microscale isotopic zonation in graphite crystals evidence for channelled co influx in granulites abstract coarse graphite in association with cordierite and quartz within a vein in a metapelite locality at chittikara cht in southern india illustrates precipitation of graphite from co 2 rich fluids carbon isotope traverses within individual graphite crystals using a microsampling technique reveal strong isotopic zonations in graphite crystal from the vein with 13 c values oscillating between 13 in the core and 8 5 in the rim co 2 trapped within fluid inclusions in the cordierite shows 13 c 5 suggesting isotopic equilbrium with the core composition of the graphite a graphite crystal from the metapelite immediately adjacent to the vein is also zoned with a smooth rimward increase in 13 c disseminated graphite flakes in the host metapelites ca 1 m from the vein are however unzoned and possess strongly negative 13 c values 34 4 the rimward increase in 13 c the absence of other carbon bearing phases and the sluggish exchange rates for carbon in graphites preclude diffusive re equilibration and suggest that the different zoning patterns in the coarse graphite flakes within and adjacent to the vein assemblage at cht have resulted from precipitation in different parts of a highly channelled fluid regime where fluids are non wetting and move episodically by a hydraulic fracture mechanism our study provides the first unambiguous insight into graphite precipitation mechanisms and has potential implications for the nature of fluid interconnectivity and co 2 transport and equilibration length scales within the crust

stratigraphy and origin of an area of hummocky glacial topography northern wisconsin u s a abstract the winegar phase of the wisconsin glaciation produced a band of hummocky glacial topography in northern wisconsin some hummocks are composed of flow till and somewhat sorted till like debris flow sediment these hummocks formed when ice melted beneath a cover of debris that flowed to its present position other hummocks contain interlayered lodgement and meltout till flow till debris flow and slopewash sediment lake and meltwater stream sediment these hummocks formed where sediment was stacked near the ice margin in other hummocks till and supraglacial debris flow and slopewash sediment deposited during the winegar phase form a thin veneer over older meltwater stream sediment these hummocks formed when ice buried in pre winegar phase stream sediment melted and the overlying sediment collapsed

complex kame belt morphology stratigraphy and architecture the development of glacier karst at the margins of melting ice sheets produces complex glaciofluvial sediment landform assemblages that provide information on ice sheet downwasting processes we present the first combined geomorphological sedimentological and geophysical investigation of the brampton kame belt an important glaciofluvial depositional zone at the centre of the last british irish ice sheet ground penetrating radar gpr data allow the broad scale internal architecture of ridges eskers and flat topped hills ice walled lake plains to be determined at four sites in combination with sediment exposures these provide information on lateral and vertical variations in accretion styles depositional boundaries and grain size changes building on existing work on the subject we propose a refined model for the formation of ice walled lake plains resulting from the evolution and collapse of major drainage axes into lakes as stable glacier karst develops during deglaciation the internal structure of esker ridges demonstrates variations in sedimentation that can be linked to differences in ridge morphologies across the kame belt this includes low energy flow conditions and multiple accretion phases identified within large s n oriented esker ridges and fluctuating water pressures hyperconcentrated flows and significant deformation within a fragmented sw ne oriented esker ridge in combination with updated geomorphological mapping this work allows us to identify two main styles of drainage within the kame belt 1 major drainage axes aligned broadly s n that extend through the entire kame belt and collapsed into a chain of icewalled lakes and 2 a series of smaller fragmented sw ne aligned esker ridges that represent ice marginal drainage as the ice sheet receded south eastwards up the vale of eden our study demonstrates the importance of integrated geomorphological sedimentological and geophysical investigations in order to understand complex and polyphase glaciofluvial sediment landform assemblages

an exotic mesoarchean microcontinent the coorg block southern india abstract sandwiched between the dharwar craton in the north and the neoarchean proterozoic crustal blocks to the south the coorg block in southern india is composed dominantly of a suite of arc magmatic rocks including charnockites ttg tonalite trondhjemite granodiorite related granitoid suite and felsic volcanic tuffs together with minor accreted oceanic remnants along the periphery of the block coeval mafic and felsic magmatism with magma mixing and mingling in an arc setting is well represented in the block here we present the petrology geochemistry zircon u pb geochronology and lu hf isotopes of all the major lithologies from this block computation of metamorphic p t conditions from mineral chemical data shows consistent granulite facies p t conditions of 820 870 c and up to 6 kbar our geochemical data from major trace and ree on representative samples of the dominant rock types from the coorg block corroborate an arc related signature with magma generation in a convergent margin setting the zircon data yield weighted mean 207pb 206pb ages of 3153 4 9 to 3184 0 5 5 ma for syenogranites 3170 3 6 8 ma for biotite granite 3275 5 1 ma for trondhjemite 3133 12 to 3163 8 6 9 ma for charnockites 3156 10 to 3158 3 8 2 for mafic enclaves 3161 16 ma for diorite and 3173 16 ma for felsic volcanic tuff an upper intercept age of 3363 59 ma and a lower intercept age of 2896 130 ma on zircons from a charnockite as well as an evaluation of the th u values of the zircon domains against respective 207pb 206pb ages suggest that the mesoarchean magma emplacement which probably ranged from 3 3 to 3 1 ga was immediately followed by metamorphism at ca 3 0 to 2 9 ga the ages of magmatic zircons from the charnockites and their mafic granulite enclaves as well as those from the volcanic tuff and biotite granite are all remarkably consistent and concordant marking ca 3 1 ga as the peak of subduction related crust building in this block within the tectonic milieu of an active convergent margin the majority of zircons from the coorg rocks show hf isotope features typical of crystallization from magmas derived from juvenile sources their hf crustal model ages suggest that the crust building might have also involved partial recycling of basement rocks as old as ca 3 8 ga the crustal blocks in the southern granulite terrane in india preserve strong imprints of major tectonothermal events at 2 5 ga 2 0 ga 0 8 ga and 0 55 ga associated with various subduction accretion collision or rifting events however the coorg block is exceptional with our data suggesting that none of the above events affected this block importantly there is also no record in the coorg block for the 2 5 ga pervasive regional metamorphism that affected all the other blocks in this region the geochronological data raise the intriguing possibility that this block is an exotic entity within the dominantly neoarchean collage in the northern domain of the southern granulite terrane of india the mesoarchean arc related rocks in the coorg block suggest that the magma factories and their tectonic architecture in the early earth were not markedly different from those associated with the modern style plate tectonics

characteristics and evolution of supraglacial ponds on debris covered tasman glacier new zealand supraglacial ponds on tasman glacier new zealand initiated the development of the large tasman lake during the 1980s and still play an important role for ice loss and further terminus disintegration limnological and glaciological measurements between 2001 and 2003 reveal distinct differences between ponds the hydraulic connection of a pond to the englacial water level exerts a key control on whether the pond contributes to longer term terminus disintegration in the earlier stages of pond development ice loss occurs predominantly in the horizontal dimension by subaerial melt subaqueous calving at later stages plays a major role for ice loss during the capture of a pond by the lake substantial limnological changes lead to changes in relative significance and rates of ice loss processes the most important being the change from melting to predominantly calving as a result ice loss accelerated from around 11 m a 1 of melt under partial debris cover to a retreat by calving and melting of 34 m a 1 ice loss at the ponds accounted for only 10 of the surface loss in the lower terminus area but is likely to increase in the future with enlargement and coalescence of ponds

contrasting carbon and oxygen isotopic evolution in metacarbonates from the kerala khondalite belt southern india abstract the kerala khondalite belt is a proterozoic metasupracrustal granulite facies terrain in southern india comprising garnet biotite gneiss garnet sillimanite gneiss and orthopyroxene granulites as major rock types calc silicate rocks and marbles occurring as minor lithologies in the kerala khondalite belt show different mineral assemblages and reaction histories of which indicate a metamorphic p t fluid history dominated by internal fluid buffering during the peak metamorphism followed by external fluid influx during decompression the carbon and oxygen isotopic compositions of calcite from three representative metacarbonate localities show contrasting evolutionary trends the ambasamudram marbles exhibit carbon and oxygen isotope ratios 13c 0 and 18o 20 typical of middle to late proterozoic marine carbonate sediments with minor variation ascribed to the isotopic exchange due to the devolatilization reactions the 13c and 18o values of 9 and 11 respectively for calcite from calc silicate rocks at nuliyam are considerably low and heterogeneous the wollastonite formation here possibly corresponds to an earlier event of fluid infiltration during prograde to peak metamorphism which resulted in decarbonation and isotope resetting further petrologic evidence supports a model of late carbonic fluid infiltration that has partially affected the calc silicate rocks with subsequent isotope resetting more towards the contact between calc silicate rock and charnockite at korani only oxygen isotopes have been significantly lowered 18o 13 and the process involved might be a combination of metamorphic devolatilization accompanied by an aqueous fluid influx supported by petrologic evidence the stable isotope signatures obtained from the individual localities thus indicate heterogeneous patterns of fluid evolution history within the same crustal segment

origins of the ice contact stratified ridges eskers of ireland abstract an extensive system of ridged landforms composed of ice contact stratified sediment was deposited in the central lowland of ireland during the most recent deglaciation 18 000 bp the ridges have been interpreted by others as deposits of an ice sheet drainage system i e eskers and as such have been used with other data to reconstruct the deglacial history the traditional deglaciation model shows systematic retreat of ice from south to north our study which involves an analysis of the ridged landforms using lithofacies sedimentary structures and paleocurrent data in conjunction with the geomorphology indicates that the pattern and nature of the ridges are not compatible with this model and support a new model of deglaciation warren 1991 in which the esker system fo med in an interlobate area during the simultaneous shrinking of two main glacial outflow centers an extensive lake system developed in the lowland between the two outflow centers ridges formed both perpendicular and parallel to ice margins involved both active and stagnating ice are both continuous and segmented beaded and were deposited in subaqueous and subaerial environments almost all of the ridges are associated with lacustrine sediments ice contact ridges are polygenetic and a genetic classification is proposed those that formed perpendicular to the ice margin are termed eskers those that formed parallel are termed moraines distinction between esker types continuous or beaded subglacial tunnel fills fluvial ice channel fills and subaqueous fans and moraine types s baqueous or subaerial is crucial to a reconstruction of the mode and pattern of deglaciation in the central irish lowlands

