mobility and fractionation of rare earth elements in argillaceous sediments implications for dating diagenesis and low grade metamorphism abstract we report sm nd and rb sr data for the fine fractions of lower paleozoic argillaceous rocks from wales uk and new york usa spanning the range of low grade metamorphic conditions from the diagenetic zone zeolite facies to the epizone greenschist facies in all cases leaching of the fine fractions results in a high 147 sm 144 nd 0 09 0 29 acid soluble component and a complementary low 147 sm 144 nd 0 05 0 14 residual component the observed fractionation is an ancient feature related to diagenesis burial and metamorphism the magnitude of sm nd fractionation between leachates and residues as well as the resulting sm nd ages vary as a function of grain size and metamorphic grade uncleaved welsh mudrocks of the diagenetic zone yield sm nd leachate residue ages of 453 484 ma in agreement with their llanviian to caradocian biostratigraphic ages whereas higher grade rocks of the anchizone and epizone yield sm nd ages as young as 413 ma these ages are transitional between the time of deposition and the time of regional deformation related to the acadian orogeny at 390 ma distinct convex upward rare earth element ree patterns of the leachates suggest that the precipitation of early diagenetic apatite controls the trace element budget of the rock forcing a depletion of middle rees on the subsequently formed diagenetic phyllosilicates the amount of organic matter present and the extent of later prograde reactions are probable modifiers of this fractionation process ordovician and devonian clastic rocks associated with the trenton and onondaga limestones of new york yield single sample and multi sample sm nd isochron ages that agree well with their biostratigraphic ages of 454 ma and 390 ma respectively the ree fractionation observed in shale leachates of the ordovician utica formation is related to ca mg of the bulk rock and hence to the composition of the diagenetic carbonate cement in all cases the sm nd system remained closed subsequent to the peak of diagenesis or metamorphism including the north american rocks that show no evidence of being isotopically reset during widespread remagnetization of the subjacent limestone units in the late paleozoic

tubular symplectic inclusions in olivine from the fukang pallasite olivine from the fukang meteorite like that from many other pallasites contains distinctive arrays of parallel straight tubular inclusions they differ in their extension and linearity from those in terrestrial olivines they comprise approximately 1 of the total volume most have lens shaped cross sections but some are rounded the major axis of the lens shaped inclusions is rigorously oriented along olivine 001 and the rounded ones lie along olivine 010 and a few along 100 the linear nature and orientations of the inclusions suggest that they nucleated on screw dislocations perhaps formed through shock triggering high resolution transmission electron microscopy tem and energy dispersive x ray spectroscopy show that the inclusions consist of symplectic intergrowths of chromite diopside and silica that appear to have formed by exsolution from the host olivine the symplectites consist of chromite lamellae with approximately 35 nm spacings that grew outward from a central plane with interstitial diopside and silica contrast modulations having an average spacing of 4 4 nm occur within the chromite lamellae using a reaction front model we estimate that exsolution occurred over a period of 30 to 100 min suggesting rapid cooling at high temperature the crystallographic observations and inferences on growth rate are consistent with the hypothesis that the inclusions nucleated during heating following dislocation formation in a shock event perhaps concurrent with that proposed to have disrupted the pallasite parent body

evidence for olivine deformation in kimberlites and other mantle derived magmas during crustal emplacement this paper highlights published and new field and petrographic observations for late stage crustal level deformation associated with the emplacement of kimberlites and other mantle derived magmas thus radial and tangential joint sets in the competent 183 ma karoo basalt wall rocks to the 5 ha lemphane kimberlite blow in northern lesotho have been ascribed to stresses linked to eruption of the kimberlite magma further examples of emplacement related stresses in kimberlites are brittle fractures and close spaced parallel shears which disrupt olivine macrocrysts in each of these examples there is no evidence of post kimberlite regional tectonism which might explain these features indicating that they reflect auto deformation in the kimberlite during or immediately post emplacement on a microscopic scale these inferred late stage stresses are reflected by fractures and domains of undulose extinction which traverse core and margins of some euhedral and anhedral olivines in kimberlites and olivine melilitites undulose extinction and kink bands have also been documented in olivines in cumulates from layered igneous intrusions our observations thus indicate that these deformation features can form at shallow levels crustal pressures which is supported by experimental evidence undulose extinction and kink bands have previously been presented as conclusive evidence for a mantle provenance of the olivines i e that they are xenocrysts the observation that these deformation textures can form in both mantle and crustal environments implies that they do not provide reliable constraints on the provenance of the olivines an understanding of the processes responsible for crustal deformation of kimberlites could potentially refine our understanding of kimberlite emplacement processes

role of microtopography in the formation of sodic soils in the semi arid part of the indo gangetic plains india abstract in the northwestern part of the indo gangetic plains igp india non sodic and moderately sodic soils occur on microhigh mh and highly sodic soils on microlow ml positions under a semi arid climate the main soil forming processes have been clay illuviation deposition of pedogenic calcium carbonate and concomitant development of sodicity the microlows are repeatedly flooded with surface water during brief high intensity showers so the soils are subject to cycles of wetting and drying this provides a steady supply of alkalis by hydrolysis of feldspars leading to precipitation of calcium carbonate at high ph and development of subsoil sodicity this impairs the hydraulic conductivity of soils and eventually leads to the development of natrustalfs with exchangeable sodium percentages increasing rapidly up the profile the semi arid climate and topography interact to facilitate greater penetration of bicarbonate rich water in microlow than microhigh positions thin sections show deformational pedofeatures such as cross and reticulate striation of plasmic fabric disruption of clay pedofeatures and carbonate nodules and elongation of voids as a result of tectonic activity during the holocene in view of the persistent build up of stresses in the igp in general and the study area in particular it seems that the neotectonics have caused the microtopographical variations 0 5 1 m that control the formation of sodic soils

symplectic exsolution in olivine from the nakhla martian meteorite abstract the nakhla meteorite commonly accepted to have originated from mars is a cumulus clinopyroxenite with 10 vol of fe rich olivine almost all olivine grains in nakhla contain dark lamellar inclusions less than 2 3 m wide high resolution scanning and transmission electron microscopy revealed that the inclusions are complex intergrowths of augite and magnetite such a symplectic intergrowth of augite and magnetite in olivine was known in some terrestrial rocks lunar rocks and a few meteorites the inclusion in nakhla olivine is the first symplectite found in a martian rock apparently the presence of fe3 in olivine under an oxidizing condition on mars caused symplectic exsolution at high temperature 900 c during cooling

