early archean crust in bastar craton central india a geochemical and isotopic study abstract high a12o3 trondhjemitic gneisses occur in enclaves within granites at markampara in the bastar craton central india these gneisses exhibit a highly fractionated rare earth element ree pattern frsol la yb n 60 83 and may have been produced by partial melting of an amphibolitic protolith a zircon u pb age of 3509 14 7 ma dates primary crystallization of the trondhjemites a granite surrounding the gneissic enclaves yields a zircon u pb age of 2480 3ma rb sr wholerock data for the trondhjemitic gneisses are somewhat disturbed and indicate initial 87 sr 86 sr ratios of 0 7016 pb isotopic data are poorly correlated and suggest a three stage evolution with an early period of high u pb growth 9 5 10 5 after emplacement at 3 5 ga followed by isotopic disturbance and u depletion at 2 5 ga during widespread magmatism and metamorphism loss of rb and other mobile elements may also have occurred at this time

archean paleoproterozoic transition the indian perspective abstract india has perhaps the richest paleoarchean to paleoproterozoic crustal components on earth miller et al 2018 notwithstanding this much of the indian subcontinent remains unexplored compared to other ancient cratons in north america australia brazil and africa there are five archean cratonic nuclei in india the aravalli bundelkhand singhbhum bastar and the dharwar with well preserved proterozoic supracrustal sequences this paper critically reviews the paleoarchean to paleoproterozoic supracrustal record of the indian subcontinent with special emphasis on the archean paleoproterozoic transition which is generally placed at 2 5 ga based on the emplacement age of the great dyke of zimbabwe in general the archean paleoproterozoic transition in indian cratonic blocks is associated with high continental freeboard condition unlike north america south africa and western australia the indian cratonic blocks except bastar are devoid of paleoproterozoic glacial diamictite mazumder et al 2015 however similar to the pongola supergroup of south africa there are evidences of neoarchean glaciation in dharwar ojakangas et al 2014 in contrast to the global scenario of extensive development of bif across the archean paleoproterozoic transition the indian paleoproterozoic successions are devoid of banded iron formation bif except the 1 85 ga old bif in bundelkhand in contrast the majority of the indian bifs are of paleoarchean or neoarchean age thus the geodynamic and supracrustal data collected from five indian archean cratonic blocks do not correspond uniquely and precisely to a global change in tectonic style onset of neoarchean global magmatism and rifting or lithostratigraphic and environmental changes suggested across the archean paleoproterozoic transition van kranendonk et al 2012 therefore a revision and redefinition of the archean proterozoic boundary is outstanding this article is part of a special issue entitled archean earth processes edited by rajat mazumder and patrick eriksson

characterization of lake water and ground water movement in the littoral zone of williams lake a closed basin lake in north central minnesota williams lake minnesota is a closed basin lake that is a flow through system with respect to ground water ground water input represents half of the annual water input and most of the chemical input to the lake chemical budgets indicate that the lake is a sink for calcium yet surficial sediments contain little calcium carbonate sediment pore water samplers peepers were used to characterize solute fluxes at the lake water ground water interface in the littoral zone and resolve the apparent disparity between the chemical budget and sediment data pore water depth profiles of the stable isotopes 18o and 2h were non linear where ground water seeped into the lake with a sharp transition from lake water values to ground water values in the top 10 cm of sediment these data indicate that advective inflow to the lake is the primary mechanism for solute flux from ground water linear interstitial velocities determined from 2h profiles 316 to 528 cm yr were consistent with velocities determined independently from water budget data and sediment porosity 366 cm yr stable isotope profiles were generally linear where water flowed out of the lake into ground water however calcium profiles were not linear in the same area and varied in response to input of calcium carbonate from the littoral zone and subsequent dissolution the comparison of pore water calcium profiles to pore water stable isotope profiles indicate calcium is not conservative based on the previous understanding that 40 50 of the calcium in williams lake is retained the pore water profiles indicate aquatic plants in the littoral zone are recycling the retained portion of calcium the difference between the pore water depth profiles of calcium and 18o and 2h demonstrate the importance of using stable isotopes to evaluate flow direction and source through the lake water ground water interface and evaluate mechanisms controlling the chemical balance of lakes published in 2003 by john wiley sons ltd

effect of anisotropy and groundwater system geometry on seepage through lakebeds 1 analog and dimensional analysis abstract distribution of seepage through lakebeds is controlled partly by geometric configuration of the lake and of the groundwater system interacting with the lake to evaluate the effect of these factors conductive paper electric analog models were used to analyze a number of lake and groundwater settings having different geometric configurations most settings analyzed are of lakes that do not penetrate the groundwater system the width ratio the ratio of half the lake width to thickness of the groundwater system is the principal geometric characteristic used in this study because the distribution of groundwater seepage into a lake is not uniform across the lakebed the concept of a streamlinecrowding factor is developed and is used to determine seepage patterns from geometric characteristics of the lake and its contiguous groundwater system analysis of fourteen different width ratios of lake and groundwater systems indicates that lakes can be defined by three general groups of seepage patterns which include flow patterns volumes and rates 1 lakes having width ratios less than 0 6 show relatively uniform distribution of seepage across the lakebed 2 lakes having width ratios of 0 6 to 2 0 change in absolute and relative streamline crowding in the near shore region and 3 lakes having width ratios greater than 2 0 show stable flow patterns near shore however with increasing lake width the relative streamline crowding increases relative to that width for deep lakes and those in anisotropic media the crowding effect is decreased resulting in more uniform seepage across the lakebed

high precision 207pb206pb zircon geochronology using a small ion microprobe abstract a small geometry ion microprobe cameca ims 4f has been successfully used for the routine measurement of 207 pb 206 pb ratios in individual zircons with a spatial resolution of 20 m in spite of the lower sensitivity of the small ion microprobe resulting from operating at high mass resolution m m 4600 in order to resolve isobaric molecular interferences we can discern archean components whose ages differ by 50 ma a single measurement requires 90 min of data acquisition thus a comprehensive study of a zircon population can be accomplished in a few days three sets of precambrian zircons analyzed earlier by other techniques yielded ages which are within 2 of their true values as our first unknown we analyzed zircons from a sample of orthogneiss collected from the aravalli craton of northwestern india for this sample we obtained a minimum age of 3281 3 ma 1 which we believe closely approximates the time of crystallization of the gneiss s igneous protolith

quantitative analysis of detrital modes statistically rigorous confidence regions in ternary diagrams and their use in sedimentary petrology abstract detrital modes are the basic type of quantitative data used in sedimentary petrology they represent estimates of the petrographic framework composition of sand or sandstone obtained by point counting of thin sections at present geological inferences from analysis of these numerical data are semi quantitative only because many of the data processing methods employed in sedimentary petrology lack a firm theoretical basis a review of existing methods reveals a number of fundamental statistical problems associated with the use of univariate statistics and the construction of so called hexagonal fields of compositional variation it is shown that these problems can be overcome by using multivariate methods that honour the non negativity and unit sum constraints on compositional data and incorporate the covariance structure spread in compositional data can be modelled on two levels 1 by regarding the grain as unit of observation and the total point count as a sample from a multinomial distribution 2 by regarding the total count as unit of observation and a set of counts as a sample from an additive logistic normal distribution numerical methods are presented for constructing statistically rigorous confidence regions in ternary diagrams by inversion of significance tests for these two distributions statistical analyses of the framework composition and heavy mineral assemblages of modern beach and river sands illustrate their use the case histories are followed by a brief overview of popular multivariate methods for reconstructing sediment provenance

la sf icp ms zircon u pb geochronology of granitic rocks from the central bundelkhand greenstone complex bundelkhand craton india abstract the central bundelkhand greenstone complex in bundelkhand craton northern india is one of the well exposed archaean supracrustal amphibolite banded iron formation bif and felsic volcanic rocks fv and associated with grey and pink porphyritic granite tonalite trondhjemite granodiorite ttg here we present high precision zircon u pb geochronological data for the pinkish porphyritic granites and ttg the zircons from the grey pinkish porphyritic granite show three different concordia ages of 2531 21 ma 2516 38 ma and 2514 13 ma which are interpreted as the best estimate of the magmatic crystallization age for the studied granites we also report the concordia age of 2669 7 4 ma for a trondhjemite gneiss sample which is so far the youngest u pb geochronological data for a ttg rock suite in the bundelkhand craton this ttg formation at 2669 ma is also more similar to precambrian basement ttg gneisses of the aravalli craton of north western india and suggests that crust formation in the bundelkhand craton occurred in a similar time frame to that recorded from the aravalli craton of the north western india

groundwater interaction with a kettle hole lake relation of observations to digital simulations abstract observations made on a small fully penetrating kettle hole lake are used to test predictions made using digital stimulation about the exchange of water between lakes and groundwater systems on the upgradient side of lower nashotah lake groundwater inseepage decreases exponentially away from the shore water exchange on the downgradient side is controlled by the presence and strength of a groundwater mound but that mound and its effects are ephemeral when the mound increases in strength it generates a local groundwater flow cell beneath it which contains water of chemical composition distinct from deeper regional groundwater the growing mound also causes local inseepage of groundwater to the lake in an expanding zone along the downgradient shore all of these phenomena occur as they have been predicted in published studies where digital simulation of relatively simple groundwater lake systems has been carried out the field observations thus confirm the validity of the simulation studies and their usefulness as a tool for understanding water exchanges in unmonitored systems

rapid sea level rise in the aftermath of a neoproterozoic snowball earth earth s most severe climate changes occurred during global scale snowball earth glaciations which profoundly altered the planet s atmosphere oceans and biosphere extreme rates of glacioeustatic sea level rise are predicted by the snowball earth hypothesis but supporting geologic evidence has been lacking we use paleohydraulic analysis of wave ripples and tidal laminae in the elatina formation australia deposited after the marinoan glaciation 635 million years ago to show that water depths of 9 to 16 meters remained nearly constant for 100 years throughout 27 meters of sediment accumulation this accumulation rate was too great to have been accommodated by subsidence and instead indicates an extraordinarily rapid rate of sea level rise 0 2 to 0 27 meters per year our results substantiate a fundamental prediction of snowball earth models of rapid deglaciation during the early transition to a supergreenhouse climate