comment on formation and thrusting in some great valley rocks near the franciscan complex california and implications for the tectonic wedging hypothesis by r a glen

u pb ages of detrital zircons in pacheco pass metagraywackes sierran klamath source of mid cretaceous and late cretaceous franciscan deposition and underplating 1 using laser ablation icp ms techniques u pb ages are reported for 338 detrital zircons separated from four franciscan metagraywacke samples from imbricate thrust sheets cropping out in the pacheco pass area east central california coast ranges structurally higher slabs are clastic quartz albite bearing rocks typified by neoblastic lawsonite jadeitic pyroxene the lowest exposed slab lacks jadeitic pyroxene but contains traces of newly grown pumpellyite and lawsonite in addition to abundant quartz albite studied specimens contain moderate amounts of phengite titanite chlorite stilpnomelane carbonate iron oxides rock fragments and carbonaceous matter these diablo range clastic sediments were deposited in mid cretaceous and late cretaceous time the highest allochthon unit i was deposited after 102 ma unit iv was deposited after 90 102 ma and unit v was deposited after 86 ma metagraywacke depositional accretionary ages within slab iv young upward but ages of the slabs decrease progressively downward in the four sample aggregate most zircons have igneous ages falling in the 135 170 ma range with a smaller population at 85 120 ma the rocks contain rare zircons of middle proterozoic late archean ages a minor source in northern california and nw nevada seems likely for the pacheco pass metagraywackes but the sierran klamath calcalkaline arc provided most of the clastic debris judging by the volcanic nature of lithic clasts in these eastern belt metagraywackes and because massive sierran plutonism occurred at 85 120 ma the abundant 135 170 ma zircons probably were derived chiefly from the eroding comagmatic volcanic arc rather than from the less voluminous jurassic arc plutons

mesozoic transpression transtension subduction and metallogenesis in northern and central california middle paleozoic to middle jurassic terrane assemblies in the klamaths and sierran foothills consist of mafic ultramafic complexes fine grained terrigenous strata derived from previously accreted continental margin belts sutured oceanic terranes reflect c 230 myr of margin parallel slip involving chiefly transtension and transpression quartzofeldspathic clastic rocks and blueschists eclogites are very rare little devolatilization occurred at magmagenic depths hence coeval hydrothermal ore deposits and granitoids are uncommon in contrast nearly head on cretaceous subduction of the farallon plate generated the massive klamath sierra nevada volcanic plutonic arc reflecting dewatering of the eastward descending oceanic lithosphere in the magmagenic zone immature great valley forearc and franciscan trench deposits shed from the arc record c 70 myr of rapid crustal growth au bearing solutions rising from magmagenic depths exsolved from plutons and expelled from heated wall rocks were mobilized attending arc construction precipitation of gold bearing quartz veins occurred where h2o co2 bearing fluids encountered major geochemical discontinuities in the wall rocks

a carbon isotope study of graphites from the kerala khondalite belt southern india evidence for co_ 2 infiltration in granulites field relations of arrested charnockite patches felsic pegmatite dikes and coarse cordierite graphite veins in the granulite facies supracmstal belt of southern kerala suggest paleo fluid channels we have investigated the stable isotopic composition of graphites associated with these structures as well as those in association with charnockites adjacent to calcsilicate horizons the remarkably high delta 13 c values displayed by graphites from the structurally controlled zones 8 6 to 13 4 o together with the narrow spread in individual localities pm 1 2 0 correlate with precipitation from isotopically homogeneous co 2 rich fluids that either infiltrated along structural pathways faults shears or were transferred through magmatic conduits graphites from charnockite calcsilicate associations show extreme 13 c enrichment delta 13 c up to 4 8 changing fluid regimes are detected from up to 5 0 variation in delta 13 c among graphites sampled adjace

raman spectra of carbonaceous material in metasediments a new geothermometer metasedimentary rocks generally contain carbonaceous material cm deriving from the evolution of organic matter originally present in the host sedimentary rock during metamorphic processes this organic matter is progressively transformed into graphite s s and the degree of organisation of cm is known as a reliable indicator of metamorphic grade in this study the degree of organisation of cm was systematically characterised by raman microspectroscopy across several mesozoic and cenozoic reference metamorphic belts this degree of organisation including within sample heterogeneity was quantified by the relative area of the defect band r2 ratio the results from the schistes lustres western alps and sanbagawa japan cross sections show that 1 even through simple visual inspection changes in the cm raman spectrum appear sensitive to variations of metamorphic grade 2 there is an excellent agreement between the r2 values calculated for the two sections when considering samples with an equivalent metamorphic grade and 3 the evolution of the r2 ratio with metamorphic grade is controlled by temperature t along the tinos cross section greece which is characterised by a strong gradient of greenschist facies overprint on eclogite facies rocks the r2 ratio is nearly constant consequently the degree of organisation of cm is not affected by the retrogression and records peak metamorphic conditions more generally analysis of 54 samples representative of high temperature low pressure to high pressure low temperature metamorphic gradients shows that there is a linear correlation between the r2 ratio and the peak temperature t c 445 r2 641 whatever the metamorphic gradient and probably the organic precursor the raman spectrum of cm can therefore be used as a geothermometer of the maximum temperature conditions reached during regional metamorphism temperature can be estimated to 50 c in the range 330 650 c a few technical indications are given for optimal application

time transgressive deposits of repeated depositional sequences within interlobate glaciofluvial esker sediments in koylio sw finland abstract evidence of conspicuous repeated seasonal to annual deposition of glaciofluvial and glaciolacustrine sequences within a structurally complex interlobate esker segment in sw finland is presented the time transgressive overlapping depositional sequences consist of deposits from two successive melt seasons including three vertically stacked lithofacies associations 1 massive to stratified coarse gravels summer deposits 2 trough and ripple cross stratified fine grained deposits autumn to winter deposits and 3 sandy stratified beds spring deposits the depositional environment of each lithofacies association involves a transition from subglacial or submarginal tunnel to a subaqueous re entrant environment which then passes to a proglacial glaciolacustrine environment the study also presents evidence of headward extension of subglacial tunnel deposits related to the rapid shifting of a tunnel expansion point during the increasing spring discharge which occupied the old tunnel exit this mode of annual deposition has not been reported previously in esker studies the good preservation of the rhythmic lithofacies associations is suggested as resulting from interlobate depositional conditions associated with rapidly decaying icestreams therefore the depositional model may provide a key to recognizing time transgressive interlobate eskers that form an important geomorphological and sedimentological record of meltwater activity during the last deglaciation of the fennoscandian and laurentide ice sheets the identification of time transgressive interlobate eskers and associated palaeo icestream behaviour is an essential step forward for more accurate models of ice sheet behaviour and palaeoclimatic reconstructions

mineralogical and isotopic characterization of graphite deposits in the western part of the north qaidam orogen and east kunlun orogen northeast tibetan plateau china abstract medium to high grade metamorphic rocks comprising numerous graphite deposits are widely distributed in the periphery of the qaidam basin northern tibetan plateau china we present textural xrd and raman spectroscopy characteristics of graphite 13c results of graphite and cogenetic calcite and 18o results of calcite in three graphite occurrences located at the periphery of qaidam basin graphite displays hexagonal platy flaky irregular polygonal ovate morphologies with occasional spherulitic textures graphite morphologies combined with xrd and raman spectroscopy indicate that graphite has relatively high crystallinity raman microspectroscopy of graphite shows that peak metamorphic temperatures vary between 690 and 801 c graphite 13cv pdb values range between 26 3 and 21 6 indicating organic carbon as the major carbon source for graphite calcite 13cv pdb and calcite 18ov smow values range between 10 8 and 3 9 and between 6 6 and 29 5 respectively calcite 13cv pdb results show that organic carbon was mixed with inorganic carbon which resulted in an increase of 13cv pdb calcite 18ov smow values indicate that the graphite deposits experienced late stage water rock interaction the positive and negative anomalies of calcite 13cv pdb indicate that organic matter oxidation and recycling locally occurred during the final stage of the great oxidation event the wide distribution of regional metamorphic organogenic graphite deposits provides evidence for large scale paleoproterozoic biological activity in the periphery of the qaidam basin

