the micromorphology of last glacial maximum sediments in the southern north sea abstract the terrestrial ice limits of the last glacial maximum ice sheets are well understood but areas submerged during postglacial sea level rise have proved more difficult to accurately map fine grained diamicts in the southern north sea have been variously interpreted as glacial glacioaqueous or periglacial in origin implying different sedimentary environments this has resulted in contrasting opinions regarding the position of the last ice sheets in this area micromorphology is presented as a useful technique to aid the analysis of such sediments using systematic description of the physical characteristics of the sediments related to an interpreted seismic stratigraphy results indicate that the british ice sheet deposited glaciomarine sediments during an early advance and then advanced over an extensive part of the southern north sea as terrestrial ice

sedimentation in a large lake a reinterpretation of the late pleistocene stratigraphy at scarborough bluffs ontario canada a lithofacies code developed for diamicts emphasizes facies variability in the classic upper pleistocene glaciogenic sequence at scarborough bluffs ontario canada lithological breaks along the bluffs are traditionally assigned to incursions of grounded ice margins and to interstadial lakes formed during ice retreat during the early and middle wisconsin detailed sedimentological logging through three diamict units previously formalized as sunnybrook seminary and meadowcliffe tills and intervening sandy lithofacies shows absence of glaciotectonic structures and diamicts associated with grounded glacier ice traction current activity during diamict accumulation postdepositional resedimentation of diamicts into topographic lows accompanied by turbidite activity a subaqueous deltaic origin for intervening sandy lithofacies and loaded transitional and interbedded contacts between sand and diamict the scarborough bluffs sequence may be the preserved bottom stratigraphy of a large lake the bottom stratigraphy results from repeated basinward progradation of deltaic sandy lithofacies over glaciolacustrine diamicts deposited below floating ice whether ice shelf ramp bergs or lake ice a facies model is presented for glaciolacustrine diamict deposition on the floors of enlarged pleistocene lakes trapping substantial volumes of fine grained suspended sediment

mega ejecta on asteroid vesta 1 asteroid 4 vesta sometimes called the smallest terrestrial planet will be orbited next july by nasa s dawn mission this will be the first time a small planet is visited by a spacecraft and novel geological structures are expected a key issue regarding vesta mean diameter 530 km is to what extent its geology is dominated by the 460 km diameter impact basin on its southern hemisphere we model the basin s formation using a very high resolution 3d smooth particle hydrodynamics simulation to establish some of the major impact related aspects of vesta s geology the goal is to provide a framework for interpreting anticipated observations of landforms a collision of this magnitude a 50 km diameter impactor at 5 km s exposes many deep strata from within the planet and offsets the center of mass by 10 km from the center of figure vesta spins every 5 3 hr so that a hemispheric scale impact evolves in a non inertial frame and deposits variably shaped multiply folded and abruptly terminated ejecta sequences of regional scale since little of this ejecta would have been molten these massive sequenced deposits could be mistaken in images of vesta for other geologic forms such as thrusts and folds detailed mapping and the piecing together of mega ejecta via impact models will enable an informed understanding of the interior geology of vesta

petrology of the indian eucrite piplia kalan piplia kalan is an equilibrated eucrite consisting of 60 80 vol lithic clasts in a subordinate brecciated matrix ophitic subophitic clasts fall into two groups finer grained lithology a and coarser grained lithology b very fine grained clasts with equigranular textures lithology c also occur and originally were hypocrystalline in texture the variety of materials represented in piplia kalan suggests cooling histories ranging from quenching to slower crystallization despite textural differences clasts and matrix have similar mineral and bulk compositions thus piplia kalan is probably best classified as a genomict breccia that could represent fragments of a single lava flow or shallow intrusive body including fine grained or glassy outer margin and more slowly cooled coarser grained interior bulk composition suggests that the meteorite is most closely related to the main group eucrites but it probably was affected by minor amounts of fractional crystallization piplia kalan displays evidence of an early shock event including brecciated matrix and areas of lithic clasts that contain very fine grained granular pyroxene between deformed feldspar laths the meteorite also displays evidence of at least one episode of extensive thermal metamorphism hypocrystalline materials are recrystallized to hornfelsic textures and minerals throughout the meteorite contain abundant inclusions that are relatively large in size veins of brown glass transect both clasts and matrix and indicate a second postmetamorphism shock event

ice keel scour marks in the geological record evidence from carboniferous soft sediment striated surfaces in the parana basin southern brazil abstract soft sediment glacially striated surfaces are common structures in ancient glacial successions such as the gondwanic paleozoic record and document ice erosion on non lithified beds in most cases they have been interpreted as the product of subglacial erosion beneath advancing marine or terrestrial glaciers although direct evidence for glacial sedimentation in associated strata is infrequent in this paper we document soft sediment striated surfaces of carboniferous age occurring in cross laminated sandstones of the lower itarare group southern parana basin brazil and interpret them as scour marks generated by keels of floating ice striated surfaces occur in closely spaced multiple stratigraphic horizons in the lower half of a deglacial sequence whose facies characteristics indicate sedimentation in subaqueous outwash and deltaic settings surfaces are laterally discontinuous commonly bordered by marginal berms and in some cases capped by mudstones with dropstones they have orientations that deviate from the regional paleo ice flow indicated by glacial grooves carved on the pre glacial basement the characteristics observed are consistent with modern and pleistocene ice keel scour marks in addition soft sediment striated surfaces from other gondwanic localities have similar attributes suggesting that ice keel scour marks may be more common in the geological record than previously considered and that vertically repeated striated surfaces do not necessarily indicate multiple ice sheet advances therefore paleo ice flow reconstructions based on soft sediment striated surfaces need to be revaluated considering that the movement of free floating ice masses is controlled by phenomena other than glacier advance

spectral reflectance properties of ureilites abstract the 0 35 2 6 m reflectance spectra of 18 ureilites have been examined in order to improve our understanding of the spectral reflectance properties of this meteorite class across this spectral range ureilite spectra are characterized by a steep rise in reflectance over the 0 3 to approximately 0 7 m range low overall reflectance 25 and weak mafic iron silicate absorption bands in the 1 and 2 m region the weakness of these bands and the low reflectance are attributed to the presence of dispersed graphite and related carbonaceous phases metal and possibly shock wavelength positions of the mafic silicate absorption bands span a range of values but are consistent with the presence of pyroxene and olivine ureilite spectra generally exhibit blue slopes across the 0 7 2 6 m interval and exhibit many overall similarities to some carbonaceous chondrites the weak features and spectral diversity of ureilites make reflectance spectroscopy based identification of a ureilite parent body challenging as terrestrial alteration of ureilites is prevalent spectral studies of falls are most useful for determining the spectral properties of likely parent bodies

