soil mineralogy trends in california landscapes california s diverse environmental gradients serve as natural experiments for examining controls on soil mineral distribution in landscapes in this paper we use example soilscapes from throughout california to examine how lithology climate topography and duration of pedogenesis interact to produce distinctive weathering environments and characteristic suites of soil minerals seven soil geomorphic sequences were assembled from the literature to illustrate major soil mineralogical trends 1 granitic terrain of the peninsular ranges 2 granitic terrain of the central sierra nevada 3 andesitic terrain of the northern sierra nevada 4 fluvial terraces on the east side of the great valley 5 marine terraces of the central coast 6 ultramafic terrain of the klamath mountains and 7 an alluvial fan in the mojave desert results of this analysis show that kaolin is present in virtually all pedons irrespective of climate parent material age or topographic position kaolin does not form in ultramafic soils due to insufficient aluminum many secondary clay minerals reflect the state s strong climatic influence with palygorskite smectite and vermiculite in the dry hot environments hydroxy interlayered minerals gibbsite and short range ordered minerals in the cool moist environments in arid and semi arid regions the distribution of calcite gypsum and soluble salts is strongly related to patterns of eolian dust deposition and water infiltration and leaching

geochemistry of vanadium in an epigenetic sandstone hosted vanadium uranium deposit henry basin utah the epigenetic tony m vanadium uranium orebody in south central utah is hosted in fluvial sandstones of the morrison formation upper jurassic although the deposit is mined for uranium vanadium has a higher average abundance in the ore thus the geochemistry of vanadium in the orebody was studied to characterize ore forming processes within the inferred ground water flow regime measurements of the relative amounts of v super 3 and v super 4 in ore minerals show that v super 3 is more abundant thermodynamic calculations show that vanadium was more likely transported to the site of mineralization as v super 4 the ore formed as v super 4 was reduced by hydrogen sulfide followed by hydrolysis and precipitation of v super 3 in oxide minerals e g montroseitc or paramontroseite or chlorite uranium was transported as uranyl ion u super 6 or some complex thereof and reduced by hydrogen sulfide forming coffinite detrital organic matter in the rocks served as the carbon source for sulfate reducing bacteria it was this bacteriogenic h 2 s that reduced the metals in the mineralization process possible sources for the v and u in this deposit have been identified previously vanadium most likely was derived from the dissolution of iron titanium oxides which liberated fe as well as v a zone of titanium rich remnants is observed updip and up the hydrologic gradient from the deposit m goldhaber and r l reynolds unpub data uranium probably was derived from the overlying brushy basin member of the morrison formation northrop 1982 a preliminary age date for the deposit of 115 ma k ludwig 1986 pers commun indicates that the ore formed after deposition of the brushy basin member previous studies have shown that the ore formed at the density stratified interface between a basinal brine and dilute meteoric water the mineralization processes described above occurred within the mixing zone between these two fluids stable isotope analyses of ore stage dolomite show a progressively heavier carbon and oxygen isotope signature with increasing depth through an ore horizon consistent with the two solution interface model

authigenic uranium relationship to oxygen penetration depth and organic carbon rain we have measured u in benthic incubation chambers sediment pore waters and in sediments along the california continental margin sedimentary u uptake rates based on a combination of sediment pore water profiles and benthic incubation chambers generally agree with those predicted from sediment accumulation rate data this agreement supports the view that most of the continental margin sedimentary u is delivered by diffusion across the seawater sediment boundary the average rate of authigenic u accumulation for all the sites examined here is 0 2 nmol cm 2 y 1 which is consistent with published global estimates of sedimentary u uptake in addition the accumulation rate of u in sediments exhibits a nonlinear relationship with the oxygen penetration depth and a linear relationship with the organic carbon rain rate these relationships highlight the potential utility for the u accumulation rate as a proxy for these processes

distribution and properties of soft weathered bedrock at 1 m depth in the contiguous united states the weathered bedrock zone is increasingly recognized as an important part of ecological and hydrologic systems but its distribution is poorly known in the contiguous united states we used spatial and laboratory characterization data from the us department of agriculture usda natural resources conservation service to assess the distribution and soil like properties of soft weathered bedrock saprock and saprolite within the 48 contiguous united states because usda soil inventories generally do not extend below 2 m and because the upper 1 m is clearly involved in ecosystem function and vadose zone hydrology we restricted our inquiry to soft weathered bedrock within 1 m of the land surface soft weathered bedrock within 1 m of the land surface is widespread throughout the contiguous united states underlying at least 6 of the land area in depth analysis of three states showed that soft weathered bedrock at the 1 m depth underlies 22 of the total land area in california 33 in wyoming and 18 in north carolina soft weathered bedrock hosts pedogenic activity as indicated by morphological features such as roots clay films and iron fe manganese mn oxide concretions recorded in pedon descriptions in the database the physical and chemical properties of soft weathered bedrock are often similar to those of the overlying soil suggesting that in many respects soft weathered bedrock behaves like soil it supplies water and nutrients to plants whose roots penetrate into it and it modulates throughflow runoff to streams for a more complete understanding of soft weathered bedrock systematic data are needed on its thickness across landscapes and a consistent terminology for its various forms needs to be adopted and widely used copyright 2012 john wiley sons ltd

mineralogy early marine diagenesis and the chemistry of shallow water carbonate sediments abstract shallow water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of earth s chemical and climatic history one of the main limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post depositional diagenetic alteration in this study we use paired measurements of calcium 44ca 40ca or 44ca and magnesium 26mg 24mg or 26mg isotope ratios in sedimentary carbonates and associated pore fluids as a tool to understand the mineralogical and diagenetic history of neogene shallow water carbonate sediments from the bahamas and southwest australia we find that the ca and mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis the observed variability in bulk sediment ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid fluid buffered to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment sediment buffered our results indicate that this process together with variations in carbonate mineralogy aragonite calcite and dolomite plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers 13c 18o major minor and trace elements in shallow water carbonate sediments in the geologic record our results also provide evidence that a large shallow water carbonate sink that is enriched in 44ca can explain the mismatch between the 44 40ca value of rivers and deep sea carbonate sediments and call into question the hypothesis that the 44 40ca value of seawater depends on the mineralogy of primary carbonate precipitations e g aragonite seas and calcite seas finally our results for sedimentary dolomites suggest that paired measurements of ca and mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo environmental information preserved in these enigmatic but widespread carbonate minerals

effect of dolomitization on isotopic records from neoproterozoic carbonates in southwestern mongolia abstract carbon isotope values from shallow marine carbonate rocks including those from many dolomitized successions are the primary lens through which we interpret the ancient carbon cycle carbon isotopes are typically regarded as being robust to alteration during dolomitization due to the high carbon content of the rock compared to the fluid however chemostratigraphic studies of the neoproterozoic tsagaan olom group in southwestern mongolia exhibit 3 12 differences in carbon isotopes between stratigraphically equivalent limestone and dolomitized successions to understand the origins of this geochemical variation we conducted detailed geological mapping petrographic isotopic 13c 18o 44 40ca and 26mg and fluid inclusion analyses of carbonates in the taishir ol and shuurgat formations of the tsagaan olom group stratigraphic and textural constraints distinguish fabric retentive early dolomitization dolomitization event 1 that occurred in the taishir and ol formations during and soon after deposition of the ca 635 ma marinoan cap dolomite of the ol formation and fabric destructive dolomitization that occurred after the deposition of the younger shuurgat formation dolomitization event 2 either prior to or during early cambrian foreland basin formation the dolomitizing fluids moved through porous stratigraphic units bound by impermeable shale of the khongor and zuun arts formations dolomitization homogenized the isotopic records of all neoproterozoic tsagaan olom group dolomites undolomitized successions show more extreme negative excursions from more positive background values the salinity and isotopic values of seawater the dolomitizing fluids and the original platform carbonate were estimated from fluid inclusion data and a numerical model of diagenetic dolomitization these results demonstrate that both early and late dolomitization can have a profound effect on carbon isotopic records of carbonates however with a multi isotope approach the original carbon isotopic composition of platform top carbonate can be distinguished from that of seawater and other dolomitizing fluids

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

weathering rock to regolith the amount of pore space in most unweathered granite is too small to support a plant based ecosystem but porosity grows as intact rock interacts with surface waters beneath the soil

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

arctic ocean mn stratigraphy genesis synthesis and inter basin correlation abstract across the arctic ocean late quaternary deep marine sediments are characterized by the occurrence of brownish layers intercalated with yellowish to olive gray sediments these layers show enhanced levels of bioturbation peaks in mn content and typically contain elevated abundances of planktonic and benthic micro and nannofossils it was early surmised that these layers were deposited under interglacial conditions and that their cyclical downcore occurrence could be correlated to the global benthic oxygen isotope curve however the synchronicity of mn layers with interglacial conditions and the underlying mechanisms responsible for their formation remain controversial here we compile and synthesize findings of the last decades with several recent studies that shed light on issues such as the sources of mn to the arctic ocean the processes and pathways for mn to the deep sea the chemical processes active in the sediment and the spatial and temporal distribution of mn rich layers in arctic deep marine sediments budget calculations show that about 90 of mn input to the arctic ocean originates from arctic rivers or coastal erosion two sources effectively shut down during mid to late quaternary glacial intervals by continental ice sheets blocking or re directing the rivers and vast subaerial exposure of the shelf areas thus the strong late quaternary interglacial glacial cyclicity in mn content is clearly an input related signal and only secondarily influenced by chemical processes in the water column and in the sediment on the shelves the mn undergoes repeated geochemical recycling caused by the high organic carbon content in the sediments before it is ultimately exported to the deep basins where scavenging processes in the water column effectively bring the mn to the sea floor in the form of mn oxyhydr oxides the close synchronicity with enhanced bioturbation and elevated micro and nannofossil abundances shows that the mn peaks are preserved at a stratigraphic level closely corresponding to the interglacial intervals however under certain biogeochemical conditions mn oxyhydr oxides may diagenetically become both dissolved and re precipitated deep in the sediments as shown by pore water analyses and x ray radiograph studies dissolution is particularly conspicuous in late quaternary sediments from the lomonosov ridge where in rapidly deposited coarse grained intervals diamictons with elevated total organic carbon toc contents mn appears almost completely removed from within the glacial sediments and also the surrounding interglacial sediments correspondingly bundles of closely spaced mm thick mn rich horizontal bands are observed in sediment otherwise devoid of indicators for interglacial conditions suggesting that these bands were purely formed by diagenetic processes redistributing the mn from deeper sediment layers this type of diagenetic mn redistribution within the sediment can be recognized in xrf core scanner data combined with sedimentological information from x ray radiographs while pore water data are highly promising if clear diagenetic features in the sediment are missing with this increasing ability to recognize intervals where a diagenetic overprint exists in the mn record the recently improved understanding of the mn cycle in the arctic ocean provides a conceptual paleoenvironmental framework in which carefully applied mn stratigraphy can provide a powerful correlation tool when combined with other paleoceanographic proxies and sedimentological data

cadmium diagenesis in laurentian trough sediments the depth distributions of cd mn and fe in pore water and sediment were determined on three replicate box cores collected at a 325 m deep station in the laurentian trough the results reveal a surface layer in which the content of solid phase cd first decreases but then increases sharply with depth in contrast mn decreases regularly over the same depth interval in the oxygenated zone of this layer cd probably associated with organic matter is released to the pore water resulting in concentrations that are more than an order of magnitude higher than in the overlying water column some of the dissolved cd is returned to the water column and some migrates downward and is precipitated at depth this part of the cd cycle is virtually complete within the surface layer the base of which corresponds to the base of the zone of mn enrichment in the subsurface layer solid phase cd and mn show little or no concentration change however dissolved cd which reaches often non detectable concentrations 0 05 nm in this layer increases once again deep within the anaerobic zone and attains concentrations even higher than in the surface layer the presence of dissolved cd complexes revealed by 1 5 to 8 fold increases in electrochemically active cd in pore water following uv treatment as well as inconsistent distributions of dissolved and solid phase cd indicate complexities in diagenesis that merit further investigation

