the speciation of marine particulate iron adjacent to active and passive continental margins abstract we use synchrotron based chemical species mapping techniques to compare the speciation of suspended 1 51 m marine particulate iron collected in two open ocean environments adjacent to active and passive continental margins chemical species mapping provides speciation information for heterogeneous environmental samples and is especially good for detecting spectroscopically distinct trace minerals and species that could not be detectable by other methods the average oxidation state of marine particulate iron determined by chemical species mapping is comparable to that determined by standard bulk x ray absorption near edge structure spectroscopy using chemical species mapping we find that up to 43 of particulate fe in the northwest pacific at the depth of the adjacent active continental margin is in the fe ii state with the balance fe iii in contrast particulate iron in the eastern tropical north atlantic which receives the highest dust deposition on earth and is adjacent to a passive margin is dominated by weathered and oxidized fe compounds with fe iii contributing 90 of total iron the balance is composed primarily of fe ii containing species but we detected individual pyrite particles in some samples within an oxygen minimum zone in the upper thermocline several lines of evidence point to the adjacent mauritanian continental shelf as the source of pyrite to the water column the speciation of suspended marine particulate iron reflects the mineralogy of iron from the adjacent continental margins since the solubility of particulate iron has been shown to be a function of its speciation this may have implications for the bioavailability of particulate iron adjacent to passive compared to active continental margins

relation between depositional environment and the elemental composition of early diagenetic siderite early diagenetic siderites from marine and fresh water depositional environments are characterized by distinctive compositional trends siderite from fresh water environments is often relatively pure i e greater than 90 mol feco sub 3 and commonly attains end member composition siderite from marine environments however is always extremely impure and has extensive substitution of mg up to 41 mol and to a lesser extent ca up to 15 mol for fe in the siderite lattice in addition marine siderite generally contains less mn and has a higher mg ca ratio than fresh water siderite this compositional variation appears to result from differences in the chemistry of early marine and meteoric pore waters inasmuch as early marine pore waters generally have a higher mg sup 2 ca sup 2 ratio and contain less mn sup 2 and fe sup 2 and more ca sup 2 and mg sup 2 than meteoric waters

models of aggradation versus progradation in the himalayan foreland a frequent goal of decompaction analysis is to reconstruct histories of basin subsidence and tectonic loading in marine environments eustatic and paleobathymetric uncertainties limit the resolution of these reconstructions whereas in the terrestrial basins these ambiguities are absent it is still necessary to account for depositional slopes between localities in order to analyze three dimensional patterns of subsidence we define two end members for depositional surfaces aggradation and progradation the relative importance of either end member is a function of the interplay between the rate of net sediment accumulation and the rate of basin subsidence the models predict the patterns of major drainages transverse versus longitudinal and the way in which provenance should be reflected within different portions of a basin consequently paleocurrent and provenance data from the ancient stratigraphic record can be used to distinguish between these endmembers the subhorizontal depositional surfaces that dominate during times of aggradation provide a well defined reference frame for regional analysis of decompacted stratigraphies and related subsidence depositional slopes during progradation can not be as precisely specified and consequently yield greater uncertainties in reconstructions of subsidence these models are applied to the mio pliocene foreland basin of the northwestern himalaya where sequences of isochronous strata have been analyzed throughout the basin these time controlled data delineate a distinctive evolution from largely aggradational to largely progradational depositional geometries as deformation progressively encroaches on the foreland such a reconstruction of past depositional surfaces provides a well constrained reference frame for subsequent integration of subsidence histories from throughout the foreland

concealed thrusts in the middle gangetic plain india a ground penetrating radar study proves the truth against the geomorphic features supporting normal faulting abstract as no evidence for thrusting has yet been reported from the indo gangetic plain so the himalayan frontal thrust hft has been considered to be the southern most limit of the siwaliks to the indo gangetic plain the present study highlights the thrusting activities between the gandak and kosi megafan area in the middle gangetic plain as these thrust sheets are concealed beneath thick sediment cover direct surficial studies of the discontinuity planes are not possible further the topographic breaks formed by the backward erosion of the uplifted thrust faces resemble normal faults with hanging walls to south due to gradual decreasing upliftment and or erosion from north to south the area shows a step like topographic appearance ground penetrating radar gpr studies reveal the concealed thrust planes beneath the sediments and the topographic breaks looking like normal faults are interpreted to be the relief created by backward erosion of the thrust sheets along with the overlying sediments out of four gpr profiles taken using 100 mhz antennae three are across the topographic breaks along which most of the terminal fans are formed and one across the basement fault to study its subsurface nature initially gpr failed to strike any subsurface discontinuities at the topographic breaks however at certain distance to the south of the topographic breaks gpr was able to strike the northerly dipping subsurface discontinuity planes by combining the seismological signatures distribution of earthquake epicenters with geomorphology these discontinuities are identified as thrusts the gpr profiles show a gradual decrease of dip of the thrust planes from north to south across the area hence by the geomorphology seismological behavior topography orientation and continuity other topographic breaks can be compared with the proven thrusts gpr study on the basement fault revealed that the ne sw trending basement faults are not active in the area the compression between the south muzaffarpur fault and the peninsular shield led to the generation of the n s trending extensional hathauri simariaghat fault with downthrown block towards east due to depth penetration limit the gpr study was confined within 15 m depth the presence of the discontinuity planes up to the base of the gpr profiles indicate their continuity at least up to the base of holocene sediments although this study brought out the presence of concealed thrusts to the south of the hft more detailed work is needed further to study their depth extension relation to the basement and their implication in himalayan tectonics in a broad manner at present we consider these thrusts to be the splays of the hft for confirmation we propose to carryout detail seismic surveys in future research work

emplacement of the cuera and picos de europa imbricate system at the core of the iberian armorican arc cantabrian zone north spain new precisions concerning the timing of arc closure the final stages of the variscan orogeny mostly carboniferous in the western european variscan belt involved the development of the iberian armorican arc which is cored by the cantabrian zone nw iberia the cantabrian zone is the foreland of the western european variscan belt and it is interpreted to record the waning stages of the closure of the rheic ocean the distalmost tectonic units within the cantabrian zone the cuera unit and the picos de europa province were the last tectonic units emplaced at the core of the western european variscan belt orocline together they form an imbricate system and associated wedge top basins that are key to understanding the development of the orocline the emplacement of the cuera unit and the picos de europa province occurred in the latest pennsylvanian between moscovian and gzhelian times new detailed mapping together with stratigraphic sedimentologic and biostratigraphic data analysis of syntectonic successions and structural information constrain the timing and evolution of this imbricate system our analysis indicates that the thrust sheets were emplaced roughly perpendicular to previous tectonic units of the cantabrian variscan foreland fold and thrust belt most probably during the oroclinal bending of the sw european variscan belt that formed the iberian armorican arc the n s directed imbricate system was characterized by a shallow dip of the topographic surface 150 15 km and complex structure of the orogenic wedge are thought to result from the progressive increase in the dip of the basal decollement during bending of the underlying gondwana lithosphere and may reflect the closure of the iberian armorican arc

iron solubility driven by speciation in dust sources to the ocean particulate aerosols are thought to be the primary source of iron to the oceans but the factors determining their solubility and thus bioavailability are unclear x ray absorption analysis reveals that speciation controls the solubility of iron in three large sources of aerosol iron

hydrothermal vents as a kinetically stable source of iron sulphide bearing nanoparticles to the ocean hydrothermal vents emit metals such as iron to the ocean a chemical analysis of hydrothermal fluids suggests that up to 10 of the iron is present as stable iron bearing nanoparticles

collapse of the luzon volcanic arc during onset of arc continent collision evidence from a miocene pliocene unconformity eastern taiwan a regional miocene pliocene unconformity in the coastal range of eastern taiwan provides information about vertical motions that affected the colliding volcanic arc during initiation of arc continent collision the unconformity separates precollisional volcanic and volcaniclastic rocks of the miocene luzon arc and forearc basin from an overlying thick sequence of syncollisional pliocene pleistocene sedimentary rocks derived from the metasedimentary accretionary wedge of taiwan the duration of time represented by the unconformity averages 1 2 m y and locally ranges up to 4 m y the basal unit of the younger syncollisional sequence consists of bathyal mega slump folded mudstone pebbly mudstone and thin bedded turbidites sharp stratigraphic juxtaposition of these deep marine deposits directly above shallow marine limestone and epiclastic rocks upper part of the older arc sequence requires extremely rapid subsidence during initiation of the collisional basin the coastal range unconformity is interpreted to represent a period of latest miocene nondeposition and or erosion in the luzon arc that was related to initial subduction of the eurasian continental margin along the manila trench this period was followed in pliocene time by very rapid subsidence or collapse of the arc platform to 1 2 km water depth there are two dissimilar mechanisms of basin subsidence that may have controlled initiation of the collisional basin 1 extension rifting and crustal thinning in the luzon arc massif to form a series of small rift or pull apart subbasins or 2 flexural subsidence of oceanic lithosphere in a foreland style basin due to crustal loading in the expanding accretionary wedge of proto taiwan although data are insufficient to provide a unique solution the flexural subsidence model is supported by systematic younging of the initial subsidence event from west to east which may record eastward migration of an outer flexural bulge notable differences between the unconformity and paleogeography of the early collisional basin and analogous present day basins in the offshore region to the south suggest that arc continent collision and basin development in eastern taiwan have experienced secular change since late pliocene time

tectonic loading and subsidence of intermontane basins wyoming foreland province results of two dimensional flexural modeling of the northern bighorn and northern green river basins in the wyoming foreland province suggest that these basins formed as flexures in response to loading by basin margin uplifts and basin sedimentary sequences the northern bighorn basin subsided due to loading by the beartooth uplift along its western margin the northern green river basin developed as a result of concurrent loading by the wyoming thrust belt to the west and the wind river uplift to the east tectonic loading from basement involved uplifts played a major role in subsidence and sedimentation as evidenced by isopach patterns within each basin lithospheric flexural rigidities of 1021 to 1022 newton metres n m can adequately explain subsidence in both basins

