a continental drift flipbook abstract forty six miniature plate tectonic reconstructions are presented that can be assembled into a flipbook that illustrates the movement of the continents since the late precambrian 750 m yr ago six principal lines of evidence have been used to reconstruct the past positions of the continents 1 linear magnetic anomalies produced by sea floor spreading 2 paleomagnetism 3 hotspot tracks and large igneous provinces 4 the tectonic fabric of the ocean floor mapped by satellite altimetry 5 lithologic indicators of climate e g coals salt deposits tillites and 6 the geologic record of plate tectonic history i discuss the probable uncertainties associated with the plate tectonic reconstructions and give an estimate of the uncertainty in the positions of the continents back through time

glacier meltwater stream chemistry in wright and taylor valleys antarctica significant roles of drift dust and biological processes in chemical weathering in a polar climate article this study examines stream chemistry within glacial drainages in wright and taylor valley antarctica in con junction with geochemical modeling and sediment leach experiments in order to assess the source of chem ical weathering fluxes within polar drainages the targeted catchments are underlain by granitoid basement with streams flowing through glacial drifts of variable composition analyses of meltwater from clark glacier in wright valley and howard glacier delta stream in taylor valley show increases in solute concentrations as a function of distance from the glaciers surface area normalized weathering rate estimates based on si and k fluxes within the streams confirm that significant chemical weathering is occurring in these systems at rates comparable to field and laboratory rates of silicate weathering under much warmer conditions down stream increases in several cations ca na k and mg occur within both drainages however solute concen trations between the two streams differ significantly clark glacier stream contains na ca whereas howard glacier stream contains ca na distally geochemical reaction path modeling for clark glacier predicts in creasing concentrations of ca na and mg over the reaction progress paralleling the results of field data from clark stream modeling of howard glacier stream also shows an increase in several cations however na concentrations exceed those for ca which differs from the observed field data and suggests that the dif ferences in stream chemistry are not due to differing bedrock mineralogy instead ion leaching experiments conducted on drift sediments demonstrate that 1 glacial deposits within wright valley and taylor valley may significantly affect stream chemistry through direct water rock interactions within the stream channel and or 2 the water chemistries are influenced by eolian additions of locally sourced dust to glacier surfaces differences in fe concentrations between the two stream systems indicate that biological activity may also significantly influence iron concentrations within howard glacier stream

eolian deposition of trace elements onto taylor valley antarctic glaciers abstract the major ion and trace element chemistry in four 60 110 cm deep snow pits was examined from three antarctic taylor valley glaciers commonwealth canada and howard all located within 20 km of the ross sea taylor valley tv 77 30 s 163 15 e is part of the mcmurdo dry valleys mdv the largest ice free area in antarctica snow chemistry of these glaciers is strongly influenced by cross valley sw ne and ne sw winds that deposit eolian materials including mineral dust and soluble salts arsenic cd cu mo pb sb and sn in recent tv glacier snow are almost exclusively derived from eolian dust the relative magnitude of element variations with depth relate to the exposure of snow sites to prevalent winds eolian deposition is a primary source of these elements to canada glacier snow and supra and proglacial streams eolian processes are likely very important to the delivery and availability of nutrients and potentially toxic elements to dry valley antarctic ecosystems

geochemical flood deconvolution in a mediterranean catchment herault france by sr isotopes major and trace elements summary this study based on a chemical and isotopic approach major trace elements and strontium isotopes focuses on the geochemical hydrograph separation during flood events in a mediterranean watershed herault southern france major element contents present a typical decreasing logarithmic curve when plotted against river discharge the concentrations measured during floods are however always higher than the theoretical dilution curve and can be related to 1 rainfall input in this sea side basin especially for cl and 2 water rock interactions which release elements in solution especially from the carbonate compartment of the watershed ca and hco 3 are not correlated with the river discharge their content in the dissolved phase being controlled by calcite and aragonite mineral phases sr is a proxy of ca regarding its physico chemical properties but it has been demonstrated that sr is not controlled by these mineral phases and it presents a logarithmic variation with discharge it is also very well correlated with cl which is a conservative element par excellence sr and its isotopic ratio can thus be used to constrain the geochemical behaviour of the dissolved phase during flood events the main tributaries characterised under various hydrological conditions defined very well constrained end members as the result of the diversity of the lithologies drained monitoring at the outlet of the watershed during four flood events showed that 1 during low flow periods the signature at the outlet results from a binary mixing between the two main water sources in the basin 2 each flood event studied presents a different temporal geochemical evolution counter or clockwise evolution in a 87 sr 86 sr vs reciprocal sr content diagram reflecting the predominance of different water sources during the flood i e the tributaries versus the karst aquifers depending on rainfall intensity duration and location 3 the sequence of water origins during the flood seems also be controlled by the initial state of the soil and epikarst karst continuum inducing a more or less rapid and pronounced response after rainfall events

recognition of insufficient bleaching by small aliquots of quartz for reconstructing soil erosion in greece optical dating of sediments requires sufficient bleaching of the material to be dated using single aliquot techniques the statistical parameter of the coefficient of variation v in combination with the reduction of mineral grains per aliquot enables the detection of insufficiently bleached samples this was empirically tested on quartz extracts from the greek study area which were artificially bleached differently dosed and then mixed to simulate insufficiently bleached samples the single aliquot regenerative dose protocol was applied the test measurements show that for the studied quartz material the detection of insufficient bleaching is possible if small aliquots of 200 500 grains and a threshold value of v 10 are used the technique was applied to the age determination of colluvial and alluvial torrential deposits from the study area the basin of phlious in greece the optically stimulated luminescence age data allow reconstruction of the history of holocene soil erosion which essentially started in the 7th millennium bc simultaneous with the onset of agricultural activities in the early neolithic

bet surface area distributions in polar stream sediments implications for silicate weathering in a cold arid environment abstract bet surface area values are critical for quantifying the amount of potentially reactive sediments available for chemical weathering and ultimately prediction of silicate weathering fluxes bet surface area values of fine grained 2 g of surface area values samples from one delta stream taylor valley of the four sampled stream transects exhibit high values up to 70 6 m 2 g which greatly exceed surface area values from three temperate proglacial streams 0 3 12 1 m 2 g only clark stream in wright valley exhibits a robust trend with distance wherein surface area systematically decreases and particle size increases in the mud fraction downstream interpreted to reflect rapid dissolution processes in the weathering environment the remaining transects exhibit a range in variability in surface area distributions along the length of the channel likely related to variations in eolian input to exposed channel beds adjacent snow drifts and to glacier surfaces where dust is trapped and subsequently liberated during summer melting additionally variations in stream discharge rate which mobilizes sediment in pulses and influences water rock ratios the origin and nature of the underlying drift material and the contribution of organic acids may play significant roles in the production and mobilization of high surface area sediment this study highlights the presence of sediments with high surface area in cold based glacier systems which influences models of chemical denudation rates and the impact of glacial systems on the global carbon cycle

effects of drying techniques on grain size analyses of fine grained sediment abstract to assess the effects of drying on subsequent grain size analyses a variety of drying approaches including drying in ambient air oven drying and freeze drying were applied to sediment collected from modern fluvial lacustrine and paludal settings containing a wide range of clay size fraction 16 61 samples were subsequently rehydrated and subjected to grain size analysis in a laser particle size analyzer and histograms compared with those from control samples never subjected to drying results indicate that drying techniques induced no effect on grain size distribution for samples containing 39 clay size material only freeze drying produced reproducible results statistically identical to the control samples

water tracks and permafrost in taylor valley antarctica extensive and shallow groundwater connectivity in a cold desert ecosystem water tracks are zones of high soil moisture that route water downslope over the ice table in polar environments we present physical hydrological and geochemical evidence collected in taylor valley mcmurdo dry valleys antarctica which suggests that previously unexplored water tracks are a significant component of this cold desert land system and constitute the major flow path in a cryptic hydrological system geological geochemical and hydrological analyses show that the water tracks are generated by a combination of infiltration from melting snowpacks melting of pore ice at the ice table beneath the water tracks and melting of buried segregation ice formed during winter freezing the water tracks are enriched in solutes derived from chemical weathering of sediments as well as from dissolution of soil salts the water tracks empty into ice covered lakes such as lake hoare resulting in the interfingering of shallow groundwater solutions and glacier derived stream water adding complexity to the geochemical profile approximately four orders of magnitude less water is delivered to lake hoare by any given water track than is delivered by surface runoff from stream flow however the solute delivery to lake hoare by water tracks equals or may exceed the mass of solutes delivered from stream flow making water tracks significant geochemical pathways additionally solute transport is two orders of magnitude faster in water tracks than in adjacent dry or damp soil making water tracks salt superhighways in the antarctic cold desert accordingly water tracks represent a new geological pathway that distributes water energy and nutrients in antarctic dry valley cold desert soil ecosystems providing hydrological and geochemical connectivity at the hillslope scale