metal accumulation rates in northwest atlantic pelagic sediments measurements of 230th 87sr86sr and twenty four metals were made on cores from the nares abyssal plain the sediment is characterized by slowly accumulating 0 3 0 7 g cm2 103 yr pelagic red clays and rapidly deposited grey clays transported by turbidity currents despite their colour differences and the enrichment of mn fe cu co ni zn v and to a lesser degree the rare earths in the red clays sr isotope evidence demonstrates that the clays have the same terrigenous origin the excesses of metals in the red clays have been attributed to metal removal from the water column and a comparison with the grey clays has enabled the authigenic fluxes of metals to be estimated the fluxes obtained are in the ranges 20 50 mol cm2 103 yr for mn and fe 0 1 0 4 mol cm2 103 yr for cu co ni zn v sr and ce 10 20 nmol cm2 103 yr for la and nd and 0 5 3 nmol cm2 103 yr for sm eu gd dy er and yb authigenic fluxes of y nb cr zr rb u and th were not resolvable fluxes appear to be near constant on the plain but comparison with other areas shows that they are quite variable both between and within ocean basins the chief factor controlling authigenic fluxes is the geochemical abundances of the elements but fractionation within both the transition element and rare earth series can be recognized from inter element comparisons and from differences in fluxes between atlantic and pacific red clays corresponding to the oceanic reactivities of the elements

molybdenum and uranium geochemistry in continental margin sediments paleoproxy potential abstract we measured solid phase mo and u concentrations in marine sediments from the california mexico peru and chile margins to ascertain the behavior of mo and u during early diagenesis in continental margin settings at sites along the california mexico and peru margins where there are estimates of mass accumulation rates authigenic u accumulation rates range from 0 50 nmol m 2 day 1 at the california and mexico margin sites mo accumulation rates range from 0 to 134 nmol m 2 day 1 whereas at the peru margin site rates may be as high as 550 nmol m 2 day 1 we observe relationships between metal accumulation rates and the delivery and burial rates of organic carbon corg in the case of mo there appears to be at least two relationships between metal accumulation rate and organic carbon burial for most of the data presented in this manuscript continental margin sediments have a mo corg accumulation rate ratio of 20 mol mol 1 this value is significantly lower however than those reported for anoxic basins 100 mol mol 1 but is consistent with reported mo corg rain ratios from mexico margin sediment traps in contrast to mo there appears to be a single u corg burial ratio of 5 mol mol 1 which includes a range of environments from anoxic basins and open ocean sites we interpret the relationships between metal accumulation and organic carbon to indicate that the reactions that govern authigenic metal accumulation are primarily sensitive to the delivery and burial of organic carbon in these particular settings however we note that any relationship between metal accumulation and organic carbon could be indirect in the particular case of mo based on what is known about mo geochemistry from the literature it is possible that mo authigenesis is coupled to sulfur cycling in many of the environments covered by this study and that the observed association between mo and organic carbon burial is a consequence of the coupling between carbon and sulfur burial using the observed relationships between mo and corg burial as well as constraints from the mo isotope budget we estimate that continental margin sediments are an important sink for mo the magnitude of this sink 0 4 108 mol y 1 or larger may be as much as one quarter of the oceanic removal term and is likely to be larger than the modern anoxic basin sink

the geometry and petrogenesis of hydrothermal dolomites at navan ireland the dolomites at navan ireland formed in courceyan peritidal and shallow shelf limestones the dolomite body has a plume like geometry cross cutting both lithological boundaries and diagenetic barriers generated by sea floor cementation and emergence the dolomitizing fluids rose parallel to major faults to diffuse laterally through the succession controlled by variations in permeability that reflect both facies variation on deposition and pre dolomitization diagenesis cathodoluminescent zones reveal three principal stages of dolomite emplacement separated by dissolution surfaces with each stage reflecting several changes in the character of dolomitizing solutions the predominance of dull zones indicates burial rather than surface conditions the dolomites formed some time after burial in response to an areally limited hydrothermally driven flow isotope values 18o of 6 6 to 10 4 and 13c of 0 2 to 2 5 pdb and fluid inclusion data suggest that these fluids had compositions similar to those of carboniferous seawater however these became hotter with time with temperature increasing from 60 to 160 c the navan dolomites are closely associated with europe s largest zinc lead deposit the distribution of the ores follows the same trend as that of the dolomites and paragenetic relationships indicate that dolomitization and mineralization were temporally and genetically related

peralkaline granitoid magmatism in the mongolian transbaikalian belt evolution petrogenesis and tectonic significance article i nfo the central asian orogenic belt caob is well known for its massive generation of juvenile crust in the phanerozoic in eastern caob voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanics were emplaced in three stages from early permian to late mesozoic 295 270 ma 230 190 ma and 150 120 ma they occur as huge granitoid belts in extensional tectonic settings and form a complex network of about 12 million km 2 in area among them the 2500 km long mongolian transbaikalian belt mtb is the most spectacular and it comprises more than 350 granite syenite plutons and stocks with numerous co genetic volcanic fields the three stages of granitoids have similar chemical compositions but show temporal variation in nd isotopic composition initial end t values range from 1t o 5 for the early permian 0 to 4 for the early mesozoic and 2t o 3 5 for the late mesozoic granitoids the negative end t values observed in the mtb are not typical of the caob granitoids which are generally characterized by positive values however several pieces of evidence suggest that the mtb peralkaline and alkali feldspar granitoids were produced from enriched mantle derived sources the evidence includes 1 felsic and mafic rocks formed in the same stage have similar initial nd sr isotopic ratios and sm nd model ages tdm 2 the granitoid belts extend over thousands of kilometers and intersect distinct crustal provinces but no correlation is found in chemical compositions between the granitoids and country rocks 3 the abundant syenites are considered to be cogenetic or in some cases parental to the granites experimental and isotope data argue for the derivation of syenites from an enriched mantle source thus the granites and comendites are regarded as mantle derived 4 a study of melt inclusions in quartz phenocrysts of comendite indicates a high liquidus temperature of 1000 1100 c for the magma generation this suggests that the silicic magma was generated in an unusually high temperature condition which is likely produced by basaltic magma that underplated the lower crust the generation of voluminous peralkaline and alkaline alkali feldspar granitoids and genetically related bimodal volcanic rocks represents an important addition of juvenile crustal mass to the earth s continental crust during a time span of about 150 ma from late paleozoic to late mesozoic

early diagenesis and accumulation of redox sensitive elements in east siberian arctic shelves abstract the arctic shelf makes up half of the area within the arctic ocean it plays an important role in the global carbon cycle whilst its part in the recycling process of redox sensitive elements rses is still not clear this study has selected nine sediment cores 30 to 40 cm in length covering a wide area over the east siberian arctic shelves esas and analyzed a suite of rses s mn mo u v cd in the sediments along with al fe total organic carbon toc grain size and sedimentation rate the redox environment in surface sediments was clearly divided based on the s and mn contents of the cores ranging from being more oxidized on the western east siberian sea shelf to more reduced on the chukchi sea shelf toc also showed an increasing trend eastward in the study region statistically significant correlations were found between cd and s v and fe mo and mn and u and toc implying their close relationships during early diagenetic processes at the sediment water interface across the study area authigenic accumulation occurred for all rses except mn the estimated authigenic accumulation fluxes for mo u v and cd over the entire esas are 0 21 0 09 0 086 0 043 11 0 9 2 and 0 019 0 014 108 mol y 1 respectively which are comparable to values reported in suboxic marginal sediments for mo u and cd but exceptionally high for v although the sampling resolution was coarse and there are uncertainties in the sedimentation rates and detrital background values of v we propose the authigenic accumulation flux for v on the broad and shallow esas may be a significant but missing sink term for the global v cycle

the summer hydrography and surface circulation of the east siberian shelf sea during the ice free summer season in 1995 the authors deployed and subsequently tracked 39 surface drifters to test the hypothesis that the discharge from the kolyma river forces a buoyancy driven coastal current from the east siberian sea toward bering strait the observed mean flow is statistically significant at the 95 level of confidence but its direction contradicts their initial hypothesis instead of a coastally trapped eastward flow the authors find a laterally sheared westward flow with maximum velocities offshore that correlate only weakly with the local winds at a daily wind dominated timescale the drifter data reveal spatially coherent flows of up to 0 5 m s21 the lagrangian autocorrelation scale is about 3 days and the lagrangian eddy length scale reaches 40 km this spatial scale exceeds the nearshore internal deformation radius by a factor of 3 however it more closely corresponds to the internal deformation radius associated with the offshore ice edge bulk estimates of the horizontal mixing coefficient resemble typical values of isotropic open ocean dispersion at midlatitudes hydrographic observations and oxygen isotope ratios of seawater indicate a low proportion of riverine freshwater relative to sea ice melt in most areas of the east siberian sea except close to the kolyma delta the observations require a reevaluation of the conceptual view of the summer surface circulation of the east siberian sea eastward buoyancy driven coastal currents do not always form on this shelf despite large river discharge instead ice melt waters of a retreating ice edge act as a line source of buoyancy that in 1995 forced a westward surface flow in the east siberian sea

stratigraphic and tectonic implications of a newly discovered glacial diamictite cap carbonate couplet in southwestern mongolia we report here the discovery of a new end cryogenian glacial diamictite and an overlying basal ediacaran cap carbonate within the tsagaan oloom formation of southwestern mongolia the identifi cation of the cryogenian ediacaran boundary coupled with new 13 c chemostratigraphic profi les facilitates the integration of the neoproterozoic stratigraphy of mongolia with records elsewhere these correlations indicate that a previously unrecognized 16 cryogenian 13 c anomaly is present in the newly defi ned tayshir member informal of the tsagaan oloom formation furthermore chemostratigraphic and lithostratigraphic relationships suggest an 35 m y depositional hiatus below the phosphorite bearing zunne arts member informal of the upper tsagaan oloom formation and that subsidence renewed in the latest ediacaran early cambrian we propose that the lower 1500 m of the tsagaan oloom formation was deposited on a thermally subsiding passive margin after rodiniaage rifting whereas the zunne arts member and the overlying 1600 m of early cambrian strata were deposited in a foredeep basin that formed as the southern margin of the dzabkhan terrane was subducted beneath the khantayshir dariv arc

weathering of rock to regolith the activity of deep roots in bedrock fractures abstract many areas in the world are characterized by shallow soils underlain by weathered bedrock but root rock interactions and their implications for regolith weathering are poorly understood to test the role of tree roots in weathering bedrock we excavated four pits along a catena in a shale dominated catchment at the susquehanna shale hills critical zone observatory sshczo in central pennsylvania we measured a variety of biological physical and chemical properties including 1 root density distribution and respiration 2 soil gas and 3 elemental compositions mineralogy and morphology of soil rock and rock fracture fill at ridge top mid slope toe slope and valley floor sites as expected root density declined rapidly with depth nevertheless fine roots were present in rock fractures even in the deepest least weathered shale sampled 180 cm below the land surface root densities in shale fractures were comparable between the ridge top and mid slope pits however they were significantly lower in the toe slope despite increasing rock fracture densities which is likely due to a shallower water table depth at the downslope site average root respiration per mass of dry root tissue in rock fractures was comparable to rates in the soil thus the total flux of co2 from root respiration tracked root densities decreasing with depth potential microbial respiration estimated as the laboratory c mineralization potential was about an order of magnitude lower than measured root respiration in both the soil and shale fractures roots were only observed in large aperture 50 m shale fractures that were filled with particulate material the fill in these fractures was mineralogically and geochemically similar to the lowest soil horizons with respect to clay composition element mobility extractable dissolved organic c doc inorganic n species and potentially mineralizable c and n while total c and total n values for the fracture fill were similar to the shale bedrock in the bulk soil depletion profiles al fe k mg and si relative to unweathered shale reflected characteristic weathering of illite and vermiculized chlorite to kaolinite and are similar between soils and fracture fill such similarities indicate that the fracture coatings are likely the result of pedogenic processes that occur at depth in the fractures rather than translocation of soil particles downward into the fractures overall our data suggest that roots and fill in shale fractures down to 180 cm are qualitatively similar to those in surface soil horizons thus the deepest manifestation of the chemical depletion profiles observed in the pits consists of the rock fracture fill and this fill is present at low concentrations with similarly low concentrations of fine roots

