dop t and c s fe relationships along with redox sensitive trace elements e g v and mo and ratios ni co v cr and v v ni were used to assess redox conditions in addition organic carbon to total phosphorus ratios c org p tot were used to assess levels of paleoproductivity that were possibly enhanced by the productivity anoxia feedback mechanism results suggest variable bottom water conditions existed during accumulation of the new albany shale of west central kentucky including predominantly anoxic conditions for the clegg creek member dysoxic conditions for the camp run and morgan trail members and dysoxic to oxic conditions for the blocher member however throughout deposition all members exhibited some variability in redox conditions thus overall lowest oxygen levels were likely experienced during deposition of the clegg creek followed by the camp run and morgan trail members the blocher member was probably deposited under conditions closer to normal marine yet still dysoxic at most times high c p ratios observed in these members suggest regeneration of p enhanced productivity and sequestration of organic carbon as described by the productivity anoxia feedback paf mechanism during anoxic periods variations in redox indications obtained from different proxies suggest that multiple parameters should be utilized rather than relying on a single proxy reasonably good agreement is seen between c s dop t c s fe and mo levels ni co and v cr tend to agree well with each other but suggest higher oxygen levels than the other proxies values for v v ni tend to be an outlier suggesting more anoxic to euxinic conditions compared to other proxies

provenance and paleoweathering reconstruction of the mesoproterozoic hongshuizhuang formation 1 4 ga northern north china this is the first study presenting major and trace elemental data from the mesoproterozoic hongshuizhuang formation shales in yanshan basin north china in order to reconstruct its provenance and chemical weathering history the shales are strongly depleted in na2o and sr and enriched in y and transition metal elements relative to upper continental crust low zr concentrations and various discriminant plots e g th sc zr sc and al2o3 tio2 zr indicate insignificant mineral sorting or recycling of these shales the rocks show light rare earth element ree enrichment la ybcn 3 99 6 92 flat heavy ree and significantly negative eu anomalies euan 0 57 0 68 in chondrite normalized ree patterns similar to post archean australian average shales the fairly uniform ree patterns and trace element ratios indicate that the hongshuizhuang formation shales were derived from a felsic source area with granodiorite as the dominant contributor mixing calculations suggest a mixture of 30 granite porphyry 5 basalt and 65 granodiorite as the possible source of the shales also supporting that granodiorite was the predominant source intense chemical weathering of the source terrain is indicated by high values of the premetasomatized chemical index of alteration plagioclase index of alteration rb sr a strong positive correlation between tio2 and al2o3 depletion of cao na2o and sr and mineral compositions such strong chemical weathering suggests a warm and wet paleoclimate perhaps due to high atmospheric co2 and ch4 concentrations and a near equatorial location of the north china craton in the columbia supercontinent at 1 4 ga

trace elements as palaeoenvironmental markers in strongly mature hydrocarbon source rocks the cretaceous la luna formation of venezuela abstract the late cretaceous la luna formation is the main hydrocarbon source rock formation in venezuela in the lake maracaibo area the formation shows a steep maturation gradient affecting sedimentary organic matter om and clay minerals related to local burial history and thrusting events the influence of the gradient is examined through geochemical organic and inorganic and mineralogical investigations carried out on samples from five cored boreholes in the maracaibo basin the analytical procedure comprises rock eval pyrolysis vitrinite reflectance measurement palynofacies observation major and trace element content determination performed on bulk rock samples or after a sequential leach protocol dop calculation and the examination and analysis of clay mineral assemblages the maturation gradient seems to have had no effect upon the distribution of the trace elements referred to as proxy indicators for palaeodepositional conditions of om rich sediments ba p v mo ni co cu cd cr and mn consequently trace elements appear to be reliable palaeoenvironmental markers they indicate that during the la luna fm deposition the water column must have had variable conditions with high primary production near the surface and the correlative development of euxinic conditions at the bottom this provides further arguments for an upwelling system affecting the northern platform of south america during late cretaceous time the relative scarcity of reactive iron in the depositional environment must have taken an active part in a process involving sulphur and acting on the environmental conditions as well as on om vulcanisation this process favours aliphatic om storage and may be relevant for many other om rich facies or hydrocarbon source rocks