shallow marine to fluvial transition in the siwalik succession of the kameng river section arunachal himalaya and its implication for foreland basin evolution abstract an understanding of the depositional environment and paleogeography of the siwalik foreland basin are crucial in interpreting the basin configuration sediment transport pathways and its evolutionary history this study examines the sedimentology of the siwalik succession of the kameng river valley arunachal himalaya northeastern india the facies characteristics of the fine grained well sorted sediments of the dafla formation and its complex polymodal paleocurrent pattern in this section reveals deposition in a variety of open marine to deltaic environment the overlying subansiri formation characterized by coarse grained thick multistoried sandstone and showing more consistent sw ward paleocurrent indicate deposition from a large axial braided river system the proposed redefinition of the boundary between the lower siwalik dafla and the middle siwalik subansiri formations implies their transition at around 7 5 ma instead of 10 5 ma suggested earlier the revised age of the transition is consistent with the age of arrival of the transhimalayan sediments at 7 ma and also denotes the time of marine to fluvial transition in this area presence of marine sediments in the kameng section with similar records further west indicates the existence of an extensive seaway in the eastern himalaya during the lower siwalik time the extant paleodrainage reconstructions have been recast on the basis of new data on the sedimentology and paleocurrent from this section it is inferred that the changing sea level uplifting shillong plateau and drainage evolution in the eastern himalayan foreland during the middle miocene time controlled the marine to fluvial transition in the basin

the magnitude timing and abruptness of changes in north african dust deposition over the last 20 000 yr reconstructions of eolian dust accumulation in northwest african margin sediments provide important continuous records of past changes in atmospheric circulation and aridity in the region existing records indicate dramatic changes in north african dust emissions over the last 20 ka but the limited spatial extent of these records and the lack of high resolution flux data do not allow us to determine whether changes in dust deposition occurred with similar timing magnitude and abruptness throughout northwest africa here we present new records from a meridional transect of cores stretching from 311 nt o 191n along the northwest african margin by combining grain size endmember modeling with 230 th normalized fluxes for the first time we are able to document spatial and temporal changes in dust deposition under the north african dust plume throughout the last 20 ka our results provide quantitative estimates of the magnitude of dust flux changes associated with heinrich stadial 1 the younger dryas and the african humid period ahp 11 7 5 ka offering robust targets for model based estimates of the climatic and biogeochemical impacts of past changes in north african dust emissions our data suggest that dust fluxes between 8 and 6 ka were a factor of 5 lower than average fluxes during the last 2 ka using a simple model to estimate the effects of bioturbation on dust input signals we find that our data are consistent with abrupt synchronous changes in dust fluxes in all cores at the beginning and end of the ahp the mean ages of these transitions are 11 870 2 ka 1s and 4 970 2 ka respectively

ten million year history of a thrust sheet the final deformed state of a fold and thrust belt may be reached by an infinite number of kinematic paths two end member kinematic paths are due to continuous or discontinuous rates of deformation we have used a new magnetostratigraphic section from the spanish pyrenees to calibrate the emplacement history over 10 m y of a major thrust sheet the sierras marginales thrust sheet and the deformation of both its hanging wall and footwall six time windows from before 36 5 ma until after 24 7 ma were recognized on the basis of structural and stratigraphic relationships between syntectonic strata and major structures footwall deformation of the sierras marginales thrust sheet occurred continuously on a detachment within the foreland basin sequence 4 5 km net shortening shortening rates steadily increased from 0 14 to 1 5 mm yr with time although the detachments at the base of the foreland and the detachment at the base of the sierras marginales thrust sheet were active coevally the rate of displacement on the sierras marginales detachment decayed with time and shows considerable variability emplacement of the thrust sheet may be divided into three distinct periods a rapid 13 8 km translation from 37 0 to 36 5 ma 27 6 mm yr a gradual climb of the toe of the thrust sheet up a 4 3 km long ramp across the foreland basin succession from 36 5 to 32 0 ma 0 95 mm yr and a final 8 9 km translation from 32 0 to 29 5 ma 3 56 mm yr internal deformation of the thrust sheet occurred only after it reached its present position at some time before 29 5 ma shortening rates steadily decreased from 0 6 mm yr between 29 5 and 27 8 ma to 0 26 mm yr from 27 8 until after 24 7 ma only 1 km of shortening accumulated during each of the two periods the last shortening localized on the most northerly thrust in the study area folding and subsequent faulting above the detachment beneath the foreland suggest that slip was transmitted to its tip point continuously throughout the deformation in contrast translation followed by internal deformation on the hinterland side of the toe of the sierras marginales thrust sheet indicates a successive deactivation of the southern parts of the detachment with time rate of deformation on both detachments was discontinuous and shows substantial variability about the mean in general the spatial and temporal pattern of deformation was distributed and continuous in detail however shortening was spatially and temporally discontinuous above each detachment and structures related to each one display distinctly different deformational patterns rates and styles

application of a chemical leach technique for estimating labile particulate aluminum iron and manganese in the columbia river plume and coastal waters off oregon and washington in order to determine the total concentration of bioavailable trace metals in seawater measurement of both the dissolved and labile particulate fractions is necessary comparison of labile particulate metal concentrations from various researchers is limited because of differing definitions of the fraction that is potentially available to phytoplankton on a time frame of generations a comparison experiment was conducted on coastal and riverine suspended particulate matter to determine the difference between several commonly used techniques that operationally define the labile particulate trace metal fraction furthermore we compared two leach techniques for surface transect samples from within the columbia river plume and water offshore of oregon and washington united states the particulate trace metal concentration in the leachate was determined by high resolution inductively coupled plasma mass spectrometry from this comparison one chemical leach was chosen to best define the labile particulate fraction of al fe and mn a weak acid leach 25 acetic acid at ph 2 with a mild reducing agent 0 02 m hydroxylamine hydrochloride and a short heating step 10 min 90 95 c this leach was applied to three surface transects within the columbia river plume these coastal waters were found to be rich in labile particulate trace metals that are directly delivered from the columbia river and indirectly supplied via resuspension from upwelling over a broad continental shelf

structural and sedimentological development of footwall growth synclines along an intraforeland uplift east central bighorn mountains wyoming structural sedimentological and provenance data from paleogene synorogenic deposits of the east central flank of the bighorn mountains provide new information about the development of footwall growth synclines the evolution of fault related folds and the erosional unroofing history of intraforeland uplifts three conglomerate units the upper conglomerate member of the fort union formation and the kingsbury and moncrief members of the wasatch formation are incorporated within an asymmetric east verging growth syncline in the footwall of the main range bounding thrust system three stages of footwall deformation are recorded within these conglomerates analysis of mapped progressive unconformities retrodeformed balanced cross sections and conglomerate clast composition data define these stages as part of a continuum of deformation associated with the development of footwall growth synclines development of an anticline syncline pair marked the earliest stage of growth syncline formation stage i rotation of the shared fold limb resulted in amplification of the growth syncline fine grained synorogenic sediment derived from easily eroded mesozoic mudstone bypassed the growth syncline during this stage by the end of lebo shale deposition an average of 12 1 of shortening and 6 46 km of uplift had occurred along the range margin continued growth syncline development was marked by the deposition of the kingsbury conglomerate the kingsbury conglomerate was derived from resistant middle and lower paleozoic carbonate strata in the uplifted source terrane intraformational unconformities recording as much as 55 of bed rotation were developed within the kingsbury conglomerate as fold limb rotation occurred coeval with deposition cross sections indicate that during this early stage of fault related folding an average of 16 9 shortening and 8 12 km of uplift occurred along the eastern flank of the bighorn mountains end of stage i the intermediate stage stage ii of footwall growth syncline development involved partial truncation of the growth syncline by the advancing thrust faults and deposition of the moncrief conglomerate the lower portion of the moncrief conglomerate was rotated basinward in the developing growth syncline the final stage of deformation stage iii was dominated by the thrust faulting of middle and lower paleozoic strata eastward over steeply dipping mesozoic strata and rotated eocene synorogenic conglomerate during this stage of deformation the moncrief conglomerate was deformed as the initially blind thrusts propagated into the near surface conglomerate deposits truncated the entire footwall syncline and overrode the synorogenic conglomerate package cross sections in areas where this final stage of deformation is well developed indicate that an average of 24 1 shortening and 9 7 km of uplift had occurred along the eastern margin of the bighorn mountains the caliber of synorogenic deposition in the powder river basin was linked directly to the lithologic composition of the bighorn mountains approximately half of the 3 6 km thick source stratigraphic section of the eastern bighorn mountains was eroded prior to accumulation of conglomerate the majority of this eroded material was derived from mesozoic mudstone and poorly indurated sandstone that were incapable of generating coarse detritus the first paleogene conglomerates deposited along the east central bighorn mountains therefore do not represent the initiation of laramide uplift but instead represent the exposure of coarse clast forming rock types from the lower half of the hanging wall stratigraphic section i e the mississippian madison limestone and ordovician bighorn dolomite

influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean empirical estimates for island sites in the north atlantic the results of several recent studies challenge the reigning paradigm that continental soil dust provides the only significant atmospheric source of dissolved iron to the surface ocean this evidence includes correlations between the operational solubility of aerosol iron and atmospheric loadings of black carbon and aluminum normalized vanadium and nickel each of which are associated with emissions from the combustion of fossil fuel oil these observations suggest that the relative solubility of aerosol iron hence the eolian flux of soluble iron to the surface ocean may be significantly impacted by anthropogenic oil combustion products using recent field data from the bermuda region we have developed an empirical method to estimate the solubility of aerosol iron using bulk aerosol concentrations of fe v and al we apply this method to a large body of published data from the aeroce program for north atlantic island sites on tenerife barbados bermuda and ireland where the relative proportions of anthropogenic aerosols range from minor to major respectively our aerosol iron solubility estimates suggest that anthropogenic emissions contribute approximately 70 and 85 of the annual dry deposition of soluble iron to the surface ocean near bermuda and ireland respectively implying that human activities have profoundly affected the iron budget of the north atlantic region the annual mean dry deposition of soluble iron at barbados and izana is dominated by soil dust the anthropogenic contribution at these two sites ranges from 12 to 30 and is highly dependent on the soil dust solubility of fe employed in the model the low end 12 estimate appears to be more representative of these high dust sites