trace metals and organic carbon in sediments of the northeastern chukchi sea abstract concentrations of al fe and selected trace metals as ba be cd cr cu hg mn ni pb sb se sn v zn in surface sediments from the northeastern chukchi sea necs varied considerably as a function of sediment texture i e grain size however essentially all metals when normalized to al were present at natural background values total organic carbon content ranged from 0 06 1 56 with a marine origin for at least two thirds of the organic matter at each station based on 13c values and c n ratios recent sedimentation rates from 137cs and 210pb dating were 0 03 0 14 cm yr 1 corresponding vertical distributions for most metals in age dated sediment cores showed 100 yr records of uniform metal al ratios including pb and hg concentrations of as mn and cd were modified in surface sediments at a few stations by early chemical diagenesis surveys around two exploratory oil and gas drilling sites that were occupied in 1989 showed that ba concentrations were as high as 10 000 g g 1 within 200 m of one drilling site relative to background values of 700 g g 1 barium enrichment was from barite a drilling mud additive that was discharged to the seafloor above background concentrations of cu hg pb and zn also were found in sediments from 3 4 stations within 200 m of the two drilling sites at present sediments in the necs are essentially pristine with respect to trace metals of anthropogenic origin excluding small areas around drilling sites these data should be of value for detecting and tracking future chemical changes in the sediments of the necs particularly in light of planned oil and gas exploration and production as well as environmental changes that may be associated with climate change

chemostratigraphy indicates a relatively complete late permian to early triassic sequence in the western united states although the latest permian mass extinction and associated 13 c excursion are well documented from the tethys ocean carbonate rocks preserving these events in the eastern panthalassic ocean western pangea are unknown we present 13 c carb from the gerster and thaynes permian and triassic formations in the western united states and document a negative excursion with no evidence for major breaks in continuity to further constrain the age of the 13 c carb excursion in the absence of index fossils we analyzed the same samples for 87 sr 86 sr when examining our new carbon and sr data in the context of biostratigraphy and sequence stratigraphy we conclude that parts of the western united states may preserve carbonate successions that span the latest permian extinction

concentration vertical flux and remineralization of particulate uranium in seawater abstract concentrations and fluxes of particulate u were measured throughout the water column at several locations in the atlantic and pacific oceans with in situ filtration systems and sediment traps the results indicate that dissolved u is fixed to particles in surface seawater organic matter appears to be the carrier phase formation of particulate authigenic u below the surface waters could not be detected authigenic u is remineralized within the bathypelagic layers at the open ocean sites studied in the panama basin an upwelling area with high biological productivity remineralization of authigenic u in the deep water column was not observed the rate of remineralization of authigenic u in the deep sea is insufficient to produce a measurable concentration gradient between surface and deep waters within the mixing time of the oceans formation of authigenic u in the water column in areas such as the panama basin is not a significant sink for u on an ocean wide basis

contributions of water supply from the weathered bedrock zone to forest soil quality one measure of forest soil quality is the ability of the soil to support tree growth in mediterranean type ecosystems such as most of california s forests there is virtually no rainfall during the summer growing season so trees must rely on water stored within the substrate water is the primary limitation to productivity in these forests many forest soils in california are relatively thin but are underlain by thick zones of weathered bedrock weathered granitic bedrock the most prevalent lithology has available water capacities 0 12 cm water cm rock that approach those of soils 0 2 cm water cm soil and because the weathered rock zone is usually so much thicker several meters than the soil 1 m it almost always constitutes the larger storage reservoir for plant available water the weathered bedrock retains the original rock fabric and is friable and easily excavated but the primary minerals are not thoroughly altered to clay minerals so it is not considered saprolite roots of ponderosa pine pinus ponderosa seedlings penetrate through the soil and encounter weathered bedrock within the first 2 years on many sites thus the influence of the weathered bedrock zone on plant growth begins early root access to the weathered bedrock is restricted to fractures which are often spaced about 50 cm apart water is extracted from the intervening rock matrix through unsaturated flow toward the root mat in the fractures and by mycorrhizal fungal hyphae that penetrate the rock matrix at one site in the sierra nevada 30 year old jeffrey pine p jeffreyi depleted the soil held water by mid june and relied on water stored in the weathered bedrock until the rainy season began in october in this case the weathered bedrock supplied at least 70 of the water used by the trees during the growing season in the same area we found that thin soils are not a detriment to pine productivity when they are underlain by a thick zone of weathered bedrock in mediterranean type ecosystems the weathered bedrock zone is an essential component of the plant water supply system and is thus an important contributor to forest soil quality

persistence of a freshwater surface ocean after a snowball earth geochemical data from cap carbonates deposited above cryogenian glacial deposits have been widely used to infer the conditions that prevailed in the aftermath of snowball earth however the time scale over which these carbonates were deposited and the degree to which they record the chemistry of a globally well mixed ocean have remained poorly constrained during deglaciation a large volume of meltwater entered the ocean creating two distinct layers the fresh hot and light upper layer and the salty cold and dense lower layer here we estimate the ocean mixing time scale based on energetic constraints we find that the mixing time scale is 10 4 10 5 yr with a best estimate of 5 10 4 yr or up to 100 times longer than that of the modern ocean mixing of the surface temperature anomaly implies a delayed sea level rise of 40 50 m associated with pure thermal expansion this result reconciles geological geochemical and paleomagnetic data from basal ediacaran cap carbonates with physical oceanographic theory in particular our model suggests that 1 the cap dolostones formed predominantly in a freshwater environment 2 the waters in which the dolostones formed were not well mixed with saline deep water allowing for large geochemical differences between the cap dolostones and the deep ocean and 3 the cap carbonate sequences formed in a two phase transgression that lasted 10 4 yr which is consistent with both local sea level records and the preservation of magnetic excursions and reversals

field hydrological monitoring of a sloping shallow pyroclastic deposit many mountainous areas in campania southern italy are characterized by steep slopes covered by unsaturated volcanic deposits shallow landslides are frequently triggered by intense and persistent

a major perturbation of the carbon cycle before the ghaub glaciation neoproterozoic in namibia prelude to snowball earth 1 a large 11 15 negative shift in 13c is observed in shallow water carbonates directly beneath neoproterozoic glacial deposits or correlative disconformity in northwest namibia ascribed to a snowball earth reproducibility and stratigraphic concordance of this anomaly in 16 sections across the ancient continental shelf support a primary origin and field relations show it predates the fall in sea level associated with the ghaub glaciation we crudely estimate the duration of the isotopic shift as 0 6 106 years from a simple thermal subsidence model similar or larger 13c anomalies are found directly beneath neoproterozoic glacial units in australia canada china scotland and svalbard after considering conventional interpretations for negative 13c anomalies we conclude that a prolonged methane release to the atmosphere is most consistent with the timescale magnitude and geological context of the anomaly in namibia counterintuitively an anomalous methane flux that is sustained for 100s kyr may be consistent with a snowball glaciation

depletion of perennial sea ice in the east arctic ocean 1 the extent of perennial sea ice in the east arctic ocean 0 180 e decreased by nearly one half with an abrupt reduction of 0 95 106 km2 while the west arctic ocean 0 180 w had a slight gain of 0 23 106 km2 between 2004 and 2005 as observed by satellite scatterometer data during november december the net decrease in the total perennial ice extent is 0 72 106 km2 about the size of texas perennial ice in the east arctic ocean continued to be depleted with an areal reduction of 70 from october 2005 to april 2006 with the east arctic ocean dominated by seasonal sea ice a strong summer melt may open a vast ice free region with a possible record minimum ice extent largely confined to the west arctic ocean simultaneous scatterometer measurements of sea ice and winds will be crucial for sea ice monitoring and forecasts

preservation of particulate non lithogenic uranium in marine sediments particulate non lithogenic uranium pnu excess u above detrital background levels found in marine particulate matter is formed in surface waters throughout the ocean previous studies have shown that pnu is regenerated completely prior to burial of particles in sediments within well oxygenated open ocean regions however the fate of pnu has never been examined in ocean margin regions or in anoxic basins here we evaluate the preservation of pnu in ocean margin sediments and within semi enclosed basins using samples from sediment traps deployed at multiple depths and surface sediments organic carbon fluxes at the sediment trap locations ranged from 0 1 to 4 3 g cm 2 kyr while the dissolved oxygen concentration in the water column ranged from 3 mt o 270 m preservation of pnu increases with decreasing dissolved oxygen concentration approaching 100 preservation at oxygen concentration 25 m pnu contributes as much as 40 to 70 of the total authigenic u in sediments in the santa barbara basin and seasonally anoxic saanich inlet and some 10 to 50 of the total authigenic u in sediments off the central california margin copyright 2002 elsevier science ltd

ca and mg isotope constraints on the origin of earth s deepest δ13c excursion abstract understanding the extreme carbon isotope excursions found in carbonate rocks of the ediacaran period 635 541 ma where 13 c of marine carbonates 13 c carb reach their minimum 12 for earth history is one of the most vexing problems in precambrian geology known colloquially as the shuram excursion the event has been interpreted by many as a product of a profoundly different ediacaran carbon cycle more recently diagenetic processes have been invoked with the very negative 13 c values of ediacaran carbonates explained via meteoric alteration late stage burial diagenesis or growth of authigenic carbonates in the sediment column thus challenging models which rely upon a dramatically changing redox state of the ediacaran oceans here we present 257 44 40 ca and 131 26 mg measurements along with mg mn and sr data from carbonates of the ediacaran aged wonoka formation fm of south australia to bring new isotope systems to bear on understanding the shuram excursion data from four measured sections spanning the basin reveal stratigraphically coherent trends with variability of 1 5 in 26 mg and 1 2 in 44 40 ca this ca isotope variability dwarfs the 0 2 0 3 change seen coeval with the permian triassic mass extinction the largest recorded in the rock record and is on par with putative changes in the 44 40 ca value of seawater seen over the phanerozoic eon changes in both isotopic systems are too large to explain with changes in the isotopic composition of ca and mg in global seawater given modern budgets and residence times and thus must be products of alternative processes relationships between 44 40 ca and sr and 26 mg and mg are consistent with mineralogical control e g aragonite vs calcite limestone vs dolostone on calcium and magnesium isotope variability the most pristine samples in the wonoka dataset preserving sr concentrations in the 1000s of ppm range and 44 40 ca values inherited from an originally aragonitic polymorph have 13 c carb of 8 to 7 thereby providing strong geochemical evidence that extremely negative 13 c carb values are primary products of the ediacaran surface environment

probing deep weathering in the shale hills critical zone observatory pennsylvania usa the hypothesis of nested chemical reaction fronts in the subsurface weathering is both an acid base and a redox reaction in which rocks are titrated by meteoric carbon dioxide co2 and oxygen o2 in general the depths of these weathering reactions are unknown to determine such depths cuttings of rose hill shale were investigated from one borehole from the ridge and four boreholes from the valley at the susquehanna shale hills observatory ssho pyrite concentrations are insignificant to depths of 23 m under the ridge and 8 9 m under the valley likewise carbonate concentrations are insignificant to 22 and 2 m respectively in addition a 5 6 m thick fractured layer directly beneath the land surface shows evidence for loss of illite chlorite and feldspar under the valley secondary carbonates may have precipited the limited number of boreholes and the tight folding make it impossible to prove that depth variations result from weathering instead of chemical heterogeneity within the parent shale however carbonate depletion coincides with the winter water table observed at 20 m ridge and 2 m depth valley it would be fortuitous if carbonate containing strata are found under ridge and valley only beneath the water table furthermore pyrite and carbonate react quickly and many deep reaction fronts for these minerals are described in the literature we propose that deep transport of o2 initiates weathering at ssho and many other localities because pyrite commonly oxidizes autocatalytically to acidify porewaters and open porosity according to this hypothesis the mineral distributions at ssho are nested reaction fronts that overprint protolith stratigraphy the fronts are hypothesized to lie subparallel to the land surface because o2 diffuses to the water table and causes oxidative dissolution of pyrite pyrite derived sulfuric acid h2so4 plus co2 also dissolve carbonates above the water table to understand how reaction fronts record long term coupling between erosion and weathering will require intensive mapping of the subsurface copyright 2013 john wiley sons ltd

reconstruction of ice conditions in the northern chukchi sea during recent centuries geochemical proxy compared with observed data abstract this paper presents the first results of the quantitative reconstruction of ice conditions in the arctic based on a comparison of the data for periods of meteorological observations with variations in the chemical compositions of the sediments accumulated during the same times the biogenic elements br ca and sr and some redox sensitive as and fe elements are the most informative for the reconstruction of changes in ice conditions with positive correlations and the lithogenic elements k and ti are predominantly negatively correlated the reconstruction results for the last 300 400 years of average annual air temperature anomalies for all cores in general terms coincide with the reconstruction for the northern hemisphere the common features of all reconstructions are low temperatures during the little ice age lia and a rapid warming in the middle of the 19th century and in the last decades of the 20th and first decades of the 21st centuries the results of the reconstruction of the duration of the ice free period generally coincide with the temperature changes for the last two centuries although for lia there is an inverse correlation between the variations in temperature and the duration of the ice free period a possible reason for this may be changes in the structure of the surface currents in the chukchi sea and the northern part of the bering sea because of which the inflow of warm and freshened waters through the bering strait to the arctic increased occasionally