arkose subarkose quartz sand and associated muds derived from felsic plutonic rocks in glacial to tropical humid climates abstract in the range of climates from high latitude glacial to equatorial tropical the mineral and chemical compositions of over 600 modern nonmarine first cycle sands and muds produced from felsic crystalline basement provenance in various tectonic settings were studied under glacial conditions sediments are developed by mostly mechanical weathering and thus are mineralogically and chemically similar to their source rocks humid tropical climates yield quartz rich sands kaolinite rich muds along with si mg ca na and k in solution between these extremes a wide range of detrital sediment compositions are developed in arid to wet climates in arid climate and semi arid climate sands feldspar is commonly more abundant than quartz and plagioclase k feldspar except in the cases of granite source rocks the muds are feldspathic with smectite dominant in the clays with increasing temperature and moisture in temperate to subtropical climates mafic silicates and feldspars are destroyed so that the sands range from arkoses with plagioclase as the major feldspar to subarkoses with dominant k feldspar through this range of climate muds become more kaolinitic and thus more aluminous with increasingly severe weathering typically feldspathic sands are associated with feldspathic muds with decreasing feldspar in sands there is less feldspar in muds with increasingly intense chemical weathering rare earth elements ree are more fractionated into muds typically sands contain 150 ppm ree with much of the ree in heavy minerals abundance differences are greatest between humid tropical sands and muds in many samples the ree are mostly in monazite allanite sphene and apatite more intensely weathered samples contain more xenotime and zircon evidenced by yb enrichment

fluvial system response to middle and upper pleistocene climate change in the meurthe and moselle valleys eastern paris basin and rhenish massif abstract research in the meurthe and moselle valleys downstream from the vosges massif has resulted in the definition of the terrace system and in the recognition of the climatic influence on its formation eight alluvial terraces were recognized at less than 100 m relative height an absolute chronology was established for the youngest alluvial terraces based on infrared optically stimulated luminescence and radiocarbon dating this provides evidence that each terrace corresponds to a single glacial interglacial cycle this result is confirmed by the study of numerous sections which present a constant succession of lithofacies in each valley part four alluvial sequences were also defined along the meurthe and moselle valleys reflecting middle and late pleistocene climate change their upper basin developed in the vosges massif was actually covered by glaciers during the pleistocene cold periods the differences between these four alluvial sequences are attributed to the unequal expansion of ice in the upper basins of the meurthe and moselle rivers and their tributaries in spite of these differences the sequences show important similarities main aggradation events correlate with cold periods pleniglacial and lateglacial whereas erosional phases occurred at the warm to cold transitions and secondarily at the pleniglacial lateglacial transitions this evolution is comparable with those already described in other northwestern european valleys especially since the upper saalian

responses of floods to holocene climatic change in the upper mississippi valley abstract dimensions of holocene relict channels and sedimentological characteristics of point bars associated with these relict channels were used to reconstruct a holocene history of long term changes in magnitudes of 1 58 yr floods in upper mississippi valley watersheds of southwestern wisconsin the reconstructed record of floods shows relatively large and persistent nonrandom departures from contemporary long term average flood magnitudes the flood history indicates climatic changes that are broadly similar to climatic changes indicated from fossil pollen in the same region the holocene floods ranged from about 10 15 larger to 20 30 smaller than contemporary floods of the same recurrence frequency large floods were characteristic between about 6000 4500 and 3000 2000 yr b p and during a brief interval after 1200 yr b p small floods were common between about 8000 6500 4500 3000 and 2000 1200 yr b p these fluvial responses were found to be closely associated with a long term episodic mobility and storage of sediments in the wisconsin watersheds during periods of relatively large floods relatively rapid lateral channel migration either reworked or removed extensive tracts of valley bottom alluvium in contrast during periods of relatively small floods relatively slow lateral channel migration is apparent and the channel and floodplain system appear to have been relatively stable

rates of flood plain sedimentation on the central amazon river field measurements of water and sediment discharge and floodplain topography numerical simulations of hydrology and landsat data on sediment concentrations were combined to estimate rates of transport and the fate of water and sediment in a 200 km reach of the central amazon river results from field data collected during the annual flood in july 1986 indicate that sediment was transported to the flood plain at rates ranging from 3 to 5 t d 1 m 1 with percentage deposition 80 yielding vertical rates of 0 8 to 1 6 cm day comparable rates were calculated from geographic information system overlays of numerically simulated specific water discharge and land sat derived sediment concentrations rates for july 31 1977 include 4 to 18 t d 1 m 1 of transport onto the flood plain and an average of 64 deposition at vertical rates from 0 4 to 3 3 cm d a 1 m higher flow on august 2 1989 yielded on average higher rates of transport onto the flood plain 8 to 15 t d 1 m 1 but lower percentage 46 deposition implying vertical rates between 0 3 and 2 9 cm d

riverine silicon isotope variations in glaciated basaltic terrains implications for the si delivery to the ocean over glacial interglacial intervals marine primary production is dominated by diatoms and these are dependent upon the riverine delivery of silicon si to the ocean in paleoreconstruction of silicic acid utilisation by diatoms it is assumed that the isotopic composition of the si that is delivered from the continent to the oceans remains constant in this study it is shown that glacier fed icelandic rivers differ from those directly draining basaltic catchments in their dissolved si isotope compositions lighter values 30si 0 17 0 18 are associated with the high physical erosion rates in glacial rivers and heavier values 30si 0 97 0 31 are associated with lower physical erosion rates and enhanced formation of secondary minerals in direct runoff rivers the si isotopic compositions correlate with those of li and provide evidence of a climatic dependence that is likely to have led to glacial interglacial differences based on existing 30si measurements from diatoms in a sediment record from the southern ocean the interpretation of changes in si utilisation between the last glacial maximum lgm and the early holocene is revisited taking into account changing isotopic compositions of the river water delivered to the ocean over glacial interglacial intervals during the lgm si utilisation values are higher when allowing for changing si isotope input to the ocean 59 5 than when a constant si isotope input is assumed 42 47 5 this reduces but does not eliminate the difference relative to the holocene 88 5 therefore changes in si isotope delivery to the ocean need to be taken into account in the precise reconstruction of ocean si utilisation and primary productivity over glacial interglacial timescales

paleobiogeography of africa how distinct from gondwana and laurasia abstract although africa was south of the tethys sea and originally belonged to the gondwana its paleobiogeographical history appears to have been distinct from those of both gondwana and laurasia as early as the earliest cretaceous perhaps the late jurassic this history has been more complex than the classical one reconstructed in the context of a dual world gondwana vs laurasia geological and paleobiogeographical data show that africa was isolated from the mid cretaceous albian aptian to early miocene i e for ca 75 million years the isolation of africa was broken intermittently by discontinuous filter routes that linked it to some other gondwanan continents madagascar south america and perhaps india but mainly to laurasia interchanges with gondwana were rare and mainly out of africa dispersals whereas interchanges with laurasia were numerous and bidirectional although mainly from laurasia to africa despite these intermittent connections isolation resulted in remarkable absences poor diversity and emergence of endemic taxa in africa mammals suggest that an african faunal province might have appeared by late jurassic or earliest cretaceous times i e before the opening of the south atlantic during isolation africa was inhabited by vicariant west gondwanan taxa i e taxa inherited from the former south american african block that represent the african autochthonous forms and by immigrants that entered africa owing to filter routes nearly all or all immigrants were of laurasian origin trans tethyan dispersals between africa and laurasia were relatively frequent during the cretaceous and paleogene and are documented as early as the earliest cretaceous or perhaps late jurassic i e perhaps by the time of completion of the tethys between gondwana and laurasia they were permitted by the mediterranean tethyan sill a discontinuous route that connected africa to laurasia and was controlled by sea level changes interchanges first took place between southwestern europe and africa but by the middle eocene a second eastern route the iranian route involved southeastern europe and southwestern asia the iranian route was apparently the filtering precursor of the definitive connection between africa and eurasia the relationships and successive immigrations of mammal mostly placental clades in africa allow the recognition of five to seven phases of trans tethyan dispersals between africa and laurasia that range from the late cretaceous to the eocene oligocene transition these dispersal phases involve dispersals toward laurasia and or toward africa immigrations the immigrations in africa gave rise to faunal assemblages the african faunal strata afss all successful and typical african radiations have arisen from these afss we recognize four to six afss each characterized by a faunal association even major old african clades such as paenungulata or the still controversial afrotheria which belong to the oldest known afs involving placentals ultimately originated from a laurasian stem group africa was an important center of origin of various placental clades their success in africa is probably related to peculiar african conditions endemicity weak competition although strongly marked by endemicity the african placental fauna did not suffer extinctions of major clades when africa contacted eurasia the present geographic configuration began to take shape as early as the mid cretaceous at that time the last connections between africa and other gondwanan continents began to disappear whereas africa was already connected to eurasia by a comparatively effective route of interchange

