weichselian land sea interactions western norway norwegian sea abstract six major weichselian glacier expansions including the younger dryas are recorded in western norway three of the advances reached the continental shelf while the others were restricted to the coastal areas during the upper weichselian glacial maximum 18 20 ka there was an ice free corridor between the british and the scandinavian ice sheets in the northern north sea more or less complete deglaciation of southern norway seems to have happened some time around 90 and 70 ka large parts of the norwegian sea were at least seasonally open with influx of atlantic surface water in periods through isotope substage 5d to stage 4 possibly also during a short time interval close to the 2 3 boundary a small area in the southeastern norwegian sea was ice free all these influxes of atlantic water seem to correlate to periods with interstadial conditions in western norway during times with the most extensive continental glaciations there are no traces of any influx of atlantic surface water the western norwegian glacial record and the norwegian sea surface circulation record seem to vary with a ca 20 ka cycle during the weichselian this indicates a dominance of the precessional orbital forcing between the ca 100 ka interglacial glacial interglacial cycle

saalian to weichselian stratigraphy and sedimentation along the lagjaeren hogjaeren escarpment southwest norway quaternary sediments along a profile crossing the southern part of the jaeren escarpment southwestern norway have been investigated with regard to their glacial history and sea level variations deposits from at least three glaciations and two ice free periods between oxygen isotope stage 6 and the late weichselian have been identified subglacial till directly overlain by a glaciomarine regressional succession indicates a deglaciation and amino acid ratios in elphidium excavatum between 0 083 and 0 118 date this event to oxygen isotope stage 6 sea level dropped from 130 to below 110 m a s l subsequently a short lived ice advance deposited a marginal moraine and a sandur locally on the escarpment stratigraphical position and luminescence dates around 148 ka bp suggest deposition during the final stage 6 deglaciation a late weichselian till covers most of the surface of jaeren in addition to a well documented westerly ice flow glaciotectonic indications of ice flow towards the north have been found ice flow directions and a hiatus between oxygen isotope stage 6 and the weichselian indicate enhanced erosion along the escarpment and the influence of a norwegian channel ice stream copyright 1999 john wiley sons ltd

evolution of depressions on comet 67p churyumov gerasimenko role of ice metamorphism abstract this work is intended to investigate the influence of temperature dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei we are mainly interested in the role of initial cohesivity of a nucleus for this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of different initial structure the simulations account for the diurnal and orbital changes of insolation and its dependence on the current shape of the depressions our model includes heat transport in the cometary material and metamorphism of ice we present the results obtained for the nucleus of the comet 67p churyumov gerasimenko target of the esa cornerstone mission rosetta

stream driven high density gravelly traction carpets possible deposits in the trabeg conglomerate formation sw ireland and some theoretical considerations of their origin within high density flood flows a prominent mechanism of gravel transport and deposition is by stream driven high density traction carpet with a rheology similar to grain flow these gravel carpets are envisaged to form the basal portion of a bipartite high density flood flow decoupled from an overlying sand and silt laden turbulent flow several examples already documented in the literature are reviewed and an additional case from the lower old red sandstone of southwest ireland is presented two mechanisms of traction carpet initiation are discussed by rapid entrainment of gravel into suspension on rising stage followed by settling into the gravel traction carpet at peak and falling stage and by overconcentration of a normal low density bedload gravel entrainment suspension and traction carpet development are significantly easier if the flood water already carries a high concentration of sand and silt in suspension theoretical consideration further shows that gravelly traction carpets can be maintained in channels of relatively low gradient by the shear stress exerted by the high density sand bearing turbulent flood flow above this tangential shear stress is converted to dispersive pressure which aids buoyancy and quasi static grain to grain contacts in the support of the clasts within the gravel carpet the carpet is thought to have a quasi plastic rheology but behave much like a viscous fluid at high shear rates stream driven gravelly traction carpets are expected to produce sheet like units of clast to matrix supported conglomerate characterized by a parallel or an a p a i clast fabric these units may be ungraded normally or inversely graded depending on the rate of shear the viscosity of the flow and the celerity of deposition

surface of young jupiter family comet 81p wild 2 view from the stardust spacecraft images taken by the stardust mission during its flyby of 81p wild 2 show the comet to be a 5 kilometer oblate body covered with remarkable topographic features including unusual circular features that appear to be impact craters the presence of high angle slopes shows that the surface is cohesive and self supporting the comet does not appear to be a rubble pile and its rounded shape is not directly consistent with the comet being a fragment of a larger body the surface is active and yet it retains ancient terrain wild 2 appears to be in the early stages of its degradation phase as a small volatile rich body in the inner solar system

the geology and geophysics of kuiper belt object 486958 arrokoth the cold classical kuiper belt a class of small bodies in undisturbed orbits beyond neptune is composed of primitive objects preserving information about solar system formation in january 2019 the new horizons spacecraft flew past one of these objects the 36 kilometer long contact binary 486958 arrokoth provisional designation 2014 mu69 images from the flyby show that arrokoth has no detectable rings and no satellites larger than 180 meters in diameter within a radius of 8000 kilometers arrokoth has a lightly cratered smooth surface with complex geological features unlike those on previously visited solar system bodies the density of impact craters indicates the surface dates from the formation of the solar system the two lobes of the contact binary have closely aligned poles and equators constraining their accretion mechanism