zebra dolomitization as a result of focused fluid flow in the rocky mountains fold and thrust belt canada discordant zebra dolomite bodies occur locally in the middle cambrian cathedral and eldon formations of the main ranges of the canadian rocky mountains fold and thrust belt they are characterized by alternating dark grey a and white b bands forming an abba diagenetic cyclicity these bands developed parallel to both bedding and cleavage dark grey a bands consist of fine 300 m non planar crystalline impure dolomite the white b bands are composed of coarse up to several millimetres milky white pure saddle dolomites b1 which are often covered by pore lining zoned dolomite b2 the b phases often possess a saddle shaped morphology in contrast to the replacement origin of the a dolomite the zoned b2 dolomite rims are interpreted as a cement formed in open cavities the b1 dolomite is interpreted as the result of recrystallization with diagenetic leaching of non carbonate components all the zebra dolomites studied are nearly stoichiometric and are characterized by enriched na and depleted sr concentrations fe and mn concentrations in these dolomites differ depending on the sample locality fluid inclusion data indicate that the dolomites formed from relatively hot th 130 200 c saline 20 23 wt cacl2 eq fluids a diagenetic high temperature origin is also supported by depleted 18o values 20 to 14 vpdb a contribution of 87sr enriched fluids is reflected in the 87sr 86sr values 0 7091 0 7123 zebra dolomite development is explained by focused fluid flow which exploited areas of structural weaknesses e g basin platform rim areas faults etc expulsion of hot basinal brines in a tectonically active regime generated overpressures which explains the development of secondary porosity during zebra dolomitization as well as the intra zebra fracturing at decimetre to micrometre scale

evidence for resetting of fluid inclusion temperatures from quartz cements in oilfields abstract quartz is a major pore occluding cement in north sea oilfield reservoir sandstones fluid inclusions yield homogenization temperatures t h which have been thought to represent growth temperatures for the host quartz however early diagenetic inclusions from the detrital grain overgrowth boundary yield excessively high palaeotemperatures which do not match the growth temperatures calculated from the depth of cementation the temperatures of these inclusions increase with present day depth of burial and approach present day reservoir temperatures this suggests that the inclusions have begun to reset towards present day pressure temperature conditions the t h of the inclusions hence represent burial temperatures rather than growth temperatures for the quartz experimental studies indicate that the amount of resetting undergone by an inclusion varies depending on its size shape and fluid composition a relationship between inclusion t h and these variables has been observed in inclusions from deeply buried quartz cements in the north sea

characterization of siberian arctic coastal sediments implications for terrestrial organic carbon export surface sediments were collected during the 2000 transarctic expedition along the siberian arctic coastline including the ob yenisey khatanga lena and indigirka estuaries sediments were chara

redox sensitive element uptake in north east atlantic ocean sediments benthic boundary layer experiment sites regularly increasing radiocarbon age depth profiles and near constant sediment composition with depth have demonstrated that sediment accumulation has been relatively constant during the late holocene at two north east atlantic sites on rockall bank and feni drift uk benthic boundary layer experiment sites in such a quasi steady state situation the geochemical responses to early diagenesis of the redox sensitive elements cd mn mo re se and u are readily discerned through changes in element concentrations with depth collectively a colour change in the sediments surficial mnox enriched layers and 210pbexcess profiles allow an estimate of the mean position of the oxic post oxic boundary in the sediments at both sites this boundary is situated deeper than the 210pbexcess surface mixed layer but shallower than the 14c surface mixed layer which represent mixing on 102 and 103 year time scales respectively this implies that the well defined surface mnox enrichment and its associated 226ra and mo fractions must have been efficiently recycled first by downwards mixing into anoxic conditions and then by subsequent reduction and diffusive migration back up into oxic conditions this occurs in 40 years at the feni drift site and in 103 years at the rockall bank site authigenic enrichments of se cd and u are evident immediately below the oxic post oxic boundary although re enrichment does not occur until a few centimetres deeper the long term fluxes of authigenic se cd u and re uptake are evaluated with steady state assumptions while diffusion from bottom waters can supply sufficient se u and re an additional source likely corg is required for cd

carbon oxygen and strontium isotopes in paleozoic carbonate components an evaluation of original seawater chemistry proxies abstract brachiopods trilobites cements and whole rock matrix material were evaluated for their reliability as proxies of original seawater carbon oxygen and strontium isotope chemistry in this process coeval material was evaluated from individual horizons of formations spanning the permian to cambrian unaltered shells of low mg calcite articulated brachiopods retain original seawater oxygen carbon and strontium isotope compositions as old as late ordovician assessments of older specimens are hampered by a lack of suitable material coeval brachiopod whole rock sets a definitive assessment of cement marine chemistry is difficult due to the paucity of material but despite this caveat cements hold some promise for retaining original carbon and possibly strontium isotope seawater values in contrast the potential of whole rock material as a proxy of original seawater chemistry is quite complex in some but not all instances the carbon isotopic composition of whole rock after detailed scrutiny and evaluation appears to represent an original seawater chemistry signal in a few instances their oxygen isotope compositions reflect original seawater values unlike the stable isotope compositions the strontium isotopes of all studied whole rock material permian to upper cambrian appear not to reflect original seawater chemistry values thus the potential for retaining original seawater isotope chemistry and serving as specific proxies in order of decreasing reliability are 1 unaltered low mg calcite brachiopods c o and sr isotopes 2 pristine marine cements c and sr isotopes and 3 whole rock material c isotopes carbon oxygen and strontium isotope compositions of ordovician trilobites mirror those of coeval unaltered brachiopods cambrian trilobites hold significant promise as an important proxy of original seawater isotope chemistry but further studies are needed to ascertain their full potential the survey of isotopes in some ordovician and cambrian intermediate low mg calcite trilobites demonstrates their potential as an important proxy of original seawater chemistry

early diagenesis and trace element accumulation in north american arctic margin sediments abstract concentrations of redox sensitive elements s mn mo u cd re were analyzed in a set of 27 sediment cores collected along the north american arctic margin naam from the north bering sea to davis strait via the canadian archipelago sedimentary distributions and accumulation rates of the elements were used to evaluate early diagenesis in sediments along this section and to estimate the importance of this margin as a sink for key elements in the polar and global oceans distributions of mn total s and reduced inorganic s demonstrated that diagenetic conditions and thus sedimentary carbon turnover in the naam is organized regionally undetectable or very thin layers

cryogenian of yukon abstract cryogenian strata of the windermere supergroup were deposited in tectonically active basins throughout the north american cordillera from alaska to mexico the windermere supergroup of yukon canada hosts key geochronological constraints on the start of the cryogenian period and the onset of the sturtian snowball earth glaciation at ca 717 ma a 57 million year duration for the sturtian glaciation has been suggested by correlations of the glacigenic rapitan group in yukon with equivalent strata in the mackenzie mountains of northwest territories where it is overlain by organic rich argillaceous carbonate of the ca 660 ma twitya formation however syn depositional faulting and large lateral facies variation complicate these stratigraphic correlations here we describe cryogenian strata of the northern wernecke mountains yukon where correlations with the rapitan and hay creek groups of the mackenzie mountains have been previously established these units are then traced south across cryogenian structures to the southern wernecke mountains and west through the hart river inlier to the coal creek and tatonduk inliers of the ogilvie mountains in order to construct a new regional stratigraphic framework the coal creek inlier preserves volcanic rocks in the mount harper group and the eagle creek formation of the rapitan group for which we provide new u pb ca idtims zircon ages we further formalize the glacigenic cryogenian eagle creek formation together the new correlations and geochronological data allow us to more precisely integrate geological data from northwest canada with the rest of the cordillera and beyond particularly these data refine the onset of the sturtian glaciation in northwestern canada to between 716 9 0 4 and 717 4 0 2 ma and demonstrate that syn sedimentary tectonism resulted in unconformities throughout northwest laurentia between the end of the sturtian glaciation at 660 ma and the end of the marinoan glaciation at 635 ma these unconformities confound correlations throughout the cordillera by commonly preserving only one of the two cryogenian glacial deposits

an early diagenetic deglacial origin for basal ediacaran cap dolostones abstract the beginning of the ediacaran period 635 ma is marked by conspicuous dolostone units that cap marinoan glacial deposits worldwide the extent and sedimentary characteristics of the cap dolostones indicate that anomalous carbonate over saturation coincided with deglacial sea level rise and ocean warming however the geochemical variability within cap dolostones both between continents across single continental margins and within individual stratigraphic sections has been difficult to reconcile with depositional models using a compilation of new calcium and magnesium isotope measurements in marinoan cap dolostone successions worldwide we show that the geochemical variability can be explained by early diagenetic dolomitization of aragonite along a spectrum of fluid and sediment buffered conditions dolostones from the outer platform formed under fluid buffered conditions whereas dolostones on the inner platform and foreslope environment formed under sediment buffered conditions this spatial pattern of dolomitizing conditions is consistent with buoyant recirculation of glacial seawater within carbonate platforms driven by the deglacial sea level rise and development of a meltwater surface ocean using a numerical diagenetic model to evaluate the geochemical differences between sediment and fluid buffered cap dolostone units we constrain the chemical and isotopic composition of both the dolomitizing fluid glacial seawater 13 c 0 2 the meltwater lens 13 c 11 and the primary aragonite sediment 13 c 6 to 3 these model end members do not imply that primary geochemical variability did not exist but demonstrates that it is not necessary to change the chemistry of seawater to explain the global stratigraphic variability in the geochemistry of basal ediacaran cap dolostones our results provide a novel framework for understanding the geochemical variability of cap dolostone units including large excursions in carbon isotopes and how this variability is the product of local diagenetic processes expressed globally in continental margin environments following the last snowball earth

recent change in organic carbon flux to arctic ocean deep basins evidence from acid volatile sulfide manganese and rhenium discord in sediments evidence of recent large scale change in redox conditions in arctic ocean basin sediments is found in profiles of solid phase acid volatile sulfide avs mn and re avs occurs at 2 5 5 5 cm in sediment cores collected from all major arctic basins implying that presently there is a sufficient supply of organic carbon oc to deplete o 2 and form sulfide re which is mobile under oxic conditions but precipitates under suboxic or anoxic conditions is not found enriched in the sediments suggesting that avs is a recent product of enhanced oc fluxes estimated diffusion rates suggest that avs production is recent and that a change from oxic to anoxic diagenesis has taken place within the past 50 y the most likely origin for such widespread change is the ice climate and we infer that reduction in ice cover over the past several decades has led to enhanced oc fluxes to the sea floor

arctic shelves as platforms for biogeochemical activity nitrogen and carbon transformations in the chukchi sea alaska abstract continental shelves comprise 50 of marine denitrification the hanna shoal region part of the continental shelf system in the northeast chukchi sea alaska is recognized for its high biodiversity and productivity we investigated the role of sediments in organic matter decomposition and nutrient cycling at five stations on the shallow hanna shoal in particular we asked 1 how much sediment organic matter is remineralized in the chukchi sea and what factors drive this degradation 2 do sediments function as a net source for fixed nitrogen thus fueling primary production in the overlying water or as a net sink for fixed nitrogen thereby removing it from the system and 3 what is the balance between sediment nh4 uptake and regeneration and what factors drive nh4 cycling we conducted dark sediment core incubations to measure sediment o2 consumption net n2 and nutrient nh4 no3 no2 po43 fluxes and rates of sediment nh4 cycling including uptake and regeneration rates of sediment o2 consumption and nh4 and po43 efflux suggest that high organic matter remineralization rates occurred in these cold 2 c sediments we estimated that total organic carbon remineralization accounted for 20 57 of summer export production measured on the chukchi shelf net n2 release was the dominant nitrogen flux indicating that sediments acted as a net sink for bioavailable nitrogen via denitrification organic carbon remineralization via denitrification accounted for 6 12 of summer export production which made up 25 of the total organic carbon oxidized in hanna shoal sediments these shallow productive arctic shelves are hotspots for organic matter remineralization