focused ion beam fib combined with sem and tem advanced analytical tools for studies of chemical composition microstructure and crystal structure in geomaterials on a nanometre scale abstract in order to make meaningful interpretations of trace element and isotopic information from geomaterials prior characterization of the material of interest with respect to structural and chemical homogeneity radiation damage and microstructure is often required transmission electron microscopy tem is a powerful analytical tool that may be used to fully characterise a wide range of synthetic and natural materials the focused ion beam technique fib is an ideal tool for tem sample preparation that allows for the fabrication of electron transparent foils with typical dimensions of 15 10 0 150 m from any region of interest i e site specific and in virtually any material fib sample preparation consumes only a small volume of material approximately 2300 m 3 for a standard foil with the dimensions 15 10 0 150 m leaving most of the material essentially unaffected by the sampling process modern tem facilitates the measurement of chemical composition with unsurpassed spatial resolution e g nanometer scale high resolution imaging and electron diffraction provide important complimentary structural information it is the combination of crystal structure information and chemical composition that allows for the complete characterization of the volume of interest high resolution elemental mapping or line scans may be used to acquire complete energy dispersive x ray analysis edx spectra of a material pixel by pixel subsequent evaluation of the data allows for the correlation of the edx spectrum with the respective elemental map or line scan with an image thus illustrating spatially resolved chemical composition variations at the 0 5 1 0 wt level frequently minerals enclose sub micrometer or even nanometre sized inclusions of minerals fluids or silicate melt which are of great interest to geoscientists nanoinclusions e g in diamond or olivine are of particular interest because they may have preserved their original crystal structure thus providing a geobarometer recording the pressure conditions at the time of formation of the inclusion fib tem are appropriate techniques to sample and subsequently define the chemical composition and the structural state of mineral inclusion on the nanometre scale the combination of fib with an sem allows for 3d information to be obtained from samples including 3d imaging e g phase distribution and volume of the individual phases in symplectites 3d distribution of elements in a specific volume 3d elemental maps and three dimensional texture analysis using electron backscatter diffraction ebsd

lunar apatite with terrestrial volatile abundances the moon is thought to be depleted relative to the earth in volatile elements such as h cl and the alkalis nevertheless evidence for lunar explosive volcanism has been used to infer that some lunar magmas exsolved a co rich and co 2 rich vapour phase before or during eruption although there is also evidence for other volatile species on glass spherules until recently there had been no unambiguous reports of indigenous h in lunar rocks here we report quantitative ion microprobe measurements of late stage apatite from lunar basalt 14053 that document concentrations of h cl and s that are indistinguishable from apatites in common terrestrial igneous rocks these volatile contents could reflect post magmatic metamorphic volatile addition or growth from a late stage interstitial sulphide saturated melt that contained 1 600 parts per million h 2o and 3 500 parts per million cl both metamorphic and igneous models of apatite formation suggest a volatile inventory for at least some lunar materials that is similar to comparable terrestrial materials one possible implication is that portions of the lunar mantle or crust are more volatile rich than previously thought

chemical processes affecting the mobility of major minor and trace elements during weathering of granitic rocks abstract the behaviour of 38 major and trace elements as well as changes in the mineralogy have been examined in 10 weathering profiles developing on some portuguese granitic rocks element mobilities are calculated from geochemical data normalized with respect to ti in the fresh parent rock chemical elements are divided into two groups immobile and mobile on the basis of their geochemical distribution during weathering elements that are immobile during weathering are zr hf fe al th nb sc and the ree very mobile are ca na p k sr ba rb mg and si mobile elements are derived mainly from leachable minerals such as feldspars micas and apatites whereas immobile elements are either concentrated in resistate phases or strongly adsorbed by secondary minerals the geochemical behaviour of mn cr v fe and ce is very dependent on redox conditions redox transformations of these elements can be used to set limits on the oxidation state of a weathering suite the ree are mobilized or fractionated during late stages of weathering but not during moderate stages of weathering this fractionation is caused by selective leaching of rocks composed of both stable and unstable minerals containing ree

higher erosion rates in the himalaya geochemical constraints on riverine fluxes the modern erosion rate of continental scale mountains is difficult to estimate and is usually based on measurement of the suspended load flux of rivers combined with assumptions about river bedload transport and sedimentation in flood plains these two parameters are very difficult to measure directly in continental scale basins in this paper we examine the chemical composition of the suspended load bedload and dissolved load of the ganga and brahmaputra rivers and compare them with the average composition of himalayan source rocks a mass balance equation of erosion fluxes shows that a si rich component is needed in addition to suspended and dissolved load fluxes to account for the composition of the source rock it corresponds to bedload sediment and flood plain deposits which are enriched in quartz by mineral sorting during transport the combined budget of si al and fe in the river system allows us to estimate this si rich flux by this method the total himalayan erosion is estimated to be twice the measured flux of suspended load the comparison between the brahmaputra and the ganga shows that the eastern himalaya has a higher erosion rate 2 9 mm yr than the western himalaya 2 1 mm yr this is likely the result of the higher runoff in the brahmaputra basin the intensity of the monsoon acts as a first order control of the erosion rate in the range

mobilization and redistribution of rees and thorium in a syenitic lateritic profile a mass balance study abstract ree th geochemistry and mineralogy have been studied in a lateritic profile derived from a syenite at akongo in sw cameroon ree and th mass balance calculations for the host rock minerals show that at least 70 of the lree s and 50 of the hrees are contained in allanite apatite titanite and epidote and at least 50 of the th is controlled by the same accessory minerals which represent about 2 wt of the unaltered syenite these accessory phases are destroyed during the first stages of weathering causing most of the rees and th to be rapidly released into the soil comparison of the variation in the zr ti and th content as a function of the apparent density of the different zones of the saprolite shows that th is the least mobile element the presence of secondary thorianite tho2 the etched surface on zircon grains and the presence of ti in secondary cerianite support this geochemical interpretation the concentration of thorium was therefore chosen as invariant relative to the concentration of the other elements especially the rees in mass balance calculations most of the rees are leached in the iron rich upper horizons loose nodular horizon iron crust and top of mottled clay horizon where the groundwater table moves saprolite and bottom of the mottled clay horizon the rees are fractionated and redistributed there is a juxtaposition of leached and accumulation zones with precipitation of lree aluminous hydrated phosphates this study supports the existence of two different cycles for the redistribution of elements in the soil 1 1 as dissolved ions in the saprolite horizon and 2 2 as individual particles in the upper part of the profile

luminescence chronology of river adjustment and incision of quaternary sediments in the alluvial plain of the sabarmati river north gujarat india river adjustment and incision in the sabarmati basin gujarat india have been examined at a site near mahudi towards this the morphostratigraphy and depositional chronometry of the middle alluvial plains were investigated the upper fluvial sequence along with the overlying aeolian sand and riverbed scroll plains provide clues to the evolution of the present sabarmati river sedimentological analyses of the upper fluvial sequence indicate its deposition by a meandering river system during what is believed to be a persistent wetter phase luminescence chronology bracketed this sequence to between 54 and 30 ka which corresponds to oxygen isotope stage 3 during which the sw monsoon was enhanced the overlying aeolian sand has been dated to 12 ka indicating that dune accretion occurred simultaneously with the strengthening of the sw monsoon during the early holocene adjustment of the sabarmati along a n s transect is placed around 12 ka and the incision is bracketed between 12 and 4 5 ka river adjustment could have been tectonic however the incision was facilitated by the availability of continuous flow in the river caused by the sw monsoon the basin experienced two tectonic events at about 3 and 0 3 ka as demonstrated by the morphology of the scroll plains

