facies and architectural element analysis of a meandering fluvial succession the permian warchha sandstone salt range pakistan abstract the 30 to 155 m thick early permian artinskian warchha sandstone of the salt range pakistan is a conglomerate sandstone and claystone succession within which seven lithofacies types gt st sp sr sh fl and fm occur in a predictable order as repeated fining upward cycles common sedimentary structures in the conglomerates and sandstones include planar and trough cross bedding planar lamination soft sediment deformed bedding compound cosets of strata with low angle inclined bounding surfaces and lags of imbricated pebbles structures in the finer grained facies include desiccation cracks raindrop imprints caliche nodules and bioturbation groups of associated facies are arranged into nine distinct architectural elements channels gravel bars sandy bedforms downstream and laterally accreting barforms sand sheets crevasse splays levees floodplain units and shallow lakes which is consistent with a fluvial origin for the succession the types of architectural elements present and their relationship to each other demonstrate that the warchha sandstone preserves a record of a meandering river system that drained the northern margin of gondwanaland the dominance of fine grained floodplain facies over gravel grade channel base facies and the widespread occurrence of large scale lateral accretion elements supports the interpretation of a high sinuosity meandering fluvial system in which channel bodies accumulated via the lateral accretion of point bars but in which the active channels covered only a small part of a broad floodplain at any time instant although the regional and temporal distribution of these deposits is complex in broad terms the lower part is dominated by stacked multistorey channel bodies whereas single storey channel elements isolated in abundant fine grained floodplain deposits dominate the middle and upper parts of the formation

isotopic constraints on the structural relationships between the lesser himalayan series and the high himalayan crystalline series garhwal himalaya nd and sr isotope systematics may provide important constraints on the location of major thrust systems that separate lithologically similar sedimentary sequences the potential of the technique is illustrated by this isotopic study of the main central thrust system of the himalaya nd isotope data from the garhwal himalaya indicate that metasedimentary rocks from the vaikrita group nd 14 to 19 correlate closely with those from the high himalayan crystalline series which constitutes the hanging wall lithologies of the main central thrust in contrast metasedimentary rocks from the munsiari group nd 23 to 28 show marked similarities to the lesser himalayan series in the footwall of the main central thrust sr isotopes support the correlations in that the vaikrita group shows partial reequilibration at 500 ma whereas the munsiari group has not undergone sr isotope homogenization since 1800 ma thus the vaikrita thrust that juxtaposes these two formations is recognized as the main central thrust in garhwal himalaya the thrust coincides approximately with the location of the kyanite isograd confirming that inverted metamorphism is characteristic of both hanging wall and footwall of the main central thrust along the tons thrust known locally as the srinagar thrust 50 km south of the main central thrust low grade quartzarenites with nd sr isotope and trace element characteristics typical of lesser himalayan formations have been emplaced on phyllites and siltstones with geochemical characteristics of the high himalayan crystalline series the field relationships most probably result from out of sequence thrusting in which lesser himalayan series rocks to the north were emplaced over low grade equivalents of the high himalayan crystalline series preserved in the external part of the orogen this study establishes the value of isotope data for lithostratigraphic correlations within orogenic belts

new age constraints for the proterozoic aravalli delhi successions of india and their implications abstract proterozoic sedimentary successions of india are important archives of both the tectonic history of the indian subcontinent and the geochemical evolution of earth surface processes however the lack of firm age constraints on many of these stratigraphic units limits their current utility here we present new detrital zircon age data from strata of the southern aravalli delhi orogenic belt adob and the rajasthan vindhyan successions the alwar group of the southern delhi supergroup yielded a large population of 1 2 ga detrital zircon grains which refutes the 1 9 1 7 ga age assertion for this unit detrital zircon age distributions from the southern alwar group differ strongly from the alwar group of the north delhi belt demonstrating miscorrelation between these two regions the jhamarkotra formation of the lower aravalli group contains a large population of 1 9 1 7 ga detrital zircon grains therefore the unit cannot be 2 1 ga as traditionally assumed age distributions of the aravalli and delhi supergroups are similar to those of the lower and upper vindhyan successions and we postulate contiguous sediment sources for both regions with strata of the tectonically deformed adob representing the distal margin equivalents of the vindhyan successions additionally a late paleoproterozoic age for the jhamarkotra formation nullifies the hypothesis that the markedly positive carbonate 13c values in this unit are linked to the 2 3 2 0 ga lomagundi jatuli positive isotope excursion the potential of a large late paleoproterozoic ca 1 7 ga positive 13c excursion contrasts with the long held view of a prolonged period of carbon isotope stasis during the so called boring billion

benthic oxygen consumption rates during hypoxic conditions on the oregon continental shelf evaluation of the eddy correlation method 1 three stations at 80 m water depth on the oregon shelf between 44 7 n and 43 9 n were studied under hypoxic conditions in late spring and summer of 2009 to determine benthic oxygen consumption rates oxygen fluxes were derived from eddy correlation ec measurements made from an autonomous lander deployed for 11 15 h at a time average oxygen consumption rates ranged from 3 2 to 9 8 mmol m 2 d 1 and were highest at the southernmost station methods for separating eddy components and rotating coordinates were examined for effects on ec fluxes it was found that oscillations at frequencies associated with surface and internal waves made significant contributions but horizontal component biasing could be minimized by wave based rotation methods additional measurements included benthic boundary layer properties and sediment permeability and profiles of sediment organic c chlorophyll a excess 210pb and fines comparative flux estimates were determined from benthic chamber measurements and microelectrode profiles at two of the stations the chamber o2 consumption rates exceeded the ec fluxes by factors of 1 2 1 8 which may reflect enclosure effects the different spatial and temporal scales of the measurements and or inhomogeneous benthic respiration rates the magnitudes of the fluxes by either method however are low for shelf depths thus for benthic o2 consumption to contribute to oregon shelf hypoxia bottom waters must be slowly renewed and minimally ventilated by along or across shelf advection and turbulent mixing circulation studies indicate these conditions are favored by increased near bottom stratification during persistent summer upwelling relaxation cycles

