stratigraphic and sedimentological evidence for late wisconsinan sub glacial outburst floods to laurentian fan abstract sub glacial meltwater produces a distinctive stratigraphic and sedimentological response on the continental margin seismo stratigraphy of laurentian channel reveals thick till deposits at its seaward end that pass laterally into stratified sediment in deeper basins that may record periods of water build up beneath the ice two scales of meltwater discharge are recognised large scale that caused catastrophic erosion and transported large volumes of coarse sediment to the abyssal plain and smaller scale yielding principally muddy sediment sub glacial outburst floods from the laurentian channel ice stream delivered distinctive red sediment derived from permian carboniferous strata of the gulf of st lawrence directly to laurentian fan between ca 17 and 14 14 c ka separate from north atlantic heinrich events on levees of laurentian fan three major pulses of meltwater plume muds are separated by intervals dominated by hemipelagic sediments these meltwater intervals are recognised distally as periods of plume sedimentation on the scotian slope and ice rafting of hematite stained quartz to the north atlantic ocean in channels of laurentian fan at least one major sediment transport event is recognised that eroded the upper slope and the major fan valleys depositing a bed of gravel at least 3 m thick in the characteristically wide fan valleys and thick sand on the sohm abyssal plain the same event was probably responsible for giant flute like scours the age of the gravel bed is directly constrained only by the presence of local overlying holocene sediment much of the surface of the gravel bed was re worked by the 1929 grand banks turbidity current an erosional event on the upper slope likely correlative with the flood generated gravel bed has been dated at 16 5 14 c ka such large scale erosional flood events can be recognised back through several glacial cycles and have played an important role in the architectural evolution of laurentian fan

the influence of shelf crossing glaciation on continental slope sedimentation flemish pass eastern canadian continental margin abstract flemish pass is a small perched slope basin seaward of the grand banks on the eastern canadian continental margin glacial ice crossed the grand banks to reach the upper continental slope during some mid to late quaternary glaciations but terminated on the middle shelf 200 km distant at the last glacial maximum this study investigates the effect of ice extent on slope sedimentation processes sediment in flemish pass comprises muds of hemipelagic and proglacial plume origin minor thin bedded turbidite sands and thick bedded mass transport deposits mtds a regional stratigraphy based on 500 km of high resolution seismic profiles and 60 piston cores up to 11 m long was dated using 30 radiocarbon dates the presence of ash zone ii and oxygen isotope stratigraphy this provided stratigraphic control for till tongues in water depths

gas hydrates off eastern canada velocity models from wide angle seismic profiles on the scotian slope abstract coincident single channel reflection and wide angle ocean bottom seismometer obs reflection refraction profiles were taken on the central continental slope off nova scotia in a region of possible gas hydrate occurrence as evidenced by recent identification of bottom simulating reflectors bsrs joint travel time inversions of wide angle reflections and refractions in the obs data result in three similar velocity models which all display anomalies consistent with the presence of gas hydrate and underlying free gas a high velocity zone hvz 60 120 m thick has velocity increases of 70 130 m s above a low velocity zone lvz 150 260 m thick where velocities decrease by 50 75 m s sensitivity analysis indicates that the refracted phase from the hvz offers better velocity resolution than the reflected phase from the top of the lvz comparison of synthetic seismograms for alternate models can further help to resolve details in the structure of the hvz and lvz layers depth migrations of the reflection profiles using the velocity models show that the depths of the velocity inversions and bsrs are consistent preliminary predictions of 2 6 bulk gas hydrate and

multistage progradational clinoform set characterisation and evolution analysis of the early oligocene in the baiyun sag pearl river mouth basin south china sea abstract conventional seismic based techniques for analysis of the progradational stages usually proceed qualitatively according to the facies identified by 2d seismic or cross well sections in this study we try to apply a more quantitative and practical approach to depict the distribution and stacking patterns of the progradational clinoform set pcs based on the integrated analysis of well tie seismic stratigraphy seismic sedimentology and seismic geomorphology the baiyun sag a subbasin of the pearl river mouth basin in the south china sea provides a suitable example for characterising the clinoform sets with typical progradational seismic reflections the characterisation results indicate that there were three pcss and at least nine stages of clinoform that developed during the deposition of the upper member of the enping formation lower oligocene the spatial temporal distribution of the pcss can be easily detected by the energy half time seismic attribute based on the manual interpretation of top and bottom interfaces of each clinoform integrated with the progradational seismic facies progradational angles based rose diagrams and seismic geomorphology analysis the characteristics of each pcs are depicted with stable and gradually increasing sediment supply along the nw se direction azimuths of 130 160 the three pcss display obviously continuous prograding towards the basin centre whereas several clinoforms pcs 1 a and pcs 1 b pcs 3 a and pcs 3 b exhibit a retrogradational characteristic within one pcs the overall progressive characteristics which include having some short period regressive stacking patterns exhibit a combined effect of sea level change of the south china sea and the increasing sediment supply intensity from the south china block

the moldanubian granitoid plutons of austria chemical and isotopic studies bearing on their environmental setting abstract the late palaeozoic moldanubian plutonic terrain of upper austria consists of granitoids that range from s type to i type in composition although many units show transitional compositional characteristics the austrian terrain displays some of the features of continent margin main arc batholiths the expanded compositional range monzodiorite to leucogranite of the rock types the high sr i types and the low to intermediate 87 sr 86 sr initials 0 705 0 708 of these i types however there are also important differences the austrian i types are low cao and high k2o units and transitional and s type granitoids are volumetrically dominant in the austrian terrain there is a scarcity of gabbros and an absence of rocks with positive nd initials the austrian terrain is dominated by granitoids of crustal or predominantly crustal origin we suggest that these formed in an inner continental arc setting rather than a main arc and can be correlated with those of the schwarzwald f r g together these are interpreted as components of a moldanubian inner continent plutonic belt

origin ore forming fluid evolution and timing of the logrosan sn w ore deposits central iberian zone spain the logrosan sn w ore deposits in the metallogenic sn w province of the european variscan belt consist of endo and exogranitic greisen type and quartz cassiterite veins associated with a s type granite mineral characterization fluid inclusion study isotope geochemistry and ar ar geochronology have been combined in order to reconstruct the conditions for sn w mineralization the endo and exogranitic mineralization must have been developed in a relatively long lived system 308 303 ma during or soon after the emplacement of the logrosan related granite at ca 308 ma the mineralizing fluids are characterized by complex aqueous and volatile h2o n2 co2 ch4 nacl fluid inclusions microthermometry and raman analyses indicate that fluid composition evolved from n2 ch4 to n2 rich followed by co2 rich fluids with varying amounts of h2o the presence of n2 and ch4 suggests the interaction with fluids derived from the nearby metasedimentary host rocks a model of host rock interaction assimilation and mixing of metamorphic and magmatic fluids resulting in change of the redox conditions is proposed for tin deposition later sulfide minerals were precipitated as a result of pressure and temperature release