micromorphology of iceberg scour in clays glacial lake agassiz manitoba canada abstract icebergs plough through unconsolidated lake sea sediments gouging out kilometre long grooves 100s of metres wide and tens of metres deep although the surface morphology of iceberg scours is well documented little is known about what scours look like in stratigraphic section particularly where surface characteristics are absent e g through decay or burial this investigation establishes a definitive suite of diagnostic criteria for identifying iceberg scours in clays by macroscopically and microscopically 2d thin sections examining sediment deformation below iceberg scours in former glacial lake agassiz manitoba canada structures unequivocally attributed to iceberg scour in this investigation include sub horizontal microfabrics folds sheath folds augen shapes normal faults reverse thrust faults discrete shears partially destroyed clasts intraclasts type iii multiple domains water escape structures flow structures unistrial plasmic fabric dropstones realigned bedding and specific structural sequences this research will be particularly valuable in palaeoenvironmental reconstruction and in predicting glacial dynamics in addition it may eventually aid structural engineering on polar shelves which could be of great value to oil and gas companies

chemical studies of differentiated meteorites i labile trace elements in antarctic and non antarctic eucrites abstract we report data for ag au bi cd co cs ga in rb sb se te tl u and zn determined by rnaa in 25 antarctic and 9 non antarctic eucrites including the cumulate eucrites moore co and serra de mage compositional variations for a given element in a population range from

pore water controlled grain fracturing as an indicator for subglacial shearing in tills genetic classification of glacial deposits still proves to be highly controversial in many cases it remains unclear whether a particular sediment has been sub glacially deformed in the present paper it is suggested that micromorphological research is helpful where current techniques fail to lead to unambiguous interpretations it is argued that the occurrence of fractured grains in glacial sediments is indicative of subglacial shearing and that such grains may be used as diagnostic evidence of glaciotectonism deformational mechanisms associated with the fracturing process are outlined and explained using a series of thin sections from wijnjewoude the netherlands

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

repeated advance and retreat of the east antarctic ice sheet on the continental shelf during the early pliocene warm period abstract diatom analysis of a sediment core recovered at iodp site u1358 on the continental shelf off the adelie coast indicated that the lower section of the core contained an assemblage dating back to the thalassiosira innura zone of the lower pliocene that ranges from 4 2 to 5 12 ma based on lithological descriptions at both a macro and micro scale of this early pliocene part of the core four facies were interpreted from the diamictons representing the progressive advance and retreat of the grounding line over the site facies 1a and 1b contain a distinct directional signal from the orientation of the a axis of clasts with several phases of fabric development along with both brittle and ductile deformation features that are common in sediments that have been subglacially deformed facies 1c and 1d are finely laminated and were deposited in open marine conditions the four facies within the depositional model provide for the first time direct evidence for ice advancing across the shelf adjacent to the wilkes subglacial basin on at least four occasions separated by three periods of open marine conditions indicating retreat of grounded ice inland of the site during a warmer than present early pliocene the times of open marine conditions are correlated with previous findings from the neighbouring rise sites that also indicated an oscillating ice margin this has significant implications because firstly it suggests a dynamic east antarctic ice sheet eais that is probably far more sensitive to climatic and oceanic forcing even during relatively short time periods than had previously been thought secondly it suggests that proxies used to interpret the advance and retreat of the grounding line from the rise can be linked with direct evidence of grounding line migration from the shelf it also has important implications for the future behaviour and sensitivity of the eais under present continuing warming conditions together with results from the rise this paper provides a crucial ice extent target for a new ice sheet model of this region during the pliocene

quartz microtextures and microstructures owing to deformation of glaciolacustrine sediments in the northern venezuelan andes glaciolacustrine sediments ranging in age from early to late merida wisconsinan in sections in the northern venezuelan andes near pedregal were studied to assess the effect of small scale folding and faulting on the surface microtextures of individual grains at site ped5 faulting of sediments beneath 35 m of middle to late merida glaciolacustrine glaciofluvial and probable till deposits has resulted in a maximum displacement of 1 m and many crushed sand grains are found along the shear zone these dominantly quartz particles are typically smoothed and or faceted with surface skins split from parent grains to produce adhering blade or wafer shaped coarse silts faulting with displacement of 40 cm occurs in late merida glaciolacustrine beds at sites ped13 and ped11 beneath ca 1 5 m of sediment and is thought to result from the removal of lateral support during valley erosion and possibly seismic disturbance associated sediments exhibit a greater incidence of small scale fold structures and convoluted bedding but with similar numbers and types of crushed grains all of the fault traces examined exhibit microstructural modifications including microfaulting folding and multiple domains associated with fluidisation and liquefaction the microtextures described are distinct from those produced by glacial or glaciofluvial transport processes and potentially may be used to infer glaciotectonic or other post depositional disturbance of sediments rare euhedral quartz grains with distorted crystallographic axes may derive from the shear zone of the regional trans form boconofault although many of these grains appear to be overprinted by glacial and or recent deformation processes copyright 2004 john wiley sons ltd

microdistribution of primordial ne and ar in fine grained rims matrices and dark inclusions of unequilibrated chondrites clues on nebular processes the low temperature fine grained material in unequilibrated chondrites which occurs as matrix rims and dark inclusions carries information about the solar nebula and the earliest stages of planetesimal accretion the microdistribution of primordial noble gases among these components helps to reveal their accretionary and alteration histories we measured the ne and ar isotopic ratios and concentrations of small samples of matrix rims and dark inclusions from the unequilibrated carbonaceous chondrites allende cv3 leoville cv3 and renazzo cr2 and from the ordinary chondrites semarkona ll3 0 bishunpur ll3 1 and krymka ll3 1 to decipher their genetic relationships the primordial noble gas concentrations of semarkona and with certain restrictions also of leoville bishunpur and allende decrease from rims to matrices this indicates a progressive accretion of nebular dust from regions with decreasing noble gas contents and cannot be explained by a formation of the rims on parent bodies the decrease is probably due to dilution of the noble gas carrying phases with noble gas poor material in the nebula krymka and renazzo both show an increase of primordial noble gas concentrations from rims to matrices in the case of krymka this indicates the admixture of noble gas rich dust to the nebular region from which first rims and then matrix accreted this also explains the increase of the primordial elemental ratio 36ar 20ne from rims to matrix larger clasts of the noble gas rich dust form macroscopic dark inclusions in this meteorite which seem to represent unusually pristine material the interpretation of the renazzo data is ambiguous rims could have formed by aqueous alteration of matrix or as in the case of krymka by progressive admixture of noble gas rich dust to the reservoir from which the renazzo constituents accreted the leoville and krymka dark inclusions as well as one dark inclusion of allende show noble gas signatures different from those of the respective host meteorites the allende dark inclusion probably accreted from the same region as allende rims and matrix but suffered a higher degree of alteration the leoville and krymka dark inclusions must have accreted from regions different from those of their respective rims and matrices and were later incorporated into their host meteorites the noble gas data imply a heterogeneous reservoir with respect to its primordial noble gas content in the accretion region of the studied meteorites further studies will have to decide whether these differences are primary or evolved from an originally uniform reservoir