cambrian depositional history of the zanskar valley region of the indian himalaya tectonic implications a well preserved cambrian section in the zanskar valley of northern india has previously been interpreted to record the transition from a passive to an active tectonic margin related to cambrian ordovician orogenesis this interpretation has been used to support the tectonostratigraphic interpretation of other successions across the tethyan himalaya our detailed paleoenvironmental analysis significantly revises the tectonic and depositional history of these cambrian deposits no definitive record of impending cambrian ordovician orogenesis is recorded in these late middle cambrian rocks a critical transition from an 125 m thick stromatolite bearing carbonate deposit the karsha formation into shale and sandstone of the kurgiakh formation was interpreted to represent tectonically induced drowning of a carbonate platform siliciclastic strata of the kurgiakh formation were thought to record deep water flysch deposition in a tectonically active foreland basin next to an arc trench system this interpretation was based on sandstone beds with classic bouma sequences we show that these event beds in the kurgiakh instead contain hummocky cross stratification quasi planar lamination and combined flow ripple stratification all of which reflect deposition in shallow marine storm influenced environments thus although the karsha carbonate platform may have been drowned it did not culminate in deep sea flysch deposition and this in turn eliminates a major line of evidence linking kurgiakh deposition to the onset of cambrian ordovician orogenesis other aspects of cambrian ordovician deposits of northern india also shed doubt on the proposed link between kurgiakh sedimentation and the cambrian ordovician orogenic event first our improved biostratigraphic database suggests that the transition from the karsha carbonate to the kurgiakh formation may have predated the main phase of cambrian ordovician orogenesis as recorded by overlying ordovician molasse by as much as 20 30 my second published data from the ordovician molasse indicate northward paleocurrents which are parallel to those recorded by siliciclastic deposits of the parahio formation below the karsha and thus are at odds with standard models of foreland basin development for the cambrian ordovician event our sedimentological analysis of depositional cycles of the parahio formation indicates that these strata record storm influenced environments from offshore marine to shoreface to fluvial settings this is at odds with previous paleoenvironmental interpretations that ranged from deep sea flysch to intertidal deposits paleocurrent data for marine and fluvial facies of the parahio formation in both zanskar and the spiti valley to the south indicate northeast sediment transport this supports the view that the parahio and overlying carbonate of the karsha formation record the ancient northern passive margin of india during the cambrian and that these strata may be distal equivalents of the younger cambrian deposits of the lesser himalaya

neogene marine isotopic evolution and the erosion of lesser himalayan strata implications for cenozoic tectonic history abstract an extensive northward deepening blanket of neoproterozoic and cambrian sedimentary rocks once extended from the himalayan margin far onto the indian craton cambrian deposits of this upper lesser himalayan succession which include deposits of the outer lesser himalaya tectonic unit are enriched in radiogenic 187os they make up part of a proximal marine facies belt that extends onto the craton and along strike from india to pakistan by contrast age equivalent facies in the tethyan himalaya are more distal in nature neoproterozoic to cambrian strata of the upper lesser himalayan succession are now missing in much of the lesser himalaya with their erosion exposing older precambrian lesser himalayan strata we suggest that exhumation and weathering of the upper lesser himalaya and related strata caused dramatic changes in the 187os 188os and 87sr 86sr neogene record of seawater starting at 16 ma first order estimates for the volume of upper himalayan strata as well as the volume of all lh rock eroded since this time and geochemical box modeling support this idea exhumation at 16 ma is a fundamental event in the evolution of the himalayan orogeny and the geochemical evolution of the oceans and will be a critical part of the construction of future models of himalayan thrust belt evolution

the importance and challenge of hyporheic mixing the hyporheic zone is the interface beneath and adjacent to streams and rivers where surface water and groundwater interact the hyporheic zone presents unique conditions for reaction of solutes from both surface water and groundwater including reactions which depend upon mixing of source waters some models assume that hyporheic zones are well mixed and conceptualize the hyporheic zone as a surface water groundwater mixing zone but what are the controls on and effects of hyporheic mixing what specific mechanisms cause the relatively large 1m mixing zones suggested by subsurface solute measurements in this commentary we explore the various processes that might enhance mixing in the hyporheic zone relative to deeper groundwater and pose the question whether the substantial mixing suggested by field studies may be due to the combination of fluctuating boundary conditions and multi scale physical and chemical spatial heterogeneity we encourage investigation of hyporheic mixing using numerical modeling and laboratory experiments to ultimately inform field investigations

paleozoic and mesozoic stratigraphy of the peshawar basin pakistan correlations and implications the most complete paleozoic sequence described from pakistan is exposed in bedrock inliers and in ranges fringing the eastern peshawar basin interbedded quartzite and argillite of the precambrian and cambrian tanawal formation is overlain unconformably by the cambrian ambar formation the misri banda quartzite unconformably overlies the ambar and contains ordovician cruziana ichnofossils new conodont discoveries restrict the ages of overlying formations as follows panjpir formation llandoverian to pridolian nowshera formation lochkovian to frasnian and jafar kandao formation kinderhookian to westphalian the karapa greenschist consisting of metamorphosed lava flows separates the jafar kandao from upper triassic carnian marbles of the kashala formation the upper triassic and jurassic nikanai ghar formation forms the top of the section correlatives to the peshawar basin stratigraphy are present locally in the sherwan synclinorium of hazara and in the khyber pass region the sequence contrasts markedly with the paleozoic and mesozoic section exposed south of the khairabad thrust in the attock cherat range this thrust and its northeastern continuation in hazara north of abbottabad thus form the boundary in pakistan between the lesser himalayan and tethyan himalayan sections a function performed by the main central thrust mct in the central himalaya of india and nepal the newly dated carboniferous to triassic horizons provide the first firm age constraints on the protoliths of the high grade swat metasediments the dating of the metasediments has in turn provided age constraints on pre himalayan tectonism and associated intrusions two major tectonic episodes during the late cambrian and carboniferous produced positive areas north of the peshawar basin that provided coarse detritus to the misri banda quartzite and jafar kandao formation

the age and rate of displacement along the main central thrust in the western bhutan himalaya abstract in western bhutan the main central thrust mct is broadly folded creating multiple exposures of the fault surface over a 70 km across strike distance this unusual map pattern presents a unique opportunity to map the mct and document both the magnitude and age of displacement in situ th pb sims and la icp ms geochronology of metamorphic monazite from the immediate hanging wall of the mct indicates that prograde monazite growth in greater himalayan gh rocks continued until 20 8 1 1 ma whereas crystallization of in situ melts characterized by high y monazite overgrowths occurred during cooling from ca 15 10 ma prograde monazite growth at 15 ma in lesser himalaya lh rocks in the immediate footwall requires that lh footwall strata began to be buried at this time and the mct had reached its southernmost exposed extent by combining prograde monazite ages in the immediate hanging wall and footwall the duration of mct displacement is bracketed between 20 8 1 1 and 15 0 2 4 ma immediately north of our study area a published estimate of shearing along the outer south tibetan detachment std argues for displacement between 20 and 15 ma coeval with the age range for mct displacement that we document in this study however retrograde monazite grains as young as 10 ma suggest that gh rocks were cooling until 10 ma 5 myr later than motion on the outer std immediately to the north this cooling was either the result of continued displacement on the mct or growth of a duplex that passively folded the mct using a sequential reconstruction we estimate a total displacement of 230 km which is the sum of displacements on the mct and the structurally lower paro thrust over a duration of 5 8 2 6 myr this indicates a horizontal shortening rate of 4 0 3 2 1 3 cm yr which exceeds present rates estimated from geodetic measurements across the himalaya and mct displacement rates c 2 cm yr inferred from petrologic and thermal models in central nepal but is indistinguishable from plate convergence rates calculated for eastern bhutan between 23 and 20 ma 3 3 0 7 cm yr our study highlights that displacement on the mct alone achieved plate velocity rates in western bhutan and that the age and rate of mct displacement varied significantly across the himalaya