2d waveform tomography applied to long streamer mcs data from the scotian slope detailed velocity models of the earth s subsurface can be obtained through waveform tomography the accuracy of the long wavelength component of such velocity models which is the background velocity field is particularly sensitive to modeling low frequency refracted waves that have long paths through target structures thus field examples primarily have focused on the analysis of long offset wide angle data sets collected using autonomous receivers in which refractions arrive at significantly earlier times than reflections modern marine acquisition with long streamers now offers the ability to record refracted waves with high spatial density and uniform source both in shallow and deep water we used 2d multichannel seismic mcs data acquired with a 9 km long streamer over the scotian slope in water depths of 1600 m the refracted arrivals although mostly restricted to far offset receivers provided sufficient information to successfully invert for a high resolution background velocity field usin

acoustic interpretation of quaternary sedimentation and erosion on the channelled upper laurentian fan atlantic margin of canada about 1000 km of single channel seismic reflection profiles from a 50 km 100 km area on the upper laurentian fan shows no evidence of the large slumps interpreted by previous workers in this area our detailed profile grid indicates that slump like masses are commonly in depositional continuity with definite autochthonous sediments and surfaces previously interpreted as slide planes are either facies changes or the result of valley wall erosion only a few small slump blocks of relatively consolidated sediment are found on the uppermost fan acoustic facies distribution shows a single early pleistocene fan valley crossing the northeast part of the survey area with thick overbank sediments to the southwest in the middle pleistocene this valley became incised its upper reaches then ceased to receive sediment and a new valley was cut extending southward from the upper slope and intercepting the lower reaches of the old fan valley this channel diversion was probably related either to the glacia

the late devonian frasnian famennian f f biotic crisis insights from δ13ccarb δ13corg and 87sr 86sr isotopic systematics a severe biotic crisis occurred during the late devonian frasnian famennian f f transition f367 myr here we present d 13 ccarb d 13 corg and 87 sr 86 sr isotopic systematics from identical samples of two sections across f f boundary in south china which directly demonstrate large and frequent climatic fluctuations 200 kyr from warming to cooling during the f f transition these climate fluctuations are interpreted to have been induced initially by increased volcanic outgassing and subsequent enhanced chemical weathering linked to the rapid expansion of vascular plants on land which would have increased riverine delivery to oceans and primary bioproductivity and subsequent burial of organic matter thereby resulting in climate cooling such large and frequent climatic fluctuations together with volcanic induced increases in nutrient e g biolimiting fe toxin sulfide and anoxic water supply and subsequent enhanced riverine fluxes and microbial bloom were likely responsible for the stepwise faunal demise of f f biotic crisis d 2005 elsevier b v all rights reserved

geophysical evidence of a late pleistocene glaciation and paleo ice stream on the atlantic continental shelf offshore massachusetts usa abstract interpretations of seismic reflection data collected offshore massachusetts usa reveal the first conclusive geophysical evidence of a pre wisconsinan glaciation that extended beyond the limits of the last glacial maximum lgm in the region the data image numerous glacial geomorphic features that define the extent of a paleo ice stream including 1 a regionally distributed erosion surface that forms a 50 km wide trough with steeply eroded sidewalls 4 18 and nearly 100 m in relief at the margins 2 a network of sub ice sheet meltwater channels and 3 a transparent glacigenic seismic unit the orientation of the paleo ice stream trough indicates that the ice stream flowed to the south southwest toward the shelf break this suggests that the ice stream formed further to the north where it appears that georges bank southeast of the gulf of maine usa redirected ice flow limited well data constrain the glacial erosion event up to 300 m below sea level to occur within the pleistocene the glacial event represents a time of larger ice volume on the northern atlantic continental shelf as compared to the lgm thus we suggest that the event corresponds to marine oxygen isotope stage 12 late pleistocene when the first major pleistocene shelf crossing glaciation began offshore southeastern canada these geophysical constraints on a late pleistocene glaciation offshore massachusetts have important implications for 1 models of the laurentide ice sheet as the geomorphic evidence of pre lgm ice streams are difficult to characterize yet account for most of the ice sheet s mass flux and 2 the pore water salinity pattern offshore new england as sedimentary basins near an ice sheet margin often contain large volumes of glacially emplaced freshwater

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

interbedded late quaternary turbidites and contourites in flemish pass off southeast canada their recognition origin and temporal variation abstract the recognition of contourite and turbidite deposits in deep marine sequences can be challenging as deposits may show similar sedimentary characteristics in flemish pass a small 1100 m deep perched basin along the southeast canadian continental margin both types of deposits occur late quaternary sediments include thin sand layers interbedded with hemipelagic muds the distribution age sedimentary structures and petrology of these sands were used to distinguish between turbidite and contourite deposits which were then characterized by detailed grain size distribution for understanding the conditions leading to deposition of each type seven sediment facies each with a distinctive grain size distribution were recognized they are 1 transported contourites 2 winnowed beds 3 possible jokulhlaup deposits 4 sandy turbidites 5 muddy turbidites 6 hemipelagic sediment and 7 turbidites from well sorted materials sand packets comprised of several stacked turbidite sand beds some with erosive contacts were correlated from the margin to the basin floor showing clear distal fining and creating a small lobe the temporal distribution of the sand beds indicates that most turbidites and contourites were deposited at stadial to interstadial transitions this linkage may be related to variations in the oceanic circulation in flemish pass which winnowed turbidites and may have triggered turbidity currents by moving sands into canyon heads

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

u pb investigations on zircons from pre variscan gneisses i a study from the schwarzwald west germany abstract field observations in the schwarzwald indicate that pre variscan rocks were formed by the following events 1 1 intrusion of granitic to granodioritic magma into sediments 2 2 a sequence of two anatectic events with an intervening regional metamorphism and development of a gneissic schistosity the absolute chronology of these older gneisses and migmatites has not yet been satisfactorily resolved we collected several samples of a coarse grained homogeneous orthogneiss of granodioritic composition and one sample of a metasedimentary source rock related to this orthogneiss body in the einetwald forest north of steinach kinzig valley the metasedimentary rock corresponds to the biotitepoor paragneisses in the schwarzwald the zircons in the latter sample are detrital and only very small specimens 45 m are euhedral the zircons from the orthogneiss samples are euhedral some are zoned and some have dark inclusions analyses of the three coarser fractions of the paragneiss form a linear array on a concordia diagram with upper and lower intercepts of about 2000 myr and 524 20 myr respectively the 2000 myr value is interpreted as the average age of the sedimentary source rocks for this material the 524 myr intercept defines an event responsible for most of the lead loss in the zircons as well as new zircon growth analyses of the zircons from the orthogneiss samples do not show a linear array on the concordia diagram because of inclusions of older inherited zircons stepwise leaching of two zircon fractions shows newly grown u rich zircon rims around old cores a 207 pb 206 pb age of 517 15 myr was found for the first dissolution steps about 50 of the zircons dissolved in subsequent steps with progressive dissolution of the residue 207 pb 206 pb age increased to 950 myr the u pb zircon data for the paragneiss and the orthogneiss establish an age of 520 15 myr for the magma intrusion