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

iceberg hosted nanoparticulate fe in the southern ocean mineralogy origin dissolution kinetics and source of bioavailable fe abstract sediments from icebergs and glaciers contain nanopartculate fe iii oxyhydroxides including ferrihydrite which form in aqueous oxic micro environments where fe ii bearing rock minerals oxidise and high degrees of supersaturation are promoted by freezing and thawing an ascorbic acid extraction dissolves only labile fe present in fresh loosely aggregated ferrihydrite that is directly or indirectly bioavailable glacial and iceberg sediments contain ferrihydrite aggregates that provide 0 04 to 0 17 fe soluble in ascorbic acid rather larger than the concentrations in a limited suite of atmospheric dusts the dissolution behaviour of labile fe from glacial and iceberg sediments by ascorbic acid is controlled by the access of reactant or removal of solute through micropores to or from active sites in the interior of ferrihydrite aggregates a first order kinetic model is presented to examine the rates at which bioavailable fe can be supplied by melting icebergs in the weddell sea the model utilizes rate constants from the literature for the processes which solubilise fe from nanoparticulate ferrihydrite dissolution photochemical reduction and grazing and the processes that remove fe nanoparticulates sinking scavenging and incorporation in faecal material and render them less reactive transformation aging model results demonstrate that icebergs can supply bioavailable fe to the weddell sea by the dissolution of nanoparticulate ferrihydrite despite loss removal of nanoparticles by sinking aging transformation scavenging and incorporation into faecal pellets at rates that are comparable to atmospheric dust dissolution enhanced by photochemical reduction and grazing provides the most rapid rates of bioavailable fe production

anomalous clastic wedge development during the sevier laramide transition north american cordilleran foreland basin usa new high resolution regional correlation and isopach maps provide evidence that 1 laramide style deformation began as early as ca 77 ma in central utah and 2 rapid 208 km m y 1 and extensive 400 km progradation of a clastic wedge was facilitated by reduced subsidence during the transition from sevier to laramide style deformation this study defi nes three campanian alluvialto marine clastic wedges that traversed 200 400 km eastward across the utah colorado segment of the cordilleran foreland basin wedges a and c are thicker successions with rising trajectory shoreline stacking patterns blackhawk formation and lower castlegate sandstone bluecastle tongue and rollins sandstone that refl ect relatively slow overall progradation 50 81 km m y 1 of narrow 10 20 km wide wave dominated shorelines in contrast wedge b consists of lower volume successions with a fl at to falling shoreline stacking pattern middle castlegate sandstone sego sandstone neslen formation corcoran and cozzette members of the iles formation that suggests rapid progradation 208 km m y 1 of embayed 60 80 km wide mixed energy wave and tide infl uenced shore lines wedges a and c prograded 200 250 km in more than 3 m y whereas wedge b prograded 340 400 km in 2 m y 170 km m y 1 the anomalously extensive wedge b is unique in the utah colorado segment because of its long extent rapid progradation rate dominance of tidally infl uenced facies long transit transgressions regressions and low accommodation nested sequence architecture stratigraphic relationships indicate development of wedge b coeval with both sevier and laramide style deformation in utah assuming a constant sediment supply the extensive 300 400 km sheet like amalgamated wedge wedge b may have been caused by 1 reduced subsidence driven by a fl exural interference pattern whereby two short wavelength 200 km fl exural profi les are superimposed during the uplift of both basement cored and thin skinned thrust belt 2 an increase in or eastward migration of dynamic subsidence during tectonic transitions associated with slab fl attening or rollback i e long wavelength fl exure or 3 reduced subsidence due to short wavelength fl exural interference augmented by the reduction or migration of long wavelength fl

thrusting and gravel progradation in foreland basins a test of post thrusting gravel dispersal the use of gravels as syntectonic indicators of thrusting has recently been questioned by foreland basin models that assign gravels to a post thrusting interval of progradation except in very proximal areas on the basis of precise temporal control provided by magnetostratigraphically dated sections the history of gravel progradation after a major thrusting and uplift event in the northwestern himalaya is shown to be a virtually syntectonic phenomenon despite considerable crustal subsidence driven by a thick skinned thrust gravels prograded approximately 70 km during a 1 5 m y long thrusting event by 3 m y after the start of thrusting gravels extended more than 110 km into the basin although delayed gravel progradation appears appropriate for many rocky mountain foreland basins it is clearly not valid for the himalaya the authors attribute the difference in depositional response between these basins to difference in the quantity of sediment supplied to them sediment starved vs overfilled the availability of resistates in the source area and the size of the antecedent drainage

mineralogy as a critical factor of dust iron solubility 1 to understand the impact of dust deposition on ocean primary productivity the evaluation of dust input is not sufficient and the soluble iron supply is also needed measurements of iron in aerosols suggest a much higher solubility than in soil implying substantial atmospheric processing of chemical or physical nature here we have investigated the effect of the mineralogy on iron solubility we have measured iron solubility from some minerals commonly found in dust clay feldspar and iron hydr oxides firstly we observe a greater solubility of iron resulting from clays 4 in comparison to iron hydr oxides 1 independently of specific surface of minerals secondly by considering amount of dissolved iron and the mineralogical composition of dust our results indicate that dissolved iron fraction mainly comes from clay dissolution in contrast to that assumed in some biogeochemical models in consequence it appears that iron solubility is closely linked to the mineralogical composition of aerosol

schwertmannite in wet acid and oxic microenvironments beneath polar and polythermal glaciers glacial and iceberg sediments contain nanoparticulates of schwert mannite ferrihydrite and goethite formed where pyrite was oxidized by dissolved oxygen in aqueous subglacial environments schwertmannite typically found in acid mine drainage only forms at low ph by the oxidative weathering of pyrite stoichiometric models show that these conditions can be created in closed system microenvironments containing at least 10 4 m dissolved oxygen where volume ratios of water pyrite are 105 to 106 ferrihydrite is the only product at higher and lower volume ratios in these microenvironments the oxidation of pyrite to form schwertmannite is possible in several decades schwertmannite and ferrihydrite are metastable in contact with water and are transformed to goethite in 100 yr unless preserved in ice the presence of these nanoparticulates demonstrates the existence of transient acidic and oxic aqueous microenvironments where enhanced biochemical and or geochemical activity occurs beneath glaciers and ice sheets

late cretaceous fluvial megafan and axial river systems in the southern cordilleran foreland basin drip tank member of straight cliffs formation and adjacent strata southern utah u s a abstract the upper cretaceous lower campanian drip tank member of the straight cliffs formation in the grand staircase region of southern utah is an upward coarsening sandstone rich low sinuosity fluvial deposit in the cordilleran foreland basin the drip tank member thins from 75 m to 30 m eastward across the basin foredeep approximately parallel to its dominant eastward sediment dispersal direction and thins southward along the foredeep to as little as 17 m near its southern outcrop extent along modern cliff lines it overlies and underlies mudstone rich fluvial strata of the john henry member of the straight cliffs formation and lower member of the wahweap formation respectively both of which were deposited by northeast flowing rivers the john henry drip tank contact lies in an interfingering progradational stratigraphic transition from medium grained lenticular sandstone bodies to tabular coarse grained amalgamated sandstone bodies the contact with the overlying wahweap formation is locally a prominent surface of erosion or sediment reworking sandstone petrography and detrital zircon age populations of the strata indicate detrital sources in basement south of the foreland basin thrust sheets to the west and magmatic arc rocks to the southwest the uppermost part of the john henry member contains as much as 10 feldspar and abundant 1 84 1 60 ga detrital zircons derived from yavapai mazatzal basement rocks in the mogollon highlands the drip tank member ranges from quartzarenite to chert bearing sublitharenite with grenville 1 2 1 1 ga neoproterozoic and early paleozoic detrital zircons derived from proterozoic through jurassic strata exposed in the sevier orogenic belt lower member wahweap litharenites contain abundant thrust belt derived detrital carbonate grains absent from compositionally mature drip tank sandstones as well as a broad range of zircon ages the drip tank member constitutes deposits of a sand rich fluvial megafan or distributive fluvial system that displaced a subjacent but partly time equivalent axial fluvial system eastward as the megafan driven in part by seasonally high discharge fed by monsoonal precipitation prograded across the basin foredeep a thick amalgamated fan axis succession present in northern exposures contrasts with a thinner fan flank succession in southern localities tabular sixth order lithosomes each containing channels on the order of 7 m deep define three individual fluvial fans or fan lobes in the megafan system younger wahweap fluvial channels eroded uppermost drip tank deposits of the fan axis and fan flank transverse fan progradation across the foredeep recorded falling accommodation sediment supply in an aggradational to progradational systems tract erosion and reworking of the upper fan surface record decreased accommodation sediment bypass and erosion prior to reoccupation of the foredeep by the wahweap axial fluvial system the upper contact of the drip tank member is thus the primary sequence boundary in this multi component fluvial system and the lower wahweap represents transitional systems tract deposits accumulated as accommodation sediment supply increased

the detrital record of orogenesis a review of approaches and techniques used in the himalayan sedimentary basins the sediment archive of material eroded from an active tectonic region and stored in adjacent basins can provide a valuable record of hinterland tectonism especially when information in the source region itself is obscured by later metamorphism or removed by tectonism or erosion using the sediment record to document tectonism is a well established approach but more recently there has been a burgeoning of the number of isotopic techniques which can be applied to detrital material in particular single grain analyses thus the scope for application of detrital studies to a number of different tectonic problems has widened considerably in this review the example of sediments eroded from the himalayan orogen and preserved in the suture zone basin foreland basin remnant ocean basins and deep sea fans is used to illustrate the approach techniques as diverse as petrography heavy mineral xrf and sr nd studies single grain dating by ar ar u pb and fission track methodologies and single grain sm nd and pb isotopic analyses are described the paper documents how the sediment record can be used to determine the thermal and tectonic evolution of the orogen constrain mechanisms of continental deformation exhumation rates and palaeodrainage

contrasting tectonic and sedimentary history of the central and eastern parts of the polish carpathian foredeep basin results of seismic data interpretation polish carpathian foredeep basin pcfb is located at the junction between western and eastern european platforms such location caused different evolution of various parts of this basin in the central part of the pcfb growth fault propagation folds related to latest badenian stages of thrusting in this segment of the carpathians developed only minor normal faulting related to miocene reactivation of older basement faults was detected paleovalleys mapped within the mesozoic basement were interpreted as palaeogene tectonically controlled erosional features developed after inversion of the polish trough in the central pcfb post evaporitic sediments were supplied into the foredeep basin from south from the eroded carpathians in the eastern part of the pcfb a system of large normal faults related to miocene flexure induced reactivation of inherited mesozoic faults was identified within the hangingwall of this system reverse faults rotated blocks and basement pop up structures were described their formation was related to combined effect of compressional stresses transferred from the carpathian collision zone and reactivation of older large scale fault caused by both flexural extension and strike slip movements during deposition of the miocene foredeep sediments differential compaction also played an important role gentle onlap of the middle badenian evaporites by post evaporitic sediments towards the nw was interpreted as a result of tectonically driven relative sea level rise and re establishment of marine connections with eastern paratethys

short term sediment accumulation rates determined from eocene alluvial paleosols a new method uses alluvial paleosols to calculate sediment accumulation rates for thin 25 m stratigraphic intervals and allows the reliable interpolation of ages for stratigraphic levels within a thick stratigraphic interval bounded by established dates sediment accumulation rates calculated for a 650 m composite section in the eocene willwood formation of wyoming span time intervals ranging from only 0 05 to 0 25 m y important sedimentologic changes coincide with changes in accumulation rate and indicate close and direct relations between the history of basin subsidence and depositional patterns