81kr terrestrial ages and grouping of yamato eucrites based on noble gas and chemical compositions the ages and the groupings of yamato eucrites recovered in antarctica as well as terrestrial ages of nine yamato eucrites were determined based on cosmic ray produced noble gases including the radionuclide 81kr the terrestrial ages of y 792511 y 793164 and y 794043 are 0 14 0 11 and 0 28 ma respectively due to the relatively long storage time in ice the ce anomaly caused by the terrestrial alteration was significant in these three eucrites short terrestrial ages of 0 08 ma and long cosmic ray exposure ages of about 65 ma as well as similar noble gas and ree compositions for six eucrites y 75011 791826 793547 793548 793570 and 794002 strongly suggest that they belong to a single fall for these eucrites negative eu anomalies were found considering the data of yamato eucrites previously reported 1 fall s are required for monomict and 5 falls for polymict eucrites during the past 0 3 ma fissiogenic xe from 244pu was observed in nine eucrites in which the concentration of 244pu at the beginning of xe retention was calculated to be 0 5 2 2 ppb the 244pu nd weight ratio of 1 1 2 1 10 4 agrees with that reported for angra dos reis 244pu nd 1 5 10 4 within 40 244pu u ratios of y 793164 and y 793548 are 0 0027 0 0004 and 0 0045 0 0011 respectively assuming the u abundances occurred at 4 5 ga ago these ratios are somewhat lower than the ratio of 0 004 0 007 for the solar system

refined data of alpha proton x ray spectrometer analyses of soils and rocks at the mars pathfinder site implications for surface chemistry 1 an extensive recalibration of the alpha proton x ray spectrometer apxs was performed to improve the data evaluation of the mars pathfinder mpf rock and soil in situ measurements many samples and geostandards were measured with an mpf identical spare apxs under simulated martian atmospheric pressure and low night temperature conditions precise calibration curves for major and minor elements were obtained using an improved spectral evaluation method for the original mpf spectra refined and new elemental compositions of the mpf rocks and soils were derived however all initial conclusions about soils and rocks remained valid the mpf soil composition revealed the mafic nature of the surface as inferred from the results of viking 1 and 2 data however the mpf rocks reflect a felsic composition for all samples linear correlations of sulphur with all other elements were noticed reflecting the fact that the rocks were covered with varying degrees of soil which compared to the rocks is rich in sulphur extrapolating to low sulphur abundance 0 3 the composition of a soil free rock was calculated the mpf rock composition is high in si and k and low in mg and fe compared to the soil using elemental data from mpf and martian meteorites a global estimation of the martian crust composition was derived the crust is of basaltic nature with a high abundance of incompatible elements k rb nd u th and volatile elements s cl while carbonates are lower or absent

micromorphological evidence for polyphase deformation of glaciolacustrine sediments from strathspey scotland a combination of field investigation and micromorphological analysis has been applied to polydeformed late devensian rhythmites and glacigenic diamicton exposed in strathspey scotland this provided information on the geometry kinematics and relative ages of ductile and brittle structures and records a complex subglacial deformation history the deformation is interpreted as resulting from a single progressive event associated with over riding of proglacial lake sediments by wet based ice the earliest deformation d1 resulted from compaction loading pure shear and imposed a bedding parallel s1 fabric throughout the rhythmites s1 was subsequently deformed by kink bands and minor ductile shearing during d2 a later d3 event characterized by soft sediment deformation and fluidization of matrix poor sands was accompanied by an increase in pore water pressure this lead to hydrofracturing of the rhythmites the most intense deformation d4 which resulted from simple shear was partitioned into the upper part of the sequence it produced folding thrusting and brittle microfaulting in response to nnw directed ice push these findings indicate that in general subglacial deformation is not homogeneous and can extend to depths of 3 m below the presumed ice sediment interface

evidence from microstructures of deformable bed conditions within drumlins chimney bluffs new york state abstract discussion on the process of drumlin formation has been ongoing for over a century at present two dominant schools of thought prevail viz formation by a subglacial hydraulic mechanisms and b due to subglacial sediment deformation the latter mechanism depends on the existence of a subglacial deformable bed evidence from part of the large central new york drumlin field reveals evidence of syn depositional deformation during the emplacement of diamictons that constitute the major portion of drumlins exposed along shore bluffs in chimney bluffs state park these diamictons cannot be lodgement till facies members but appear to comprise facies indicative of melange style deposition under subglacial deformable bed conditions the evidence obtained from microstructures and plasma fabric within these diamictons supports the existence of a deformable bed during diamicton emplacement it is likely that formation of the drumlins occurred under these same subglacial bed conditions

new insights into the formation of submarine glacial landforms from high resolution autonomous underwater vehicle data abstract autonomous underwater vehicles auvs deployed close to the seafloor can acquire high resolution geophysical data about the topography and shallow stratigraphy of the seabed yet have had limited application within the fields of glacial geomorphology and ice sheet reconstruction here we present multibeam echo sounding side scan sonar sub bottom profiler and high resolution synthetic aperture sonar hisas data acquired during three auv dives on the northeast antarctic peninsula continental shelf these data enable glacial landforms including mega scale glacial lineations msgls grounding zone wedges gzws and iceberg ploughmarks to be imaged at a horizontal resolution of a few tens of centimetres allowing for the identification of subtle morphological features we map tidal ridges that are interpreted as having been formed 1 along the ice sheet grounding line by the squeezing up of soft seafloor sediments by vertical motion of the grounding line during tidal cycles and 2 by the tidally driven motion of grounded or near grounded icebergs these data also enable the mapping of small gzws that show the location of short term still stands or re advances of the ice sheet grounding zone no meltwater channels are identified from our data suggesting that free flowing meltwater may not be essential for the formation of gzws or msgls the examples presented here show how high resolution auv derived geophysical data provide a step change in our ability to image seafloor glacial landforms enabling new interpretations about past ice dynamics and glacial sedimentation at fine temporal and spatial scales