late cenozoic sea level changes and the onset of glaciation impact on continental slope progradation off eastern canada abstract late cenozoic sedimentation from four varied sites on the continental slopes off southeastern canada has been analysed using high resolution airgun multichannel seismic profiles supplemented with some single channel data biostratigraphic ties are available to exploratory wells at three of the sites uniform slow accumulation of hemipelagic sediments was locally terminated by the late miocene sea level lowering which is also reflected in changes in foraminiferan faunas on the continental shelf data are very limited for the early pliocene but suggest a return to slow hemipelagic sedimentation at the beginning of the late pliocene there was a change in sedimentation style marked by a several fold increase in accumulation rates and cutting of slope valleys this late pliocene cutting of slope valleys corresponds to the onset of late cenozoic growth of the laurentian fan and the initiation of turbidite sedimentation on the sohm abyssal plain although it corresponds to a time of sea level lowering the contrast with the late miocene lowstand indicates that there must also have been a change in sediment delivery to the coastline perhaps as a result of increased rainfall or development of valley glaciers high sedimentation rates continued into the early pleistocene but the extent of slope dissection by gullies increased gully cutting episodes alternated with sediment draping episodes throughout the southeastern canadian continental margin there was a change in sedimentation style in the middle pleistocene that resulted from extensive ice sheets crossing the continental shelf and delivering coarse sediment directly to the continental slope

ree systematics in hydrothermal fluorite abstract ree patterns of fluorite from 63 post variscan hydrothermal veins of the schwarzwald area germany can be divided into two major groups type a fluorite shows roof shaped paas normalized patterns with enriched mree the turning point of the curvature is at ho or er position all patterns of type a show a distinct positive eu anomaly type b fluorite shows roof shaped patterns with enriched mree and strongly depleted hree and a characteristic steep slope between nd and sm the turning point of the curvature is at gd to dy all patterns of type b show negative or no eu anomalies laser ablation icp ms traverses through single grains combined with cathodoluminescence imagery revealed either i identical ree patterns and total ree concentrations from core to rim ii identical ree patterns but concentration gradients or iii variable ree patterns and concentration gradients from core to rim these features are explained by different degrees of supersaturation or different fluid fluorite ratios during crystallization and by complexly controlled precipitation processes under closed system conditions petrographically late fluorites from several deposits show the characteristics of new fluid batches rather than the expected remobilization features lree enrichment close to the crystal faces in some grains may result from the copreciptiation of a submicrometer sized lree enriched phase or from lree clustering in late cool fluids by comparison with literature data on natural waters from gneissic and granitic aquifers and of leachates of granites and gneisses we show that the hydrothermal vein fluorite preserves the characteristic source related ree feature of the hydrothermal fluid that migrated through either gneissic type a or granitic type b host rocks the immediate host rocks of the veins however are not the source rocks of the ree which indicates large scale fluid convection in the basement gneiss related type a fluorite shows tb ca tb la trends of primary hydrothermal crystallization whereas granite related type b fluorite indicates remobilization of possibly pegmatitic or variscan fluorite

sedimentary and rock magnetic signatures and event scenarios of deglacial outburst floods from the laurentian channel ice stream abstract eastern canadian margin sediments bear testimony to several catastrophic deglacial meltwater discharges from the retreating laurentide ice sheet the reddish brown plumite layers deposited on the levees of the laurentian fan valleys have been recognized as indications of multiple outburst floods between heinrich events 2 and 1 five event layers have been consistently recorded in three new gravity cores retrieved on the sw grand banks slope and comply with the previously published laurentian fan core md95 2029 the apparently huge extent of these outburst plumes around the laurentian fan as well as their causes and consequences are investigated in this study using physical properties rock magnetic and grain size analyses together with seismoacoustic profiling we provide the first detailed 14c ages of the outburst event sequence and discuss their recurrence intervals in the context of regional ice retreat compared to the hemipelagic interlayers event layers have overall uniform and systematic changes of rock magnetic properties hematite contents increase over time and proximally while magnetite grain sizes fine upwards and spatially away from the fan based on the sediment composition and load we argue that these plumites were formed by recurrent erosion of glacial mud deposits in the laurentian channel by meltwater outbursts three alternative glaciological scenarios are evaluated in each case the provenance of the transported sediment is not an indicator of the precise source of the meltwater

late cenozoic architecture of the st pierre slope the late cenozoic seismic stratigraphy of the continental slope south of western newfoundland is interpreted using new seismic reflection profiles new miocene pliocene biostratigraphic palynology age determinations on the hermine e 94 well on the northwestern grand banks of newfoundland are correlated to the study area the quaternary section of st pierre slope is disrupted by numerous failure scarps and mass transport deposits but correlation from the mid slope to the continental rise is achieved using major mass transport deposits as markers on the upper slope stacked downslope thinning wedges of acoustically incoherent sediment are interpreted as till deposits of mid to late pleistocene age sedimentation rates in the youngest part of the succession are estimated from a 30 ka radiocarbon date 25 m below the horizon of the youngest till tongue which is exposed on a 60 m deep failure surface extrapolation of sedimentation rates and comparison with dated sections on the j anomaly ridge and bermuda rise provides a consistent interpreted age model for the till tongues that corresponds to marine isotope stages 2 4 6 8 10 and 12

effects of meteoric water interaction on hercynian granites from the sudschwarzwald southwest germany abstract hercynian granites from the sudschwarzwald plutons of klemmbach st blasien schluchsee barhalde show a wide range of whole rock 18 o values from 2 5 to 10 9 smow detailed 18 o analysis of separated minerals indicates strong isotopic disequilibrium a feature which can be explained by large scale post magmatic hydrothermal interaction of the granites with isotopically light meteoric water at temperatures below 500 c microthermometric investigation of homogenization and melting temperatures from two phase vapour liquid secondary fluid inclusions in quartz indicates a temperature range between 200 and 400 c for the alteration the aqueous fluid inclusions typically have low salinities but reach values up to 9 eq wt nacl in samples with evidence for secondary mineral development i e chloritization sericitization etc trace element variations in k feldspar rb sr ba tl pb bi provide a guide to elemental mobilization with increasing water rock ratios a gain of rb tl and bi and a loss of sr ba and pb is observed during alteration combining all data a three stage reaction scheme for the hydrothermal alteration of the granites is proposed 1 t 400 c granite prim fluid 1 granite alter fluid 2 2 t 200 300 c fluid 2 granite alter secondary mineralization fluid 3 3 t 200 c fluid 3 gangue mineralization

rb sr and u pb isotope studies on migmatites from the schwarzwald germany constraints on isotopic resetting during variscan high temperature metamorphism mineral and isotope studies were undertaken on migmatites from the schwarzwald moldanubian zone of the variscan belt the aims of the study were to date the migmatite formation and to determine the processes involved in migmatization in order to evaluate their influence on isotopic resetting textural evidence and the comparison of mineral compositions from leucosomes and mesosomes of two centimetre scale migmatite profiles respectively suggest that migmatitic textures and mineral assemblages were formed by metamorphic segregation deformation enhanced mass transport rather than by partial melting anatexis the results of rb sr thin slab dating on these profiles indicate that sr isotopes were not completely reset during migmatization no true isochron ages but ages of approximate isotopic homogenization were obtained on the thin slabs by calculating 87sr 86sr ratios back to various stages in their evolution the coincidence of these rb sr data with u pb ages of monazites from migmatites and non migmatitic gneisses shows that gneisses and migmatites were formed during the same high temperature event in the carboniferous 330 335 ma the observation that high temperature metamorphism failed to equilibrate sr isotopes on the centimetre scale imposes limitations on the use of conventional whole rock isochron techniques in dating migmatites

