glacial and submarine processes on the shelf margin of the disko bay trough mouth fan abstract fast flowing ice streams and outlet glaciers exert a major control on glacial discharge from contemporary and past ice sheets improving our understanding of the extent and dynamic behaviour of palaeo ice streams is crucial for predictions of how the cryosphere will respond to climate warming and the associated implications for global sea level this paper presents results from two 3d seismic surveys located on the continental shelf adjoining the disko bay trough mouth fan tmf one of the largest glacial outlet systems in greenland located at the seaward terminus of the c 370 km long cross shelf disko trough the disko bay tmf was generated by highly efficient subglacial sediment delivery onto the continental slope during repeated ice stream advances a variety of submarine glacial landform assemblages are recognised on the seabed reflecting past ice stream activity the 3d seismic study covers the shallow banks located north and south of the disko trough and sheds focus on the seabed and the uppermost stratigraphic interval associated with the late pleistocene development the buried section probably of saalian age contains a prominent grounding zone wedge gzw in the northern and low angle progradational packages in the southern area indicating a period of major glacial advances to the shelf margin subsequently the outer margin was influenced by glacimarine sedimentation localized shelf edge ice advances and sediment transport by contour currents that possibly began in the last interglacial period eemian during the last de glaciation the northern bank appears to have been covered by passive ice leaving a field of dead ice deposits in contrast multiple sets of terminal moraine ridges observed on the southern bank suggest a slow retreat of active grounded ice from the last glacial maximum lgm position on the outer shelf isostatic and tectonic influences on relative sea level may have played a role in generating the divergent glacial configurations of the northern and southern bank areas

a seismic reflection study of northern baffin bay implication for tectonic evolution reflection profiles offshore of baffin island south of lancaster sound reveal coast parallel half grabens containing flat lying sedimentary sections typical of a rifted margin in northernmost baffin bay adjacent to devon and southern ellesmere islands four sedimentary basins are identified in these basins the sedimentary sections are faulted folded and laterally discontinuous the basement shows linear trends steep faults and abrupt variations in depth in one basin a 50 km long and 10 km wide flower structure is observed a transpressive tectonic regime is suggested to explain the uplifted sedimentary and basement section and the change in depth to basement across it a 150 km long paleoshelf buried by a thickening sedimentary wedge is present offshore of devon island because strike slip and compressional features are observed on seismic profiles north of lancaster sound and extensional features are observed to the south differences in the plate tectonic development are inferred the inte

mixing processes in modern estuarine sediments from the gulf of khambhat western india abstract sandy and muddy detritus from two distinctive end member provenance terrains basaltic and granitic are transported to the estuaries of the gulf of khambhat by fluvial discharge and opposing tidal currents making this embayment ideal for investigating the effects of mineralogical and geochemical mixing on sediment composition in estuarine depositional systems rivers flowing predominantly from the north over precambrian metasediments and granites supply a felsic plutoniclastic sand to the gulf whilst a mafic volcaniclastic sand sourced by deccan basalts is transported by rivers draining the western ghats and from the local coastal erosion in the southern part of the gulf sediments from the tapti estuary are rich in basaltic rock fragments 50 and are characterised by a distinctly basaltic source composition la sc 0 25 0 86 th sc 0 12 0 40 cr th 13 121 eu eu 0 93 1 68 and lree hree 2 96 6 57 by contrast the sediments of the sabarmati inner estuary are rich in quartz grains 80 as evident from the major and trace element compositions la sc 1 38 6 63 th sc 0 58 2 98 cr th 0 58 19 39 eu eu 0 46 0 86 and lree hree 2 90 11 40 the detrital compositions of the remaining major estuaries the narmada dhadhar and mahi scatter across a broad range in a qfr diagram and contain varying amounts of quartz feldspar and rock fragments in the narmada estuary the mixed signature characterised by ree values including eu eu 0 42 2 28 and lree hree 4 37 14 80 is caused by the presence of diverse rock types that crop out in the source area in the mahi estuary which largely flows across felsic source terrains the compositional signature is controlled by mixing of felsic detritus from riverine input with mafic sediments from seaward side in the estuary the two end member detrital compositions plutoniclastic and volcaniclastic are mixed in the macro tidal estuaries mixing of sediment takes place where fluvial currents and tidal flows interact and the proportion of mixing varies systematically from outer to central to inner estuary a high degree of mixing of felsic sediments with deccan basalt derived sediments takes place in the outer estuary resulting in felsic mafic ratios of 40 60 sediments in the central estuaries 65 35 and in the fluvial dominated inner estuaries 90 10 are characterised by moderate to minor degrees of mixing the mixing in estuaries is systematic and is reflected in both the mineralogy and geochemistry of the sediments provenances of ancient estuarine successions should therefore be interpreted with great care incorporating awareness of the mixing processes which influence sediment compositions to different degrees in estuaries especially those characterised by strong tidal currents

opening of the fram strait gateway a review of plate tectonic constraints abstract we have revised the regional crustal structure oceanic age distribution and conjugate margin segmentation in and around the lena trough the oceanic part of the fram strait between the norwegian greenland sea and the eurasia basin arctic ocean the lena trough started to open after eurasia greenland relative plate motions changed from right lateral shear to oblique divergence at chron 13 times 33 3 ma earliest oligocene a new bouguer gravity map supported by existing seismic data and aeromagnetic profiles has been applied to interpret the continent ocean transition and the influence of eocene shear structures on the timing of breakup and initial seafloor spreading assuming that the onset of deep water exchange depended on the formation of a narrow oceanic corridor the gateway formed during early miocene times 20 15 ma however if the initial lena trough was blocked by terrigenous sediments or was insufficiently subsided to allow for deep water circulation the gateway probably formed with the first well developed magnetic seafloor spreading anomaly around chron 5 times 9 8 ma late miocene paleoceanographic changes at odp site 909 northern hovgard ridge are consistent with both hypotheses of gateway formation we cannot rule out that a minor gateway formed across stretched continental crust prior to the onset of seafloor spreading in the lena trough the gravity seismic and magnetic observations question the prevailing hypotheses on the yermak plateau and the morris jesup rise as eocene oceanic plateaus and the hovgard ridge as a microcontinent

chemical weathering indices applied to weathering profiles developed on heterogeneous felsic metamorphic parent rocks abstract chemical weathering indices are commonly used for characterizing weathering profiles by incorporating bulk major element oxide chemistry into a single metric for each sample generally on homogeneous parent rocks weathering indices change systematically with depth however the weathering of heterogeneous metamorphic rocks confounds the relationship between weathering index and depth in this paper we evaluate previously defined chemical weathering indices for their suitability in characterizing weathering profiles developed on felsic heterogeneous metasedimentary bedrock from coweeta hydrologic laboratory north carolina usa among the weathering indices evaluated here the weathering index of parker wip is the most appropriate for application to weathering profiles on heterogeneous and homogeneous parent rock because the wip includes only the highly mobile alkali and alkaline earth elements in its formulation it yields values that differ greatly from those of the parent rock in addition the wip allows for aluminum mobility unlike other weathering indices these characteristics combine to make the weathering index of parker the most applicable index for studying the weathering of heterogeneous metasedimentary rocks however the wip should be applied judiciously as alkali and alkaline earth metals may be readily depleted during weathering in addition to reflecting weathering the chemical index of alteration cia chemical index of weathering ciw plagioclase index of alteration pia and vogt s residual index v may be sensitive to subtle geochemical changes such as hydrothermal alteration along a fault and or alteration at the water table weathering indices that include iron in their calculations were not included in this study because they do not distinguish between ferric and ferrous iron the oxidation state and distribution of iron in a weathering profile is influenced by the proportion of oxidation states in the pre weathered metamorphic rock and interaction with groundwater during weathering

the recycled orogenic sand provenance from an uplifted thrust belt betic cordillera southern spain the betic cordillera of southern spain represents an uplifted foreland fold thrust belt source rock types of the betic cordillera include metamorphic mainly phyllite schist quartzite and gneiss sedimentary siliciclastic and carbonate volcanic felsic to intermediate pyroclasts and mantle derived peridotite gabbro serpentinite and serpentine schist rocks the fluvial systems range that transect the betic cordillera are the major detrital source of sediment along the southern spanish coast supplying sand to beaches and offshore depositional systems in the alboran sea basin three key sand petrofacies derived from the betic mountain belt reflect the main clastic contribution of known source rocks all the sands are quartzolithic ranging from quartz rich to lithic rich fluvial systems draining the sierra de los filabres the sierra nevada the sierra de gador and the ma laga mountains and their related beaches constitute a metamorphic sedimenticlastic quartzolithic sand petrofacies qm34610 f463 lt6269 lm72614 lv264 ls26613 derived dominantly from the nevado fila bride alpuja rride and mala guide complexes this quartzolithic petrofacies extends from northeast of almeria to torremolinos southwest of ma laga and northeast of algeciras only one beach sand sample east of cabo de gata is volcanolithic volcanic detritus mainly having felsitic textures is derived from miocene 15 7 ma pyroclastic sequences cropping out in the southeast of the chain this metamorphic sedimenticlastic quartzolithic petrofacies changes in the coastal stretch from torremolinos to marbella where drainage systems cut across the serrania de ronda here source rock types include peridotite gabbro and serpentinite of the ronda peridotite massif and metamorphic rocks of the ma laguide and alpuja rride units the fluvial and beach sands of this area are quartzolithic qm32612 f1063 lt58611 and include abundant peridotite and serpentinite grains the latter quartzolithic petrofacies changes abruptly from algeciras to ca diz where the sand becomes quartz rich qm7765 f462 lt1964 this sand petrofacies is derived predominantly from recycling of sedimentary sequences mainly the quartzarenite turbidite units of the gibraltar arc the algeciras flysch this petrofacies is characterized by higher proportion of quartz grains and abundant sedimentary lithic fragments lm163 lv161 ls9863 the three onshore petrofacies plot in the recycled orogen provenance compositional field and the lithic to transitional to quartzose recycled subfields of dickinson 1985 they vary from lithic to transitional and quartzose depending on their source lithologies in the betic foreland fold thrust belt these actualistic petrofacies best describe the nature and distribution of sand petrofacies derived from a collisional fold thrust belt where primary and recycled source rocks are interfingered deep marine turbidites of the alboran basin have basinwide quartzolithic sands having close compositional relations with betic cordillera onshore sand petrofacies comparison of detrital modes from mainland to deep marine environments provides a suitable basis for interpreting the miocene to pleistocene sand dispersal history in the alboran basin these modern quartzolithic petrofacies are used to interpret analogous ancient collisional sandstone petrofacies of the alpine orogenic belt of the western central mediterranean region and of other collisional orogenic systems as a broader point of view