role of a strong oxygen deficient zone in the preservation and degradation of organic matter a carbon budget for the continental margins of northwest mexico and washington state rates of organic carbon oxidation in marine sediments were determined for the continental margins of northwest mexico and washington state with the goal of assessing the role of oxygen in the preservation of organic matter on a margin with a strong oxygen deficient zone and on a typical western continental margin total carbon oxidation rates including rates for individual electron acceptors o2 no3 and so4 were determined at depths ranging from 100 to 3000 m on both margins carbon oxidation rates were generally higher on the washington margin than on the mexican margin the relative importance of the different electron acceptors varied across the two margins and was related primarily to the availability of o2 and no3 from the overlying water the relative contribution of o2 consumption increased in deeper sediments 2000 m as aerobic processes began to dominate the total carbon oxidation rate denitrification rates were highest in washington sediments however denitrification represented a larger fraction of the total carbon oxidation rate in the mexican sediments 40 for mexico vs 30 for washington sulfate reduction accounted for as much as 79 of the total carbon oxidation rate in shallow sediments and less than 20 in deep sediments on both margins the offshore trends in carbon oxidation rate appeared to be related to the organic carbon input rate pore water o2 and no3 penetration depths were shallowest in nearshore stations and increased offshore regeneration ratios of c n p reveal non redfield behavior on both margins carbon budgets for the two margins demonstrate that off mexico a much greater percentage of the organic matter produced in the surface ocean reached the sediments 15 vs 8 for mexico and washington respectively on the mexican margin 8 of the primary production escaped oxidation in the surface sediments to be permanently buried as compared with only 1 2 of the primary production on the washington margin this suggests that oxygen deficient conditions on mexican margin are linked to enhanced carbon preservation

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

processes controlling the distribution of ti and al in weathering profiles siliciclastic sediments and sedimentary rocks abstract the ratio of ti to al varies greatly in primary igneous source rocks these elements are considered to be relatively immobile in most weathering regimes so that tio2 al2o3 ratios have been used to investigate the provenance of sediments and sedimentary rocks in modern weathering profiles that have undergone moderate weathering ti al ratios remain fairly constant so that siliciclastic sediments derived from them should have ti al ratios like that of the source materials under extreme weathering conditions however the upper most weathered parts of profiles commonly show a marked increase in ti al ratio that is thought to be due to preferential translocation of al rich phases under steady state weathering conditions one particular level of the profile may act as the main source of detrital material and may thus control the ti al ratio of sediments produced from it in a glacio fluvial setting minimum weathering moderate sorting there is considerable variation in ti content but al is nearly constant this is due to concentration of ti bearing mafic minerals such as biotite in the fine fraction in modern sediments derived from moderately weathered and sorted material the ti al distribution reflects mixing of al and ti enriched fine grained materials with sands that are depleted in these elements when a plot of tio2 vs al2o3 is constructed for a suite of such sands and muds the resultant trend differs significantly from that shown by a similar suite of unweathered glacio fluvial sediments comparison of these results with data from sedimentary rock suites suggests that trends shown by plots of tio2 vs al2o3 may provide insight into weathering and depositional history in addition to their use as provenance indicators