geochemistry of tectonically expelled fluids from the northern coast ranges rumsey hills california usa tectonic compression has created abnormally high pressure on deep basinal fluids causing their expulsion from areally exposed upper cretaceous rock along the eastern margin of the california coast ranges the fluids emerge as near neutral perennial sodium chloride springs at high elevations with flow rates as high as 10 l per min higher spring discharges are more common around the exposure of a west vergent fault propagation fold axis spring waters range from 1000 to 27 000 mg l tds the least saline water 18o 7 5 closely represents local meteoric water that mixes with saline fluid 18o 5 3 and forms a slope of 3 5 on a d vs 18o plot a na 125 to 8000 mg l vs cl 150 to 17 000 mg l plot shows a linear dilution trend that extends close to but below the values for modern seawater calcium 75 3000 mg l is considerably enriched relative to seawater and forms a nonlinear trend with chloride in detail the na deficit defined by the difference between the measured na content and the na concentration on a hypothetical seawater dilution line is approximately balanced by the ca excess similarly defined by the seawater dilution line this relationship strongly suggests that the fluid is diluted seawater that is being modified by active albitization of plagioclase at different depths simultaneous b and 18o enrichment of the fluids accompanied by deuterium depletion further suggest that the seawater modification is influenced by clay diagenesis bicarbonate and sio2 concentrations show an inverse correlation with cl with most waters being saturated or slightly oversaturated with calcite and quartz at the discharge temperatures some freshwater springs with near meteoric stable isotope values may represent mixing of young groundwater from perched aquifers but in many cases the freshwater springs emerge along the same structures and have the same perennial nature as the saline fluids and expulsion of an older fresh groundwater component that is under abnormal fluid pressures cannot be ruled out basinal fluids elsewhere commonly show dilution trends with local meteoric water and in the case of the rumsey hills some of the dilute saline waters may indicate deep penetration of meteoric water 1 km in the pleistocene before the latest tectonic uplift geothermometry of the spring waters maximum 90 c suggest an origin from as deep as 4 0 km this depth is consistent with the depth of the core of a fault propagation anticline below the surface of the rumsey hills developed by active internal deformation of an east tapering wedge beneath the southwestern sacramento valley active tectonic compression causes near lithostatic fluid pressures in the shallow subsurface below the rumsey hills and volume strain within the core of the anticline that results in upward expulsion of the saline fluids from the indicated depths

post peak fluid mediated modification of granulite facies zircon and monazite in the trivandrum block southern india the quarry at kottavattom in the trivandrum block of southern india contains spectacular examples of fluid assisted alteration of high grade metamorphic rocks garnet biotite gneiss has undergone a change in mineral assemblage to form submetre scale orthopyroxene bearing patches later retrogressed to form an amphibole bearing lithology these patches often referred to as arrested or incipient charnockite crosscut the original metamorphic foliation and are typically attributed to passage of a low ah2o fluid through the rock whilst this conversion is recognised as a late stage process little detailed chronological work exists to link it temporally to metamorphism in the region zircon and monazite analysed from kottavattom not only record metamorphism in the trivandrum block but also show internal lobate textures crosscutting the original zoning consistent with fluid aided coupled dissolution reprecipitation during formation of the orthopyroxene bearing patches high grade metamorphism at the quarry occurred between the formation of metamorphic monazite at 585 ma and the growth of metamorphic zircon at 523 ma the fluid assisted alteration of the garnet biotite gneiss is poorly recorded by altered zircon with only minimal resetting of the u pb system whereas monazite has in some cases undergone complete u pb resetting and records an age for fluid infiltration at 495 ma the fluid event therefore places the formation of the altered patches at least 25 myr after the zircon crystallisation in the garnet biotite gneiss the most likely fluid composition causing the modification and u pb resetting of zircon and monazite is locally derived hypersaline brine

age and sedimentary provenance of the southern granulites south india u th pb shrimp secondary ion mass spectrometry abstract southern india lies at a junction in the gondwana forming orogenic belts between the east african orogen and the kuunga orogen it contains voluminous high grade metasedimentary gneisses that make up an important component of the record of collision and amalgamation of gondwana here we present u pb secondary ion mass spectrometry sims isotopic data from detrital zircon cores from throughout southern india that demonstrate dominant neoarchaean to palaeoproterozoic age components that are incompatible with the known ages of potential southern and central indian source regions the original sediments to the trivandrum block gneisses were deposited between 1900 and 515 ma whereas a sample from the achancovil unit and possible also a sample from the madurai block were deposited in neoproterozoic times we speculate that these rocks broadly correlate with southern and western malagasy metasedimentary rocks including the itremo and molo groups and formed an extensive basin or basins that lay on the west side present orientation of the neoproterozoic continent azania in addition metamorphic zircon from four samples yielded an age of 513 6 ma that is interpreted as dating high grade metamorphism throughout much of the southern granulite terrane

formation and thrusting in some great valley rocks near the franciscan complex california and implications for the tectonic wedging hypothesis on the western side of sacramento valley in northern california the upper jurassic and cretaceous great valley sequence dips east at 40 to 70 in what has been regarded as a tilted but otherwise undeformed east dipping homocline containing strata collectively up to 15 km in thickness this paper reports the results of structural mapping in the paskenta area which suggests that in contrast steep dips are caused by westward directed thrusting and folding which led to tectonic thickening of the sedimentary pile in a mainly east dipping sequence thrusts are recognized by changes in the structural facing and vergence of both folds and cleavage although mainly affecting undated rocks of the great valley sequence one major thrust rides on a serpentine matrix melange which forms the substrate of the great valley sequence differential shortening occurring in different blocks during thrusting was accommodated by left lateral movement on the paskenta and elder creek fault zones which acted as tear faults ductile and brittle faulting have also occurred throughout the sequence in the melange and on the tear faults from work described in this paper and from other reports of thrusts and deformation in the great valley sequence in the foothills west of sacramento valley the hypothesis is advanced that these strata have all been tectonically thickened by westward directed thrusting of possible early tertiary age while the regional applicability of this hypothesis awaits future detailed structural work it is no longer sufficient to assume that east dipping strata have been merely tilted the proposed thrusting model is compatible with the recent tectonic wedge model proposed for the coast ranges sacramento valley by wentworth et al 1984 with respect to such a crustal model in which a tectonic wedge of franciscan complex was thrust east above older continental basement but below rocks of the coast range ophiolite and great valley sequence thrusts of this paper are back thrusts developed above a gently west dipping floor thrust back thrusting shortening and structural elevation of the great valley sequence are direct consequences of this wedging the uplifted strata lie east of a poorly defined triangle zone and define the western limb of a regional synclinorium that has some analogies with the alberta syncline of the canadian foothills

berriasian early cretaceous radiometric ages from the grindstone creek section sacramento valley california abstract the grindstone creek section glenn county northern california is a sequence of hemipelagic mudstone siltstone and sandstone interbedded with concretionary limestone and a few thin tuffs and bentonites two tuffs have been collected from a narrow interval of this sequence and subjected to mineralogical and isotopic analyses uzpb isotopic analyses of zircon fractions from these volcanic horizons indicate an age of 137 1 1 6 0 6 ma a detailed investigation has been conducted on the calcareous nannofossil stratigraphy of this section based on numerous samples with moderately preserved assemblages the nannoflora is largely of tethyan affinity and allows direct correlation with the berriasian stratotype section with sections with published magnetostratigraphies and with a dsdp site drilled between known magnetic anomalies the dated tuffs lie in the lower part of the upper berriasiancretarhabdus angustiforatus zone assipetra infracretacea subzone and within the narrow range ofrhagodiscus nebulosus at three different sections this subzone can be correlated with m sequence polarity zones m16 and m16n an independent magnetostratigraphic correlation is provided at dsdp site 387 drilled between anomalies m15 and m16 where basal sediments containr nebulosus buchia collected within a meter of the lower tuff lie within theb uncitoides zone which is berriasian in age the upper tuff level which occurs 65 m above the lower tuff is situated within the overlyingb pacifica zone this zone had previously been correlated with the early valanginian but is clearly also partly of berriasian age based on nannofossil stratigraphy our results allow an estimate of the age of the berriasian valanginian and jurassic cretaceous boundaries of 135 1 ma and 141 1 ma respectively and these fall within the range of but differ significantiy from several published time scales

hierarchical dynamic stratigraphy in various quaternary gravel deposits rhine glacier area sw germany implications for hydrostratigraphy the approach of dynamic stratigraphy aims to understand genetic processes that form stratigraphic units in a hierarchy of spatial and temporal scales this approach was used to investigate quaternary gravel deposits in terms of their sedimentology and in order to characterize the various sedimentary units in terms of their hydrogeological properties facies analysis within 62 gravel pits laboratory permeability measurements of field samples and geophysical surveys 3 d georadar 2 d seismic reflection led to the detection and classification of sedimentary heterogeneity according to the following six scales whereby each scale can be translated into defined hydrostratigraphic units 1 particles and pores micro scale that reflect depositional and diagenetic fluid dynamics as well as source material behaviour e g grain size roundness lithological composition this was found to be important for the hydrogeochemistry of groundwater in gravel aquifers e g higher sorption capacity of carbon rich limestone particles for organic pollutants 2 strata meso scale contain the recognition of sorting fabric texture and stratinomic features which can give an indication of transport and depositional dynamics five major lithofacies groups for example were distinguished within fluvial gravel bed deposits their variable hydraulic properties led to their subdivision into 12 hydrofacies types they form the smallest mappable hydrostratigraphic units which may result in either preferred pathways for fluid flow or flow barriers 3 depositional elements macro scale enable reconstruction of sedimentary geomorphic elements and their dynamics within a depositional system e g gravel bed braided river systems are dominated by gravel sheet gravel dunes and scour pool depositional elements hydrostratigraphically the architecture of depositional elements influences the hydraulic connectivity and local permeability structure distribution within an aquifer body five types of depositional elements in fluvial gravel bed deposits were distinguished and their geometries dimensions quantified 4 facies bodies mega scale composed of a stack of depositional elements and strata recording distinct environmental systems and their dynamics e g a coarse grained prograding delta system hydrostratigraphically facies bodies represent major compartments of an aquifer six major types of meltwater controlled facies bodies were identified in the study area 5 genetic sequences mega scale reflect the shifts of depositional environments caused by allocyclic changes e g glacial advance recorded by a coarsening upward sequence or autocyclic changes of landscape shaping events these sequences may form separate hydrostratigraphic units or aquifer storeys 6 basin fill giga scale comprising the lateral and vertical stacking of facies bodies and genetic sequences controlled by either long term glacier dynamics or short term flood events the regional distribution of permeable gravel units and for example less permeable diamicts builds the larger scale hydrostratigraphy