climate variability in the early pliocene arctic annually resolved evidence from stable isotope values of sub fossil wood ellesmere island canada abstract tree ring analyses have contributed significantly to investigations of past climate stable isotope climate proxies 18o d and 13c values enhance traditional ring width data although poor preservation of ancient wood has tended to limit development of stable isotope proxy records to the holocene and the late pleistocene here we apply stable isotope techniques to wood that represent the remains of mixed coniferous boreal vegetation preserved in early pliocene 4 5 ma deposits at strathcona fiord ellesmere island canada ca 78 n four well preserved tree trunks identified through wood anatomical characteristics as larix larch from this high arctic site provide annually resolved sequences of up to 250 years from which we developed a high resolution record of pliocene climate stable oxygen isotope values in conjunction with ring width measurements were used to derive annually resolved temperature records for this site our ring width and isotope based reconstructions provide an annually resolved record up to 250 years of temperature and indicate growing season jj temperatures 15 8 5 0 c 11 8 5 1 c and mean annual temperatures mat 1 4 4 0 c 18 3 4 1 c warmer than present estimated isotope values of precipitation of 16 3 2 18o and 150 1 8 9 d were calculated from the isotopic values of wood cellulose relative humidity estimated from both 13c and d records ranged from 60 to 80 paleotemperature source water and humidity estimates are comparable to those of a modern boreal forest growing ca 15 20 south of modern ellesmere island

a persistent and dynamic east greenland ice sheet over the past 7 5 million years 10be and 26al isotopic evidence in quartz sand from the seafloor shows that a dynamic east greenland ice sheet has existed for the past 7 5 million years understanding the growth and stability of the greenland ice sheet is a long standing priority in palaeoclimate research and one that is at the heart of modern discussion of sea level rise paul bierman and colleagues present marine records of cosmogenic isotopes and conclude that an ice sheet in east greenland was continuously eroding sediments over the past 7 5 million years although the method could miss transient deglaciations and cannot firmly distinguish between remnant and larger ice sheets the results are consistent with model simulations of a waxing and waning but continuously present regional ice sheet climate models show that ice sheet melt will dominate sea level rise over the coming centuries but our understanding of ice sheet variations before the last interglacial 125 000 years ago remains fragmentary this is because terrestrial deposits of ancient glacial and interglacial periods1 2 3 are overrun and eroded by more recent glacial advances and are therefore usually rare isolated and poorly dated4 in contrast material shed almost continuously from continents is preserved as marine sediment that can be analysed to infer the time varying state of major ice sheets here we show that the east greenland ice sheet existed over the past 7 5 million years as indicated by beryllium and aluminium isotopes 10be and 26al in quartz sand removed by deep ongoing glacial erosion on land and deposited offshore in the marine sedimentary record5 6 during the early pleistocene epoch ice cover in east greenland was dynamic in contrast east greenland was mostly ice covered during the mid to late pleistocene the isotope record we present is consistent with distinct signatures of changes in ice sheet behaviour coincident with major climate transitions although our data are continuous they are from low deposition rate sites and sourced only from east greenland consequently the signal of extensive deglaciation during short intense interglacials could be missed or blurred and we cannot distinguish between a remnant ice sheet in the east greenland highlands and a diminished continent wide ice sheet a clearer constraint on the behaviour of the ice sheet during past and ultimately future interglacial warmth could be produced by 10be and 26al records from a coring site with a higher deposition rate nonetheless our analysis challenges the possibility of complete and extended deglaciation over the past several million years

compositional evolution of siliciclastic sediments recording the tectonic stability of a pericratonic rift mesozoic kutch basin western india abstract this study presents a combined petrographical and geochemical investigation to track the compositional changes in the mesozoic sedimentary record during the evolution of the pericratonic rift basin of kutch the mesozoic sequence of the proven petroliferous basin of kutch representing 3000 m thick siliciclastic and carbonate deposition within a time frame of 70 ma consists of jhurio jhumara jhuran and bhuj formations in ascending order of succession the dominance of arkosic sandstones and the abundance of zircon and monazite indicate predominantly felsic source rocks the concentration of individual trace elements such as th sc zr v ni and ratios like th sc cr v y ni th co la sc support the predominantly felsic source rock the lree enrichment and the negative eu anomaly corroborate the predominantly felsic source however concentrations of v ni and ti reveal the mafic input in older stratigraphic units while gdn ybn indicates dominant post archean source across the mesozoic succession younger stratigraphic units reveal contributions from the archean rocks from nagar parkar and aravalli highland regions the cia values suggest intermediate to intense weathering while the icv data record a shift from immature sediments in the older formations to mature and recycled types in the younger formations the high value of zr sc as well a high content of hf reflects the addition of zircon by recycling or by erosional unroofing of older continental rocks major oxide sio2 na2o and k2o and trace elements la th and hf bear the passive margin setting for the kutch basin during the mesozoic the decrease in feldspar content in sandstones increase in the concentration of zr and hf in shale and a decrease in values of icv from older to younger stratigraphic units corresponds to the compositional evolution related to increased stability of the kutch basin during the transition from early syn rift to post rift

geochemistry of the loessic sediments on delhi ridge eastern thar desert rajasthan implications for exogenic processes abstract quartzite ridges in the delhi region include in their local depressions thick piles of unconsolidated unstratified yellowish brown homogenous loamy sediments these delhi ridge sediments drs have textural mineralogical and geochemical characteristics similar to those of loess sediments geochemically drs just as other loess sediments are similar to average exposed upper continental crust of taylor and mclennan taylor s r mclennan s m 1985 the continental crust its composition and evolution blackwell london 311 pp the calculated chemical index of alteration nesbitt h w young g m 1984 prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations geochim cosmochim acta 54 1523 1534 nesbitt h w young g m 1989 formation and diagenesis of weathering profiles j geol 97 129 147 and other chemical parameters suggest a provenance of chemically less weathered rocks during the process of wind transport and deposition not only the dilution effect of silica on the ree abundance was counterbalanced but also the ree pattern was kept similar to the ucc and paas by the appropriate concentration and mixing of the ree bearing phases the immediate source to these sediments is likely to be mechanically ground sediments of glacial origin the last phase of the upliftment of the himalayas accompanied by pleistocene glaciation could have provided a vast glacio fluvial outwash plain the aeolian processes associated with prevailing w to sw winds in the hot arid condition seem to have been selectively transporting fertile silt materials leaving behind infertile desert sands

the use of mineral interfaces in sand sized rock fragments to infer ancient climate the kinds of mineral interfaces preserved in rock fragments of modern plutoniclastic sand are closely correlated with climate and topography in the source area stepwise linear regression analysis of the relationship among environmental and petrographic parameters for sand collected from 16 drainages of varying morphology developed on five granodiorite plutons demonstrates that sand composition varies systematically with temperature and precipitation and drainage steepness and area for small drainages in temperate climates the durability of each kind of mineral interface in sand sized rock fragments derived from the plutons depends on mechanical chemical and textural factors interfaces are mechanically stressed by differential expansion of minerals during unroofing interfaces between minerals of similar expansibility compressibility are more likely to remain uncracked and thus survive weathering the rate and extent of chemical dissolution of interfaces depends on the crystallography and chemistry of adjoining minerals interfaces between minerals of similar structure that have short atomicbond lengths are more likely to survive mineral inclusions are texturally isolated from rock disaggregating processes and thus more likely to survive interfaces of opaque with tectosilicate minerals are enriched relative to other interfaces by progressive disaggregation the rate and extent of which increase with increasing temperature interfaces of biotite with tectosilicates are depleted relative to other interfaces with increasing precipitation regression analysis yields statistically plausible testable models of the dependence of modem sand composition on modern climate such models can be used to quantitatively estimate ancient mean annual air temperature and precipitation based on ancient sand composition

influence of granitoid textural parameters on sediment composition implications for sediment generation the aim of this study is to determine and characterise the control exerted by parent rock texture on sand composition as a function of grain size the sands investigated were generated from granitoid parent rocks by the rhone damma and sidelen glaciers which drain the aar massif in the central alps switzerland and were deposited in glacial and fluvio glacial settings mechanical erosion comminution crystal breakdown and abrasion and hydraulic sorting are the most important processes controlling the generation of sediments in this environment whereas chemical and or biochemical weathering plays a negligible role by using a gis based microscopic information system mis five samples from the glacier drained portions of the aar basement have been analysed to determine textural parameters such as modal composition crystal size distribution and mineral interfaces types and lengths petrographic data of analysed sands include traditional point counts gazzi dickinson method minimum of 300 points as well as textural counts to determine interface types frequency and polycrystallinity in phaneritic rock fragments according to pettijohn s classification grain size dependent compositions vary from feldspathic litharenite 0 fraction via lithic arkose 1 and 2 to arkose 3 and 4 compositional differences among our data set were compared to modern plutoniclastic sands from the iberian massif spain and the st gabriel mts california usa which allowed us to assess the role exerted by glaciers in generating sediments by combining data from the mis with those from petrographic analysis we outlined the evolution of mineral interfaces from the parent rocks to the sediments

age petrogenesis and significance of 1 ga granitoids and related rocks from the sendra area aravalli craton nw india abstract we present new geochronological petrological geochemical and isotopic data for granitic and related rocks from the aravalli craton rajasthan northwestern india in the sendra area five variably deformed granitoid plutons ranging in composition from tonalite to granite cut across carbonate rich metasedimentary rocks of the delhi supergroup the largest of these bodies the chang pluton 15 km2 is dominated by monzogranitic gneisses and aplitic dykes composed of subequal proportions of quartz plagioclase an7 20 and microcline or92 98 with lesser biotite fe 0 8 0 9 and accessory muscovite fe 0 7 0 8 u pb zircon data tims method for a biotite granite gneiss yield a weighted mean 207pb 206pb age of 967 8 1 2 ma which we interpret as representing the time of magmatic crystallization rb sr whole rock isotopic data for the chang pluton including new analyses as well as previously published ones yield a regression of 906 67 ma mswd 82 which is barely within error of the u pb age there is evidence for open system behaviour in the rb sr system particularly for whole rock samples with low sr concentrations and consequently high rb sr sm nd isotopic data fail to yield meaningful age information initial isotopic ratios at 968 ma for chang pluton granitoids isr 0 7110 14 end 3 28 0 47 are compatible with source materials similar to archaean amphibolitic rocks of the banded gneiss complex spatially associated with the chang pluton is a massive metagabbro composed of plagioclase an45 68 and magnesio hornblende fe 0 3 0 4 with secondary cl rich scapolite and ferrian zoisite the scapolite and zoisite likely crystallized from metamorphic fluids that interacted with nearby calc silicate schists and gneisses of the delhi supergroup aside from slight enrichments in rb u th and ba this metagabbro retains a primitive chemical signature similar to n morb lree depletion low k and initial isotopic ratios isr 0 7058 end 2 9 that approach model depleted mantle at 968 ma the metagabbro is chemically and isotopically similar to mafic metavolcanic and related rocks that have been considered to represent ocean floor and island arc basaltic magmas all available data are compatible with the idea that these rocks represent the products of convergent margin processes during the early neoproterozoic a conclusion that could have important implications for the construction of the rodinia supercontinent

bounded influence magnetotelluric response function estimation author posting blackwell 2004 this article is posted here by permission of blackwell for personal use not for redistribution the definitive version was published in geophysical journal international 157 2004 988 1006 doi 10 1111 j 1365 246x 2004 02203 x