short paper a note on rb sr whole rock ages from cleaved mudrocks in the welsh basin two cleaved epizone grade palaeozoic mudrock suites from snowdonia yield a mean rb sr whole rock age of 409 11 ma this is consistent with resetting of the rb sr whole rock isotope systems of the mudrocks during cleavage development in end silurian early devonian acadian deformation in contrast cleaved palaeozoic anchizone mudrocks from north and central wales give a silurian mean age of 430 9 ma this dates either a pre tectonic isotopic event preserved through acadian anchizone metamorphism or mid silurian deformation and metamorphism at anchizone grade unaffected by the acadian event the precise timing of the main caledonian deformation in wales has never been established firmly powell phillips 1985 suggest that it occurred in north and south wales in latest silurian time whereas ashgill and end llandovery tectonic events were dominant in central wales see also george 1963 however woodcock 1984 1987 and soper et al 1987 have argued in favour of a single tectonic event of early to middle devonian age this chronological study was undertaken to address this controversy the only previous attempt to define precisely the timing of cleavage development in wales was the k ar dating of cleavage parallel chlorite from a volcanic greywacke from north wales fitch et al 1969 when recalculated using modern decay constants these data give an age of 399 10 ma bath 1974 demonstrated the feasibility of obtaining rb sr ages from cleaved mudrocks of the welsh caledonides and this work produced caledonian ages of 409 20ma and 393 22ma from north wales and late

an igneous fragment from cluster idp l2011 21 an analog for the source of pyrrhotite and taenite in comet 81p wild 2 captured in stardust aerogel

sedimentation beneath ice shelves the view from ice stream b abstract ice shelf development is favored by rapid flow of cold ice from outlet glaciers or ice streams into protected embayments with localized high spots basal melting of ice shelves is rapid near the ice front and may occur near the grounding line ice from outlet glaciers may contain significant englacial debris that is deposited as a dropstone diamicton in regions of basal melting englacial debris is sparse or absent in ice streams evidence from ice stream b draining into the ross ice shelf of west antarctica suggests that the rapid ice velocity arises from deformation of a several meter thick water saturated basal till layer that is eroding an unconformity on sediments beneath and that has deposited a till delta tens of meters thick and tens of kilometers long at the grounding line sea level fall would cause conveyor belt recycling of this till delta and grounding line advance across the ross sea to the edge of the continental shelf forming an ice sheet with a low ice stream profile resting on a several meter thick deforming till layer eroding an unconformity the modern ross sea is characterized by a regional unconformity overlain by a diamicton of probable latest pliocene pleistocene age measuring several meters to tens of meters thick we hypothesize that this diamicton is a deformed glacial till and that the ross sea sediments record one or more expansions of the till lubricated west antarctic ice sheet to the edge of the continental shelf

the shape topography and geology of tempel 1 from deep impact observations deep impact images of the nucleus of comet tempel 1 reveal pervasive layering possible impact craters flows with smooth upper surfaces and erosional stripping of material there are at least 3 layers 50 200 m thick that appear to extend deep into the nucleus and several layers 1 20 m thick that parallel the surface and are being eroded laterally circular depressions show geographical variation in their forms and suggest differences in erosion rates or style over scales 1 km the stratigraphic arrangement of these features suggests that the comet experienced substantial periods of little erosion smooth surfaces trending downslope suggest some form of eruption of materials from this highly porous object the deep impact images show that the nucleus of tempel 1 cannot be modeled simply as either an onion layer or rubble pile structure

surface geomorphology of jupiter family comets a geologic process perspective abstract recent spacecraft encounters with jupiter family comets have revealed markedly diverse surface morphologies wild 2 is dominated by steep walled and flat floored depressions tempel 1 is relatively smooth and exhibits evidence for flows and layering while hartley 2 is bi lobed with knobby terrain at its ends and a much smoother terrain in its middle this diversity of surface morphologies has been interpreted as an evolutionary sequence belton m j s 2010 icarus 210 881 897 where jupiter family comets evolve from wild 2 morphology then to tempel 1 morphology and finally to hartley 2 morphology we propose instead that the diversity of surface morphology reflects geologic processing with diverse outcomes in addition to impact cratering we consider surface modification driven by the cometary activity which is responsible for gas and dust production we consider eolian erosion that may be driven by the outflow of cometary vapor making use of information from wind tunnel experiments and in situ studies of eolian erosion on mars we adopt the model of van der waals cohesion recently proposed by scheeres et al scheeres d hartzell c sanchez p swift m 2010 icarus 210 968 984 and find that the average co 2 vapor outflow flux at hartley 2 of 0 95 10 17 cm 2 s 1 implies wind speeds sufficient to mobilize particles of 10 cm size even close to the icy reservoirs where the vapor is evolved below the surface we suggest that particles are mobilized and entrained in flows within sub surface outflow channels emerging to be readily lifted into the coma and fragmenting in the process although water production from hartley 2 is greater most of it is evolved in the coma from icy particles and does not contribute to eolian erosion of the nucleus on the other hand the much lower vapor outflow flux at tempel 1 of 4 10 14 cm 2 s 1 is insufficient in the present model to mobilize particles but is consistent with generating repeated fluidization episodes the wild 2 case is intermediate with average outflow flux 7 10 16 cm 2 s 1 which would be in our model sufficient to support eolian erosion the steep walled flat floor depressions on wild 2 may have originated as impact features but have been subsequently modified by eolian erosion causing slope recession we do not have definitive evidence to discriminate between an evolutionary sequence and diverse geologic outcomes but we suggest future in situ observations at comets that may do so