bidirectional bedform fields at the head of a submarine canyon ne atlantic abstract submarine canyons are known to force ocean mesoscale circulation and local hydrodynamics alternate up and down canyon near bottom flows have been widely documented along the upper reaches connecting the canyon heads with the contiguous outer shelves and vice versa nonetheless we still miss clear evidence of bedform fields expressing these complex patterns in this study through a multi scale analysis in both space and time we document rare asymmetric bedforms up to 880 m long and 10 m high developing within a depth range of 168 220 m at the head of the whittard canyon ne atlantic one field of well developed sandwaves has an atypical up slope asymmetry with the steeper slope facing the shallower regions of the shelf and contrasting with surrounding down slope sandwaves facing the canyon the bedforms are interpreted to represent both up slope and down slope bottom currents connecting the upper reaches of the canyon to the outer shelf on the southern celtic margin in the bay of biscay the sandwaves were surveyed with shipboard multibeam bathymetry 5 m grid cell resolution auv sidescan sonar 0 15 m grid cell resolution and rov footage and sampled with three rov mounted vibro cores and two box cores sidescan sonar mosaics groundtruthed by sediment samples and rov footage show with unprecedented detail spectacular trains of fresh overprinting megaripples previously undocumented sand peaks and bowl shaped depressions on the crests of the tallest sandwaves differences in sedimentary settings and benthic habitats indicate that these features are currently active in particularly dynamic areas allowing for very slow migration of sandwaves numerical modelling together with concurrent hydrographic observations suggest large amplitude semi diurnal internal tides possibly transitioning to asymmetric internal bores as the main mechanism maintaining the mapped up slope sandwaves this work highlights the importance of uncommon sediment dynamics in canyon head environments and adds insight to the traditional notions of gravity driven processes being dominant in these environments envisaging implications for improving geo hazard assessment of mobile substrates and quantification of offshore sediment and carbon fluxes

the impact of bedform migration on benthic oxygen fluxes permeable sediments are found wide spread in river beds and on continental shelves the transport of these sediments is forced by bottom water currents and leads to the formation of bedforms such as ripples and dunes the bottom water flow across the bedforms results in pressure gradients that drive pore water flow within the permeable sediment and enhance the supply of reactive substrates for biogeochemical processes this transport reaction system has been extensively studied for the case of stationary bedforms whereas bedform migration the most ubiquitous form of sediment transport has been often ignored to study the impact of sediment transport on pore water flow we incorporated an empirical model of bedform migration into a numerical transport reaction model for porous media using oxygen as reactive solute the modeled oxygen flux changes significantly as soon as the sediment divides into an upper mobile layer migrating bedform and a stationary layer underneath the bedform is increasingly flushed with oxic bottom water whereas pressure gradients and pore water flow reverse at increasing rate underneath the bedform this suppresses net pore water displacement and reduces the oxygen penetration depth up to 90 in effect the overall oxygen uptake decreases significantly with bedform migration although bottom water velocities increase this counterintuitive effect is systematically described for a range of different sediment types current velocities and respiration rates and should be considered in future studies

syndepositional shallow water precipitation of glauconitic minerals abstract numerous studies have demonstrated that glauconitic minerals predominantly form in water depths of mid shelf to upper slope in modern oceans these areas tend to have slow sedimentation rates another commonly cited requisite for glauconitic mineral precipitation cambro ordovician strata from the southwestern us are rich in glauconitic minerals stratigraphic sedimentological and petrographic constraints indicate that the glauconitic minerals are autochthonous in marked contrast to the modern environments of deposition these cambro ordovician strata formed under very shallow water to tidal flat conditions the trough cross stratified deposits of the most glauconitic mineral rich accumulations glaucarenites indicate a high energy environment and probably a normal to high rate of sedimentation the presence of fibroradiated rims of glauconitic minerals on glauconitic mineral pellets echinoderm fragments and quartz grains demonstrates that the cambro ordovician glauconitic minerals precipitated on or in close proximity to the sea floor and prior to calcite precipitation consequently glauconitic minerals must have formed under markedly different conditions in the lower paleozoic than they do today thus the occurrence of glauconitic minerals in the rock record cannot be used a priori as an environmental indicator of either mid shelf and deeper water and or a slow rate of sedimentation

neoproterozoic early cambrian biota and ancient niche a synthesis from molecular markers and palynomorphs from bikaner nagaur basin western india abstract the time frame of present study is neoproterozoic early cambrian an enigmatic and consequential time in the history of earth the present study elucidates the terminal proterozoic biota and palaeoenvironment by characterizing the soluble and insoluble fractions of organic matter extracted from sediment core samples recovered from marwar supergroup bikaner nagaur basin western india the normal alkanes range from c15 to c33 wherein c19 to c21n alkanes predominate and carbon preference index ranges from 1 12 to 1 19 pristane phytane ratio varies between 0 9 and 1 2 the kerogen matter occurs as homogenous laminae and discrete organic remains which are mostly derived from microbial mat triterpenoids include cheilanthanes and hopanes which are confirming evidences of microbial input algal presence has also been confirmed from palynological data green algae evolved to be a major biota during the neoproterozoic early cambrian time and this is validated by the appreciable abundance of c29 steranes in the bitumen fraction the amorphous pieces of kerogen residues lack any visibly distinct internal features however a very few simple ornamented acritarchs like micrhystridium sp lophosphaeridium sp and leiosphaeridia sp are observed in the organic residues micro ftir spectroscopy of the amorphous organic particles reveals the presence of long chain aliphatic components and unusually high c c aromatic ring stretching band the organic remains were deposited in restricted marine water and elevated saline condition as indicated by several salinity biomarkers the present study clearly demonstrates a microbial mat dominated niche with significant eukaryotic green algae that had been capable of surviving in the high salinity of the terminal proterozoic oceans

the negligible effect of bed form migration on denitrification in hyporheic zones of permeable sediments bed form celerity the migration rate of ripples along a sediment bed has previously been shown to have dramatic effects on oxygen distribution and transport within the hyporheic zone of permeable sediments this has the potential to influence denitrification rates in particular by increasing the coupling of nitrification and denitrification to further understand this we numerically modeled nitrogen cycling under migrating ripples while the simulated oxygen profiles match with expected behavior almost no effect on denitrification or coupled nitrification denitrification was observed with increasing celerity instead denitrification rates were dominantly controlled by the flow velocity of water overlying the sediment