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

effect of ground water recharge on configuration of the water table beneath sand dunes and on seepage in lakes in the sandhills of nebraska u s a abstract analysis of water level fluctuations in about 30 observation wells and 5 lakes in the crescent lake national wildlife refuge in the sandhills of nebraska indicates water table configuration beneath sand dunes in this area varies considerably depending on the configuration of the topography of the dunes if the topography of an interlake dunal area is hummocky ground water recharge is focused at topographic lows causing formation of water table mounds these mounds prevent ground water movement from topographically high lakes to adjacent lower lakes if a dune ridge is sharp the opportunity for focused recharge does not exist resulting in water table troughs between lakes lakes aligned in descending altitudes parallel to the principal direction of regional ground water movement generally have seepage from higher lakes toward lower lakes

subduction related tectonic evolution of the neoarchean eastern dharwar craton southern india new geochemical and isotopic constraints the neoarchean eastern dharwar craton edc is distinct from the mesoarchean western dharwar craton wdc in many aspects of its geology the important distinguishing features of the edc are the predominance of younger granitoids abundance of gold mineralization and the exposure at lower crustal depths no consensus exists on evolutionary models for edc mutually exclusive plume and subduction derived tectonic models have been proposed geochemical and radiogenic isotopic studies on the granitoids and volcanic rocks of three greenstone belts along a cross section in the northern part of edc are presented herein the evolved nd isotopic signatures radiogenic pb isotopic ratios and arc like geochemical signatures are suggestive of a subduction regime and the involvement of recycled older crust in the derivation of these rocks the proposed petrogenetic mechanism involves multi stage processes in a supra subduction regime involving slab dehydration formation of hydrous basaltic melts and re melting and interaction with sub arc basaltic crust at low pressures where amphibole plagioclase is the dominant residual phase there is a notable systematic decrease in the extent of older crustal involvement from west to east in the edc this is in concurrence with the younging of dharwar craton from west to east and eastward subduction the proposed petrogenetic model can efficiently explain the variations in older crustal involvement which is very common in other archean cratons c 2012 elsevier b v all rights reserved

uraniferous paleoplacers of the mesoarchean mahagiri quartzite singhbhum craton india depositional controls nature and source of 3 0 ga detrital uraninites abstract the quartz pebble conglomerate qpc hosted detrital uranium mineralization is unique in character in terms of their restricted distribution before 2 2 ga atmosphere during pre great oxidation event pre goe such qpc paleoplacer deposits over the world are good targets for moderate to high tonnage and low grade uranium deposits and more importantly for their gold content the mahagiri quartzite dated c 3 02 ga for their youngest detrital zircon population is developed unconformably over the mesoarchean singhbhum granite 3 44 ga to 3 1 ga the mahagiri quartzite includes a conglomerate pebbly sandstone dominated subaerial alluvial fan to coastal braided plain sequence in the lower parts and shallow marine mature quartz arenite in the upper parts the alluvial fan braided plain deposits in the lower parts host a number of pyritiferous and uraniferous conglomerate and pebbly sandstone beds the uraninite grains are rounded to subrounded in outline suggesting mechanical transport and detrital origin together with detrital pyrite and uraninite constitute the example of 3 0 ga paleoplacer closely comparable to the witwatersrand au u deposits epma and sem eds studies suggest that the uraninite grains are rich in th 4 wt s and ree y chemical formula calculations from epma analyses suggest uraninite grains belong to two populations with different oxidation states as revealed from y ree and cation u4 u6 apfu ratios the u contents of the detrital uraninite grains from mahagiri are significantly lower than that of the ideal stoichiometric composition of uo2 this is mainly due to higher amount of heterovalent cationic substitution by th ree y pb and ca in mahagiri qpc uraninite structures and partial alteration and metamictization of uraninites alteration due to metamictization resulted in elevated concentration of si al p and ca in more altered and metamict uraninite grains the ree pattern is typically flat with comparable lree hree concentration the high th content flat ree pattern suggests that the uraninitere presents high temperature phases 350 c and are magmatic in origin the mahagiri detrital uraninite grains suggest existence of highly felsic and k rich richer than ttg granodiorite granite monzogranite suites ggm of rocks older than 3 1 ga in the singhbhum craton

size shape and orientation of grains in sands and sandstones image analysis applied to rock thin sections abstract a computer based image analysis system is used to determine the grain size distribution grain shape and grain orientation from rock thin sections a monte carlo simulation allows correction of the grain size distribution for the corpuscle effect grains cut marginally in the thin section plane have smaller apparent diameters thin section derived grain size distributions of modern and ancient samples have been compared with distributions obtained from sieving of the same samples different grain shape parameters have been compared with the wadell formula the grain orientation can be easily and reliably measured in thin sections from different cuts of a sample grain orientation data can help to determine paleocurrent directions

single zircon evaporation ages constraining the growth of the archaean aravalli craton northwestern indian shield single grain 207 pb 206 pb zircon ages were determined for granitoids and gneisses which constitute the archaean basement rocks of the aravalli craton of rajasthan northwestern indian shield the protolith ages for two gneisses collected from east of udaipur are 3230 ma and 2887 ma respectively the granitoids display an intrusive relationship with the gneisses and yielded ages ranging between 2666 ma and 2620 ma these ages provide the basis for a geochronological model of evolution of the oldest basement of the aravalli craton

magmatic and metamorphic history of paleoarchean tonalite trondhjemite granodiorite ttg suite from the singhbhum craton eastern india texturally controlled dating of zircon from paleoarchean tonalite trondhjemite granodiorites of the older metamorphic tonalitic gneisses and the singhbhum granite batholith phases i ii and iii from the singhbhum craton in eastern india reveals a polycyclic evolution of the archean crust the granitoid suites were emplaced in two pulses at 3 45 3 44 ga and 3 35 3 32 ga tonalites and trondhjemites of the older metamorphic tonalitic gneisses were emplaced at ca 3 45 3 44 ga together with phase iii of the singhbhum granite pluton while granites belonging to the older metamorphic tonalitic gneisses were emplaced at ca 3 35 3 32 together with phase i and phase ii of the singhbhum granite pluton both crustal units underwent an early phase of relatively high grade metamorphism at 3 30 3 28 ga followed by extensive fluid induced alteration during low grade metamorphism at 3 19 3 12 ga and 3 02 2 96 ga the two units have also been marginally affected at ca 2 52 ga and 1 06 ga by major metamorphic events in the north singhbhum mobile belt and the singhbhum shear zone at the northern margin of the craton the zircon grains in granites have inherited cores with ages of ca 3 61 ga and 3 46 3 41 ga and with well developed oscillatory growth zonation which suggests the granitic magmas were derived by partial melting of an igneous precursor or sedimentary rocks derived from an igneous source the emplacement of the expansive granitoids belonging to the older metamorphic tonalitic gneisses and the singhbhum granite was synchronous with the amphibolite facies metamorphism ca 3 32 ga of older meta igneous and metasedimentary rocks belonging to the older metamorphic group major felsic crust formation in the craton occurred in a narrow time interval between 3 46 and 3 32 ma with minor contributions of material as old as 3 6 ga the complex polycyclic evolution of the paleoarchean crust in the singhbhum craton can account for the wide range of often disparate ages obtained using whole rock isochron dating techniques with some of the isochron dates being geologically meaningful while others representing mixing lines or disturbance of the isotopic systems during metamorphism

transient hydrogeological controls on the chemistry of a seepage lake a solute mass balance method was used to estimate groundwater inflow and outflow rates for nevins lake michigan a seepage lake in the upper peninsula that historically has shown extremely variable water chemistry compared with most other seepage lakes a 4 year study 1989 1992 of the hydrology and geochemistry of nevins lake and its contiguous groundwater system revealed that changes in the mass of dissolved solutes are the result of annual hydraulic gradient reversals a pronounced acidification of nevins lake from 1986 to 1988 was likely caused by drought induced diminished groundwater inflow rates in this study dissolved calcium the major cation in water of nevins lake groundwater and precipitation was used for estimating mass flow rates during the 1989 1992 period nevins lake showed a reproducible annual cycle in calcium mass immediately following spring snowmelt and the resulting hydraulic gradient reversal the mass of dissolved calcium in the lake increases rapidly and then it decreases steadily throughout the summer and early fall at which time the lake becomes hydraulically mounded and receives no groundwater inflow groundwater flow rates estimated by the solute mass balance method are sensitive to assumed solute concentrations in discharging groundwater pore water samples from the lake bed are shown to be more representative of water discharging to the lake than are samples from piezometers near the lake shore but spatial and temporal variability in pore water chemistry must be considered stable isotope analyses 18o and 2h of lake water groundwater and pore water samples show that water discharging to nevins lake in the spring is entirely recycled lake water and no groundwater derived from terrestrial recharge reaches the lake the conceptual model formulated during this study linking lake chemistry and the contiguous groundwater system and general groundwater flow patterns surrounding highly transient lake systems are likely transferable to other similar systems

the lower crust of the dharwar craton southern india patchwork of archean granulitic domains u pb geochronological major and trace element and isotope geochemical data identify crustal domains of contrasted petrological origins and histories in the lower crust of the dharwar craton all affected by granulite facies metamorphism and deformation in the neoarchean four lower crustal domains have been identified and investigated across the neoarchean amphibolite to granulite facies transition zone 1 in the southern part of the western dharwar craton wdc high grade metamorphism affects rocks formed before 3 0 ga high grade metamorphism is recorded at ca 2 51 ga followed by possible complex cooling and resetting until 2 2 ga 2 the br hills mm hills domain represents the lower crust of the central dharwar province cdp which is here defined as a transitional crust between the old 3 ga wdc and the eastern dharwar province edp not older than 2 7 ga this granulitic domain contains the oldest rocks of the dharwar craton with ttg suites formed at ca 3 4 ga and ca 2 6 ga suites of probable crustal recycling origin both suites are involved in 2513 5ma granulite facies metamorphism 3 the nilgiri granulitic domain is tectonically juxtaposed with the deepest level of the wdc as a consequence of neoarchean dextral slip along the moyar shear zone the massif consists of rocks of orogenic affinities formed between 2 70 and 2 56 ga and overprinted by granulite facies metamorphism at 2518 10 ma 4 the krishnagiri domain exposes the deepest levels of the eastern dharwar craton it is composed of ttg and calc alkaline igneous protoliths formed between 2 55 and 2 53 ga migmatization in the upper part of the domain took place at 2507 6ma and granulite facies overprint in the deepest parts of the domain is constrained at 2516 5 ma the krishnagiri domain was magmatically accreted to the lower crust of both the cdp and edp by interaction with mafic magmatism inducing reworking of the 2 7 2 6 ga or older overlying crust the nilgiri granulites share several temporal and petrological properties with the madras granulites that make the easternmost outcrop of the dharwar craton we tentatively suggest that the nilgiri and madras granulites evolved as parts of a common madras domain in the lower crust of the edp before activation of the moyar shear zone in this sense the nilgiri massif may be considered as an allochtonous unit in a context of neoarchean ultra hot orogeny in south india

post fire ecohydrological conditions at peatland margins in different hydrogeological settings of the boreal plain in the boreal plain of canada the margins of peatland ecosystems that regulate solute and nutrient fluxes between peatlands and adjacent mineral uplands are prone to deep peat burning whether post fire carbon accumulation is able to offset large carbon losses associated with the deep burning at peatland margins is unknown for this reason we examined how post fire hydrological conditions i e water table depth and periodicity soil tension and surface moisture content and depth of burn were associated with moss recolonization at the peatland margins of three sites we then interpreted these findings using a hydrogeological systems approach given the importance of groundwater in determining conditions in the soil plant atmosphere continuum in peatlands peatland margins dominated by local groundwater flow from adjacent peatland middles were characterized by dynamic hydrological conditions that when coupled with lowered peatland margin surface elevations due to deep burning produced two common hydrological states 1 flooding during wet periods and 2 rapid water table declines during dry periods these dynamic hydrological states were unfavorable to peatland moss recolonization and bryophytes typical of post fire recovery in mineral uplands became established in contrast at a peatland margin where post fire hydrological conditions were moderated by larger scale groundwater flow flooding and rapid water table declines were infrequent and subsequently greater peatland dwelling moss recolonization was observed we argue that peatland margins poorly connected to larger scale groundwater flow are not only prone to deep burning but also lags in post fire moss recovery consequently an associated reduction in post fire peat accumulation may occur and negatively affect the net carbon sink status and ecohydrological and biogeochemical function of these peatlands

palaeo environment in an ancient low latitude arid lacustrine basin with loessite the smith bank formation early triassic in the central north sea uk continental shelf acknowledgements this work was conducted as part of the triassic mudstones joint industry project which was sponsored by bp conocophillips eon e p esso exploration and production uk limited gdf suez e p uk ltd jx nippon maersk oil shell and total the guidance of prof steve hillier of the james hutton institute in quantitative mineralogical analysis is acknowledged with gratitude dr stuart jones and an anonymous referee are thanked for their incisive and constructive reviews that significantly helped in the revision of the manuscript