carbon isotope variability across the ediacaran yangtze platform in south china implications for a large surface to deep ocean δ13c gradient new isotope data obtained from relatively conformable carbonate rich strata of the ediacaran yangtze platform in south china reveal substantial 13 c variability in platform sections four negative 13 c anomalies with a nadir down to 8 pdb are present in the interval between the cap carbonate level 635 ma and the precambrian cambrian boundary 542 ma while in slope and basinal sections 13 c values are negative through the entire doushantuo formation 635 551 ma if these 13 c values are close to their primary seawater signature they imply a strong 10 surface to deep ocean 13 c gradient that is consistent with long term deep ocean anoxia and the presence of a large dissolved organic carbon doc reservoir the two prominent negative 13 c excursions within the doushantuo formation above the cap carbonate level are associated with shoaling and local exposure of the platform the anomalies may thus record remineralization of a large oceanic doc pool via sulfate reduction that transferred 13 c depleted carbon from the oceanic doc reservoir to the surface ocean during regression inconsistencies in ediacaran 13 c profiles globally and variations in south china in particular highlight the need for further evaluation of local departures in 13 c from an inferred average seawater signature

roots rock and regolith biomechanical and biochemical weathering by trees and its impact on hillslopes a critical literature review the role of trees and forests as a critical component of the biosphere and critical zone and of the earth system more generally is widely appreciated less known and acknowledged are the geomorphological functions of tree roots although their importance has been widely referred to in soil studies paleopedology and paleobotany tree roots and their impact on weathering processes and soil production were incorporated in the devonian plant hypothesis and tree root casts served as a key evidence of recognition of past soils in geology sedimentology and paleopedology however knowledge of biomechanical and biochemical weathering induced by vascular plant roots mainly trees has been rarely utilized in geomorphic studies biogeomorphic and pedologic studies in recent decades have highlighted the importance of tree uprooting in which roots play a primary role in soil development regolith disturbance and bedrock mining other important functions of roots were also recognized e g soil displacement by growing roots infilling of stump holes and root cavities root groove development direct and indirect effects taking place in the rhizosphere and mycorrhizosphere mainly biochemical weathering of minerals support by microbial communities and symbiotic fungi and changes in porosity permeability and hydrology of soils in the root zone however further studies are urgently needed because many aspects of biochemical and biomechanical weathering are not well understood this is especially true with respect to taxa specific impacts variations in root architectures edaphic settings ecological relationships and geographic ranges result in substantially different biogeomorphic impacts of different tree species additionally the same species in different environmental settings may have different effects

calcium isotopes in deep time potential and limitations abstract calcium is an essential element in the biogeochemical cycles that regulate the long term climate state of earth the removal of co2 from the ocean atmosphere system is controlled by the burial of carbonate sediments caco3 ultimately linking the global calcium and carbon cycles this fundamental link has driven the development of the stable calcium isotope proxy with application to both ancient skeletal and non skeletal bulk carbonate sediments calcium isotope ratios 44 40ca have been used to track long term changes in seawater chemistry e g aragonite vs calcite seas and to elucidate short term climatic perturbations associated with mass extinction events however developments in the calcium isotope proxy have shown that 44 40ca values in carbonate minerals also are sensitive to changes in precipitation rates mineralogy and diagenesis thereby complicating the application of the proxy to the reconstruction of global cycles first inorganic carbonate precipitation experiments have demonstrated that carbonate 44 40ca values are sensitive to precipitation rates with higher rates generally leading to larger fractionation second 44 40ca values are sensitive to carbonate mineralogy with inorganic aragonite and calcite being on average 1 5 and 0 9 depleted relative to contemporaneous seawater respectively the effects of both changes in carbonate mineralogy and precipitation rates affect primary and secondary minerals but are particularly pronounced during carbonate diagenesis where relatively slow rates of recrystallization and neomorphism can lead to significant changes in bulk sediment 44 40ca values third changes in faunal composition expressed in skeletal fossil archives can lead to large changes in carbonate 44 40ca values that are decoupled from changes in global cycles nevertheless when these factors are appropriately considered the application of calcium isotopes in ancient carbonate sediments becomes a powerful tool for understanding biogeochemical processes that operate over many scales from diagenetic changes within the sediment pore space to regional changes across ancient carbonate platforms and to global changes in seawater chemistry through time importantly the processes that contribute to variability in carbonate 44 40ca values are likely to impact other carbonate bound proxies highlighting the potential for calcium isotopes as a tool to better understand the variability of other isotope systems

mg and ca isotope signatures of authigenic dolomite in siliceous deep sea sediments abstract authigenic carbonates in marine sediments frequently have carbon isotope ratios that reflect local organic carbon processing rather than the c 13 of the global dic dissolved inorganic carbon reservoir but their contributions to ancient sedimentary sections are difficult to assess in this study of authigenic dolomite from the miocene age monterey formation of offshore california mg and ca isotopes are shown to vary with stratigraphic depth as a result of early diagenetic processes the dolomite is a pre compaction authigenic phase that occurs as beds and nodules with c 13 ranging from 16 to 9 light c 13 values were likely acquired from the sedimentary zone of microbial sulfate reduction while heavy c 13 values were acquired from the zone of methanogenesis mg and ca isotopes are roughly anti correlated with intervals of negative c 13 associated with low mg 26 and higher ca 44 40 values the variability is observed over a wide range of length scales from 10 2 meters within individual authigenic beds nodules to 10 2 meters over the entire stratigraphic column and can be understood as the consequence of dolomite precipitation in pore fluids where mg supply is limited by diffusive transport the relationship of mg 26 and ca 44 40 to the more common stable isotope measurements of c 13 and o 18 represents a new diagenetically robust geochemical fingerprint for identifying synsedimentary authigenic carbonates in the geological record

the eco geomorphological roles of rocky deep crevices for water supply on arid zone mountain slopes case study mehriz yazd iran rocky slope landscapes are widely distributed on arid land mountains where there are many restoration and forestation project sites this study has surveyed the role of deep crevices and stone layers for supplying water to establish trees and shrubs on arid lands rocky slopes the research was concentrated on the layers of limestone granite and andesite in central iran thirty transects each 25 m long were randomly laid out throughout the studied lithologic units correlation of vegetation cover percentage and abundance of trees were studied along with crack dimensions including width depth and length categorized into three classes large medium and low sizes along those transects the amount of ec ph organic materials caso4 caco3 soil texture n p k and soil moisture content in the cracks were also measured the results showed significant differences p 0 05 among crack properties vegetation cover and life forms in the study units also the vegetation cover and life forms have positive significant relationships with increase of crevice width as well as length and depth of each lithologic unit the findings demonstrated that the inherent potential of limestone rocky slopes with deep layers is higher than other rocky units for restoration and afforestation in this arid region

dolomite occurrence evolution and economically important associations abstract dolomite is not a simple mineral it can form as a primary precipitate a diagenetic replacement or as a hydrothermal metamorphic phase all that it requires is permeability a mechanism that facilitates fluid flow and a sufficient supply of magnesium dolomite can form in lakes on or beneath the shallow seafloor in zones of brine reflux and in early to late burial settings it may form from seawater from continental waters from the mixing of basinal brines the mixing of hypersaline brine with seawater or the mixing of seawater with meteoric water or via the cooling of basinal brines bacterial metabolism may aid the process of precipitation in settings where sulfate reducing species flourish and microbial action may control primary precipitation in some hypersaline anoxic lake settings dolomite is a metastable mineral early formed crystals can be replaced by later more stable phases with such replacements repeated a number of times during burial and metamorphism each new phase is formed by the partial or complete dissolution of an earlier dolomite this continual re equilibration during burial detracts from the ability of trace elements to indicate depositional conditions and resets the oxygen isotope signature of the dolomite at progressively higher temperatures because subsurface dolomite evolves via dissolution and reprecipitation a bed of dolomite can retain or create porosity and permeability to much greater burial depths and into higher temperature realms than a limestone counterpart dolomitization also creates new crystals with new rhomb growth following the dissolution of less stable precursors repetition of this process without complete pore cementation can generate intercrystalline porosity a number of times in the rock s burial history intercrystalline porosity is a highly interconnected style of porosity that gives dolomite reservoirs their good fluid storage capacity and efficient drainage the fact that many dolomite reservoirs formed via brine reflux means that they sit beneath an evaporite seal in both platform and basinwide evaporite settings the same association of evaporites sulfate source and entrained hydrocarbons means that burial conditions are also suitable for thermochemical sulfate reduction and the precipitation of base metals this tends to occur at higher temperatures 60 c 80 c and so the resulting dolomites tend to be ferroan and consist of saddle shaped crystals

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

zircon ages from the baydrag block and the bayankhongor ophiolite zone time constraints on late neoproterozoic to cambrian subduction and accretion related magmatism in central mongolia central mongolia represents a heterogeneous crustal domain of the central asian orogenic belt and is composed of contrasting lithotectonic units with distinct preorogenic histories we report single zircon evaporation and shrimp ages for high grade rocks of the neoarchean paleoproterozoic baydrag block and for metaigneous rocks of the junction between the late neoproterozoic bayankhongor ophiolite zone boz and the baydrag block zircon ages for metamorphic rocks of the baydrag block indicate a major tectonothermal event between 1840 and 1826 ma coeval with the emplacement of granitic rocks at middle crustal level dated at 1839 ma a granite gneiss yielded a much younger crystallization age of 1051 ma the first grenvillian age reported for this region together with predominantly mesoproterozoic detrital zircon ages for a quartzite lens from the burd gol accretionary complex these data attest to the heterogeneity and long precambrian history of the baydrag block crystallization ages for granite gneisses from the northeastern margin of the baydrag block indicate prolonged plutonic activity between 579 and 537 ma probably related to southward subduction of the bayankhongor oceanic crust a syntectonic granite vein yielded a crystallization age of 519 ma probably linked to accretion of the boz onto the northeastern active margin of the baydrag block lastly a felsic metavolcanic rock from the southeastern termination of the boz yielded a crystallization age of 472 ma and suggests that punctuated volcanic centers developed during the early ordovician in response to protracted convergence

ca isotopes in carbonate sediment and pore fluid from odp site 807a the ca2 aq calcite equilibrium fractionation factor and calcite recrystallization rates in pleistocene sediments abstract the calcium isotopic compositions 44ca of 30 high purity nannofossil ooze and chalk and 7 pore fluid samples from odp site 807a ontong java plateau are used in conjunction with numerical models to determine the equilibrium calcium isotope fractionation factor s f between calcite and dissolved ca2 and the rates of post depositional recrystallization in deep sea carbonate ooze the value of s f at equilibrium in the marine sedimentary section is 1 0000 0 0001 which is significantly different from the value 0 9987 0 0002 found in laboratory experiments of calcite precipitation and in the formation of biogenic calcite in the surface ocean we hypothesize that this fractionation factor is relevant to calcite precipitation in any system at equilibrium and that this equilibrium fractionation factor has implications for the mechanisms responsible for ca isotope fractionation during calcite precipitation we describe a steady state model that offers a unified framework for explaining ca isotope fractionation across the observed precipitation rate range of 14 orders of magnitude the model attributes ca isotope fractionation to the relative balance between the attachment and detachment fluxes at the calcite crystal surface this model represents our hypothesis for the mechanism responsible for isotope fractionation during calcite precipitation the ca isotope data provide evidence that the bulk rate of calcite recrystallization in freshly deposited carbonate ooze is 30 40 myr and decreases with age to about 2 myr in 2 3 million year old sediment the recrystallization rates determined from ca isotopes for pleistocene sediments are higher than those previously inferred from pore fluid sr concentration and are consistent with rates derived for late pleistocene siliciclastic sediments using uranium isotopes combining our results for the equilibrium fractionation factor and recrystallization rates we evaluate the effect of diagenesis on the ca isotopic composition of marine carbonates at site 807a since calcite precipitation rates in the sedimentary column are many orders of magnitude slower than laboratory experiments and the pore fluids are only slightly oversaturated with respect to calcite the isotopic composition of diagenetic calcite is likely to reflect equilibrium precipitation accordingly diagenesis produces a maximum shift in 44ca of 0 15 for site 807a sediments but will have a larger impact where sedimentation rates are low seawater circulates through the sediment pile or there are prolonged depositional hiatuses