flood deposits in the tweed esker southern ontario canada sequences of openwork gravel and framework supported cobble to boulder beds are noted at three locations over a 20 km stretch of the tweed esker southern ontario each sequence is characterized by a lower massive framework supported cobble bed succeeded by a graded bed of openwork cobbles to granules this sequence is remarkably consistent in internal structure from site to site there is a similar frequency of these beds and their stratigraphic position is consistently at the top of the esker sequence a significant down esker fining of the coarsest component of the beds is also noted these beds were probably deposited by flood events occurring after the primary phase of esker deposition the massive basal unit is identified as a flood deposit the normally graded openwork cobbles to granules moved as bedload during the late stage of their transport following transport in suspension winnowing occurred at the bedload transport stage these deposits indicate the presence of an extensive fluvio glacial drainage focused on the tweed esker and provides indirect support for theories of regional ice stagnation in the late wisconsinan in this area of ontario

graphitization in a high pressure low temperature metamorphic gradient a raman microspectroscopy and hrtem study the graphitization of carbonaceous material cm in a high pressure metamorphic gradient is characterized along a cross section in the schistes lustres formation western alps along this 25 km cross section both the cm precursor and the host rock lithology are homogeneous and the prograde evolution of the pressure temperature metamorphic conditions from the lower blueschist facies 13 kbar 330 c to the eclogite facies 20 kbar 500 c is tightly constrained by literature data raman microspectroscopy shows that at the micrometre scale this process is progressive and continuous with increasing metamorphic grade and that the structure of cm is very sensitive to temperature variations at the nanometre scale hrtem the cm is composed of a mixture of a microporous phase and an onion ring like phase both known as non graphitizing under the effect of temperature at ambient pressure the hp lt graphitization produces structurally and microtexturally heterogeneous cm with increasing metamorphic grade the graphitization of the two types of cm proceeds up to the triperiodic graphite stage because of microtextural and structural changes that are specific to each type of cm the microporous material is progressively transformed into graphite through a macroporous transitional stage in this case graphitization mainly occurs on the pore walls as a result of pore growth in the case of concentric onion ring like material graphitization occurs in the regions with the largest radius of curvature i e on the outer part of the ring in comparison with 1 bar experiments pressure seems to induce microtextural changes which allows the subsequent structural modifications of the starting material

the depositional history of the bloomington complex an ice contact deposit in the oak ridges moraine southern ontario canada abstract the oak ridges moraine is a major physiographic feature of south central ontario canada that is made up of a number of distinct depositional elements one of these elements the bloomington complex is a body of sand gravel and diamict that was deposited largely within an east west trending interlobate lake basin that formed as the continental glacier split into two lobes a northern lobe termed the simcoe lobe and a southern lobe termed the ontario lobe the oldest exposed sediment in the bloomington complex is a sequence of stratified sand and gravel that is interpreted to have been deposited as coalesced subaqueous outwash fans that developed where several glacial meltwater conduits emptied into the proglacial lake these deposits are locally sharply incised by stratified sand and gravel that is interpreted as a glaciofluvial deposit laid down when the lake basin drained as ice margin retreat caused outlets to open along the niagara escarpment 60 km to the west the fan complex and glaciofluvial deposits are overlain in turn by stratified sand silt and clay that was deposited within the lake basin after the ice margins readvanced closing the drainage outlets and allowing the lake to rise the glaciolacustrine deposits pass gradationally upward into a heterogeneous deposit of sand silt clay and diamict that is interpreted as an ice marginal deposit of the last stages of closing of the lake basin as the northern and southern ice lobes converged finally a cap of diamict covers the area deposited as glacial ice advancing from the south over rode the study area the complete package of sediment that makes up the bloomington complex illustrates the effects of fluctuating ice margins on proglacial deposition in a glaciolacustrine setting

tectonic evolution of the jurassic cretaceous great valley forearc california implications for the franciscan thrust wedge hypothesis interpretation of seismic reflection data and restoration of depositional geometries of cretaceous forearc basin strata in the northwest great valley of california provide important controls on structural reconstructions of the western margin of the sacramento valley and northern coast ranges monoclinal eastward dips of great valley group strata and fault systems striking northwest southeast which are features proposed as evidence for a west dipping blind great valley franciscan sole thrust and related backthrusts instead are expressions of bedding geometry that resulted from folding of the paskenta and related synsedimentary normal faults depositional onlap and a major structural stratigraphic discontinuity the discontinuity separates east dipping aptian and younger great valley group strata from beds of lower great valley group and coast range ophiolite that were deformed and erosionally or structurally truncated by mid cretaceous time dip divergence imaged between the supracrop and subcrop of the discontinuity is not unique to the ancient great valley forearc but is also observed in modern forearc basins advocates of the franciscan thrust wedge model have also proposed that west dipping shingled patterns of seismic events imaged beneath the sacramento valley are imbricate thrust slices of the great valley group this hypothesis however is incompatible with borehole potential field and seismic refraction data that characterize the sacramento valley basement as ophiolitic seaward dipping reflections in the ophiolitic basement of the sacramento valley are analogous to layering developed in the oceanic crust of volcanic rifted margins or generated along midocean ridges thus late stage tectonic mechanisms are not required to interpret a forearc that owes much of its present day bedding architecture to processes coeval with deposition thickening of the great valley group stratigraphic section valanginian turonian in the hanging walls of the paskenta elder creek and cold fork fault zones combined with attenuation or complete omission of preextensional units including the coast range ophiolite and geometric evidence based on seismic reconstructions suggest that these faults are jurassic cretaceous normal faults that developed in a submarine setting down structure views of the great valley outcrop belt simplify otherwise complex map relations and portray the paskenta and related faults as half graben bounding faults that accommodated significant northwestward tectonic transport of hanging wall rocks it is significant that these faults sole into the coast range fault an enigmatic forearc structure that juxtaposes rocks of the franciscan complex blueschists with rocks of the coast range ophiolite and great valley group that have sustained only zeolite grade metamorphism discovery of jurassic cretaceous crustal scale extension in the great valley forearc suggests that a significant part of coast range fault related attenuation developed early in the history of the subduction complex

formalising an inversion methodology for reconstructing ice sheet retreat patterns from meltwater channels application to the british ice sheet glacial meltwater channels yield important information regarding patterns of palaeo ice sheet retreat however it is important to distinguish between channels formed at different positions in relation to the ice mass e g lateral subglacial in britain whilst meltwater channels have been widely reported in the literature such categorisation is often lacking here we develop an inversion methodology for extracting ice margin retreat patterns from meltwater channels diagnostic geomorphological criteria are presented derived from published descriptions of meltwater channel form by which a channel of unknown origin may be assigned to its appropriate category these criteria are applied to channels recorded in the britice gis database of glacial landforms and we find most channels to be of lateral or subglacial origin the categorisation of channels enables palaeo margin positions and the direction of retreat stage ice flow to be approximated and a preliminary reconstruction is made of fragments of the ice sheet retreat pattern further mapping and integration of melt traces with other geomorphic data will permit a more complete palaeo glaciological reconstruction of the last british ice sheet copyright 2007 john wiley sons ltd

coupled laser raman spectroscopy and carbon stable isotopes of graphite from the khondalite belt of kerala southern india abstract graphite in high grade meta supracrustal rocks provide an important proxy to characterize biogenic and abiogenic carbon sources here we investigate graphite in various associations within the granulite facies metapelites khondalites of kerala in southern india with a view to characterize the textural varieties and their genesis through the application of laser raman spectroscopy and carbon isotopes we trace the increasing intensity of metamorphism from the raman spectra of the different graphite types the 13c values of the graphite show two distinct origins the relatively lighter values in the range of 17 5 to 20 7 represent a mixture of biogenic and magmatic carbon whereas the heavier isotopes in the range of 11 7 to 13 8 are suggested to present graphite precipitation from co2 rich fluids from sub crustal magmatic sources our study provides insights on the spectral properties of graphite in relation to the intensity of metamorphism and also reveals both biogenic and abiogenic sources of carbon

late palaeoproterozoic depositional age for khondalite protoliths in southern india and tectonic implications abstract shrimp dating of detrital zircons from garnet sillimanite cordierite paragneisses khondalites of the trivandrum block southern india revealed nanometer scale pb isotopic inhomogeneity in most grains that we ascribe to annealing processes during ultra high temperature metamorphism at ca 570 ma our age data for zircons from six representative khondalite samples do not document any neo or mesoproterozoic detrital grains and we conclude from the concordant ages and discordant minimum 207pb 206pb ages that the khondalite precursor sediments were deposited more than 2 1 ga ago and were subsequently intruded by granitoid rocks at ca 1765 2100 ma some detrital zircons in the khondalites contain late palaeoproterozoic metamorphic domains suggesting that these grains are derived from an unknown crustal source that most likely experienced late palaeoproterozoic high grade metamorphism both the metasedimentary assemblage and granitoids were severely ductilely deformed metamorphosed and migmatized during the pervasive pan african event at ca 550 580 ma this caused many detrital zircons in the khondalites to become variably recrystallized and to develop metamorphic rims proper interpretation of cathodoluminescence images and zircon morphology is important in interpreting detrital populations the southern indian khondalites were part of an extensive palaeoproterozoic metasedimentary assemblage that may have extended from southern madagascar via the trivandrum block to the highland complex of sri lanka and seems to reflect a continental margin sequence that was deposited on an archaean to early palaeoproterozoic continental terrane possibly the southern margin of the indian dharwar craton the tectonic history of this terrane remains obscure due to the pervasive overprint during the pan african event