redox conditions and trace metal cycling in coastal sediments from the maritime antarctic abstract redox sensitive trace metals mn fe u mo re nutrients and terminal metabolic products no 3 nh 4 po 4 3 total alkalinity were investigated for the first time in pore waters of antarctic coastal sediments the results of this study reveal a high spatial variability in redox conditions in surface sediments from potter cove king george island western antarctic peninsula particularly in the shallower areas of the bay the significant correlation between sulphate depletion and total alkalinity the inorganic product of terminal metabolism indicates sulphate reduction to be the major pathway of organic matter mineralisation in contrast dissimilatory metal oxide reduction seems to be prevailing in the newly ice free areas and the deeper troughs where concentrations of dissolved iron of up to 700 m were found we suggest a combination of several factors to be responsible for the domination of metal oxide reduction over sulphate reduction in these areas these include the increased accumulation of fine grained material with high amounts of reducible metal oxides a reduced availability of metabolisable organic matter and an enhanced physical and biological disturbance by bottom water currents ice scouring and burrowing organisms based on modelled iron fluxes we calculate the contribution of the antarctic shelf to the pool of potentially bioavailable iron feb to be 6 9 103 to 790 103 t yr 1 consequently these shelf sediments would provide an feb flux of 0 35 39 5 mg m 2 yr 1 median 3 8 mg m 2 yr 1 to the southern ocean this contribution is in the same order of magnitude as the flux provided by icebergs and significantly higher than the input by aeolian dust for this reason suboxic shelf sediments form a key source of iron for the high nutrient low chlorophyll hnlc areas of the southern ocean this source may become even more important in the future due to rising temperatures at the wap accompanied by enhanced glacier retreat and the accumulation of melt water derived iron rich material on the shelf

timing of deformation in overthrust belt and foreland of idaho wyoming and utah a review of the timing and displacement evidence of the major structures of the western wyoming overthrust belt and foreland shows there is a progression in thrust displacement apparent duration of motion and palinspastic position of thrust traces from west to east those toward the west moved farther for an apparently longer period of time and are more widely spaced in their restored positions than those toward the east however average thrust velocities are all on the order of 0 5 0 5 cm yr 0 2 in yr foreland events are in part synchronous with thrust belt events and had an effect on them although dating precision varies widely on major normal faults present evidence does not contradict the generally held view that all normal faults postdate the youngest thrusting

collapsibility and seismic settlement of loess loess collapsibility and seismic settlement have proven to be costly geotechnical hazards in china since collapsibility assessment and mitigation are now conventional practices in chinese design codes some previous efforts have been made to relate collapsibility and seismic settlement in order to simplify assessment of the latter however these works have neglected mechanical difference between the two phenomena in this study the similarity and difference between collapsibility and seismic settlement of loess are analyzed which shows that both are based on the metastable microstructure of loess but their triggering mechanisms are different collapsibility is primarily driven by suction loss whereas seismic settlement is caused by shear failure of the loess matrix during dynamic loading though both of them result in collapse of trellis structure pores consequently the lack of a common mechanism demonstrates there is no tenable physical basis to relate collapsibility and seismic settlement

evolving alluvial stratigraphy and thrust front development in the west jaca piggyback basin spanish pyrenees in the southwestern pyrenees distinctive alluvial mega sequences correlate with the development of a shallow mountain front thrust structure the pena flexure the flexure evolved during the oligocene to early miocene and is interpreted as a duplex marking the limit of thrust front advance three main depositional facies preserved completely across the pena flexure are described a pre thrust emergence high sinuosity fluvial sequence the c 2300 m thick sheet sandstone facies of the campodarbe formation a syn thrust emergence conglomeratic alluvial fan sequence the c 1100 m thick conglomeratic facies of the bernues formation and a post thrust emergence low sinuosity fluvial sequence the 700 m thick ribbon sandstone facies of the uncastillo formation collectively their continuous exposure across the pena flexure provides a more or less complete record of the sedimentary evolution of a mountain front syn deformational features in the alluvial fan sequence of the bernues formation and marked contrasts in palaeochannel morphology sandstone body geometry and palaeocurrent patterns between the two fluvial sequences are best understood by invoking a strong tectonic control over their deposition an increased rate of vertical sediment accretion was a key process in determining fluvial style the onset of major thrusting led to more rapid basin floor subsidence thereby promoting a change from lateral to vertical accretion as channels responded to the rising base level

tectonic control on coarse grained foreland basin sequences an example from the cordilleran foreland basin utah newly released reflection seismic and borehole data combined with sedimentological provenance and biostratigraphic data from upper cretaceous paleocene strata in the proximal part of the cordilleran foreland basin system in utah establish the nature of tectonic controls on stratigraphic sequences in the proximal to distal foreland basin during campanian time coarse grained sand and gravel were derived from the internally shortening charleston nebo salient of the sevier thrust belt a rapid regional campanian progradational event in the distal foreland basin 200 km from the thrust belt in 8 m y can be tied directly to active thrust generated growth structures and an influx of quartzose detritus derived from the charleston nebo salient eustatic sea level variation exerted a minimal role in sequence progradation

evolution of miocene fluvial environments eastern potwar plateau northern pakistan the miocene pliocene siwalik group records changing fluvial environments in the himalayan foreland basin the nagri and dhok pathan formations of this group in the eastern potwar plateau northern pakistan comprise relatively thick tens of metres sandstone bodies and mudstones that contain thinner sandstone bodies metres thick and palaeosols thick sandstone bodies extend for kilometres normal to palaeoflow and are composed of large scale stratasets storeys stacked laterally and vertically adjacent to each other sandstone bodies represent single or superimposed braided channel belts and large scale stratasets represent channel bars and fills channel belts had widths of km bankfull discharges on the order of 103 cumecs and braiding parameter up to about 3 individual channel segments had bankfull widths maximum depths and slopes on the order of 102 m 101 m and 10 4 respectively and sinuosities around 1 1 these rivers are comparable to many of those flowing over the megafans of the modern indo gangetic basin and a similar depositional setting is likely thin sandstone bodies within mudstone sequences extend laterally for on the order of 102 m and have lobe wedge sheet and channel form geometries they represent crevasse splays levees and floodplain channels mudstones are relatively bioturbated disrupted and represent mainly floodbasin and lacustrine deposition mudstones and sandstones are extremely disrupted in places showing evidence of prolonged pedogenesis these mature palaeosols are m thick and extend laterally for km lateral and vertical variations in the nature of their horizons apparently depend mainly on deposition rate the 500 m thick nagri formation has a greater proportion and thicker sandstone bodies than the overlying 700 m thick dhok pathan formation the thick sandstone bodies and their large scale stratasets thicken and coarsen through the nagri formation then thin and fine at the base of the dhok pathan formation compacted deposition rates increase with sandstone proportion 0 53 mm year for nagri 0 24 mm year for dhok pathan and palaeosols are not as well developed where deposition rates are high within both formations there are 100 m scale variations representing on the order of 105 years in the proportion and thickness of thick sandstone bodies and tens of m scale alternations of thick sandstone bodies and mudstone sandstone strata that represent on the order of 104 years formation scale stratal variations extend across the potwar plateau for at least 100 km although they may be diachronous however 100 m and smaller scale variations can only be traced laterally for up to tens of km alluvial architecture models indicate that increases in the proportion and thickness of thick sandstone bodies can be explained by increasing channel belt sizes mainly average deposition rate and avulsion frequency on a megafan comparable in size to modern examples 100 m scale variations in thick sandstone body proportion and thickness could result from regional shifts in the position of major channels possibly associated with fan lobes on a single megafan or with separate megafans however such variations could also be related to local changes in subsidence rate or changes in sediment supply to the megafan system formation scale and 100 m scale stratal variations are probably associated with interelated changes in tectonic uplift sediment supply and basin subsidence increased rates of hinterland uplift sediment supply and basin subsidence recorded by the nagri formation may have resulted in diversion of a relatively large river to the area alternatively changing river sizes and sediment supply rates may be related to climate changes affecting the hinterland possibly linked to tectonic uplift climate during deposition of the siwalik group was monsoonal although the deposits contain no direct evidence for climate change independent evidence indicates global cooling throughout the miocene and the possibility of glacial periods e g around 10 8 ma corresponding to base of nagri formation if the higher himalayas were periodically glaciated a mechanism would exist for varying sediment supply to megafans on time scales of 104 105 years although eustatic sea level changes are related to global climatic change they are not directly related to siwalik stratigraphic changes because the shoreline was many 100 km away during the miocene

tertiary provenance history of the northern and central altiplano central andes bolivia a detrital record of plateau margin tectonics abstract the internally drained altiplano plateau in the high elevation hinterland of the central andes contains an extremely thick up to 12 km succession of tertiary nonmarine strata that recorded the topographic evolution of eastern and western plateau margins in this study temporal and spatial variations in detrital composition based on 113 sandstone thin sections and 31 conglomerate clast counts combined with sediment dispersal patterns and regional stratigraphic correlations help delineate the tertiary history of altiplano basin development in relationship to thrust deformation and arc magmatism along plateau margins stratigraphic and provenance data suggest limited subsidence and west directed sediment dispersal during the early tertiary history of the altiplano region by late eocene time development of a rapidly subsiding basin probable foredeep was underway as recorded by extensive east directed fluvial systems of the 3 6 5 km thick potoco formation potoco compositional data are compatible with sediment sources in the incipient western cordillera and regions farther west including 1 a probable thrust belt source terrane composed of paleozoic mesozoic strata and precambrian granitic gneissic basement and 2 a subordinate magmatic arc source terrane composed of tertiary volcanic rocks increased abundances of plagioclase grains and volcanic lithic fragments upsection indicate a progressively greater arc influence due to either enhanced volcanism or eastward arc migration by late oligocene time west directed fluvial and alluvial fan systems of the upper potoco formation and the 3 km thick coniri formation reached the altiplano basin providing a minimum uplift age for the backthrust belt along the western flank of the eastern cordillera paleozoic clast conglomerate and relatively quartz rich sandstone containing sedimentary and metasedimentary lithic fragments show unroofing of predominantly paleozoic strata in the backthrust belt continued late oligocene to quaternary accumulation in the altiplano reveals that the basin persisted as a depositional region during a well documented period of neogene shortening and uplift in the andean thrust belt farther east this intra orogenic hinterland deposition between eastern and western highs during ongoing shortening suggests that the altiplano basin existed as a crustal scale piggyback basin possibly in an internally drained plateau like geomorphic setting since 25 ma provenance data and independent structural and thermochronological evidence for spatially and temporally varying tectonic histories along the eastern and western plateau margins imply that several modes of basin development were active during growth of the altiplano although flexural subsidence due to thrust loading along both plateau margins initially in the west and subsequently in the east may explain most tertiary subsidence possible closed basin conditions due to structural damming could have promoted additional sediment accumulation from late oligocene to quaternary time