impact excavation on asteroid 4 vesta hubble space telescope results hubble space telescope images of asteroid 4 vesta obtained during the favorable 1996 apparition show an impact crater 460 kilometers in diameter near the south pole color measurements within the 13 kilometer deep crater are consistent with excavation deep into a high calcium pyroxene rich crust or olivine upper mantle about 1 percent of vesta was excavated by the crater formation event a volume sufficient to account for the family of small vesta like asteroids that extends to dynamical source regions for meteorites this crater may be the site of origin for the howardite eucrite and diogenite classes of basaltic achondrite meteorites

fluxes of fast and epithermal neutrons from lunar prospector evidence for water ice at the lunar poles maps of epithermal and fast neutron fluxes measured by lunar prospector were used to search for deposits enriched in hydrogen at both lunar poles depressions in epithermal fluxes were observed close to permanently shaded areas at both poles the peak depression at the north pole is 4 6 percent below the average epithermal flux intensity at lower latitudes and that at the south pole is 3 0 percent below the low latitude average no measurable depression in fast neutrons is seen at either pole these data are consistent with deposits of hydrogen in the form of water ice that are covered by as much as 40 centimeters of desiccated regolith within permanently shaded craters near both poles

paired renazzo type cr carbonaceous chondrites from the sahara ten chondrites with chemical and mineralogical similarities to the carbonaceous chondrite renazzo were recovered at two locations of the sahara acfer 059 087 097 114 139 186 187 209 270 and el djouf 001 although the el djouf location is more than 500 km away from the acfer location all samples appear to result from a single fall based on chemical and petrographic similarities and supported by light element stable isotope geochemistry noble gas record and similar 26al contents the acfer el djouf meteorite is classified as a cr renazzo type carbonaceous chondrite this group presently comprises three non antarctic members al rais renazzo acfer el djouf and five antarctic meteorites the major lithological components of the acfer el djouf meteorite are large chondrules up to 1 cm in size mean diameter 1 0 0 6 mm chondrule and mineral fragments ca al rich inclusions feni metal about 8 10 vol and dark inclusions embedded in a fine grained fragment bearing groundmass mineral compositions of the ten acfer el djouf samples are similar to those of other cr chondrites most of the ca al rich inclusions are below 300 m in size and rich in melilite and spinel in some cais the rare phase caal4o7 is dominant fo rich cr bearing olivine fa0 4 and enstatite fs0 4 are the major phases of the chondrite the meteorite is mildly shocked with a shock stage of s2 indicating a peak shock pressure of 5 10 gpa for the bulk meteorite the oxygen isotopic compositions and carbon and nitrogen stable isotope geochemistry of the acfer el djouf samples are very similar to those of the other cr type chondrites the major element composition of the acfer el djouf meteorite is indistinguishable from cr chondrites when compared to renazzo the acfer el djouf samples however have systematically lower contents of the moderately volatile elements zn ga as au sb and se and the highly volatile elements br c and n this is thought to reflect primary differences between renazzo and the acfer el djouf meteorite

experimental study of soil microfabrics induced by isotropic stresses of wetting and drying this experimental study examines the relationship between texture and microfabric under isotropic stresses generated by wetting and drying this can be achieved by observing and measuring the reorganization of microfabrics plasmic fabrics and related distribution pattern rdp microfabrics are produced in the laboratory by mixing montmorillonite with various proportions of sand and silt and subjecting them to wetting and drying without confinement thin sections are cut to study their microfabrics results show broad and systematic variations in fabric with changes in texture fine matrix silt plus clay in physical continuity is developed in samples with low sand silt ratio and regardless of this ratio at high clay levels coarse porphyric and fine porphyric rdp are formed at low and high clay contents respectively plasmic fabrics are represented mainly by insepic and weakly developed mosepic and masepic fabrics in the matrix in the form of small plasma separations with random orientation and weak skelsepic plasma as embedded grain argillans on the other hand coarse matrix sand grains in physical continuity dominates the sandy samples which are associated with relatively thick and strongly birefringent free grain argillans giving well developed skelsepic fabric the rdp follows two major paths beginning with orthogranic very low clay content along the iunctic sequence at low clay silt ratio and along the chlamydic sequence at high ratio the regularities in fabric development are interpreted in the light of the dynamic properties and behaviour of the active clay fraction in a clay water system the pedogenetic implications of the results are explored and the term erdic fabric defined

the sedimentary record of drifting ice early wisconsin sunnybrook deposit in an ancestral ice dammed lake ontario canada abstract outcrops of pebbly mud diamict at scarborough in southern ontario canada the so called sunnybrook till are associated with the earliest incursion of the laurentide ice sheet lis into mid continent north america some 45 000 years ago the sunnybrook is a blanket like deposit containing deepwater ostracodes and occurs conformably within a thick 100 m succession of deltaic and glaciolacustrine facies that record water depth changes in a large proglacial lake contextual evidence associated facies sedimentary structures deposit geometry and landforms indicates a low energy depositional setting in an ice dammed ancestral lake ontario in which scouring by floating ice masses was an important process u shaped iceberg cut scours with lateral berms up to 7 m deep occur on the upper surface of the sunnybrook and are underlain by sub scour structures that extend several meters below the scour base ice rafted concentrations of clasts clast layers grooved surfaces formed by floating ice glissading over a muddy lake floor soft sediment striations and melanges of sand and mud mixed by grounding ice keels ice keel turbates are present and are all well known from modern cold environments the wider significance of this depositional model is that the lis margin lay east of scarborough and did not overrun southern ontario this finding is in agreement with recent data from the erie basin of canada ohio and indiana where deposits formerly correlated with the sunnybrook and thus implying an extensive early wisconsin ice sheet are now regarded as illinoian a speculative hypothesis is proposed that relates deposition of the sunnybrook and two younger deposits of similar sedimentology to surge like instabilities of the southern lis margin

micromorphology of a debris flow deposit evidence of basal shearing hydrofracturing liquefaction and rotational deformation during emplacement abstract micromorphological analysis has been applied to a very coarse debris flow deposit and associated sand dominated glaciofluvial sediments exposed in westend wood quarry carstairs central scotland the microstructures present folds faults plasmic fabrics within this diamicton and underlying predominantly sandy sediments are interpreted in terms of sedimentary processes active during emplacement of the debris flow these processes include the formation of a basal shear zone the deformation and mixing of fine grained sediments incorporated into the base of overriding debris flow features associated with liquefaction sediment remobilisation and water escape are also present and developed in response to increasing overburden pressure during debris flow emplacement these microstructures have also been recorded elsewhere within subglacial diamictons and an evaluation is made between microstructures in palaeo debris flow deposits and those found in modern debris flows