biogeochemistry of glacial landscape systems abstractglaciers affect biogeochemistry of landscapes through their sediments glacial erosion rates are high and the sediments produced are distinctively fine grained hence glaciers can be thought of as producers of mineral surface area although this mineral surface area is highly reactive temperature limits chemical weathering fluxes from glaciers and their surroundings more significant effects may be associated with silt deposited in loess and on continental margins thick deposits in both settings contribute to carbon cycling through both silicate weathering and organic carbon burial the impact of glaciers on biogeochemical cycles will be long lasting as the legacy of glacial erosion processes continues as long as sediment yields are elevated

surficial geology and geomorphology of eastern and central wright valley antarctica abstract surficial deposits in eastern and central wright valley antarctica record multiple inland incursions of grounded ice from the ross sea embayment glacial geologic mapping coupled with 42 ams 14 c dates of lacustrine algae and 10 40 ar 39 ar dates of basalt erratics indicate westward ice expansion at least eight times during the pliocene and quaternary the most extensive westward incursion resulted in an advance of at least 21 km beyond the margin of present day wright lower glacier accompanied by ice thickening of 500 m at the location of the present day wilson piedmont glacier in the eastern valley mouth large proglacial lakes and glaciolacustrine sedimentation coincide with at least some of these advances

paleoflood analysis of an alluvial channel in the south central great plains black bear creek oklahoma abstract late holocene floodplain of the black bear basin in north central oklahoma was chronologically developed based upon slackwater deposition and radiocarbon dating of associated paleosols major paleoflood events occurred 3590 80 yr bp and 1150 100 yr bp assumptions developed for application in semi arid bedrock channels were tested and modified maximum accumulation of slackwater deposits were located some 400 m up tributaries rather than at the intersection of the mouths of present day tributary junctions these sites represent the intersection with tributaries during the extreme widths of floods on an alluvial floodplain physically tracing slackwater units up tributaries was possible in some cases 8 km an accurate estimate of flood stage was determined by measuring up terrace perpendicular to the tributary during floods aggradation and degradation of the main channel were insignificant because the broad floodplain is the most impacted feature in an alluvial setting the preflood landscapes determined from paleosol elevations were recreated to estimate the manning roughness coefficients and paleoflood discharges the hec 2 water surface profile hydrologic engineering center 1982 determined that paleodischarges of 4391 cm in 3590 bp and 8782 cm in 1150 bp emplaced the slackwater deposits along the tributaries of black bear creek

surface glaciochemistry of taylor valley southern victoria land antarctica and its relationship to stream chemistry we have analysed a series of surface samples from the alpine glaciers of taylor valley southern victoria land antarctica for their geochemical composition this was done to better establish the role of glaciochemical variation on the chemical composition of meltwater streams emanating from the glaciers the chemistry of the snow and ice changes with proximity to the ocean and with elevation of the glacier surface the aeolian transport of dry valley dust as indicated by both chemical and particulate matter variations is a major process affecting the overall glacier chemistry and the chemistry of the meltwaters streams originating on the western edges of the glaciers are more impacted by the aeolian input as they are in the direct path of the major regional wind direction our data strongly suggest that the variation in stream geochemistry in taylor valley is a result in part of the differences in chemical composition of glacier melt copyright 2003 john wiley sons ltd

recent and historical discharge of a large european river system oxygen isotopic composition of river water and skeletal aragonite of unionidae in the rhine abstract seasonal variations in the oxygen isotopic composition of rhine river water were analyzed in detail and compared with the oxygen isotopic record from recent and historical specimens of freshwater bivalves unionidae the purpose of this study was to investigate the potential use of these aragonitic bivalves as proxy recorders for varying amounts and sources of discharge and thereby infer climate change seasonal variations in the river water 18 o are on the order of 1 2 during summer alpine melt water contributes significantly to the total discharge resulting in average values of 10 to 10 5 whereas the non alpine contribution is higher during winter as indicated by mean 18 o values of 8 5 to 9 the basic pattern of the modern seasonal variation of 18 o of river water can be described by a numerical mass balance approximation of the various contributions from the alpine and non alpine catchments with their average 18 o composition the 18 o of growth increments in the prismatic shell layer of anodonta corresponds perfectly to what is predicted by known fractionation of 18 o between water and aragonite shell growth is restricted to water temperatures above 8 10 c so variations in 18 o and the river water temperature are faithfully recorded by relatively large growth increments during summer the distinctive isotopic signatures of individual flood events during summer and autumn are also recorded in the shells

estimating specific surface area of fine stream bed sediments from geochemistry specific surface area ssa of headwater stream bed sediments is a fundamental property which determines the nature of sediment surface reactions and influences ecosystem level biological processes measurements of ssa commonly undertaken by bet nitrogen adsorption are relatively costly in terms of instrumentation and operator time a novel approach is presented for estimating fine 2 5 mg kg 1 four elements were identified as significant predictors of ssa ordered by decreasing predictive power v ca al rb the optimum model from these four elements accounted for 73 of the variation in bed sediment ssa range 6 46 m2 g 1 with a root mean squared error of prediction based on leave one out cross validation of 6 3 m2 g 1 it is believed that v is the most significant predictor because its concentration is strongly correlated both with the quantity of fe oxides and clay minerals in the stream bed sediments which dominate sediment ssa sample heterogeneity in ssa based on triplicate measurements of sub samples was a substantial source of variation standard error 2 2 m2 g 1 which cannot be accounted for in the regression model the model was used to estimate bed sediment ssa at the other 1792 sites and at 30 duplicate sites where an extra sediment sample had been collected 25 m from the original site by delineating sub catchments for the headwater sediment sites only those sub catchments were selected with a dominant 50 of the sub catchment area bedrock formation and land use type the bedrock and land use classes accounted for 39 and 7 of the variation in bed sediment ssa respectively variation in estimated fine bed sediment ssa from the paired duplicate sediment sites was small 2 7 m2 g 1 showing that local variation in ssa at stream sites is modest when compared to that between catchments how the approach might be applied in other environments and its potential limitations are discussed

pre breakup continental extension in east gondwanaland and the early opening of the eastern indian ocean abstract extension of continental crust by up to 360 km on a north northeast azimuth in the great australian bight occurred prior to the middle cretaceous 96 ma onset of seafloor spreading between australia and antarctica this large amount of continental extension is constrained to the late jurassic 160 ma middle cretaceous interval about a pole estimated to lie about 40 southeastward of southeastern australia using bathymetric data combined with seismic and magnetic determinations of the continent ocean boundaries off australia india and antarctica we determine a revised fit of east gondwanaland prior to continental extension and at various stages thereafter in the first stage from 160 to 132 5 ma m11 india australia rotated from antarctica with continental crustal extension between australia and antarctica and largely transform motion between the coromandel coast margin of india and the kron prins olav kyst margin of antarctica in the second stage from 132 5 to 96 ma india rotated northwestward away from australia antarctica producing m10 and younger magnetic anomalies along the western margin of australia continental extension was greatest between australia and antarctica during this stage the newly determined 132 5 96 ma rotation between india and australia provides an improved fit between the orientation of observed m10 m0 magnetic anomalies and the southward decrease in spreading rate off the western australian margin together with bathymetry the new rotation parameters lead to identification of the abandoned 96 ma spreading ridge along the lost dutchmen and dirck hartog ridges the naturaliste fracture zone is found to lie nearly parallel to the early cretaceous transform direction between india and antarctica suggesting that slow seafloor spreading required between australia and antarctica to accommodate the continental extension further east occurred between naturaliste fracture zone and the m4 m0 anomalies adjacent to the naturaliste plateau the revised fit of india in east gondwanaland reduces the eastward extent of greater india to 95 e but does not change its extent as far north as the cape range fracture zone the new pole determined for the early cretaceous rotation between india and australia antarctica lies within 15 of the southern tip of india significantly closer than in previous determinations thereby reducing the amount of seafloor spreading generated between africa and antarctica by the india antarctica rotation and thus offering a possible solution to the perceived spreading rate problems between m11 and m0 in the somali mozambique and antarctic basins