exotic conglomerates of the neogene siwalik succession and their implications for the tectonic and topographic evolution of the western himalaya

the shelf to basin iron shuttle in the black sea revisited continental shelf sediments are a major source of iron fe for phytoplankton in surface waters in this study we investigate the mechanisms that control release of fe from shelf sediments and its lateral transport shuttling in oxic and hypoxic waters on the northwestern black sea shelf we find that at two coastal stations near the outflow of the danube river high input of organic matter drives strong reductive dissolution of fe oxyhydr oxides henceforth termed fe oxides in surface sediments supporting high rates of fe release to oxygenated bottom waters 0 36 mmol m 2 d 1 we suggest that bioirrigation plays a key role in the release of fe from these sediments at four stations further offshore organic matter deposition is lower resulting in limited mobilization of fe2 in the sediment and low benthic fluxes of fe 0 2 m in the lower part of the water column likely through repeated deposition and resuspension of fe oxides from surface sediments using synchrotron based x ray spectroscopy and sequential chemical extractions we demonstrate that the suspended matter and surface sediments are enriched in easily reducible fe oxides mostly ferrihydrite and fe associated with clay the mobilization of fe in the coastal zone and subsequent lateral transport of these fe bearing particles results in higher ratios of fe al in surface sediments at outer shelf stations ca 1 2 to 2 wt wt 1 than at coastal stations ca 0 5 to 0 9 wt wt 1 however below the sediment surface layer fe al ratios are similar at all stations indicating limited burial of the laterally transported fe our results highlight the critical role of organic matter input associated biological activity and riverine fe input as drivers of fe shuttling on continental shelves we also show that in shelf areas where sediments receive low inputs of organic matter physical transport controls the ultimate fate of the shuttled fe

impact of anthropogenic combustion emissions on the fractional solubility of aerosol iron evidence from the sargasso sea we report empirical estimates of the fractional solubility of aerosol iron over the sargasso sea during periods characterized by high concentrations of saharan dust summer 2003 and by low concentrations of aerosols in north american maritime north atlantic air masses spring 2004 and early summer 2004 we observed a strong inverse relationship between the operational solubility of aerosol iron defined using a flow through deionized water leaching protocol and the total concentration of aerosol iron whereby the operational solubility of aerosol iron was elevated when total aerosol iron loadings were low this relationship is consistent with source dependent differences in the solubility characteristics of our aerosol samples and can be described by a simple mixing model wherein bulk aerosols represent a conservative mixture of two air mass end members that carry different aerosol types saharan air which contains a relatively high loading of aerosol iron 27 8 nmol fe m 3 that has a low fractional solubility 0 44 and north american air which contains a relatively low concentration of aerosol iron 0 5 nmol fe m 3 that has a high fractional solubility 19 historical data for aerosols collected on bermuda indicate that the low iron loadings associated with north american air masses are typically accompanied by elevated v al fe al and v mn mass ratios in the bulk aerosol relative to saharan dust which are indicative of anthropogenic fuel combustion products the identification of similar compositional trends in our sargasso sea aerosol samples leads us to suggest that the elevated solubility of iron in the aerosols associated with north american air masses reflects the presence of anthropogenic combustion products which contain iron that is readily soluble relative to iron in saharan soil dust we thus propose that the source dependent composition of aerosol particles specifically the relative proportion of anthropogenic combustion products is a primary determinant for the fractional solubility of aerosol iron over the sargasso sea this hypothesis implies that anthropogenic combustion emissions could play a significant role in determining the atmospheric input of soluble iron to the surface ocean

holocene tectono geomorphic evolution of parts of the upper and middle gangetic plains india abstract using multispectral scanning mss images and digital elevation models dems 26 terrain morphological units were delineated in the study area between the rapti and kosi rivers in the gangetic plains based on the degree of soil development and the infrared stimulated luminescence chronology these terrain morphological units have been grouped into six members of a morphostratigraphic sequence with ages 1 65 1 65 5 3 5 3 7 5 7 5 8 5 8 5 10 and 10 ka integrated use of geomorphic markers including different drainage patterns identified from mss images significant breaks in topographic profiles terminal fans and artifact terrain features e g cliffs and significant breaks in slopes in dems digital terrain models dtms with highly exaggerated vertical dimensions were made to infer and map 20 nascent faults in the region between the ghaghara and kosi rivers in the flat gangetic plains the three major tectonic blocks are the upland ghaghara rapti block of the upper gangetic plain and the rapti gandak and gandak kosi blocks of the middle gangetic plain marked by high rates of subsidence and sedimentation the ghaghara rapti block bounded by the incised ghaghara and rapti rivers is an upland region and is primarily overlain by 10 ka old soils subsequent activity along the ne sw trending transverse normal faults led to deposition of young terminal fans southward tilt of the ghaghara rapti block generated two e w trending terraces on the left bank of the ghaghara river southwestward tilting of the upper part of the ghaghara rapti block led to development of the widest old ghaghara plain and rapti floodplain in the sw direction northeastward tilting of the rapti gandak block shifted the gandak river from west to east over a distance of 80 km during the period from 10 to 8 5 ka further compression from the sw caused development of four extensional normal faults the activity of three faults between 5 7 and 1 0 ka generated four terminal alluvial fans on this block the gandak kosi block is marked by a set of seven thrust splays off the himalayan frontal thrust hft in the footwall activity of these thrust splays in the foothill region caused progradation of the gravel piedmont and thus developed the widest piedmont zone 124 km in the gangetic plains this is the first report of gravel piedmont progradation from a modern environment and role of thrust splays in such a progradation in the southernmost part of this block the continuous occurrence of terminal fans over a length of 140 km south of the south muzaffarpur fault forms a terminal fan piedmont bajada orientation of the faults was used to interpret compression from the sw in the ghaghara rapti interfluve plain in the west since 10 ka and compression from the south in the gandak kosi interfan region in the east after 4 5 ka the rapti gandak region in the central part shows the effects of mainly compression from the sw and compression from the south at different times in addition to terminal fans formed because of low relief terrain features created by the activity of faults by involvement of the entire discharge of small meandering braided streams a new type of fan formed by splays from a large river on the downthrown sides of faults called splay terminal fans is observed from the rapti gandak block

the transition from passive to active margin sedimentation in the cantabrian mountains northern spain devonian or carboniferous abstract in the cantabrian mountains of northern spain a cambrian through pennsylvanian sedimentary succession is preserved that was deformed during the hercynian orogenic cycle within this succession silurian and devonian strata indicate sedimentation on a passive margin pennsylvanian deposits are the product of syndeformational uplift and erosion of the newly forming orogen and were deposited in a rapidly filling foreland basin in front of the orogenic belt the intervening mississippian succession is strongly condensed and consists of coarse grained sandstones mantling a regional angular unconformity crinoidal limestones followed by phosphatic black shales nodular limestones and siliceous shales this succession shows abundant erosional surfaces and mass flow deposits and it is here interpreted as the initial starved foreland basin fill if this interpretation is correct the foreland basin system had already developed during the late devonian much earlier than hitherto assumed its initiation can be correlated to processes in the internal zones of the iberian hercynian orogen where during the late devonian there is the change from subduction of oceanic lithosphere to intended continental subduction its blocking and the subsequent collisional type deformation as a direct long distance effect of these changes in the plate tectonic regime the cantabrian hercynian foreland basin was created

beyond the black sea paradigm the sedimentary fingerprint of an open marine iron shuttle we present iron fe concentration and fe isotope data for a sediment core transect across the peru upwelling area which hosts one of the ocean s most pronounced oxygen minimum zones omzs the lateral progression of total fe to aluminum ratios fet al across the continental margin indicates that sediments within the omz are depleted in fe whereas sediments below the omz are enriched in fe relative to the lithogenic background rates of fe loss within the omz as inferred from fet al ratios and sedimentation rates are in agreement with benthic flux data that were calculated from pore water concentration gradients the mass of fe lost from sediments within the omz is within the same order of magnitude as the mass of fe accumulating below the omz taken together our data are in agreement with a shuttle scenario where fe is reductively remobilized from sediments within the omz laterally transported within the anoxic water column and re precipitated within the more oxic water below the omz sediments within the omz have increased 56fe 54fe isotope ratios relative to the lithogenic background which is consistent with the general notion of benthic release of dissolved fe with a relatively low 56fe 54fe isotope ratio the fe isotope ratios increase across the margin and the highest values coincide with the greatest fe enrichment in sediments below the omz the apparent mismatch in isotope composition between the fe that is released within the omz and fe that is re precipitated below the omz implies that only a fraction of the sediment derived fe is retained near shore whereas another fraction is transported further offshore we suggest that a similar open marine shuttle is likely to operate along many ocean margins the observed sedimentary fingerprint of the open marine fe shuttle differs from a related transport mechanism in isolated euxinic basins e g the black sea where the laterally supplied reactive fe is quantitatively captured within the basin sediments we suggest that our findings are useful to identify omz type fe cycling in the geological record

chemical and physical characteristics of iron oxides in riverine and glacial meltwater sediments abstract the speciation and grain size distribution of iron have been examined in several riverine and glacial sediments in order to evaluate controls on the concentrations and modes of occurrence of iron oxides in weathering derived particulates three operationally defined fractions have been recognised relating to the reactivity of iron towards dissolved sulphide 1 highly reactive iron fe hr consisting of ferric oxides 2 poorly reactive iron fe pr consisting of magnetite and some sheet silicate iron and 3 unreactive residual silicate iron fe u the finer fractions of each riverine and glacial suite are enriched in fe hr and usually also have higher fe hr fet ratios however coarser fractions may also have elevated fe hr contents and relationships of fe hr to both surface area and al indicate that iron oxides dominantly occur in association with the surfaces of aluminosilicate minerals which are common in finer grained fractions but may also be relatively enriched in coarser fractions a similar range of fe hr surface loadings is evident in the riverine and glacial meltwater suites from 0 6 to 1 8 mg fe m 2 for the riverine sediments and 0 5 to 1 5 mg fe m 2 for the glacial meltwater sediments despite wide variations in catchment bedrock lithology and climatic conditions significantly lower iron oxide loadings 0 1 mg fe m 2 were found in subglacial sediments most fe hr is closely associated with organic c although the latter occurs as blebs or smears rather than continuous coatings e g ransom et al 1997 ransom b bennett r h baerwald r shea k 1997 tem study of in situ organic matter on continental margins occurrence and the monolayer hypothesis mar geol 138 1 9 electron microscope observations show that iron oxides may occur as nanoparticulate 10 20 nm spheres at the edges of sheet aluminosilicate minerals as crystalline oxides infilling surface pits in coarser grained aluminosilicate minerals and occasionally as discrete crystalline oxides the similar occurrences of iron oxides in both riverine and glacial environments indicates that the delivery of reactive iron oxides to the oceans during glacial interglacial cycles will be affected by the masses and grain size characteristics of sediments delivered by glacial and riverine fluxes rather than by differences in iron mineralogy these delivery rates will be modified by behaviour of the oxide nanoparticles during transport from the continents