the morphology and surface processes of comet 19 p borrelly the flyby of the nucleus of the comet 19p borrelly by the deep space 1 spacecraft produced the best views to date of the surface of these interesting objects it transformed borrelly from an astronomical object shrouded in coma of gas and dust into a geological object with complex surface processes and a rich history of erosion and landform evolution based on analysis of the highest resolution images stereo images photometry and albedo we have mapped four major morphological units and four terrain features the morphological units are named dark spots mottled terrain mesas and smooth terrain the features are named ridges troughs pits and hills in strong contrast to asteroids unambiguous impact craters were not observed on borrelly s surface because of the relatively short period of this comet surface erosion by volatile sublimation is in geologic terms a very active process the formation and the morphologies of units and features appear to be driven by differential rates of sublimation erosion erosional rates across the comet are probably controlled by solar energy input and the location of the subsolar point during perihelion differences in energy input may produce different varieties of sublimation erosional landforms the terrains on borrelly suggest that solar energy input could map directly into erosional processes and landforms

forms at the base of till units indicating deposition by lodgement and melt out with examples from the wartanian tills near belchatow central poland abstract observations from a 2 to 4 km long till section in the belchatow quarry central poland show that the contact between till and sub till deposits is generally sharp and undeformed the tills contain a range of features typical of melt out processes however in laterally equivalent till bodies features typical of lodgement and subglacial shearing e g sub till deformation structures clast ploughing are common recognition of melt out and lodgement tills as separate subglacial facies indicating different subglacial conditions may prove rather simplistic in palaeoenvironmental reconstruction so called melt out and lodgement till facies probably represent only extreme end members of a range of basal till facies types till sections described here show features suggesting that both basal melt out and lodgement processes operated during one episode of subglacial deposition

procedures used for luminescence dating of sediments abstract an account of the procedures for thermoluminescence tl and optically stimulated luminescence osl dating of sediments used at the nordic laboratory for luminescence dating is given the topics discussed include sampling sample preparation separation of quartz and feldspars using heavy liquids dose rate estimation and methods for estimating the equivalent dose special attention is paid to the partial bleach tl technique of mejdahl 1988 which appears to give reliable results for partially bleached sediments optically stimulated luminescence dating using stimulation by infra red ir and green light has been taken up and especially added dose methods using stimulation by ir or green light have been tried with some success some sources of error are discussed including the adverse effect of shallow traps

deep impact excavating comet tempel 1 deep impact collided with comet tempel 1 excavating a crater controlled by gravity the comet s outer layer is composed of 1 to 100 micrometer fine particles with negligible strength 1000 kelvins a large increase in organic material occurred during and after the event with smaller changes in carbon dioxide relative to water on approach the spacecraft observed frequent natural outbursts a mean radius of 3 0 0 1 kilometers smooth and rough terrain scarps and impact craters a thermal map indicates a surface in equilibrium with sunlight

vegetation dynamics in southern france during the last 30 ky bp in the light of marine palynology the composition of the glacial vegetation of southern french plains has been a matter of debate for several decades vegetation is considered as steppic according to french and spanish lacustrine pollen records whereas cave deposits suggest the presence of mesothermophilous trees through the last glacial maximum in our paper we display new palynological records from marine sediments of the gulf of lions they indicate the presence of abies picea and deciduous quercus in the gulf of lions certainly located in the drainage basins of the pyreneo languedocian rivers these populations that were sensitive to short climatic events during marine isotopic stage 2 could have been linked to northeastern spanish and southeastern french relicts already evidenced by phylogenetic data these trees were absent from the rhone drainage basin during the deglaciation and certainly also disappeared from the pyreneo languedocian drainage basins from ca 17 to 15 ky cal bp finally the last glacial maximum does not appear as stable cold and dry as previously thought

the response of nw iberian vegetation to north atlantic climate oscillations during the last 65 kyr pollen and oceanographic data from deep ocean core md95 2039 provide a centennial to millennial scale record of conditions offshore and of the vegetation of north west iberia for the period 10 65 ka the planktonic oxygen isotope record of this core reflecting predominantly sea surface temperature sst shows a pattern of millennial scale oscillations that is very similar to climatic changes recorded by the greenland ice core records over the same interval in turn tree populations show a pattern of rapid expansions and contractions that follow the pronounced and abrupt isotopic shifts recorded offshore through marine isotope stage mis 3 this millennial scale pattern of vegetation change alternating between steppe and open woodland is superimposed on a longer term pattern of shrinking ericaceous heathland and decreasing size of successive interstadial tree populations trees persisted during the last glacial maximum lgm at greater abundance than during many of the coldest episodes of mis 3 this agrees with the marine data which indicate that lgm sea surface temperatures here were significantly warmer than the minima recorded in mis 3 our combined marine terrestrial record together with data from nearby sequences provides a stepping stone between terrestrial sequences and the greenland ice core and north atlantic marine records this will permit a better understanding of the behaviour of vegetation across different regions at several scales of climatic forcing