isotopic geochemistry of burial metamorphosed volcanogenic sediments great valley sequence northern california isotopic and mineralogic data from an 8500 m thick section of the great valley sequence northern california indicate that changes in the 18o values of authigenic minerals resulted from the conversion of smectite to a 10 a clay mineral as temperature increased with burial in the jurassic cretaceous outer arc basin the clay mineral assemblage in mudstone is characterized by a proportional increase of the 10 a clay mineral with increasing stratigraphic depth and by a depletion in the 18o value of the mixed layer smectite 10 a clay mineral with descending stratigraphic position from 21 9 to 15 5 smow modeling of the oxygen isotopic data from authigenic phases based on equilibrium fractionation during clay mineral diagenesis indicates that 18o values of calcite in mudstones and of calcite cements in sandstone precipitated along a temperature gradient of about 25 c km during maximum burial to about 6 7 km d values of the mixed layer smectite 10 a clay mineral range between 69 to 44 smow using temperatures calculated from the oxygen isotopic data the deuterium and oxygen isotopic data indicate that the smectite underwent late stage dehydration and probably buffered the composition of formation waters from sea water values to isotopic compositions of 18o 8 smow and d 25 smow the 13c values of calcite from mudstone and sandstone imply that crystallization of authigenic calcite was linked to organic diagenesis during which dissolved hcot 3 was continuously enriched in 13c as temperature increased with burial at the base of the sequence and immediately overlying the ophiolitic basement rocks several hundred meters of strata were altered by more oxygen depleted 18o 4 to 5 hydrothermal fluids emanating from the ophiolitic rocks probably at maximum burial depth

macroforms large bedforms and rhythmic sedimentary sequences in subglacial eskers south central ontario implications for esker genesis and meltwater regime abstract eskers of south central ontario were deposited in closed subglacial conduits which were continuous main conduits this interpretation is supported by the intimate association of eskers with an anastomosing network of tunnel channels relatively continuous esker ridges minimal post formational disturbance of esker sediments intercalation of till and stratified sand and gravel diapiric folding at an esker core low variability in palaeocurrent direction and upslope flow paths down esker trends in clast lithology roundness and sphericity indicate continuous conduits with sediment supply by subglacial deformation of adjacent material into the conduits melt out of sediment from the conduit walls and fluvial resedimentation esker ridge morphology is attributed to synchronous erosion transportation and deposition along the main conduits such that ridge discontinuities are primarily explained as zones of non deposition during esker formation composite pseudoanticlinal and oblique accretion avalanche bed macroforms are identified gravel facies within these macroforms were deposited from fluidal flows or hyperconcentrated dispersions progradation of macroforms or migration of constituent large bedforms through the main conduits may have temporarily blocked constricted portions of those conduits and acted as possible internal autogenic controls on sediment availability and flow resistance the location of macroforms within conduits was primarily controlled by conduit geometry and sediment availability and later by feedback between macroform and conduit geometries sand and gravel units alternate rhythmically in vertical section rhythmicity is interpreted as a response to episodic flood flows controlled by seasonal changes in water supply but not necessarily representing annual events fans beads anabranched reaches and extended hummocky deposits are intimately associated with the main esker ridges they are interpreted in terms of subglacial cavities and localized flotation zones connected to the main conduits during flood events in phase wave structures are the products of hydraulic jumps in hyperconcentrated flood flows at flow expansions into swells within the main conduits into cavities connected to the main conduits or at a grounding line esker ridges record only the most powerful flood events whereas fans and beads record flow events in finer detail being primarily depositional reservoirs laterally fining deposits record the waning stages of conduit operation

origin of graphite and temperature of metamorphism in precambrian eastern ghats mobile belt orissa india a carbon isotope approach abstract the carbon isotope composition of graphite and carbon and oxygen isotope composition of associated calcite from different locations of the eastern ghats mobile belt egmb of orissa have been measured in order to understand the origin of graphite the 13c values of graphite range from 2 4 to 26 6 forty four of sixty one samples have 13c values less than 20 most of these low 13c values graphite corresponds to schists and disseminations in khondalite and calc silicate granulites thus indicating graphitization of organic matter the remaining light carbon graphite occurs as veins which is the result of graphitization of transported organic matter the graphite with intermediate 13c value 13 to 19 indicates carbon contributions from both organic and carbonates sources and or mantle sources the higher 13c values graphite 2 4 to 8 8 represent mantle carbon and or carbonate sources without significant contribution from organic carbon the temperatures of metamorphism have been estimated using carbon isotope ratios of graphite and associated calcite of calc silicate granulites where typical cation exchange thermometer assemblages are lacking and significant mineral reaction textures used to calculate pressure temperature of metamorphic events are absent metamorphic temperatures obtained 945 c are close to the ultrahigh temperature reported from the egmb the minimum temperature estimated using the graphite carbonate carbon isotope ratio is 90 c the lower estimates of temperatures probably indicate changes in the carbon isotope ratio of calcite by decarbonation reaction or armoring of carbonaceous matter in silicates during metamorphism preventing continuous exchange with calcite

hydrothermal alteration of volcanic rocks at the mclaughlin gold deposit northern california the plio pleistocene mclaughlin mine is a large hot spring gold silver mercury deposit located in the northern coast ranges of california two distinctly different suites of volcanic rocks host mineralization an upper jurassic basalt part of the coast range ophiolite and an upper cenozoic basaltic andesite part of the clear lake volcanic field the two suites of volcanic rocks range from least altered rocks showing primary igneous mineralogy to intensely altered rocks composed of an assemblage of quartz montmorillonite sericite and adularia mass balance calculations indicate almost total loss of na ca mg and sr and large gains in and ba as a result of the hydrothermal alteration the mass flux corresponds to the replacement of plagioclase feldspar with sericite and adularia and mafic minerals with montmorillonite trace elements show no evidence for mobility rocks adjacent to the hydrothermal system have the greatest 18o values and the highest calculated mass flux suggesting the greates

metamorphic p t conditions of the kerala south india khondalite belt a granulite facies supracrustal terrain the khondalite belt of southernmost india is an immense section of granulite facies metasediments of probable early proterozoic age dominant rock types are migmatized khondalites garnet sillimanite pm cordierite metapelites acid biotite garnet graphitic gneisses and charnockites quartzofeldspathic gneisses with orthopyroxene throughout much of southern kerala the biotite gneisses are in a state of arrested conversion to charnockite partially decrepitated co 2 inclusions in quartz at the ponmudi mixed biotite gneiss charnockite quarry have significant ch 4 and or n 2 and are texturally late the probable sequence of events in metasediments was 1 migmatization 2 charnockite formation 3 symplectitic cordierite formation and 4 late co 2 entrapment phase equilibrium diagrams of anatexis in aluminous systems and fe mg exchange between garnet and biotite indicate metamorphic temperatures of 650 850 c for the khondalites temperatures based on garnet orthopyroxene

multiple tectonothermal events in the granulite blocks of southern india revealed from epma dating implications on the history of supercontinents abstract we report age data on zircon monazite uraninite and huttonite from a suite of 29 samples covering four major granulite blocks in southern india using an electron microprobe technique the rocks analysed in this study cover all of the major lithounits in these terrains and include garnet bearing and garnet free charnockites garnet biotite gneisses khondalites calc silicate rocks and a suite of orthogneisses biotite gneiss biotite hornblende gneiss two pink metagranites representing the magmatic phase were also analysed zircons from the madras block yield well defined isochrons at 2 5 2 6 ga core to rim analyses of single zircon grains show age zoning with 2 6 2 9 ga igneous cores mantled by 2 4 2 5 ga rims detrital zircons show age up to ca 3 2 ga monazites in this block have cores and rims with 2 5 2 3 ga a suite of 19 samples from the madurai block brings out the multiple tectonothermal events in this terrain zircons from an orthogneiss yield well defined isochrons at 1 7 0 1 ga 0 82 0 05 ga and 0 58 0 04 ga from core inner rim and rim portions respectively zircon grains in other rocks preserve either core or secondary growth ages at 0 8 1 0 ga zircons in a pink metagranite from this block show sharply defined isochrons of 0 68 0 03 ga for the core and 0 57 0 01 ga for the secondary portion a late pan african overprint is observed throughout this block with zircon rims monazite uraninite and huttonite yielding age values in the range of 0 45 0 60 ga zircons from both the trivandrum and nagercoil blocks show a major tectonothermal event at 0 55 ga with faint indications of previous tectonothermal events during 0 8 1 0 and 1 7 2 0 ga monazite data from both the trivandrum and nagercoil blocks are essentially similar to those from the madurai block except for presence of relic monazite in the former our study confirms the notion that the palghat cauvery shear zone marks the major terrain boundary between an archean craton in the north and proterozoic terrains in the south it also strengthens the view of paleoproterozoic accretion and pan african reworking of blocks south of this shear zone the ages of production accretion and reworking in the terrains of southern india yield important information for the histories of columbia 1 8 1 5 ga rodinia 1 1 1 0 ga and gondwana 0 6 0 5 ga supercontinents the southern indian terrains formed part of a worldwide network of orogenic belts that is centered around 1 8 ga and outlines the configuration of columbia accretion of terrains in the madurai block to archean rocks north of the palghat cauvery shear zone at this time is consistent with the ages suggested to be the oldest metamorphic event in the eastern ghats orogen of eastern india and the rayner belt of coastal east antarctica our data confirm earlier evidence that all of southernmost india underwent resetting of isotopic systems during the final accretion of gondwana at the time of the pan african orogeny 0 5 ga the possibility that the trivandrum and nagercoil terrains accreted to the madurai block after 0 7 ga suggests that this pan african zone may also have involved accretion and closure of ocean basins if that happened then this zone may be the long sought suture between east and west gondwana

under pressure clastic dykes in glacial settings abstract clastic dykes are widespread in glacial settings and we provide examples from switzerland patagonia iceland and the antarctic ranging in age from tertiary to recent on the basis of these examples we establish the general characteristics of clastic dykes and proceed to establish the direction of propagation on sedimentological grounds micromorphological analysis reveals that sedimentation in the dykes is ruled by pressure gradients and that ordinary sedimentological rules do not apply clastic dykes act like safety valves in the subglacial hydraulic system their development depends on specific subglacial conditions like water volume and pressure the nature of the bed sediments or bedrock and the hydraulic properties of the bed a number of scenarios for clastic dyke development are presented as there is not just one set of conditions under which they form development of clastic dykes affects glaciodynamics like velocity and surging and landform formation like till thickness and bedrock disruption