biogenic iron oxyhydroxide formation at mid ocean ridge hydrothermal vents juan de fuca ridge here we examine fe speciation within fe encrusted biofilms formed during 2 month seafloor incubations of sulfide mineral assemblages at the main endeavor segment of the juan de fuca ridge the biofilms were distributed heterogeneously across the surface of the incubated sulfide and composed primarily of particles with a twisted stalk morphology resembling those produced by some aerobic fe oxidizing microorganisms our objectives were to determine the form of biofilm associated fe and identify the sulfide minerals associated with microbial growth we used micro focused synchrotron radiation x ray fluorescence mapping mu xrf x ray absorption spectroscopy mu exafs and x ray diffraction mu xrd in conjunction with focused ion beam fib sectioning and highresolution transmission electron microscopy hrtem the chemical and mineralogical composition of an fe encrusted biofilm was queried at different spatial scales and the spatial relationship between primary sulfide and secondary oxyhydroxide minerals was resolved the fe encrusted biofilms formed preferentially at pyrrhotite rich fe1 xs 0 x 0 2 regions of the incubated chimney sulfide at the nanometer spatial scale particles within the biofilm exhibiting lattice fringing and diffraction patterns consistent with 2 line ferrihydrite were identified infrequently at the micron spatial scale fe mu exafs spectroscopy and mu xrd measurements indicate that the dominant form of biofilm fe is a short range ordered fe oxyhydroxide characterized by pervasive edge sharing fe o6 octahedral linkages double corner sharing fe o6 linkages which are common to fe oxyhydroxide mineral structures of 2 line ferrihydrite 6 line ferrihydrite and goethite were not detected in the biogenic iron oxyhydroxide bio the suspended development of the bio mineral structure is consistent with fe iii hydrolysis and polymerization in the presence of high concentrations of fe complexing ligands we hypothesize that microbiologically produced fe complexing ligands may play critical roles in both the delivery of fe ii to oxidases and the limited fe iii oxyhydroxide crystallinity observed within the biofilm our research provides insight into the structure and formation of naturally occurring microbiologically produced fe oxyhydroxide minerals in the deep sea we describe the initiation of microbial seafloor weathering and the morphological and mineralogical signals that result from that process our observations provide a starting point from which progressively older and more extensively weathered seafloor sulfide minerals may be examined with the ultimate goal of improved interpretation of ancient microbial processes and associated biological signatures

a critical look at iron paleoredox proxies new insights from modern euxinic marine basins enrichments in reactive iron occur under euxinic marine conditions that is where dissolved sulfide is present in the water column these enrichments result primarily from the export of remobilized iron from the oxic shelf which is scavenged from the euxinic water column during syngenetic pyrite formation and deposited in the underlying sediments strongly elevated ratios of highly reactive iron to total iron fehr fet and total iron to aluminum fet al and high degrees of pyritization dop are each products of this enrichment process these paleoredox proxies are among the most faithful recorders of ancient euxinia contrary to previous arguments iron enrichment is decoupled from biogenic sediment inputs but it does appear to be a uniquely euxinic phenomenon in other words we can rule out a major contribution from preferential physical transport of fehr rich detrital sediment to the deep basin which could also operate under oxic conditions furthermore enrichment via the shuttling of iron remobilized from oxic shelves appears to be limited by inefficient transport and trapping processes in deep oxic basins elevated fet al ratios in the euxinic sediments also cannot be a product of internal enhancement of the reactivity of the detrital iron pool without net fehr addition these conclusions are supported by observations in the modern black sea orca basin and effingham inlet fet al ratios are unambiguous recorders of paleoredox even in sediments that have experienced high degrees of metamorphic alteration however this study suggests that high siliciclastic accumulation rates can swamp the enrichment mechanism resulting in only intermediate dop values for euxinic sediments and fet al ratios that mimic the oxic shelf such dilution effects are well expressed in black sea basinal turbidites and rapidly accumulating muds on euxinic basin margins under conditions of persistent euxinia varying extents of fehr enrichment can illuminate spatial and temporal gradients in siliciclastic sedimentation the magnitude of enrichment is a function of the source shelf to sink ocean basin areal ratio suggesting that iron proxies can also record ocean scale paleoenvironmental properties through muted enrichments at times of very widespread euxinia for the first time manganese data are interpreted in light of the redox shuttle model as for the iron data the black sea orca basin and effingham inlet show enrichments in total manganese in the deep euxinic basin suggesting export from the suboxic porewaters of the oxic shelf and scavenging and burial in the basin the black sea data reveal iron and manganese enrichment across the broad deep euxinic basin suggesting efficient lateral transport and deep water mixing tied to the physical properties of the water column

geochemical characteristics and organic matter enrichment mechanism of black shale in the upper triassic xujiahe formation in the sichuan basin implications for paleoweathering provenance and tectonic setting abstract the first third and fifth members henceforth referred to as t 3 x 1 t 3 x 3 and t 3 x 5 respectively of the upper triassic coal bearing xujiahe formation black shale are among the most significant hydrocarbon source rocks in the sichuan basin here we present geochemical data for the upper triassic black shales from core from well ld 1 to determine their paleoenvironmental conditions paleoweathering provenance transitions and tectonic setting the v v ni vs u th v cr vs u th and ni co vs u th bivariate plots and the tfe toc ts total fe total organic carbon total sulphur ternary diagram indicate that the synsedimentary redox regime of almost all the shale samples was oxidizing ba al sr al and p ti data combined with quantitative biogenic ba data indicate that moderate high primary paleoproductivity levels prevailed during deposition the sr cu ratio and c value combined with the sedimentary features are indicative of warm humid climate conditions the ti al deposition rate proxy and decompacted sedimentation rate are positively correlated with the total organic carbon toc content according to our multiproxy approach black shale development in the xujiahe formation was mainly controlled by the primary productivity level foreland basin setting high tectonic subsidence and sedimentation rate and exhibited a limited correlation with water column redox conditions through the compilation and calculation of various weathering indices for the xujiahe black shale we suggest that caution must be taken when inferring paleoclimate characteristics based on the chemical index of alteration cia because of the influence of multiple nonweathering factors provenance sensitive elemental ratios th sc vs zr sc and co th vs la sc indicate that the clastic contribution to xujiahe black shales was of a predominantly felsic character the black shales exhibit a transition from t 3 x 1 to t 3 x 3 to t 3 x 5 whereby t 3 x 1 was primarily sourced from the proterozoic to early paleozoic strata of the qinling orogeny t 3 x 3 was primarily sourced from the neoproterozoic complex in the longmen shan and t 3 x 5 was primarily sourced from the songpan ganzi flysch strata which contributed recycled material because of folding and strong southeastward thrusting

thrust loads and foreland basin evolution cretaceous western united states two dimensional modeling of loading during the formation of the idaho wyoming thrust belt shows that regional isostatic compensation by flexure of an elastic lithosphere is sufficient to control the formation of a foreland basin the flexural rigidity of the lithosphere is inferred to have been approximately 1023 nm 1030 dyne cm on the basis of palinspastic comparison of predicted downwarping due to the thrust plate loads to the shape of the sedimentary wedge on the west side of the cretaceous western interior seaway erosion of part of the uplifted thrust plates redistributed the load depositing it farther to the east thereby causing subsidence over a much wider area than could have been accomplished only by the loading by thrust plates paleotopography after major cretaceous thrust events was calculated the resulting mountainous terrain gentle alluvial plain and flat sea floor correspond well with the topography of the modern foreland thrust belt and basin system in the andes of south america and to paleogeographic reconstructions in the western united states thrust belt topography is controlled by the subsurface geometry of the thrust faults particularly the positions of ramp zones and by isostatic subsidence

intensive mixing along an island chain controls oceanic biogeochemical cycles 1 the subarctic pacific is a high nutrient low chlorophyll hnlc region in which phytoplankton growth is broadly limited by iron fe availability however even with fe limitation the western subarctic pacific wsp has significant phytoplankton growth and greater seasonal variability in lower trophic levels than the eastern subarctic pacific therefore differences in fe supply must explain the west to east decrease in seasonal phytoplankton growth the fe flux to the euphotic zone in the wsp occurs at a moderate value in that it is significantly higher than its value on the eastern side yet it is not sufficient enough to cause widespread macronutrient depletion that is hnlc status is maintained although we recognize several fe supply processes in the wsp the mechanisms that account for this moderate value of fe supply have not previously been explained here we demonstrate the pivotal role of tidal mixing in the kuril islands chain kic for determining the moderate value a basin scale meridional fe section shows that fe derived from sediments in the sea of okhotsk is discharged through the kic into the intermediate water masses 800 m of the western north pacific the redistribution of this fe rich intermediate water by intensive mixing as it crosses the kic is the predominant process determining the ratio of micronutrient fe to macronutrients e g nitrate in subsurface waters this ratio can quantitatively explain the differences in surface macronutrient consumption between the western and eastern subarctic as well as the general formation and biogeochemistry of hnlc waters of the subarctic north pacific

climatic tectonic and volcanic controls of sediment supply to an oligocene foredeep basin the val d aveto formation northern italian apennines abstract the val d aveto formation is a turbidite sequence deposited in the northern apennines during the oligocene 32 29 ma the occurrence of calcareous siliciclastic volcaniclastic and carbonatoclastic deposits makes the val d aveto formation a natural laboratory to study the interplay among climate tectonics and volcanism in a subduction related context eight logs have been studied in order to reconstruct the stratigraphic architecture of the succession ten different facies one limestone senso lato facies four siliciclastic facies four volcaniclastic facies and one carbonatoclastic facies have been recognized on the basis of their different sedimentary features microtextures and matrix compositions through thin section analysis and x ray powder diffraction for the first time syn volcanic facies pyroclastic density current and epiclastic deposits have been distinguished from post volcanic facies in the volcaniclastic facies compositional trends of sandy to muddy detritus together with image analyses on gravel dimensions highlight spatial and temporal persistence of the syn depositional volcanic activity across the source to sink system lithological and petrographic analyses on the gravel size fraction of the siliciclastic and volcaniclastic detritus point out a se france provenance and reveal the strong influence that tectonics has on sediment production the comparison between the geodynamic evolution of the source area and the stratigraphic evolution of the val d aveto formation can help unravel the importance of climate on the redistribution of tectonically produced sediments and shaping of the resulting submarine fan