textural trends in turbidites and slurry beds from the oligocene flysch of the east carpathians romania deep water sandstone beds of the oligocene fusaru sandstone and lower dysodilic shale exposed in the buza uu valley area of the east carpathian flysch belt romania can be described in terms of the standard turbidite divisions in addition mud rich sand layers are common both as parts of otherwise normal sequences of turbidite divisions and as individual event beds eleven units interpreted as the deposits of individual flows were densely sampled and 87 thin sections were point counted for grain size and mud content s3 ta divisions which form the bulk of most sedimentation units have low internal textural variability but show subtle vertical trends in grain size most commonly coarse tail normal grading is associated with finetail inverse grading the mean grain size can show inverse grading normal grading or a lack of grading but sorting tends to improve upward in most beds fine tail inverse grading is interpreted as resulting from a decreasing effectiveness of trapping of fines during rapid deposition from a turbidity current as the initially high suspended load fallout rate declines if this effect is strong enough the mean grain size can show subtle inverse grading as well thus thick inversely graded intervals in deep water sands lacking traction structures do not necessarily imply waxing flow velocities if the suspendedload fallout rate drops to zero after the deposition of the coarse grain size populations the remaining finer grained flow bypasses and may rework the top of the s3 division forming well sorted coarser grained current structured tt units alternatively the suspended load fallout rate may remain high enough to prevent segregation of fines leading to the deposition of significant amounts of mud along with the sand mud content of the sandstones is bimodal either 3 13 or more than 20 two types of mud rich sandstones were observed coarser grained mud rich sandstones occur towards the upper parts of s3 ta divisions these units were deposited as a result of enhanced trapping of mud particles in the rapidly deposited sediment finer grained mud rich units are interbedded with ripple laminated very fine grained sandy tc divisions during deposition of these units mud floccules were hydraulically equivalent to the very fine sand and silt sized sediment the mud rich sandstones were probably deposited by flows that became transitional between turbidity currents and debris flows during their late stage evolution

anatomy of a water escape cusp in upper proterozoic torridon group sandstones scotland abstract evidence from recently published experiments is applied to the interpretation of a typical soft sediment deformation structure in coarse fluvial sandstones from the applecross formation of the upper proterozoic torridon group in northwest scotland the structure is an interfacial cusp formed at the contact between two cross bedded sandstone units in an upward coarsening sequence the characteristics of the structure suggest that deformation took place while the sediment was in a fluidized state during fluidization a water filled cavity developed near the top of the lower unit separating fluidized sediment beneath from a static couplet above the cavity became narrower and taller as fluidization continued focussing fluidization at a point primary stratification was destroyed in the fluidized zone but there is no evidence that fluidized sediment burst through the overlying zone a rupture may be out of the plane of the section or alternatively fluidization could have stopped before this stage was reached or fluid pressures could have been dissipated upwards the cavity closed leaving the lower part of the static couplet as a distinct unit estimates of the fluidization velocity and the duration of fluidization suggest the volume of water required for fluidization this could have been derived from packing changes following liquefaction of underlying sediment or from groundwater movements within the braided fluvial environment

a new conceptual model for the deposition process of homogenite application to a cretaceous megaturbidite of the western pyrenees basque region sw france abstract the north pyrenean megaturbidite is a 19 63 m exceptional thick bed deposited during the late turonian and extending over more than 90 km in the basque region country sw france its thickness varies from more than 63 m to about 19 m from east mauleon area to west basque coast it represents a total compacted volume of about 90 km3 of carbonates on the field rare sedimentary structures are visible in the turbidite bed they consist of laminar planar lamination and rare cross laminations in the eastern region and antidune like structures in the western region five sites have been sampled with a vertical step of 50 cm to 1 m thin sections have been quantitatively analyzed for counting the terrigeneous fraction the quartz grain size and the mineral orientation the deposits fine westward which suggests a source located in the east of the mauleon basin this is consistent with the quartz grain orientation in the lower part of the megaturbidite the deposits fine upward from medium sand to clayey silt this is consistent with the classical definition of homogenites and suggests that these kinds of deposits are turbidites these observations also suggest that the term megaturbidite is appropriated for these deposits the sedimentary analysis indicates that the deposit results from a single event the volume of sediment involved in the process as well as the quartz grain orientation indicating flow motion in the opposite direction of the initial flow and the antidune like structure suggest the formation of reflected flows and the formation of standing waves over the complete water column in the basque flysch sub basins corresponding to a seiche effect the origin of the megaturbidite is probably an earthquake generated collapse on the carbonate platform this example allows providing a new conceptual model for the process of homogenite deposition this model explains the deposition of thick fine grained crudely graded megaturbidites

middle to late pleistocene coastal deposits of alghero northwest sardinia italy chronology and evolution the shallow marine to coastal deposits of alghero have been dated using the optically stimulated luminescence osl method and studied to define the palaeoenvironmental evolution of coastal areas in northwest sardinia dating coupled with sedimentological and stratigraphical analyses allowed the subdivision of the succession in four unconformity bounded units u2 u3a u3b u4 unit u2 of penultimate glacial stage mis 6 ca 150 ka is composed of dune deposits formed intermittently along rocky coastal areas under strong wind conditions subunit u3a is composed of cliff bounded gravelly dominated pocket beach deposits commonly highly fossiliferous and is assigned to the interglacial mis 5e ca 125 ka subunit u3b is characterized by sandy beach to coastal systems of the isotopic sub stage mis 5c ca 100 ka the unconformity between u3b and u4 marks the initiation of last glacial regression mis 5a 4 ca 77 ka during which shelf areas were exposed and small incised valleys developed along the valley flanks colluvial or sheetflood sediments were deposited and in the central part thick reddish paleosols formed valleys were eventually filled by thick aeolian dune deposits mis 4 3 indicating persistent inland sand transport around alghero coastal carbonate rich dunes preferentially formed and migrated inland during lowstand and falling stages when the climate is relatively cold vegetation is quite open winds are fairly strong and sediment supply from exposed shelf areas is high

a hydrologic assessment of a saline spring fen in the athabasca oil sands region alberta canada a potential analogue for oil sands reclamation canada s post mined oil sands will have a higher concentration of salts compared with freshwater peatlands that dominate the landscape while rare naturally occurring saline wetlands do exist in alberta s boreal plains and may function as analogues for reclamation however little is known about their hydrology this paper investigates the geochemical and hydrologic characteristics of a natural saline spring peatland in alberta s oil sands region the fen is located within a saline groundwater discharge area connected to the erosional edge of the grand rapids formation na 195 25 680 mgl 1 and cl 1785 56 249 mg l 1 were the dominant salts and the fen transitioned sharply to freshwater along its margins because in part of subsurface mineral ridges that restricted shallow groundwater exchange salinity decreased from hypersaline to brackish along the local groundwater flow path but no active spring outlets were observed over the two year study vertical groundwater discharge was minimal because of the very low permeability of the underlying sediments subsurface storage was exceeded during periods of high flow resulting in flooding and surface runoff that was enhanced by the ephemerally connected pond network these findings have implications for reclamation as mechanisms such as subsurface mineral ridges may function as effective saline groundwater control structures in the post mined environment incorporating saline wetlands into regional monitoring networks will help to better quantify natural discharge which has implications for belowground wastewater storage related to in situ bitumen extraction copyright 2015 john wiley sons ltd

effect of anisotropy and groundwater system geometry on seepage through lakebeds 2 numerical simulation analysis abstract the interaction of lakes and groundwater is controlled partly by the geologic framework through which the water flows two interrelated geometric factors of the groundwater system that affect flow are overall geometry of the system and anisotropy of the porous media within the system numerical simulation analysis was made for variations in the coefficient of anisotropy for each of several lake and groundwater settings having different geometric configurations these analyses indicate that for a given geometric setting as the anisotropy of geologic materials decreases seepage from a lake decreases and depth of the local groundwater flow system associated with the lake increases transformation of scale of groundwater systems that have anisotropic media to isotropic equivalents results in a change in the overall geometry because of the different slopes of the water table and lakebed resulting from the scale transformations a series of numerical experiments were made for various geometric configurations for a given anisotropy these analyses indicate that as thickness of the groundwater system decreases relative depth of the local flow system increases and seepage from the lake decreases

comparison of the hydrological role of two reclaimed slopes of different ages in the athabasca oil sands region alberta canada establishing hydrological connectivity in reconstructed landscapes and understanding how this connectivity evolves over time is critical for the development of effective water management strategi

influence of subhumid climate and water table depth on groundwater recharge in shallow outwash aquifers 1 hypothetical one dimensional models of unsaturated flow were used to estimate the probability of groundwater recharge to shallow glacial outwash aquifers simulations were supported by field data previous three dimensional modeling and cross sectional models of water table response to precipitation events for a research area in northern alberta canada groundwater recharge rates were found to depend on the year to year climate variation the depth to the water table and were largely driven by annual snowmelt simulations indicate that in summer months when transpiration and canopy interception were considered explicitly groundwater recharge was negligible for water table depths less than 6 m below ground surface the occurrence of recharge depends on climatic conditions water deficit or surplus of the current and previous year and can vary from 0 to 266 mm yr 1 for water table depths of 6 m or more recharge will depend on climate conditions from the most recent decade have less annual variability and a mean annual rate of approximately 45 mm yr 1

sub aqueous sand extrusion dynamics extruded sandstone mounds and sandstone sheets are increasingly recognized in the geological record and seismic data yet the underlying mechanisms that control these features and determine whether deposits form discrete accumulations or areally extensive sheets remain poorly understood here we address these issues through study of a well exposed ancient sand sheet in the shannon basin ireland sand volcanoes are shown to have erupted contemporaneously following liquefaction and fluidization of delta front mouth bar sands and silts the expelled sediment forming an extruded sheet of sand the sand sheet formed during a single prolonged eruption event with the interaction of radial gravity currents from the hundreds of vents exerting control on the internal architecture of the extrudite based on our observations here we develop a process based model that demonstrates that sand extrusions can form sheets only if 1 multiple vents are extruding coevally causing gravity currents to interact or 2 topographic forcing such as channelling redirects the otherwise radial gravity currents resulting in sheet like deposition of extruded material away from the vent site this study provides a new model of sand extrudite formation and examines the potential for identifying extrudites from core and bed scale studies and differentiating them from liquefied beds

influence of glacial landform hydrology on phosphorus budgets of shallow lakes on the boreal plain canada summary a comparative study of three shallow lake catchments in contrasting glacial landscapes coarse textured outwash fine textured till hummocky moraines and glacio lacustrine clay till plains demonstrated a distinct landform control on the proportion and type of surface and groundwater sources influencing total phosphorus p and total dissolved phosphorus dp concentrations and p budgets of lakes on the boreal plain of the western boreal forest alberta canada lakes located on fine textured landforms had high p and dp median 148 and 148 g l 1 glacio lacustrine plains 99 and 63 g l 1 moraine respectively linked to shallow groundwater loadings from near surface peat with high p from adjacent wetlands in contrast the lowest lake p and dp median 50 and 11 g l 1 respectively occurred on the coarse textured landform reflecting greater inputs of deep mineral groundwater with low p from quartz rich substrates annual lake p budgets reflected lake connectivity to the surrounding landform and relative contributions of p by surface versus groundwater they also reflected distinct scales of groundwater larger scale versus short shallow flow paths with differing p between landform types and occurrence of internal biogeochemical p cycling within landforms a regional lake survey reflected trends from the catchment scale linking landform type to potential p sources as well as topographic position to potential trophic status across the boreal plain together the results provide a conceptual framework for the scale of interactions between lakes and surrounding source waters influencing p loadings in differing hydrogeological landscapes important to management strategies and predicting impacts of land use disturbances on productivity of boreal plain lakes