micromorphological criteria for discriminating subglacial and glacimarine sediments evidence from a contemporary tidewater glacier spitsbergen abstract sedimentological and micromorphological evidence is presented from four sites within st jonsfjorden western spitsbergen sedimentological and geomorphological evidence is used to distinguish sites comprising undisturbed glacimarine sediments from glacially over ridden glacimarine sediments and subglacial diamicts impregnated thin sections are used to define associations of micromorphological characteristics that allow diamicts formed under these different conditions to be discriminated in situ glacimarine deposits display winnowed textures dropstone structures and distinct vertical orientations of sand grains whilst subglacial conditions result in structures indicative of deformation under moderate to high stress regimes these criteria may help to determine the origin of ancient and quaternary diamicts of questionable subglacial or glacimarine origin

microstructures within a modern debris flow deposit derived from quaternary glacial diamicton a comparative micromorphological study abstract examination of a modern debris flow in comparison with a quaternary diamicton from which it has been derived reveals significant differentiating sedimentological characteristics the two sediments were examined using micromorphological analyses thin sections of the debris flow show distinct primary microstructure sets that appear indicative of debris flow processes of turbate micro deformation during flow and subsequent flow deceleration comparison of the micromorphological character of both sediments reveal many similarities but the differences seem indicative of flow processes within the active debris flow large turbate structures are common within the debris flow sediment and although many more turbate structures occur within the in situ diamicton they are smaller in size possibly indicative that those structures within the debris flow sediment are not inherited but are neo formed perhaps the most distinctive and individual characteristic separating the debris flow sediment from the older diamicton is the presence of tiled structures these structures result from downslope flow deceleration and dewatering resulting in transverse bands of clays developing in rhythmic like patterns likewise the debris flow sediment exhibits a marbled appearance presumably indicative of intense deformation a characteristic not found in the in situ quaternary diamicton

sedimentological and deformational criteria for discriminating subglaciofluvial deposits from subaqueous ice contact fan deposits a pleistocene example ireland a pit located near ballyhorsey 28 km south of dublin eastern ireland displays subglacially deposited glaciofluvial sediments passing upwards into proglacial subaqueous ice contact fan deposits the coexistence of these two different depositional environments at the same location will help with differentiation between two very similar and easily confused glacial lithofacies the lowermost sediments show aggrading subglacial deposits indicating a constrained accommodation space mainly controlled by the position of an overlying ice roof during ice bed decoupling these sediments are characterized by vertically stacked tills with large lenses of tabular to channelized sorted sediments the sorted sediments consist of fine grained laminated facies cross laminated sand and channelized gravels and are interpreted as subglaciofluvial sediments deposited within a subglacial de coupled space the subglaciofluvial sequence is characterized by glaciotectonic deformation structures within discrete beds triggered by fluid overpressure and shear stress during episodes of ice bed recoupling clastic dykes and folds the upper deposits correspond to the deposition of successive hyperpycnal flows in a proximal proglacial lake forming a thick sedimentary wedge erosively overlying the subglacial deposits gravel facies and large scale trough bedding sand are observed within this proximal wedge while normally graded sand beds with developed bedforms are observed further downflow the building of the prograding ice contact subaqueous fan implies an unrestricted accommodation space and is associated with deformation structures related to gravity destabilization during fan spreading normal faults this study facilitates the recognition of subglacial submarginal depositional environments formed in part during localized ice bed coupling episodes in the sedimentary record the sedimentary sequence exposed in ballyhorsey permits characterization of the temporal framework of meltwater production during deglaciation the impact on the subglacial drainage system and the consequences on the irish sea ice stream flow mechanisms

petrology and geochemistry of the unbrecciated achondrite northwest africa 1240 nwa 1240 an hed parent body impact melt nwa 1240 is an unusual eucrite recently recovered in morocco as a single stone of 98 g it is an unbrecciated greenish brown rock nearly devoid of fusion crust it displays porphyritic texture consisting of skeletal hollow low ca pyroxene phenocrysts set in a variolitic fan spherulitic mesostasis of fine elongate pyroxene and plagioclase crystals minor phases are skeletal chromite iron silica troilite ilmenite and minute amounts of phosphate and fayalite pyroxenes are unequilibrated and show one of the widest ranges of composition so far described for a eucrite from en 76 0 wo 1 9 fs 22 1 to compositions nearly devoid of mg unusual ferrosilite and fe augite symplectites and possibly pyroxferroite plagioclase crystals contain significant amounts of fe and mg which are possibly controlled by the ca mg fe2 si3o8 plagioclase component

observing artificially induced strain implications for subglacial deformation by analysing a series of four successive thin sections from a ceramic clay that was subjected to uniaxial compression we were able to monitor the development of microstructures in a fine grained sediment the artificially induced microstructures such as unidirectional clay reorientations and linear and circular grain arrangements are identical to features that have been observed in thin sections of subglacially deformed tills and therefore may be used as representative analogues we argue that the structures reflecting slip planar shear displacements as well as rotational movements can be explained by assuming a coulomb plastic response to imposed shear we conclude that sediments subjected to subglacial deformation behave as coulomb materials at least during the final stages of the deformation the present study bridges the gap between field studies experimental studies and theoretical modelling the microscopic observations assist in visualising inferred subglacial processes and facilitate up and downscaling between diverse methodological approaches copyright 2003 john wiley sons ltd

spectroscopic characterization of mineralogy and its diversity across vesta the mineralogy of vesta based on data obtained by the dawn spacecraft s visible and infrared spectrometer is consistent with howardite eucrite diogenite meteorites there are considerable regional and local variations across the asteroid spectrally distinct regions include the south polar rheasilvia basin which displays a higher diogenitic component and equatorial regions which show a higher eucritic component the lithologic distribution indicates a deeper diogenitic crust exposed after excavation by the impact that formed rheasilvia and an upper eucritic crust evidence for mineralogical stratigraphic layering is observed on crater walls and in ejecta this is broadly consistent with magma ocean models but spectral variability highlights local variations which suggests that the crust can be a complex assemblage of eucritic basalts and pyroxene cumulates overall vesta mineralogy indicates a complex magmatic evolution that led to a differentiated crust and mantle