cambrian biostratigraphy of the tal group lesser himalaya india and early tsanglangpuan late early cambrian trilobites from the nigali dhar syncline precise biostratigraphic constraints on the age of the tal group are restricted to 1 a basal level correlative with the anabarites trisulcatus protohertzina anabarica assemblage zone of southwest china 2 a level near the boundary of the lower and upper parts of the tal group correlative with the early tsanglangpuan stage drepanuroides zone and 3 an interval low in the upper part of the tal group correlative with later in the tsanglangpuan stage palaeolenus zone these correlations are based on small shelly fossil and trilobite taxa other chronostratigraphic constraints include the marked negative 13 c isotopic excursion coincident with the transition from the krol group to the tal group this excursion is used as a proxy for the precambrian cambrian boundary in several sections worldwide and if applied to the lesser himalaya indicates that the boundary is at or just above the base of the tal group the upper parts of the tal group may be of middle or late cambrian age and might form proximal equivalents of sections in the zanskar spiti region of the tethyan himalaya both faunal content and lithological succession are comparable to southwest china furthering recent arguments for close geographic proximity between the himalaya and the yangtze block during late neoproterozoic and early cambrian time trilobites from the uppermost parts of the sankholi formation from the nigali dhar syncline are described and referred to three taxa one of which drepanopyge gopeni is a new species they are the oldest trilobites yet described from the himalaya

nature of magmatism and sedimentation at a columbia active margin insights from combined u pb and lu hf isotope data of detrital zircons from nw india abstract detrital zircons from a palaeoproterozoic quartzite deposited between 1 85 and 1 82 ga in the northern aravalli orogen of nw india show a distinctive age peak of ca 1 85 ga and variable but largely subchondritic ehf1 85 ga between 1 3 and 21 0 corresponding to hafnium model ages of 2 5 to 3 6 ga these data indicate an important period of reworking of ancient eo to neoarchaean strongly heterogeneous continental crust at this time prevalence of ca 1 85 ga subduction related granitoids almost identical u pb age spectra and ehft of detrital zircons in ca 1 85 ga metasedimentary rocks in the aravalli orogen and the inner lesser himalaya indicate similar sediment provenances and thus a geological connection between these two terranes during late palaeoproterozoic all together the data constrain a rapid succession of sedimentation metamorphism and subduction related magmatic activity and support the interpretation of an active geodynamic realm along the entire north indian margin at ca 1 85 ga comparison of detrital zircon data in conjunction with published paleomagnetic data from north india and other crustal blocks of the columbia supercontinent additionally suggest a close affinity of north india with madagascar the cathaysia block of south china and south korea during columbia times

thrust geometries and deep structure of the outer and lesser himalaya kumaon and garhwal india implications for evolution of the himalayan fold and thrust belt the kumaon garhwal region of the himalaya lies near the center of the himalayan fold and thrust belt we have drawn two balanced cross sections 100 km apart through the outer and lesser himalaya the cross sections incorporate all the surface well log and earthquake seismic data currently available from the region two branch line maps showing trailing and leading branch lines and cutoff lines of the major thrusts in the region are also drawn the three dimensional deep structure of the outer and lesser himalaya is interpreted based on the balanced cross sections and the branch line maps deep structure of the higher and tethyan himalaya is extrapolated based on surface geology and is subject to revision as more surface and seismic data become available from these areas a sequential evolutionary model for the kumaon himalaya along the eastern pindari section is proposed according to this model the kumaon himalaya evolved by an overall forelandward progression of thrusting with some reactivation along the munsiari thrust mt the main boundary thrust mbt and the main central thrust mct we use structural stratigraphic and radiometric criteria to place time constraints on the motion of these thrusts earliest motion along the mbt may have occurred in early middle paleocene but the main episode probably started in late eocene and may still be continuing emplacement of the mt had occurred by middle late eocene whereas the mct shows activity around 20 ma thus exhibiting break back thrusting with respect to the mt shortening estimates are obtained from the pindari section minimum shortening in the sedimentary thrust sheets of the outer and lesser himalaya is 161 km or 65 as a first approximation we have also restored the crystalline sheets in order to obtain shortening estimates for the entire himalaya minimum shortening for the himalaya after restoring the mct sheet varies from 354 76 to 421 km 79 these estimates were further combined with published data from the area between the mct sheet and the indus tsangpo suture zone itsz minimum shortening between the indo ganga foreland and the itsz thus obtained lies in the range 687 754 km or 69 72 we compare our shortening estimates with those available from the pakistan and nepal himalaya

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

mean flow and turbulence structure over fixed two dimensional dunes implications for sediment transport and bedform stability detailed measurements of flow velocity and its turbulent fluctuation were obtained over fixed two dimensional dunes in a laboratory channel laser doppler anemometry was used to measure the downstream and vertical components of velocity at more than 1800 points over one dune wavelength the density of the sampling grid allowed construction of a unique set of contour maps for all mean flow and turbulence parameters which are assessed using higher moment measures and quadrant analysis these flow field maps illustrate that 1 the time averaged downstream and vertical velocities agree well with previous studies of quasi equilibrium flow over fixed and mobile bedforms and show a remarkable symmetry from crest to crest 2 the maximum root mean square rms of the downstream velocity values occur at and just downstream of flow reattachment and within the flow separation cell 3 the maximum vertical rms values occur within and above the zone of flow separation along the shear layer and this zone advects and diffuses downstream extending almost to the next crest 4 positive downstream skewness values occur within the separation cell whereas positive vertical skewness values are restricted to the shear layer 5 the highest reynolds stresses are located within the zone of flow separation and along the shear layer 6 high magnitude high frequency quadrant 2 events ejections are concentrated along the shear layer kelvin helmholtz instabilities and dominate the contribution to the local reynolds stress and 7 high magnitude high frequency quadrant 4 events occur bounding the separation zone near reattachment and close to the dune crest and are significant contributors to the local reynolds stress at each location these data demonstrate that the turbulence structure associated with dunes is controlled intrinsically by the formation magnitude and downstream extent of the flow separation zone and resultant shear layer furthermore the origin of dune related macroturbulence lies in the dynamics of the shear layer rather than classical turbulent boundary layer bursting the fluid dynamic distinction between dunes and ripples is reasoned to be linked to the velocity differential across the shear layer and hence the magnitude of the kelvin helmholtz instabilities which are both greater for dunes than ripples these instabilities control the local flow and turbulence structure and dictate the modes of sediment entrainment and their transport rates

flow induced uptake of particulate matter in permeable sediments we demonstrate the fast transfer of suspended particles from the boundary layer into the upper strata z 2 x 10 l l m2 incubated in a laboratory flume increased pressure up and downstream of small mounds z 2 5 cm drove water 5 5 cm into the core carrying suspended particles 1 pm to 2 2 cm sediment depth within 10 h simultaneously decreased pressure at the downstream slope of the protrusions drew pore fluid from deeper layers z 5 10 cm to the surface in the sediment friction reduced the velocity of the particulate tracers resulting in size fractionation and layers of increased particle concentration ripple topography 0 8 2 8 cm high enhanced interfacial particle 1 pm flux by a factor 2 3 when compared to a level control core the pathways of the particle and solute tracers below a sediment ripple are explained with a source sink model that describes the pore flow velocity field our results suggest that bedform induced interfacial flows are important for the uptake of particulate organic matter into permeable shelf sediments