landscape reconstruction and major flood events of the river main hesse germany in the environs of the roman fort at groβkrotzenburg abstract detailed geoarchaeological studies were conducted at the gro krotzenburg floodplain southern hesse germany in order to reconstruct the fluvial palaeogeography and search for roman harbour installations another objective was to reconstruct the local flood history based on stratigraphic and geochronological data prospection based on electrical resistivity tomography vibracoring and direct push electrical conductivity logging were carried out to detect and analyze subsurface stratigraphies altogether 6 sediment cores up to 7 m long were drilled along transects along and perpendicular to the present course of the river main based on sedimentological and geochemical data we classified four sedimentary units vibracore data helped to detect the pre holocene bedrock topography and to differentiate between sedimentary facies we present geophysical sedimentary and geochronological evidence of a river channel right in front of the roman fort that was probably active during roman times moreover we found another bridge pier candidate in the prolongation of a well documented roman bridge our findings further indicate that the northern riverbank has shifted towards south since roman times however neither sedimentary nor archaeological evidence for harbour installations could be brought to light nevertheless we assume that conditions favorable of a river harbour namely permanent water flow and sufficient water depth were guaranteed in front of the fort where an undercut slope was probably already existing during roman times several sequences of coarse grained sandy to gravelly river deposits were found associated with major flood events that affected the site at gro krotzenburg during late medieval and modern times at that time central germany was repeatedly influenced by extreme meteorological conditions and associated extreme runoff events based on radiocarbon data we were able to define two periods of major flooding namely between 1435 and 1484 cal ad and 1646 1792 cal ad these periods are contemporaneous with periods of increased flood frequency in central europe derived from historical sources namely 1430 1460 ad and 1730 1790 ad based on sedimentary and geo chronostratigraphic evidence major flood events detected at the gro krotzenburg alluvial plain are most probably related with the ad 1480 ad 1573 and ad 1780 events known from historical records our results document that few historical flood events controlled the overall development of the fluvial landscape at gro krotzenburg at least since roman times until the late 19th century namely by eroding pre existing fluvial deposits accumulating thick sequences of event deposits and narrowing the riverbed since the late 19th century river regulation measures severely changed the hydrological conditions of the river main

weathering reactions and hyporheic exchange controls on stream water chemistry in a glacial meltwater stream in the mcmurdo dry valleys 1 in the mcmurdo dry valleys antarctica dilute glacial meltwater flows down wellestablished streambeds to closed basin lakes during the austral summer during the 6 12 week flow season a hyporheic zone develops in the saturated sediment adjacent to the streams longer dry valley streams have higher concentrations of major ions than shorter streams the longitudinal increases in si and k suggest that primary weathering contributes to the downstream solute increase the hypothesis that weathering reactions in the hyporheiczonecontrolstreamchemistrywastestedbymodelingthedownstreamincreasein solute concentration in von guerard stream in taylor valley the average rates of solute supplied from these sources over the 5 2 km length of the stream were 6 1 10 9 mol si l 1 m 1 and 3 7 10 9 mol k l 1 m 1 yielding annual dissolved si loads of 0 02 1 30 mol si m 2 of watershed land surface silicate minerals in streambed sediment were analyzed to determine the representative surface area of minerals in the hyporheic zone subject to primary weathering two strategies were evaluated to compute sediment surface area normalized weathering rates the first applies a best linear fit to synoptic data in order to calculate a constant downstream solute concentration gradient dc dx constant weathering rate contribution crc method the second uses a transient storage model to simulate dc dx representing both hyporheic exchange and chemical weathering hydrologic exchange he method geometric surface area normalized dissolution rates of the silicate minerals in the stream ranged from 0 6 10 12 mol si m 2 s 1 to 4 5 10 12 mol si m 2 s 1 and 0 4 10 12 mol k m 2 s 1 to 1 9 10 12 mol k m 2 s 1 these values are an order of magnitude lower than geometric surface area normalized weathering rates determined in laboratory studies and are an order of magnitude greater than geometric surface area normalized weathering rates determined in a warmer wetter setting in temperate basins despite the cold temperatures lack of precipitation and lack of organic material these results suggest that the continuous saturation and rapid flushing of the sediment due to hyporheic exchange facilitates weathering in dry valley streams index terms 1045 geochemistry low temperature geochemistry 1806 hydrology chemistry of fresh water 1625 global change geomorphology and weathering 1824 1886 1890 hydrology wetlands keywords hyporheic zone chemical weathering flow path antarctica stream

lower rhine historical flood magnitudes of the last 450years reproduced from grain size measurements of flood deposits using end member modelling abstract objective the objective of this research was to unlock the potential of fluvial archives to create flood chronologies based on grain size characteristics of flood deposits located in two recently formed fluvio lacustrine sequences methods grain size data was compared with contemporaneous discharge measurements for the lower rhine the netherlands regression relations between coarse tail grain size parameters and measured discharge were established for the last 240 years and applied to the older parts of both cores resulting in peak discharge estimates back to ad 1550 results grain size descriptive parameters such as the 95th percentile and end member modelling outcomes correlate well with discharge and turn out to be sensitive proxies for inferring flood magnitudes locally geomorphological changes influence the relation between peak discharge magnitudes and flood bed coarseness but these can be assessed using continuous flood layer and background sedimentation measurements to standardize grain size descriptive parameters conclusion implications flood records distilled from sedimentary archives hold great potential for extending existing records of observed discharge and aid establishment of design discharge for flood protection measures and assessment of non stationarity of the flooding regime due to climatic and anthropogenic forcing

paleoenvironmental reconstruction of the lower mogi guacu river basin sao paulo state brazil morphopedosedimentary records and fluvial processes abstract the mogi guacu river rises in bom repouso minas gerais state brazil in the mantiqueira ridge and flows into the rio pardo river at an elevation of 483 m in pontal sao paulo state brazil after running a 530 km long course especially along the lower mogi guacu basin the river morphology is extremely sinuous characterized by intense processes of channel migration avulsion abandonment and reactivation of the channel producing an extensive alluvial plain composed of a series of associated relief forms and sedimentary facies among these forms point bar deposits by lateral accretion abandoned meanders paleo channels and fluvial terraces are notable features in this sense the objective of this work was to investigate whether these features could be linked to environmental changes to reach this goal soil properties of a catena of the jatai ecological station luiz antonio sao paulo state were analyzed in four sectors slope terrace i terrace ii and alluvial plain the results from grain size determination geochemical and isotopic studies dating paleopalynology coal fragments and micromorphology are presented in this paper from these analyses a paleo environmental evolution divided in three stages is proposed for the area 130 000 ybp upper pleistocene when the mogi guacu river base level was approximately 6 m above the present one a drier second phase 10 250 years bp lower holocene when an organic horizon was formed inside of an abandoned meander oxbow lake and a third phase 2096 ybp upper holocene of reactivation of a warm and humid climate that promoted the development of a two meters thick typic udifluvent in a sector where the mogi guacu river no more floods due to the incision of its thalweg reaching more than six meters depth in the last 130 000 years bp thus this paper used a fluvial geomorphologic approach and its interplay with climate to understand how the landscape was shaped from upper pleistocene to holocene however neotectonics might have played a relevant role as well not only in the mogi guacu river basin but also in the parana sedimentary basin

glaciers show direct linkage between erosion rate and chemical weathering fluxes field studies suggest a linkage between high physical erosion rates and rates of chemical denudation mechanical erosion by temperate glaciers is commonly an order of magnitude higher than in mountainous fluvial catchments leading to an expectation that chemical weathering fluxes should also be high from glacierized basins yet solute fluxes from glaciers are not found to be higher than non glacierized catchments application of a model of silicate weathering from glaciers based on mineral surface area production and mineralogy shows that solute fluxes are consistent with the low temperatures dilute water chemistry and high mineral surface area production in these environments low temperatures reduce silicate weathering rates this effect explains the difference between silica fluxes from glaciers and from non glacierized basins as in laboratory flow through reactors glacial solute flux should depend on surface area production and mineral weathering rate constants the surface area production is significant a typical glacial erosion rate and grain size distribution produces on the order of 104 km2 of mineral surface area per square kilometer per year this new surface area is highly reactive because mineral weathering rates decline with surface age application of the reactor model yields results largely consistent with measured solute fluxes for the example of bench glacier alaska the model underpredicts potassium fluxes probably due to accelerated initial dissolution of biotite strained by abrasion the success of the model in predicting other silicate weathering fluxes reflects the far from equilibrium conditions in glacial runoff such that mineral weathering rate constants are not limited by saturation state in a small data set from glacial catchments both annual silica fluxes and mean concentrations increase with water discharge this suggests that mineral surface area increases with water discharge from glaciers an effect plausibly linked to erosion rates those glaciers for which both erosion rate and silica flux data are available support the idea that production of new reactive mineral surface area by glacial erosion drives silicate weathering fluxes