crystallographic orientation relationships in host inclusion systems new insights from large ebsd data sets crystallographic orientation relationships cors between mineral inclusions and their hosts could potentially deliver information about inclusion formation processes and conditions most previous studies are based on small numbers of analyses this paper uses ebsd to study host inclusion cors in an inclusion rich permian metapegmatite garnet koralpe region eastern alps austria demonstrating the importance of large data sets and of ebsd in particular for the analysis of cors the distribution of measured orientations reflects host garnet point group symmetry for 89 of inclusions analyzed total n 530 each inclusion phase rutile corundum and ilmenite shows at least three different cors to host garnet statistical cors are introduced to describe distributions of inclusion orientations that have one or two degrees of freedom with respect to the host but still reflect host crystal symmetry two end member characteristics of statistical cors are distinguished rotation and dispersion most statistical cors observed show a mixture of both each inclusion phase shows at least one statistical cor multiple coexisting cors and statistical cors are not restricted to rutile re examination of previous garnet rutile cor studies in light of the new results indicates that cor information may have been overlooked when using small data sets variation in cor parameters correlates with broad differences in assumed metamorphic conditions for new and literature samples suggesting that petrogenetic information may be available if cor formation can be understood the favorability of the detected cors cannot be explained by a simple model involving minimization of misfit between lattice planes implying that other interface properties or the inclusion formation mechanism are important controls on cor development

an authigenic calcite layer in the sediments of the sea of marmara a geochemical marker horizon with paleoceanographic significance abstract three sediment cores taken from the central sea of marmara were sedimentologically and geochemically investigated all the cores show a continuous sedimentation record according to isotopic age dating measurements two of the cores cover an age range of more than 20 000 years since the sea of marmara was an isolated lacustrine system during the last glacial maximum about 20 ka bp the two cores should include the transition from lacustrine to marine environmental conditions the third core has a very high sedimentation rate 70 cm ka and therefore does not reach the transitional section in two cores however a very calcite rich layer unit c was observed carbon isotope investigations show that this calcite is not of diagenetic or biogenic origin but may represent a direct inorganic precipitate out of a deepwater layer in order to prove this hypothesis we used a geochemical model based on thermodynamic calculations this model shows that the calcite precipitation can only be explained by mixing of anoxic deep lacustrine water with oxic marine mediterranean water the necessary aqueous conditions are also obtained the model presented thus provides an important contribution to the evolution of the sea of marmara during the transition from lacustrine to marine conditions the thickness of the unit c layer indicates that this environmental change lasted approximately 1 5 ka

polygenetic soils of the north central part of the gangetic plains a micromorphological approach abstract micromorphology indicates that soils of the central part of the gangetic plains are polygenetic they occur on surfaces originating at 13 500 8000 2500 500 and

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

ree geochemistry of recent clastic sediments from the kaveri floodplains southern india implication to source area weathering and sedimentary processes abstract the kaveri river drains through archean gneissic and charnockitic terranes in south india the rare earth element ree chemistry of the floodplain sediments along with their major and trace element composition in different size fractions are discussed we observe a strong coherence between ree and tio2 contents in the sediments which is suggestive of strong control by titanite or its weathered products on the ree chemistry ree concentrations also show a general increase with decreasing size of bulk sediments different size fractions and of light and heavy mineral fractions this suggests the presence of ree in the fe oxy hydroxide surface coatings on clastic grains formed by the weathering of hornblende and titanite in the granodioritic to dioritic protoliths we also interpret the data as showing that ree patterns of clastic sediments notably eu anomaly are affected by the degree of source rock weathering as well as by the fluvial processes of sorting and mineral differentiation therefore for provenance study sediments having all granulometric grades such as the floodplain sediments are preferable because they most closely represent the source particularly when the source region suffered little chemical weathering in the present case the sediments were derived from the high standing hills of archean charnockites because of their recent uplift and physical denudation

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

the sources of water in martian meteorites clues from hydrogen isotopes abstract h isotope measurements of carbonate phosphate feldspathic and mafic glasses and post stishovite silica phase in the shergottites zagami shergotty sau 005 dag 476 alha 77005 and eeta 79001 as well as in chassigny and alh 84001 show that all these phases contain deuterium enriched water of extraterrestrial origin the minerals and glasses analyzed may contain an initial primary hydrogen component but their isotopic composition was modified to varying degrees by three different processes interaction with a fractionated exchangeable water reservoir on mars hydrogen devolatilization by impact melting and terrestrial contamination positive correlations between d and water abundance in feldspathic glass and post stishovite silica in zagami shergotty and sau 005 is indicative of mixing of a high d component 3000 4000 and a less abundant low d component 0 the high d component is primarily derived from the martian exchangable reservoir but may also have been influenced by isotopic fractionation associated with shock induced hydrogen loss the low d component is either a terrestrial contaminant or a primary magmatic component the negative correlation between d and water abundances in mafic and feldspathic glasses in alh 84001 alha 77005 and eeta 79001 is consistent with the addition of a low d terrestrial contaminant to a less abundant high deuterium martian component the low d of magmatic glass in melt inclusions suggests that the d of martian parent magma was low and that the initial h isotope signature of mars may be similar to that of earth

quaternary paleoclimatic paleoceanographic and tectonic evolution of the marmara sea and environs strabo 63 bc 21 ad book 1 3 4 jones 1954 themarmarasea fig 1 hasalwaysattractedinterestasagreatgatewaylinkingtheblackseato the eastern mediterranean sea through a net work of narrow straits with shallow sills straitsof bosphorus istanbul and dardanelles c anakkale forthepast2500 3000yr informa tion about surface and bottom currents depthsoundings and sea level variation were crucialforsafenavigationacrossthesestraitsbysea far ingpeopleandexplorers thusconstitutingama jorstrategicassetandyieldingenormouseconom icandpoliticaladvantages throughoutantiquity sailors knew that the bottom waters across thestraits of dardanelles and bosphorus owednorthward and utilized this knowledge to sailintothemarmaraseaandblackseabyloweringlargebasketswithweightsintothenorth owingmediterranean water to counteract the strongsouth directed surface out ow from the blacksea systematic scienti c investigations in the mar marasearegionstartedinthelate19thcentury the rstbathymetricsurveyrevealedthepresenceof three deep basins and their intervening ridges andrussow 1901 p nar 1943 subsequentlyproposedthatasinglefaulttransectedthesethreebasins extending from the izmit bay in the eastto the gulf of saros in the west pfannensteil 1944 noted the rhombohedric shape of thedeepmarmaraseabasinsandproposedthattheridgesseparatingthebasinsrepresenthorstblocksbounded by normal faults healsosuggested inadditiontothestraitofbosphorus thepresenceofasecondchannel thesakaryabosphorus fig 1 which connected the black sea to the mar mara sea during the quaternary in 1948 ketinpublished his renowned paper revealing the truenatureofthenorthanatolianfaultasoneoftheworld slargest active intra continental strike slipfaults ketin 1948 pavoni 1961 and kopp etal 1969 proposedthataseriesofsyntheticand