late archaean granites a typology based on the dharwar craton india abstract extensive field work in the eastern dharwar craton associated with petrographic and geochemical major and trace elements investigations allows four main types of late archaean granitoids to be distinguished 1 na rich granitoids of trondhjemitic tonalitic and granodioritic composition ttg that are characterised by strongly fractionated ree patterns and low hree contents and generally interpreted as slab melts generated by partial melting of metamorphosed hydrated basalt most likely in a subduction environment 2 sanukitoids which are k and mg rich monzonites and granodiorites with ttg like ree patterns associated with marked lile enrichment and considered to result from the reaction of slab melts generated in a subduction environment with and assimilation of mantle wedge peridotite 3 uncommon high hfse mg and k granites with strongly ree and lile enrichment that probably formed by partial melting of an enriched mantle source unlike in the genesis of sanukitoids in this case the slab melt is considered to be wholly consumed by reaction with mantle minerals resulting in mantle enrichment subsequent melting of this enriched mantle probably in a post subduction setting gives rise to high hfse mg and k magmas as demonstrated for the closepet granite dharwar craton the hot mantle derived magma can induce melting of continental crust and then mix with the anatectic products 4 k rich mg poor anatectic biotite granites with ree patterns that are less fractionated and show negative eu anomalies these granites result from the remelting of old basement or recently accreted plutons both with ttg compositions such anatexis can occur either in a subduction or in a post subduction environment this typology based on the well exposed dharwar craton can be extended to late archaean granitoids from all over the world about such 500 analysis were compiled and a number of discriminant diagrams based on both major and trace elements are proposed the most likely tectonic setting for the observed rock types is an accretionary orogen with accretion of continental blocks above a subduction system followed by thermal reworking of the newly accreted continental material however it has been found that archaean subduction related granitoids are significantly different from their modern counterparts implying progressive changes in the modes of magma generation at convergent margins from the archaean to the present

ion microprobe 207pb 206pb ages of zircons from the bundelkhand massif northern india implications for crustal evolution of the bundelkhand aravalli protocontinent abstract 207pb 206pb ages of zircon from gneissic rocks and granitoids representing all major lithological units of the bundelkhand massif northern india have been determined using an ion microprobe the presence of early archaean granitic crust in this region is established from these ages ages for the kuraicha and the mahoba gneisses and associated metabasic enclaves suggest the oldest partial and metamorphic melting event in this region occurred at 3 3 ga the presence of younger gneisses with ages of 2 7 and 2 5 ga suggests the existence of multiple protolith age components within the massif three major granitoid suites hornblende biotite leuco granitoids were emplaced at 2 5 ga within a time span of a few tens of millions of years felsic volcanism also occurred around this time an age of 2 49 ga for the youngest phase of leucogranitoid marks the time of overall stabilization of this massif the geochronological history of the bundelkhand massif appears to be remarkably similar to that of the basement complex of the aravalli delhi orogenic belt another prominent archaean crustal block to the west of this massif geochemical features of the different rock types in these two regions are also very similar we propose that these two apparently discrete blocks evolved as a single crustal unit with stabilization taking place at 2 5 ga

influence of regional setting on the interaction between shallow lakes and aquifers 1 interaction between surface water and groundwater depends on the position of a lake within the regional flow system the approach in this paper is to nest a local scale two dimensional 2 d lake aquifer model within a 1 d regional aquifer model to examine the effect of the regional setting on surface water groundwater interaction this extends previous steady state flow modeling which is presented in earlier publications the results indicate that the type of regional setting and position of the lake within that setting impose constraints on the near field flow geometry only nine of 39 previously identified flow regimes are possible in the regional flow system considered flow through lakes are dominant and can occur anywhere within the regional flow recharge and discharge lakes are more likely to occur near the groundwater divide where regional hydraulic gradients are flattest and can be counteracted by local forcing in and near the lake

compositional variations in deep sea gravity flow deposits a case study from the voirons flysch voirons wagital complex chablais prealps france abstract grain size control is frequently invoked to explain the compositional variation of detrital sediments in fluvial sediments a similar possibility is here investigated in the fossil deep sea gravity flow deposits from the voirons flysch voirons wagital complex chablais prealps about 270 samples of diverse depositional settings were analysed using the framework composition including cement and porosity mutti facies and grain size measurements six lithofacies have been identified from cluster analysis they correspond to channel l1 to l3 and lobe l4 and l5 depositional settings and to reworked turbidites l6 our results emphasize the close relationship between petrography and grain size which alters the detrital signal from extrabasinal sources the abundant polycrystalline component of proximal deposits is progressively removed while skeletal grains and additional intrabasinal grains become more abundant in distal deposits alongside porosity is reduced by the simultaneous increase of cement which constrains subsequent diagenetic modifications hence proximal depositional settings keep most of the inherited signal from extrabasinal sources whereas distal deposits will be homogenised when plotted in provenance analysis diagrams the successive depositional settings show distinct fields possibly corresponding to different tectonic settings of the dickinson model this compositional variation thus creates a bias in provenance interpretation resulting from both grain size control and flow mechanisms finally our results emphasize that petrographic data must be handled with care in provenance analyses especially when comparing various deep sea gravity flow systems with different grain size ranges

time response of the water table and saltwater transition zone to a base level drop 1 this paper investigates the effect of a drainage base level drop on the groundwater system in its vicinity using theoretical analysis simulations and field data we present a simple and novel method for analyzing the effect of a base level drop by defining two characteristic times that describe the response of the water table and the transition zone between the fresh and saline water the dead sea was chosen as a case study for this process because of the lake s rapid level drop rate during a continuous lake level drop the discharge attains a constant value and the hydraulic gradient remains constant we describe this new dynamic equilibrium and support it by theoretical analysis simulation and field data using theoretical analysis and sensitivity tests we demonstrate how different hydrological parameters control the response rate of the transition zone to the base level drop in some cases the response of the transition zone may be very rapid and in equilibrium with the water table or alternatively it can be much slower than the water table response as is the case in the study area

paleo to mesoarchean ttg accretion and continental growth in the western dharwar craton southern india constraints from shrimp u pb zircon geochronology whole rock geochemistry and nd sr isotopes a multidisciplinary study involving field petrographic shrimp u pb zircon titanite ages whole rock geochemical and nd sr isotope data is presented for the peninsular gneisses and associated plutons forming core of the dharwar craton two major periods 3350 3280 ma and 3230 3200 ma of crustal growth through ttg accretion sub contemporaneous with greenstone volcanism are documented elemental and nd sr isotope data suggest that the ttgs originated by low and high pressure melting of heterogeneous mafic sources thickened island arc or oceanic plateau crust at different depths among the early accreted ttgs magmatic protoliths of low al gneisses formed by low pressure 10 12 kbar melting of a depleted mafic source at shallow levels island arc type crust with plagioclase amphibole ilmenite in the residue whilst high al gneisses were probably produced by high pressure melting 14 18 kbar of a chondritic or a less depleted mafic source with garnet amphibole pyroxene ilmenite in the residue base of island arc crust or thickened oceanic plateau the 3230 3200 ma trondhjemitic plutons marking the second accretion event derived by higher pressure 14 16 kbar melting of a mafic source island arc type crust with garnet plagiocalse hornblende ilmenite with a minor involvement of previously accreted ttgs this plutonism was coeval with a major phase of crustal scale diapiric overturn that had a major imprint on crustal reworking a later magmatic episode at ca 3100 ma produced granitic plutons derived from crustal melting and leucocratic gneisses derived from a depleted mafic source in the lower crust documentation of depleted shallow and deep mantle reservoirs during 3350 3280 ma magmatism implies massive differentiation of the mantle during an earlier episode of crust formation around 3800 600 ma as substantiated by nd model ages and published pb isotope data as well as u pb detrital zircon ages with in situ hf isotope data

hydrological controls on deep burning in a northern forested peatland while previous boreal peatland wildfire research has generally reported average organic soil burn depths ranging from 0 05 to 0 20 m here we report on deep burning in a peatland in the utikuma complex forest fire swf 060 90 000 ha may 2011 in the sub humid climate of alberta s boreal plains deep burning was prevalent at peatland margins where average burn depths of 0 42 0 02 m were fivefold greater than in the middle of the peatland we examined adjacent unburned sections of the peatland to characterize the hydrological and hydrophysical conditions necessary to account for the observed burn depths our findings suggest that the peatland margin at this site represented a smouldering hotspot due to the effect of dynamic hydrological conditions on margin peat bulk density and moisture specifically the coupling of dense peat bulk density 100 kg m 3 and low peat moisture m 250 at the peatland margin allowed for severe smouldering to propagate deep into the peat profile we estimated that carbon release from this margin hotspot ranged from 10 to 85 kg c m 2 mean 27 kg c m 2 accounting for 80 of the total soil carbon loss from the peatland during the wildfire as such we suggest that current estimations of peatland carbon loss from wildfires that exclude and or miss these hotspots are likely underestimating total carbon emissions from peatland wildfires we conclude that assessments of natural and managed peatland vulnerability to wildfire should focus on identifying dense peat on the landscape that is vulnerable to drying copyright 2015 john wiley sons ltd

origin and paleoenvironmental reconstruction of phosphorus bearing sandstones of the cambrian xinji formation southwestern margin of the ordos basin china increasing exploration interest in oil and gas hosted by early cambrian strata has focused research efforts on early cambrian sandstones the origin of phosphorus and the paleoenvironment of phosph

the stratigraphic record and processes of turbidity current transformation across deep marine lobes sedimentary facies in the distal parts of deep marine lobes can diverge significantly from those predicted by classical turbidite models and sedimentological processes in these environments are poorly understood this gap may be bridged using outcrop studies and theoretical models in the skoorsteenberg formation south africa a downstream transition from thickly bedded turbidite sandstones to argillaceous internally layered hybrid beds is observed the hybrid beds have a characteristic stratigraphic and spatial distribution being associated with bed successions which generally coarsen and thicken upward reflecting deposition on the fringes of lobes in a dominantly progradational system using a detailed characterization of bed types including grain size grain fabric and mineralogical analyses a process model for flow evolution is developed this is explored using a numerical suspension capacity model for radially spreading and decelerating turbidity currents the new model shows how decelerating sediment suspensions can reach a critical suspension capacity threshold beyond which grains are not supported by fluid turbulence sand and silt particles settling together with flocculated clay may form low yield strength cohesive flows development of these higher concentration lower boundary layer flows inhibits transfer of turbulent kinetic energy into the upper parts of the flow ultimately resulting in catastrophic loss of turbulence and collapse of the upper part of the flow advection distances of the now transitional to laminar flow are relatively long several kilometres suggesting relatively slow dewatering several hours of the low yield strength flows the catastrophic loss of turbulence accounts for the presence of such beds in other fine grained systems without invoking external controls or large scale flow partitioning and also explains the abrupt pinch out of all divisions of these sandstones estimation of the point of flow transformation is a useful tool in the prediction of heterogeneity distribution in subsurface systems

effect of groundwater recharge on configuration of the water table beneath sand dunes and on seepage in lakes in the sandhills of nebraska u s a comment