cretaceous vertebrate fauna of the cauvery basin southern india palaeodiversity and palaeobiogeographic implications abstract the vertebrate fauna from the late albian to maastrichtian succession of the cauvery basin south india has been known since 1845 but it received only scant attention as compared to the vertebrates already known from the deccan volcanic province of peninsular india recent fossil discoveries appear to support the emergence of significantly diverse marine and non marine vertebrates comprising fishes frogs reptiles ichthyosaurs plesiosaurs turtles crocodiles and dinosaurs and a mammal from the cauvery basin have revived the interest in the fauna of the basin as it has significant implications for understanding the palaeobiogeography of india the latest albian to turonian marine vertebrates such as sharks ichthyosaurs and plesiosaurs show a wide geographic distribution and marine territory while sharks are typically cooler water fauna of high palaeolatitudes the latest maastrichtian non marine vertebrates especially turtles crocodiles dinosaurs and a mammal are considered to show mixed gondwanan and laurasian affinities thus providing new lines of evidence in favour of a latest cretaceous biotic links between india and the neighbouring continents an overview of the vertebrate faunal diversity of the cretaceous sequences of the cauvery basin and its palaeobiogeographic considerations are presented

late quaternary alluvial fan terraces langshan inner mongolia china abstract alluvial fan terraces of the langshan range in the northwestern hetao basin of northern china records uplift on range bounding faults and late quaternary climate change alluvial fan profiles are segmented in the central part of the range front which lack strath terraces that developed in the southwest sw and northeast ne parts the stream channels in the central part have higher channel gradients and lower ratios of the valley floor width to valley height v four episodes of alluvial fan terraces were upstream from the range bounding fault which formation ages were estimated as 116 64 35 and 10 ka bp according to optically stimulated luminescence osl dating combined with previous 14 c and osl ages the correlation between time of the terraces formation and climatic fluctuations recorded in a guliya ice core reveals that alluvial fan aggradation was concentrated during the cold stages and that incision occurred during the succeeding cold to warm transitions a majority of alluvial fan terraces developed in accelerated uplift since 64 ka which indicates that tectonic uplift provided the driving force for continuous downcutting after climatic change triggered it geomorphic indices channel gradient and v distribution reconstructs the model of discrepant uplift in the langshan range with the fastest uplift rate in the central part which is controlled by range bounding faults

a synoptic and photographic climatology of low precipitation severe thunderstorms in the southern plains abstract the occurrence of an unusual type of severe thunderstorm difficult to identify by radar has been documented in the southern plains all of the three storms previously studied occurred near the dryline although tornadoes and large hail were produced little rain was observed at the ground and there was no evidence of a strong surface downdraft two were described as bell shaped ten more cases of this rare type of storm have been recently documented visually and on radar a photographic and synoptic climatology of this class of storm the low precipitation severe storm is suggested on the basis of an analysis of the comparison among 11 of these cases it is found that these storms form in a supercell like environment which is drier in the moist layer and more weakly sheared than that of well documented supercells in oklahoma implications of our findings and additional storm characteristics are discussed in light of the larger sample size

a transgressive storm and fair weather wave dominated shelf sequence cretaceous nimar formation chakrud madhya pradesh india abstract the lithologic assemblage of the cretaceous nimar formation in the area around chakrud madhya pradesh india has been classified in five marine facies a polymictic conglomerate resting on granite basement largely representing a lag deposit b coarse grained pebbly sandstone with normal and reverse coarse tail grading and also frequency grading c sandstone with alternate hummocky cross stratified and small scale wave rippled units d mudstone and e limestone facies c bears the definite stamp of alternations between storm and fair weather waves probable parameters of the fair weather waves have been determined from the grain size and morphometric parameters of the wave ripples the depth of the generation of the wave corresponds to a modern mid shelf region facies b shows gradational contact with facies c and was deposited shoreward above fair weather wave base bed shear stresses calculated from variable grain size parameters within individual cross laminae indicate that the nature of the current that deposited the pebbly sands was similar to that of storm currents it has been postulated that storm ebb surges initially moved as fluid gravity flows pushing ahead the bed loads and eventually turned into density currents farther offshore carrying most of the sediment in suspension the other two facies d and e were deposited largely below storm wave base the overall fining upward sequence reflects gradual deepening of the basin local aberrations in the facies sequence as represented by short phase coarsening upward sequences suggest temporary reversals of this trend

10 000 yr record of extreme hydrologic events well dated lacustrine sediments provide a hydrologic record indicating that the frequency and magnitude of runoff events and by inference storms have varied over the past 10 k y in northern new england we used five sediment cores and radiocarbon dating to develop a chronology of holocene hydrologic events for the ritterbush pond basin northern vermont chemical and physical analyses allow us to identify 52 distinct layers of predominately inorganic sediment that represent terrestrially derived material delivered to the pond by runoff events the thickness of some layers suggests hydrologic events at least equal in size to and probably much larger than any storm or flood recorded during nearly 300 yr of written regional history layer thickness and frequency and by analogy storm size and recurrence change through the holocene the largest events occurred 2620 6840 and 9440 calibrated 14c years before present cal 14c yr b p the most frequent hydrologic events occurred in three periods 1750 to 2620 6330 to 6840 and 8600 cal yr b p the recurrence interval of layer deposition during stormy periods averages 130 100 cal yr whereas the recurrence interval during less stormy periods is longer 270 170 cal yr the ritterbush pond event record illustrates the potential of inorganic lacustrine sediment to serve as a proxy record for estimating paleoflood frequency and deciphering climate change

chemical weathering trends in fine grained ephemeral stream sediments of the mcmurdo dry valleys antarctica abstract we investigated chemical weathering trends within the fine grained 40 m 2 g utilization of mfw mafic felsic weathered and a cn k al 2 o 3 cao na 2 o k 2 o plots however are more effective in discerning the extent and nature of chemical weathering in these stream systems ca and na depletion observed within the sediments exhibiting the highest surface area in delta stream suggest that chemical weathering may result in pitting and or incongruent dissolution of pyroxenes and feldspars as well as the development of amorphous and or nanophase weathering products in contrast clark glacier stream sediments do not have similar leaching trends in the fine grained sediment fraction and exhibit minimal weathering overall this may suggest that fine grained material is being trapped on top of the clark glacier surface and has not yet been transported into the weathering environment of the hyporheic zone due to timing of sampling alternatively complete dissolution of very fine grained sediment could be occurring in this stream transect and is therefore not preserved in the fine sediment fraction overall the magnitude of chemical weathering observed between the two stream systems is ultimately related to the nature of the underlying drift cold and wet based drift deposition dispersal patterns of eolian fines and variable stream discharge rates thus incorporation of local fine grained sediment derived from the underlying glacial drift deposits and distributed via the varying wind regimes within the hyper arid climate into active stream channels may facilitate incongruent mineral dissolution and development of weathering products and ultimately influence the composition and concentration of meltwater stream solutes

reconstruction of madagascar and africa evidence from the davie fracture zone and western somali basin new seismic reflection gravity and magnetic data from offshore east africa allow the davie fracture zone to be traced from 11 s to its intersection with the kenyan coast at 2 s constraining the relative motion of madagascar and africa seasat derived free air gravity anomalies and slope rise positive magnetic anomalies observed in shipboard data help to locate the continent ocean boundaries cob off the shore of east africa and madagascar seismic reflection data further document a diapirprovince off madagascar presumably conjugate to that observed off kenya and somalia the dhow and very large crude carrier vlcc basement ridges are complex features and do not appear to be simple fracture zones owing their existence entirely to the separation of madagascar and africa from these data we determine a predrift fit of madagascar and africa involving a 14 2 rotation of madagascar to africa about a pole at 10 n 150 e the geometry of the reconstruction adheres to seismic and potential field data indicating the oceanic nature and extent of the comoros basin and of the somali basin between kenya and the seychelles and it does not conflict with onshore or offshore stratigraphy timing of the opening of the western somali basin is constrained by mesozoic marine magnetic anomalies and extrapolation to the interpreted cob and occurred between approximately 165 and 130 ma