transmission electron microscopy of subsolidus oxidation and weathering of olivine olivine crystals in basaltic andesites which crop out in the abert rim south central oregon have been studied by high resolution and analytical transmission electron microscopy the observations reveal three distinct assemblages of alteration products that seem to correspond to three episodes of olivine oxidation the olivine crystals contain rare dense arrays of coherently intergrown ti free magnetite and inclusions of a phase inferred to be amorphous silica we interpret this first assemblage to be the product of an early subsolidus oxidation event in the lava the second olivine alteration assemblage contains complex ordered intergrowths on 001 of forsterite rich olivine and laihunite distorted olivine structure with fe3 charge balanced by vacancies based on experimental results for laihunite synthesis kondoh et al 1985 these intergrowths probably formed by olivine oxidation between 400 and 800 c the third episode of alteration involves the destruction of olivine by low temperature hydrothermal alteration and weathering elongate etch pits and channels in the margins of fresh olivine crystals contain semi oriented bands of smectite olivine weathers to smectite and hematite and subsequently to arrays of oriented hematite crystals the textures resemble those reported by eggleton 1984 and smith et al 1987 we find no evidence for a metastable phase intermediate between olivine and smectite m eggleton 1984 the presence of laihunite exerts a strong control on the geometry of olivine weathering single laihunite layers and laihunite forsteritic olivine intergrowths increase the resistance of crystals to weathering preferential development of channels between laihunite layers occurs where growth of laihunite produced compositional variations in olivine rather than where coherency strain is associated with laihunite olivine interfaces

another look at rare earth elements in shales linear correlation and mass balance considerations indicate that clays are more important than zircon or other heavy minerals in hosting both light and heavy ree in cratonic shales considering the uniformity of the eu anomaly and ree distributions in cratonic shales it seems likely that detritus is thoroughly mixed during weathering and sediment transport and that the ree patterns in shales reflect the average ree pattern of the sources regardless of the ratio of clays to heavy minerals in the shales shales suspended river loads and near shore marine sediments all have broadly similar ree patterns and reported hree depletions in the latter two groups may reflect incomplete dissolution of heavy minerals during sample preparation ree distributions in shales and suspended river loads determined by inna are similar to those in average upper continent crust and ree distributions in shale averages nasc and paas seem to be reasonably representative of the average composition of post archean upper continental crust

diffusion kinetics of cr in olivine and 53mn 53cr thermochronology of early solar system objects we have determined the diffusion coefficient of cr in olivine as function of temperature oxygen fugacity fo2 and crystallographic orientation and used these data to develop a quantitative understanding of the resetting of the short lived 53 mn 53 cr decay system in olivine during cooling within meteorite parent body the diffusion of cr in olivine was found to be anisotropic and effectively indepen dent of fo2 between wustite iron buffer and two orders of magnitude above this buffer the diffusion data were used to calculate the spatially averaged mean closure temperature of the 53 mn 53 cr decay system in olivine as function of the initial temperature cooling rate and grain size and also the closure age profile of this system in olivine single crystal as function of radial distance and a dimensionless parameter that incorporates the effects of various parameters that affect the closure age we also present a thermochronolgic formulation that permits retrieval of cooling rates from the extent of resetting of the bulk 53 mn 53 cr closure age of olivine during cooling this method was applied to determine the cooling rate of the pallasite omolon which showed 53 mn 53 cr bulk age of olivine that is 10 myr younger than the age of the solar system the calculated cooling rate which is 20 40 c myr at 985 1000 c is in good agreement with the metallographic cooling rate at 500 c when the two results are considered in terms of a cooling model in which the reciprocal temperature increases linearly with time the inferred cooling rate of omolon which seems to be a sample from the core mantle boun dary yields a burial depth of 30 km in a parent body of at least 100 km radius

westward propagation of the north anatolian fault into the northern aegean timing and kinematics we present new evidence for the propagation processes of the north anatolian fault folding in the dardanelles straits region allows us to document the timing of the deformation preceding and the finite displacement after the passage of the propagating tip of the fault the accuracy of the observations is due to interplay between deformation and the sea level changes in the mediterranean the well known messinian regression followed by the pliocene transgression the long term kinematics around the sea of marmara pull apart total displacement of about 85 km over the past 5 m y is similar to the present day kinematics deduced from space geodesy at a larger scale westward propagation of the north anatolian fault over nearly 2000 km in the past 10 m y appears to be associated with strain recovery suggesting that the continental lithosphere retains long term elasticity

oriented chromite diopside symplectic inclusions in olivine from lunar regolith delivered by luna 24 mission abstract calcium chromium rich lamellae in olivine grain no 1611 from the luna 24 regolith were studied with feg empa and tem the lamellae consist of a worm like intergrowth of fecr 2 o 4 chromite chr and camgsi 2 o 6 diopside di with a chr di modal proportion of 1 3 the linear extension of the lamellae and crystallographic orientation relationships among the symplectite phases and the olivine suggest that the lamellae nucleated at deformation defects in the olivine host calcium depletion haloes surrounding the lamellae amount to about 75 m and indicate that the chromite diopside lamellae were formed by segregation of calcium and chromium from the host olivine into the lamellae without addition of calcium and or chromium from outside the olivine the segregation of calcium and chromium and consequently the growth of the symplectic lamellae were diffusion controlled the segregation of a calcium chromium component from the host olivine was associated with oxidation of divalent to trivalent chromium oxidation was facilitated by dehydrogenation which was driven by decompression and or a change in redox potential hydrogen point defects in the original olivine with h substituting for divalent cations on the m sites provided the necessary electron acceptors for the oxidation of chromium and after electron transfer left olivine as molecular h 2 the internal microstructure of the lamellae suggests that exsolution of the calcium chromium rich lamellae from the host olivine and formation of the chromite diopside symplectic intergrowth occurred simultaneously the time scale derived from diffusion modeling of the calcium depletion haloes around the lamellae indicates a thermal event on the order of several months to several hundred years at most symplectic inclusions found in olivine from lunar martian and terrestrial rocks are similar with respect to their shape crystallographic orientation relationships and internal microstructure of the spinel clinopyroxene intergrowth these features are inconsistent with dry olivine oxidation that is by the uptake of oxygen dehydrogenation of oh bearing precursor olivine is suggested as a general mechanism of oxidation accompanied by chemical segregation and phase separation resulting in symplectite formation

detection of structurally bound hydroxyl in fluorapatite from apollo mare basalt 15058 128 using tof sims fluorapatite grains from apollo 15 mare basalt 15058 128 were analyzed by raman spectroscopy raman spectral imaging time of flight secondary ion mass spectrometry tof sims field emission scanning electron microscopy fe sem and electron probe microanalysis epma in an attempt to detect structurally bound oh in the fluorapatite although oh could not be definitively detected by raman spectroscopy because of ree induced photoluminescence hydroxyl was detected in the fluorapatite by tof sims the tof sims technique is qualitative but capable of detecting the presence of hydroxyl even at trace levels electron microprobe data indicate that on average f and cl f cl fill the monovalent anion site in these fluorapatite grains within the uncertainties of the analyses about 0 07 0 01 atoms per formula unit however some individual spot analyses have f cl deficiencies greater than analytical uncertainties that could represent structural oh on the basis of epma data the fluorapatite grain with the largest f cl deficiency constrains the upper limit of the oh content to be no more than 4600 2000 ppm by weight the equivalent of 2400 1100 ppm water the tof sims detection of oh in fluorapatite from apollo sample 15058 128 represents the first direct confirmation of structurally bound hydroxyl in a lunar magmatic mineral this result provides justification for attributing at least some of the missing structural component in the monovalent anion site of other lunar fluorapatite grains to the presence of oh moreover this finding supports the presence of dissolved water in lunar magmas and the presence of at least some water within the lunar interior