the effects of source lithology transport deposition and sampling scale on the composition of southern california sand the transverse ranges of southern california represent an uplifted and variably dissected mesozoic magmatic arc and mesozoic to holocene sedimentary and volcanic strata deposited in convergent and transform tectonic settings modern sand within part of the western transverse ranges represents first order sampling scale of the santa monica and the san gabriel mountains second order sampling scale of the santa clara river draining both mountain ranges and third order sampling scale of the beach system between the mouth of the santa clara river and the eastern santa monica mountains and turbidite sand of the hueneme mugu submarine fan source lithology includes plutonic and metamorphic rocks of the san gabriel mountains and sedimentary and volcanic rocks of the santa monica mountains first order sands have large compositional variability sand from local coastal drainage of the santa monica mountains ranges from basaltic feldspatholithic to quartzofeldspathic sand of the san gabriel mountains local drainages has three distinct petrofacies ranging from metamorphiclastic feldspatholithic to mixed metamorphi plutoniclastic and plutoniclastic quartzofeldspathic second order sand is represented by the main channel of the santa clara river the sand has an abrupt downstream compositional change from feldspathic to quartzofeldspathic third order sand beaches and deep sea turbidite samples of the santa monica basin is quartzofeldspathic beach sand is more quartz rich than is santa clara river sand whereas turbidite sand is more feldspar rich than is beach sand deep sea sand has intermediate composition with respect to second order samples of the santa clara river and third order samples of the beach system suggesting that 1 the santa clara river is the main source of sediments to the marine environment and 2 local entry points from canyons located near local drainages may generate turbidity currents during exceptional flood conditions petrologic data of modern sand of the study area are highly variable at first and second order scale whereas third order sand is homogenized the homogenized composition of deep marine sand is similar to the composition of most ancient sandstone derived primarily from the mesozoic dissected magmatic arc of southern california this study of the western transverse ranges illustrates the effects of source lithology transport depositional environment and sampling scale on sand composition of a complex system which provides insights regarding actualistic petrofacies models

sequence stratigraphy biotic change 87sr 86sr record paleoclimatic history and sedimentation rate change across a regional late cenozoic unconformity in arctic canada eustasy tectonics and climate contributed to a remarkable miocene pliocene regional unconformity in the beaufort mackenzie area of arctic canada the unconformity extends from beneath deep basin turbidites on the continental rise upslope across an erosional paleocontinental shelf onto the cratonic margin as a regional paleosurface peneplain in the mackenzie delta area and into pediment surfaces cut into the orogenic highlands of the richardson mountains the unconformity was initiated by shelf exposure during latest messinian or earliest pliocene eustatic lowstand and was accentuated by tectonic uplift from the culmination of a major late miocene compressional pulse on the basin margin palynomorph benthic foraminiferal strontium isotopic paleomagnetic and radiometric data document the climatic and chronological events surrounding the unconformity a widespread hardground k 59 limestone occurs at the unconformity and caps the late miocene akpak sequence the hardground yields the benthic fora

sand composition in an iberian passive margin fluvial course the tajo river the tajo river the 10th largest river in europe drains part of the western passive margin of europe that includes multiple tectonic elements of the iberian plate modern fluvial sand composition in the tajo river drainage basin reflects the nature of the source region which lies in the central part of the iberian peninsula four fluvial petrographic provinces a b c and d can be established in the tajo drainage basin corresponding well with the four principal structural units drained 1 the iberian range 2 the hesperian massif 3 the tertiary tajo basin and 4 the neogene santarem lisboa basin province a corresponds to the tajo river head and is characterized by quartzolithic sedimenticlastic sands qm67f4lt29 and rs79rg3rm18 these sands have been derived from diverse mesozoic siliciclastics and carbonates of the iberian range province b appears in the upper reaches of the tajo river course and is quartzofeldspathic qm57f34lt9 with diverse rock fragments rs34rg23rm43 sources are hercynian granitoids and metasediments and neogene clastics and minor carbonates of the tertiary tajo basin province c extends along the middle course of the tajo river with quartzofeldspathic metamorphiclastic sand modes qm60f33lt7 rs4rg21rm75 the sources are metamorphic rocks intruded by plutonites of the hesperian massif province d is quartzofeldspathic qm55f39lt6 with a dominance of phaneritic rock fragments rs5rg33rm62 and corresponds to the lower reaches of the tajo river where siliciclastic deposits of the neogene santarem lisboa basin are the main sources sands plot on provenance discrimination diagram qmflt within the recycled orogen field tajo river head and continentalblock fields upper middle and lower course in addition we have proven the usefulness of the rsrgrm diagram to discriminate the defined fluvial provinces originating from heterogeneous parent rock textures and mineralogy climate does not exert any strong influence on the petrogenesis of the tajo river drainage basin sand and erosion in the source areas may be described in terms of weathering limited denudation regime by contrast mixing with tributary supplies is the main process that modifies composition in the tajo river sand the establishment of fluvial provinces related to the main bedrock structural units reflects the great relevance of tributaries from each province in the generation of the tajo river sand and the low significance of inherited sandy load from previous provinces the abundance of granitoid rock fragments rsrgrm rg in fluvial sand of both tributaries and main channel of the tajo river drainage basin faithfully represents the relative abundance of granodiorite monzogranite bedrock exposure in each subbasin metasedimentary and metamorphic bedrock outcrop area is overrepresented by metamorphic rock fragments rsrgrm rm in both sand from tributaries and from the tajo main trunk river this is manifested by differences of 18 23 between means of metasedimentary outcrop area and the rsrgrm rm mean in the sand from provinces b and c d respectively sedimentary mainly carbonate outcrop area is underrepresented or not represented by sedimentary rock fragments rsrgrm rs in sand of the tajo river this underrepresentation causes a difference between means of sedimentary outcrop area and the rsrgrm rs mean of 21 17 1 and 10 7 in sands from province a b and c d respectively this fact confirms the rapid loss of these grains during transport because of their labile nature

alkenone and boron based pliocene pco2 records abstract the pliocene period is the most recent time when the earth was globally significantly 3 c warmer than today however the existing pco2 data for the pliocene are sparse and there is little agreement between the various techniques used to reconstruct palaeo pco2 this disagreement coupled with the general low temporal resolution of the published records does not allow a robust assessment of the role of declining pco2 in the intensification of the northern hemisphere glaciation inhg and a direct comparison to other proxy records are lacking for the first time we use a combination of foraminiferal 11b and organic biomarker alkenone derived carbon isotopes proxies to determine the concentration of atmospheric co2 over the past 5 ma both proxy records show that during the warm pliocene pco2 was between 330 and 400 ppm i e similar to today the decrease to values similar to pre industrial times 275 285 ppm occurred between 3 2 ma and 2 8 ma coincident with the inhg and affirming the link between global climate the cryosphere and pco2

clay mineral variations in holocene terrestrial sediments from the indus basin abstract we employed x ray diffraction methods to quantify clay mineral assemblages in the indus delta and flood plains since 14 ka spanning a period of strong climatic change assemblages are dominated by smectite and illite with minor chlorite and kaolinite delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7 5 ka indicating stronger chemical weathering as the summer monsoon intensified changes in clay mineralogy postdate changes in climate by 5 3 ka reflecting the time needed for new clay minerals to form and be transported to the delta samples from the flood plains in punjab show evidence for increased chemical weathering towards the top of the sections 6

a contourite drift system on the baffin bay west greenland margin linking pliocene arctic warming to poleward ocean circulation terrestrial records from the canadian arctic archipelago indicate that a temperate and moist climate prevailed during the pliocene i e before the intensification of northern hemisphere glaciations but the controlling factors causing these conditions remains elusive here we present marine seismic reflection evidence of contiguous kilometer scale sedimentary drifts or contourites buried below the west greenland shelf which relates high latitude pliocene warmth to intense geostrophic currents along the eastern baffin bay margin seismic to borehole correlation indicates that enhanced current induced deposition began during the middle miocene ca 17 15 ma and terminated during the late pliocene onset of global cooling the transition from along slope sediment transport to trough mouth fan progradation designates the onset of greenland ice sheet glaciers advancing across the continental shelf and coincides with increasing iceberg productivity in baffin bay and the nordic seas from 3 3 to 2 7 ma our results suggest that the baffin bay west greenland margin formed a late neogene passageway for persistent ocean boundary currents and we infer that the pliocene high latitude warmth was to a significant extent caused or enhanced by advection of subtropical heat and moisture to the arctic regions attenuation of the poleward heat flux conveyed by the paleo current system may have been critical for allowing glacial buildup in the canadian arctic and northern greenland during the late pliocene we further surmise that vertical tectonic adjustments of the continental margin played a role in this attenuation which eventually caused the demise of meridional ocean circulation through baffin bay

quantitative provenance analysis of sediments review and outlook provenance analysis of sediments is aimed at reconstructing the parent rock assemblages of sediments and the climaticphysiographic conditions under which sediments formed inferring sediment provenance from the final product a basin fill is anything but straightforward because the detrital spectrum evolves as the sediment is transported along the pathway from source to basin successful provenance analysis requires that the nature and extent of compositional and textural modifications to the detrital spectrum be recognised if not quantified the history of quantification in sediment provenance studies is summarised and illustrated by tracking two fundamental ideas the concept of the sediment petrological province or petrofacies and the relation between sandstone composition and plate tectonic environment progress in sedimentary provenance analysis has been closely linked with advancements in measurement technology a brief survey of modern data acquisition tools illustrates the possibilities and limitations of modern provenance research an operational definition of quantitative provenance analysis qpa is presented in which the central role of mass balance is acknowledged extension of this definition to include quantitative predictions obtained by forward modelling computer simulation of sediment production as well as methodological improvements in data acquisition and processing is needed to cover likely future developments in qpa the contributions to the special issue quantitative provenance analysis of sediments illustrate the intrinsic multidisciplinarity and rapid expansion of qpa d 2004 elsevier b v all rights reserved

greenland ice sheet retreat history in the northeast baffin bay based on high resolution bathymetry new swath bathymetric data acquired in 2010 and 2015 indicate a variety of glacial landforms in cross shelf troughs of the melville bay northeast baffin bay these landforms reveal that at their maximum extent ice streams in the troughs crossed the shelf all the way to the shelf edge moraines grounding zone wedges gzws and subglacial till lobes on the continental shelf define a pattern of variable ice stream retreat in the individual troughs on the outer shelf in the northern cross shelf trough ice stream retreat was slow compared to more episodic retreat in the central at least one stabilization on the outer shelf and southern cross shelf trough re advances at the shelf edge and fast retreat thereafter large gzws on the mid to inner shelf of the troughs indicate periods of grounding zone stabilization according to glacial landforms the final retreat across the inner shelf before 8 41 ka bp was episodic to slow furthermore evidence has been found for localized ice domes with minor ice streams on inter trough banks the glacial landforms in melville bay thus indicate the varying and discontinuous ice sheet retreat history across the northwest greenland continental shelf