preliminary stratigraphic and structural architecture of bhutan implications for the along strike architecture of the himalayan system article i nfo preliminary mapping and stratigraphic correlation of lesser himalayan rock in eastern bhutan using field characteristics u pb detrital zircon dating and nd geochemistry define the first order stratigraphic architecture of the indian passive margin sequence in the eastern himalaya we use this new image of the lateral and vertical relationships of the original stratigraphy to determine the structural framework of the eastern himalayan fold thrust belt in bhutan we propose that lesser himalayan rock in bhutan can be divided into lower lesser himalayan rocks with a paleoproterozoic detrital zircon signal and upper lesser himalayan rocks with detrital zircon signals of 1000 500 ma the 500 ma detrital grains are from rocks in the frontal portions of the fold thrust belt north of the main boundary thrust as well as directly in the footwall of the main central thrust in the hinterland our preliminary stratigraphic study coupled with mapping allows us to construct a composite balanced cross section through the kuru chu valley in eastern bhutan which provides the first image of the geometry and amount of shortening through bhutan the main frontal thrust tilts a 6 km of thick section of neogene foreland basin deposits these deposits are separated from folded and faulted upper lesser himalayan rocks by the main boundary thrust north of the main boundary thrust we propose two duplex systems the southernmost duplex contains 9 repeated sections of upper lesser himalayan units including the permian gondwana sequence and the cambrian or younger baxa group the northernmost duplex is located in the footwall of the main central thrust and is comprised of two repeated sections of the proterozoic shumar and daling formations the southern boundary of this northern duplex is the shumar thrust which acts as a roof thrust for the southern duplex system and may correlate to the ramgarh thrust in nepal and india we propose that the development of the duplex systems passively folded overlying tethyan and greater himalayan rocks minimum shortening for this part of the himalayan fold thrust belt is 359 km all of which has occurred from 22 ma to present defining a long term shortening rate of 16 mm yr

biomarker signatures from neoproterozoic early cambrian oil western india abstract the neoproterozoic early cambrian time is the cradle of multicellular eukaryotic life and thereafter metazoan life started populating the planet biomarkers which record the chronicles of biotic events on earth have been investigated using gas chromatography mass spectrometry from a suite of nine oil samples extracted from oil stained sediments and a crude oil of neoproterozoic early cambrian age from bikaner nagaur basin western india the biomarker distribution is characterized by high concentration of both tricyclic terpanes and pentacyclic hopanes the predominance of c 29 regular sterane over c 27 and c 28 steranes indicates green algal contribution and may imply the prominence and diversification of the same algal group the low pristane phytane ratio and occurrence of substantial quantity of gammacerane monomethyl 2 methyl 2 2 4 8 trimethyltridecyl chroman and 1 1 7 8 tetramethyl 1 2 3 4 tetrahydrophenanthrene are indicative of stratified water column as well as anoxic and enhanced salinity condition of the environment of deposition this paper reports for the first time the presence of methyltrimethyltridecyl chromans mttcs from neoproterozoic early cambrian time putative c 19 norsteranes probably indicative of sponge input are recorded in the studied samples and also reported from other infracambrian oils and sediments normal alkanes n c 17 and n c 18 and isoprenoids pristane and phytane are highly depleted in 13 c the overall biomarker distribution and carbon isotope data of oils from bikaner nagaur basin show similarities with those of other infracambrian oils like huqf oils from oman and baykit high oils from eastern siberia

isotopic and structural constraints on the location of the main central thrust in the annapurna range central nepal himalaya five isotope enhanced geologic transects in the southern annapurna range of central nepal elucidate structural geometries near the main central thrust whole rock nd isotopes and u pb ages of detrital zircons unambiguously distinguish greater himalayan hanging wall and lesser himalayan footwall metasedimentary rocks nd 0 values for lower lesser himalayan rocks typically range from 20 to 26 whereas greater himalayan rocks usually have nd 0 values of 19 to 12 lower lesser himalayan rocks yield detrital zircons with an age peak at ca 1880 ma and no detrital zircons younger than ca 1550 ma in contrast greater himalayan rocks yield detrital zircons with a prominent broad peak of ages at ca 1050 ma and no detrital zircons younger than ca 600 ma the protolith boundary between greater and lesser himalayan rocks is up to 1 km farther south than usually mapped on the basis of lithology field and microstructural observations indicate the presence of a top to the south ductile shear zone superimposed on this boundary confirming this shear zone as the main central thrust no evidence exists for large scale structural mixing of greater and lesser himalayan rocks along the main central thrust in the annapurna range

transport and degradation of phytoplankton in permeable sediment in flume and field experiments we demonstrate that interfacial water flows generated when bottom currents interact with sea bed topography provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments the advective transport associated with small mounds and ripples as commonly found on shelf sediments increased penetration depth of unicellular algae dunaliella spec into sandy sediment permeability k 5 4 3 10 211 m 2 up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment the pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes algal penetration depths and degradation rates with increasing permeability of the sediment two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings showing permeability dependent penetration of planktonic algae into embedded sand cores of different grain sizes the significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands and we suggest the concept of a decomposition layer in contrast to muddy sea beds with low permeabilities where transport of solutes is mainly driven by diffusion water can flow through marine sands providing a fast carrier for the exchange of substances between the water column and the upper sediment layers surface gravity waves cause pressure oscillations that increase fluid exchange at the sediment water interface and dispersion of solutes within the

regulation of benthic oxygen fluxes in permeable sediments of the coastal ocean large areas of the oceanic shelf are composed of sandy sediments through which reactive solutes are transported via porewater advection fueling active microbial communities the advective oxygen transport in permeable sands of the north sea was investigated under in situ conditions using a new benthic observatory to assess the dynamic interaction of hydrodynamics sediment morphodynamics and oxygen penetration depth during 16 deployments concurrent measurement of current velocity sediment topography and porewater oxygen concentration were carried out in all cases the oxyclines were found at depths of 1 6 cm correlating with the topography of stationary and migrating bedforms ripples different conditions in terms of bottom water currents and bedform migration led to fluctuating oxygen penetration depths and hence highly variable redox conditions in up to 2 5 cm thick layers beneath the surface volumetric oxygen consumption rates of surface sediments were measured on board in flow through reactors bedform migration was found to reduce consumption rates by up to 50 presumably caused by the washout of organic carbon that is otherwise trapped in the pore space of the sediment based on the observations we found oxygen penetration depths to be largely controlled by oxygen consumption rates grain size and current velocity these controlling variables are summarized by an adapted damkohler number which allows for prediction of oxygen penetretion depths based on a simple scaling law by integrating the oxygen consumption rates over the oxygen penetration depth oxygen fluxes of 8 34 mmol m 2 d 1 were estimated