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

shock and annealing in the amphibole and mica bearing r chondrites mil 11207 r6 and lap 04840 r6 contain hornblende and phlogopite mil 07440 r6 contains accessory titan phlogopite and no hornblende all three meteorites have been shocked mil 11207 contains extensive sulfide veins pyroxene that formed from dehydrated hornblende and an extensive network of plagioclase glass mil 07440 contains chromite plagioclase assemblages chromite veinlets and blebs pincer shaped plagioclase patches but no sulfide veins lap 04840 contains olivine grains with chromite bleb laden cores and opaque free rims rare grains of pyroxene that formed from dehydrated hornblende and no sulfide veins these meteorites appear to have been heated to maximum temperatures of approximately 700 900 c under conditions of moderately high ph2o perhaps 250 500 bars all three samples underwent postshock annealing during this process olivine crystal lattices healed giving the rocks the appearance of shock stage s1 and diffusion of fe and s from thin sulfide veins to coarse sulfide grains caused the veins to disappear in mil 07440 and lap 04840 this latter process apparently also occurred in most s1 s2 ordinary chondrites of high petrologic type the pressure temperature conditions responsible for forming the amphibole and mica in these rocks may have been present at depths of a few tens of kilometers as suggested in the literature a giant impact or a series of smaller impacts would then have been required to excavate the hornblende and biotite bearing rocks and bring them closer to the surface it was in that latter location where the samples were shocked deposited in a hot ejecta blanket of low thermal diffusivity and annealed

testing the physical oceanographic implications of the suggested sudden black sea infill 8400 years ago 1 we apply a shock capturing numerical model based on the single layer shallow water equations to an idealized geometry of the black sea and the sea of marmara in order to test the implications of a suggested sudden black sea infill 8400 years ago the model resolves the two dimensional flow upstream and downstream of the hydraulic jump provoked by the cascade of water from the sea of marmara into the black sea which would occur during a sudden black sea infill the modeled flow downstream of the hydraulic jump in the black sea would consist of a jet that is in part constrained by bathymetric contours guided by the bosporus canyon the modeled jet reaches depths of up to 2000 m and could explain the origin of the sediment waves observed at this depth at a late stage of the infill the modeled jet is attached to the coast and might account for the course of a submerged channel at the mouth of the bosporus the preservation of continuous barrier washover lagoonal fill systems occurring on the black sea shelf is however not easily reconcilable with the large flows over the southwest black sea shelf predicted by the model intensified flow in the upstream basin sea of marmara is restricted to the immediate vicinity of the bosporus suggesting that a sudden reconnection need not have disturbed sediments in the wider sea of marmara

instability of deformation this chapter addresses the mechanisms by which instabilities can develop in rocks in the nominally ductile regime under conditions that the authors believe are relevant to earth we will not address brittle failure or frictional sliding processes in detail but much of our discussion will be couched in terms of knowledge gained in studies of these processes as a consequence we will begin by discussing why brittle failure and frictional sliding cannot be the mechanism by which rocks become unstable at depth despite the strong evidence that they are the underlying mechanism of earthquakes at shallow depths e g scholz 1990 2002 brittle shear failure in the normal sense is fundamentally a tensile process tensile microcracks must first nucleate and self organize via interaction of the stress concentrations at their tips as a consequence brittle failure and frictional sliding are strongly inhibited by pressure because work must be done against the pressure to open the mode i cracks the inhibition is so strong that the stress required to create a fault or initiate sliding on an existing fault becomes greater than the room temperature flow stress of many rocks at pressures equivalent to only a few tens of kilometers in earth increasing temperature has little effect on brittle processes but in contrast the ductile flow stress of rocks falls exponentially with temperature because both pressure and temperature increase with depth in earth earthquakes by unassisted brittle fracture mechanisms or frictional sliding can only occur at depths less than 30 50 km nevertheless earthquakes occur to depths of almost 700 km in earth and seismological evidence demonstrates unequivocally that they occur by displacement across a surface or narrow zone i e they occur by faulting this conundrum can be explained qualitatively by certain specific types of mineral reactions occurring under certain restricted conditions the

oscillating quaternary water levels of the marmara sea and vigorous outflow into the aegean sea from the marmara sea black sea drainage corridor abstract detailed interpretation of single channel air gun and deep tow boomer profiles demonstrates that the marmara sea turkey experienced small amplitude 70 m fluctuations in sea level during the later quaternary limited in magnitude by the sill depth of the strait of dardanelles moderate subsidence along the southern shelf and quaternary glacio eustatic sea level variations created several stacked deltaic successions separated by major shelf crossing unconformities which developed during the transitions from global glacial to interglacial periods near the strait of dardanelles a series of sand prone deposits are identified beneath an uppermost holocene transparent mud drape the sandy deposits thicken into mounds with the morphology and cross sectional geometries of barrier islands sand waves and current generated marine bars all cross stratification indicates unidirectional flow towards the dardanelles prior to the deposition of the transparent drape which began 7000 years bp in strong support of the notion that the marmara sea flowed westwards into the aegean sea through the dardanelles at times of deglaciation in northern europe the global sea level curve shows that at 11 000 and 9500 years bp sea level rose to the sill depths of the straits of dardanelles and bosphorus respectively the effect from 11 000 to 9500 years bp was seawater incursion into the marmara sea drowning and formation of algal serpulid bioherms atop lowstand barrier islands and transgression of shelves and lowstand deltas at 9500 years bp glacial meltwater temporarily stored in the black sea lake developed into a vigorous southward flow toward the aegean sea forming west directed sandy bedforms in the western marmara sea and initiating deposition of sapropel s1 in the aegean sea this strong outflow persisted until 7000 years bp after which a mud drape began to accumulate in the marmara sea and euryhaline mediterranean mollusks successfully migrated into a progressively more saline black sea where sapropel deposition began most eastern mediterranean sapropels from s1 to s11 appear to correlate with periods of rising sea level and breaching or near breaching of the bosphorus sill these events are believed to coincide with times of vigorous outflow of low salinity fresh surface waters transiting the black sea marmara sea corridor and ultimately derived from melting of northern european ice sheets