early diagenesis of redox sensitive trace metals in the peru upwelling area response to enso related oxygen fluctuations in the water column pore water and solid phase data for redox sensitive metals mn fe v mo and u were collected on a transect across the peru upwelling area 11 s at water depths between 78 and 2025 m and bottom water oxygen concentrations ranging from 0 to 93 m by comparing authigenic mass accumulation rates and diffusive benthic fluxes we evaluate the respective mechanisms of trace metal accumulation retention and remobilization across the oxygen minimum zone omz and with respect to oxygen fluctuations in the water column related to the el nino southern oscillation enso sediments within the permanent omz are characterized by diffusive uptake and authigenic fixation of u v and mo as well as diffusive loss of mn and fe across the benthic boundary some of the dissolved mn and fe in the water column re precipitate at the oxycline and shuttle particle reactive trace metals to the sediment surface at the lower and upper boundary of the omz at the lower boundary pore waters are not sufficiently sulfidic as to enable an efficient authigenic v and mo fixation as a consequence sediments below the omz are preferentially enriched in u which is delivered via both in situ pre cipitation and lateral supply of u rich phosphorites from further upslope trace metal cycling on the peruvian shelf is strongly affected by enso related oxygen fluctuations in bottom water during periods of shelf oxygenation surface sediments receive particulate v and mo with metal oxyhydr oxides that derive from both terrigenous sources and precipitation at the retreating oxycline after the recurrence of anoxic conditions metal oxyhydr oxides are reductively dissolved and the hereby liberated v and mo are authigenically removed this alternation between supply of particle reactive trace metals during oxic periods and fixation during anoxic periods leads to a preferential accumulation of v and mo compared to u on the peruvian shelf the decoupling of v mo and u accumulation is further accentuated by the varying susceptibility to re oxidation of the different authigenic metal phases while authigenic u and v are readily re oxidized and recycled during periods of shelf oxygenation the sequestration of mo by authigenic pyrite is favored by the transient occurrence of oxidizing conditions our findings reveal that redox sensitive trace metals respond in specific manner to short term oxygen fluctuations in the water column the relative enrichment patterns identified might be useful for the reconstruction of past omz extension and large scale redox oscillations in the geological record

δ44ca evolution in a carbonate aquifer and its bearing on the equilibrium isotope fractionation factor for calcite abstract to improve understanding of ca isotope transport during water rock interaction on the continents we measured dissolved 44 ca values along a 236 km flow path in the madison aquifer south dakota where fluids have chemically evolved according to dolomite and anhydrite dissolution calcite precipitation and ca for na ion exchange over a timescale spanning 15 kyr we used a reactive transport model employing rate data constrained from major ion mass balances to evaluate the extent to which calcite precipitation and ion exchange fractionate ca isotopes elevated 44 ca values during the initial and final stages of water transport possibly result from calcite precipitation under supersaturated conditions and ca for na ion exchange respectively however for the bulk of the flow path 44 ca values evolve by mixing between anhydrite and dolomite dissolution with no fractionation during calcite precipitation under saturated conditions we attribute the absence of ca isotope fractionation to the long timescale of water rock interaction and slow rate of calcite precipitation which have enabled fluids to chemically and isotopically equilibrate with calcite we therefore conclude that the equilibrium ca isotope fractionation factor between calcite and water cal w is very close to zero to the extent that the madison aquifer typifies other groundwater systems where calcite slowly precipitates from solutions at or near chemical equilibrium this study suggests that groundwater contributions to 44 ca variability on the continents can be modeled according to simple mixing theory without invoking isotope discrimination

topographic controls on the depth distribution of soil co2 in a small temperate watershed accurate measurements of soil co2 concentrations pco2 are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon c cycle while there have been many studies of soil pco2 most sample or model only one or at most a few landscape positions and therefore do not account for complex topography here we test the hypothesis that soil pco2 distribution can predictably vary with topographic position we measured soil pco2 at the susquehanna shale hills critical zone observatory sshczo pennsylvania where controls on soil pco2 e g depth texture porosity and moisture vary from ridge tops down to the valley floor between planar slopes and slopes with convergent flow i e swales and between north and south facing aspects we quantified pco2 generally at 0 1 0 2 m depth intervals down to bedrock from 2008 to 2010 and in 2013 of the variables tested topographic position along catenas was the best predictor of soil pco2 because it controls soil depth texture porosity and moisture which govern soil co2 diffusive fluxes the highest pco2 values were observed in the valley floor and swales where soils are deep 0 7 m and wet resulting in low co2 diffusion through soil profiles in contrast the ridge top and planar slope soils have lower pco2 because they are shallower 0 6 m and drier resulting in high co2 diffusion through soil profiles aspect was a minor predictor of soil pco2 the north i e south facing swale generally had lower soil moisture content and pco2 than its south i e north facing counterpart seasonally we observed that while the timing of peak soil pco2 was similar across the watershed the amplitude of the pco2 peak was higher in the deep soils due to more variable moisture content the high pco2 observed in the deeper wetter topographic positions could lower soil porewater ph by up to 1 ph unit compared to porewaters equilibrated with atmospheric co2 alone co2 is generally the dominant acid driving weathering in soils based on our observations models of chemical weathering and co2 dynamics would be improved by including landscape controls on soil pco2

regolith production and transport at the susquehanna shale hills critical zone observatory part 2 insights from meteoric 10be 1 regolith mantled hillslopes are ubiquitous features of most temperate landscapes and their morphology reflects the climatically biologically and tectonically mediated interplay between regolith production and downslope transport despite intensive research few studies have quantified both of these mass fluxes in the same field site here we present an analysis of 87 meteoric 10be measurements from regolith and bedrock within the susquehanna shale hills critical zone observatory ssho in central pennsylvania meteoric 10be concentrations in bulk regolith samples n 73 decrease with regolith depth comparison of hillslope meteoric 10be inventories with analyses of rock chip samples n 14 from a 24 m bedrock core confirms that 80 of the total inventory is retained in the regolith the systematic downslope increase of meteoric 10be inventories observed at ssho is consistent with 10be accumulation in slowly creeping regolith 0 2 cm yr 1 regolith flux inferred from meteoric 10be varies linearly with topographic gradient determined from high resolution light detection and ranging based topography along the upper portions of hillslopes at ssho however regolith flux appears to depend on the product of gradient and regolith depth where regolith is thick near the base of hillslopes meteoric 10be inventories at the north and south ridgetops indicate minimum regolith residence times of 10 5 3 7 and 9 1 2 9 ky respectively similar to residence times inferred from u series isotopes in ma et al 2013 the combination of our results with u series derived regolith production rates implies that regolith production and erosion rates are similar to within a factor of two on ssho hillcrests

fluid inclusions in sedimentary and diagenetic systems abstract some of the major problems in sedimentary geology can be solved by using fluid inclusions in sedimentary and diagenetic minerals important fluids in the sedimentary realm include atmospheric gases fresh water of meteoric origin lake water seawater mixed water evaporated water formation waters deep in basins oil and natural gas preserving a record of the distribution and composition of these fluids from the past should contribute significantly to studies of paleoclimate and global change research is essential for improving understanding of diagenetic systems and provides useful information in petroleum geology applications of fluid inclusions to sedimentary systems are not without their complexities some fluid inclusions exposed to natural conditions of increasing temperature may be altered by thermal reequilibration which results in stretching or leakage and refilling of some fluid inclusions similarly overheating in the laboratory can also cause reequilibration of fluid inclusions so fluid inclusions from the sedimentary realm must be handled carefully and protected from overheating natural overheating of fluid inclusions must be evaluated through analysis of the most finely discriminated events of fluid inclusion entrapment fluid inclusion assemblages fia consistency in homogenization temperatures within a fluid inclusion assemblage consisting of variably sized and shaped inclusions is the hallmark of a data set that has not been altered through thermal reequilibration in contrast fluid inclusion assemblages yielding variable data may have been altered through thermal reequilibration if a fluid inclusion assemblage has not been altered by thermal reequilibration its fluid inclusions may be useful as geothermometers for low and high temperature systems or useful as geobarometers applicable throughout the sedimentary realm if a fluid inclusion assemblage has been altered partially by thermal reequilibration techniques for distinguishing between altered and unaltered fluid inclusions may be applied in studies of global change fluid inclusions can be used as sensitive indicators of paleotemperature of surface environments fluid inclusions also preserve microsamples of ancient seawater and atmosphere the analysis of which could figure prominently into discussions of past changes in chemistry of the atmosphere and oceans in petroleum geology fluid inclusions have proven to be useful indicators of migration pathways of hydrocarbons they can delineate the evolution of the chemistry of hydrocarbons and they remain important in understanding the thermal history of basins and relating fluid migration events to evolution of reservoir systems in studies of diagenesis fluid inclusions can be the most definitive record most diagenetic systems are closely linked to temperature and salinity of the fluid thus fluid inclusions are sensitive indicators of diagenetic environments

authigenic molybdenum formation in marine sediments a link to pore water sulfide in the santa barbara basin pore water and sediment mo concentrations were measured in a suite of multicores collected at four sites along the northeastern flank of the santa barbara basin to examine the connection between authigenic mo formation and pore water sulfide concentration only at the deepest site 580 m where pore water sulfide concentrations rise to 0 1 mm right below the sediment water interface was there active authigenic mo formation at shallower sites 550 430 and 340 m where pore water sulfide concentrations were consistently 0 05 mm mo precipitation was not occurring at the time of sampling a sulfide concentration of 0 1 mm appears to be a threshold for the onset of mo fe s co precipitation a second threshold sulfide concentration of 100 mm is required for mo precipitation without fe possibly as mo s or as particle bound mo mass budgets for mo were constructed by combining pore water and sediment results for mo with analyses of sediment trap material from santa barbara basin as well as sediment accumulation rates derived from 210 pb the calculations show that most of the authigenic mo in the sediment at the deepest site is supplied by diffusion from overlying bottom waters there is however a non lithogenic particulate mo associated with sinking particles that contributes 15 to the total authigenic mo accumulation analysis of sediment trap samples and supernant brine solutions indicates the presence of non lithogenic particulate mo a large fraction of which is easily remobilized and perhaps associated with mn oxides our observations show that even with the very high flux of organic carbon reaching the sediment of santa barbara basin active formation of sedimentary authigenic mo requires a bottom water oxygen concentration below 3 mm however small but measurable rates of authigenic mo accumulation were observed at sites where bottom water oxygen ranged between 5 and 23 mm indicating that the formation of authigenic mo occurred in the recent past but not at the time of sampling copyright 2000 elsevier science ltd

constraining magnesium cycling in marine sediments using magnesium isotopes abstract magnesium concentrations in deep sea sediment pore fluids typically decrease down core due to net precipitation of dolomite or clay minerals in the sediments or underlying crust to better characterize and differentiate these processes we have measured magnesium isotopes in pore fluids and sediment samples from ocean drilling program sites 1082 1086 1012 984 1219 and 925 that span a range of oceanographic settings at all sites magnesium concentrations decrease with depth at sites where diagenetic reactions are dominated by the respiration of organic carbon pore fluid 26mg values increase with depth by as much as 2 because carbonates preferentially incorporate 24mg low 26mg the increase in pore fluid 26mg values at these sites is consistent with the removal of magnesium in mg carbonate dolomite in contrast at sites where the respiration of organic carbon is not important and or weatherable minerals are abundant pore fluid 26mg values decrease with depth by up to 2 the decline in pore fluid 26mg at these sites is consistent with a magnesium sink that is isotopically enriched relative to the pore fluid the identity of this enriched magnesium sink is likely clay minerals using a simple 1d diffusion advection reaction model of pore fluid magnesium we estimate rates of net magnesium uptake removal and associated net magnesium isotope fractionation factors for sources and sinks at all sites independent estimates of magnesium isotope fractionation during dolomite precipitation from measured 26mg values of dolomite samples from sites 1082 and 1012 are very similar to modeled net fractionation factors at these sites suggesting that local exchange of magnesium between sediment and pore fluid at these sites can be neglected our results indicate that the magnesium incorporated in dolomite is 2 0 2 7 depleted in 26mg relative to the precipitating fluid assuming local exchange of magnesium is minor at the rest of the studied sites our results suggest that magnesium incorporated into clay minerals is enriched in 26mg by 0 to 1 25 relative to the precipitating fluid this work demonstrates the utility of magnesium isotopes as a tracer for magnesium sources sinks in low temperature aqueous systems