late archaean 2550 2520 ma juvenile magmatism in the eastern dharwar craton southern india constraints from geochronology nd sr isotopes and whole rock geochemistry the results of field geochronologic geochemical and isotopic studies are presented for the granitoids that occur east of the closepet batholith up to the kolar schist belt ksb field data such as common foliation strong shear deformation occasionally leading to mylonitization together with petrographic data including reduction in grain size with corroded borders show characteristics of the syn kinematic emplacement of the granitoids single zircon evaporation ages define a minimum age of 3127 ma for the tonalitic trondhjemitic granodioritic ttg basement and 2552 2534 ma plateau ages for the emplacement of the granitoids which slightly predate 20 30 ma the emplacement of the 2518 ma closepet batholith major and trace element data together with isotopic data suggest at least four magmatic suites from closepet batholith to the east which have independent magmatic evolution histories the observed data are compatible with magma mixing for the closepet batholith melting of ttg and assimilation fractional crystallization processes for bangalore granites either melting of heterogeneous source or different degree of melting of the same source for the granitoids of hoskote kolar and fractional crystallization for the western margin of the ksb isotopic nd sr and geochemical data lree and lil elements suggest highly enriched mantle and ancient ttg crust for the closepet batholith enriched mantle and ttg crust for the bangalore granites c a chondritic mantle source for the granitoids of hoskote kolar and the quartz monzonites of the western margin of the ksb and slightly depleted mantle for granodiorites of the eastern margin of the ksb we interpret all these geochronologic geochemical and isotopic characteristics of granitoids from the closepet batholith to the east up to the ksb in terms of a plume model the centre of the plume would be an enriched hot spot in the mantle that lies below the present exposure level of the closepet batholith melting of such an enriched mantle hot spot produces high temperature magmas closepet that penetrate overlying ancient crust where they strongly interact and induce partial melting of the surrounding crust these magmas cool very slowly as the hot spot maintains high temperatures for a long time thus they appear younger 2518 ma on the contrary to the east the plume induces melting of c a chondritic or slightly depleted mantle that produces relatively colder and less enriched magmas which show less or no interactions with the surrounding crust and cool rapidly and appear slightly older 2552 2534 ma this plume model can also account for late archaean geodynamic evolution including juvenile magmatism heat source for reworking inverse diapirism and granulite metamorphism in the dharwar craton

eolianite grain size distributions as a proxy for large changes in planetary atmospheric density a digitized version of the ahlbrandt 1979 global dune dataset and data for distributions in figure are available at https github com erikgoosmann aeoliandata

carbonate budget of a cold water coral mound challenger mound iodp exp 307 abstract cold water coral ecosystems represent a worldwide distributed carbonate factory which is so far not considered in global carbonate budget estimations the herein presented study evaluates the carbonate budget of a complete cold water coral mound sequence from challenger mound belgica mound province porcupine seabight sw offshore ireland drilled during iodp expedition 307 reaching back to the late pliocene versus background sediment derived calcite dominated carbonate cores from adjacent drift deposits were examined for comparison studies challenger mound which developed in a fast growth phase unit m1 2 7 to 1 6 ma and a slower growth phase or mound decline unit m2 0 8 ma until today separated by a so called mound crisis displays increased carbonate accumulation rates for both phases 17 3 g cm 2 ka for unit m1 and 5 7 g cm 2 ka for unit m2 compared to adjacent drift deposits but only about 33 to 40 wt of the carbonate is derived from corals bulk sedimentation rates of on and off mound deposits suggest a decline of challenger mound since the onset of drift deposition in the area about 1 2 ma ago yet total carbonate accumulation rates as well as hemipelagic background sediment derived carbonate accumulation rates from challenger mound unit m2 still exceed the carbonate accumulation rates of the adjacent drift deposits the selective enrichment of background sediment derived carbonate by a factor of 2 0 in a cwc mound is herein observed for the first time this might be caused by the different hydrodynamic behaviour and slower settlement of marine fluff rich in calcareous detritus compared to siliciclastic sediments and its effective baffling by the coral framework and or the active catch of the calcareous plankton by the corals the carbonate accumulation rates of challenger mound are about 4 to 12 of the carbonate accumulation rates of tropical shallow water reefs but exceeds the carbonate accumulation rates of continental slopes by a factor of 3 9 to 11 8 the carbonate production for the entire belgica mound province is estimated with 3 2 10 3 t a for unit m1 and 1 0 10 3 t a for unit m2

3 56ga tonalite in the central part of the bastar craton india oldest indian date abstract the lack of information regarding early achaean rocks from the indian peninsula is mainly due to the absence of high quality u pb zircon ages a tonalite sample from the ttg gneiss supracrustal association from the central part of the bastar craton in central india is dated at 3 56 ga this is the oldest protolith age so far recorded from india these ttg gneisses have enclaves of metasedimentary and metavolcanic rocks that may provide important information on the first billion year history of the indian craton this new date for tonalite from the bastar craton is the first precise u pb zircon age from india s first u pb geochronology laboratory located at the geological survey of india which hopefully will remedy the paucity of good geochronological data for older rocks of the indian peninsula

the central india tectonic zone a geophysical perspective on continental amalgamation along a mesoproterozoic suture abstract the central india tectonic zone citz is a prominent divide and a major suture zone between the north indian and south indian crustal blocks the resistive upper crust as modeled in the magnetotelluric data from citz suggests a dominant tonalite trdondhjemite granodiorite composition associated with an accretionary complex characterized by mainly felsic rock components the highly conductive bodies in this zone might represent mafic ultramafic layered intrusives derived from a deeper reservoir of underplated basaltic magma related to the formation of the cretaceous deccan flood basalts the uniformly thick mafic lower crust below the cratons on both sides of the suture is interpreted as the accreted remnants of archaean and paleoproterozoic subducted slabs we redefine the nature of deep faults traversing the citz which were described as steep and penetrating the moho by previous workers and classify them as listric faults with gentle dips at depth seismic reflection data from the eastern side of the suture suggest a northwestward subduction of the bhandara craton reflection data from the central part of the citz show northerly dip in the southern part suggesting northward subduction of the dharwar craton however an opposite trend is observed in the northern part of the suture with a southward dip of the bundelkhand craton based on these features and in conjunction with existing magnetotelluric models we propose a double sided subduction history along the citz this would be similar to the ongoing subduction accretion process in the western pacific region which possibly led to the development of paired collision type and pacific type orogens one important feature is the domal structure along the central part of the suture with a thick felsic crust occurring between mafic and intermediate crust the high resistivity felsic domain suggests underplated sediments felsic crust that would have caused the doming our model also accounts for the extrusion of regional metamorphic belts at the orogenic core and the occurrence of high pressure ultrahigh temperature paired metamorphic belts within the suture

common reflection surface stack imaging of the proterozoic chambal valley vindhyan basin and its boundary fault in the northwest india constraints on crustal evolution and basin formation

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

morphology genesis and distribution of nanometer scale pores in siliceous mudstones of the mississippian barnett shale research on mudrock attributes has increased dramatically since shale gas systems have become commercial hydrocarbon production targets one of the most significant research questions now being asked focuses on the nature of the pore system in these mudrocks our work on siliceous mudstones from the mississippian barnett shale of the fort worth basin texas shows that the pores in these rocks are dominantly nanometer in scale nanopores we used scanning electron microscopy to characterize barnett pores from a number of cores and have imaged pores as small as 5 nm key to our success in imaging these nanopores is the use of ar ion beam milling this methodology provides flat surfaces that lack topography related to differential hardness and are fundamental for high magnification imaging nanopores are observed in three main modes of occurrence most pores are found in grains of organic matter as intraparticle pores many of these grains contain hundreds of pores intraparticle organic nanopores most commonly have irregular bubblelike elliptical cross sections and range between 5 and 750 nm with the median nanopore size for all grains being approximately 100 nm internal porosities of up to 20 2 have been measured for whole grains of organic matter based on point count data from scanning electron microscopy analysis these nanopores in the organic matter are the predominant pore type in the barnett mudstones and they are related to thermal maturation nanopores are also found in bedding parallel wispy organic rich laminae as intraparticle pores in organic grains and as interparticle pores between organic matter but this mode is not common although less abundant nanopores are also locally present in fine grained matrix areas unassociated with organic matter and as nano to microintercrystalline pores in pyrite framboids intraparticle organic nanopores and pyrite framboid intercrystalline pores contribute to gas storage in barnett mudstones we postulate that permeability pathways within the barnett mudstones are along bedding parallel layers of organic matter or a mesh network of organic matter flakes because this material contains the most pores

microdepression focused recharge in a coastal wetland la plata argentina depression focused recharge dfr has been well documented for the clay till plains of western canada kettle lakes of southeastern wisconsin the sandhills region of nebraska and elsewhere in this study the importance of dfr in a fine grained estuarine coastal plain environment with extremely low topographic relief is shown the southwestern coastal plain of the rio de la plata near the city of la plata argentina extends 8 9 km inland from the river and ranges in elevation from 0 to 3 m above sea level the holocene postpampeano sediments predominantly composed of silty clay in the study area mantle the coastal plain and exert a major control on the hydrodynamics of groundwater of the region the average hydraulic conductivity of the unit ranges from 1 0 10 9 m s 1 when estimated on a small scale single well and oedometer tests to approximately 1 0 10 8 m s 1 when estimated on a larger scale tritium profiles and seepage meters a study of the groundwater flow system has established that recharge is occurring in the marshes of the central coastal plain which are 0 5 1 0 m lower than the surrounding land a broad 50 cm high groundwater mound a significant feature in the context of a regional hydraulic gradient of 0 0005 was documented below the marshland using nests of monitoring wells recharge rates are further controlled by subtle 10 40 cm elevation variations within the marsh four nests of six monitoring wells each were installed in the marsh and sampled for tritium recharge rates were then estimated through calibration simulations using a 1 d analytical solute transport model in the two nests in the lower wetter areas recharge rates were estimated at 4 6 cm year 1 whereas estimated recharge rates in the higher drier areas ranged from 0 3 cm year 1 these differences are consistent with 1 near neutral vertical hydraulic gradients in higher areas vs persistent downward gradients in lower areas 2 chloride concentrations almost an order of magnitude lower in groundwater underlying lower areas than in that of higher areas due to flushing of older more saline groundwater in the lower areas and 3 isotopic evidence for evapotranspiration only in the higher areas the present study suggests that ponding of surface water in local depressions can lead to significant recharge from coastal wetlands this finding has implications for the study of water balance soil salinity and nutrient budgets in these environments 1997 elsevier science b v all rights reserved

estimating groundwater exchange with lakes 2 calibration of a three dimensional solute transport model to a stable isotope plume a three dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of 18o and used to calculate groundwater inflow and outflow rates at a lake in northern wisconsin the flow model was calibrated to observed hydraulic gradients and estimated recharge rates calibration of the solute transport submodel to the configuration of a stable isotope 18o plume in the contiguous aquifer on the downgradient side of the lake provides additional data to constrain the model a good match between observed and simulated temporal variations in plume configuration indicates that the model closely simulated the dynamics of the real system the model provides information on natural variations of rates of groundwater inflow lake water outflow and recharge to the water table inflow and outflow estimates compare favorably with estimates derived by the isotope mass balance method krabbenhoft et al this issue model simulations agree with field observations that show groundwater inflow rates are more sensitive to seasonal variations in recharge than outflow

groundwater s dynamic role in regulating acidity and chemistry in a precipitation dominated lake abstract the role of groundwater in regulating the hydrologic and chemical regime ofan acid susceptible lake situated in a sandy silicate aquifer in northern wisconsin was determined by direct groundwater measurements using a network of 68 piezometers groundwater inputs were compared with precipitation and dryfall components of the hydrologic and chemical budgets for the lake groundwater contributed only 10 of the water to crystal lake in 1982 but was the major source of alkalinity calcium magnesium sodium potassium silicon and chloride precipitation contributed 90 of the water and was the major source of hydrogen and sulfate ions continuing analyses suggest that groundwater consistently supplies the bulk of the inoorganic constituents to the lake on annual basis the flux of groundwater and dissolved solids to the lake is highly seasonal with large pulses of groundwater inflow occuring after spring snowmelt and in the fall for certain nonconservative elements such as silicon the periodic influx of chemically concentrated groundwater can trigger significant changes in the chemical and biological balance in the lake despite the fact that the aquifer contains no carbonate minerals and the area experiences acid precipitation ph 4 6 the alkalinity of the small amount of groundwater entering crystal lake is more than enough to neutralize all of the acidity contributed by precipitation in lake sulfate reduction may generate an equal amount of alkalinity this buffering of ph helps to regulate aluminum concentrations at low levels thus minimizing potential aluminum toxicity in the lake most lakes in the region probably receive even larger amounts of alkalinity rich groundwater than crystal lake because most lie further downgradient in the regional flow system this may help to explain why most lakes in this acid susceptible area are no more acidic today than they were 50 years ago