weathering of gneissic rocks in the upper reaches of cauvery river south india implications to neotectonics of the region in the upper reaches of the cauvery catchment area in southern india the archean peninsular gneisses exhibit a greater degree of weathering in the field relative to the massive charnockites and granites although the gneisses have been physically broken down along foliation planes fractures and compositional discontinuities secondary mineral such as chlorite smectite kaolinite and fe oxyhydroxide formation is insignificant consequently there is little chemical change even up to the stage of saprolite development only in the regolith there is some loss of ca na sr ba mg and sio2 other elements such as fe mn al cr ni and ree all show enrichment relative to tio2 in areas which have developed profiles by in situ weathering the chondrite normalized ree patterns however show little change excepting a slight flattening of the patterns because of greater hree mobility during weathering clay minerals also have flattened ree patterns because of relative hree enrichment the depletion and the enrichment of different elements appear to be related to mild leaching of primary mafic minerals by meteoric water rather than by mineral breakdown this and the extent of variation in chemical index of alteration values suggest that that the gneisses have suffered only incipient chemical weathering for the extent of physical weathering undergone by them it is likely that this contrasting weathering extents of these 2500 ma rocks is due to their exposure to surface geological processes only recently because of ongoing periodic uplift and physical erosion of this region

the influence of t asio2 and fo2 on exsolution textures in fe mg olivine an example from augite syenites of the ilimaussaq intrusion south greenland two samples from the augite syenite unit of the 1 13 ga alkaline to peralkaline ilimaussaq intrusion in south greenland contain olivine fa 75 85 with micrometer sized exsolution lamellae of intergrown augite and magnetite the exsolved olivine contains only about 0 6 wt cao whereas the reintegrated magmatic composition contained about 1 4 cao corresponding to about 3 mol of a larnite la component the exsolved olivine bears no measurable na al or ti but the reintegrated magmatic olivine contained up to 0 4 wt na 2 o 0 2 wt al 2 o 3 and 0 3 wt tio 2 magmatic baddeleyite in the same samples indicates an extremely low silica activity of below 0 4 during the early stages of magmatic crystallization at 900 c and 1 kbar according to the equilibrium ca 2 sio 4 la in ol sio 2 2 casio 3 wo in cpx the low silica activity is thought to be responsible for the unusually ca rich compositions of the primary olivines which in these samples formed at 875 15 c and at oxygen fugacities between 1 2 and 2 3 log units below the qfm buffer the composite exsolution lamellae formed during cooling due to an overstep of the schematic reaction fa kst ca rich component in olivine 1 3 o 2 hd 2 3 mt phase equilibria indicate temperatures between 300 and 750 c and oxygen fugacities close to qfm for this exsolution process the lamellae only developed in samples where the olivines were both especially high in ca and presumably rapidly cooled although not chilled as the lamella bearing samples were collected at the outermost rim of the augite syenite unit and close to the top of the ilimaussaq intrusion schreinemakers analysis shows that ca rich olivine of the kirschsteinite monticellite solid solution series ca fe mg sio 4 would exsolve from ca bearing olivine of the fayalite forsterite series only at unusually low silica activities whereas at higher silica activities the observed exsolutions of clinopyroxene with magnetite are more stable hence both cooling history and evolution of intensive variables during cooling are important for the formation of olivine exsolution textures

holocene sea level oscillations and environmental changes on the eastern black sea shelf abstract a multi proxy study of four sediment cores from the eastern caucasian black sea shelf revealed five transgressive regressive cycles overprinted on the general trend of glacioeustatic sea level rise during the last 11 000 14c yr these cycles are well represented in micro and macrofossil assemblages sedimentation rates and grain size variations the oldest recovered sediments were deposited in the neoeuxinian semi freshwater basin 10 500 9000 14c yr bp and contain a caspian type mollusk fauna dominated by dreissena rostriformis low 18o and 13c values are measured on this species the first appearance of marine mollusks and ostracodes from the mediterranean is established in this part of the black sea at 8200 14c yr bp i e about 1000 2000 yr later than the appearance of marine microfossils in the deeper part of the sea the early holocene bugazian to vityazevian condensed section of shell and shelly mud sediments with at least two hiatuses represent a high energy shelf edge facies it contains a transitional assemblage representing a mixture of caspian and mediterranean fauna this pattern suggests a dual flow regime via the bosphorus after 8200 14c yr bp caspian species disappear and oligohaline species decrease in abundance during the vityazevian prekalamitian cycle later during the middle to late holocene low sea level stands are characterized by shell layers whereas silty mud with various mollusk and ostracode assemblages rapidly accumulated during transgressions restricted mud accumulation as well as benthic faunal composition and abundance suggest high energy and well ventilated bottom water during low sea level stands a trend of 18o enrichment in mollusk shells points to an increase in bottom water salinity during the vityazevian to kalamitian transgressions 7000 to 5700 14c yr bp due to a more open connection with the mediterranean while a pronounced increase in polyhaline species abundance is established during the kalamitian to djemetean transgressions 6400 to 2700 14c yr bp however the composition of the faunal assemblage indicates that bottom water salinity never exceeded modern values of 18 20 psu

early holocene marine flooding of the black sea abstract echo sounding data recorded in the black sea in 1969 imaged a chain of hills 5 to 150 m high at a depth of 2000 2200 m that resemble hills on the lower continental rise like those hills the features in the western black sea may have been created by bottom currents the easterly flowing currents inferred to have formed the hills may be related to a catastrophic flood of the black sea from the sea of marmara 7150 yr ago

mineralogical and chemical changes of soil and stream sediment formed by intense weathering of the danburg granite georgia u s a abstract a series of soil and stream sediments developed during intense weathering on the metaluminous danburg granite northeastern georgia u s a have been analyzed mineralogically and chemically the concentrations of ba na rb and cs in the silt and coarser fractions are controlled mainly by feldspars and biotite hf is controlled by zircon and the ree rare earth elements and th are largely controlled by sphene variations in feldspar sphene and zircon may produce small variations in eu sm and la lu ratios ferromagnesian minerals control ta fe co sc and cr concentrations the mineralogical and chemical composition of the danburg granite is more closely reflected in the silt than in the sand or gravel fractions of stream sediments in the silt the contents of rb ree th ta fe co and sc and the ratios of la sc th sc la co th co eu sm and la lu are similar to those in the unweathered granite in contrast these element contents or ratios in the sands and gravels are 0 05 3 the concentration in the unweathered granite ta and ba contents are an exception to the above the ta and ba contents of the sands and gravels are similar to those of the granite in the kaolinite halloysite clays the content of na is depleted relative to the source rb cs ba hf and ta are depleted or enriched in the clays relative to the source while the ree th fe co sc and cr are enriched the eu sm eu anomaly size and la lu ratios and the ree patterns of the clays are similar to those of the source thus the mineralogy and element contents of a siltstone developed from metaluminous granitic sources during intense weathering would be expected to be more similar to the source rock than the sandstones and conglomerates claystones should contain similar ree patterns and eu sm ratios as the source rock but such fine grained sediments might represent much larger areas of source rocks than the more locally derived sandstones or conglomerates

modern and holocene sublittoral ostracod assemblages crustacea from the caspian sea a unique brackish deep water environment abstract we present a reconnaissance study of sublittoral ostracods from a number of caspian sea core tops collected during a joint french russian scientific cruise in 1994 cores from between 13 and 875 m water depth the modern ostracods show little depth restriction and this reflects the hydrography of the caspian sea which maintains relatively constant conditions 5 c 13 salinity below 50 m throughout the year we also present the ostracod faunal record from a 10 m core of laminated sediments recovered from the central caspian basin at a water depth of 475 m which we believe shows repetitive quasi cyclic changes in bottom water conditions over approximately the last 14 15 000 years with a major change at about the late glacial to holocene transition the faunal record from this core illustrates the potential of these sediments for reconstructing environmental changes in the caspian region during the late quaternary to holocene the continuous occurrence of in situ benthic meiofauna throughout the core also indicates that the bottom water must have remained ventilated throughout this period although variability in the faunal assemblages may reflect long and short term changes in the strength of ventilation