common asteroid break up events of eucrites diogenites and howardites and cosmic ray production rates for noble gases in achondrites we determined the cosmic ray produced noble gas abundances in eight diogenites four eucrites and four howardites using these and additional noble gas and chemical data from the literature composition and shielding dependent production rates of achondrites for 3he 21ne 38ar 78kr 83kr and126xe were derived based on 81krkr exposure ages the cosmogenic ratio 22ne 21ne is found to be a valid shielding indicator for all howardites eucrites and diogenites heds this ratio correlates with other shielding dependent ratios such as 78kr 83kr 80kr 83kr 124xe 131xe 126xe 131xe and 128xe 131xe we show that strong correlations for these ratios also exist for basaltic lunar rocks the new production rates were used for the calculation of exposure ages for all heds with known noble gas abundances two major exposure age clusters at 21 ma and 38 ma are observed in all three classes we find that five asteroid break up events characterized by exposure ages 6 1 ma 12 2 ma 21 4 ma 38 8 ma and 73 3 ma produced all diogenites fifteen out of seventeen howardites and twenty eight out of thirty nine eucrites we conclude that asteroidal or cometary impact events at such times on one or several parent bodies are responsible for the ejection of eucrites howardites and diogenites probable parent bodies are multiple 4 vesta derived kilometer sized objects of basaltic achondritic composition reaching the 3 1 resonance region a proposed source area for meteorites the direct ejection from vesta and capture by earth of basaltic meteorites has been shown to be dynamically difficult in such a scenario large events 38 ma and 21 ma ago are required liberating simultaneously material representing vesta s surface eucrites howardites and interior regions diogenites

elemental mapping by dawn reveals exogenic h in vesta s regolith using dawn s gamma ray and neutron detector we tested models of vesta s evolution based on studies of howardite eucrite and diogenite hed meteorites global fe o and fe si ratios are consistent with hed compositions neutron measurements confirm that a thick diogenitic lower crust is exposed in the rheasilvia basin which is consistent with global magmatic differentiation vesta s regolith contains substantial amounts of hydrogen the highest hydrogen concentrations coincide with older low albedo regions near the equator where water ice is unstable the young rheasilvia basin contains the lowest concentrations these observations are consistent with gradual accumulation of hydrogen by infall of carbonaceous chondrites observed as clasts in some howardites and subsequent removal or burial of this material by large impacts

microdistribution of primordial noble gases in cm chondrites determined by in situ laser microprobe analysis decipherment of nebular processes abstract in situ noble gas analyses using a laser microprobe with a beam diameter of 50 100 m were performed on thin slices of murchison and yamato y 791198 cm carbonaceous chondrites in order to see microdistribution of primordial noble gases petrographic observations prior to noble gas analyses showed that the two meteorite slices are entirely composed of chondrules pcps poorly characterized phases and other chondritic components that are rimmed by layers of fine grained dust based on an existing classification scheme for texture of cm chondrites the two samples are classified as primary accretionary rocks pars the noble gas analyses showed that primordial noble gases are rich in the fine grained rims around chondrules in the two meteorite slices this suggests that large amounts of carrier phases of the primordial noble gases in cm chondrites are located in these rims which seem to have accreted on the surfaces of chondrules prior to the formation of the meteorite parent bodies rims on different chondrules within a given meteorite showed similar concentrations of heavy primordial noble gases suggesting that phase q is distributed homogeneously in the rims and possibly in the nebular region where the chondrules had acquired their dust rims 20 ne diamond 20 ne q ratios are relatively constant among rims in a given meteorite indicative of homogeneous mixing of interstellar diamonds and phase q on a 10 g scale one location in a rim around a chondrule in the murchison sample showed an enrichment of 22 ne which suggests presence of carrier phases of ne e in the rim a stepped heating analysis of a chip of y 791198 was carried out to characterize the noble gases of bulk par abundances of primordial noble gases are only 50 of those of rims around chondrules consistent with the relative abundances of gas rich fine grained material and gas poor chondrules and inclusions in par solar gases were not detected which implies that pars the primitive cm bodies had grown to at least centimeter size in a dense solar nebula which shielded these objects from direct exposure to solar wind

widening of the krafla fissure swarm during the 1975 1981 volcano tectonic episode frequent distance measurements across the krafla fissure swarm north iceland recorded the extension accompanying the sequence of rifting events which started in december 1975 and lasted for 6 years an 80 to 90 km long section of the fissure swarm extended during this sequence of rifting and volcanic events maximum widening of about 8 m occurred 10 to 12 km north of leirhnjukur which is located above the center of the krafla magma reservoir from that location the amount of widening decreased north wards and is estimated to exceed 2 m where the seismicity indicated the northern termination of the present rifting off the north coast about 70 km north of leirhnjukur the amount of widening also decreased southwards and approached zero at 15 to 20 km south of leirhnjukur the ground deformation associated with these rifting events can be summarised as a narrow strip 1 to 2 km wide along the fissure swarm is heavily fractured with numerous open cracks parallel to the fissure swarm this fractured strip has subsided 2 to 3 m relative to its flanks the flanks of the fractured zone have been uplifted relative to regions farther away the uplift is not well constrained but tilt observations at several locations indicate about 1 m uplift the flanks of the rift zone have contracted perpendicular to the fissure swarm the maximum contractional strain exceeds 300 mm per km the amount of areal expansion windening of the fissure swarm times the length of the fractured zone associated with these rifting events is estimated to be about 0 30 km2 for individual events the area of expansion has been roungly proportional to the volume of subsidence above the krafla magma reservoir if the width of a new dike is equal widening of surface fissures the ratio of the subsidence volume to the area of expansion for the best observed events indicated a height of a new dike system as 2 4 to 2 8 km this ratio is significantly less for events of large lava production but even during these events the majority of magma leaving the krafla reservoir was apparently emplaced in subsurface fissures

stress shear deformation and micromorphological clay orientation a synthesis of various concepts summary microscopic oriented clay bodies known as plasma separations to soil micromorphologists show various degrees of symmetry and regularity in their patterns they could be regarded as sensitive and reliable indicators of stress strain regime of a soil empirical and experimental evidence signifies the importance of stress specifically that generated by in situ swelling in the genesis of plasmic fabrics hitherto most work in this field is confined to geometric characterization with limited attempts to dynamic interpretations of their origin this paper enlists appropriate concepts in soil mechanics structural geology and agricultural engineering to interpret the possible stress strain components that rearrange fabric units into plasma separations some pertinent concepts including physico chemical behaviour of the clay water system shrink swell phenomenon stress strain deformation and failure of soil are employed to explain the origin of plasmic fabrics by mechanical principles a conceptual model is suggested to synthesize the conditions changes and consequences related to the formation of plasmic fabrics strongly developed plasma separations in natural soils are attributed to the establishment of an anisotropic state of stress generated by in situ swelling in conjunction with the passive pressure of lateral confinement and vertical overburden the difference between the maximum and minimum principal stresses produces a deviatoric stress that can at certain stages of a shrink swell cycle exceed the shear strength of the soil the extra stress is relieved plastically by shear deformation which is manifested as the alignment of platy particles in domain configuration by rotation and translation along the shear planes soil mainly fails in compressive plastic mode along a large number of small shear planes which form the plasma separations the formation of different types of sepic plasmic fabrics is discussed in relation to the stress strain regimes of soils