sequential late cenozoic structural disruption of the northern himalayan foredeep chronologies for the siwalik molasse and intermontane basins along the southern margin of the himalaya and hindu kush ranges constrain the timing and pattern of facies migration and structural disruption of the indo gangetic foredeep this synthesis indicates that quiescent intervals are punctuated by pulses of rapid deformation as thrusting migrates in a stepwise fashion across the foredeep

two phase stratigraphic model of foreland basin sequences application of flexural models to nonmarine foreland basin evolution indicates that two different stratigraphic styles of basin fill may develop over time basin subsidence is most rapid during times of thrust load emplacement associated sedimentation is coarse grained immediately adjacent to the thrust front and grades rapidly into fine grained deposits that cover most of the basin the distal part of the basin may also contain deposits derived from streams that flow from beyond the basin toward the thrust belt subsequent removal of the thrust load by erosion and other processes results in flexural rebound of the thrust belt and adjacent foreland basin during this postorogenic phase of adjustment a regional unconformity develops in the proximal part of the foreland basin proximal deposits along with thrust derived sediment are redeposited in the distal foreland basin and beyond this two phase model of foreland sedimentation predicts that coarsening upward sequences in the proximal and distal parts of the basin have reciprocal significance the proximal sequence represents thrust belt advance whereas the distal sequence represents thrust belt cessation

tectonic control on sedimentary facies pattern and sediment accumulation rates in the miocene foreland basin of the southern alborz mountains northern iran 1 the southern alborz mountains of northern iran are an integral part of the arabia eurasia collision zone a magnetostratigraphic and rock magnetic investigation of the eyvanekey stratigraphic section in the southern alborz mountains reveals the spatiotemporal character of sedimentary facies migration in the alborz foreland basin the section constitutes three coarsening upward units units 1 2 and 3 comprising the upper red and hezardarreh formations our data reveal that the upper red formation was deposited between 17 5 and 7 5 ma while the depositional age of the top of the hezardarreh formation can be extrapolated to 6 2 ma slow sediment accumulation rates correlate with sedimentary facies comprising prograding coarsening upward units this is likely the result of intraforeland uplift units 1 and 2 and basin inversion probably associated with a growth syncline located in the proximal foreland unit 3 in contrast fine grained strata at the bottom of each cycle are associated with faster sediment accumulation rates testifying to enhanced flexural basin subsidence in the course of thrust loading progradation of coarse grained facies also occurred during relatively fast sediment accumulation top of unit 2 suggesting that the influx of coarse grained sediment outpaced the storage capacity of the proximal foreland thus despite an overall southward propagation of deformation into the southern alborz foreland the locus of active deformation must have migrated back and forth on a time scale of circa 0 7 to 2 ma

the continental margin is a key source of iron to the hnlc north pacific ocean here we show that labile particulate iron and manganese concentrations in the upper 500m of the western subarctic pacific an iron limited high nutrient low chlorophyll hnlc region have prominent subsurface maxima between 100 200 m reaching 3 nm and 600 pm respectively the subsurface concentration maxima in particulate fe are characterized by a more reduced oxidation state suggesting a source from primary volcagenic minerals such as from the kuril kamchatka margin the systematics of these profiles suggest a consistently strong lateral advection of labile mn and fe from redox mobilized labile sources at the continental shelf supplemented by a more variable source of fe from the upper continental slope this subsurface supply of iron from the continental margin is shallow enough to be accessible to the surface through winter upwelling and vertical mixing and is likely a key source of bioavailable fe to the hnlc north pacific

iron species determination to investigate early diagenetic reactivity in marine sediments iron speciation was determined in hemiplegic sediments from a high productivity area to investigate systematically the early diagenetic reactivity of fe a combination of various leaching agents 1 m hci dithionite buffered in citrate acetic acid hf h2so4 acetic cr ii was applied to sediment and extracted more than 80 of total fe subsequent fe species determination defined specific mineral fractions that are available for fe reduction and fractions formed as products of fe diagenesis to determine the fe speciation of sheet silicates we explored an extraction procedure hf h2so4 and verified the procedure by application to standard rocks variations of fe speciation of sheet silicates reflect the possible formation of fe bearing silicates in near surface sediments the same fraction indicates a change in the primary input at greater depth which is supported by other parameters the fe ii fe iii ratio of total sediment determined by extractions was compared with mossbauer spectroscopy at room temperature and showed agreement within 10 m6ssbauer spectroscopy indicates the occurrence of siderite in the presence of free sulfide and pyrite supporting the importance of microenvironments during mineral formation the occurrence of other fe ii bearing minerals such as ankerite ca fe mg carbonate can be presumed but remains speculative

cycling of lithogenic marine particles in the us geotraces north atlantic transect in this paper we present describe and model the first size fractionated 0 8 51 m 51 m water column particulate trace metal results from the us geotraces north atlantic zonal transect in situ pumping survey with a focus on the lithogenic tracer elements al fe and ti this examination of basin wide full depth distributions of particulate elements elucidates many inputs and processes some for bulk lithogenic material others element specific which are presented via concentration distributions elemental ratios size fractionation dynamics and steady state inventories key lithogenic inputs from african dust north american boundary interactions the mediterranean outflow hydrothermal systems and benthic nepheloid layers are described using the refractory lithogenic tracer ti we develop a 1 d model for lithogenic particle distributions and test the sensitivities of size fractionated open ocean particulate ti profiles to biotically driven aggregation disaggregation rates vertical sinking speeds and dust input rates we discuss applications of this lithogenic model to particle cycling in general and to poc cycling specifically

time of initial thrusting in the sevier orogenic belt idaho wyoming and utah reexamination of the distribution of fossils found in the earliest preserved synorogenic conglomerates within the sevier thrust belt suggests that initial thrust movement may be no older than aptian age this interpretation is corroborated by subsidence analyses of sedimentary sequences lying within and east of the idaho wyoming and utah thrust belts a major episode of middle cretaceous aptian cenomanian subsidence is interpreted as recording the initiation of thrust loading deformation in the adjacent sevier orogenic belt an earlier subsidence event took place during middle jurassic time more than 30 m y prior to the cretaceous event and may be the result of tectonic events to the west that are unrelated to thrust deformation in the idaho wyoming and utah thrust belts we find no verifiable evidence to support previous interpretations that sevier belt deformation and uplift began in late jurassic time

evolution of miocene fluvial systems in the himalayan foredeep through a two kilometer thick succession in northern pakistan abstract sedimentological variations through a kilometer thick coarsening upward succession in the miocene himalayan foredeep basin fluvial chinji and nagri formations of the siwalik group are documented in the chinji village area on the potwar plateau of northern pakistan from the chinji formation upwards into the nagri formation 1 the proportion of major sandstone bodies increase relative to mudstone dominated beds 2 average thickness and mean grainsize of channel deposits increase 3 sediment aggradation rates increase 4 there is a reported change in sediment providence 5 paleocurrents are generally to the southeast and vary little upsection and 6 paleosols are more distinct lower in the section where there is also more evidence of ponding of water on the floodplain smaller scale 100 m thick cyclic variations in the proportion of major channel sandstone bodies also occur in both formations in the modern himalayan basin sediment dispersal away from the mountain belt is associated with 1 major rivers that flow along the basin axis 2 large rivers that drain substantial areas of the mountain belt and deposit low relief sediment fans extending hundreds of kilometers into the basin and 3 smaller rivers in fan and interfan areas that drain local areas and carry finer sediment loads sediment variations through the chinji nagri formation boundary can be related to a shifting of depositional environments within such fan and interfan areas major basin axial rivers are not exposed in this area it appears that kilometer thick upsection variations in these deposits record the progradation of the sediment fan formed by a large river system river discharge on the order of 104 m3 s over the floodplain of a smaller river system river discharge on the order of 103 m3 s large scale vertical sediment variations over hundreds of meters to kilometers appear to reflect changes in the basin subsidence and the rate of sediment input to the basin over time scales on the order of 105 106 years upsection variations can not easily be related to climatic change or eustatic variations in sea level the most likely explanation for upsection changes is tectonism deposition rates and shifting positions of river systems within the basin responded more quickly to changes in basin subsidence rate whereas increases in the proportion of sandstone bodies and increases in floodplain slopes lagged behind deposit variations in the siwalik group clearly record variations between different scale river systems delivering sediment to the basin as well as the overall basin evolution

magnetic polarity stratigraphy and ages of siwalik group rocks of the potwar plateau pakistan abstract six magnetic polarity sections have been established over the potwar plateau region of pakistan including the major stratotypes of the siwalik group in all six sections the dominant feature of the magnetic polarity stratigraphy is a long normal polarity zone which is contained within the nagri formation this conspicuous normal polarity zone has been radiometrically dated at 9 5 0 6 m y which identifies it as magnetic chron 9 radiometric dates from the upper siwalik formation have also been used to identify the chron 2 3 boundary in two of the sections the magnetic polarity stratigraphy of three of the sections has been correlated securely with the accepted magnetic polarity time scale so that the ages of the local stratigraphy are indexed accordingly based exclusively on data from stratotype sections the chinji nagri and dhok pathan formations have nominal age ranges of 10 1 13 1 7 9 10 1 and 5 1 7 9 m y age fluctuations on the order of 105 years may be anticipated for these formational boundaries within radius of some 20 km of the designated stratotype mean sediment accumulation rates during the chinji nagri and dhok pathan interval range from 13 to 52 cm 103 yr essentially linear sediment accumulations are locally maintained over time intervals of several million years the chinji nagri lithofacies boundary marks a transition from slow to faster sediment accumulation over much of the potwar plateau indicating a fundamental sedimentary tectonic change at this time