a link between geomagnetic reversals and events and glaciations abstract the apparent duration of geomagnetic polarity events in arctic ocean sediments is much longer than in sediments from lower latitudes in fact while the remanence of brunhes age sediment cores from the yermak plateau at 82 n is fully reversed for 30 of their lengths 1 the events often evade detection in many other continuously deposited sediments for example the laschamp event is absent in an otherwise high resolution record of secular variation from lac du bouchet 2 which is located near the laschamp volcanics where the event was first detected very short event durations of a few hundred years at the most have been suggested before 2 3 because sedimentation rates in the arctic ocean were increased during glaciations the exaggerated proportion of reverse polarities in sediments from high latitudes suggests a link between glaciation and field reversals this suggestion is supported by magnetostratigraphic results obtained from thick loess paleosol sequences in china 4 these demonstrate that all polarity boundaries separating chrons and subchrons since the gauss matuyama field reversal have been recorded in loess and thus during periods of cold climate although conflicting evidence exists for some boundaries furthermore the ages of 22 events and chron boundaries have been compared with the oxygen isotope record 5 thought to represent global ice volume all events and reversals younger than 2 6 ma may have occurred during periods of global cooling or during cold stages however some ages are still too poorly dated for a definite correlation climatic signals also exist in the two longest relative paleointensity records 6 7 but these are suspected to be caused by climatically driven variations in the rock magnetic parameters a mechanism for field reversals may be the acceleration of the earth s rotation caused by lowering of the sea level during glaciations the short duration of events also implies that the geomagnetic field can reverse an order of magnitude faster than commonly assumed

high primary productivity during the ediacaran period revealed by the covariation of paired c isotopic records from south china abstract remarkable carbonate carbon isotope 13ccarb excursions accompanied by invariant organic carbon isotope 13corg values have been observed in many late neoproterozoic successions this decoupled relationship between 13ccarb and 13corg in the precambrian differs from most phanerozoic records which have been substantially imprinted by aqueous photosynthesis and it has been tentatively interpreted as resulting from exotic organic matter inputs or diagenesis in this study we present high resolution 13corg records in combination with previously published 13ccarb data from a continuous drill core from the yangtze platform of south china the studied interval spans the cryogenian nantuo formation the ediacaran doushantuo and dengying formations and the base of the cambrian yanjiahe formation the 13ccarb profile of this drill core can be reliably correlated with contemporaneous sequences and it reveals multiple negative 13ccarb excursions associated with phosphorite deposits intriguingly the 13corg profile exhibits a co varying trend with the 13ccarb profile and the coupled relationship between 13ccarb and 13corg is rare in geological records of the precambrian the 13corg values of the drill core vary from 22 13 to 34 12 and the overall isotopic difference 13ccarb org between 13ccarb and 13corg ranges between 19 61 and 34 58 most of the 13corg and 13ccarb org data can be interpreted in terms of oxygenic photosynthesis probably mainly by eukaryotic algae however it is possible that exotic organic matter most likely doc from the deep ocean may also have contributed to the sedimentary organic matter composition of specific intervals studied herein moreover high primary productivity in shallow water may have been sustained for a long period in phosphate rich conditions and the organic matter generated by photosynthesis may have been quantitatively sufficient to overwhelm the doc buffering effect in the total 13corg signal throughout the ediacaran period the enhanced burial of organic matter in sediments would gradually result in the accumulation of oxygen both in the ocean and atmosphere which would likely have paved the way for macroscopic animal evolution

upper crustal fluids in a large fault system microstructural trace element and oxygen isotope study on multi phase vein quartz at the bavarian pfahl se germany fault systems are zones of crustal weakness and are used as pathways for ascending hydrothermal fluids one impressive example is the more than 150 km long bavarian pfahl system at the sw boundary of the bohemian massif dextral ductile shearing of moldanubian basement has shaped a several hundred meter wide zone of mylonites and ultramylonites this setting was reactivated under brittle conditions and infiltrated by fluids resulting in a multi phase quartz lode structural analysis using scanning electron microscopy cathodoluminescence sem cl images has been carried out in combination with trace element and oxygen isotope analysis on quartz along the system three successive quartz phases have been distinguished due to their structural details and trace element contents cryptocrystalline quartz fabric in the first quartz phase results from crystallization from a silica gel whereas in phases ii and iii quartz precipitation is characterized by repeated fragmentation and sealing visible due to strongly varying cl intensities the 18o of bavarian pfahl quartz decreases from 13 8 in the nw to 8 5 in the se whereas quartz from the close by situated wolsendorf fluorite deposit shows 18o between 15 9 and 18 5 vs smow flat shale normalized rare earth element patterns point towards an upper crustal origin of the hydrothermal fluids the southeastern part of the bavarian pfahl is interpreted to represent a deeper crustal level with higher mineralization temperatures about 350 c compared to the rest of the pfahl 250 c

hematite in porous red clouded feldspars evidence of large scale crustal fluid rock interaction abstract transmission electron microscopy shows that red clouded alkali feldspars from granitic rocks contain numerous open pores up to several hundred nanometres in cross section and that almost every pore contains rosettes or needles of crystalline hematite in the samples described here the hematite forms at the reaction interfaces at which plagioclase feldspar is replaced by alkali feldspar these observations together with the fact that the origin of the porosity can be explained by the mechanism of sub solidus mineral fluid replacement processes indicate that hematite is a direct product of fluid rock interaction and is not a solid state exsolution product from the feldspar

buried preglacial fluvial gorges and valleys preserved through quaternary glaciations beneath the eastern laurentide ice sheet the geomorphology geometry and sedimentary infill of buried gorges and v shaped valleys observed at the base of major river valleys in the formerly glaciated southeastern canadian shield region have been revealed from excavation and drilling data acquired during the construction of hydro electric dams and seismic data collected on lakes and offshore compilation of these previously published and unpublished data provided an exceptional opportunity to examine the morphology and spatial distribution of buried bedrock gorges and the mechanical processes responsible for their erosion in some valleys detailed observations of deep gorges have been allowed by their exhumation over large areas archive photographs show deep and large potholes natural pillars furrows flutes and scallops on the well polished bedrock walls of the gorges they also reveal that gorges and valleys have a sharp ending v shape and very narrow base and are superimposed by a u shaped valley forming a buried valley within valley topography the narrow and deep cross profile of these gorges their well polished slopes and the type of bedforms observed within them are typical features of fluvial bedrock channels drilling operations at many sites have also provided data on bedrock topography of these gorges within valleys and on the nature of their sedimentary infill the different lines of evidence presented in this paper indicate that gorges and v shaped valleys of the region were not eroded by the laurentide ice sheet during quaternary glaciations but are relics of a preserved preglacial fluvial system eroded during a lower base level this paleofluvial system is interpreted to be linked to fluvially cut channels observed on the seafloor of the estuary and gulf of st lawrence