distribution of groundwater seepage to large surface water bodies the effect of hydraulic heterogeneities abstract at 26 sites on the upper great lakes and their connecting channels where groundwater seepage measurements have been made seepages decrease continually offshore at only seven 26 instead 17 63 of the sites have offshore seepages which substantially exceed those at some locations closer to shore the distributions fall into two consistent patterns one where a nearshore decrease in seepage with increasing distance is succeeded offshore by an increase and a second where nearshore seepages are relatively constant and then increase farther offshore the patterns have been observed in two independent studies using two totally different seepage meter designs and emplacement methods and are attributed to hydrogeologic heterogeneities beneath the surface water body detailed marine geophysical measurements at seven sites on green bay show that the anomalously high offshore seepages there are associated with local thinning of the relatively low hydraulic conductivity glacial sediments separating the bay from the underlying aquifer a fractured dolomite at these locations heterogeneity in sediment thickness is a stronger factor in causing seepage anomalies than is heterogeneity of either sediment or bedrock hydraulic conductivity insufficient information exists to confirm a parallel cause effect relation at the other sites but evidence points in that direction similar seepage anomalies have been observed at other smaller lakes by other researchers but never with this frequency it is argued that the cause of the difference is the size of the great lakes seepage occurs and measurements have been made over much greater offshore distances than in smaller lakes and the likelihood that heterogeneities will occur within the zone of measurement is thus also much greater

evaluating the mechanical compaction of quartzarenites the importance of sorting llanos foreland basin colombia abstract mechanical compaction is the main porosity reducing process in sandstones including high reservoir quality rigid grain sandstones for such sandstones the extrapolation of theoretical or experimental compaction algorithms needs calibration with rocks having well constrained burial histories evaluating the compaction of these rocks is achieved by comparing current intergranular volume igv with depositional igv which is strongly dependent on sorting however because sandstone sorting is difficult to measure accurately its impact on depositional porosity and compaction state is largely underestimated we use the quartzarenites of the oligocene carbonera formation in the subsurface of the hydrostatically pressured llanos basin to illustrate the importance of sorting when evaluating the compaction of rigid grain sandstones igv and sorting were measured in core samples using a combination of transmitted light and cathodoluminescence images resulting in improved accuracy over standard procedures the compaction state of clean quartzarenites at given depths is best described using igv versus sorting plots which are used to derive compaction curves for specified sorting values the igv versus sorting trends are displaced to lower igv values with increasing burial depth the differences in igv caused by differences in sorting exceed the differences in igv resulting from 1000 m of burial illustrating the high impact of sorting when evaluating compaction contrasting with published experimental results the compaction of the llanos basin ductile grain poor quartzarenites is independent of grain size and grain rearrangement is the main compaction mechanism during the first 1 6 km of burial based on the llanos data we have generated igv versus depth curves for clean pure quartzarenites of specific sorting which can be used to predict their maximum primary porosity up to moderate burial depths differences with other published burial curves are probably related to unaccounted variations in sorting ductile grain content and framework strengthening cements however the llanos basin quartzarenites contain virtually no cements explaining their high degree of compaction relative to other rigid grain sandstones and making them ideal to isolate the effects of compaction on the igv of quartzarenites the llanos basin data suggest that below 2 5 km of depth clean well to moderately well sorted quartzarenites continue reducing their igv by mechanical compaction below the 26 limit which should apply only to extremely well sorted rigid grain uncemented sandstones

thin section grain size analysis revisited existing proposals for converting thin section data to their sieve equivalents are all flawed in various ways while questions concerning the significance of the grain size of spherical grains measured on a volume frequency basis in thin section using units and of non spherical ellipsoidal grains using both millimetres and units have not been satisfactorily resolved in the literature it can be shown mathematically that the mean thin section diameters of spherical grains or axis lengths of a series of parallel sections through ellipsoidal grains will underestimate the dimensions of the corresponding central section i e one passing through the grain centre by 0 2023 when measured on a volume frequency basis in order to approximate the effect of measuring particle size on random cuts through ellipsoidal grains the dimensions of a series of sections cut in 49 unique directions symmetrically arranged and evenly spread with respect to the ellipsoidal axes were calculated this calculation was carried out for five different ellipsoids which between them covered the mean sphericity and thin section axial ratio values normally encountered among naturally occurring quartz grain populations the data indicated that the mean true nominal diameters d of ellipsoidal quartz grains can be obtained in thin sections from the mean nominal sectional diameters d and major axes of the central sections derived from the observed values by multiplying the millimetre means by 1 1318 and subtracting 0 2023 from the means using the following equations a rough estimate to within c 5 of both the mean nominal diameters and the mean long axes of ellipsoidal quartz grains can be arrived at by applying a simple correction factor to the mean long axis lengths as measured in thin section using either millimetres or units

hydrogeological controls on post fire moss recovery in peatlands summary wildfire is the largest disturbance affecting boreal peatlands however little is known about the controls on post fire peatland vegetation recovery while small scale variation in burn severity can reduce post fire moss water availability high water table wt positions following wildfire are also critical to enable the re establishment of keystone peatland mosses i e sphagnum thus post fire moss water availability is also likely a function of landscape scale controls on peatland wt dynamics specifically connectivity to groundwater flow systems i e hydrogeological setting for this reason we assessed the interacting controls of hydrogeological setting and burn severity on post fire moss water availability in three burned sphagnum dominated peatlands in alberta s boreal plains at all sites variation in burn severity resulted in a dichotomy between post fire surface covers that 1 exhibited low water availability regardless of wt position and had minimal i e lightly burned feather mosses and severely burned sphagnum fuscum or 2 exhibited high water availability depending on wt position and had substantial 50 moss re establishment i e lightly burned s fuscum and where depth of burn was 0 05 m notably hydrogeological setting influenced the spatial coverage of these post fire surface covers by influencing pre fire wts and stand characteristics e g shading because feather moss cover is controlled by tree shading lightly burned feather mosses were ubiquitous 25 in drier peatlands deeper pre fire wts that were densely treed and had little connection to large groundwater flow systems moreover hydrogeological setting also controlled post fire wt positions thereby affecting moss re establishment in post fire surface covers that were dependent on wt position e g lightly burned s fuscum accordingly higher recolonization rates were observed in a peatland located in a groundwater flow through system that had a shallow post fire wt therefore we argue that hydrogeological setting influences post fire recovery in two ways 1 by influencing vegetation structure prior to wildfire thereby controlling the coverage of post fire surface covers and 2 by influencing post fire wt positions these results suggest that post fire moss recovery in peatlands isolated from groundwater flow systems may be particularly susceptible to droughts and future climate change

factors influencing groundwater seepage in a large mesotrophic lake in new york abstract groundwater seepage is gaining recognition as a critical feature of lake shoreline environments yet our understanding of this process is complicated by the considerable spatial heterogeneity observed in flow rates within and among lakes this research investigated spatial patterns in groundwater seepage around the shoreline of oneida lake a 207 km2 lake located in central new york usa replicated shielded seepage meters with associated controls were used to quantify rates and directions of groundwater flow along a 120 m stretch of shoreline throughout the summers of 1997 1999 these reference meters exhibited an average flow rate of 72 ml m 2 h 1 n 840 se 5 with individual flow rates as high as 1200 ml m 2 h 1 additional meters monitored in 1998 indicated that seepage patterns were highly synchronous but increased in magnitude of flow rate with increasing distances offshore up to 100 m from shore in 1999 private landowners assisted in weekly monitoring of seepage meters at 28 additional sites distributed around the 88 km perimeter of oneida lake the highest groundwater flow rates averaging 100 ml m 2 h 1 consistently occurred along the northern and eastern shorelines lowest flow rates including areas of groundwater recharge occurred along the western and southwestern shorelines proximal to the lake s outlet spatial patterns in groundwater flow were surprisingly unrelated to substrate texture despite wide variability observed around the lake edge from silty clays to sands gravels and boulders broad scale factors of underlying bedrock geology and regional precipitation patterns appear to be driving the observed spatial patterns in oneida lake s groundwater contributions

the oldest zircons of africa their u pb hf o isotope and trace element systematics and implications for hadean to archean crust mantle evolution abstract more than 450 detrital zircon grains from two limpopo belt quartzite samples were investigated by a combination of scanning electron imaging u pb dating 18 o lu hf isotope and trace element analyses in order to get robust information about the early earth s crust mantle evolution the detrital zircon grains have crystallization ages between 3 95 ga and 3 18 ga show hf t between 1 to 15 1 unit and 18 o vsmow mostly between 5 5 and 8 1 0 2 pristine zircon domains reveal ti in zircon temperatures between 700 and 865 c and th u of 0 3 2 3 trace elements point to zircon formation in predominately granitoid rocks metamorphic zircon rims have ages 2 65 ga hf 2 65ga 15 18 o 7 0 8 1 and th u mostly hf t age array i which starts from a chondritic uniform reservoir chur at about 4 5 ga and requires 176 lu 177 hf 0 020 indicative for mafic crust most zircon grains however plot on or above an hf t age array ii which runs parallel to array i 176 lu 177 hf 0 021 and starts from chur at 4 01 ga oxygen isotope compositions of 18 o 5 5 indicate that the magmatic host rocks of the zircons have been formed either by melting of altered mafic crust which interacted with cold water prior to granitoid formation and or that ancient sedimentary and or magmatic rocks were involved in the melting process the new u pb hf 18 o datasets together with compiled data from worldwide sources indicate a significant gap of about 5 epsilon units between arrays i and ii furthermore they illustrate that many hadean zircon analyses plot well below array i and some above chur these findings support an interpretation that the hadean earth was covered by a long lived mafic protocrust perhaps forming a partially open stagnant lid this protocrust was affected by internal reworking but also injected and overlain by ultra mafic rocks derived from chondritic and highly depleted mantle sources at

dynamic temporal patterns of nearshore seepage flux in a headwater adirondack lake abstract although seepage in lakes is known to vary as a function of precipitation and watershed characteristics temporal patterns of seepage flux over daily and weekly time scales have not been extensively studied with a concentrated effort of direct measurement of seepage in nearshore areas in this study seepage was intensively measured with seepage meters over two summers and during snowmelt in lower sylvan pond a small lake in the adirondack mountains region of new york state usa a consistent pattern of slight discharge never exceeding 105 ml m 2 h 1 was observed at three stations along a segment of the shoreline near the inlet stream a distinct temporal pattern of seepage was observed at three stations along another portion of the shoreline seepage discharged 400 ml m 2 h 1 for a portion of the summer in 1998 and then shifted to recharge 2 h 1 for the remainder of the summer a similar temporal pattern was observed again in 1999 but the transition to recharge occurred earlier and higher rates of discharge 610 ml m 2 h 1 and recharge 608 ml m 2 h 1 were recorded additionally seepage at these three stations increased after large rainfall events and a pronounced episodic increase of seepage was measured during snowmelt distinct seepage patterns along portions of the shoreline show that seepage can vary considerably within seasons and suggests a need to consider changes of seepage over time periods of days to weeks as well as among seasons and years this study demonstrates that the resolution of temporal seepage data can be important to the understanding of water fluxes to aquatic ecosystems