paleomagnetic chronology fluvial processes and tectonic implications of the siwalik deposits near chinji village pakistan a 2800 m section of siwalik strata containing the stratotypes for both the chinji and nagri formations has been dated by magnetic polarity stratigraphy and the observed polarity zonation has securely been correlated with the chron 17 7 segment of the time scale the base of the section is the base of the kamlial formation which occurs near the top of chron 17 18 3 m y the kamlial chinji formation boundary occurs in the middle of chron 15 14 3 m y the chinji nagri boundary near the bottom of chron 10 10 8 m y and the nagri dhok pathan boundary at the chron 8 9 boundary 8 5 m y the siwalik deposits near chinji village consist of four distinct classes of fluvial cycles each with a characteristic periodicity a first order of 10 7 years a second order of 10 6 years a third order of 10 4 10 5 years and a fourth order of 10 0 10 4 years the river system responsible for siwalik sedimentation flowed from west to east and had properties much like the modern ganges river syste

solid phase arsenic speciation in aquifer sediments a micro x ray absorption spectroscopy approach for quantifying trace level speciation abstract arsenic as is a geogenic contaminant affecting groundwater in geologically diverse systems globally arsenic release from aquifer sediments to groundwater is favored when biogeochemical conditions especially oxidation reduction redox potential in aquifers fluctuate the specific objective of this research is to identify the solid phase sources and geochemical mechanisms of release of as in aquifers of the des moines lobe glacial advance the overarching concept is that conditions present at the aquifer aquitard interfaces promote a suite of geochemical reactions leading to mineral alteration and release of as to groundwater a microprobe x ray absorption spectroscopy xas approach is developed and applied to rotosonic drill core samples to identify the solid phase speciation of as in aquifer aquitard and aquifer aquitard interface sediments this approach addresses the low solid phase as concentrations as well as the fine scale physical and chemical heterogeneity of the sediments the spectroscopy data are analyzed using novel cosine distance and correlation distance hierarchical clustering for fe 1s and as 1s xas datasets the solid phase fe and as speciation is then interpreted using sediment and well water chemical data to propose solid phase as reservoirs and release mechanisms the results confirm that in two of the three locations studied the glacial sediment forming the aquitard is the source of as to the aquifer sediments the results are consistent with three different as release mechanisms 1 desorption from fe oxyhydr oxides 2 reductive dissolution of fe oxyhydr oxides and 3 oxidative dissolution of fe sulfides the findings confirm that glacial sediments at the interface between aquifer and aquitard are geochemically active zones for as the diversity of as release mechanisms is consistent with the geographic heterogeneity observed in the distribution of elevated as wells

dissolved iron distribution in the western and central subarctic pacific hnlc water formation and biogeochemical processes it is well known that phytoplankton growth is broadly limited by iron fe availability in the subarctic pacific to investigate which fe sources control the amplitude of seasonal variation in biogeochemical parameters in the subarctic pacific we examined the spatial variation in the west to east distribution of dissolved fe dfe across the western and central subarctic pacific through the japanese geotraces program the vertical section profile of the western subarctic pacific gyre showed high dissolved fe concentrations from the bottom of the surface mixed layer to as deep as approximately 3000 m suggesting that fe rich intermediate water is transported laterally and distributed across the western subarctic gyre over 2000 km the section data also indicate that the influence of the western fe rich intermediate water does not reach the alaskan gyre fe index dfe observed po4 observed rfe p distribution clearly indicates that the western fe rich intermediate water is well explained by external sedimentary fe sources and water transport systems from a subpolar marginal sea the sea of okhotsk and the continental margin the spatial pattern of fe to nutrient stoichiometry supplied from the intermediate water to the surface in comparison with reported fe and nutrient demand in surface phytoplankton quantitatively explains the differences in surface macronutrient consumption between the western and eastern gyre as well as the formation of the high nutrient and low chlorophyll region in the whole subarctic pacific

a magnetostratigraphic age constraint for the proximal synorogenic conglomerates of the late cretaceous cordilleran foreland basin northeast utah usa

tectonic impact on the fluvial deposits of plio pleistocene himalayan foreland basin india abstract the himalayan foreland basin comprises a number of subbasins developed in various sedimentary environments during the plio pleistocene phases of himalayan orogeny this paper describes the evolutionary processes that led to the development of the himalayan foreland basin in the dehra dun and subathu subbasins the dehra dun subbasin essentially consists of conglomerate facies whereas subathu subbasin is primarily composed of sandstone mudstone intercalated with conglomerate the two subbasins were sites of braided river systems evidence from chronostratigraphy provenance and tectonic and climatic conditions suggests that differential tectonic movement sedimentation rate and basin subsidence coupled with climatic variation were responsible for the contrasting fluvial facies in these subbasins following the merger of the two subbasins at about 5 23 ma the conglomerate facies assemblage of the dehra dun subbasin passes laterally into a sandstone mudstone conglomerate facies assemblage of the subathu subbasin thickly bedded amalgamated sheet conglomerate of dehra dun subbasin has a high sedimentation rate 0 70 mm year between 5 23 and 4 8 ma with a slow rate of basin subsidence in contrast a slow sedimentation rate 0 39 mm year in coeval sediments of the subathu subbasin with relatively fast subsidence produced a succession of thick multistorey sandstone body with mature paleosols petrographic and clast composition data from dehra dun subbasin suggest that the detritus was derived from the pre tertiary lesser himalayan sequence lying in the north during an active tectonic phase of the main boundary thrust between 4 8 and 1 77 ma progradation of posttectonic conglomerate of the dehra dun subbasin continued during a quiescent phase of the main boundary thrust however as a consequence of partitioning of subathu subbasin along the intra foreland thrust interfingering of buff piedmont drainage and grey trunk drainage sandstones took place in contrast the syntectonic conglomerate of subathu subbasin originated from the uplifted proximal part of the foreland basin tertiary belt during the active phase of intra foreland thrust around 1 77 ma

detrital cosmogenic 21ne records decoupling of source to sink signals by sediment storage and recycling in miocene to present rivers of the great plains nebraska usa the preservation of conglomerates far from mountainous sources is commonly interpreted in terms of tectonic or climatic forcing to relate a depositional signal to changing conditions in source areas the process and duration of sediment routing from source to sink need to be determined for the first time we quantified sediment transport histories using cosmogenic 21ne in quartzite pebbles from modern river gravels and neogene conglomerates from the modern and ancient north platte river of the great plains of nebraska united states we demonstrate that at 400 km distance from the front ranges of the rocky mountains the majority of pebbles were stored in older channel deposits for up to several millions of years before being recycled this was enabled by very slow to zero basin subsidence rates this implies that upstream tectonic or climatic controls on surface processes were decoupled from the downstream depositional record a result supported by the similarities in cosmogenic 21ne values among miocene pliocene and modern river channel pebbles despite known changes in tectonic and climatic forcing

estuarine removal of glacial iron and implications for iron fluxes to the ocean while recent work demonstrates that glacial meltwater provides a substantial and relatively labile flux of the micronutrient iron to oceans the role of high latitude estuary environments as a potential sink of glacial iron is unknown here we present the first quantitative description of iron removal in a meltwater dominated estuary we find that 85 of dissolved fe is removed in the low salinity region of the estuary along with 41 of total dissolvable iron associated with glacial flour we couple these findings with hydrologic and geochemical data from gulf of alaska goa glacierized catchments to calculate meltwater derived fluxes of size and species partitioned fe to the goa iron flux data indicate that labile iron in the glacial flour and associated fe minerals dominate the meltwater contribution to the fe budget of the goa as such goa nutrient cycles and related ecosystems could be strongly influenced by continued ice loss in its watershed

development of tectonic cyclothems in rift pull apart and foreland basins sedimentary response to episodic tectonism the thickest part of asymmetric rift pull apart and foreland basin fills commonly consists of large scale hundreds to thousands of metres thick tectonically generated cyclothems of fine grained marine lacustrine or longitudinal fluvial deposits and coarse grained transverse braid plain or alluvial fan deposits the appearance of coarse clastics in these basin fills is typically noted as the time of tectonically rejuvenated source area uplift based on the conceptual tie between relief and coarse grain size and on the application of the davis theory of landform development we propose the opposite interpretation that the commencement of fine grained sedimentation above coarse grained deposits in a tectonic cyclothem is the best indicator of renewed tectonic activity this reinterpretation is more consistent with 1 modern examples 2 the consideration of source area and sedimentary basin geomorphology 3 the disparity between the reaction rates of the various environments to subsidence 4 the disparity between the rates of tectonic uplift and erosion and 5 the controls on elastic wedge progradation in our model extensive coarse grained clastic wedge progradation is an indicator of tectonically quiescent phases

biolabile ferrous iron bearing nanoparticles in glacial sediments abstract glaciers and ice sheets are a significant source of nanoparticulate fe which is potentially important in sustaining the high productivity observed in the near coastal regions proximal to terrestrial ice cover however the bioavailability of particulate iron is poorly understood despite its importance in the ocean fe inventory we combined high resolution imaging and spectroscopy to investigate the abundance morphology and valence state of particulate iron in glacial sediments our results document the widespread occurrence of amorphous and fe ii rich and fe ii bearing nanoparticles in arctic glacial meltwaters and iceberg debris compared to fe iii rich dominated particulates in an aeolian dust sample fe ii is thought to be highly biolabile in marine environments our work shows that glacially derived fe is more labile than previously assumed and consequently that glaciers and ice sheets are therefore able to export potentially bioavailable fe ii containing nanoparticulate material to downstream ecosystems including those in a marine setting our findings provide further evidence that greenland ice sheet meltwaters may provide biolabile particulate fe that may fuel the large summer phytoplankton bloom in the labrador sea and that fe ii rich particulates from a region of very high productivity downstream of a polar ice sheet may be glacial in origin

water masses and currents in the upper tropical northeast atlantic off northwest africa recent current measurements in the tropical eastern north atlantic reproduce the components of the large scale flow field however the observations as well as the 1 12 flame model computations indicate that a lot of eddy scale variability is superimposed on the mean flow field despite of the disturbance by variability the signature of the guinea dome is well present in november 2002 the guinea dome transport from direct observations was about 2 8 sv above 25 8 kg m3 and 4 sv between 25 8 and 27 1 kg m3 the oxygen minimum in the shadow zone comprises the central water and the antarctic intermediate water aaiw layers and is located between the equatorial current system and the north equatorial current the north equatorial counter and undercurrents at 3 to 6 n are major oxygen sources for the central water layer of the low oxygen regions in the northeastern tropical atlantic a second northern north equatorial countercurrent nnecc band exists at 8 to 10 n the nnecc carries oxygen rich water from the southern hemisphere eastward but with an admixture of water from the northern hemisphere a float at 200 m depth was spreading eastward in the north equatorial undercurrent neuc at 28 w it shifted northward into the nnecc and then was trapped in the guinea dome region for more than 3 years the model indicates the region 22 to 32 w as the area of exchange between the necc neuc and the nnecc bands in the aaiw layer the northern intermediate countercurrent acts as oxygen source for the oxygen minimum zone