cambrian trace fossils of the cruziana ichnofacies from the bikaner nagaur basin north western indian craton abstract the marwar supergroup of the bikaner nagaur basin is composed of sediments deposited from the late neoproterozoic ediacaran to upper cambrian the nagaur sandstone formation of the nagaur group uppermost division of the marwar supergroup preserves trace fossils significant for establishing early cambrian biostratigraphic zones and depositional facies fifteen ichnospecies and eight ichnogenera identified in the nagaur sandstone formation include treptichnus pedum cruziana cf tenella cruziana isp diplichnites ispp a b and c gyrophyllites isp lockeia isp merostomichnites isp monomorphichnus gregarius isp nov monomorphichnus isp planolites isp psammichnites isp rusophycus bikanerus isp nov rusophycus cf carbonarius rusophycus isp and radial trace fossils these trace fossils belong to ethological categories pascichnia repichnia cubichnia and fodinichnia and represent arthropod and worm like burrowing biota the assemblage and a regional comparison with contemporaneous trace fossils in the eastern gondwanan realm suggest that the sequence in the study area belongs to the cruziana tenella ichnozone and to stage 2 upper part of terreneuvian however the middle cambrian is not excluded the trace fossil assemblage belongs to the archetypal cruziana ichnofacies cross bedded sandstone mud cracks and rainprints in the ichniferous strata of the nagaur sandstone formation indicate deposition in an intertidal sand flat with channels that was exposed episodically

revealing coseismic displacements and the deformation zones of the 1999 chi chi earthquake in the tsaotung area central taiwan using digital cadastral data 1 the 1999 chi chi taiwan earthquake mw 7 6 was the largest earthquake to strike taiwan in the twentieth century this earthquake is associated with a 100 km long surface rupture in order to reveal the details of displacement near the surface rupture we use a digital cadastral system to calculate coseismic displacement around the tsaotung area central taiwan the digital cadastral system was originally conceived to survey land and building boundaries in the tsaotung area taiwan authorities have taken digital cadastral measurements before and after the chi chi earthquake the cadastral system affords high density control points that reach 1421 points km2 a system denser than that of the gps accuracy is to within 11 cm a level that is higher than spot imaging and one that allows us to study surface deformation in detail coseismic displacement is 4 3 4 6 m at distance from the surface rupture and decreases to 3 4 m near the surface rupture the azimuth of horizontal displacements is 310 315 and rotates to 280 305 near the surface rupture this produced a compression left lateral deformation zone with 10 3 compression strain near the surface rupture coseismic displacement of the footwall is 1 1 2 m in 110 which is similar to that from using gps data in the tsaotung thrust slice we observed that the azimuth of horizontal displacement rotates from a nw trend to a south trend as a result of slip partitioning and gravity slide effect

changing mechanical response during continental collision active examples from the foreland thrust belts of pakistan abstract we have used data from teleseismic seismic reflection and field geologic studies along with both geomechanical and gravity modeling to contrast the tectonics of four active orogenic wedges in pakistan the kashmir himalaya the salt range potwar plateau foldbelt the sulaiman range and the makran accretionary wedge in makran oceanic crust is still being subducted and a thick pile of sediments is being accreted and underplated undercompaction and excess pore pressures can explain the narrow cross sectional taper and frontal aseismicity of this wedge beneath the sulaiman wedge continental crust is just starting to be underthrust indirect evidence suggests that fine grained carbonate rocks found in abundance deep in the stratigraphic section may be deforming ductilely at the base of the sulaiman wedge and provide a zone of ductile detachment the collision has proceeded to a much more mature stage in the salt range potwar plateau foldbelt and the kashmir himalaya isostatic response to underthrusting of continental crust has kept the sedimentary pile quite thin in both of these wedges so in that respect the two foldbelts are similar however thick eocambrian salt beneath the salt range and potwar plateau permits that foldbelt to be much wider in map view with a thinner cross sectional taper and a mixture of thrust vergence directions a major normal fault in basement causes the salt range to rise in front of the mildly deformed molasse basin of the southern potwar plateau much of the diversity among these mountain belts can be understood in terms of differences in the maturity of the collision process in each area the resulting thickness of the sedimentary pile encountered at the deformation front and the presence or absence of large contrasts in strength between the various layers of the stratigraphic section and basement relief

microbially induced sedimentary structures miss from the ediacaran jodhpur sandstone marwar supergroup western rajasthan abstract fourteen microbially induced sedimentary structures miss have been described from the middle part of the jodhpur sandstone they have been subdivided under three headings a those microbially induced structures which could be compared with the structures also produced by the inorganic processes b those structures which have unique morphologies and could not have produced by inorganic processes alone and c those structures which could not acquire specific morphologies and can be referred to as textured morphological surfaces in the sense of gehling and droser 2009 these forms are described and their stratigraphic significance discussed there are some morphologies like arumberia banksi rameshia rampurensis and jodhpuria circularis which have been restricted to latest neoproterozoic sediments

ripples on stream bed some 30 years ago john f kennedy laid the foundations for the description of the geometry of sand waves on stream beds by the potential flow model since then the analysis has been extensively refined and extended but no rigorous description of the small features called ripples exists the present study attempts a stock taking of the data and the various behavioral concepts with the aim of encouraging researchers to improve our knowledge of the physics of features called ripples various trends are identified from the data it is deduced that ripples act as roughness elements of the boundary the ripple troughs are filled with the energy consuming lee vortices the main flow is over the ripple crests and lee vortices and does not interact with the bed geometry the roughness layer of ripples and vortices is within the constant shear layer and is affected by the flow depth only as far as it affects the velocity distribution and alters the shear stress on the bed

the himalayan passive margin from precambrian to cretaceous times abstract the himalaya passive margin should be separated into the indian himalaya and the pakistan himalaya divided by the nanga parbat haramosh basement uplift in the northwestern syntaxes the indian passive margin shows a complex history involving splitting of microcontinents off the northern gondwana margin from early paleozoic times until the jurassic in contrast the pakistan himalaya formed part of the stable indian shelf until separation from africa started in the jurassic each margin has a distinct stratigraphic history until the mid mesozoic after which they show similar histories until the tertiary the himalaya mountains in india consist of three distinct tectonic units juxtaposed during the neogene by southward thrusting of the northern indian precambrian to mesozoic passive margin the lesser himalaya on the south forms a late precambrian passive margin usually directly overlain by late cretaceous to tertiary clastics its stratigraphy is closest to that of the indian shield in contrast the high himalaya has a thin ordovician to carboniferous shelf sequence deposited after early ordovician deformation and granite intrusion above this thick permian and mesozoic shelf sequences mark the separation of continental blocks off the northern indian margin and the opening of the neotethys ocean the north himalaya formed the slope and basin of this ocean and consists of reactivated paleozoic gneiss domes overlain by thick mesozoic sediments which pass in the northeastern himalaya into an enormously thick sedimentary sequence resting on oceanic crust paleomagnetic and structural evidence indicates at least 500 km of southward thrusting along the main central thrust between the lesser and high himalaya this thrusting together with a further 250 km of erosion at the front of the nappes has removed the entire inner shelf of the himalaya passive margin and can explain the startling contrast between the high and lesser himalaya stratigraphic sequences but there are still discrepancies particularly in the eastern himalaya where precambrian basement is juxtaposed with the north himalaya mesozoic slope these discrepancies can be partly resolved by strike slip movements roughly parallel to the himalaya which have removed parts of the northern indian passive margin such faults of the requisite orientation displacement and age occur in southeast asia where their cumulative displacements can add up to several thousand kilometres similar faults of undoubted pre tertiary age occur in the pakistan himalaya here the passive margin shows a much simpler history of jurassic to miocene subsidence