hyporheic exchange with heterogeneous streambeds laboratory experiments and modeling 1 hyporheic exchange is generally analyzed with the assumption of a homogeneous hyporheic zone in reality streambed sediments have a heterogeneous structure and this natural heterogeneity produces spatially variable interfacial fluxes and complex hyporheic exchange patterns to assess the basic effects of sediment structure on hyporheic exchange we performed salt and dye injection experiments in a recirculating laboratory flume with two heterogeneous sediment beds characterized by negative exponential correlated random hydraulic conductivity fields dye injections showed that the hyporheic flow structure was controlled by the spatial relationship of bed forms to high and low permeability regions of the streambed as no existing model could represent these effects we developed a new finite element model to calculate the pore water flow field resulting from the interaction of the bed form induced boundary head distribution and the heterogeneous sediment structure a numerical particle tracking approach was then used to assess the resulting hyporheic exchange the combined flow transport model did an excellent job of predicting the complex hyporheic flow pathways in the heterogeneous bed and the net hyporheic exchange up to t 30 hours the heterogeneous hydraulic conductivity field caused both greater spatial variability in the water flux through the bed surface and a greater average interfacial flux than would have occurred with a homogeneous bed the layered correlation structure of the streambed produced an effective anisotropy that favored longitudinal pore water flow and caused a relatively rapid decrease of the mean pore water velocity with depth as a result solute penetration into the bed was confined to a more shallow region than would have occurred with a homogeneous bed the combination of faster near surface transport and shallower solute penetration produced a shorter mean hyporheic residence time on the basis of the combination of experimental results and model simulations we conclude that the structural heterogeneity of streambed sediments produces more spatially limited hyporheic exchange that occurs with greater spatial variability and at a higher overall rate

a multiscale model for integrating hyporheic exchange from ripples to meanders 1 it is necessary to improve our understanding of the exchange of dissolved constituents between surface and subsurface waters in river systems in order to better evaluate the fate of water borne contaminants and nutrients and their effects on water quality and aquatic ecosystems here we present a model that can predict hyporheic exchange at the bed form to reach scale using readily measurable system characteristics the objective of this effort was to compare subsurface flow induced at scales ranging from very small scale bed forms up to much larger planform geomorphic features such as meanders in order to compare exchange consistently over this range of scales we employed a spectral scaling approach as the basis for a generalized analysis of topography induced stream subsurface exchange the spectral model involves a first order approximation for local flow boundary interactions but is fully three dimensional and includes the lateral hyporheic zone in addition to the flow directly beneath the streambed the primary model input parameters are stream velocity and slope sediment permeability and porosity and detailed measurements of the stream channel topography the primary outputs are the distribution of water flux across the stream channel boundary the resulting pore water flow paths and the subsurface residence time distribution we tested the bed form exchange component of the model using a highly detailed two dimensional data set for exchange with ripples and dunes and then applied the model to a three dimensional meandering stream in a laboratory flume having spatially explicit information allowed us to evaluate the contributions of both gravitational and current driven hyporheic flow through various classes of stream channel features including ripples dunes bars and meanders the model simulations indicate that all scales of topography between ripples and meanders have a significant effect on pore water flow fields and residence time distributions furthermore complex interactions across the spectrum of topographic features play an important role in controlling the net interfacial flux and spatial distribution of hyporheic exchange for example shallow exchange induced by current driven interactions with small bed forms dominates the interfacial flux but local pore water flows are modified significantly by larger scale surface groundwater interactions as a result simplified representations of the stream topography do not adequately characterize patterns and rates of hyporheic exchange

interactions between hyporheic flow produced by stream meanders bars and dunes 1 stream channel morphology from grain scale roughness to large meanders drives hyporheic exchange flow in practice it is difficult to model hyporheic flow over the wide spectrum of topographic features typically found in rivers as a result many studies only characterize isolated exchange processes at a single spatial scale in this work we simulated hyporheic flows induced by a range of geomorphic features including meanders bars and dunes in sand bed streams twenty cases were examined with 5 degrees of river meandering each meandering river model was run initially without any small topographic features models were run again after superimposing only bars and then only dunes and then run a final time after including all scales of topographic features this allowed us to investigate the relative importance and interactions between flows induced by different scales of topography we found that dunes typically contributed more to hyporheic exchange than bars and meanders furthermore our simulations show that the volume of water exchanged and the distributions of hyporheic residence times resulting from various scales of topographic features are close to but not linearly additive these findings can potentially be used to develop scaling laws for hyporheic flow that can be widely applied in streams and rivers