210pb and 137cs in margin sediments of the arctic ocean controls on boundary scavenging 1 210pb and 137cs were measured in 25 sediment cores collected during the international polar year from a transect spanning the north american arctic margin from the north bering sea to baffin bay davis strait profiles and inventories of the radioisotopes were used to determine sediment mixing and accumulation at each site and to assess the intensity of scavenging and burial sediment accumulation rates derived from 210pb and validated using 137cs are between 0 04 and 0 23 g cm 2 yr 1 210pb cannot be used to derive sedimentation rates for vigorously biomixed sediments from the north bering chukchi shelf elevated 137cs activities and inventories in recently deposited sediments imply delayed inputs of particle associated 137cs to the sediments likely transported from the watershed to the coast and subsequently redistributed to shelf slope sediments inventories of 210pbex in all cores meet or exceed the estimated supply of 210pbex from atmospheric deposition and decay of 226ra in the water column this implies that in contrast to the deep arctic ocean basin there is a sufficient supply of suspended particulates along the north american arctic margin to scavenge the supply of 210pbex 210pbex inventories in sediments are up to 21 fold greater than the in situ supply at some sites large inventories of 210pbex in sediments along the north bering chukchi shelf result primarily from focusing while those along the north chukchi slope barrow canyon and in baffin bay davis strait reflect strong boundary scavenging likely supported by lateral exchanges with deep interior atlantic origin waters

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

the nature of the δ13c of periplatform sediments implications for stratigraphy and the global carbon cycle the carbon isotopic composition y 13 c of bulk carbonates obtained from a transect of sites drilled through platform and periplatform sediments of holocene to early miocene age has been compared to ascertain whether changes in the y 13 c can be correlated between sediments of equivalent ages and whether such changes can be related to global changes in the y 13 c of the dissolved inorganic carbon in the oceans over this time period five of the sites were drilled during leg 166 of the ocean drilling project 1003 1007 in a transect ranging from five km to 25 km away from the platform margin and penetrating sediments of holocene to oligocene age that are contained in 17 depositional sequences a q two shallow water sites clino and unda were situated on a extension of the same transect on great bahama bank in a water depth of 10 15 m with the exception of unda and clino the y 13 c of the carbonates ranges from 5x in the younger sequences to 1x in the early miocene in each of the sites the y 13 c is strongly positively correlated with the percentage of aragonite as a consequence the y 13 c of sequences a through f is strongly correlated reflecting the decreasing amount of aragonite with increasing depth in the two platform sites the y 13 c is significantly lower in the younger portions of the cores as a result of the influences of meteoric diagenesis during repeated exposure during the pleistocene although the y 13 c of the individual sequences can be correlated in most instances between the odp holes the changes are not related to global changes in the y 13 c of the oceans which in contrast to the y 13 c of the platform sediments become isotopically lower towards the present day instead variations in the y 13 c appear to be related to varying mixtures of y 13 c rich banktop sediments and pelagic material

recent changes in shelf hydrography in the siberian arctic potential for subsea permafrost instability summer hydrographic data 1920 2009 show a dramatic warming of the bottom water layer over the eastern siberian shelf coastal zone 10 m depth since the mid 1980s by 2 1 c we attribute this warming to changes in the arctic atmosphere the enhanced summer cyclonicity results in warmer air temperatures and a reduction in ice extent mainly through thermodynamic melting this leads to a lengthening of the summer open water season and to more solar heating of the water column the permafrost modeling indicates however that a significant change in the permafrost depth lags behind the imposed changes in surface temperature and after 25 years of summer seafloor warming as observed from 1985 to 2009 the upper boundary of permafrost deepens only by 1 m thus the observed increase in temperature does not lead to a destabilization of methane bearing subsea permafrost or to an increase in methane emission the ch4 supersaturation recently reported from the eastern siberian shelf is believed to be the result of the degradation of subsea permafrost that is due to the long lasting warming initiated by permafrost submergence about 8000 years ago rather than from those triggered by recent arctic climate changes a significant degradation of subsea permafrost is expected to be detectable at the beginning of the next millennium until that time the simulated permafrost table shows a deepening down to 70 m below the seafloor that is considered to be important for the stability of the subsea permafrost and the permafrost related gas hydrate stability zone

the effects of diagenesis and dolomitization on ca and mg isotopes in marine platform carbonates implications for the geochemical cycles of ca and mg abstract the ca mg o and c isotopic and trace elemental compositions of marine limestones and dolostones from odp site 1196a which range in depth 58 to 627 mbsf and in depositional age 5 and 23 ma are presented the objectives of the study are to explore the potential for non traditional isotope systems to fingerprint diagenesis to quantify the extent to which geochemical proxies are altered during diagenesis and to investigate the importance of diagenesis within the global ca and mg geochemical cycles the data suggest that ca which has a relatively high solid to fluid mass ratio can be isotopically altered during diagenesis in addition the alteration of ca correlates with the alteration of mg in such a way that both can serve as useful tools for deciphering diagenesis in ancient rocks bulk carbonate 44 ca values vary between 0 60 and 1 31 srm 915a scale the average limestone 44 ca is 0 97 0 24 1sd identical within error to the average dolostone 1 03 0 15 1sd magnesium isotopic compositions 26 mg dsm 3 scale range between 2 59 and 3 91 and limestones 3 60 0 25 and dolostones 2 68 0 07 are isotopically distinct carbon isotopic compositions 13 c pdb scale vary between 0 86 and 2 47 with average limestone 1 96 0 31 marginally offset relative to average dolostone 1 68 0 57 the oxygen isotopic compositions 18 o pdb scale of limestones 1 22 0 94 are substantially lower than the dolostones measured 2 72 1 07 the isotopic data from 1196a suggest distinct and coherent trends in isotopic and elemental compositions that are interpreted in terms of diagenetic trajectories numerical modeling supports the contention that such trends can be interpreted as diagenetic and suggests that the appropriate distribution coefficient k mg associated with limestone diagenesis is 1 to 5 10 3 distinctly lower than those values 0 015 reported in laboratory studies with respect to mg isotopes the modeling also suggest that diagenetic fractionation factors of 0 9955 4 5 and 0 9980 2 are appropriate for limestone diagenesis and dolomitization respectively

uranium diagenesis in sediments underlying bottom waters with high oxygen content we measured u in sediments both pore waters and solid phase from three locations on the middle atlantic bight mab from the eastern margin of the united states a northern location on the continental shelf off massachusetts oc426 75 m water depth and two southern locations off north carolina en433 1 647 m water depth and en433 2 2648 m water depth these sediments underlie high oxygen bottom waters 250 270 m but become reducing below the sediment water interface due to the relatively high organic carbon oxidation rates in sediments en433 1 212 mol c cm2 y oc426 120 10 mol c cm2 y en433 2 33 mol c cm2 y pore water oxygen goes to zero by 1 4 1 5 cm at en433 1 and oc426 and slightly deeper oxygen penetration depths were measured at en433 2 4 cm all of the pore water profiles show removal of u from pore waters calculated pore water fluxes are greatest at en433 1 0 66 0 08 nmol cm2 y and less at en433 2 and oc426 0 24 0 05 and 0 13 0 05 nmol cm2 y respectively solid phase profiles show authigenic u enrichment in sediments from all three locations the average authigenic u concentrations are greater at en433 1 and oc426 5 8 0 7 nmol g and 5 4 0 2 nmol g respectively relative to en433 2 4 1 0 8 nmol g this progression is consistent with their relative ordering of reduction intensity with greatest reducing conditions in sediments from en433 1 less at oc426 and least at en433 2 the authigenic u accumulation rate is largest at en433 1 0 47 0 05 nmol cm2 y but the average among the three sites on the mab is 0 2 nmol cm2 y pore water profiles suggest diffusive fluxes across the sediment water interface that are 1 4 1 7 times greater than authigenic accumulation rates at en433 1 and en433 2 these differences are consistent with oxidation and loss of u from the solid phase via irrigation and or bioturbation which may compromise the sequestration of u in continental margin sediments that underlie bottom waters with high oxygen concentrations previous literature compilations that include data exclusively from locations where o2 bw 150 m suggest compelling correlations between authigenic u accumulation and organic carbon flux to sediments or organic carbon burial rate sediments that underlie waters with high o2 bw have lower authigenic u accumulation rates than would be predicted from relationships developed from results that include locations where o2 bw 150 m

hypsometry and volume of the arctic ocean and its constituent seas 1 this paper presents an analysis of the arctic ocean and its constituent seas for seafloor area distribution versus depth and ocean volume the bathymetry from the international bathymetric chart of the arctic ocean ibcao is used together with limits defining this ocean and its constituent seas from the international hydrographic organization iho as well as redefined limits constructed to confine the seas to the shallow shelves ibcao is a bathymetric grid model with a resolution of 2 5 2 5 km which significantly improved the portrayal of the arctic ocean seafloor through incorporation of newly released bathymetric data including echo soundings from u s and british navies scientific nuclear submarine cruises and icebreaker cruises this analysis of seafloor area and ocean volume is the first for the arctic ocean based on this new and improved portrayal of the seafloor as represented by ibcao the seafloor area and volume are calculated for different depths starting from the present sea level and progressing in increments of 10 m to a depth of 500 m and in increments of 50 m from 550 m down to the deepest depth within each of the analyzed seas hypsometric curves expressed as simple histograms of the frequencies in different depth bins and depth plotted against cumulative area for each of the analyzed seas are presented the area and volume calculations show that the entire iho defined arctic ocean makes up 4 3 of the total ocean area but only 1 4 of the volume furthermore the iho arctic ocean is the shallowest mean depth 1201 m of all the major oceans and their adjacent seas the continental shelf area from the coasts out to the shelf break make up as much as 52 9 of the total area in the arctic ocean defined in this work as consisting of the oceanic deep arctic ocean basin the broad continental shelves of the barents kara laptev east siberian chukchi and beaufort seas the white sea and the narrow continental shelf off both the canadian arctic archipelago and northern greenland this result indicates that the arctic ocean has significantly larger continental shelves compared with all the other oceans where previous studies show that the proportion of shelves from the coasts out to the foot of the continental slopes only ranges between about 9 1 and 17 7 furthermore the derived hypsometric curves show that most of the arctic ocean shelf seas besides the barents sea beaufort sea and the shelf off northern greenland have a similar shape with the largest seafloor area between 0 and 50 m the east siberian and laptev seas in particular show area distributions concentrated in this shallow depth range and together with the chukchi sea they form a large flat shallow shelf province composing as much as 22 of the entire arctic ocean area but only 1 of the volume this implies that the circulation in the arctic ocean might be very sensitive to eustatic sea level changes one of the aims with this work is to make up to date high resolution area and volume calculations for the arctic ocean at various depths available for download

evidence against the dorag mixing zone model for dolomitization along the wisconsin arch a case for hydrothermal diagenesis ordovician carbonates near the wisconsin arch represent the type locality in ancient rocks for the dorag or mixing zone model for dolomitization field petrographic and geochemical evidence suggests a genetic link between the pervasive dolomite trace mississippi valley type mvt minerals and potassium k silicate minerals in these rocks which preserve a regional hydrothermal signature constraints were placed on the conditions of water rock interaction using fluid inclusion methods cathodoluminescence and plane light petrography stable isotopic analyses and organic maturity data homogenization temperatures of two phase aqueous fluid inclusions in dolomite sphalerite and quartz range between 65 and 120c freezing data suggest a na ca mg cl h2o fluid with salinities between 13 and 28 wt nacl equivalent the pervasive dolomitization of paleozoic rocks on and adjacent to the wisconsin arch was the result of water rock interaction with dense brines at elevated temperatures and it was coeval with regional trace mvt mineralization and k silicate diagenesis a reevaluation of the dorag mixing zone model for dolomitization in conjunction with convincing new petrographic and geochemical evidence has ruled out the dorag model as the process responsible for pervasive dolomitization along the wisconsin arch and adds to the abundant body of literature that casts serious doubt about the viability of the dorag model in general

a model for uranium rhenium and molybdenum diagenesis in marine sediments based on results from coastal locations abstract the purpose of this research is to characterize the mobilization and immobilization processes that control the authigenic accumulation of uranium u rhenium re and molybdenum mo in marine sediments we analyzed these redox sensitive metals rsm in benthic chamber pore water and solid phase samples at a site in buzzards bay massachusetts usa that has high bottom water oxygen concentrations 230 300 mol l and high organic matter oxidation rates 390 mol c cm2 y the oxygen penetration depth varies from 2 to 9 mm below the sediment water interface but pore water sulfide is below detection release of rsm to pore waters during the remineralization of solid phases occurs near the sediment water interface at depths above the zone of authigenic rsm formation this release occurs consistently for mo at both sites but only in the winter for re in buzzards bay and intermittently for u at the buzzards bay site re removal to the solid phase extends to the bottom of the profile while the zone of removal is restricted to 2 9 cm for u and mo authigenic re formation is independent of the anoxic remineralization rate which is consistent with an abiotic removal mechanism the rate of authigenic u formation and its modeled removal rate constant increase with increasing anoxic remineralization rates and is consistent with u reduction being microbially mediated authigenic mo formation is related to the formation of sulfidic microenvironments the depth and extent of mo removal from pore water is closely associated with the balance between iron and sulfate reduction and the consumption of pore water sulfide via iron sulfide formation pore water rsm reach constant asymptotic concentrations in sulfidic sediments but only pore water re is constant at depth in buzzards bay the increases in pore water u at the buzzards bay site are consistent with addition via irrigation and subsequent upward diffusion to the removal zone deep pore water mo concentrations exceed its bottom water concentration due to irrigation induced oxidation and remobilization from the solid phase in sulfidic sediments there is no evidence for higher pore water u or mo concentrations at depth due to the absence of irrigation and or the presence of more stable authigenic rsm phases there are good correlations between benthic fluxes and authigenic accumulation rates for u and mo in sulfidic sediments however results from buzzards bay suggest irrigation ultimately results in the partial loss of u and mo from the solid phase with accumulation rates that are 20 30 of the modeled flux irrigation can augment re possibly u or compromise u mo authigenic accumulation in sediments and is important when determining burial rates in continental margin sediments