the effects of source rocks and chemical weathering on the petrogenesis of siliciclastic sand from the neto river calabria italy implications for provenance studies plutonic and gneissic rocks of the sila massif in the uppermost portion of the neto drainage basin calabria southern italy weather and erode under a humid mediterranean climate during the development of weathering profiles a combination of chemical weathering and granular disintegration processes occurred chemical weathering involves a loss of both plagioclase mainly during grus generation and k feldspar mainly during soil formation this loss is attributed to transformation of plagioclase to clay minerals and to leaching and dissolution of k feldspar sand composition is quartzofeldspathic and nearly homogeneous along the main channel of the neto river even where the river cuts across a blanket of sedimentary cover thus fluvial transport does not alter sand composition within the neto drainage basin petrographic indices are effective in 1 discriminating between contributions from similar granite and gneiss source rocks qm f 2 relating the provenance of plutoniclastic and gneissiclastic sand found in the headwaters to grus horizons qm f q rg and 3 distinguishing between upstream first cycle and downstream multicycle sand q rg this last distinction is further emphasized by considering both aphanitic and phaneritic varieties of rock fragments rgrmrs diagram chemical weathering is the main sand producer within the regolithic environment in northern calabria in addition rapid erosion resulting from steep slopes removes weathered products and rapid and short transport leads to minimal sediment maturation in general the f q index is climate and relief dependent thus it should be used in conjunction with palaeoclimatic and palaeophysiographic evidence for provenance interpretations of ancient quartzofeldspathic sandstones

seismic architecture and evolution of the disko bay trough mouth fan central west greenland margin abstract the present study is the first to document the large scale glacigenic evolution of a west greenland trough mouth fan tmf system i e the disko bay tmf from onset of shelf based glaciation to present we have constrained the paleo ice sheet configuration in the disko bay region and determine the controlling factors of ice stream development using 2d and 3d seismic reflection data seabed bathymetry and stratigraphic information from two exploration wells this has revealed three stages of the disko bay tmf development the early stage probably of pliocene early pleistocene age marks the onset of a central depocentre located below the modern mid shelf and constructed by sediment progradation delivered through at least two erosive pathways related to fast flowing grounded ice at that time ice stream routing in the disko bay shelf region was strongly controlled by the pre glacial topography and structural boundaries associated with fracture zones and deep seated faults during the middle evolutionary stage the focus of deposition shifted from the mid shelf to two elongate areas fringing the outer margin the marginal depocentres were not only related to glacial processes but also alongslope deposition by contour currents which may have developed as a consequence of basin subsidence surrounding the davis strait high and the kangerluk structure the late stage of tmf development presumably representing the late pleistocene to holocene is characterized by the marginal depocentres becoming less significant and sediment aggradation occurring over wide parts of the mid outer shelf while features of subglacial erosion are generally absent in contrast to the inferred fast flowing ice streams of the early middle evolutionary stages this points to the existence of a rather thin and lightly grounded ice sheet i e at the threshold of floatation the lightly grounded ice sheet scenario applying to the late pleistocene interval of the disko bay tmf was possibly associated with floating ice shelves during periods of maximum cooling while intermittent and short lived advances of grounded ice streams may have occurred during interstadial stadial climate transitions a controlling factor for the development of the aggradational stage may relate to the prominent basement ridge that separates the disko trough from the egedesminde dyb depression we suggest that a neotectonic emergence of the ridge gradually restricted the flow of ice through the central disko trough forcing glaciers to diverge along the entire length of the ridge and find complementary drainage routes

effects of chemical weathering and sorting on the petrogenesis of siliciclastic sediments with implications for provenance studies the bulk chemical compositions mineralogy and mineral proportions of sands and muds of the mallacoota basin in southeastern australia reflect the composition of weathering profiles mantling source rocks rather than bedrock muds contain abundant clay minerals that are virtually absent from the source rocks but abundant in the weathering profiles sands are strongly enriched in quartz relative to source rocks even in the headwaters of the fluvial system demonstrating that feldspar destruction occurs by in situ chemical weathering within profiles and before detritus enters the fluvial system k feldspar is proportionally more abundant in fluvial sands than in source rocks because plagioclase is more rapidly destroyed than either quartz or k feldspar in weathering profiles subsequent erosion and sorting produce sands enriched in quartz with high k feldspar plagioclase ratios relative to source rocks the composition of plagioclase incorporated into the fluvial sands is also controlled by chemical weat

submarine geomorphology of northeast baffin bay and its implications for local paleo ice sheet dynamics abstract high resolution bathymetric data from close to the northwest greenland coast in northern melville bay northeast baffin bay reveal a range of glacial and nonglacial landforms the glacial landforms include crag and tails mega scale glacial lineations msgl rock drumlins and roche moutonnees that indicate paleo ice sheet dynamics the nonglacial landforms include steep ridges that are interpreted as volcanic dykes neoproterozoic thule dyke swarms and paleoproterozoic melville bugt dyke swarms these dykes are glacially overprinted and may have channeled ice and subglacial meltwater flow through narrow subglacial cavities some of the glacial landforms eroded into bedrock indicate a southward paleo ice stream orientation while other glacial landforms including the sedimentary depositional landforms indicate a westward paleo ice stream orientation the glacial landforms were likely produced during at least two epochs and under changing thickness of the ice streams the glacial landforms eroded into the bedrock are likely older than the sedimentary glacial landforms and were likely produced by a thin south southeastward ice stream that allowed cavity formation the westward oriented glacial landforms were likely produced by a thick ice stream that was probably active during the last glacial maximum lgm the different orientations of the glacial landforms indicate a reorganization of the ice streams that may have occurred during retreat and subsequent readvance this reorganization likely coincided with a migration of the ice divide from south to north

pliocene pleistocene ice rafting history and cyclicity in the nordic seas during the last 3 5 myr a continuous 3 5 myr ird record was produced from ocean drilling program odp site 907 a timescale based on magnetic polarity chrons oxygen isotope stratigraphy for the last 1myr and orbital tuning was developed the record documents a stepwise inception of large scale glacial cycles in the nordic seas region the first being a marked expansion of the greenland ice sheet at 3 3 ma a second step occurred at 2 74 ma by an expansion of large scale ice sheets in the northern hemisphere ice sheet variability around the nordic seas was tightly coupled to global ice volume over the past 3 3 myr between 3 and 1 ma most of the variance of the ird signal is in the 41 kyr band whereas the last 1 myr is characterized by stronger 100 kyr variance the gamma ray porosity evaluator grape density record is closely linked with ird variations and documents sub orbital variability resembling the late quaternary heinrich bond cycles

modelling pliocene warmth contribution of atmosphere oceans and cryosphere the relative role of the atmosphere oceans and cryosphere in contributing towards middle pliocene warmth ca 3 ma bp is investigated using the hadcm3 coupled ocean atmosphere general circulation model the model was initialised with boundary conditions from the usgs prism2 data set and a pliocene atmospheric co2 level of 400 ppmv and run for 300 simulated years the simulation resulted in a global surface temperature warming of 3degreesc compared to present day in contrast to earlier modelling experiments for the pliocene surface temperatures warmed in most areas including the tropics 1 5degreesc compared with present day the model predicts a general pattern of ocean warming 1 5degreesc in both hemispheres to a depth of 2000 m below which no significant differences are noted sea ice coverage is massively reduced up to 90 the flow of the gulf stream north atlantic drift is up to 100 mm s 1 greater in the pliocene case analysis of the model predicted meridional streamfunction suggests a global pattern of reduced outflow of antarctic bottom water aabw up to 5 sv a shallower depth for north atlantic deep water formation and weaker thermohaline circulation 3 sv the decrease in aabw occurs mainly in the pacific rather than atlantic ocean model diagnostics for heat transports indicate that neither the oceans nor the atmosphere are transporting significantly more heat in the pliocene scenario rather these results indicate that the major contributing mechanism to global pliocene warmth was the reduced extent of high latitude terrestrial ice sheets 50 reduction on greenland 33 reduction on antarctica and sea ice cover resulting in a strong ice albedo feedback these results highlight the need for further studies designed to improve our knowledge regarding pliocene terrestrial ice configurations

is chemical index of alteration cia a reliable proxy for chemical weathering in global drainage basins the chemical weathering of silicate rocks in continents as an important sink of atmospheric co2 is of great significance for global environmental change rivers play a key role in earth surface processes and are regarded as the most important carrier of terrigenous materials into the sea the chemical index of alteration cia has been widely used as a proxy for chemical weathering in sediment source area in this paper the cia values of suspended particulate matters from 44 rivers worldwide are recalculated the cia values vary significantly with the highest average value occurring in african rivers and the lowest in north american rivers the correlation analyses suggest that on a global scale the cia is sensitive to land surface temperature latitude at river mouth and soil depth in the drainage basins but poorly correlated with drainage area precipitation average elevation and runoff however the cia of the rivers draining east china are closely related to temperature precipita tion latitude and runoff primarily reflecting the dominant control of monsoon climate on chemical weathering in the catchments it is therefore unrealistic to find a simple law of regulating chemical weathering in continents the cia actually reflects the integrated weathering history in the drainage basins and therefore caution should be taken while using it as a direct and quantitative proxy for evaluating the intensity of instantaneous chemical weathering in continents

prediction of some weathering trends of plutonic and volcanic rocks based on thermodynamic and kinetic considerations abstract the exposed crust consists mainly of plagioclase 35 quartz 20 k feldspar 11 volcanic glass 12 biotite 8 and muscovite 5 quartz is a resistate thus feldspars and glass represent approximately 75 percent of the labile minerals the weathering characteristics of these constituents are summarized in the context of thermodynamic mass balance and kinetic considerations experimentally determined release rate constants were used to predict the proportions of ca na and k released by feldspars of plutonic rocks granites to gabbros to weathering solutions the chemical weathering trends of the weathered residues calculated from the kinetic data conform closely to the initial trends observed in some recent weathering profiles demonstrating the accuracy of the predictions since the weathering of feldspars is controlled by processes that should not change through geological time the relative release rates of ca na and k from the feldspars of granitic rocks can be calculated for future and past episodes of continental weathering experimentally determined release rate constants are not available for a wide range of volcanic glass compositions but the limited data indicate that compositional trends are predictable in weathering profiles developed on volcanic rocks the kinetic data available for rhyolitic glasses accurately predict the initial weathering trends observed in a recent rhyolite weathering profile

variations in the electrical conductivity of the upper mantle beneath north america and the pacific ocean variations in the electrical conductivity of the mantle beneath carty lake in the canadian shield tucson in the southwest united states and honolulu and midway in the north central pacific were determined through the inversion of long period magnetotelluric and geomagnetic depth sounding data inversion of computed response functions is carried out using a minimum structure regularized approach the upper mantle beneath carty lake is approximately an order of magnitude more resistive than the upper mantle beneath tucson and nearly 1 5 orders of magnitude more resistive than honolulu and midway island inversions were also carried out where the minimum structure constraint was removed at known upper mantle discontinuities these models show a jump in conductivity of 1 5 orders of magnitude across the 660 km discontinuity a result that is consistent with laboratory experiments on realistic mantle assemblages mantle conductivity profiles at carty lake are significantly more resistive than those at tucson honolulu and midway to depths of 300 400 km these observations likely reflect differing thermal states the presence or absence of partial melt and volatiles and may also be related to chemical differences between depleted and undepleted upper mantle the observed conductivity variations may be interpreted as lateral variations in temperature partial melt and or dissolved hydrogen in olivine