micromorphological aspects of glaciolacustrine sediments in northern patagonia argentina in this study the sedimentology micromorphology and structure of four deformation sites in end moraines or near end moraine settings are presented micromorphology has proven to be a powerful tool in the interpretation of the sediments the four sites are related to three of the four major glaciations known from this part of patagonia nahuel huapi anfiteatro and pichileufu all four sites are characterised by glaciolacustrine environments in which sedimentation occurred at least partly on and or against dead ice with the exception of one section in the san martin de los andes area where deformation occured by active ice push all major disturbances faults and folds are the result of dead ice collapse comparison with micromorphological observations on basal tills shows that the sediments all lack a clear subglacial imprint

iceberg deformation and erosion in soft sediments southeast norway abstract trenches in soft glaciomarine sediments have been excavated through two relict iceberg scours one upslope and the other horizontal and through one iceberg gravity crater the scours are 70 and 30 m wide respectively and are 1 m deep the grounding features were formed by current driven icebergs during flooding of previously emergent sea bottom 9200 yrs b p the clay beneath the scours and craters is deformed and small and larger scale folding small faults and thrusts joints fissures and collapsed lamination are found different scouring mechanisms apply for initial phases of upslope scouring and horizontal scouring at the start of upslope scouring the sediment mass is removed by thrusting and the depth of deformation within the subsoil is shallow in horizontal scouring two thirds of the scour depression is due to erosion and one third to deformation of the subsoil the deformation can in this case be detected down to four times the scour depth the current velocities are critical for survival of the plough ridges along the horizontal scour the plough ridges are missing because of current erosion during and after scouring

description and numerical model of pleistocene iceberg scours and ice keel turbated facies at toronto canada near toronto in southern ontario canada glaciolacustrine muds and shoreface sands of late pleistocene age early wisconsin glaciation 45 ka were deformed by icebergs ploughing the floor of an ancestral ice dammed lake ontario outcrop mapping and a ground penetrating radar survey identify ice scour structures up to 4 m deep up to 10 m wide and at least several hundred metres long with high standing lateral margins berms ploughing of lake floor sediment is also recorded by ice keel turbated facies in which storm deposited shoreface sands have been mechanically mixed with underlying muds palaeoenvironmental information for one prominent scour such as water depths estimates of the mass and draft of the ice mass and scouring forces can be determined using a simple finite element numerical model a mass of 0 04 million tonnes a keel draft of between 10 and 30 m and a scouring force of 5 103 kn is consistent with scouring by a small iceberg bergy bit or pressure ridged lake ice the former is preferred because of the considerable depth of the scour and the overall glacial depositional setting estimates of ice mass dimensions agree with independent reconstructions of palaeobathymetry no greater than 20 m derived from storm deposited hummocky and swaley cross stratified facies that fill the scour data presented here aid the identification of ice scour structures and turbated sediment in the ancient record despite being a common process on modern high latitude shelves descriptions of ancient structures and facies are few

the nilpena ureilite an unusual polymict breccia implications for origin nilpena 173 g a new ureilite find from the parachilna area of south australia is an unusual polymict breccia containing polymineralic aggregates mineral fragments and achondritic and chondritic lithic enclaves in a dark c rich matrix the polymineralic aggregates consist of equigranular textured olivine fa20 and pigeonite en75wo9fs16 and exhibit evidence of shock in the form of undulose extinction and kink banding monomineralic fragments consist of olivine fa19 24 with highly forsteritic rims up to fa3 and pigeonite and appear to be derived by brecciation of the polymineralic aggregates the enclave material consists of lithic granular olivine fragments porphyritic enstatite fragments either enstatite chondrite or aubrite olivine clinobronzite fragments resembling an h3 chondrite and eucritelike lithic fragments composed of plagioclase an98 salitic clinopyroxene wo48 5en31 4fs20 1 and olivine fa49 53 the matrix contains kamacite generally rich in p schreibersite and troilite the texture of nilpena suggests formation by disruption of a olivine pigeonite granular aggregate while the presence of the diverse chondritic and achondritic enclave material suggests an origin as a surface or near surface breccia like other ureilites nilpena is strongly differentiated with respect to cosmic abundances but is significantly enriched in ba and lree a lack of correlation of lithophile elements with fe fe mg ratio among ureilites suggests that the differentiation was not caused by varying degrees of partial melting of a homogeneous source a cumulate origin therefore seems more plausible

particle and aggregate mobility in till microscopic evidence of subglacial processes abstract microscopic studies of tills show that the deforming bed of glaciers is made up of minute rotational elements or wheels consisting of a nucleus alone or a nucleus with spiralling arms of fine grains these fine grains can move from one wheel to the next providing a process of high grain mobility within a deforming subglacial till recognition of this process explains a variety of glacial distribution patterns i e the mineralogical reflection of subjacent lithologies in the till matrix the side by side occurrence of far travelled erratics and locally derived matrix and the shape of geochemical anomalies

storm influenced deltas and ice scouring in a late pleistocene glacial lake this paper identifies the sedimentary record of storms and bottom scouring ice masses that is preserved in upper pleistocene glaciolacustrine delta sediments deltaic sedimentation occurred on the margin of an enlarged ice dammed ancestral lake ontario with a surface elevation at least 80 m above the modern level beds of amalgamated hummocky and swaley cross strata separated by fairweather muds represent delta front storm deposits and overlie laminated prodelta clays the central and thickest part of a 5 km long outcrop exposes variably cross stratified sand in multiple channels inset within tabular sheets of rippled sand this complex represents a broad distributary channel system about 1 6 km wide and 20 m deep cut into delta front storm sequences a large scour and related deformation structures are attributed to bottom dragging ice masses possibly pressure ridged lake ice the depositional setting outlined in this paper emphasizes the importance of storm waves in large continental glacial lakes and provides a contrast with better known low energy conditions in small glacial lake basins