contrasting early and late mesozoic petrotectonic evolution of northern california devonian middle jurassic terrane assemblies in the klamath mountains and sierra nevada foothills consist chiefly of ophiolite chert argillite sequences mafic ultramafic complexes are oceanic whereas associated fine grained deep water terrigenous sediments were derived mainly from adjacent previously docked klamath sierran terranes coeval calc alkaline arc rocks are volumetrically rare geologic and petrochemical relations suggest a rifted arc origin for klamath mafic metavolcanic units inter layered with distal turbidites in the 170 200 ma north fork terrane detrital zircon u pb ages indicate that the clastic debris had a regional eastern klamath source the eastern hayfork cherty melange contains ophiolitic scraps and distinctive olistostromal sandstone blocks evidently derived from the nearby eastern klamath antelope mountain quartzite the seaward 200 ma rattlesnake creek terrane is an ophiolitic melange with north fork petrotectonic affinities the north fork eastern hayfork rattlesnake creek amalgam correlates with the calaveras complex and the outboard jura triassic arc belt in the sierran foothills geochemical bulk rock and zircon u pb age data support interpretation of the 200 ma jura triassic arc as an adjacent offshore mafic belt overlying a 300 ma ophiolitic basement these oceanic complexes were sutured against the central metamorphic belt eastern klamath feather river northern sierra terrane backstop before deposition and deformation of the outboard upper jurassic galice and mariposa formations klamath sierran terrane assemblies reflect 230 m y of transpression transtension involving only minor episodes of subduction producing ubiquitous ophiolite chert argillite lithologies and rare felsic arc rocks in contrast the late jurassic to largely cretaceous klamath sierra nevada quartzo feldspathic volcanic plutonic arc attests to massive calc alkaline magmatism attending a strong eastward component of underflow by the farallon plate the coeval galice mariposa formations followed by the cretaceous great valley forearc and franciscan trench deposits are first cycle felsic debris shed mainly from the klamath sierran arc these units record 70 m y of rapid sialic crustal growth attending major periods of approximately margin normal convergence this profound transition in northern california included devonian middle jurassic rifting drifting and stranding of ophiolite chert argillite terranes along an adjacent curvilinear continental margin then nearly head on cretaceous subduction that resulted in massive calc alkaline igneous activity the erosion of which generated the felsic great valley group forearc basin and franciscan complex trench clastic sedimentary units

deposition in an esker bead and fan complex lanark ontario canada abstract a glaciofluvial landform complex comprising a single esker ridge proximally multiple ridges and beads in the middle section and a complex of ridges and fans distally is mapped and described we present detailed successions in the associated sediment showing sedimentary structure grain size and palaeocurrent estimates sediment in the esker is mainly coarse grained and varies from boulders with a fine sand matrix deposited at maximum discharges to diamicton interpreted as a product of ice pressing under low discharges early stage deposition in the esker at high flow was from suspension and bed load intermediate stage deposition was mainly from bed load and late stage deposition was from hyperconcentrated suspension the esker rests in a bedrock channel which functioned as a nye channel prior to esker formation the channel surface carries a variety of fluvial erosional marks short distributary ridges of the ridges and beads complex contain mainly cobbles and boulders but beads are mainly in sand with rapid down flow fining and change in sedimentary structure faulting and overfolding of bead sediment suggest a subglacial origin deposition of the esker fan complex was highly variable in space and time down fan sedimentary changes with transitions from gravel to cross laminated fine sand in a few tens of metres indicate rapid loss in competence fan location lateral to the esker indicates a broadening of the zone of subglacial meltwater with time deposition from suspension and steep sided scours are interpreted to result from deposition and erosion by hyperconcentrated flows a model of underflows with submerged hydraulic jumps spilling laterally from the esker tunnel into subglacial cavities explains the morphological and sedimentary characteristics of the fans detailed analysis of small scale fining upwards sequences in the fans and beads indicates deposition by a large number of flow events these events are explained by glacier hydraulics whereby periodic separation of the glacier from its bed caused water with a high suspended sediment concentration to spill out from the esker tunnel into adjacent subglacial cavities evolution of the subglacial drainage system indicates a complexity of subglacial sedimentation near to a grounding line which is not readily apparent from observations at modern glaciers terminating in relatively deep water

facies history of the upper jurassic lower cretaceous great valley sequence response to structural development of an outer arc basin abstract the facies history of the great valley sequence is closely linked to structural events in an arc trench system upper jurassic lower cretaceous marine rocks as much as 8 500 m thick along the western margin of the sacramento valley northern california were deposited on slopes and submarine fans that extended over an unstable basement floored by ophiolitic rocks paleocurrent and paleoslope analyses indicate that eastward subduction initiated as early as kimmeridgian created an outer arc ridge which bounded the west side of the basin debris was shed dominantly from the north and east but significant contributions were ridge derived sediment fabrics structures and bedding styles indicate that earliest deposition on basin plains and on eastward facing slopes was followed at le st until the valanginian by a stable sedimentological framework of prograding and avulsing submarine fans characterized by broad shallow midfan channels depositional lobes and abundant thick deposits of interchannel mud the great valley rocks are transected by northwest trending faults that produced strike separation of the east dipping strata smooth facies transitions but with abrupt thickness variations across faults suggest that faulting with some normal component of motion was contemporaneous with deposition during latest jurassic and earliest cretaceous later movement either strike slip or reverse brought coarse inner fan facies that were deposited on klamath basement into fault contact with basin plain facies that were deposited on ophiolitic basement

structures and hydrologic function of soil landscapes with kettle holes using an integrated hydropedological approach the hummocky post glacial soil landscapes with kettle holes as internal drainage systems are characterized by ponds that trap lateral fluxes in topographic depressions a quantitative description is mostly limited by the unknown complexity of hydraulically relevant soil and sediment structures this paper is focussing on a structure based approach to identify relevant field scale flow and transport processes illustrative examples demonstrate extreme variations in water table fluctuation for adjoining kettle holes explanations require a pedohydrologic concept of the arable soil landscape identification of structures is based on geophysical methods and soil hydraulic measurements electrical resistivity imaging yields 0 5 m scale spatial structures that correspond with soil texture distributions electromagnetic induction provides larger scale field maps that reflect major soil and sediment features results of both methods correspond within the limits of the different spatial resolutions with geophysical exploration methods colluvial areas with textural differences between upper and deeper soil layers coarse textured sediment lenses and stony colluvial regions around kettle holes are identified as potentially relevant flow structures the colluvial fringe around the pond seems to be a sensitive area with important lateral exchange fluxes tensiometer measurements perpendicular to this boundary indicate hydraulic gradients directed from the pond towards the partially saturated soil the localized infiltration of trapped water in kettle holes can control large fractions of ground water recharge and may have implications for the fate of agricultural chemicals in post glacial landscapes while surface and subsurface hydraulic structures may be inferred using minimal invasive techniques better understanding of processes and properties governing lateral exchange fluxes between pond and surrounding soil are required

13c 12c exchange between calcite and graphite a possible thermometer in grenville marbles the fractionation of 13c between calcite and graphite cc gr is consistently small 2 6 4 8 permil in 34 assemblages from upper amphibolite and granulite facies marbles of the grenville province in 25 samples from the adirondack mountains new york it decreases regularly with increasing metamorphic temperature the fractionations are independent of absolute 13c values of calcite 2 9 to 5 0 for t 600 800 c the adirondack data are described by cc gr 0 00748t c 8 68 this good correlation between and t suggests that carbon isotope equilibrium was attained in these high grade marbles and that the theoretical calculations of this fractionation by bottinga are approximately 2 permil too large in this temperature range because of the relatively high temperature sensitivity suggested by these results and by bottinga s calculations and the pressure independence of isotope fractionation cc gr may provide a very good thermometer for high grade marbles comparison of this field calibration for cc gr vs temperature with results from other terranes supports the utility of cc gr for geothermometry and suggests that graphite is much more sluggish to exchange than calcite that exchange between calcite and graphite occurs at temperatures as low as 300 c and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500 600 c because 13c exchange is an unavoidable metamorphic process at temperatures above 300 c high values of 13c gr in moderate to high grade carbonate bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite

hot orogens and supercontinent amalgamation a gondwanan example from southern india abstract the southern granulite terrane in southern india preserves evidence for regional scale high to ultrahigh temperature metamorphism related to the amalgamation of the supercontinent gondwana here we present accessory mineral zircon and monazite geochronological and geochemical datasets linked to the petrological evolution of the rocks as determined by phase equilibria modelling the results constrain the duration of high to ultrahigh temperature 900 c metamorphism in the madurai block to be c 40 ma with peak conditions achieved c 60 ma after the formation of an orogenic plateau related to the collision of the microcontinent azania with east africa at c 610 ma a 1d numerical model demonstrates that the attainment of temperatures 900 c requires that the crust be moderately enriched in heat producing elements and that the duration of the orogenic event is sufficiently long to allow conductive heating through radioactive decay both of these conditions are met by the available data for the madurai block our results constrain the length of time it takes for the crust to evolve from collision to peak p t i e the prograde heating phase then back to the solidus during retrogression this evolution illustrates that not all metamorphic ages date sutures