benthic phosphorus regeneration net primary production and ocean anoxia a model of the coupled marine biogeochemical cycles of carbon and phosphorus we examine the relationships between ocean ventilation primary production water column anoxia and benthic regeneration of phosphorus using a mass balance model of the coupled marine biogeochemical cycles of carbon c and phosphorus p the elemental cycles are coupled via the redfield c p ratio of marine phytoplankton and the c p ratio of organic matter preserved in marine sediments the model assumes that on geologic timescales net primary production in the oceans is limited by the upwelling of dissolved phosphorus to the photic zone the model incorporates the dependence on bottom water oxygenation of the regeneration of nutrient phosphorus from particulate matter deposited at the water sediment interface evidence from marine and lacustrine settings modern and ancient demonstrates that sedimentary burial of phosphorus associated with organic matter and ferric oxyhydroxides decreases when bottom water anoxia dysoxia expands steady state simulations show that a reduction in the rate of thermohaline circulation or a decrease of the oxygen content of downwelling water masses intensifies water column anoxia dysoxia and at the same time increases surface water productivity the first effect reflects the declining supply of oxygen to the deeper parts of the ocean the second effect is caused by the enhanced benthic regeneration of phosphorus from organic matter and ferric oxyhydroxides sedimentary burial of organic carbon and authigenic calcium phosphate mineral francolite on the other hand is promoted by reduced ocean ventilation according to the model global scale anoxia dysoxia leads to a more efficient recycling of reactive phosphorus within the ocean system consequently higher rates of primary production and organic carbon burial can be achieved even when the continental supply of reactive phosphorus to the oceans remains unchanged

spatial variation in sediment fluxes redox conditions and productivity in the permian triassic panthalassic ocean abstract two permian triassic boundary sections in central japan provide a rare window into environmental conditions within the panthalassic ocean which encompassed more than half the earth s surface at 252 ma integration of petrographic geochemical and time series data provides new insights regarding the fluxes of major and trace components to the sediment as well as environmental conditions in both the deep and intermediate water masses at each study site the ubara section was located in a high productivity peri equatorial location whereas the gujo hachiman section was located in a moderate productivity location at some distance from the paleoequator an upward transition from gray organic poor cherts to black siliceous mudstones at both sites occurred in conjunction with increased primary productivity intensified euxinia within the oxygen minimum zone omz and decimation of the radiolarian zooplankton community euxinia in the omz of the equatorial panthalassic ocean developed episodically for a 200 250 kyr interval during the late permian followed by an abrupt intensification and lateral expansion of the omz around the permian triassic boundary throughout the study interval bottom waters at both sites remained mostly suboxic a finding that counters hypotheses of development of a superanoxic permo triassic deep ocean as a consequence of stagnation of oceanic overturning circulation

influence of water column anoxia on the burial and preservation of carbon and phosphorus in marine shales abstract organic p and organic c concentrations were measured in several well characterized phanerozoic marine shale sequences with the primary focus being the camp run member of the devonian mississippian new albany shale sequences were selected with close spatial association of bioturbated and laminated sediments which reflect deposition from oxic and anoxic waters respectively average organic c p mole ratios calculated from the data are 150 for bioturbated shales and 3900 for the laminated shales of the new albany differences in the extent and mechanisms of early diagenesis related to the oxygenation of waters at the sediment water interface can account for the c p ratios of buried organic matter low c p ratios of bioturbated sediments are attributed to 1 1 the increased ability of bacteria to store p in well oxygenated environments which leads to the production of low c p ratio bacterial biomass and 2 2 the extensive oxidation of sedimentary organic matter resulting in the formation of residual organic phases with low c p ratios high organic c p ratios of laminated sediments are explained by a combination of 1 1 the limited ability of bacteria to store p under anoxic conditions 2 2 extensive p regeneration from sedimentary organic matter 3 3 enhanced c preservation relative to the bioturbated shales it is also shown that relative to organic c laminated shales are not as effective a p sink as are bioturbated shales this provides a mechanism in anoxic environments for burying large quantities of organic matter without simultaneously sequestering the p needed to sustain further productivity