evidence for geologic processes on comets spacecraft missions have resolved the nuclei of six periodic comets and revealed a set of geologically intriguing and active small bodies the shapes of these cometary nuclei are dominantly bilobate reflecting their formation from smaller cometesimals cometary surfaces include a diverse set of morphologies formed from a variety of mechanisms sublimation of ices driven by the variable insolation over the time since each nucleus was perturbed into the inner solar system is a major process on comets and is likely responsible for quasi circular depressions and ubiquitous layering sublimation from near vertical walls is also seen to lead to undercutting and mass wasting fracturing has only been resolved on one comet but likely exists on all comets there is also evidence for mass redistribution where material lifted off the nucleus by subliming gases is deposited onto other surfaces it is surprising that such sedimentary processes are significant in the microgravity environment of comets there are many enigmatic features on cometary surfaces including tall spires kilometer scale flows and various forms of depressions and pits furthermore even after accounting for the differences in resolution and coverage significant diversity in landforms among cometary surfaces clearly exists yet why certain landforms occur on some comets and not on others remains poorly understood the exploration and understanding of geologic processes on comets is only beginning these fascinating bodies will continue to provide a unique laboratory for examining common geologic processes under the uncommon conditions of very high porosity very low strength small particle sizes and near zero gravity

the jaeren area a border zone of the norwegian channel ice stream abstract the coastal lowlands of jaeren southwestern norway have an extensive cover of quaternary sediments lithological biostratigraphical and geochronological investigations of a series of boreholes across jaeren have allowed us to combine earlier and new information on these deposits into a temporal model of quaternary sedimentation the cores show evidence of at least four ice free episodes with marine deposition during mainly arctic conditions the oldest of these is considered to be ca 200 ka old and the youngest one is the sandnes interstadial which is 14 c ams dated to 32 ka bp interbedded between these units are 10 40 m thick units of till with components of marine material these findings together with a re evaluation of distinct morphological features on jaeren as well as earlier provenance studies strongly suggest that jaeren has been a boundary zone between an ice stream following the norwegian channel draining a substantial part of the southern region of the fennoscandian ice sheet and local ice from south western norway through multiple periods of glaciation starting ca 1 1 myr million years ago the norwegian channel ice stream has been the main conduit of erosion products from southern scandinavia to the deep norwegian sea comparison with ice stream profiles from antarctica suggests that the deposition of relatively young marine sediments as high as ca 200 m a s l on jaeren is a result of glacial isostasy rather than regional tectonic movements

alluvial responses to the changing earth system alluvial systems are complex self organizing and hierarchical in structure they represent stored and transitory sediment bodies transported by rivers that have eroded their catchments and created multiscalar landforms and sedimentary architectures over a range of time scales the central question we address in this paper is how environmental signals are autogenically processed and recorded by the fluvial sediment system we compare databases of alluvial units that are well constrained in terms of dating control with direct or proxy records of environmental change river system responses to environmental change are evaluated over three nested time periods spanning the past 200 000 years first focusing on mediterranean european and african catchments river responses to relatively abrupt and short term late pleistocene dansgaard oeschger and heinrich climate events are examined second the effects of rapid and globally significant episodes of holocene climate change on european rivers together with anthropogenic land use impacts are assessed last little ice age flooding and alluvial responses to modern climate warming are reviewed with particular reference to upland britain these studies are shown to have significant implications for modelling local regional and global scale alluvial responses to future environmental change they highlight the necessity for numerical simulation models to be fully informed by field based knowledge and understanding of the memory effects of whole fluvial sediment systems particularly those that have experienced repeated phases of environmental change copyright 2008 john wiley sons ltd

thermochronology of the torlesse accretionary complex wellington region new zealand the torlesse complex comprises several mesozoic accretionary prism complexes together forming continental basement over large parts of new zealand this study focuses on the thermal history of relatively low grade graywacke rocks exposed in a transect in southern north island that crosses the structural grain of the torlesse complex including its older and younger parts zircon fission track ft ages for the late triassic rakaia terrane which is the most inboard of the accretionary complexes are partially annealed some possibly reset and may indicate early cretaceous 134 10 ma cooling from maximum temperatures tmax probably related to imbrication of younger complexes of the pahau terrane numerical modeling of the zircon ft ages and published 40ara 39ar muscovite and biotite ages for the rakaia terrane suggest tmax values of 265 310 c and exhumation from depths of 10 12 km the rocks underlying the aorangi range and involving the youngest accretionary complex have experienced much lower tmax values of 210 and 110 c bracketed by reset apatite ft ages and detrital zircon ft ages the occurrence of a circa 100 ma component of zircon ft ages in both the weakly and highly indurated rocks beneath the aorangi range as well as in remnants of an overlying albian accretionary slope basin whatarangi formation imply multistorey accretion and incorporation of sediment into the youngest prism this circa 100 ma zircon ft age component also places a maximum age on the termination of mesozoic subduction beneath the new zealand region the occurrence of reset apatite ft ages across the whole of the wellington transect indicates that at least 4 km of exhumation occurred during the late miocene