subnormal geothermal gradients in the great valley forearc basin california during franciscan subduction a fission track study outboard parts of forearcs commonly have subnormal geothermal gradients because relatively cold lithosphere subducts beneath them the strata of the 10 to 15 km thick late jurassic tertiary great valley forearc basin accumulated in the forearc of the franciscan subduction zone of coastal california in this study paleogeothermal gradients in this basin were reconstructed to constrain the tectonic history of the convergent plate margin backstripping was used to reconstruct the burial histories of outcropping basin strata and apatite fission track analysis was used to determine the maximum burial temperatures experienced by 64 rock samples plots of maximum burial temperatures versus maximum burial depths indicate earliest tertiary time of deepest burial forearc basin geothermal gradients of about 9 c km backstripping shows that strata from the lower parts of two sections were deeply buried 6 5 km for the period 90 65 ma without experiencing high temperatures 105 c indicating that gradients were at least moderately subnormal throughout that period the data permit gradients no greater than about 15 c km at 90 ma decreasing to no greater than about 9 c km at 65 ma lower strata in another section were probably deeply buried without experiencing high temperatures from 130 or 120 ma until the latest cretaceous or early tertiary indicating that subnormal gradients probably existed throughout that period k ar ages of franciscan complex blueschists indicate subnormal gradients in the california forearc in the late jurassic and early cretaceous fission track data from the sierra nevada indicate subnormal gradients in the early and middle cenozoic and modern heat flow patterns indicate subnormal gradients in the late cenozoic together these indicators suggest that thermal gradients in the forearc were continuously subnormal from the initiation of franciscan subduction in the late jurassic until the termination of subduction in the late cenozoic gradients in the range that would permit blueschist facies metamorphism in the franciscan complex were thus long lived the broad range of k ar ages noted for franciscan blueschists need not reflect multiple discrete metamorphic events but are also consistent with a continuous extended period of high p t conditions blueschists need not have been uplifted soon after metamorphism to avoid overprinting by normal p t conditions but rather may have remained at depth for extended periods preliminary modeling indicates that an interruption in subduction of longer than 5 20 m y should cause detectable heating of forearc basin strata while a much shorter interruption should heat accretionary wedge rocks since there is no evidence of such heating it appears that convergence at the franciscan trench was essentially continuous if allochthonous terranes traveled northward parallel to the california margin during the late jurassic to late cenozoic period of franciscan subduction they apparently did so during oblique subduction not during extended interludes of pure transform motion

discovery of llandovery silurian graptolites and probable devonian corals in the southalpine metamorphic basement of the eastern alps agordo ne italy we report the discovery of aeronian middle llandovery graptolites and corals of probable devonian age in boudins hosted by greenschists within the southalpine metamorphic basement these discoveries provide key constraints to the depositional age range of the protoliths this remarkable occurrence of almost undeformed graptolites and compound corals in boudins within a metamorphic shear zone indicates very marked local strain partitioning

syncollisional basin development in the appalachian orogen the saint daniel melange southern quebec canada the saint daniel melange is an orogen scale sedimentary basin of the quebec appalachians that is commonly interpreted as the remnant of a subduction complex formed during the taconian orogeny however geochronological structural and stratigraphical data from laurentian continental margin rocks and adjacent ophiolitic rocks in southern quebec indicate that the saint daniel melange is an olistostromal syncollisional piggyback basin that represents the base of the magog group forearc basin the regional stratigraphic framework of the saint daniel melange and its relationships with underlying and overlying rock units have been established on the basis of six stratigraphic sections from the thetford mines asbestos and mont orford ophiolitic complexes our results imply that 1 the saint daniel melange is a sedimentary sequence that unconformably overlies different structural and pseudostratigraphic levels of the southern quebec ophiolites 2 it is made up of four distinct and laterally discontinuous units that record the obduction of ophiolites onto laurentia and exhumation of basement rocks followed by subsidence and deposition of the overlying saint victor formation of the magog group 3 the sedimentary rocks of the saint daniel record a transition from ophiolite dominated to continental sources indicating progressive exhumation of both the ophiolite and the continental margin upon which it was obducted 4 0 ar 3 9 ar analysis of muscovite from metamorphic rock fragments in debris flows of the melange yield an age of 467 2 ma which is within the range of ar ages measured in metamorphic rocks that underlie the ophiolites and indicates the uplift of metamorphosed continental deposits during or shortly after obduction 4 the saint daniel melange is stratigraphically overlain by the magog group and represents the base of a syncollisional basin developed in a forearc setting during the taconian orogeny

the origin of graphite of sri lanka abstract a model for the origin of graphite occurrences of sri lanka is discussed in the light of recent views on the geologic history of sri lanka the three modes of graphite occurrences in sri lanka are i as disseminated flakes in the country rocks ii as lenses pods and vugs and iii as veins occupying fractures in rocks the source of carbon of all three types is shown to be organic matter from microorganisms now known to have lived in precambrian sedimentary basins the highland series of sri lanka in which graphite is found in abundance is considered to be a precambrian sedimentary basin filled by sandstones limestones and shales the continuous filling of the basin followed by deformation resulted in intense folding accompanied by metamorphism during this process the hitherto disseminated carbonaceous matter was mobilized in a semi fluid state with the aid of magmatic fluids known to have pervaded the sediments during the intense folding the vein graphite deposits were formed in the axial regions of the anticline while the graphite not pressed into pre existing faults and fractures remained in the disseminated form

pattern and timing of retreat of the last british irish ice sheet during the last glacial the ice sheet that subsumed most of britain ireland and the north sea attained its maximum extent by 27 ka bp and with an ice volume sufficient to raise global sea level by ca 2 5 m when it melted we reconstruct the demise of this british irish ice sheet biis and present palaeo glaciological maps of retreat stages between 27 and 15 ka bp the whole land area was investigated using remote sensing data and we present maps of moraines meltwater channels eskers and drumlins and a methodology of how to interpret and bring them together for the continental shelf numerous large moraines were discovered recording an extensive pattern of retreat stretching from sw ireland to the shetland isles from an integration of this new mapping of glacial geomorphology 26 000 landforms with previously published evidence compiled in the britice database we derive a pattern of retreat for the whole biis we review and compile relevant dates 881 examples that constrain the timing of retreat all data are held within a geographic information system gis and are deciphered to produce a best estimate of the combined pattern and timing of retreat pattern information reveals an ice sheet mainly comprised of a shelf parallel configuration from sw ireland to ne scotland but it spread far enough to the south to incorporate outlying ice domes over wales the lake district and kerry final disintegration was into a number of separate ice caps rather than reduction as a single mass and paradoxically retreat was not always back to high ground by 23 ka bp ice withdrew along its northern boundaries at the same time as the southern margins were expanding including transient ice streaming down the irish sea and advances of lobes in the cheshire basin vale of york and east coast of england ice divides migrated south by 19 ka the ice sheet was in crisis with widespread marine based ice losses particularly in the northern north sea and the irish sea considerable dynamic thinning occurred during this phase final collapse of all marine sectors occurred by 17 ka bp and with most margins beginning to back step onshore disintegration of the north sea ice bridge between britain and norway remains loosely constrained in time but the possibility of catastrophic collapse of this sector is highlighted the north channel and irish sea ice streams had finally cleaved the ice sheet into separate irish and scottish ice sheets by 16 ka bp rates of ice loss were found to vary widely over space and time e g 65 260 km3 per year the role of ice streams and calving losses of marine based sectors are examined retreat rates of up to ca 150 ma 1 were found for some ice stream margins that large parts 2 3 of the biis were marine based drained by ice streams and possibly with fringing ice shelves in places makes it a useful analogue for the west antarctic ice sheet wais this is especially so because the biis deglaciated in response to rising temperatures and a rising sea level driven by melting of other ice masses which are the current forcings that might cause collapse of the wais our reconstruction when viewed from the opposite perspective documents when fresh land became exposed for exploitation by plants animals and man and records for how long such land has been available for soil and geochemical development and ecological succession

early cretaceous transition from nonaccretionary behavior to strongly accretionary behavior within the franciscan subduction complex 1 during subduction at the franciscan trench beginning at 170 160 ma and continuing to the present marine sedimentary and lesser volcanic rocks have been underthrust accreted and metamorphosed to form the franciscan accretionary wedge the south fork mountain schist sfms forms the eastern margin and structural top of the wedge and so was apparently the first unit of substantial size to accrete into the franciscan new u pb ages of detrital zircons and 40ar 39ar ages of metamorphic white micas indicate that the sfms accreted surprisingly late in the time span of franciscan subduction probably at ca 123 ma at least parts of the valentine spring formation and yolla bolly terrane accreted soon thereafter therefore accretion of the sfms apparently marks a fundamental transition from virtually nonaccretionary behavior to strongly accretionary behavior in the franciscan forearc about 75 of modern forearcs are nonaccretionary so recognition of an early nonaccretionary period is consistent with modern examples the franciscan mafic high grade exotic blocks and related very small slabs which yield ca 132 to 169 ma metamorphic ages are the only well documented rock record of the early 40 m y long nonaccretionary period and represent very sparse accretion during that interval the transition into an accretionary regime at ca 123 ma was essentially synchronous with the end of the late jurassic early cretaceous magmatic lull in the sierra nevada magmatic arc with the waning of early cretaceous faulting and warping within the great valley forearc basin and possibly with changes in motion vectors of the pacific and farallon plates