greater india basin hypothesis and a two stage cenozoic collision between india and asia cenozoic convergence between the indian and asian plates pro duced the archetypical continental collision zone comprising the himalaya mountain belt and the tibetan plateau how and where india asia convergence was accommodated after collision at or be fore 52 ma remains a long standing controversy since 52 ma the two plates have converged up to 3 600 35 km yet the upper crustal shortening documented from the geological record of asia and the himalaya is up to approximately 2 350 km less here we show that the discrepancy between the convergence and the shortening can be explained by subduction of highly extended continental and oceanic indian lithosphere within the himalaya be tween approximately 50 and 25 ma paleomagnetic data show that this extended continental and oceanic greater india promontory resulted from 2 675 700 km of north south extension between 120 and 70 ma accommodated between the tibetan himalaya and cratonic india we suggest that the approximately 50 ma india asia collision was a collision of a tibetan himalayan microconti nent with asia followed by subduction of the largely oceanic greater india basin along a subduction zone at the location of the greater himalaya the hard india asia collision with thicker and contiguous indian continental lithosphere occurred around 25 20 ma this hard collision is coincident with far field deforma tion in central asia and rapid exhumation of greater himalaya crys talline rocks and may be linked to intensification of the asian monsoon system this two stage collision between india and asia is also reflected in the deep mantle remnants of subduction imaged with seismic tomography

grain size and depositional environment as predictors of permeability in coastal marine sands more than half of the surface sediments covering the continental shelves are sandy which may permit substantial sub seafloor pore water advection knowledge of sediment permeability is required for quantifying advection and associated solute transport but studies of marine sediments typically report grain size analyses rather than permeability here data from 23 studies were examined to determine the range in permeabilities reported for sublittoral marine sands and to assess the utility of permeability grain size relationships in this setting in the resulting database the permeability of small w30 cm undisturbed cores collected from the sea floor all fell between 2 10 12 and 4 10 10 m 2 a range where advective transport induced by wave and current action should be pervasive the range in grain size was very similar for near shore 10 m water depth but the permeability of the continental shelf samples was consistently lower for the same median grain size empirical permeability grain size relationships generated a poor fit r 2 0 35 for the aggregate data but separate relationships for near shore and continental shelf samples were significantly better r 2 0 66 and 0 77 respectively permeability grain size relationships thus may be useful for sublittoral sands but a larger database needs to be accumulated before reliable fit parameters and variability can be predicted thus it is recommended that permeability be routinely determined when characterizing sedimentological properties of marine sand deposits concurrent determinations of sediment bulk density and porosity may further improve estimates of permeability 2008 published by elsevier ltd

bed form development based upon the results of a series of 47 bed development experiments the evolution of bed features subsequent to their initial generation from flat bed conditions is examined for each such experiment bed profiles were measured at frequent time intervals as sand wave configurations developed under the action of open channel water flow the two sediments used for these experiments were of geometric mean size 0 20 mm and 0 82 mm respectively in line with the bed form unification model of bed development postulated by saudkivi and witte in 1990 the principle of bed form propagation speed decreasing with increasing bed form height and the mechanisms of bed form coalescence and bed form throughpassing are all found to be central to bed evolution processes a quantitative relation between bed form speed and bed form height is presented bed development predictions based upon bed form unification models can be seen to clearly parallel the present experimental results stability analyses based upon potential

geometry migration and evolution of wave orbital ripples at leo 15 observations of the temporal evolution of the geometric properties and migration of wave formed ripples are analyzed in terms of measured suspended sand profiles and water velocity measurements six weeks of bedform observations were taken at the sandy medium to coarse sized sand leo 15 site located on beach haven ridge during the late summer of 1995 with an autonomous rotary sidescan sonar during this period six tropical storms several of hurricane strength passed to the east of the study site ripples with wavelengths of up to 100 cm and with 15 cm amplitudes were observed the predominant ripples were found to be wave orbital scale ripples with ripple wavelengths equal to 3 4 of the wave orbital diameter although orbital diameters become larger than 130 cm during the maximum wave event it is unclear if a transition to non orbital scaling is occurring ripple migration is found to be directed primarily onshore at rates of up to 80 cm day suspended transport due to wave motions calculated by multiplying acoustic backscatter measurements of suspended sand concentrations by flow velocity measurements are unable to account for a sufficient amount of sand transport to force ripple migration and are in the opposite direction to ripple migration thus it is hypothesized that the onshore ripple migration is due to unobserved bedload transport or near bottom suspended transport bedload model calculations forced with measured wave velocities are able to predict the magnitude and direction of transport consistent with observed ripple migration rates sequences of ripple pattern temporal evolution are examined showing mechanisms for ripple directional change in response to changing wave direction as well as ripple wavelength adjustment and erosion due to changing wave orbital diameter and relative wave to current velocities

bedform contributions to cross shore sediment transport on a dissipative beach abstract field measurements of hydrodynamics suspended sediment transport rates and bedform sediment transport rates were made in the intertidal section of a dissipative sandy beach d50 0 26 mm slope 1 80 at perranporth uk pressure transducers acoustic doppler velocimeters optical backscatter sensors and an acoustic sand ripple profiler were deployed for 12 tides measuring in a range of wave heights from 0 5 to 2 2 m water depths from 1 to 6 m and in current strengths up to 0 4 m s data were analysed in terms of the distance to shore x normalised by the surf zone width xs and spanned the region 0 4 1 5 the fractional contribution of the shoreward directed bedform transport to the total absolute transport was up to 100 and occurred broadly in the region of the breakpoint 0 5

early palaeozoic orogenesis along the indian margin of gondwana tectonic response to gondwana assembly abstract shrimp u pb dating of zircons from a peralkaline s type lesser himalayan granite from the kathmandu region nepal indicate an age of emplacement of 475 ma the granites along with metasedimentary xenoliths show a similar signature of inherited detrital zircon ages ranging from archaean to early palaeozoic with prominent late mesoproterozoic grenvillian and neoproterozoic pan african age peaks and have a maximum age of 500 ma based on the youngest detrital grains deformation structures in xenoliths are truncated by the granite and along with the granites are assigned to a cambro ordovician orogenic event herein termed the bhimphedian orogeny that can be traced across the himalaya from pakistan to the eastern himalaya and possibly extends west into afghanistan we interpret the orogeny as being related to andean type orogenic activity on the northern margin of the indian continent following gondwana assembly the magmatic arc was associated with andesitic and basaltic volcanism and was active from c 530 to 490 ma the arc activity overlaps with and is succeeded by regional deformation crustal melting and s type granite emplacement that extended to 470 ma orogenic activity was driven by coupling across the plate margin either during on going subduction or through accretion of microcontinental ribbons possibly represented by the lhasa and qiangtang blocks it represents the termination of an orogenic cycle termed the north indian orogen that commenced with neoproterozoic rifting and passive margin development and terminated with the bhimphedian orogeny this was succeeded by a return to passive margin setting along the northern indian margin of gondwana which continued until the cenozoic himalayan orogeny