paleoflood hydrology and extraordinary flood events paleoflood hydrology is the study of past or ancient flood events the most accurate technique involves the analysis of slackwater deposits and paleostage indicators swd psi slackwater deposits are sand and silt emplaced from suspension in exceptionally deep high velocity floods that characterize narrow deep canyons in resistant geologic materials these and other paleostage indicators are used to establish hydraulic grade lines for the generating flow events favorable sites for slackwater deposition include channel margin areas where stresses and velocities are reduced below critical values necessary to maintain fine grained bedload material sand and silt in suspension computerized procedures for hydraulic flow modeling are used to tie the elevations of the highest slackwater deposits to surveyed river cross sections the flood discharges calculated by this method can be calibrated through the study of modern floods on gaged rivers correlation of multiple swd psi sites along a river reach is used to identify the maximum paleostage achieved by a given flood advances in the dating of flood deposits permit estimates of flood frequency to be made extending over a data base of thousands of years the major geochronologic tool is radiocarbon dating of various kinds of organic matter intercalated with the slackwater deposits an important development is the use of the tandem accelerator mass spectrometer for direct measurement of 14c tiny blebs of charcoal seeds and other organics can be analyzed in order to date ancient flood deposits of hydrologic significance since swd psi studies yield very accurate determinations of paleoflood ages and magnitudes there is a pressing need for new statistical procedures that make optimum use of the information content in paleoflood records for flood frequency analysis nevertheless swd psi paleoflood hydrology has moved beyond the research phase its use should be encouraged in evaluating past experience of extraordinary floods at appropriate hazardous sites

trends in grain size and bet surface area in cold arid versus warm semiarid fluvial systems abstract sediment grain size and surface area impose critical controls on the rates of chemical weathering even in cold based i e polar glacial systems where extensive chemical weathering traditionally has been considered minimal owing to low temperatures production of fine grained material increases the surface area of sediments priming mineral surfaces for chemical weathering comparison among grain size and reactive surface area of sediments along granitoid sourced fluvial transects between a cold arid glacial wright valley antarctica and a warm semiarid nonglacial wichita mountains oklahoma environment indicates opposing trends downstream within the silt and clay

dimorphism and a new record of barroisiceras de grossouvre ammonoidea from the coniacian of bagh central india barroisiceras de grossouvre was hitherto unknown in india b onilahyense basse which elsewhere belongs exclusively to the coniacian has been recorded from the bryozoan limestone formation of central india this find as well as the presence of another time diagnostic coniacian ammonite placenticeras kaffrarium etheridge and two inoceramid bivalves inoceramus mytiloides incertus jimbo and i platyceramus mantelli barrois mercey in the underlying horizons help in resolving the long standing problem of the age of the bagh group b onilahyense shows wide intraspecific variability and overlaps morphometrically with the late turonian type species b haberfellneri hauer they may be conspecific the present species has been found to be sexually dimorphic a phenomenon previously not well recognised in the subfamily barroisiceratinae as in many late cretaceous ammonites dimorphism is manifest mainly by differences in relative adult sizes and in strength of ornamentation the microconch being sma

k t transition in deccan traps of central india marks major marine seaway across india deccan intertrappean sediments in central india are generally considered as terrestrial deposits of maastrichtian age but the cretaceous tertiary k t position is still unknown here we report the discovery of the k t transition a marine incursion and environmental changes preserved within the intertrappean sediments at jhilmili chhindwara district madhya pradesh integrative biostratigraphic sedimentologic mineralogic and chemostratigraphic analyses reveal the basal danian in the intertrappean sediments between lower and upper trap basalts that regionally correspond to c29r and the c29r c29n transition respectively intertrappean deposition occurred in predominantly terrestrial semi humid to arid environments but a short aquatic interval of fresh water ponds and lakes followed by shallow coastal marine conditions with brackish marine ostracods and early danian zone p1a planktic foraminifera mark this interval very close to the k t boundary this marine incursion marks the existence of a nearby seaway probably extending inland from the west through the narmada and tapti rift valleys the jhilmili results thus identify the k t boundary near the end of the main phase of deccan eruptions and indicate that a major seaway extended at least 800 km across india

floodplain deposits a geochemical archive of flood history a case study on the river rhine germany abstract based on the correlation between discharge and carbonate content of the suspended load of the river rhine germany a systematic geochemical mineralogical and granulometric study was carried out to verify whether this geochemical signal is transferred to floodplain deposits and in what way these sediments and their chemostratigraphic characterization can be used as a tool for the reconstruction of the river flood history the analysis of the time resolved changes in the composition of particulate matter during a flood event revealed that the increase of carbonate content represented by cao sr with discharge was coupled to a simultaneous decrease in the relative amount of siliciclastics k 2 o rb the association of these two groups of diametrical parameters with specific grain size fractions carbonates with 40 200 m siliciclastics with 200 m were found to be slightly shifted relative to each other and showed different gradients during the surging and fading flood wave this together with the covariance of elements pertaining to minerals with different density e g carbonate and heavy minerals suggests a chemical response to the changes in discharge which is controlled primarily by hydraulic equivalence rather than grain size there is also a time lag between the amount of suspended load and discharge with a maximum in suspended load shortly after the peak discharge when the flood has already started to abate the flood plain sediments have similar composition to the suspended load suggesting the direct transfer of the geochemical flood signal to the floodplain sediments three lithological units could be distinguished in a 240 cm long sediment core collected from the floodplain grain size and geochemical composition indicate that only the top of the section 20 70 cm represents sediments deposited in an abandoned channel of the river and may have preserved the geochemical flood signals as identified during actual flood events the comparison of the chemostratigraphy of this part of the section estimated with optical stimulated luminescence to be deposited between ca 1650 and 1920 with a record of historically documented inundations however yielded only poor agreement the possible reasons for this inconsistency are discussed and suggestions are made for continuing investigations

occurrence and formation of water laid placers a placer is a deposit of residual or detrital mineral grains in which a valuable mineral has been concentrated by a mechanical agent the agent is usually running water and the valuable mineral is usually denser than quartz for example gold diamond cassiterite ilmenite or chromite it is difficult to overemphasize the importance of placers as sources of mineral wealth the witwatersrand south africa paleoplacers discovered in 1886 alone have provided over half of all the gold ever mined in the world pretorius 1976 and alluvial placer deposits of cassiterite in southeast asia presently are the world s major source of tin toh 1978 the earliest evidence of placer mining comes from stone carvings in egypt dated at 2500 b c macdonald 1983 and as early as 7 b c strabo pointed out that in turdetania spain more gold was procured from washing sand in the rivers than by digging in the mines given the economic importance of water laid placers and the long history oftheir exploitation it is remarkable that they have received so little attention in sedimentary research mining and exploration practices for the most part have been guided by empirical rules of thumb that are locally useful but lack any firm physical basis of understanding see bateman

holocene flood plain soil formation in the southern lower mississippi valley implications for interpreting alluvial paleosols holocene mississippi river flood plain soils in central louisiana provide important insights on alluvial pedogenesis in an aggradational setting insights that are useful for interpreting alluvial paleosols the flood plain soils are younger than ca 5400 yr b p and are grouped into two categories 1 meander belt and 2 backswamp soils meander belt soils are entisols inceptisols and alfisols developed on point bar ridges and natural levee crests they consist of 3 5 m thick brown silty and sandy moderately well drained profiles with multiple parent materials common yellow brown and gray mottles and a few iron and calcite nodules backswamp soils are vertisols formed in flood plain depressions away from active and abandoned mississippi river channels and consist of up to 10 m thick gray clayey poorly drained profiles that have abundant yellow brown mottles iron and calcite nodules gypsum accumulations and slickensides the thickness of the soils and the presence of multiple parent materials show that as the flood plain aggrades concurrent or alternating episodes of sedimentation and pedogenesis produce cumulative profiles profile thickness is more closely related to sediment accumulation rates than to the depth of chemical weathering and the cumulative nature of the soils explains the difficulty of recognizing discrete paleosol profiles in many ancient alluvial deposits comparisons of soils formed on the three youngest holocene mississippi river meander belts saucier and snead 1989 show that the soils record episodes of meander belt growth abandonment and relocation meander belt 1 soils form as the active meander belt develops and consist of either vertically stacked entisols or a single inceptisol the soils contain few calcite nodules and form over intervals of a few hundred years meander belt 2 soils are alfisols lack free carbonates and form over intervals of a few thousand years following meander belt abandonment and soil leaching meander belt 3 soils are alfisols or vertisols that contain common calcite nodules and the profiles are developed in 1 to 2 m of backswamp mud that overlies meander belt silt and sand the mud inhibits profile leaching and leads to poor drainage and calcite precipitation this change in soil hydrology complicates interpretations of the effects of time on meander belt soil development backswamp soils are strongly influenced by seasonal episodes of soil wetting and drying as demonstrated by the gray colors and the abundance of mottles nodules and slickensides in the soils the distribution of calcite nodules in the backswamp and meander belt soils is more closely related to seasonal water table position than to mean annual precipitation which suggests that not all calcic paleosols in ancient alluvial deposits represent semiarid or arid climates slickensides attest to seasonal rainfall but the composition of the backswamp soils primarily reflects source area lithology and depositional influences rather than the effects of chemical weathering in general these soils provide an incomplete record of the humid subtropical climate of louisiana although short term sediment accumulation rates decrease away from mississippi river channels the backswamp soils are not better developed i e more mature than the meander belt soils because poor drainage and slow but continuous sedimentation inhibits weathering collectively these observations suggest that flood plain soils that developed in aggradational settings such as that of the mississippi river flood plain are best suited for interpreting depositional and hydrologic histories of ancient alluvial deposits rather than paleoclimates