geoelectric power spectra over oceanic distances we present initial results of simultaneous measurements of the geoelectric potential as measured across two long cable routes in the pacific guam to philippines and california to hawaii separated by 6h in local time and 30 o in latitude over the fre quency range 10 5 to 1 67 x 10 3 hz the power levels tend to be enhanced near local noon along the two routes especially during geomagnetic quiet intervals during the seven days analyzed geoelectric power levels up to 104 mv km 2 km were measured on a geomagnetically disturbed day the power levels at the longest periods 17m to 150m are gen erally found to be largest along the route at lower geomagnetic latitudes guam to philippines when comparisons are made at equivalent local times in con trast the power levels for periods in the hydromagnetic wave region periods 5m tend to be larger at all local times for the higher geomagnetic latitude route the nightside geoelectric power levels along the higher lati tude route tend to increase with increasing geomagnetic activity

earth science a wet mantle conductor arising from x huang y xu s karato nature 434 746 749 2005 huang et al reply the suggestion that the transition zone of earth s mantle 410 670 km in depth is enriched in water is of great possible significance to the geodynamics and geochemistry of earth s interior as well as for the role of the mantle in the global water cycle1 huang et al 2 compare the effect of water on electrical conductivities of transition zone phases to electromagnetic and magnetotelluric soundings of the mantle beneath the north pacific3 and conclude that the transition zone contains between 1 000 and 2 000 p p m of water which is considerably more than the 50 200 p p m present in the upper mantle4 5 6 this conclusion is predicated on the assumption that the transition zone is relatively oxidized but in fact fairly reduced conditions are more likely7 8 here i show that if the transition zone is reduced high conductivities can be explained without the requirement for large enrichments of water

geochemistry of the floodplain sediments of the kaveri river southern india abstract the floodplain sediments of the kaveri river southern india derived from archean gneissic and charnockitic source regions show interbedding of silty 4 4 7 and sandy units 1 4 3 7 the geochemistry of silty beds is remarkably uniform at a given location and over a lateral distance of nearly 250 km the sandy beds have more variable chemical compositions yet are comparable to those of silty beds except for the diluting effect of quartz silty sediments retain the geochemical signature of prominently exposed source rocks for almost all elements and provide evidence of tectonic instability in the source region the floodplain sediments contain all size grades sand silt and clay which may have resulted in minimizing the biases imposed on suspended and bedload sediments due to sorting the low chemical index of alteration cia the dominance of unweathered primary minerals and the minor proportion of smectitic clay all suggest that the region has been subjected to little chemical weathering this is possible if the region has undergone recent uplift exposing fresh archean rock to surface denudation the formation of fertile farmland along the kaveri river course and its delta is related to these recent geological processes

sand composition and sedimentary evolution of a late quaternary depositional sequence northwestern adriatic coast italy abstract in order to detect temporal and spatial variations in detrital supply in the upper part of the last depositional sequence of late pleistocene holocene age we conducted a combined petrographic and stratigraphic study in the romagna coastal plain south of the po delta northern italy we analyzed heavy minerals and the bulk composition of sands from cores and surface samples by using petrographic and stratigraphic data on composition of modern beach and major river deposits new aspects of detrital dispersal mechanisms and the depositional history of the study area are documented the heavy mineral distribution coupled with the dolostone and volcanic rock fragment contents of bulk sands allow identification of three different petrofacies petrofacies a petrofacies b and petrofacies c which have been interpreted as of apenninic mixed eastern alps po river basin and po river catchment basin provenance respectively distribution of the three petrofacies changed through time in response to landward and seaward shifting of the coastline during the late pleistocene lowstand a pure apenninic provenance characterized the romagna coastal plain petrofacies a during the holocene transgression when the shoreline migrated tens of kilometers west of its present position eastern alpine sediment sources fed littoral facies petrofacies b probably as a result of southward transport by littoral drift this sediment supply continued during the early regressive phases and was cut off by a change in coastal morphology related to the development of the early po delta this led to the establishment of a sediment supply entirely related to the po river catchment basin petrofacies c changes in the compositional signature of sand in the youngest beach ridges mark the abandonment of the early po delta due to an avulsion event and testify to the establishment of a coastal system fed by rivers draining the apennines petrofacies a we emphasize sand petrography as an important tool in studying the internal architecture of sandy clastic depositional units on detailed spatial scales and its use in deciphering the depositional history of complex sedimentary successions fig 1 location of the study area end page 829

divalent cation diffusion in mg2sio4 spinel ringwoodite β phase wadsleyite and olivine implications for the electrical conductivity of the mantle mg fe and mg ni interdiffusion coefficients have been measured in single crystal olivine alpha mg ni fe sub 2 sio sub 4 polycrystalline beta phase beta mg ni fe sub 2 sio sub 4 and silicate spinel gamma mg ni fe sub 2 sio sub 4 at 1473 k between 1 and 14 gpa under controlled thermodynamic conditions in olivine d sub mg ni sup alpha ranges from 10 sup 17 m sup 2 s sup 1 at 1 gpa to 4x10 sup 18 m sup 2 s sup 1 at 9 gpa and d sub mg fe sup alpha ranges from 3x10 sup 15 m sup 2 s sup 1 at 1 gpa to 10 sup 15 m sup 2 s sup 1 at 4 gpa at 9 gpa the cation diffusion rates in gamma spinel are approx 3 orders of magnitude higher than those in olivine between 9 and 14 gpa d sub mg ni sup gamma decreases from 8x10 sup 15 to 9x10 sup 16 m sup 2 s sup 1 and d sub mg fe sup gamma decreases from 2x10 sup 13 to 5x10 sup 14 m sup 2 s sup 1 between 10 and 14 gpa the diffusion coefficients for both fe and ni are similar in magnitude and pressure dependence between beta phase and gamma spinel the activation volumes for mg ni diffusion are 3 2 and 6 7 cm3 mol 1 in the alpha and gamma beta phases respectively and for mg fe diffusion are 5 4more and 6 1 cm3 mol 1 in the alpha and gamma beta phases respectively our results demonstrate that extreme differences in transport properties are expected to occur across the 400 km discontinuity a model for electrical conductivity in the upper mantle involving two mechanisms for electrical conduction with one mechanism being associated with a hydrogen or defect related conduction process and the other involving a straightforward application of the nernst einstein equation to our cationic diffusion data reproduces geomagnetic sounding results for the upper mantle and shallow transition zone this modeling yields an order of magnitude increase in electrical conductivity across the 400 km discontinuity with little or no change in conductivity occurring near 520 km depth our modeling suggests that divalent cation diffusion is the dominant mechanism of charge transport between 400 and 670 km depth and that the high pressure olivine polymorphs dominate the electrical behavior of the deep upper mantle comparison between field based deep mantle conductivity profiles derived from magnetotelluric studies and extrapolation of our model suggests that a discontinuity in electrical transport properties exists at the base of the transition zone as well similarly given the dramatic differences in chemical diffusion between different polymorphs of olivine it is possible that other transport property mediated processes such as viscous flow could dramatically change across the 400 and 670 km discontinuities such changes are less likely to occur at 520 km depth c 2000 american geophysical union less

tectonic history of a jurassic backarc basin sequence the gran canon formation cedros island mexico based on compositional modes of tuffaceous deposits the jurassic gran canon formation cedros island baja california mexico constitutes an unusually well preserved and exposed example of ancient backarc basin fill petrofacies analysis conducted on tuff aceous sandstone and tuff samples from this formation complement and reinforce prior lithofacies interpretations but with some modification when temporal and spatial trends in petrographic data detrital modes are analyzed and compared to mod els based on data collected from deep sea drilling project and ocean drilling pro gram cores the trends indicate a second heretofore unrecognized phase of backarc rifting basalt lavas interstratified with da citic pyroclastic rocks of the primary vol canic lithofacies previously interpreted to record the eruption of differentiated mag mas at the climax of growth of the gran canon island arc are now as a result of this study considered to be the product of arc extension and rifting our method of modal analysis uniquely combines the quantification of textural at tributes of pyroclastic and epiclastic debris that reflect eruption style and magma com position as well as the effects of reworking and mixing in marine settings this study demonstrates that detailed petrographic analysis is useful in the interpretation of ancient volcaniclastic deposits suspected of having formed in backarc basin settings

geochemistry of sandstones from the upper miocene kudankulam formation southern india implications for provenance weathering and tectonic setting abstract petrographic major trace and rare earth element compositions of sandstones from the upper miocene kudankulam formation southern india have been investigated to determine their provenance tectonic setting and weathering conditions all sandstone samples are highly enriched in quartz q but poor in feldspar f and lithic fragments l the major element concentrations of these sandstones reveal the relative homogeneity of their source geochemically the kudankulam sandstones are classified as arkose subarkose litharenite and sublitharenite the cia values chemical index of alteration mean value 44 5 for these sandstones and the a cn k diagram suggest their low weathering nature similarly their fe2o3 mgo mean 2 7 al2o3 sio2 0 09 k2o na2o 2 2 ratios and tio2 contents 0 3 are consistent with a passive margin setting the eu eu 0 5 la lu cn 21 la sc 5 9 th sc 1 9 la co 5 7 th co 1 8 and cr th 5 3 ratios support a felsic source for these sandstones chondrite normalized ree patterns with lree enrichment flat hree and negative eu anomaly also are attributed to felsic source rock characteristics for kudankulam sandstones total ree concentrations of these sandstones reflect the variations in their grain size fractions the source rocks are probably identified to be proterozoic gneisses charnockites and granites of the kerala khondalite belt which must have been exposed at least since the late miocene finally the unusual ni enrichment in the kudankulam sandstones unaccompanied by a similar enrichment in cr co and v may be related to either the presence of pyrite in the sandstones or more likely the fractionation of garnet from the source rocks during transportation