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

distribution of ree and trace elements in size and mineral fractions of high purity quartz sands eight sample sets raw quartz sand quartz fraction 2 m clay fraction 2 20 m fraction and heavy minerals of the cretaceous quartz sand deposits of haltern and weferlingen central germany and the tertiary quartz sand of frechen western germany were studied to characterize the distribution of ree and trace elements and to get genetic information about provenance and sedimentologic history of the sediments the quartz sand samples from different localities have rather similar trace element distribution and ree patterns with enriched lree and negative eu anomalies however these relations can be modified by local changes in syn or postsedimentary geochemical conditions adsorption of ree and trace elements on humic substances under reducing conditions and postsedimentary weathering in the quartz sand of weferlingen resulted in significantly modified element abundances the concentration of trace elements is most important in the 2 m fraction and in the heavy mineral fraction where they may be enriched by a factor of up to 100 the chondrite normalized ree distribution of the 2 m fraction is quite similar to those in the north american shale nas with average eu sm ratios of 0 21 and layb cn of 6 1 low trace element abundances in the 2 and 2 20 m fractions were attributed to quartz dilution and quantified among the common minerals in the heavy mineral fractions especially zircon and the fe 1bti oxides rutile ilmenite magnetite influence the trace element distribution investigations concerning the provenance of the quartz sands illustrate that the host sediments have a rather homogeneous geochemical signature due to their sedimentological history taking into account th ta variations the quartz sands of weferlingen and haltern can be distinguished from the frechen quartz sand additionally discriminations based on element ratios within the quartz fraction th sc ba sc ba co cs sc or li sc seem to be promising

seismic stratigraphy of late quaternary deposits from the southwestern black sea shelf evidence for non catastrophic variations in sea level during the last 10 000 yr abstract detailed interpretation of single channel seismic reflection and huntec deep tow boomer and sparker profiles demonstrates that the southwestern black sea shelf formed by a protracted shelf edge progradation since the miocene pliocene five seismic stratigraphic units are recognized unit 1 represents the last phase of the progradational history and was deposited during the last glacial lowstand and holocene it is divided into four subunits subunit 1a is interpreted as a lowstand systems tract 1b and 1c are interpreted as a transgressive systems tract and subunit 1d is interpreted as a highstand systems tract the lowstand systems tract deposits consist of overlapping and seaward prograding shelf edge wedges deposited during the lowstand and the subsequent initial rise of sea level these shelf edge wedges are best developed along the westernmost and easternmost segments of the study area off the mouths of rivers the transgressive systems tract deposits consist of a set of shingled shore parallel back stepping parasequences deposited during a phase of relatively rapid sea level rise and include a number of prograded sediment bodies including barrier islands beach deposits and thin veneers of seismically transparent muds showing onlap onto the flanks of older sedimentary features a number of radiocarbon dates from gravity cores show that the sedimentary architecture of unit 1 contain a detailed sedimentary record for the post glacial sea level rise along the southwestern black sea shelf these data do not support the catastrophic refilling of the black sea by waters from the mediterranean sea at 7 1 ka postulated by ryan pitman major shimkus maskalenko jones dimitrov gorur sakinc yuce mar geol 138 1997 119 126 ryan pitman touchstone book 1999 319 pp and ballard coleman rosenberg mar geol 170 2000 253 261

promotion of chemical weathering by higher plants field observations on hawaiian basalts abstract an electron microprobe and petrographic microscope were used to study the biota rock interface beneath higher plant communities and lichens as well as unvegetated surfaces on hawaiian basalt flows ranging from a few years to several thousand years in age and currently receiving moderate to extremely high annual rainfall we find dramatic order of magnitude minimum acceleration of weathering rates beneath vascular plants on the youngest flows relative to adjacent non or primitively vegetated controls notably rocks colonized by the common fruticose lichen stereocaulon uulcani bulk dissolution of plagioclase accounts for most of the weathering observed beneath higher plants on these young basalts analysis of older flows under mature forests reveals that chemical weathering beneath vascular plant communities continues unabated for thousands of years after initial colonization moreover such weathering is not limited to exterior basalt surfaces but is commonly found adjacent to joints and vesicles within the rock where it is often associated with fine sub 2 mm diameter plant roots plagioclase dissolution was also observed on lichen encrusted and unvegetated flows a few hundred to thousands of years in age but it was typically much less advanced than beneath higher plants and rarely extended more than several millimeters from exterior rock surfaces chemical denudation rates on older flows with higher plants are at minimum ten times greater than those with only lichens or microbiota in the environments studied if s uulcani and associated microflora resemble the terrestrial precursors to vascular plant communities then the results of studies such as this have implications for the history of atmospheric co 2 and the earth s climate

geomorphic characterization and diversity of the fluvial systems of the gangetic plains the extensive gangetic alluvial plains are drained by rivers which differ strongly in terms of hydrological and sediment transport characteristics these differences are manifested in the geomorphic diversity of the plains the western gangetic plains wgp are marked by a degradational topography with incised channels and extensive badland development in some parts while the eastern gangetic plains egp are characterized by shallow aggrading channels with frequent avulsions and extensive flooding we interpret such geomorphic diversity in terms of differences in stream power and sediment supply from the catchment areas the rivers draining the western plains are marked by higher stream power and lower sediment yield that result in degradation in comparison the rivers draining the eastern gangetic plains have lower stream power and higher sediment yield that result in aggradation the variation of stream power a function of channel slope and high sediment yield is attributed to differences in rainfall and rate of uplift in the hinterland it is suggested that such differences have resulted in a marked geomorphic diversity across the plains it is also suggested that such diversity has existed for a fairly long time because of climatic and tectonic variance