the role of sediment supply in esker formation and ice tunnel evolution abstract meltwater is an important part of the glacier system as it can directly influence ice sheet dynamics although it is important that ice sheet models incorporate accurate information about subglacial meltwater processes the relative inaccessibility of contemporary ice sheet beds makes direct investigation challenging former ice sheet beds contain a wealth of meltwater landforms such as eskers that if accurately interpreted can provide detailed insight into the hydrology of former ice sheets eskers are the casts of ice walled channels and are a common landform within the footprint of the last laurentide and cordilleran ice sheets in south western alberta esker distribution suggests that both water and sediment supply may have been important controls the longest esker ridge segments are located within meltwater valleys partially filled by glaciofluvial sediments whereas the shortest esker ridge segments are located in areas dominated by clast poor till through detailed esker ridge planform and crest type mapping and near surface geophysics we reveal morpho sedimentary relationships that suggest esker sedimentation was dynamic but that esker distribution and architecture were primarily governed by sediment supply through comparison of these data with data from eskers elsewhere we suggest three formative scenarios 1 where sediment supply and flow powers were high coarse sediment loads result in rapid deposition and rates of thermo mechanical ice tunnel growth is exceeded by the rate of ice tunnel closure due to sediment infilling high sedimentation rates reduce ice tunnel cross sectional area cause an increase in meltwater flow velocity and force ice tunnel growth thus ice tunnel growth is fastest where sedimentation rate is highest this positive feedback results in a non uniform ice tunnel geometry and favours macroform development and non uniform ridge geometry 2 where sediment supply is limited but flow power high the rate of sedimentation is less than the rate of thermo mechanical ice tunnel growth here the ice tunnel enlarges faster than it fills with sediment and its evolution is independent of sedimentation resulting in more uniform ice tunnel geometry in these cases esker architecture is dominated by extensive vertical accretion of tabular units and ridge geometry is more uniform 3 where sediment is truly supply limited the sedimentation rate is negligible regardless of water supply and like scenario 2 ice tunnel growth is independent of sediment deposition forming a relatively uniform ice tunnel or eroding the bed because meltwater flows transport few gravel clasts the ice tunnel is not completely filled with gravel and instead saturated and pressurized diamicton or bedrock if deformable from beneath the surrounding ice is squeezed into the relatively low pressure ice tunnel during waning flow or after ice tunnel shutdown resulting in deformation of limited gravels deposited within the ice tunnel and a landform cored with diamicton or deformed bedrock and with a relatively uniform ridge geometry our data demonstrate that an esker map is a minimum map of ice walled channel location and that continued detailed investigation of morpho sedimentary relationships is essential to gaining a complete picture of esker forming processes validating the morpho sedimentary relationships identified in south western alberta and other areas with a larger data set may allow improved remote predictive esker mapping over larger areas and inferences to be made about spatial and temporal variations in esker depositional environments and ice tunnel evolution

charnockite formation at ponmudi in southern india charnockites constituents of most precambrian high grade terrains1 2 are essential for understanding the evolution of the early continental crust the arrested development of charnockite in shear veins at kabbaldurga3 in the state of karnataka in india suggests flow of co2 rich water deficient fluids through deep seated rocks as a mechanism of granulite grade metamorphism4 5 we report here an occurrence of arrested charnockite formation well south of kabbaldurga in the khondalite belt of southern kerala where rocks with amphibolite facies give way to the vast southern india sri lanka charnockite terrain indicating that metamorphism due to co2 rich fluids carbonic metamorphism may have operated over a large area in southern india if such localities prove to be widespread the present level of exposure throughout much of the high grade terrain probably does not extend far beyond an isofacial surface marking the boundary between upper and lower crust in the late archaean

sedimentary and structural evolution of a relict subglacial to subaerial drainage system and its hydrogeological implications an example from anglesey north wales uk subglacial drainage systems exert a major control on basal sliding rates and glacier dynamics however comparatively few studies have examined the sedimentary record of subglacial drainage this is due to the paucity of modern analogues the limited recognition and preservation of upper flow regime deposits within the geological record and the difficulty of distinguishing subglacial meltwater deposits from other meltwater sediments e g glacier outburst flood deposits within this study the sedimentological and structural evolution of a subglacial to subaerial ice marginal proglacial drainage system is examined particular emphasis is placed upon the genetic development and preservation of upper flow regime bedforms and specifically recognising them within a subglacial meltwater context facies are attributed to subglacial meltwater activity and record sedimentation within a confined but progressively enlargening subglacial channel system produced under dune to upper flow regime conditions bedforms include rare large scale sinusoidal bedding with syn depositional deformation produced by current induced traction and shearing within the channel margins subglacial sedimentation culminated with the abrupt change to a more ephemeral drainage regime indicating channel abandonment or a seasonal drainage regime retreat of the ice margin led to the establishment of subaerial drainage with phases of sheet flow punctuated by channel incision and anastomosing channel development under diurnal ablation related seasonal discharge the presence of extensive hydrofracture networks demonstrate that proglacial groundwater levels fluctuated markedly and this may have influenced later overriding of the site by an ice stream

ice walled lake plains implications for the origin of hummocky glacial topography in middle north america abstract ice walled lake plains are prominent in many areas of hummocky till topography left behind as the laurentide ice sheet melted from middle north america the formation of the hummocky till topography has been explained by 1 erosion by subglacial floods 2 squeezing of subglacial till up into holes in stagnant glacial ice or 3 slumping of supraglacial till the geomorphology and stratigraphy of ice walled lake plains provide evidence that neither the lake plains nor the adjacent hummocks are of subglacial origin these flat lake plains up to a few kilometers in diameter are perched as much as a few tens of meters above surrounding depressions they typically are underlain by laminated fine grained suspended load lake sediment many ice walled lake plains are surrounded by a low rim ridge of coarser grained shore sediment or by a steeper rim ridge of debris that slumped off the surrounding ice slopes the ice walled lakes persisted for hundreds to thousands of years following glacial stagnation shells of aquatic molluscs from several deposits of ice walled lake sediment in south central north dakota have been dated from about 13 500 to 10 500 b p calibrated radiocarbon ages indicating a climate only slightly cooler than present this is confirmed by recent palaeoecological studies in nearby non glacial sites to survive so long the stagnant glacial ice had to be well insulated by a thick cover of supraglacial sediment and the associated till hummocks must be composed primarily of collapsed supraglacial till

stream capture and piracy recorded by provenance in fluvial fan strata abstract stream capture and piracy in tectonically active regions have been described in geomorphic systems worldwide however few studies show the influence stream capture has on the rock record we present an analysis of fluvial fan stratigraphy that developed as a result of multiple stream capture events building a complex stratigraphic succession beneath the lawrence livermore national laboratory llnl california the llnl site is located in the southeast portion of the tectonically active livermore basin a transpressional basin in the california coast ranges geomorphic evidence for this stream capture include 1 the arroyo seco enters the basin from the south through an uplifted fault block 2 south of this fault block lies an abandoned arroyo seco fluvial fan 3 north of the fault block in the livermore basin arroyo seco built a 7 km2 fluvial fan apparently forcing the arroyo las positas a smaller stream that enters the basin from the east northward around the arroyo seco fan and 4 a knickpoint exists near the point of capture on arroyo seco stratigraphic evidence reflecting this shift in the arroyo seco position into the livermore basin was evaluated through a provenance study of 215 gravel units from 34 boreholes spaced evenly over the 2 6 km2 llnl site the arroyo seco derives its sediment from both the jurassic cretaceous franciscan assemblage and the altamont hills which are comprised of mesozoic great valley group and tertiary continental sediments the arroyo las positas drains only the altamont hills and thus lacks the franciscan assemblage derived clasts the origin of the individual gravel units was determined by the percentage of franciscan assemblage indicator pebbles red chert green chert and blueschist in the samples through this analysis we determined that high percentage franciscan assemblage derived clasts were present below a depth of approximately 35 m below the surface low percentage franciscan assemblage derived clasts were present at depths between 35 m and 18 m and high percentage franciscan assemblage derived clasts were present from depths of approximately 18 m to the surface of the fluvial fan these results indicate that the arroyo seco flowed north and deposited sediments at the llnl site then was later absent from the basin at which time it formed a fan south of the fault block during this absence of the arroyo seco the arroyo las positas a westerly flowing stream dominated the sediment supply at the llnl site the arroyo seco was then captured by a gully headward eroding through the uplifted fault block redirecting the arroyo seco into the basin once again this history of multiple stream captures created three stratigraphic units with alternating overall channel and paleoflow orientations

long term variability of proglacial groundwater fed hydrological systems in an area of glacier retreat skeiðararsandur iceland proglacial groundwater fed features such as seeps substantially impact proglacial geomorphology hydrology and ecology however there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features this paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater fed seeps research has taken place in western skei ararsandur the large proglacial outwash plain of skei ararjokull a retreating temperate glacier in southeast iceland changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986 1997 and 2012 proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012 the western margin of skei ararjokull has retreated approximately 1 km beyond its position in 1986 however this retreat was punctuated by short periods of readvance the geomorphology and groundwater systems at the site were substantially impacted by the november 1996 jokulhlaup whose deposits altered approximately 18 of the area of groundwater seeps the surface areas of groundwater seeps and lakes in the study area have declined by 97 between 1986 and 2012 most of the decline took place after 1997 when the mean annual rate of retreat increased three fold groundwater levels also declined substantially between 2000 and 2012 although this trend varies spatially the paper provides a conceptual model of the controls on proglacial shallow groundwater systems direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps these declines are expected to adversely impact sandur ecology copyright 2014 john wiley sons ltd

carbonaceous material in the ryoke metamorphic rocks kinki district japan abstract carbonaceous material in the ryoke pelitic metamorphic rocks in the wazuka area kinki district japan has been studied by x ray diffraction xrd analysis detrital graphite in the lower grade rocks is recognized in both x ray diffractograms and transmission electron micrographs progressive graphitization is considered to have proceeded continuously on the basis of the xrd data of the bulk concentrates of carbonaceous material and a conspicuous asymmetric shape of xrd peaks in lower grade samples is ascribed to the mixture of carbonaceous materials with different crystallinities fully ordered graphite does not occur until the highest grade part of the chlorite biotite zone the variation of degree of crystallinity of carbonaceous materials inferred from xrd data is consistent with the prograde mineral zones the temperatures for the development of fully ordered graphite are estimated to be between 410 and 440 c in regional metamorphism through comparing the xrd data from low medium and high pressure types of metamorphic terrains