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

a semi global reference model for electrical conductivity in the mid mantle beneath the north pacific region 1 one dimensional electrical conductivity structure in the mid mantle of the one fourth of the earth beneath the north pacific ocean was obtained by a semi global electromagnetic induction study electromagnetic response functions estimated from electric field variations measured by submarine cables and geomagnetic field variations obtained by magnetic observatories and long term observations sites were inverted into radially symmetric conductivity distribution by taking the distribution of land and ocean at the surface into account as a most preferred model a smooth conductivity depth profile was obtained with two abrupt increases that possibly correspond to the seismic discontinuities at 410 and 660 km

the character and genesis of calcrete in late quaternary alluvial deposits gujarat western india and its bearing on the interpretation of ancient climates late quaternary deposits in mainland gujarat contain sediments deposited in subhumid and semi arid climates the 30 35 m succession shows the presence of vertisols at the base and a red bed horizon ferric calcisol when pedogenic in origin that roughly bisects the succession a widespread development of calcretes is observed throughout the succession the various varieties of calcrete include pedogenic calcrete groundwater calcrete calcrete conglomerate transported calcrete and rhizogenic calcrete pedogenic calcrete nodules associated with vertisols and the red soil show marked differences in morphology dimensions and the distribution of microscopic features these differences arise due to contrasting climate controlled physicochemical environs under which they formed pedogenic calcrete nodules associated with vertisols acquire large 5 10 cm dimensions and are characterised by either showing the presence of a nucleus of soil matter or showing a dense micritic groundmass cut by thick sparitic veins in contrast calcrete nodules that formed in the red soil are 3 cm in size and do not exhibit dense networks of sparitic veins calcretes associated with vertisols and the ferric calcisol also exhibit differences in the morphology of rhizoliths these differences also show up in the distribution of microfabrics of calcretes grain coats are present in rhizogenic and pedogenic calcretes but absent in groundwater calcretes and less profuse in hydromorphic soil calcretes clotted micrite is present in all types except groundwater calcretes sparitic veins however are observed in each type but are relatively less developed in groundwater calcretes a similar distribution of displacive and replacive textures is also seen although some grains in groundwater calcretes showed signs of corrosion the vertisol associated calcretes represent a subhumid 500 700 mm climate whereas the red soil calcretes suggest a semi arid 100 500 mm climate calcretes from the vertisol association show a range in 13c composition constrained between 9 and 5 whereas the red soil calcretes exhibit the whole spectrum of values from 9 to 1 based on mineralogical associations calcretes usually taken to reflect semi arid episodes in the earth s history may be classified further calcretes when associated with sepiolite palygorskite suggest an arid climate mean annual rainfall 50 100 mm when associated with smectite haematite and the absence of hydromorphism a semi arid climate mean annual rainfall 100 500 mm and when found in smectitic vertisols subhumid climates mean annual rainfall 500 700 mm

petrography and chemistry of sandstones from the swiss molasse basin an archive of the oligocene to miocene evolution of the central alps oligocene to miocene fluvial sandstones from the swiss molasse basin were analysed for sandstone framework composition heavy minerals whole rock geochemistry and detrital chrome spinel chemistry samples were taken from the proximal part of the basin close to the alpine main thrust and are chronostratigraphically calibrated between 31 and 13 ma sandstone composition allows the identification of different source rocks and their variation in time and space place constraints on the oligocene to miocene evolution of the central alps in the eastern part of the basin sandstones document a normal unroofing sequence with the downcutting from austroalpine sedimentary cover into austroalpine crystalline rocks and slightly later at 21 ma into penninic ophiolites in the central part downcutting into crystalline basement rocks occurred at 25 ma and the removal of the sedimentary cover was much more advanced than in the east this may be interpreted as a first signal from the doming of the lepontine area at 20 ma extensional tectonics in the hinterland led to the first exposure of low grade metamorphic rocks from the footwall of the simplon fault in the central alps erosion of these rocks persisted up to the youngest sediments at 13 ma in the western part of the basin a contribution from granitoid and ultra mafic rocks is documented as early as 28 ma the source for the ultra mafic detritus is penninic ophiolites from the piemonte zone of the western alps which were already exposed at the surface at that time

geochemistry of flood basalts of the toranmal section northern deccan traps india implications for regional deccan stratigraphy unpublished data 1998 andthe southeastern deccan particularly the poladpur andambenali formations mitchell widdowson 1991 bilgrami 1999 for as much as 350 km from their south western type sections in addition lavas isotopically andchemicallyequivalenttothoseoftheambenaliformation fm arepresentinthenortheastern sectoroftheprovinceas far as 900 km from their southwesternmost counter parts mahoney 1988 deshmukh

bathymetric controls on pliocene north atlantic and arctic sea surface temperature and deepwater production the mid pliocene warm period mpwp 3 3 to 3 0 ma is the most recent interval in earth s history in which global temperatures reached and remained at levels similar to those projected for the near future the distribution of global warmth however was different than today in that the high latitudes warmed more than the tropics multiple temperature proxies indicate significant sea surface warming in the north atlantic and arctic oceans during the mpwp but predictions from a fully coupled ocean atmosphere model hadcm3 have so far been unable to fully predict the large scale of sea surface warming in the high latitudes if climate proxies accurately represent pliocene conditions and if no weakness exists in the physics of the model then model boundary conditions may be in error here we alter a single boundary condition bathymetry to examine if pliocene high latitude warming was aided by an increase in poleward heat transport due to changes in the subsidence of north atlantic ocean ridges we find an increase in both arctic sea surface temperature and deepwater production in model experiments that incorporate a deepened greenland scotland ridge these results offer both a mechanism for the warming in the north atlantic and arctic oceans indicated by numerous proxies and an explanation for the apparent disparity between proxy data and model simulations of pliocene northern north atlantic and arctic ocean conditions determining the causes of pliocene warmth remains critical to fully understanding comparisons of the pliocene warm period to possible future climate change scenarios

the electrical conductivity of the mantle beneath europe derived from c responses from 3 to 720 hr summary the c response which connects the magnetic vertical component and the horizontal gradient of the horizontal components of electromagnetic fluctuations forms the basis for estimating the conductivity depth profile of the earth this paper describes new estimates of the c response obtained from observatory hourly mean values the z y method is applied which means that the vertical component is used locally whereas the horizontal components are used globally by expansion into terms of spherical harmonics a special evort is made to obtain unbiased estimates of c when applied to 90 months of hourly mean values from about 90 observatories the method yields consistent results for european observatories in the entire period range from 3 to 720 hr and for two diverent source mechanisms s and d st a good description of the source structure for individual time segments is essential this was achieved by a separate spherical harmonic analysis of the data for each month for d st or each day for s and by estimating a large number 120 of expansion coeycients the results are interpreted by means of 1 d conductivity models which show that the upper mantle has remarkably little structure with a monotonic decrease of resistivity from 100 v m near z 200 km to 0 7 v m below z 1000 km

bedrock morphology reveals drainage network in northeast baffin bay a subglacial drainage network underneath the paleo ice sheet off west greenland is revealed by a new compilation of high resolution bathymetry data from melville bay northeast baffin bay this drainage network is an indicator for ice streaming and subglacial meltwater flow toward the outer shelf repeated ice sheet advances and retreats across the crystalline basement together with subglacial meltwater drainage had their impact in eroding overdeepened troughs along ice stream pathways these overdeepenings indicate the location of a former ice sheet margin the troughs inherit characteristics of glacial and subglacial meltwater erosion most of the troughs follow tectonic weakness zones such as faults and fractures in the crystalline bedrock many of these tectonic features correspond with the orientations of major fault axes in the baffin bay region the troughs extend from the present sub glacial fjord systems at the greenland coast and parallel modern outlet glacier pathways the fast flowing paleo ice streams were likely accelerated from the meltwater flow as indicated by glacial landforms within and along the troughs the ice streams flowed along narrow tributary troughs and merged to form large paleo ice streams bedded in the major cross shelf troughs of melville bay apart from the troughs a rough seabed topography characterises the bedrock and we see a sharp geomorphic transition where ice flowed onto sedimentary rock and deposits

provenance of volcaniclastic beach sand in a magmatic arc setting an example from lipari island aeolian archipelago tyrrhenian sea lipari an active volcanic island in the aeolian magmatic arc is an excellent area to determine the effects of multiple source lithology climate weathering transport and depositional environment on epiclastic sand composition volcaniclastic sand samples from 12 modern beaches were petrographically characterized using the gazzi dickinson method and the proportions of source rocks in combination with topography in associated coastal drainage basins were quantified using gis several types of bedrock in the 12 drainage basins that are the likely prominent sources for sand at each sampled beach were recognized and divided into two categories of provenance lithotypes lavas and pyroclastic rocks ranging in composition from basaltic andesitic to andesitic to rhyolitic volcanic lithic fragments from lipari beach sand consist of colourless and black glassy volcanic fragments with lathwork felsitic vitric and microlitic textures moreover high amounts of detrital less durable minerals such as pyroxene olivine and fe oxides illustrate how the analysed sands preserve the source rock s provenance signals applying the concept of sand generation index we see that these lithotypes have different propensities to create detritus in terms of both grain size and composition clastic contribution from pyroclastic rock outcrops such as pumice is not found in the size ranges studied suggesting that these pumiceous source rocks probably only produce gravel or very fine sand and silt this finding has implications for the stratigraphic record because pumice clasts ranging from medium to fine grain size could be underrepresented in older volcaniclastic deposits and overrepresented in other size fractions

continental record of the southwest monsoon during the last 130 ka evidence from the southern margin of the thar desert india abstract field stratigraphy sedimentology and luminescence dating of the exposed fluvial and aeolian sequences from the southern desert margin were used to discern the pattern of southwest monsoon variability during the last 130 ka the sedimentary architecture and textural attributes of the sediments belonging to the period 130 120 ka suggests the existence of a meandering river system consequent to enhanced southwest monsoon conditions a shift from a meandering to a braided pattern during 120 100 ka indicates a phase of reduced precipitation presence of flood plain fines and bedded calcretes during 100 70 ka suggest a period of enhanced monsoon with seasonality following this a phase of weak monsoon activity was observed during 70 60 ka regional flood plain aggradation and pedogenesis during the period termination of a regional fluvial phase around 30 ka and incision of dunes dated to 20 11 ka suggest that the present rivers occupied their course between 11 ka drowned valleys in the estuarine zones suggest that the incision began during the low sea stand around 20 ka when the rivers were graded to the exposed shelf the incision intensified with the re establishment of monsoon during the early holocene

neogene overflow of northern component water at the greenland scotland ridge in the north atlantic ocean flow of north atlantic deep water nadw and of its ancient counterpart northern component water ncw across the greenland scotland ridge gsr is thought to have played an important role in ocean circulation over the last 60 ma the iceland plume has dynamically supported an area which encompasses the gsr consequently bathymetry of the gsr has varied with time due to a combination of lithospheric plate cooling and fluctuations in the temperature and buoyancy within the underlying convecting mantle here we reassess the importance of plate cooling and convective control on this northern gateway for ncw flow during the neogene period following wright and miller 1996 to tackle the problem benthic foraminiferal isotope data sets have been assembled to examine 13c gradients between the three major deep water masses i e northern component water southern ocean water and pacific ocean water composite records are reported on an astronomical timescale and a nonparametric curve fitting technique is used to produce regional estimates of 13c for each water mass confidence bands were calculated and error propagation techniques used to estimate ncw and its uncertainty despite obvious reservations about using long term variations of 13c from disparate analyses and settings and despite considerable uncertainties in our understanding of ancient oceanic transport pathways the variation of ncw through time is consistent with independent estimates of the temporal variation of dynamical support associated with the iceland plume prior to 12 ma 13c patterns overlap and ncw cannot be isolated significant long period variations are evident which are consistent with previously published work from 12 ma when lithospheric cooling probably caused the gsr to submerge completely long period 13c patterns diverge significantly and allow reasonable ncw estimates to be made our most robust result is a dramatic increase in ncw overflow between 6 and 2 ma when dynamical support generated by the iceland plume was weakest between 6 and 12 ma a series of variations in ncw overflow have been resolved