aeolian flux of biotic and abiotic material in taylor valley antarctica abstract we studied patterns and mechanisms controlling wind driven flux of soils and associated organic matter in taylor valley antarctica over a 10 year period using passive aeolian traps and dynamic mass erosion particle counters deployment of the particle counters near meteorological stations allowed us to compare the magnitude of soil flux with data on prevailing wind particulate organic c n and p measurements on transported sediment allowed us to examine connectivity of wind dispersed organic matter among landscape units most sediment entrainment occurred within 20 cm of the soil surface during saltation bursts that occupied 1 sediment movement was highest in the up valley reaches of taylor valley and transport was down valley towards mcmurdo sound the general paucity of biological organic matter production throughout the mcmurdo dry valleys in concert with low fluvial transport makes aeolian distribution or organic c n and p an important factor in the distribution of organic matter throughout this polar desert ecosystem and increases connectivity among the ecosystem components

direct observations of aluminosilicate weathering in the hyporheic zone of an antarctic dry valley stream abstract this study focused on chemical weathering and bacterial ecology in the hyporheic zone of green creek a mcmurdo dry valley antarctica stream an in situ microcosm approach was used to observe dissolution features on the basal plane surface of muscovite mica four mica chips were buried in december 1999 and dug up 39 d later atomic force microscopy afm of the basal plane surfaces revealed small anhedral 10 a deep etch pits covering 4 of the surfaces from which an approximate basal plane dissolution rate of 8 3 10 18 mol muscovite cm 2 s 1 was calculated on the basis of the geometric surface area for the study period this is an integrated initial dissolution rate on a fresh surface exposed for a relatively brief period over the austral summer and should not be compared directly to other long term field rates the observation of weathering features on mica agrees with previous stream and watershed scale studies in the dry valleys which have demonstrated that weathering occurs where liquid water is present despite the cold temperatures afm imaging of mica surfaces revealed biofilms including numerous small

implications of new data on mesozoic rocks of kachchh western india a lack of detailed facies studies has resulted in a false impression of the mesozoic depositional setting in kachchh western india previously kachchh has been termed kutch or cutch in addition designation of part of this sequence as gondawana implies by tradition a predominantly non marine origin recently we examined these jurassic cretaceous units and found numerous wave built sedimentary structures that have been previously overlooked or unreported abundant marine trace fossils and highly bioturbated and glauconite rich beds thus we now propose a marine origin for the entire kachchh succession this interpretation has important implications regarding similar sequences around the indian plate margin

control on sediment and organic carbon delivery to the arctic ocean revealed with space borne synthetic aperture radar ob river siberia an important control on river biogeochemistry and sediment load is the process of water exchange between primary channels and the flood plain particularly in low r elief areas containing lakes ephemeral channels and other aquatic ecosystems flood plain exchange may be a dominant process on the lowland rivers of arctic russia which are among the world s largest in water discharge yet are strikingly deficient in their delivery of sediment to the arctic shelf temporal synthetic aperture radar sar amplitude and interferometric images of the ob river siberia reveal a time varying limnological network controlling water sediment and nutrient exchange between flood plain wetlands and the main channel the amount of hydrologic exchange decreases by one order of magnitude from june to september enhancing sedimentation over as much as 90 of the flood plain and enriching channel waters with colloidal organic carbon this observation combined with russian field measurements of water discharge and sediment load indicates that a major sediment sink on the lower ob flood plain may be responsible for the low amount of sediment delivery by the ob river to its estuary and the kara sea

role of hydraulic sorting in the origin of fluvial placers a necessary condition for placer development is selective sorting at the grain scale by size and density the effects of differential entrainment suspension and transport on an initial distribution composed of medium size quartz and 10 fine size magnetite were modeled by solving the einstein bedload function for specific grain friction velocities u super in the range 3 63 cm sec super 1 and bed roughnesses of 0 55 2 5 and 10 mm for any value of u super and for both mineral densities the transport rate for all sizes in the initial distribution decreases with increasing roughness the decrease being greatest in the finer sizes the concentration of magnetite transported in the flow increases with increasing u super for each roughness and decreases with increasing roughness for each u super the settling velocity ratio of magnetite to quartz in transport decreases with increasing u super for any value of roughness for any value of u super the ratio first decreases then increases with increasing roughness ranging from 1 36 at low u super and roughness to 0 76 at high u super and intermediate roughness these results are due to variations in the reactive angles of grains and the extent to which grains hide in the lower inner zone of the boundary layer concentrations of heavy minerals at the bed bar and system scales are explained using these results

glacial and postglacial sedimentation in the fryxell basin taylor valley southern victoria land antarctica abstract a 9 14 m long sediment sequence was recovered from lake fryxell taylor valley southern victoria land antarctica and investigated for its chronology and sedimentological mineralogical and biogeochemical changes the basal part of the sequence is dominated by coarse clastic matter i e mainly sand the sediment composition suggests that a lake existed in fryxell basin during the middle weichselian by ca 48 000 cal year bp after a short period of lake level lowstand ca 43 000 cal year bp lower taylor valley became occupied by the proglacial lake washburn which was at least partly supplied by meltwater and sediments from the ross ice sheet that was advanced to the mouth of taylor valley evaporation of lake washburn to lower levels started during the last glacial maximum at ca 22 000 cal year bp long before the ross ice sheet retreated significantly lake level lowering was discontinuous with a series of high and low stands from ca 4000 cal year bp environmental conditions were similar to those of today and lower fryxell basin was occupied by a small lake this lake evaporated to a saline or hypersaline pond between ca 2500 and 1000 cal year bp and refilled subsequently

reconstruction of multi century flood histories from oxbow lake sediments peace athabasca delta canada floods caused by ice jams on the peace river are considered to be important for maintaining hydro ecological conditions of perched basins in the peace athabasca delta pad canada a highly productive and internationally recognized northern boreal ecosystem concerns over the potential linkages between regulation of the peace river in 1968 for hydroelectric production and low peace river discharge between 1968 and 1971 during the filling of the hydroelectric reservoir absence of a major ice jam flood event between 1975 and 1995 and low water levels in perched basins during the 1980s and early 1990s have sparked numerous environmental studies largely aimed at restoring water levels in the pad lack of sufficient long term hydrological records however has limited the ability to objectively assess the importance of anthropogenic factors versus natural climatic forcing in regulating hydro ecological conditions of the pad here we report results of a paleolimnological study on laminated sediments from two oxbow lakes in the pad which are located adjacent to major flood distributaries of the peace river sediment core magnetic susceptibility measurements supported by results from several other physical and geochemical analyses as well as stratigraphic correspondence with recorded high water events on the peace river provide proxy records of flood history spanning the past 180 and 300 years in these two basins results indicate that inferred flood frequency has been highly variable over the past 300 years but in decline for many decades beginning as early as the late nineteenth century well before peace river regulation additionally several multi decadal intervals without a major flood have occurred during the past 300 years while climate related mechanisms responsible for this variability in flood frequency remain to be determined as does quantifying the relative roles of river regulation and climate variability on hydro ecological conditions in the pad since 1968 these results suggest that ecosystem management strategies for the pad need to explicitly account for natural variations in flood recurrence intervals copyright 2006 john wiley sons ltd

sequence surfaces and paleobathymetric trends in albian to maastrichtian sediments of ariyalur area cauvery basin india abstract exposed late cretaceous albian maastrichtian marine rocks of the ariyalur area in the cauvery basin have been extensively studied based on biostratigraphy and paleobathymetry with paleobathymetric interpretation carried out using vertical and lateral relationships of rock facies macro and microfossil assemblages textural characteristics and diagenetic changes of the lithologic units the integration of these data reveals four transgressive regressive t r cycles viz dalmiapuram garudamangalam sillakkudi and kallankurichchi in stratigraphic order these t r cycles have been compared with global published relative sea level curves of the study area the major sea level changes during the late turonian and late maastrichtian in the study area correlate well with global sea level changes of vail et al 1977 haq et al 1987 and miller et al 2005 based on biostratigraphy stratal patterns and their relationship the late cretaceous succession of the ariyalur area is thus subdivided into four 2nd 3rd order sequences