oxygen isotopic compositions of the late orogenic granites in the southern piedmont of the appalachian mountains u s a and their relationship to subcrustal structures and lithologies abstract data were acquired from 143 whole rock samples from 20 late orogenic post metamorphic hercynian age granitic plutons from the piedmont of the southern appalachians principally in georgia and south carolina these plutons exhibit a regional gradient in oxygen isotopic compositions in which the granites confined to the inner piedmont to the northwest are 18 o enriched 11 4 to 7 9 whereas those toward the southeast within the charlotte slate and portions of the kiokee belts have distinctly lower 18 o 16 o compositions 8 2 to 5 5 one body that lies along the southeastern edge of the piedmont in south carolina however appears to be anomalously 18 o enriched 8 9 most plutons display 18 o 16 o variations of 18 o enriched plutons occupy areas characterized by negative anomalies whereas low 18 o bodies are invariably restricted to regions of positive anomalies 2 87 sr 86 sr data where granites with 18 o values 18 o enriched plutons 9 have ratios 0 710 3 contrasting chemical and accessory mineral compositions in which many 18 o depleted granites have a number of i type characteristics whereas several of the most 18 o enriched plutons exhibit a number of s type features it can be inferred from these data that the 18 o enriched granites were formed from continental crustal protoliths that underlie much of the inner piedmont and portions of the kiokee belt whereas the low 18 o plutons were derived from more mafic sources beneath the charlotte slate and portions of the kiokee belt the overall correspondence between the regional 18 o 16 o patterns exhibited by the granites and gravity data implies that these grantes may be essentially rooted to their protoliths in turn suggesting that the large scale translational movement recently proposed for the southern piedmont may have occurred prior to intrusion of these granites 320 m y ago

a unique sequential melting mechanism for the generation of anatectic granitic rocks from the penafiel area northern portugal abstract granitic rocks derived by sequential partial melting are very uncommon occurrences worldwide with only three known cases in portugal tourem guarda sabugal and penafiel and one in argentina achiras complex the suite documented in this paper comprises two of the three main phases of a batholith in the penafiel area these variscan peraluminous two mica granite and granodiorites formed at 310 and 305 ma during and near the end of the variscan d3 deformation and have the characteristics of s type granites none of the metamorphic country rocks have an adequate sr isotopic composition to be a protolith it is argued that progressive isotopic re equilibration of crustal material probably a metagreywacke for g1 and g3 with also some metapelitic contribution for g2 during granulization of the lower variscan crust explains the difference in isotopic composition between outcropping granitic rocks and metamorphic country rocks biotite muscovite granite g1 and biotite muscovite granodiorite g3 have similar 87 sr 86 sr i and end t values and were derived by sequential partial melting of the same source material this is indicated by coherent trends of the whole rock major and trace element compositions the compositions of feldspar biotite muscovite and tourmaline the presence and type of xenocrystic mineral phases and xenoliths and whole rock oxygen isotope compositions this mechanism was the result of post thickening variscan extension and mantle upwelling another member of the same batholith is a biotite muscovite granodiorite g2 with an intermediate age of 307 ma but with geochemical characteristics suggesting that it corresponds to a chemically distinct pulse of magma although likely stemming from a comparable though more metapelitic lower crustal source

300 million years of episodic hydrothermal activity stable isotope evidence from hydrothermal rocks of the eastern iberian central system the eastern iberian central system has abundant ore showings hosted by a wide variety of hydrothermal rocks they include sn w fe and zn w calcic and magnesian skarns shear zone and episyenite hosted cu zn sn w orebodies cu w sn greisens and w sn base metal and fluorite barite veins systematic dating and fluid inclusion studies show that they can be grouped into several hydrothermal episodes related with the waning variscan orogeny the first event was at about 295 ma followed by younger pulses associated with early alpine rifting and extension and dated near 277 150 and 100 to 20 ma respectively events ii iv the 18o d and 34s studies of hydrothermal rocks have elucidated the hydrological evolution of these systems the event i fluids are of mixed origin they are metamorphic fluids h2o co2 ch4 nacl 18o 4 7 to 9 3 d ab 34 related to w sn veins and modified meteoric waters in the deep magnesian sn w skarns h2o nacl 4 5 6 4 wt nacl eq 18o 7 3 7 8 d 77 to 74 and epizonal shallow calcic zn w and fe skarns h2o nacl 14 wt nacl eq from evaporites hosted in the post variscan sequence the d values are very similar to most of those recorded by kelly and rye in panasqueira and confirm that the upper paleozoic meteoric waters in central iberia had very negative d values 52 whereas those of early mesozoic age ranged between 65 and 36

interaction between two contrasting magmas in the albtal pluton schwarzwald sw germany textural and mineral chemical evidence the magmatic evolution of the variscan albtal pluton schwarzwald sw germany is explored using detailed textural observations and the chemical composition of plagioclase and biotite in both granite and its mafic magmatic enclaves mmes mmes probably formed in a two step process first mafic magma intruded a granitic magma chamber and created a boundary layer which received thermal and compositional input from the mafic magma this is indicated by corroded granitic quartz crystals and by large granitic plagioclase xenocrysts which contain zones of higher anorthite and partly crystallized from a melt of higher sr content texturally different plagioclase types e g zoned and inclusion rich types correspond to different degrees of overprint most likely caused by a thermal and compositional gradient in the boundary layer the intrusion of a second mafic magma batch into the boundary layer is recorded by a thin an50 zone along plagioclase rims that crystallized from a melt enriched in sr most probably the second mafic intrusion caused disruption of the boundary layer dispersal of the hybrid magma in the granite magma and formation of the enclaves rapid thermal quenching of the mmes in the granite magma is manifested by an30 overgrowths on large plagioclase grains that contain needle apatites our results demonstrate the importance of microtextural investigations for the reconstruction of possible mixing end members in the formation of granites

u th he evidence of jurassic continuous hydrothermal activity in the schwarzwald basement germany abstract u th he model and isochron ages of 21 botryoidal hematites collected from the hohberg base metal vein system in the triberg granite complex mittelschwarzwald germany cover most of the jurassic period the possibility of quantitative 4 he loss triggered by successive hydrothermal events although conceivable for individual hematites based on a 4 he retentivity study and calculated opening temperatures of hematite for 4 he of 90 180 c can largely be ruled out thus the range of model and isochron ages indicates that the majority of the hematites are not cogenetic this is supported by a broad range of pb total concentrations in the hohberg botryoidal hematites 150 2700 ppm by comparison with virtually identical pb total concentrations found in cogenetic hematites from four different vein systems in the schwarzwald the th u ratios of the hematites vary by a factor of 700 0 01 7 25 mainly as a result of the range of th concentrations 0 1 74 ppm the incorporation of substantial amounts of th in hematite is thought to result from increased th transport mobility possibly caused by association with colloids and or complexing in the ore solution 18 o analyses of a 160 ma old cogenetic hematite quartz pair indicate that precipitation occurred from a fluid of magmatic origin at a temperature of 180 c the regional temperature peak in the basement at the present erosional surface during the jurassic 130 c provides a lower temperature limit of hematite formation this implies that hematite emplacement occurred at temperatures roughly ranging between 130 and 180 c the jurassic continuous hydrothermal activity suggests that the pre rifting european craton is characterized by local thermal fluxes during a long time span