rb sr resetting ages and chemical characterization of turbidites in an accretionary wedge torlesse complex otaki gorge new zealand whole rock geochemical and rb sr isotopic analyses have been undertaken on turbidites from three discrete localities each about 2 km apart across strike within the torlesse complex a permian cretaceous accretionary wedge in new zealand overall the three suites show similar petrographic and geochemical compositions to turbidites from elsewhere in the torlesse complex but between the suites there are detectable differences for most major and trace elements particularly sr mgo and na 2 o the individual suites define three parallel rb sr whole rock isochrons with identical dates of about 205 ma the presence of monotis bivalves provides a depositional age of norian 219 225 ma hence the isochrons suggest that the rb sr clock was reset some 15 20 m y after deposition during low grade metamorphism associated with accretion and deformation of the sediment pile there is a wide variation in the initial 87 sr 86 sr ratios from 0 70683 to 0 70955 which is best explained by changes in the composition of the detritus being provided from the source area as detected by the chemical differences sea water is not considered to have played a significant role in contributing to the initial ratios the failure of some samples collected away from the main sample localities to plot on their respective isochrons suggests that domains of sr isotopic equilibration are small in the order of a few cubic meters as a result of this study we have extended the rb sr whole rock dating method of sediments now widely applied to shales and cherts to the more complex turbidite sequences from accretionary wedges and have shown that meaningful dates can be obtained this should provide an invaluable method of dating these sparsely fossiliferous terranes

provenance of the detrital component of deep sea sediments from the sw pacific ocean based on mineralogy geochemistry and sr isotopic composition abstract clay mineralogy and chemical and strontium isotope compositions have been used to determine the detrital components of deep sea sediments from the sw pacific ocean continental detritus derived mainly from the new zealand landmass is characterised by high illite and chlorite contents and 87 sr 86 sr ratios close to 0 7110 this material eroded from the eastern margin of both islands is transported into deeper water by turbidity currents and hemipelagic processes and is carried northwards by the strong western boundary current as far north as the samoan basin due to the great distance from source and unfavourable prevailing winds the contribution of aeolian dust from the australian deserts to the sediment appears to be relatively small particularly in the northernmost part of the region in the vicinity of the oceanic volcanic islands of tonga samoa and the cook islands volcaniclastic material including heavy minerals pyroxene and magnetite pumice glass shards proximally and smectite clays distally is dispersed into the sediments by turbidity currents and airfall in areas of very low sedimentation distant from landmasses the sediments contain significant amounts of authigenic material rsos characterised by high concentrations of transition metals and rare earth elements strontium isotopes together with trace element compositions have proved particularly useful in determining the relative proportions of the detrital types the contrasting 87 sr 86 sr ratios and sr contents of the various source rocks permit the use of binary mixing relationships whch indicate that sediments less than 35 km from the cook islands contain 80 volcanic detritus and those more than 1200 km away contain up to 20 volcanic detritus

development of a dust mantle on the surface of an insolated ice dust mixture results from the kosi 9 experiment astronomical observations indicate that formation and destruction of dust mantles on cometary nuclei may be the cause for erratic and systematic variations of cometary activity i e emission of dust a laboratory experiment kosi 9 has been performed to study the evolution of a dust mantle on top of a sublimating ice dust mixture in vacuum a sample consisting of water ice with a 10 by weight admixture of olivine grains has been insolated in three periods at variable intensities from 200 to 1900 w m2 both increasing surface temperature of the sample and decreasing gas and particle emissions indicated the formation of a dust mantle during the first period during the second insolation period after the gas flux had reached a critical value of a few 1021 water molecules m 2 s 1 avalanches of mantle material occurred on the inclined sample surface broke up the mantle locally and opened up a fresh icy surface enhanced ice and dust particle emission resumed for some time from these spots a large number of the emitted dust particles were of a fluffy aggregate structure i e they had large cross section to mass ratios compared to compact particles during the third period the critical gas flux was not reached and no enhanced dust and ice emission was observed a dry dust mantle of a few millimeters thickness developed during the course of the experiment consequences of these findings for cometary scenarios are discussed

kar and rbsr age studies of the metamorphism and quartz vein au mineralisation on terawhiti hill near wellington new zealand abstract k ar and rb sr ages have been determined for low grade torlesse terrane metagreywacke sequences wellington greywackes at terawhiti hill near wellington and the more schistose rocks in a narrow sheared zone containing aubearing quartz reefs a rb sr whole rock isochron age of 200 7 ma provides the best age estimate late triassic or earliest jurassic for regional metamorphism of the wellington greywackes and their initial 87 sr 86 sr ratio at this time 0 70690 0 00009 is characteristic of the extensive torlesse terrane elsewhere that is derived from a silicic continental source both k ar and rb sr ages indicate a local but intense shearing event at terawhiti hill at 125 130 ma early cretaceous after earlier metamorphism and uplift of the greywackes and possibly during imbrication of torlesse rocks on a regional scale formation of quartz veins and some deposition of au in schists and cataclastic rocks is possibly synchronous with this event but au is more importantly associated with isolated and rare later quartz reefs formed at 100 110 ma from sr isotope evidence the earlier quartz veins have a local in situ origin but the younger veins have an extraneous possibly deeper source