210pb derived chronology and the fluxes of 210pb and 137cs isotopes into continental shelf sediments east chukchi sea alaskan arctic abstract eleven sediment cores and eight sediment trap samples from the continental shelf of the eastern chukchi sea were analyzed for 210pb cs and 2226ra in selected samples the organic carbon content and stable carbon isotope ratios were also determined the excess 210pb 210pbxs concentrations in the 1 cm core tops are generally lower than those of surficial sediments of subarctic shelves and arctic lakes the sediment inventory derived depositional fluxes of 210ph vary between 0 09 and 0 38 dpm cm 2y 1 with a mean of 0 18 dpm cm 2 y 1 the apparent mass sediment accumulation rates which vary between 31 and 324 mg cm 2 y 1 with a mean value of 133 mg cm 2 y 1 are about an order of magnitude lower than the yearly particle flux obtained from the sediment trap experiments this difference between the relatively long term and short term yearly accumulation rates is likely due to the occasional resuspension of fine particles in the continental shelf areas and their advective transport to sites other than their initial deposition the sediment inventory of 137cs varied between 0 64 and 4 09 dpm cm 2 with a mean of 2 18 dpm cm 2 a comparison of this inventory with the expected fallout inventory of 137cs suggests that there had been no detectable input of 137cs to the study area from the former ussr nuclear dump sites

calcium isotope fractionation in calcite and aragonite abstract calcium isotope fractionation was measured on skeletal aragonite and calcite from different marine biota and on inorganic calcite precipitation temperatures ranged from 0 to 28 c calcium isotope fractionation shows a temperature dependence in accordance with previous observations 1000 ln cc 1 4 0 021 t c for calcite and 1000 ln ar 1 9 0 017 t c for aragonite within uncertainty the temperature slopes are identical for the two polymorphs however at all temperatures calcium isotopes are more fractionated in aragonite than in calcite the offset in 44 40 ca is about 0 6 the underlying mechanism for this offset may be related to the different coordination numbers and bond strengths of the calcium ions in calcite and aragonite crystals or to different ca reaction behavior at the solid liquid interface recently the observed temperature dependence of the ca isotope fractionation was explained quantitatively by the temperature control on precipitation rates of calcium carbonates in an experimental setting lemarchand et al 2004 we show that this mechanism can in principle also be applied to caco 3 precipitation in natural environments in normal marine settings following this model ca isotope fractionation in marine ca carbonates is primarily controlled by precipitation rates on the other hand the larger ca isotope fractionation of aragonite compared to calcite can not be explained by different precipitation rates the rate control model of ca isotope fractionation predicts a strong dependence of the ca isotopic composition of carbonates on ambient co 3 2 concentration while this model is in general accordance with our observations in marine carbonates cultured specimens of the planktic foraminifer orbulina universa show no dependence of ca isotope fractionation on the ambient co 3 2 concentration the latter observation implies that the carbonate chemistry in the calcifying vesicles of the foraminifer is independent from the ambient carbonate ion concentration of the surrounding water

a cryogenian chronology two long lasting synchronous neoproterozoic glaciations the snowball earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons here we present four new re os geochronology age constraints on sturtian 717 660 ma and marinoan 635 ma termination glacial deposits from three different paleocontinents a 752 7 5 5 ma age from the base of the callison lake formation in yukon canada confirms nonglacial sedimentation on the western margin of laurentia between ca 753 and 717 ma coupled with a new 727 3 4 9 ma age directly below the glacigenic deposits of the grand conglomerate on the congo craton africa these data refute the notion of a global ca 740 ma kaigas glaciation a 659 0 4 5 ma age directly above the maikhan uul diamictite in mongolia confirms previous constraints on a long duration for the 717 660 ma sturtian glacial epoch and a relatively short nonglacial interlude in addition we provide the first direct radiometric age constraint for the termination of the marinoan glaciation in laurentia with an age of 632 3 5 9 ma from the basal sheepbed formation of northwest canada which is identical within uncertainty to u pb zircon ages from china australia and namibia together these data unite re os and u pb geochronological constraints and provide a refined temporal framework for cryogenian earth history

geochemical behaviors of different element groups during shale weathering at the susquehanna shale hills critical zone observatory major and trace element concentrations were measured in bedrock regolith and stream sediments from a first order catchment developed entirely on grey shale in central pennsylvania usa these elements can be classified into five major groups based on statistical data analysis the presence of different elemental groups is due to the mineralogical origin cycling processes and geochemical properties of these elements during soil formation a better understanding of the behaviors of these elements during chemical weathering would allow for their possible use as natural tracers in critical zone processes

comparative geochemistry of cadmium rhenium uranium and molybdenum in continental margin sediments the concentrations of authigenic phases of cd re u and mo increase with depth in four 45 cm long sediment box cores collected along the axis of the laurentian trough gulf of st lawrence average authigenic accumulation rates estimated from element inventories are similar to rates in other continental margin environments strong regional variations in sediment accumulation rate and sulfide concentration have little influence on the accumulation rates of cd and re this suggests that slow precipitation kinetics controls the accumulation of cd and re in these sediments the accumulation rate of authigenic u is more variable it may be tied to the kinetics of microbially mediated u reduction and be controlled by the availability of reactive organic matter authigenic mo is distinguished by a sharp subsurface concentration minimum above which mo cycles with manganese mo released to pore water upon reduction of mn oxides diffuses downward and enriches the subsurface sediment mo accumulates most rapidly in the sediment with the highest sulfide content slow conversion of molybdate to thiomolybdate may explain the much slower mo accumulation rate in the less sulfidic sediments a component of authigenic mo accumulates with pyrite in an approximately constant mo fe ratio the accumulation rate of pyrite and associated mo is insensitive to avs abundance pyrite formation may be limited by the reactivity of iron oxide minerals

use of tree rings as indicator for groundwater level drawdown caused by tunnel excavation in zhongliang mountains chongqing southwest china tunnel excavation causes geological hydrological environmental and social changes the effects of groundwater level changes caused by tunnelling on tree growth have been poorly understood dendrochronology was used to evaluate the impact of groundwater level drawdown on tree growth tree cores of masson pines were collected from the areas affected by tunnel construction in the zhongliang mountains of chongqing in south western china to study the effects of tunnel excavation on the growth rate of trees by comparing with tree cores collected from unaffected areas excavation and early operation of the first tunnel in the zhongliang mountains from 1968 to 1984 caused a groundwater table drawdown in both karst aquifer and non karst aquifer the lowered groundwater table significantly reduced the growth rate of pine trees and the low growth rate remained for 15 years the effect was experienced up to at least 1 km from the tunnel axis the decline in tree growth was higher in karst than in non karst areas though the effects on the trees of the karst areas were lagging the high precipitation in 1998 contributed to groundwater recovery after which the tree growth recovered moderately but not to the original level groundwater leakage of the recently excavated tunnels did not affect pine trees heavily probably because the pines had adapted to the new hydrogeological conditions and new strategies in tunnel inflow management were adopted in the recently excavated tunnels the use of tree growth rate as an indicator of groundwater table change in tunnelling areas offers a new option to study environmental impacts and the extent of tunnelling effects

chlorophyll a in arctic sediments implies long persistence of algal pigments abstract sediment cores were collected from the shelf slope and basin of the bering chukchi and beaufort seas during may june under ice cover and july august largely ice free 2004 measurements of chlorophyll a chl a total organic carbon toc and c n ratios were made in surface and some subsurface core increments surface sediment chl a decreased with increasing water depth significant positive correlations were found between chl a and toc and chl a and c n ratios in the basin 2000 m but there were significant negative correlations between chl a and c n ratios on the shelf 200 m chl a values generally declined in down core profiles but in some deeper slope and basin cores measurable inventories of subsurface chl a were present at depth in some cases these subsurface chlorophyll inventories coincident with peak activities of the anthropogenic radionuclide 137 cs were detected which had maximal deposition following the atmospheric nuclear weapons testing era in the 1960s a sedimentation rate independently determined for one of these cores using 210 pb was consistent with the depths of subsurface 137 cs peaks in slope sediments reflecting steady relatively undisturbed deposition over a several decade period the depth of penetration of 137 cs in some continental slope sediments together with detectable chl a suggests that chl a can be buried in some of these deeper water sediments under cold conditions for decadal periods in the absence of deposit feeders because organic deposition from the water column is episodic at high latitudes and concentrated following the spring bloom these buried sources of organic materials whether on the shelf or in deeper basin sediments may ultimately be important for benthic invertebrates that could utilize this food source during times of the year when primary production flux from the overlying water column is reduced

structurally controlled hydrothermal dolomite reservoir facies an overview structurally controlled hydrothermal dolomite htd reservoir facies and associated productive leached limestones are major hydrocarbon producers in north america and are receiving increased exploration attention globally they include multiple trends in the ordovician locally silurian and devonian of the michigan appalachian and other basins of eastern canada and the united states and in the devonian and mississippian of the western canada sedimentary basin they also occur in jurassic hosts along rifted atlantic margins in the jurassic cretaceous of the arabian gulf region and elsewhere hydrothermal dolomitization is defined as dolomitization occurring under burial conditions commonly at shallow depths by fluids typically very saline with temperature and pressure t and p higher than the ambient t and p of the host formation the latter commonly is limestone proof of a hydrothermal origin for htd reservoir facies requires integration of burial thermal history plots fluid inclusion temperature data and constraints on timing of emplacement hydrothermal dolomite reservoir facies are part of a spectrum of hydrothermal mineral deposits that include sedimentary exhalative lead zinc ore bodies and htd hosted mississippi valley type sulfide deposits all three hydrothermal deposits show a strong structural control by extensional and or strike slip wrench faults with fluid flow typically focused at transtensional and dilational structural sites and in the hanging wall transtensional sags above negative flower structures on wrench faults are favored drilling sites for htd reservoir facies saddle dolomite in both replacive and void filling modes is characteristic of htd facies for many reservoirs matrix replacive dolomite and saddle dolomite appear to have formed near contemporaneously and from the same fluid and temperature conditions the original host facies exerts a major influence on the lateral extent of dolomitization resultant textures pore type and pore volume breccias zebra fabrics shear microfractures and other rock characteristics record short term shear stress and pore fluid pressure transients particularly proximal to active faults high temperature hydrothermal pulses may alter kerogen in host limestones a process designated forced maturation basement highs underlying sandstone and or carbonate aquifers probably overpressured and overlying and internal shale seals and aquitards also may constrain or influence htd emplacement although many questions and uncertainties remain particularly in terms of mg and brine source and mass balance recognition and active exploration of the htd play continues to expand increasing use of three dimensional seismic imagery and seismic anomaly mapping combined with horizontal drilling oblique to linear trends defined by structural sags helps to reduce risk