simulating the influence of lake position on groundwater fluxes groundwater flow around three hypothetical flow through lakes located in the upper middle and lower portions of a watershed was numerically simulated in cross section under steady state and transient conditions results showed that 1 groundwater fluxes into and out of the lake located in the lowest position were higher and more stable than for lakes farther upgradient and 2 periods of intense groundwater recharge caused flow reversals and the formation of a stagnation point downgradient of the uppermost lake thereby causing a net increase in groundwater inflow these simulation results provide guidance on monitoring network design including the frequency of monitoring and or sampling

aquifer characteristics derived from the interaction between water levels of a terminal lake dead sea and an adjacent aquifer the water level of the dead sea a terminal hypersaline lake total dissolved solids approximately 340 g l has decreased at an average rate of 0 5 m yr since 1960 and by 0 8 m yr between 1981 and 1989 the dramatic long term water level variation of the dead sea and the seasonal short term fluctuations are accompanied by parallel variations of groundwater levels in an adjacent aquifer a general methodology based on a simplified yet reliable one dimensional flow model together with continuous measurements of groundwater levels in observation wells enables analysis of aquifer structural and hydraulic properties furthermore this analysis enables prediction of future groundwater levels in unconfined and confined aquifers due to future changes in lake levels

interaction of groundwater and shallow lakes on outwash sediments in the sub humid boreal plains of canada abstract the hydrologic controls on the interaction between a shallow lake and a groundwater flow system have been determined for a coarse textured landscape on the boreal plains of canada lake groundwater interactions were studied to provide an understanding of the near surface hydrologic processes in a sub humid climate where annual precipitation is equal to or less than potential evapotranspiration this study was initiated to assess potential landscape impact from forestry and energy industrial activity and future scenarios of climate change expected in the western boreal forest a 39 ha lake on outwash sediments was studied for two consecutive years hydrometric measurements and stable isotopic analyses indicated that evaporation was the dominant hydrologic flux during ice free months and was primarily responsible for a 0 2 m decline in lake level during this study a combination of summer rain and consistent supply of groundwater discharge throughout each year were the dominant sources of water the near equivalence of precipitation and evaporation and relative dominance of each of these processes during the hydrologic year resulted in the formation of a water table mound downgradient of the lake and its disappearance each year the presence of these humid mound and arid complete disappearance phenomena at one location within the same year reveal the sensitivity of hydrologic systems in this sub humid region to small variations in climate the onset and duration of evaporation from the lake surface was a major controlling factor on groundwater exchange to such a degree that the shallow lakes are thought to be evaporation windows in this landscape creating sub surface capture zones that depend on lake size and landscape position these findings indicate a very dynamic relationship between atmospheric water fluxes and groundwater interaction which could potentially conceal anthropogenic impacts within natural variability

grain size distribution and cementation of the cretaceous mzamba formation of eastern cape south africa a case study of a storm influenced offshore sequence abstract the late cretaceous mzamba formation of the eastern cape south africa is a storm influenced succession deposited in an offshore marine environment the succession is composed of two fundamental lithofacies very fine sandstone and packstone shell bed lithofacies the former represents background sedimentation in a relatively deep water low energy offshore environment whereas the latter represents storm deposits occurring with variable periodicity within the quiet offshore environment the storm generated packstone lithofacies shows a bimodal grain size distribution with two saltation fractions on the cumulative frequency diagrams together with negative skewness parameters and a relatively wide kurtosis of grain size distribution these characteristics are indicative of offshore storm generated sediments initial cementation of the storm influenced sediments occurred in a marine phreatic environment when isopachous rims of phosphate isopachous fibrous rims of smectite and micrite calcite cements were formed these cementation textures also support the offshore tempestite origin of the mzamba sediments the original marine phreatic diagenetic environment of the mzamba sediments changed to a meteoric phreatic environment probably at the end of mesozoic following deposition of the overlying cainozoic sediments the mzamba formation entered a burial diagenetic environment where the sediments were affected by elevated temperature and pressure finally the sediments were entered into a meteoric vadose zone due to tectonic uplift or sea level fall new dissolution pores and pendant calcite cement were created

archaean ttgs as sources of younger granitic magmas melting of sodic metatonalites at 0 6 1 2 gpa two natural low k2o na2o ttg tonalitic gneisses one hornblende bearing and the other biotite bearing were partially melted at 0 8 1 2 gpa fluid absent the chief melting reactions involve the breakdown of the biotite and hornblende the hornblende tonalite is slightly less fertile than the biotite tonalite but melt volumes reach around 30 at 1 000 c this contrasts with results of most previous work on more potassic ttgs which generally showed much lower fertility though commonly producing more potassic melts garnet is formed in biotite bearing tonalitic protoliths at p 0 8 gpa and at 1 0 gpa in hornblende bearing tonalitic protoliths all fluid absent experiments produced peraluminous granitic to granodioritic melts typically with sio2 70 wt for the biotite tonalite increasing t formed progressively more melt with progressively lower k2o na2o however the compositions of melts from the hornblende tonalite do not vary significantly with t with increasing p melts from the biotite tonalite become less potassic due to the increasing thermal stability of biotite for the hornblende tonalite again there is no consistent trend fluid absent melting of sodic ttgs produces melts with insufficient k2o to model the magmas that formed the voluminous late potassic granites that are common in archaean terranes reconnaissance fluid present experiments at 0 6 gpa imply that h2o saturated partial melting of ttgs is also not a viable process for producing magmas that formed these granites the protoliths for these must have been more potassic and less silicic nevertheless at granulite facies conditions sodic ttgs will produce significant quantities of broadly leucogranodioritic melt that will be more potassic than the protoliths upward abstraction of this melt would result in some lile depletion of the terrane younger k rich magmatism is unlikely to represent recycling of ttg crust on its own and it seems most likely that evolved crustal rocks and or highly enriched mantle must be involved

anatomy of impactites and shocked zircon grains from dhala reveals paleoproterozoic meteorite impact in the archean basement rocks of central india abstract the dhala structure in central india has been a topic of global interest ever since the report of an ancient meteorite impact event there here we present an integrated study of the petrology geochemistry and zircon u pb zircon geochronology and rare earth element geochemistry from the structure along with and an analysis of the grain morphology and textural features our results provide new insight into the nature and timing of the impact event the zircon grains from the impactites show textures typical of shock deformation which we correlate with the impact event we also identified the presence of reidite based on raman spectroscopy and characteristics such as a persistent planar fracture bright backscattered electron images and a lack of zoning which are all diagnostic features of this mineral formed during an impact event our zircon u pb data from the various rock types in the basement show magma emplacement at ca 2 5 2 47 ga and the pb loss features suggest that the impact might have occurred between ca 2 44 ga and ca 2 24 ga another minor group of late paleoproterozoic zircons with concordant ages of 1826 and 1767 ma in the brecciated quartz reefs along the margins of the impact crater from unfractured grains represent an younger thermal event after the impact the rare earth element patterns of the neoarchean to early paleoproterozoic zircon population reflect the effects of hydrothermal alteration on a peralkaline host rock the abnormally high concentration of k2o in the impactite up to 15 91 wt is also consistent with metasomatic alteration associated with the impact event

sediment routing controls on sandstone bulk petrographic composition and texture across an ancient shelf example from cretaceous western interior basin utah and colorado u s a

shallow groundwater surface water interactions in pond peatland complexes along a boreal plains topographic gradient shallow pond peatland complexes are important water resources and waterbird habitat on the boreal plains of canada and are potentially threatened by accelerated resource development we examined two shallow pond peatland complexes located in contrasting topographic positions within a clay rich till region one on a moraine and one on a lowland clay plain to evaluate the influence of landscape position on wetland groundwater surface water interactions hydrologic function and potential response to disturbance hydrometric and geochemical measurements indicated that precipitation and evaporation dominated the annual water balance of both ponds forested mineral uplands adjacent to the pond peatland complexes contributed no runoff inputs small recharge rates 5 mm year 1 from the ponds through low permeable clay to the underlying aquifer were measured at both topographic locations shallow groundwater fluxes to from the pond were controlled by water storage in and exchange with the adjacent riparian peatlands shallow groundwater fluxes may have contributed as much as 23 of inputs and outputs and influenced pond chemistry and permanence shallow groundwater exchange between the pond and adjacent peatlands varied seasonally and differed between the moraine and lowland complex groundwater flow reversals occurred around the entire perimeter of the moraine pond recharge from the moraine pond to the peatland during dry periods was off set by discharge to the pond from the peatland during wet periods in contrast shallow groundwater flow through conditions were observed at the lowland pond for most of the study however during a high rainfall event a groundwater flow reversal within the outflow peatland initiated discharge back into the pond these results suggest that the hydrologic regimes of some pond peatland complexes in clay rich till within the boreal plains will be more sensitive to local scale disturbances that impact flow dynamics and storage of near shore peatlands rather than larger scale disturbances of mineral upland regions

a statistical approach to estimate the 3d size distribution of spheres from 2d size distributions size distribution of rigidly embedded spheres in a groundmass is usually determined from measurements of the radii of the two dimensional 2d circular cross sections of the spheres in random flat planes of a sample such as in thin sections or polished slabs several methods have been devised to find a simple factor to convert the mean of such 2d size distributions to the actual 3d mean size of the spheres without a consensus we derive an entirely theoretical solution based on well established probability laws and not constrained by limitations of absolute size which indicates that the ratio of the means of measured 2d and estimated 3d grain size distribution should be 4 785 actual 2d size distribution of the radii of submicron sized pure fe 0 globules in lunar agglutinitic glass determined from backscattered electron images is tested to fit the gamma size distribution model better than the log normal model numerical analysis of 2d size distributions of fe 0 globules in 9 lunar soils shows that the average mean of 2d 3d ratio is 0 84 which is very close to the theoretical value these results converge with the ratio 0 8 that hughes 1978 determined for millimeter sized chondrules from empirical measurements we recommend that a factor of 1 273 reciprocal of 0 785 be used to convert the determined 2d mean size radius or diameter of a population of spheres to estimate their actual 3d size

the role of permafrost and seasonal frost in the hydrology of northern wetlands in north america abstract wetlands are a common landscape feature in the arctic subarctic and north temperate zones of north america in all three zones the occurrnce of seasonal frost results in similar surface water processes in the early spring for example surface ice and snow generally melt before the soil frost thaws causing melt water to flow into depressions over the land surface and at times across low topographic divides however evapotranspiration and ground water movement differ among the three climatic zones because they are more affected by permafrost than seasonal frost the water source for plants in the arctic is restricted to the small volume of subsurface water lying above the permafrost although this is also true in the subarctic where permafrost exists where it does not plants may receive and possibly reflect more regional ground water sources where permafrost exists the interaction of wetlands with subsurface water is largely restricted to shallow local flow systems but where permafrost is absent in parts of the subarctic and all of the temperature zone wetlands may have a complex interaction with ground water flow systems of all magnitudes