the complex hydrothermal history of granitic rocks multiple feldspar replacement reactions under subsolidus conditions recurring subsolidus re equilibration of granitic feldspars induced by fluid infiltration events provides a record of fluid rock interactions that affect large volumes of the earth s continental crust this has a direct bearing on the interpretation of the present day granitic rock mineralogy and geochemistry we examine palaeoproterozoic grey and red stained granitoids from the simpevarp and laxemar areas in se sweden particularly focusing on consecutive feldspar replacement reactions to provide an in depth understanding of subsolidus re equilibration of granitic rocks with hydrothermal fluids the apparently most unaltered grey granitoids contain highly porous oligoclase grains that enclose crystallographically continuous microcline relicts this texture suggests that the oligoclase is already secondary and may be a replacement product of original microcline oligoclase is progressively replaced by albite an9 along polysynthetic twinning and intragranular fractures the features of this replacement are characteristic of a dissolution reprecipitation mechanism finegrained mica sericite is closely associated with the albite porosity within micron sized pores observable with scanning electron microscopy as well as in nanopores imaged with transmission electron microscopy the reddening phenomenon in the vicinity of fractures is contemporaneously related to the k feldspathization of sericite which is restricted to the altered oligoclase submicron size hematite precipitation within orthoclase pores at the replacement front results in the red coloration the complex associations between the fluid feldspar reactions indicate that the replacement reactions may be due to sequential fluid infiltration events and that the granitoids have undergone extensive subsolidus re equilibration changing the original magmatic mineralogy therefore the effects of large scale re equilibrations of granitic rocks through hydrothermal convection systems should be more closely considered

stable isotope composition of impact glasses from the nordlinger ries impact crater germany abstract the ries impact which today is represented by a 24 km diameter complex crater occurred at 15 ma it is estimated that a projectile of about 1 km diameter formed a transient crater of 6 to 7 km radius and 2 8 km depth impact melt glasses investigated are found within the suevite the breccia that forms the uppermost layers of the ejecta blanket around the crater the glasses are considered to represent quenched melts produced as a result of the impact the oxygen isotope compositions of several glasses sampled from widely spaced localities are very homogeneous with 18 o values in the range of 6 7 to 7 4 and 17 o of 3 3 to 3 7 with increasing devitrification and alteration the 18 o values increase up to 15 8 17 o up to 8 1 water content also increases with devitrification from fresh glasses with about 1 3 wt to 3 8 wt in devitrified glass d values decrease with increasing water content from about 87 to 127 whole rock oxygen isotope compositions of the sedimentary cover sequence range from 17 to 27 and crystalline basement rocks range from 8 8 to 13 5 for granites and gneisses whereas amphibolites have 18 o values of 5 2 and 6 1 models suggesting that the glass in the suevite represents a mixed melt derived from all the rocks present in the suevite in proportion of their occurrence engelhardt 1997 do not agree with the oxygen isotope composition of the glass the simplest explanation for the homogeneous chemical and oxygen isotope composition is that the glass represents quenched melts from a few closely spaced lithologies only high fe and ni contents in the glass cr ni and cr co ratios and relatively low 18 o values indicate involvement of amphibolites during melting the balance of the melt was made up of spatially associated granites or gneisses as indicated by the major element and rare earth element geochemistry the best agreement between major element and oxygen isotope composition of the glass and model melts is obtained by mixtures of amphibolite and granite in proportions similar to their average occurrence in the fallout suevite

seismic stratigraphy of late cenozoic sediments in the northern labrador sea a history of bottom circulation and glaciation the seismicstratigraphy of the upper 1 km of sediment in the northern labrador sea has been determined from the examination of about 26 000 line kilometres of seismic profiles four key reflectors a to d have been correlated with deep sea drilling project dsdp and ocean drilling program odp holes and range in age from mid pliocene to approximately mid pleistocene ten seismic facies have been distinguished and are interpreted as resulting from slope progradation turbidite deposition in channels and on the basin floor and widespread contourite deposition tertiary sediments are predominantly hemipelagic or contourite but in the mid pliocene turbidite deposition began in the northeast labrador basin which might reflect either greenland glaciation or lowering of sea level at the same time widespread erosion and buildup of drift deposits indicate that there was an intensification of bottom water circulation probably reflecting high latitude cooling this was followed by a return to less dynamic c

high 18o granitic plutons from the frontenac axis grenville province of ontario canada abstract 18 o 16 o ratios have been determined for whole rock as well as coexisting minerals from nine syn to post tectonic monzonite and quartz monzonite plutons in the westport gananoque area covering approximately 2500 km2 the plutons fall in two distinct isotopic groups 1 i low 18o group 8 0 11 2 rideau lake westport and wolfe lake plutons and 2 ii high 18o group 12 7 16 2 lyndhurst perth road battersea gananoque south lake and crow lake plutons the 18 o 16 o ratios of granitic rocks from the latter group are among the highest ever reported in the literature the isotopic compositions of samples within each pluton bear no relationship to the sample distance from the intrusive contacts nor are they affected by the types of country rocks marbles vs pelitic gneisses into which they are emplaced oxygen isotope fractionations among coexisting quartz feldspar biotite and magnetite all show normal plutonic values thus all lines of evidence suggest that the monzonite and quartz monzonite plutons did not acquire their characteristic 18 o 16 o ratios at the present level of exposure either by isotopic exchange with the surrounding metasedimentary country rocks or by any post crystallization low temperature alteration processes the distinct 18o 16o ratios observed in the high and low 18o groups probably reflect the difference in the isotopic compositions of the source materials the most plausible source for the high 18o group plutons is the grenville supergroup metasedimentary rocks and that for the low 18o group plutons the grenville basement gneisses mixed with a small amount of grenville supergroup metasedimentary rocks

black shale deposition atmospheric co2 drawdown and cooling during the cenomanian turonian oceanic anoxic event 1 oceanic anoxic event 2 oae2 spanning the cenomanian turonian boundary ctb represents one of the largest perturbations in the global carbon cycle in the last 100 myr the 13ccarb 13corg and 18o chemostratigraphy of a black shale bearing ctb succession in the vocontian basin of france is described and correlated at high resolution to the european ctb reference section at eastbourne england and to successions in germany the equatorial and midlatitude proto north atlantic and the u s western interior seaway wis 13c offset between 13ccarb and 13corg is shown to be a good pco2 proxy that is consistent with pco2 records obtained using biomarker 13c data from atlantic black shales and leaf stomata data from wis sections boreal chalk 18o records show sea surface temperature sst changes that closely follow the 13c pco2 proxy and confirm tex86 results from deep ocean sites rising pco2 and sst during the late cenomanian is attributed to volcanic degassing pco2 and sst maxima occurred at the onset of black shale deposition followed by falling pco2 and cooling due to carbon sequestration by marine organic productivity and preservation and increased silicate weathering a marked pco2 minimum 25 fall occurred with a sst minimum plenus cold event showing 4 c of cooling in 40 kyr renewed increases in pco2 sst and 13c during latest cenomanian black shale deposition suggest that a continuing volcanogenic co2 flux overrode further drawdown effects maximum pco2 and sst followed the end of oae2 associated with a falling nutrient supply during the early turonian eustatic highstand

constraints on the origin of damaran granites by rb sr and δ 18 o data the mean 87sr 86sr and mean 87rb 86sr ratios of the intrusive granites from the north and south of the orogen s central zone plot on straight lines these are interpreted as areal isochrons indicating the time of last sr isotope homogenization 526 and 571 ma ago in the respective source rocks