tides in the gulf of khambhat west coast of india semi diurnal tides in the gulf of khambhat cambay west coast of india amplify about threefold from mouth to head in contrast the amplification of diurnal tides is much smaller a one dimensional barotropic model with channel geometry that is representative of the gulf can reproduce the observed features of amplification the model is used to determine how amplitude in the channel varies with frequency of forcing at the mouth and this variation is compared with that seen in channels representative of other better known embayments the comparison suggests that resonance together with geometric effects and friction sets up the amplification of semi diurnal tides in the gulf of khambhat

long period geomagnetic variations and mantle conductivity an inversion using bailey s method summary we have implemented an algorithm which is based on bailey s solution of the inverse problem of electromagnetic induction in the earth the study was motivated by recent determinations of very long period data and also benefited from recent redeterminations of high frequency data the algorithm has been successfully tested to provide reliable estimates of conductivity down to a depth of 2000 km using synthetic data in the period range from 4 days to 11 years smooth data sets which are required for the inversion were constructed from various sources at a given depth the range of inverted models is less than one order of magnitude due to the lack of high frequency data the conductivity of the upper 600 km of the mantle which is found to be of the order of lo i2 l m may be overestimated the algorithm performs well in the middle mantle where conductivity rises steadily from 1 to 50 i2 l m the lack of very low frequency data and limitations of the algorithm prevent one from obtaining meaningful estimates in the lower mantle however the study of the propagation of the late 1960s secular variation acceleration provides an estimate of the mean conductivity of the whole mantle thus a complete mantle profile can be constructed it is found that deep mantle conductivity probability does not exceed a few hundred i2 l m

impact of periodicity on sediment flux in alluvial systems grain to basin scale periodicity is a common component of many sedimentological processes but seldom is it considered across all scales of fluvial processes in order to understand the complete impact on sediment supply to basins temporal changes in sediment supply within drainage systems and sedimentary basins are a consequence of the inherent instability in transport processes the causes of fluctuations are of 2 main types i changes in factors endemic to the supply of sediment but which are at least partly independent of erosive forces and ii changes in the magnitude of forces available to transport sediment fluctuations at spatial scales from grain through reach to basin scales and at temporal scales from minutes to millennia are discussed and evaluated all fluctuations are reflected in sedimentary deposits in some way for example irregular patterns of bed break up during erosion can generate bedforms that are recorded in deposits the passage of waves of sediment can cause cycles of incision and aggradation in a reach large flood events will flush sediment into coastal regions and will be recorded as an identifiable package in the deposits many models of basin processes and products assume a consistent supply of sediment which is far from the case in nature one of the challenges in the coming decade is to move away from using long term averages of sediment supply and to link models directly into geomorphic processes

eleven phases of greenland ice sheet shelf edge advance over the past 2 7 million years the reconstruction of former ice sheets is important for testing earth system models that can assess interactions between polar ice sheets and global climate but information retrieved from contemporary glaciated margins is sparse in particular we need to know when ice sheets began to form marine outlets and the mechanisms by which they advance and retreat over timescales from decades to millions of years here we use a dense grid of high quality two dimensional seismic reflection data to examine the stratigraphy and evolution of glacial outlets or palaeo ice streams that drained the northwest greenland ice sheet into baffin bay seismic horizons are partly age constrained by correlation with cores from drill sites progradational units separated by onlap surfaces record 11 major phases of shelf edge ice advance and subsequent transgression since the first ice sheet expansion 3 3 2 6 million years ago the glacial outlet system appears to have developed in four stages each potentially caused by tectonic and climatic changes we infer that an abrupt change in ice flow conditions occurred during the mid pleistocene transition about 1 million years ago when ice movement across the shelf margin changed from widespread to a more focused flow ice streams forming the present day glacial troughs eleven phases of advance of the greenland ice sheet following the first expansion between 3 3 and 2 6 million years ago are documented in analyses of a grid of seismic reflection data

constraints on the amplitude of mid pliocene 3 6 2 4 ma eustatic sea level fluctuations from the new zealand shallow marine sediment record ice volume calibrations of the deep ocean foraminiferal delta18o record imply orbitally influenced sea level fluctuations of up to 30m amplitude during the mid pliocene and up to 30 per cent loss of the present day mass of the east antarctic ice sheet eais assuming complete deglaciation of the west antarctic ice sheet wais and greenland these sea level oscillations have driven recurrent transgressions and regressions across the world s continental shelves wanganui basin new zealand contains the most complete shallow marine late neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100ka sea level cycle since ca 3 6ma this paper presents a synthesis of faunally derived palaeobathymetric data for shallow marine sedimentary cycles corresponding to marine isotope stages m2 100 ca 3 4 2 4ma our approach estimates the eustatic sea level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation the sea level estimates are consistent with those from delta18o curves and numerical ice sheet models and imply a significant sensitivity of the wais and the coastal margins of the eais to orbital oscillations in insolation during the mid pliocene period of relative global warmth sea level oscillations of 10 30m were paced by obliquity

electromagnetic induction in the oceans and the anomalous behaviour of coastal c responses for periods up to 20 days 1 electromagnetic transfer functions at coastal sites are known to be strongly distorted by the conductivity of the seawater this ocean effect is generally considered to be small for periods greater than a few days we revise this statement by detailed and systematic model studies in the period range from 1 to 64 days with subsequent comparison of the modelled and observed electromagnetic responses the conductivity model consists of a radial symmetric 1 d section that is overlaid by a thin spherical surface shell the conductance of which is compiled using the noaa etopo topography bathymetry and map of sediment thicknesses the simulations were performed for spatial resolutions of the surface shell of 5 5 2 2 and 1 1 respectively and for two continental and oceanic underlying 1 d conductivity models the inducing source is described by the spherical harmonic p10 in dipole coordinates comparisons are made for the coastal geomagnetic observatories apia hermanus kakioka kanoya and simosato where an anomalous behaviour of the local response has been previously detected from the comparison of observed and modelled responses we conclude that peculiarities in the observed coastal responses in the period range from 1 to 20 days can be explained to a large amount by induction in the oceans we show that correction for the ocean effect results in responses that are much better interpretable by 1 d conductivity models compared to the uncorrected responses

geochemical signature of provenance in sand size material in soils and stream sediments near the tobacco root batholith montana u s a abstract trace element geochemistry of sandstones are being used to determine provenance we have conducted preliminary and limited experiments to determine to what extent daughter sands retain the geochemical signature of parent rocks six sets of first order stream sediments soils from adjacent slopes and a variety of parent rocks were collected from southwestern montana u s a sampling in a low relief area ensured that climate and residence time of soils on slopes could be eliminated as variables sand size fractions of stream sediments and soils and the corresponding parent rocks granodiorite quartz monzonite granite gneiss biotite tonalite gneiss and amphibolite were analyzed for most major elements and selected trace elements petrologic modal analysis of the parent rocks and the 0 25 0 50 mm fraction of each sand was done to monitor major mineralogic control if any on chemical compositions of the samples our data show that the abundances of the si and al in sediments do not discriminate provenance abundances of ca mg fe and ti may broadly distinguish between sands derived from metamorphic and igneous source rocks at least in the area studied differences in abundances of the ba and th and the ratio of la lu between granitic tonalitic and amphibolitic parent rocks are preserved in the daughter sediments that we studied however the size of the eu anomaly in the ree patterns of different daughter sediments is not diagnostic of parent rocks abundances of co and sc distinguish between sediments derived from felsic and mafic rocks a better provenance discrimination is obtained if the ratios la sc th sc la co ba sc and ba co are used petrologic modal data show that mineral contents and chemical compositions of parent rocks are compatible with each other the chemical composition of the sands may be roughly correlated to the petrological modal data but the abundances of some minor and trace elements of sediments cannot be inferred from modal mineralogy this is expected because these elements may concentrate in accessory minerals and or may weather out into aqueous or clay mineral fractions it is also compatible with conclusions of previous studies that some of these elements do not reside in sand size fractions of siliciclastic sediments

labrador sea boundary currents and the fate of the irminger sea water abstract the general circulation of the labrador sea is studied with a dataset of 53 surface drifters drogued at 15 m and several hydrographic sections done in may 1997 surface drifters indicate three distinct speed regimes fast boundary currents a slower crossover from greenland to labrador and a slow eddy dominated flow in the basin interior mean eulerian velocity maps show several recirculation cells located offshore of the main currents in addition to the cyclonic circulation of the labrador sea above the northern slope of the basin the surface drifters have two preferential paths one between the 1000 m and 2000 m isobaths and the other close to the 3000 m isobath the vertical shear estimated from ctd data supports the presence of two distinct currents around the basin one current more baroclinic flows between the 1000 m and 2000 m isobaths the other one more barotropic flows above the lower continental slope the irminger sea water carried by the boundary currents is altered as it tr

upper mantle conductivity structure of the back arc region beneath northeastern china the upper mantle electrical conductivity structure of the pacific back arc beneath northeastern china was investigated through long period magnetotelluric mt and geomagnetic depth sounding gds experiments mt and gds responses were obtained up to periods of 105 106 seconds and were inverted to one dimensional 1 d models with minimum and smooth structure constraints respectively the resulting conductivity model was compared with past models and the mantle transition zone beneath northeastern china is more conductive than those of other tectonic settings by almost one order of magnitude in the depth range of 400 600 km this feature may correspond to the presence of a stagnant slab beneath this region in the mantle at a depth of less than 400 km the conductivity profile has a similar feature to that in the thermal and extensional tectonic region in the southwestern united states

chemical weathering in the krishna basin and western ghats of the deccan traps india rates of basalt weathering and their controls rates of chemical and silicate weathering of the deccan trap basalts india have been determined through major ion measurements in the headwaters of the krishna and the bhima rivers their tributaries and the west flowing streams of the western ghats all of which flow almost entirely through the deccan basalts samples n 63 for this study were collected from 23 rivers during two consecutive monsoon seasons of 2001 and 2002 the total dissolved solid tds in the samples range from 27 to 640 mg l 1 the rivers draining the western ghats that flow through patches of cation deficient lateritic soils have lower tds average 74 mg l 1 whereas the bhima except at origin and its tributaries that seem to receive na cl and so4 from saline soils and anthropogenic inputs have values in excess of 170 mg l 1 many of the rivers sampled are supersaturated with respect to calcite the chemical weathering rates cwr of selected basins which exclude rivers supersaturated in calcite and which have high cl and so4 are in range of 3 to 60 t km 2 y 1 this yields an area weighted average cwr of 16 t km 2 y 1 for the deccan traps this is a factor of 2 lower than that reported for the narmada tapti wainganga ntw systems draining the more northern regions of the deccan the difference can be because of i natural variations in cwr among the different basins of the deccan ii selection of river basin for cwr calculation in this study and iii possible contribution of major ions from sources in addition to basalts to rivers of the northern deccan traps silicate weathering rates swr in the selected basins calculated using dissolved mg as an index varies between 3 to 60 t km 2 y 1 nearly identical to their cwr the ca mg and na mg in these rivers after correcting for rain input are quite similar to those in average basalts of the region suggesting near congruent release of ca mg and na from basalts to rivers comparison of calculated and measured silicate ca in these rivers indicates that at most 30 of ca can be of nonsilicate origin a likely source being carbonates in basalts and sediments the chemical and silicate weathering rates of the west flowing rivers of the deccan are 4 times higher than the east flowing rivers this difference is due to the correspondingly higher rainfall and runoff in the western region and thus reemphasises the dominant role of runoff in regulating weathering rates the silicon weathering rate swr in the krishna basin is 15 t km 2 y 1 within a factor of 2 to those in the yamuna bhagirathi and alaknanda basins of the himalaya suggesting that under favourable conditions intense physical weathering high runoff granites and the other silicates in the himalaya weather at rates similar to those of deccan basalts the co2 consumption rate for the deccan is deduced to be 3 6 105 moles km 2 y 1 based on the swr the rate though is two to three times lower than reported for the ntw rivers system it still reinforces the earlier findings that in general basalts weather more rapidly than other silicates and that they significantly influence the atmospheric co2 budget on long term scales