chemical transport to the seafloor of the equatorial pacific ocean across a latitudinal transect at 135 w tracking sedimentary major trace and rare earth element fluxes at the equator and the intertropical convergence zone we have analyzed the major trace and rare earth element composition of surface sediments collected from a transect across the equator at 135 w longitude in the pacific ocean comparing the behavior of this suite of elements to the caco3 opal and corg fluxes which record sharp maxima at the equator previously documented at the same sampling stations enables us to assess the relative significance of the various pathways by which trace elements are transported to the equatorial pacific seafloor the 1 1 high biogenic source at the equator associated with equatorial divergence of surface water and upwelling of nutrient rich water and 2 2 high aluminosilicate flux at 4 n associated with increased terrigenous input from elevated rainfall at the intertropical convergence zone itcz of the tradewinds are the two most important fluxes with which elemental transport is affiliated the biogenic flux at the equator transports ca and sr structurally bound to carbonate tests and mn primarily as an adsorbed component trace elements such as cr as pb and the rees are also influenced by the biogenic flux at the equator although this affiliation is not regionally dominant normative calculations suggest that extremely large fluxes of ba and p at the equator are carried by only small proportions of barite and apatite phases the high terrigenous flux at the itcz has a profound effect on chemical transport to the seafloor with elemental fluxes increasing tremendously and in parallel with ti normative calculations however indicate that these fluxes are far in excess of what can be supplied by lattice bound terrigenous phases the accumulation of ba is greater than is affiliated with biogenic transport at the equator while the p flux at the itcz is only 10 less than at the equator this challenges the common view that ba and p are essentially exclusively associated with biogenic fluxes many other elements including mn pb as and rees also record greater accumulation beneath the itcz than at the equator thus adsorptive scavenging by terrigenous paniculate matter or phases intimately associated with them appears to be an extremely important process regulating elemental transport to the equatorial pacific seafloor these findings emphasize the role of vertical transport to the sediment and provide additional constraints on the paleochemical use of trace elements to track biogenic and terrigenous fluxes

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

geochemical characteristics redox conditions and organic matter accumulation of marine oil shale from the changliang mountain area northern tibet china abstract the organic rich changliang mountain oil shale located in the north qiangtang depression northern tibet is considered to be excellent mineral resource in china the changliang mountain oil shale reported here was deposited in a tidal flat lagoon environment and is characterized by black thin layered oil shales intercalated with dark gray marls here we present geochemical data from the changliang mountain oil shale profile in order to investigate the mechanism of organic matter om accumulation and to establish the formation model for the marine oil shale deposition total organic carbon toc values range from 2 96 to 23 47 in the oil shale samples while the marl samples contains low toc contents ranging from 0 06 to 0 21 in the organic rich oil shale sediments many redox indicators including mo al ratios v cr ratios th u ratios ni co ratios and the relationship of mo to toc suggest a deposition under dysoxic to anoxic environments subsequently the bottom water evolved into an oxic water body when the organic poor marls were deposited however the negative and or weak relationship between toc and productivity indices p ti and ba al indicates that om accumulation was not controlled mainly by primary productivity but dysoxic anoxic bottom water environment a stratified water column may be initiated by the supply of fresh water from the continent nearby combining with warm and humid climate which is beneficial to the reproduction of marine organisms the death and bury of these organisms could lead to the formation of dysoxic anoxic bottom waters and enhance the preservation of om in this study a preservation model of the changliang mountain oil shale was established the model implies that excellent preservation is the major controlling factor for om enrichment in the oil shale layer in addition factors such as mixed deposition with clay minerals and detrital matter input cannot be ignored for their influence on om enrichment