the oxygen isotope composition of hercynian granites and pre hercynian gneisses from the schwarzwald sw germany the oxygen isotope composition of 56 hercynian granites and 42 pre hercynian gneisses has been investigated in addition some mineral 18o data and 5 d values of whole rocks have been obtained the granites from the n schwarzwald show in general relatively uniform 18o values between 11 5 and 13 5 those from the s schwarzwald are less uniform and lighter in 18o and range from 2 3 to 11 5 the gneisses from the pre hercynian basement exhibit more or less the same variation and range from 1 7 to 10 4 18o values 6 only occur in the s schwarzwald and obviously indicate hydrothermal interactions of meteoric waters which probably took place after the emplacement and solidification of the granites and which equally affected granites and gneisses due to the nearly identical 18o 16o ratios of s schwarzwald granites and gneisses it is proposed that such gneisses in the pre hercynian basement qualify as the precursor rocks of the s schwarzwald granites whereas for the n schwarzwald granites crustal rocks with heavier 18o values unknown from the present surface have to be postulated this distribution is also reflected on a 87sr 86sr 18o 16o diagram

phase equilibria and oxygen isotopes in the evolution of metapelitic migmatites a case study from the pre alpine basement of northern switzerland metapelites that have undergone variable degrees of migmatization were encountered in two deep boreholes in northern switzerland microtextures and calculated phase diagrams yield three successive stages of metamorphism consistent with one p t loop 1 amphibolite grade metamorphism biotite sillimanite garnetoligoclase quartz ilmenite p t conditions are estimated at 4 5 6 5 kbars 550 650 c 2 anatectic migmatization melting reactions leucosomes do not represent pure crystallized melt but rather a mixture of melt cordierite and k feldspar grown at the expense of biotite and sillimanite 3 retrograde hydration recorded by the growth of large amounts of muscovite at the expense of cordierite and k feldspar p t conditions are estimated at 2 5 kbars 600 c oxygen isotope measurements were obtained for whole rocks and eight mineral species isotopic equilibrium among three or even four minerals grown during stage 1 can be demonstrated calculated isotopic temperatures are consistent with phase petrology migmatization did not re equilibrate the isotopic composition of the pre existing quartz grown in stage 1 even over distances as little as 10 cm high 18o in migmatitic quartz is best explained by disequilibrium melting in coexistence with an infiltrating isotopically heavy fluid lack of equilibration of oxygen isotopes between different quartz generations suggests that mineralogical and geochemical changes were rapid relative to diffusion rates a meteoric hydrothermal alteration at 300 400 c probably genetically linked to the intrusion of variscan granites strongly affected the rocks quartz did not exchange isotopes with hydrothermal fluids except in segregations where it is recrystallized the 18o values of micas feldspars and cordierite are often very low and fractionations with quartz very large which reflects significant hydrothermal effects that were previously detected in the black forest by other workers

the corossol structure a possible impact crater on the seafloor of the northwestern gulf of st lawrence eastern canada we report on a 4 1 0 2 km diameter and 185 m deep circular submarine structure exposed on the seabed in 40 m water depths in the northwestern gulf of st lawrence eastern canada from the analysis of high resolution multibeam bathymetric and seismic data the presence of a circular form characterized by a central uplift and concentric rings resembles the morphology and geometry of complex meteorite impact structures also other origins such as kimberlites intrusions karsts or diapirs can be eliminated on geological criteria a single 4 cm long breccia fragment recovered from the central uplift has numerous glassy droplets of fluorapatite composition assumed to be impact melts and a single quartz grain with planar intersection features thought to be shock induced planar deformation features pdfs the absolute age of this possible impact structure is unknown but its geological setting indicates that it was formed long after the mid ordovician and before regional pre quaternary sea level lowstands present results outline the need for further examination to confirm an impact origin and to precisely date the formation of the structure

the origin and evolution of the menderes massif w turkey a rubidium strontium and oxygen isotope study the menderes massif located in the alpine orogen of western turkey has three litho structural units a basal gneiss core a schist mantle covering the gneiss core and an overlying marble mantle this study reports isotopic data from samples of metasediments and migmatites from the southern type a and of tonalitic to granitic metaigneous rocks from the northern menderes massif type b type a rocks define a rb sr whole rock isochron age of 502 10 ma and an initial87sr 86sr ratio of 0 71174 73 this is interpreted as the age of migmatization type b rocks give a rb sr whole rock isochron age of 471 9 ma with an initial87sr 86sr ratio of 0 70684 25 which we interpret as the intrusion age k white micas from rock type a give an average rb sr mineral age of 56 1 ma which can be interpreted as the formation age of the alpine mineral paragenesis k white micas from rock type b give rb sr mixed ages of 120 230 ma between alpine and pan african orogenies biotites from both rock types yield an average rb sr age of 37 1 ma which is interpreted as an alpine cooling age the oxygen isotope ratios of type a rocks range from 10 4 to 14 6 and of type b from 8 9 to 11 8 the oxygen and strontium isotopic compositions together clearly distinguish rocks of types a and b compositions of type a rocks suggest a crustal origin type b rocks have compositions transitional between those of crustal and mantle derived materials

plio pleistocene evolution of the var deep sea fan off the french riviera abstract the var deep sea fan was deposited during the pliocene and quaternary seaward progradation of the var delta within a steep sided flat floored basin formed during the messinian salinity crisis the prominent palaeo var canyon was cut on the slope at the same time following the early pliocene transgression var sediments were initially trapped in the coastal ria formed by sea level incursion of the head of the messinian valley by middle pliocene time gilbert type deltas had prograded to the break of slope modern coastline allowing coarse sediment to reach the basin quaternary coastal uplift and sediment supply from the glaciated alps resulted in a supply of coarse sediment to the fan by the braided var river throughout the quaternary even during sea level highstands such as the present in the earliest pliocene hemipelagic clays accumulated while coarse sediment was trapped in the var ria through the rest of the pliocene a leveed fan valley extended southward from the var canyon which periodically switched locations through avulsion to the east at about the beginning of the quaternary this eastward spillover channel became the main distributary and re occupation of the older south trending channels was blocked by rapid levee progradation and aggradation of mud waves by overbanking of turbidity flows on the var sedimentary ridge during the quaternary channel shifting to the north occurred the quaternary var fan has an unusually steep concave longitudinal profile compared with most passive margin fans the laurentian fan has a similar profile to the var both have a high levee and a gravel and pebble floored fan valley that is essentially a bypass zone compared with the aggradational channel levee systems with lower levees in most passive margin fans this is a consequence of the constant supply of coarse sand gravel and pebbles to the fan even during highstands of sea level the erosive capability of this coarse sediment in ignitive turbidity currents resulted in flushing out of the upper and middle fan valley system thick muddy turbidity currents probably resulting from slumping caused by canyon incision produced the prominent mud waves on the levee the concave longitudinal profile led to rapid sediment deposition at critical points in the valley system as a result of turbidity flow expansion this in turn promoted the development of a left hook in the valley system