directional petrological characterisation of deep marine sandstones using grain fabric and permeability anisotropy methodologies theory application and suggestions for integration abstract different methods for quantifying preferred grain orientation or grain shape fabric in sandstones are reviewed and their value for the reconstruction of palaeocurrent direction and preferred direction of pore fluid flow is reassessed critically based on existing knowledge from literature and new grain fabric data it is shown that petrographic analysis has distinct merits because grain fabric can be determined with low equipment costs and population statistics are based on the orientation of individual grains several recommendations are given how to standardise procedures for acquisition of grain fabric through microscopy these recommendations include 1 the careful selection of cross section orientations to acquire apparent long grain axes that are representative of true long grain axes 2 the preferred measurement of the coarsest grains in cross section and 3 a new statistically founded method to select a subset of grains that is representative of the total population of grains in a sandstone sample magnetic techniques that use anisotropy of magnetic susceptibility ams as a proxy for grain orientation require specialised equipment and are more restricted in statistical evaluation but these methods benefit greatly from being able to measure a large number of grains in a three dimensional space in a short amount of time and with a lower sensitivity to user bias of the two magnetic techniques discussed in this paper the new enhanced ams method in which rock magnetic properties are enhanced by introducing magnetite into the pores and as precipitates on grain surfaces is regarded to be an improvement over the traditional natural ams method in which only the natural assemblage of magnetite particles present in the rock is analysed enhanced ams measures the preferred orientation of essentially all grains in a rock sample thus providing the shape fabric of a hydrodynamically more accurate representation of framework grains than natural ams through a small technical modification the enhanced ams method can be used to obtain a magnetic cast of the pore network of a rock sample so that the resulting ams is controlled by the shape anisotropy of the individual pores it is commonly assumed that long axes of sand grains in sedimentary deposits parallel the direction of the flows that formed the deposits this concept is challenged by a new systematic study of grain fabric in deep marine turbidites it indeed appears that grains in ripple cross laminated divisions of turbidites dominantly attain a preferred orientation parallel to the palaeoflow direction but grains in plane parallel laminated divisions have an additional flow perpendicular mode which suggests a contribution of rolling grain transport three different fabric modes occur in massive structureless sandstones and massive divisions in turbidites apart from flow aligned and flow perpendicular modes there is a statistically significant but hydrodynamically enigmatic flow oblique mode with an average azimuthal deviation of 40 this large variation of fabric types suggests that a similar variation exists in preferred paths of pore fluid flow within turbidites controlled to at least some degree by depositional process this is confirmed by independent laboratory measurements of permeability anisotropy on samples for which grain fabric data are available and thus defines grain fabric analysis as a viable alternative to traditional permeametry techniques

evidence for an early archaean granite from bastar craton india abstract granitoids in the early archaean are believed to be potassium poor tonalite trondhjemite granodiorite rocks only after continental crust attained sufficient thickness did true relatively potassium rich granites form no record of true granite prior to 3 4 ga is available we report a 3 6 ga true granite from the archaean bastar craton in india in contrast to the typical early archaean granitoids which are commonly deformed into gneisses this granite is relatively undeformed the age and composition of the granite implies that continental crust of the bastar craton attained sufficient thickness to permit intracrustal melting at 3 6 ga supplementary material representative major element trace element and ree composition of the dalli rajhara granite samples and a summary of shrimp u pb zircon data for the granite sample d 9 are available at http www geolsoc org uk sup18337

can liquefied debris flows deposit clean sand over large areas of sea floor field evidence from the marnoso arenacea formation italian apennines the marnoso arenacea formation in the italian apennines is the only ancient rock sequence where individual submarine sediment density flow deposits have been mapped out in detail for over 100 km bed correlations provide new insight into how submarine flows deposit sand because bed architecture and sandstone shape provide an independent test of depositional process models this test is important because it can be difficult or impossible to infer depositional process unambiguously from characteristics seen at just one outcrop especially for massive clean sandstone intervals whose origin has been controversial beds have three different types of geometries facies tracts in downflow oriented transects facies tracts 1 and 2 contain clean graded and ungraded massive sandstone deposited incrementally by turbidity currents and these intervals taper relatively gradually downflow mud rich sand deposited by cohesive debris flow occurs in the distal part of facies tract 2 facies tract 3 contains clean sandstone with a distinctive swirly fabric formed by patches of coarser and better sorted grains that most likely records pervasive liquefaction this type of clean sandstone can extend for up to 30 km before pinching out relatively abruptly this abrupt pinch out suggests that this clean sand was deposited by debris flow in some beds there are downflow transitions from turbidite sandstone into clean debrite sandstone suggesting that debris flows formed by transformation from high density turbidity currents however outsize clasts in one particular debrite are too large and dense to have been carried by an initial turbidity current suggesting that this debris flow ran out for at least 15 km field data indicate that liquefied debris flows can sometimes deposit clean sand over large 10 to 30 km expanses of sea floor and that these clean debrite sand layers can terminate abruptly

definition of a capture zone for shallow water table lakes abstract lake aquifer interaction is studied with the aim of developing simple relationships between easily measurable geometrical and aquifer parameters and the bulk behaviour of the flow system attention is focused on shallow flow through lakes which receive groundwater along the up gradient shoreline and discharge lake water along the down gradient shoreline although the flow system is physically three dimensional two idealised two dimensional geometries in plan and in vertical section are studied in detail the resulting potential flow problems are solved using a boundary integral approach based on a green s function chosen to satisfy desired homogeneous boundary conditions on a semi infinite strip results are presented for circular and elliptical lakes in plan and for lakes so shallow that they are adequately represented in vertical section by a line at the surface the size of an upstream capture zone in which all groundwater flow eventually passes through the body of the lake is defined in terms of the size of the lake inter lake spacing aquifer saturated thickness an anisotropy ratio and the ratio of downstream to upstream hydraulic gradients even in cases where the net groundwater inflow to a lake is zero it is shown that a substantial throughflow can occur

groundwater seepage into northern san francisco bay implications for dissolved metals budgets 1 nonconservative excesses of dissolved metals in northern san francisco bay indicate that there are internal sources of metals within the bay we quantified groundwater seepage and bioirrigation rates in this area to determine their roles in transporting dissolved metals from benthic sediments to surface waters we deployed seepage meters and collected sediment pore water and bottom water samples at three sites we determined seepage rates from seepage meters and modeled the transport of water through the sediment using pore water data to constrain rates of diffusion advection and bioirrigation a groundwater flow model incorporating sediment physical properties and local topography constrains more regional seepage estimates the seepage meters indicate upflow rates from 7 to 56 cm yr 1 in march and april 1999 with some large 50 cm yr 1 daily fluctuations that greatly exceed predictions based on sediment physical properties and tidally induced pore pressure variations during this period results from modeling pore water chemical data are consistent with a small bioirrigation rate 1 5 10 7 s 1 relative to values determined for southern san francisco bay and an average groundwater upwelling speed of 15 cm yr 1 the speed and direction of flow changed throughout the year with best fits to the data ranging from 20 cm yr 1 upflow to 34 cm yr 1 downflow and averaging 4 cm yr 1 upflow confidence intervals 95 are about 10 cm yr 1 for this method yet the range of acceptable seepage rates for temporally successive periods only overlap in one of four cases suggesting that temporal variability can be discerned from potential artifacts groundwater flow modeling suggests that the seepage rates determined at our sites represent 45 of the average seepage rate for the area applying one consolidation and permeability relationship to all sediments if we apply these approximations to all of northern san francisco bay benthic fluxes of dissolved metals to the surface waters could account for a relatively large amount 60 of the unknown sources of dissolved cobalt and a relatively small amount 4 of the unknown sources of dissolved silver cadmium copper nickel and zinc more focused groundwater discharge or elevated metals concentrations are required to have a larger impact on trace element budgets in this setting

the interaction of lakes with variably saturated porous media numerical simulation of variably saturated porous media indicates that groundwater recharge is variable in time and space depending on the thickness of the unsaturated zone through which infiltrating water must move the resulting complex transient groundwater flow systems have significant impact on contiguous surface water in very permeable media small local closed groundwater flow systems can develop and dissipate within a few weeks to several months after major recharge these have a direct effect on contiguous surface water by alternately causing seepage to and seepage from the surface water the transient nature of these flow systems indicates that reversals of the direction of groundwater flow may be common in less permeable media the same complex flow systems may occur but the time for development and dissipation is much greater for example it is conceivable that small local flow systems may exist for many months or years as a result of major recharge therefore directions of flow in such systems are more stable and the effect on contiguous surface water also is more stable the findings of this study indicate that wells and groundwater quality sampling sites need to be carefully located to define accurately water table configuration groundwater recharge direction of seepage through the beds of surface water bodies and complex geochemical processes related to changing directions of groundwater flow

beds comprising debrite sandwiched within co genetic turbidite origin and widespread occurrence in distal depositional environments co genetic debrite turbidite beds occur in a variety of modern and ancient turbidite systems their basic character is distinctive an ungraded muddy sandstone interval is encased within mud poor graded sandstone siltstone and mudstone the muddy sandstone interval preserves evidence of en masse deposition and is thus termed a debrite the mud poor sandstone siltstone and mudstone show features indicating progressive layer by layer deposition and are thus called a turbidite palaeocurrent indicators ubiquitous stratigraphic association and the position of hemipelagic intervals demonstrate that debrite and enclosing turbidite originate in the same event detailed field observations are presented for co genetic debrite turbidite beds in three widespread sequences of variable age the miocene marnoso arenacea formation in the italian apennines the silurian aberystwyth grits in wales and quaternary deposits of the agadir basin offshore morocco deposition of these sequences occurred in similar unchannellized basin plain settings co genetic debrite turbidite beds were deposited from longitudinally segregated flow events comprising both debris flow and forerunning turbidity current it is most likely that the debris flow was generated by relatively shallow few tens of centimetres erosion of mud rich sea floor sediment changes in the settling behaviour of sand grains from a muddy fluid as flows decelerated may also have contributed to debrite deposition the association with distal settings results from the ubiquitous presence of muddy deposits in such locations which may be eroded and disaggregated to form a cohesive debris flow debrite intervals may be extensive 26 x 10 km in the marnoso arenacea formation and are not restricted to basin margins such long debris flow run out on low gradient sea floor 0 1 may simply be due to low yield strength 50 pa of the debris water mixture this study emphasizes that multiple flow types and transformations between flow types can occur within the distal parts of submarine flow events

ttg suite from the bundelkhand craton central india geochemistry petrogenesis and implications for archean crustal evolution abstract the bundelkhand craton is one of the important archean protocontinental nuclei in peninsular india for which not much information on tectonic setting evolutionary history and petrogenetic processes is available here we provide comprehensive geochemical data on the tonalite trondhjemite granodiorite ttg rocks which form the basement rocks for the craton compositionally these rocks are variably evolved between diorite and granites and display both high and low al ttg types with geochemical features typical of convergent margin tectonic setting the evolved granitoids are essentially low pressure type further grouped into sodic true ttg and potassic transitional ttg types the low pressure and moderate shallow depths of melting conditions and low mg ni and cr contents do not support a direct slab melting scenario alternately these features favor the derivation of the bngc granitoids through the melting of a sub arc basaltic source possibly at the lower part of thickened arc crust in a suprasubduction regime the occurrence of identical lithological assemblages in other cratons in peninsular india and similar petrogenetic conditions for the emplacement of ttgs suggest the involvement of subduction accretion processes in building the ancient cratonic nuclei of the indian shield

geochemical and ion microprobe u pb zircon constraints on the archaean evolution of singhbhum craton eastern india abstract geochemical and shrimp u pb zircon analyses were obtained for nine samples of the singhbhum craton to investigate major regional granite intrusion volcanism sedimentary deposition metamorphism and deformation episodes detrital zircons within a recrystallized sandstone enclave within tonalitic gneiss provided a maximum time for deposition of 3375 3 ma all uncertainties are at 95 confidence unless otherwise specified for the host sandstone igneous crystallization dates between 3380 and 3299 ma were obtained for tonalite gneiss and foliated trondhjemite samples from widely dispersed sites whereas unfoliated granitic samples provided igneous crystallization dates