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

discontinuity bounded alluvial sequences of the southern gangetic plains india aggradation and degradation in response to monsoonal strength abstract discontinuity bounded late quaternary sequences in the southern gangetic plains himalayan foreland basin reflect floodplain aggradation and degradation in response to forcing by the powerful southwest indian monsoon the major himalayan and cratonic rivers in this area occupy narrow incised valleys and do not inundate the adjoining broad interfluves which display soil development small plains fed rivers lakes eolian deposits and badland ravines however these areas formerly experienced active alluviation because thick floodplain muds underlie the interfluve an age model suggests that interfluve areas near the major rivers aggraded periodically between about 27 ka and 90 ka marine oxygen isotope stages 3 5 they subsequently degraded or accumulated sediment only locally probably reflecting decreased monsoonal precipitation around the last glacial maximum marine isotope stage 2 when major river valleys moved to an underfit condition increased precipitation during the 15 to 5 ka period of monsoon recovery probably increased discharge and promoted incision and widespread badland formation discontinuities at deeper levels reflect earlier degradation phases and are marked by reworked gravel lenses thin channel bodies and carbonate cemented surfaces carbonate veins infilled joints that cut strata below but not above one discontinuity suggest some local tectonic influence there is no evidence that sea level fluctuations influenced stratal patterns in this elevated inland region discontinuity bounded sequences linked to climate change may characterize alluvial successions in many continental settings especially along the cratonic margins of foreland basins where subsidence rates are modest

prompt transgression and gradual salinisation of the black sea during the early holocene constrained by amino acid racemization and radiocarbon dating abstract the restricted environment of the black sea is particularly sensitive to climatic and oceanographic fluctuations owing to its connection with the mediterranean sea via the narrow bosphorus strait the exact mechanism and timing of the most recent connection between these water bodies is controversial with debate on the post glacial history of the black sea being dependent on radiocarbon dating for numerical ages here we present new 23 accelerator mass spectrometer ams radiocarbon ages on peat and bivalve molluscs supported by the first amino acid racemization aar dating of bivalve molluscs n 66 in the black sea these data indicate infilling of the black sea during the early holocene from an initial depth 107 m below sea level and 72 m below that of the bosphorus sill these data combined with a review of previous radiocarbon ages has enabled a unique perspective on the post glacial black sea a sea level curve based on conventional and ams radiocarbon ages on peat and ams based ages on dreissena sp shells indicate the water level in the earlier lake phase continued until the early holocene to be lower than the bosphorus sill after the younger dryas ended however the absence of ams dated mollusc ages from the shelves of this basin older than the younger dryas is suggestive of sub aerial exposure of the shelves and comparatively lower water levels when the younger dryas began thus post glacial outflow from the black sea occurred through a lowered or open bosphorus seaway basin wide radiocarbon ages on peat indicate a prompt increase in water level from that of the pre existing and unconnected palaeo lake during the earliest holocene 9600 9200 cal a bp mass colonisation of the black sea by mediterranean taxa did not occur until salinity had risen sufficiently a process which took 1000 a or more from the initial transgressive event this gradual change in salinity contrasts with the prompt transgression which would have taken 400 a to occur

rare earth elements in the sedimentary cycle a pilot study of the first leg the effects of source rock composition and climate on the natural abundances of rare elements ree in the first leg of the sedimentary cycle are evaluated using a study with holocene fluvia sands the medium grained sand fraction of samples collected from first order streams exclusively draining granitic plutons in montana semi arid georgia humid and south carolina humid are analyzed it is found that the ree distribution patterns but not the total absolute abundances of the daughter sands are very similar despite compositional differences between parent plutons averages of the three areas are determined to have a la lu ratio of about 103 showing a depletion of heavy ree with respect to an average granite la lu 79 or the composition of north american shales la lu 55 however the eu sm ratio in sands from these areas is about 0 22 which is very close to this ratio in north american shales 0 21 although the overall ree distribution of these sands is not similar to that of the north american shales in any way it is concluded that the major rock type but neither its minor subdivisions nor the climate controls the ree distribution patterns in first cycle daughter sands although the total and the parent rock normalized abundances of ree in sands from humid areas are much lower than those in sands from arid areas

arrested charnockite formation at kottavattam southern india at kottavattam southern kerala india late proterozoic homogeneous leptynitic garnet biotite gneisses of granitic composition have been transformed on a decimetric scale into coarse grained massive charnockite sensu stricto along a set of conjugate fractures transecting the gneissic foliation charnockitization post dates the polyphase deformation regional high grade metamorphism and anatexis and evidently occurred at a late stage of the pan african tectonothermal history geothermobarometric and fluid inclusion data document textural and chemical equilibration of the gneiss and charnockite assemblages at similar p lith t conditions 650 700 degrees c 5 6kbar in the presence of carbonic fluids internally buffered by reaction with graphite and opaque mineral phases x co2 0 7 0 6 x h2o 0 2 0 3 x n2 0 1 logf o2 l7 5 mineralogical zonation indicates that charnockitization of the leptynitic gneiss involved first the breakdown of biotite and oxidation of graphite in narrow outward migrating transition zones adjacent to the gneiss followed by the breakdown of garnet and the neoblastesis of hypersthene in the central charnockite zone compared to the host gneiss the charnockite shows higher concentrations of k na sr ba and zn and lower concentrations of mg fe ti v y zr and the hree with a complementary pattern in the narrow transition zones of biotite breakdown the p lith t x h2o data and chemical zonation patterns indicate charnockitization through subsolidus dehydration reaction in an open system subsequent residence of the carbonic fluids in the charnockite resulted in low grade alteration causing modification of the syn charnockitic elemental distribution patterns and the properties of entrapped fluids we favour an internally controlled process of arrested charnockitization in which during near isothermal uplift the release of carbonic fluids from decrepitating inclusions in the host gneiss into simultaneously developing fracture zones led to a change in the fluid regime from fluid absent in the gneiss to fluid present in the fracture zones and to the development of an initial fluid pressure gradient triggering the dehydration reaction

clay minerals in soils as evidence of holocene climatic change central indo gangetic plains north central india clay mineral assemblages of a soil chrono association comprising five fluvial surface members qgh1 to qgh5 of the indo gangetic plains between the ramganga and rapti rivers north central india demonstrate that pedogenic interstratified smectite kaolin sm k can be considered as a potential indicator for paleoclimatic changes during the holocene from arid to humid climates on the basis of available radiocarbon dates thermoluminescence dates and historical evidence tentative ages assigned to qgh1 to qgh5 are 500 yr b p 2500 yr b p 8000 tl yr b p and 13 500 tl yr b p respectively during pedogenesis two major regional climatic cycles are recorded relatively arid climates between 10 000 6500 yr b p and 3800 yr b p were punctuated by a warm and humid climate biotite weathered to trioctahedral vermiculite and smectite in the soils during arid conditions and smectite was unstable and transformed to sm k during the warm and humid climatic phase 7400 4150 cal yr b p when the humid climate terminated vermiculite smectite and sm k were preserved to the present day the study suggests that during the development of soils in the holocene in alluvium of the indo gangetic plains climatic fluctuations appear to be more important than realized hitherto the soils older than 2500 yr b p are relict paleosols but they are polygenetic because of their subsequent alterations

reduced chromium in olivine grains from lunar basalt 15555 x ray absorption near edge structure xanes the oxidation state of cr in 200 mu m regions within individual lunar olivine and pyroxene grains from lunar basalt 15555 was inferred using x ray absorption near edge structure xanes reference materials had previously been studied by optical absorption spectroscopy and included cr bearing borosilicate glasses synthesized under controlled oxygen fugacity and cr doped olivines the energy dependence of xanes spectral features defined by these reference materials indicated that cr is predominantly divalent in the lunar olivine and trivalent in the pyroxene these results coupled with the apparent f sub o sub 2 independence of partitioning coefficients for cr into olivine imply that the source magma was dominated by divalent cr at the time of olivine crystallization 29 refs 8 figs 1 tab