the nucleus of comet 9p tempel 1 shape and geology from two flybys the nucleus of comet tempel 1 has been investigated at close range during two spacecraft missions separated by one comet orbit of the sun 5 years the combined imaging covers 70 of the surface of this object which has a mean radius of 2 83 0 1 km the surface can be divided into two terrain types rough pitted terrain and smoother regions of varying local topography the rough surface has round depressions from resolution limits 10 m pixel up to 1 km across spanning forms from crisp steep walled pits to subtle albedo rings to topographic rings with all ranges of morphologic gradation three gravitationally low regions of the comet have smoother terrain parts of which appear to be deposits from minimally modified flows with other parts likely to be heavily eroded portions of multiple layer piles changes observed between the two missions are primarily due to backwasting of scarps bounding one of these probable flow deposits this style of erosion is also suggested by remnant mesa forms in other areas of smoother terrain the two distinct terrains suggest either an evolutionary change in processes topographically controlled processes or a continuing interaction of erosion and deposition

lithofacies types and vertical profile models an alternative approach to the description and environmental interpretation of glacial diamict and diamictite sequences abstract increased knowledge of modern glacial depositional environments has resulted in rapidly evolving classifications of glacial tills these are based to a large degree on theoretical considerations of likely depositional processes the classifications are sophisticated and more advanced than the establishment of simple field criteria whereby individual till facies can be identified in quaternary and pre quaternary successions this situation is compounded in many quaternary terrains by the continued description of tills in terms of laboratory derived analytical data only reflecting a traditional interest in stratigraphic correlation rather than reconstruction of depositional environment detailed sedimentological logging of lithofacies is rarely undertaken there is thus considerable confusion as to what is being described or sampled when analytical data are presented for many pleistocene tills the same remarks apply to pre pleistocene tillites a lithofacies code is presented here for the rapid description and visual appraisal of field sequences or drill cores containing unconsolidated diamicts or lithified diamictites the term till is not used as it has a strict genetic definition referring to direct aggregation and deposition by glacier ice use of a four part code in conjunction with codes already published for fluvial sediments allows fundamental field properties to be depicted independent of genetic terminology and provides a firm basis for subsequent environmental interpretation and analytical work the value of this approach is illustrated by comparing a representative suite of vertical profiles of diamict assemblages deposited by modern grounded glaciers with a classic late pleistocene glacigenic sequence at scarborough bluffs ontario

a quaternary aminostratigraphy constraining chronology of depositional environments in the north sea basin abstract the aminostratigraphy of up to 1000 m of glacial and interglacial sediments in the north sea basin nsb is compiled from multiple boreholes sites and dated using strontium isotope sr analysis to provide a chronological framework extending throughout the quaternary the quaternary aminostratigraphy within the nsb can be divided into five amino zones az az1 youngest to az5 based on alle ile ratios which are used to correlate depositional events recorded in sedimentary facies from multiple borehole sites the new relative and absolute chronology also ties to seismostratigraphy and multi generational tunnel valley fill early pleistocene sediments produce az5 ratios with sr ages around 1 4 1 5 ma deposited in marine to glacimarine conditions sediments with az4 ratios are constrained by sr ages and magnetic polarity to 1 3 0 9 ma spanning the eccentricity to axial tilt insolation periodicity change of the mid pleistocene transition mpt some coarse grained sedimentary units with az4 ratios may be linked to ice proximal deposition during the mpt sediments with az3 ratios are poorly chronologically constrained to between 1 1 and 0 26 ma at least one episode of diminished coarse clasts and increased foraminiferal diversity during this mid pleistocene time suggests a progression from ice proximal to warmer possibly interglacial conditions furthermore the stratigraphically deepest generation of tunnel valleys cut strata with az3 ratios indicating subglacial conditions at least once during the mid pleistocene sediments with az2 ratios corresponding to mis7 5 are tied to seismic units including a thick up to 40 m deformation till suggesting glacial incursion into the nsb during mis6 followed by tunnel valley cutting of the this till thought to be an mis6 event also the geometry and cross cutting complexities of such tunnel valleys precludes further correlation of this ice extent the youngest aminostratigraphic zone az1 is recognised in all boreholes and well constrained to mis4 2 and the youngest set of tunnel valleys attributed to a single or multiple glacial advances at this time