carbon isotope chemostratigraphy and sedimentary facies evolution of the ediacaran doushantuo formation in western hubei south china abstract the doushantuo formation of south china consisting of intercalated siliciclastic and carbonate rocks which exhibit considerable variation in thickness and sedimentary facies is one of the key sedimentary units in the world for understanding ediacaran geobiological processes however stratigraphic correlation and sedimentary facies evolution of the doushantuo formation remain controversial sedimentary facies analysis of the well known sections of the yangtze gorges area and new sections in northern yichang western hubei indicate that the doushantuo succession in the yangtze gorges area was deposited in an offshore intra shelf basin within the yangtze platform in contrast the doushantuo formation in the northern yichang area which is characterized by one or a few phosphate rich horizons represents deposition on the subtidal or intertidal shelf and so is similar to the succession in the weng an area central guizhou province the carbon isotope profiles of the different sections exhibit significant variation which is interpreted to result from facies differences sequence and high resolution carbon isotope stratigraphy have clarified problematic correlations and the temporal relationship between fossil assemblages of the doushantuo formation on the yangtze platform the results confirm that a prominent negative 13ccarb excursion baince nadir down to 5 in the middle portion of the second sequence of the doushantuo formation is a widely traceable event baince together with three other 13ccarb excursions namely cance at the base wance near the first sequence boundary near the middle and dounce at the top of the doushantuo formation constitute a complete carbon isotope profile for the doushantuo formation that reflects contemporaneous seawater and so serves as a reference chemostratigraphic profile for global stratigraphic correlation and for evaluating the chemical evolution of seawater during the ediacaran period

evolution of the cenozoic sedimentary wedge during rifting and seafloor spreading west of the stappen high western barents sea abstract the cenozoic sedimentary wedge west of the stappen high is divided into five main stratigraphic units from oldest to youngest these are unit r unit b unit tec unit ted and unit tee unit r was deposited in a faulted relatively deep marine basin prior to the onset of seafloor spreading in the northernmost part of the norwegian greenland sea the unit was probably deposited from early eocene to early oligocene time with the stappen high as a major source area the base of unit b represents the onset of a second episode of faulting erosion and subsidence west of the stappen high the unconformity is probably related to the early oligocene anomaly 13 change in relative plate movements to a more west northwest trend causing rifting and later seafloor spreading in the northern norwegian greenland sea a period of heavy erosion on the paleocontinental slope and shelf break occurred in mid miocene time 15 5 ma the base of unit tec the relatively deep erosion west of the stappen high was probably related to compression and uplift along northeast southwest oriented faults combined with a period of low eustatic sea level the mid miocene to intra pleistocene parts of the cenozoic sedimentary wedge units tec and ted are dominated by complex lowstand fan deposits and prograding sequences deposited during gradual thermal subsidence of the margin several unconformities related to relative sea level changes are identified within this part of the wedge the most important sequence boundaries are the 5 5 ma base of unit ted boundary and the intra pleistocene 0 8 ma base of unit tee boundary which probably represent the onset of extensive ice sheet formation on the barents shelf

timing of deep water slope evolution constrained by large n detrital and volcanic ash zircon geochronology cretaceous magallanes basin chile

petrogenesis of hercynian leucogranites from the southern armorican massif contribution of ree and isotopic sr nd pb and o geochemical data to the study of source rock characteristics and ages abstract ree geochemistry and isotopic pb sr nd o compositions have been studied in up to nine separate leucogranite massifs from three structurally adjacent zones in south brittany ages decrease from 340 ma in the north to 300 ma in the south whereas initial 87 sr 86 sr ratios increase from 0 706 to 0 710 0 717 ree abundances are relatively low la n 20 80 chondrites with a strong enrichment of lree relative to hree la n lu n 13 4 26 6 pb isotope ratios are homogeneous for a given massif but heterogeneous among massifs and plot very close to a normal terrestrial lead growth curve at 300 ma ago 18 o 16 o ratios are high and relatively uniform at 10 7 to 12 8 mean 11 9 u pb studies on zircon indicate the presence of an inherited radiogenic pb component and that the sediment dominated source region had been metamorphosed during the siluro devonian ligerian negativee nd t values imply that the source region had been enriched in lree prior to the melting episode based on the combined data large scale partial melting of crustal material dominantly of sedimentary origin is proposed the model age of the source rocks is not very old 600 700 to 1200 ma the pb and sr isotopic variations observed among different massifs is probably the result of age differences in the source materials of the different leucogranites

sediment transport processes at the head of halibut canyon eastern canada margin an interplay between internal tides and dense shelf water cascading abstract to investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin the bottom boundary layer quadrapod ralph was deployed at 276 m depth in the west halibut canyon off newfoundland during winter 2008 2009 two main sediment transport processes were identified throughout the deployment firstly periodic increases of near bottom suspended sediment concentrations ssc were recorded associated with the up canyon propagation of the semidiurnal internal tidal bore along the canyon axis carrying fine sediment particles resuspended from deeper canyon regions the recorded ssc peaks lasting less than 1 h were observed sporadically and were linked to bottom intensified up canyon flows 40 cm s 1 concomitant with sharp drops in temperature secondly sediment transport was also observed during events of intensified down canyon current velocities that occurred during periods of sustained heat loss from surface waters but were not associated with large storm waves high resolution velocity profiles throughout the water column during these events revealed that the highest current speeds 1 m s 1 were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow such flows had associated low ssc and cold water temperatures and are interpreted as dense shelf water cascading events channelized along the canyon axis sediment transport during these events was largely restricted to bedload and saltation producing winnowing of sands and fine sediments around larger gravel particles analysis of historical hydrographic data suggests that such gravity flows are not related to the formation of coastal dense waters advected towards the outer shelf that reached the canyon head rather the dense shelf waters appear to be generated around the outer shelf where convection during winter is able to reach the sea floor and generate a pool of near bottom dense water that cascades into the canyon during one or two tidal cycles a similar transport mechanism is likely to occur in other submarine canyons along the eastern canadian margin as well in other canyoned margins where winter convection can reach the shelf edge

petrographic evidence from the eastern canadian margin of shelf crossing glaciations abstract it is difficult to evaluate when and where glaciers extended across the outer continental shelf off eastern canada the outer shelf and upper slope are commonly hard bottomed or have a great thickness of post glacial sediment in either case making direct sampling and dating of ice margin sediment impossible the timing and extent of glacier ice is important for understanding continental slope sedimentation and ice sheet dynamics we have therefore determined the lithologic components of the 1 4 mm granule fraction of over 100 well dated samples from 40 cores from the more distal parts of the deep water margin off nova scotia and newfoundland this fraction is demonstrably ice rafted in these cores and geographic variation in component results from input of icebergs at different calving margins the samples show that heinrich layers have a distinctive granule fraction that shows some areal variation as a result of dilution by sources other than hudson strait heinrich event 2 ca 21 ka is widespread as far southwest as the west scotian slope but by the last glacial maximum lgm numerous discrete sources of ice rafted granules are recognised implying that calving ice margins were present in several places off newfoundland and nova scotia including off banquereau a distinctive purplish lgm gravelly mud is recognised on the eastern newfoundland margin derived from a calving margin on the ne newfoundland shelf at the time of heinrich event 1 ca 14 ka there was a calving ice outlet somewhere on the grand banks and another in halibut channel retreat of ice from the gulf of st lawrence can be tracked by changing granule petrology from the lgm to 13 ka these data suggest that final ice retreat from many parts of the outer shelf was later than is shown in many recent ice margin reconstructions