chemical weathering in streams of a polar desert taylor valley antarctica taylor valley is a cold polar desert located in the mcmurdo dry valleys the largest ice free area in antarctica for six to ten weeks a year glacial meltwater streams flow through unconsolidated boulders and pebbles to perennially ice covered closed basin lakes because there is no overland flow or groundwater input most chemical weathering reactions are restricted to the stream channels despite these limiting conditions chemical weathering rates in the stream channels are similar to or higher than those in temperate climate watersheds these high rates in taylor valley suggest that temperature and precipitation are not the primary controls on chemical denudation in this case high stream discharges high rates of physical weathering e g frost action salt weathering and or the interaction between the stream and hyporheic zone contribute to the high chemical denudation rates in the taylor valley stream channels

sediment characteristics floods and heavy metal pollution recorded in an overbank core from the lower reaches of the yangtze river overbank sediments contain abundant information about floods paleoenvironmental changes and recent pollution history of a river basin for the purpose of understanding modern overbank sediments and their environmental significance this multidisciplinary study sampled a core from the overbank and a short core from the overbank outcrop at nanjing in the lower reaches of the yangtze river the overbank deposit comprises fine grained discontinuous strata including silt sandy silt silty sand and sand layers field and laboratory observations indicated that the overbank sediment contained a series of layers of sandy silt coupled with thin silty sand layers each a few millimeters thick which formed muddy layers that were dozens of centimeters thick between the muddy layers were coarser sand layers grain size analyses 137cs dating and heavy metal measurements contained information on flood events and pollution history over the past 60 years the coarser sand layers corresponded with severe floods in 1954 and 1983 between the two severe floods the study area experienced an overbank building stage from the 1990s to the early 2000s the overbank sedimentation rate declined reflecting human activities especially the dams in the yangtze river basin that trapped more sediment the average heavy metal concentrations in the overbank sediments are higher than the background levels for suspended sediment in the yangtze river heavy metals in overbank sediments were assessed by enrichment factors and sediment quality assessment values for freshwater sediment cr and ni values were high especially from the early 1980s to the early 2000s the impacts of floods economic development and environmental management on these heavy metal variations were discussed

when and where did india and asia collide timing of the collision between india and asia is the key boundary condition in all models for the evolution of the himalaya tibetan orogenic system thus it profoundly affects the interpretation of the rates of a multitude of associated geological processes ranging from tibetan plateau uplift through continental extrusion across eastern asia as well as our understanding of global climate change during the cenozoic although an abrupt slowdown in the rate of convergence between india and asia around 55 ma is widely regarded as indicating the beginning of the collision most of the effects attributed to this major tectonic episode do not occur until more than 20 ma later refined estimates of the relative positions of india and asia indicate that they were not close enough to one another to have collided at 55 ma on the basis of new field evidence from tibet and a reassessment of published data we suggest that continent continent collision began around the eocene oligocene boundary 34 ma and propose an alternative explanation for events at 55 ma

chemical weathering in glacial environments do glaciers enhance or inhibit chemical weathering rates relative to other environments the importance of glaciers in the global carbon cycle and climate change hinges on the answer we show that catchments occupied by active alpine glaciers yield cation denudation rates greater than the global mean rate but do not exceed rates in nonglacial catchments with similar water discharge silica denudation rates are distinctly lower in glacier covered catchments than in their nonglacial counterparts because sediment yields are high from glaciers this suggests that water flux rather than physical erosion exerts the primary control on chemical erosion by glaciers potassium and calcium concentrations are high relative to other cations in glacial water probably due to dissolution of soluble trace phases such as carbonates exposed by comminution and cation leaching from biotite preferential weathering of biotite may result in higher 87 sr 86 sr in glacial runoff than expected from whole rock compositions thus although glaciers do not influence total chemical denudation rates at a given runoff they may yield compositionally distinctive chemical fluxes to the oceans disruption of mineral lattices by grinding increases dissolution rates this and high surface area should make glacial sediments exceptionally weatherable weathering of glacial erosion products in environments beyond the glacier margin deserves attention because it may figure prominently in global chemical cycles

amazon flood wave hydraulics summary a bathymetric survey of 575 km of the central amazon river and one of its tributaries the purus are combined with gauged data to characterise the amazon flood wave and for hydraulic modelling of the main channel for the period june 1995 march 1997 with the lisflood fp and hec ras hydraulic models our investigations show that the amazon flood wave is subcritical and diffusive in character and due to shallow bed slopes backwater conditions control significant reach lengths and are present for low and high water states comparison of the different models shows that it is necessary to include at least the diffusion term in any model and the rmse error in predicted water elevation at all cross sections introduced by ignoring the acceleration and advection terms is of the order of 0 02 0 03 m the use of a wide rectangular channel approximation introduces an error of 0 10 0 15 m on the predicted water levels reducing the bathymetry to a simple bed slope and with mean cross section only introduces an error in the order of 0 5 m these results show that when compared to the mean annual amplitude of the amazon flood wave of 11 12 m water levels are relatively insensitive to the bathymetry of the channel model the implication for remote sensing studies of the central amazon channel such as those proposed with the surface water and ocean topography mission swot is that even relatively crude assumptions regarding the channel bathymetry will be valid in order to derive discharge from water surface slope of the main channel as long as the mean channel area is approximately correct

thermoluminescence and excess 226ra decay dating of late quaternary fluvial sands east alligator river australia thermoluminescence tl dating was applied to seven samples of siliceous fluvial sands from the east alligator river of northern australia giving ages ranging from modern to 6000 yr b p two methods of estimating the equivalent dose ed total bleach and regenerative were applied to the 90 to 125 m quartz fraction of the samples in order to determine the reliability and internal consistency of the technique high resolution and spectroscopy were used to measure radionuclide contents these measurements revealed an excess 226ra activity compared with 230th this excess decreased with depth and was used directly to derive mean sedimentation rates and thus sediment ages both this method and one 14c date confirmed the validity of the tl values which increased systematically with depth and were consistent with site stratigraphy tl was of limited use in the dating of these late holocene deposits because of age uncertainties of 500 to 1600 yr resulting from a significant residual ed this residual probably resulted from incomplete bleaching during reworking upstream of the sampling site for pleistocene deposits the residual ed will be less significant because of higher total eds and tl dates will be correspondingly more accurate

sediment residence times in catchments draining to the gulf of carpentaria northern australia inferred by uranium comminution dating abstract uranium u isotopes are useful for constraining the timescales of weathering and erosion processes the 234u 238u activity ratio parentheses denote activity ratio of fine grained detrital minerals is proposed to record the time elapsed since mineral grains were reduced to

biodiversity during the deccan volcanic eruptive episode this paper gives a detailed overview of biotic assemblages recovered from the deccan trap intercalated sedimentary sequences infra and intertrappean beds of peninsular india as a result of extensive research done during the last 20 years the infra and intertrappean beds contain remnants of gondwanan forms such as myobatrachinae frogs pelomedusid turtles dinosaurs i e titanosaurids and abelisaurids and mammals apart from these gondwanan elements the infra and intertrappean beds also contain forms of laurasian affinity though recently doubt has been cast on such relationships based on previous fossil records laurasiatic forms were considered to be represented by a great variety of micro and megavertebrate assemblages such as discoglossid and pelobatid frogs anguid lizards alligatorid crocodiles palaeoryctid mammals charophytes and ostracodes the biotic assemblages show a remarkable similarity between the infra and intertrappean beds indicating a short time period for the deposition of these deccan volcano sedimentary beds the recovered biotic assemblages strongly indicate a maastrichtian age for the initiation of deccan volcanic activity and the sedimentary beds associated with it the cretaceous tertiary boundary as such remains to be defined in any known sections in sedimentary sequences in so far investigated localities of peninsular india what have been identified are maastrichtian age beds in the east central and western narmada river region on the basis of pollens vertebrate assemblage and planktonic foraminiferas in infratrappean offshore sequences a palaeocene intertrappean bed at lalitpur uttar pradesh that is among those lacking dinosaurian remains but having palynological assemblages similar to those from well established palaeocene sequences suggests the presence of palaeocene intertrappeans but the k t boundary is yet to be properly defined