coarse grained nonmarine volcaniclastic sediment terminology and depositional process modern and ancient volcaniclastic sedimentary sequences contain depositional units whose features cannot be attributed to fully turbulent dilute stream flow or viscous debris flow the characteristics of these poorly sorted sediments suggest rapid deposition from high concentration dispersions but not en masse sedimentation thus appears related to high discharge flows intermediate in sediment water ratio between stream flow and debris flow the term hyperconcentrated flood flow is proposed for describing this intermediate condition hyperconcentrated flood flow deposits are distinguished from debris flow deposits by lack of matrix support or reverse grading and instead exhibit distribution normal grading and horizontal stratification these deposits are distinguished from normal dilute stream flow deposits by lack of cross stratification in sand facies and by very poor sorting poor imbrication and numerous clasts with long axes oriented parallel to flow direction in gravel facies the horizontal bedding that dominates sandy hyperconcentrated flood flow deposits consists of sediment too coarse grained and strata too thick to have been produced in the boundary layer of the upper flow regime and should not be confused with the more familiar thin graded laminae of fine to medium grained sand often associated with parting lineation hyperconcentrated flood flow deposits are not unique to volcanic settings they also occur in arid alluvial fan sequences debris flow and hyperconcentrated flood flow deposits however are much thicker and more extensive in volcanic regions than on alluvial fans because explosive volcanism leads to rapid mobilization of large volumes of sediment and water on a scale unparalleled in nonvolcanic settings in volcanic regions therefore these deposits have greater preservation potential show greater lateral variability and are more voluminous transformation of channelized debris flow to hyperconcentrated flood flow by dilution with stream water recently observed at mount st helens is recorded in ancient volcaniclastic sequences and may serve as the primary mechanism for generating hyperconcentrated flood flow

the morphological diversity of comet 67p churyumov gerasimenko images of comet 67p churyumov gerasimenko acquired by the osiris optical spectroscopic and infrared remote imaging system imaging system onboard the european space agency s rosetta spacecraft at scales of better than 0 8 meter per pixel show a wide variety of different structures and textures the data show the importance of airfall surface dust transport mass wasting and insolation weathering for cometary surface evolution and they offer some support for subsurface fluidization models and mass loss through the ejection of large chunks of material

a survey of debris trails from short period comets abstract we observed 34 comets using the 24 m camera on the spitzer space telescope each image contains the nucleus and covers at least 10 6 km of each comet s orbit debris trails due to mm sized or larger particles were found along the orbits of 27 comets 4 comets had small particle dust tails and a viewing geometry that made debris trails impossible to distinguish and only 3 had no debris trail despite favorable observing conditions there are now 30 jupiter family comets with known debris trails of which 22 are reported in this paper for the first time the detection rate is 80 indicating that debris trails are a generic feature of short period comets by comparison to orbital calculations for particles of a range of sizes ejected over 2 yr prior to observation we find that particles comprising 4 debris trails are typically mm sized while the remainder of the debris trails require particles larger than this the lower limit masses of the debris trails are typically 10 11 g and the median mass loss rate is 2 kg s the mass loss rate in trail particles is comparable to that inferred from oh production rates and larger than that inferred from visible light scattering in comae

viscous relaxation on comets three jupiter family comets have now been observed by spacecraft with the surprising result that these comets lack unambiguous impact craters large scale topography generally appears to be softened on these comets although sharp topography is preserved at small scales we find that viscous relaxation of water ice may explain these observations given reasonable assumptions about ice grain size and temperatures attained in the interiors we suggest that both the shapes and the cratering records of jupiter family comets may be substantially modified and no longer reflect cometary formation processes or collisional evolution in the kuiper belt

weichselian sediments at foss eikeland jaeren southwest norway sea level changes and glaciation history the jaeren area in southwestern norway has experienced great changes in sea levels and sedimentary environments during the weichselian and some of these changes are recorded at foss eikeland four diamictons interbedded with glaciomarine and glaciofluvial sediments are exposed in a large gravel pit situated above the post glacial marine limit the interpretation of these sediments has implications for the history of both the inland ice and the norwegian channel ice stream during a middle weichselian interstadial a large glaciofluvial delta prograded into a shallow marine environment along the coast of jaeren a minor glacial advance deposited a gravelly diamicton and a glaciomarine diamicton was deposited during a following marine transgression this subsequently was reworked by grounded ice forming a well defined boulder pavement the boulder pavement is followed by glaciomarine clay with a lower laminated part and an upper part of sandy clay the laminated clay probably was deposited under sea ice whereas more open glaciomarine conditions prevailed during deposition of the upper part the clay is intersected by clastic dykes protruding from the overlying late weichselian till preconsolidation values from the marine clay suggest an ice thickness of at least 500 m during the last glacial phase the large variations in sea level probably are a combined effect of eustasy and glacio isostatic changes caused by an inland ice sheet and an ice stream in the norwegian channel copyright 2002 john wiley sons ltd

return to comet tempel 1 overview of stardust next results on february 14 2011 stardust next sn flew by comet tempel 1 the target of the deep impact di mission in 2005 obtaining dust measurements and high resolution images of areas surrounding the 2005 impact site and extending image coverage to almost two thirds of the nucleus surface the nucleus has an average radius of 2 83 0 1 km and a uniform geometric albedo of about 6 at visible wavelengths local elevation differences on the nucleus reach up to 830 m at the time of encounter the spin rate was 213 per day period 40 6 h and the comet was producing some 130 kg of dust per second some 30 of the nucleus is covered by smooth flow like deposits and related materials restricted to gravitational lows this distribution is consistent with the view that the smooth areas represent material erupted from the subsurface and date from a time after the nucleus achieved its current shape it is possible that some of these eruptions occurred after 1609 when the comet s perihelion distance decreased from 3 5 au to the current 1 5 au much of the surface displays evidence of layering some related to the smooth flows and some possibly dating back to the accretion of the nucleus pitted terrain covers approximately half the nucleus surface the pits range up to 850 m in diameter due to their large number they are unlikely to be impact scars rather they probably result from volatile outbursts and sublimational erosion the di impact site shows a subdued depression some 50 m in diameter implying surface properties similar to those of dry loose snow it is possible that the 50 m depression is all that remains of an initially larger crater in the region of overlapping di and sn coverage most of the surface remained unchanged between 2005 and 2011 in albedo photometric properties and morphology significant changes took place only along the edges of a prominent smooth flow estimated to be 10 15 m thick the margins of which receded in places by up to 50 m coma and jet activity were lower in 2011 than in 2005 most of the jets observed during the sn flyby can be traced back to an apparently eroding terraced scarp the dust instruments detected bursts of impacts consistent with a process by which larger aggregates of material emitted from the nucleus subsequently fragment into smaller particles within the coma