the 3d electromagnetic response of the earth to ring current and auroral oval excitation summary we report on a new compilation of functions representing the geoelectromagnetic response of the earth s mantle the c response functions and newly defined d response functions the latter of which constitutes a sensitive indicator of lateral heterogeneities in conductivity were estimated for periods from 5 to 106 7 days the spatial coverage and statistical quality of these response function estimates were improved over previous compilations in part by making use of a newly assembled global catalogue of magnetic observatory hourly mean values and by applying a statistically robust form of empirical orthogonal function eof analysis the eof results suggest that for periods longer than 5 days the geomagnetic field variation can be represented predominantly by a single eigenmode we have identified that the primarysource fields of the dominant mode consist of two current systems in the same direction an equatorial ring current in the magnetosphere and two conjugate auroral oval ring currents in the ionosphere the influence of the auroral current system is seen at surprisingly low latitudes 40 and 50 for the vertical and northern components respectively which results in non negligible bias on the conventional c response at high latitudes a preliminary correction of the auroral current effect has been made on the c and d responses obtained for data from 55 and 52 observatories respectively at latitudes from 60 to 60 we also present a set of approximate equivalent internal mantle electrical current distributions that prove a useful indicator of the presence of deep earth heterogeneities these new sets of electromagnetic information will increase the resolving power of 3d distribution of electrical conductivity in the earth s mantle

earth science a wet mantle conductor reply inference of the spatial distribution of water content in the mantle is critical to our understanding of the dynamics of earth s interior a model1 has been described that indicates there may be a jump in water content at the 410 km discontinuity in the earth s mantle from the electrical conductivity we have inferred2 the water content in the transition zone and concluded that it is significantly larger than that of the upper mantle hirschmann 3 questions our conclusion on the grounds of the trade off between water content and oxygen fugacity

the nature of the archean upper crust as revealed by the geochemistry of the proterozoic shales of the kaladgi basin karnataka southern india abstract major trace and rare earth element geochemical studies of the shales belonging to the 1 8 ga proterozoic kaladgi supergroup of southern india shows that they are derived from strongly chemically weathered archean upper crust this has resulted in depletion of na2o cao sr and u in these shales the shales of lower stratigraphic intervals are enriched in mgo fe2o3 cr ni co and sc relative to the upper shales the upper shales by contrast show enrichment in elements such as ba th and zr these characteristics and the barium cobalt ratios show that the early sediments were derived from a more mafic provenance and the contribution of granitoids increased towards the later stages of kaladgi sedimentation rare earth element ree modelling shows that the average kaladgi shale represents a contribution from a crust with a mafic to felsic rock ratio of 60 40 the post depositional introduction of potassium and lree in these shales has been inferred based on the overall geochemical characteristics

geochemical study of laterites of the jamnagar district gujarat india implications on parent rock mineralogy and tectonics abstract the laterite deposits occur in a linear stretch along the northern arabian sea coast in the jamnagar and porbandar districts of gujarat state india these deposits are characterised by presence of gibbsite kaoline calcite quartz anatase natroalunite goethite and hematite and relicts of mafic minerals and plagioclase on the basis of petro mineralogy and geochemistry these deposits are grouped as aluminous laterites fe2o3 1 45 3 84 av 3 13 al2o3 39 31 57 24 av 45 80 and laterites fe2o3 9 84 32 21 av 25 13 al2o3 34 74 49 59 av 41 27 the major trace and ree characteristics of laterites indicate that these were formed in situ by the alteration of parent rocks of trachytic andesitic composition and the process of bauxitisation followed the path of destruction of kaolinite and deferruginisation the correlation patterns of several trace and rare earth elements and their preferential enrichment have indicated that there is an influence of precursor rock on the distribution of trace elements the jamnagar laterite deposits occur as capping over the deccan trap basaltic lava flows and pyroclasic deposits lateritisation prevailed during palaeocene age when india was separated from the seychelles and passing over the equator during this time climate morphology and drainage conditions were favourable for lateritisation that result in the formation of jamnagar and other laterite deposits within the deccan province flood basaltic provinces of deccan columbia north australia and hawaii appear good location for hosting laterite deposits due to their wide areal extent small geological time span and uniform chemical composition however comparison of the major flood basaltic provinces of the world has indicated that their palaeopositions along with palaeoclimate morphology and drainage are equally important factors for facilitating lateritisation

thermodynamics of water solubility and partitioning when it was realized that nominally anhydrous minerals could be a major storage site of water in the mantle smyth 1987 bell and rossman 1992 it also became rather obvious that many mantle samples probably have lost most of their water during ascent e g ingrin and skogby 2000 while analyses of natural samples therefore in many circumstances only provide a lower limit of the actual water content in the mantle measurements of water solubility give an upper limit of the amount of water that might be stored in a mineral experimental measurements of water solubility have therefore naturally evolved in the last decades as a major tool for understanding the water storage capacity of the mantle closely related to studies of water solubility are studies of water partitioning among minerals if the water solubility in two minerals is known under given conditions the partition coefficient is just the ratio of the water solubilities under the same conditions provided that the composition of the fluid coexisting with the two minerals is the same since the pioneering work of bai and kohlstedt 1992 and of kohlstedt et al 1996 the water solubility in all major upper mantle minerals has been studied as well as the partitioning of water between the minerals of the lower mantle and the transition zone solubility studies by themselves do not directly give the water content in the mantle they constrain the storage capacity of the mantle i e the maximum amount of water that may be stored if the mantle were water saturated however as most of the mantle is very likely water undersaturated the actual water content is probably far below the storage capacity estimates of the actual abundance and distribution of water in the mantle may be obtained by combining solubility and partitioning data with direct

clay sediment accumulation rates on the monsoon dominated western continental shelf and slope region of india abstract clay accumulation rates shown in sediment cores from the nearshore to outer continental shelf and slope regions in water depths of 10 1246 m on the western continental margins of india were determined by the 210 pb dating technique the 210 pb excess concentration encountered in these regions is about 3 5 dpm g and is independent of water depth the range of clay accumulation rates is from 1 8 to 19 mm yr for the shelf region and decreases southward from the tapti and narbada river confluence in the gulf of cambay this pattern indicates sediment dispersal in the coastal region regulated by southwest monsoon dominated littoral currents the same trend is encountered all along the southwestern traverse this suggests that suspended matter transport across the shelf is minimal since clay accumulation rates on the outer shelf are only 1 8 2 5 mm yr the clay accumulation rate in the slope region is 3 8 mm yr the high accumulation rates encountered on the upper continental slope may be attributed to the terrigenous influx of indus river sediment

submarine landforms reveal varying rates and styles of deglaciation in north west greenland fjords during this work c l batchelor was in receipt of a junior research fellowship at newnham college cambridge the bathymetric data that was collected during jr175 of the rrs james clark ross to west greenland in 2009 was funded by natural environment research council nerc grant ne d001951 1 to c o cofaigh

weathering erosion and sediment composition in a high gradient river calabria italy source rock lithology and immediate modifying processes such as chemical weathering and mechanical erosion are primary controls on fluvial sediment supply sand composition and chemical index of alteration cia of parent rocks soil and fluvial sand of the savuto river watershed calabria italy were used to evaluate the modifications of source rocks through different sections of the basin characterized by different geomorphic processes in a sub humid mediterranean climate the headwaters with gentle topography produce a coarse grained sediment load derived from deeply weathered gneiss having sand of quartzofeldspathic composition compositionally very different from in situ degraded bedrock maximum estimated cia values suggest that source rock has been affected significantly by weathering and it testifies to a climatic threshold on the destruction of the bedrock the mid course has steeper slopes and a deeply incised valley bedrock consists of mica schist and phyllite with a very thin regolith which provides large cobble to very coarse sand sediments to the main channel slope instability with an areal incidence of over 40 per cent largely supplies detritus to the main channel sand sized detritus of soil and fluvial sand is lithic estimated cia value testifies to a significant weathering of the bedrock too even if in this part of the drainage basin steeper slopes allow erosion to exceed chemical weathering the lower course has a braided pattern and sediment load is coarse to medium fine grained the river cuts across palaeozoic crystalline rocks and miocene siliciclastic deposits sand sized detritus contributed from these rocks and homogenized by transport processes has been found in the quartzolithic distal samples field and laboratory evidence indicates that landscape development was the result of extensive weathering during the last postglacial temperature maximum in the headwaters and of mass failure and fluvial erosional processes in the mid and low course copyright 2000 john wiley sons ltd

coupling of co2 and ice sheet stability over major climate transitions of the last 20 million years the co2 content of the atmosphere has varied cyclically between 180 and 280 ppmv over the last 800 000 years closely coupled with temperature and sea level for earlier periods in earth s history pco2 is much less certain and the relationship between pco2 and climate remains poorly constrained we use boron calcium ratios in foraminifera to estimate pco2 during major climate transitions of the last 20 million years myr during the middle miocene when temperatures were 3 to 6 c

elemental composition of calcites in late quaternary pedogenic calcretes from gujarat western india abstract pedogenic calcretes commonly exhibit clotted micrite circum granular calcite grain coats and microspar spar veins the three calcite types with different dimensions were analyzed for their magnesium content to determine the relationship between crystal elongation and magnesium incorporation the results show a very low mgo content for grain coats and microspars and high values for clotted micrite indicating that the ideal kinetic model does not hold true and several variables govern the end composition of calcites the magnesium concentrations of meteoric calcites are genetically linked to the evolutionary history of the soil and climate grain coats which are elongated calcites contain the least amount of mg and is related to the initial stages of pedogenesis wherein the limiting factor is the mg ca ratio of the parent fluid lower magnesium contents arise due to smaller quantities of mg being released during incipient weathering micrite morphology and composition is controlled by the greater availability of mg ions through weathering higher pco2 in soil due to increased time dependent soil respiration which causes a rise in calcite precipitation rates and clay authigenesis this in turn exerts a physical control on morphology by occluding pore space and providing numerous nuclei for calcite precipitation the wide variability in spar cements is inherently controlled by inhomogeneties in parent fluid compositions with lower than micrite values on account of slower precipitation rates