extensive nitrogen loss from permeable sediments off north west africa the upwelling area off north west africa is characterized by high export production high nitrate and low oxygen concentration in bottom waters the underlying sediment consists of sands that cover most of the continental shelf due to their permeability sands allow for fast advective pore water transport and can exhibit high rates of nitrogen n loss via denitrification as reported for anthropogenically eutrophied regions however n loss from sands underlying naturally eutrophied waters is not well studied and in particular n loss from the north west african shelf is poorly constrained during two research cruises in april may 2010 2011 sediment was sampled along the north west african shelf and volumetric denitrification rates were measured in sediment layers down to 8 cm depth using slurry incubations with 15n labeled nitrate areal n loss was calculated by integrating volumetric rates down to the nitrate penetration depth derived from pore water profiles areal n loss was neither correlated with water depth nor with bottom water concentrations of nitrate and oxygen but was strongly dependent on sediment grain size and permeability the derived empirical relation between benthic n loss and grains size suggests that pore water advection is an important regulating parameter for benthic denitrification in sands and further allowed extrapolating rates to an area of 53 000 km2 using detailed sediment maps denitrification from this region amounts to 995 kt yr 1 average 3 6 mmol m 2 d 1 which is 4 times higher than previous estimates based on diffusive pore water transport sandy sediments cover 50 60 of the continental shelf and thus may contribute significantly to the global benthic n loss

trace fossils from the nagaur sandstone marwar supergroup dulmera area bikaner district rajasthan india abstract thirteen trace fossils are described from the nagaur sandstone the lower formation of the nagaur group these are rusophycus didymus salter 1856 chondrites isp brongniart 1828 cruziana isp d orbigny 1842 isopodichnus isp bornemann 1989 dimorphichnus obliquus seilacher 1955 monomorphichnus monolinearis shah and sudan 1983 diplichnites isp dawson 1873 skolithos isp haldeman 1840 palaeophycus tubularis hall 1847 planolites isp nicholson 1873 ichnogenus a trails and scratch marks this assemblage has been referred to as the cruziana assemblage and on this basis the nagaur sandstone has been suggested a lower cambrian age the nagaur sandstone has been correlated with the purple sandstone of pakistan the tal succession of the kumaun and himachal lesser himalaya and the garbyang lolab and kunzum la formations of the tethys himalaya

tectonostratigraphic subdivisions of the himalaya a view from the west 1 indian plate rocks in the central himalaya have traditionally been divided into orogen parallel fault bound tectonostratigraphic zones a straightforward westward extrapolation of these zones has proved problematic in part because of a lack of consensus on the existence or significance of major faults within the metamorphic zone of the indian plate in pakistan where more than 10 locations for the main central thrust mct have been proposed we address this ambiguity by systematically tracing established central himalayan tectonostratigraphy around the western himalayan syntaxis and across pakistan this exercise reveals the following stratigraphic and structural relationships 1 there is a westward decrease in neogene shortening across the himalayan fold and thrust belt such that there is no age equivalent thrust in pakistan with displacement and metamorphic juxtaposition equivalent to the central himalayan mct 2 shortening across the fold and thrust belt in western pakistan is concentrated in the unmetamorphosed foreland as opposed to the metamorphic zone in the central himalaya 3 lesser himalayan higher himalayan and tethyan rocks are in stratigraphic order within the metamorphic zone of pakistan which appears to be the metamorphic equivalent of kashmir tethyan stratigraphy 4 the combination of early paleozoic and late paleozoic tectonism in pakistan has locally eliminated upper proterozoic higher himalayan rock and lower to middle paleozoic tethyan rock from the metamorphic zone of pakistan 5 late cretaceous and or early paleocene proto himalayan deformation in the pakistan foreland telescoped and eroded stratigraphy prior to the main phase of himalayan orogeny 6 tectonostratigraphic zones are offset in eastern pakistan by the transverse jhelum balakot fault 7 there is no evidence within the indian plate of pakistan for a large scale normal fault system comparable to the south tibetan detachment system 8 stratigraphy as well as the age and tectonic setting of deformation and metamorphism must be taken into account when drawing tectonostratigraphic zones

a flume study on the development and equilibrium morphology of current ripples in very fine sand an empirical model is constructed for the development and equilibrium dimensions of small scale unidirectional bedforms in sand with a median grain size of 0 095 mm based on a series of steady flow experiments in a flume current ripples always attain a linguoid plan morphology with constant average height 13 1 mm and wavelength 115 7 mm provided that sufficient time is allowed for their formation the development pattern of these ripples on a flat bed is independent of flow velocity and involves four stages 1 incipient ripples 2 straight and sinuous ripples 3 non equilibrium linguoid ripples and 4 equilibrium linguoid ripples straight and sinuous ripples are non equilibrium bedforms at all flow velocities the time needed to reach equilibrium dimensions is related to the inverse power of flow velocity and ranges from several minutes to more than hundreds of hours at flow velocities where washed ripples are stable the equilibrium wavelength is similar to that of equilibrium linguoid ripples but the equilibrium height rapidly decreases from 13 1 mm to zero towards upper stage plane bed conditions the results of the flume experiments correspond reasonably well with those of previous studies provided that various complicating factors such as different experimental methods different sediment characteristics shallow flow depths and non equilibrium runs are accounted for

combined role of advective pumping and mechanical dispersion on time scales of bed form induced hyporheic exchange this study analyzes the effect of advective pumping and pore scale dispersion on bed form induced hyporheic exchange advection and dispersion play a competitive role in the exchange dynamics betwe

the driving forces of porewater and groundwater flow in permeable coastal sediments a review abstract advective flows rapidly transport water solutes and particles into and out of permeable sand beds and significantly affects the biogeochemistry of coastal environments in this paper we reviewed the drivers of porewater and groundwater advection in permeable shelf sediments in an attempt to bridge gaps among different disciplines studying similar problems we identified the following driving forces 1 terrestrial hydraulic gradients 2 seasonal changes in the aquifer level on land moving the location of the subterranean estuary 3 wave setup and tidal pumping 4 water level differences across permeable barriers 5 flow and topography induced pressure gradients 6 wave pumping 7 ripple and other bed form migration 8 fluid shear 9 density driven convection 10 bioirrigation and bioturbation 11 gas bubble upwelling and 12 sediment compaction while these drivers occur over spatial scales ranging from mm to km and temporal scales ranging from seconds to years their ultimate biogeochemical implications are very similar i e they are often a source of new or recycled nutrients to seawater and transform organic carbon into inorganic carbon drivers 2 12 result in no net water input into the ocean taking all these mechanisms into account we conservatively estimate that a volume equivalent to that of the entire ocean is filtered by permeable sediments at time scales of about 3000 years quantifying the relative contribution of these drivers is essential to understand the contribution of sediments to the global cycles of matter