quaternary seismic stratigraphy of the north sea fan glacially fed gravity flow aprons hemipelagic sediments and large submarine slides abstract approximately 1000 km of high resolution sleeve gun array transects on the north sea fan located at the mouth of the norwegian channel reveal three dominant styles of sedimentation within a thick 900 m quaternary sediment wedge comprising numerous sequences these are interpreted as terrigenous hemipelagic sedimentation large scale translational slides and aprons of glaciogenic debris flow deposits contributing to considerable fan construction four large buried translational slides involved sediment volumes upwards of 3000 km 3 each and preceded the similarly dimensioned first storegga slide on the ne fan flank several thick 100 m terrigenous hemipelagic deposits apparently represent long lived 150 200 kyr periods of sedimentation whose distribution indicates fan input via the norwegian channel the upper sequences are each made upper sequences are each made up of one or several thick 100 m aprons comprising stacked lensoid and or lobate forms which range from 2 to 40 km in width and 15 to 60 m in thickness they characterize debris flows attributed to periodic input from several phases of a norwegian channel ice stream reaching the shelf edge subsidence in the outer norwegian channel allowed preservation of several glaciation cycles represented by sheet erosion bounded tills and progradational units much of the shelf slope transition has been preserved allowing a preliminary chronology of the fan sequences through correlation with borehole sediments in the norwegian channel debris flows which signal the initial shelf edge glaciation are not recognized from the initial glaciation in the channel 1 1 myr but are associated with a middle pleistocene and all following glacial erosion surfaces ges in the outer norwegian channel this was followed by six further sequences probably totalling over 13 000 km 3 of sediment at least four of these were shelf edge ice maximum events the last of which was late weichselian age 14 c ams considering earlier glaciation related hemipelagic sedimentation material since removed by the large slides and extensive unmapped areas total quaternary fan sedimentation was in the vicinity of 20 000 km 3

silicate minerals and si o glass in comet wild 2 samples transmission electron microscopy a transmission electron microscope tem study of seven comet wild 2 samples shows that three samples consist mainly of olivine and pyroxene and four samples consist of mg fe bearing si o glass with minor amounts of fe ni sulfide and metal the olivine in the silicate rich samples differs in fayalite content between the samples and shows a wide range of fayalite content within individual samples indicating that the degree of thermal metamorphism on the comet if any was extremely low one olivine grain has a high density of dislocations with burgers vector b 001 suggesting that the wild 2 particles experienced hypervelocity impacts before capture the structural type and composition of pyroxene differ between the samples and within individual samples both low ca and high ca pyroxenes are present enstatite occurs as ortho and clinoenstatite suggesting that the wild 2 particles contain materials that went through distinct high temperature and cooling histories one silicate rich sample exhibits a zone texture consisting of a core of low ca pyroxene surrounded by an inner rim of mg fe bearing si o rich glass and an outer rim of melted aerogel the texture suggests that the inner rim was formed by the mixing of melted cometary low ca pyroxene and melted aerogel during capture heating the four mg fe bearing si o glass rich samples show close similarities in mineralogy and texture to the inner rim of the zoned silicate rich sample the four samples are probably secondary products formed by interaction between melted cometary silicates and melted aerogel during the capture process

quaternary erosion and depositional processes western norwegian fjords norwegian channel and north sea fan abstract the southern norwegian fjords the northern north sea and north sea margin represent major pathways of sediment flux from the southern part of fennoscandia to the deep sea basin volumes genesis and chronology of the temporary and semi permanent quaternary sediment repositories are reviewed the fjord infill is dominated by sediments from the last deglaciation 150 km 3 the norwegian channel is occupied by tills and glaciomarine marine sediments 5000 km 3 the north sea fan comprises glacially fed debris flow fingers lobes constituting 80 of deposits in the mid to late pleistocene together with hemipelagic and mass transport slide sediments totalling 15 000 km 3 the norwegian channel represents a dynamic transport conduit whereby during peak glaciation a fast flowing ice stream has drained large parts of the southern fennoscandian ice sheet several times the sediment flux to the deep sea is temporarily interrupted between glacials when stored in the channel but under glacial maxima the channel is probably largely bypassed with material transported as subglacial load and deposited as debris flows on the north sea fan sediments on the fan have a much longer storage time numerous glaciation cycles but are further transported to the deep sea in large slide events the volume of quaternary sediments found along this sediment pathway plus that which slid to the deep sea total at least 25 000 km 3 corresponding to an averaged 120 m of erosion across southern norway