geochemistry of 4 vesta based on hed meteorites prospective study for interpretation of gamma ray and neutron spectra for the dawn mission asteroid 4 vesta believed to be the parent body of the howardite eucrite and diogenite hed meteorites will be investigated by the dawn orbiting spacecraft dawn carries a gamma ray and neutron detector grand that will measure and map some major and trace element abundances drawing on hed geochemistry we propose a mixing model that uses element ratios appropriate for the interpretation of grand data because the spatial resolution of grand is relatively coarse the analyzed chemical compositions on the surface of vesta will likely reflect mixing of three endmember components diogenite cumulate eucrite and basaltic eucrite reliability of the mixing model is statistically investigated based on published whole rock data for hed meteorites we demonstrate that the mixing model can accurately estimate the abundances of all the grand analyzed major elements as well as of minor elements na cr and mn not analyzed by this instrument we also show how a similar mixing model can determine the modal abundance of olivine and we compare estimated and normative olivine data for olivine bearing diogenites by linking the compositions of well analyzed hed meteorites with elemental mapping data from grand this study may help constrain the geological context for hed meteorites and provide new insight into the magmatic evolution of vesta

facies and microfacies of slope deposits abstract this paper reviews the facies and microfacies of the main types of slope deposits lamination and sorting when preserved are good evidence for overland flow features due to deformation folds boudins coatings and tails due to the rotation of clasts are associated with the early stages of deformation in earth slides other mass movements such as debris flows rock avalanches earth flows and to a certain extent dry grain flows may be characterised by similar microscopic facies typically a poorly sorted porphyric material porosity gives evidence for both liquefaction debris flows and frost induced mass movement solifluction however this criterion is thought to be irrelevant for fossil deposits owing to the rapidity and scale of post depositional changes wetting and drying freezing and thawing bioturbation at present only a detailed analysis of both the macro and micromorphological characteristics of the deposits allows an accurate identification of past slope dynamics

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

lunar rare earth element distribution and ramifications for feo and tio2 lunar prospector neutron spectrometer observations lunar prospector neutron spectrometer data have been used to map the global surface distribution of the incompatible rare earth elements gadolinium and samarium from the low altitude 30 15 km mapping orbit these results afford improved surface resolution and detailed views of the potassium rare earth elements and phosphorus kreep distribution within and around mare imbrium and elsewhere the gd and sm results serve as a complementary and independent check of the distribution of kreep on the moon in contrast with the lunar prospector gamma ray spectrometer results for thorium the neutron spectrometer observations reflect the presence of fe and ti as well as gd and sm the contributions of fe and ti are removed using high spatial resolution clementine spectral reflectance determinations of feo and tio2 abundances overall the resulting gd and sm abundance map agrees with the th abundance map determined using the lunar prospector gamma ray spectrometer in general the detailed features of the procellarum imbrium kreep terrane are found in both for example distinct highs in gd sm and th abundances are resolved over the craters mairan aristarchus kepler reinhold lalande and aristillus over the apennine bench and fra mauro regions and over the montes jura and montes carpatus indicating an enhanced abundance of kreep in these locations the neutron observations also provide constraints on feo and tio2 abundances for some high ti locales there is a significant disagreement with tio2 abundances inferred from clementine spectral reflectance

a new source of basaltic meteorites inferred from northwest africa 011 eucrites are a class of basaltic meteorites that share common mineralogical isotopic and chemical properties and are thought to have been derived from the same parent body possibly asteroid 4 vesta the texture mineralogy and noble gas data of the recently recovered meteorite northwest africa nwa 011 are similar to those of basaltic eucrites however the oxygen isotopic composition of nwa011 is different from that of other eucrites indicating that nwa011 may be derived from a different parent body the presence of basaltic meteorites with variable oxygen isotopic composition suggests the occurrence of multiple basaltic meteorite parent bodies perhaps similar to 4 vesta in the early solar system

micromorphology of diamicton affected by iceberg keel scouring scoresby sund east greenland this research was primarily funded by the university of brighton s rising stars initiative and the school of environment and technology research investment fund with supplementary funds awarded by the quaternary research association the funding sources had no involvement in study design in collection analysis and interpretation of data in the writing of the article and in the decision to submit the article for publication

the south african polymict eucrite macibini the polymict eucrite macibini is a fragmental breccia predominantly composed of eucritic materials with minor proportions maximum 2 vol of diogenitic material hence it is intermediate between the yamato 74159 type polymict eucrites which contain negligible amounts of magnesian orthopyroxene and the howardites the present study provides mineralogical and bulk compositional data for the meteorite breccia and for six clasts these clasts include both volcanic and igneous rocks and a variety of impact generated rocks a broad range of degrees of postcrystallization metamorphism affected these materials before the final aggregation of the breccia clast a is a fragment of unequilibrated eucrite with subophitic texture the edges of the zoned pyroxenes in this clast are composed of a host of fe rich augite containing vermicules blebs and lamellae composed of a mixture of fe rich olivine and silica similar features occur as fragments in lunar breccias and are attributed by some workers to the breakdown of pyroxferroite an fe rich pyroxenoid however textures and compositions of these augite olivine silica intergrowths in clast a suggest that in this case they are the result of decomposition in a series of steps of fe rich subcalcic augite among the fragments of impact generated material in macibini is clast 2 an earlier formed clastic breccia that was lithified before being broken apart and included in the meteorite breccia clast 3 is an impact melt breccia that is composed of rock and mineral fragments in a devitrified groundmass clast c is also an impact melt breccia that has a coarser grained hornfelsic groundmass that resulted from extensive metamorphism after formation

relict ice scour marks and late phases of lake agassiz in northernmost manitoba in northern manitoba intersecting grooves 300 1800 m long are ice scour marks created by the dragging of iceberg keels along rises in the bed of a glacial lake whose water plane was at about 305 m asl the lake was bounded by glacial ice on its northern and eastern margins the occurrence of scours on topographic divides indicates that a single extensive lake thought to be a northern extremity of lake agassiz occupied the area as far north as seal river at the time the ice scours were formed the lake extended as far west as sprott lake and eastwards into the hudson bay lowlands into an area later occupied by tyrrell sea the preservation of the scour marks suggests that the lake drained suddenly ice scour marks are easily recognized on air photographs and provide a means of identifying areas that have been inundated by glacial lakes scours in emerged marine sediment are generally obliterated by littoral processes

icebergs rework shelf sediments to 500 m off antarctica icebergs and sea ice rework the sediments of high latitude shelves producing modern diamicts ice keel turbates unrelated to glacial proximity off antarctica sidescan sonar data indicate the presence of ice gouge features formed by the physical interaction between ice keels and the sea bed these are recognized as incisions a few metres deep and tens of metres wide in water depths up to 500 m on the submarine bank tops and slopes off wilkes land and in the weddell sea subcircular depressions 30 to 150 m in diameter a washboard pattern and hummocky bed features also represent iceberg resting sites the freshness of sea bed morphology nearby holocene sediment ponding and active hydraulic sedimentary processes indicate that the sea floor is being reworked by iceberg keels tabular iceberg drafts in excess of 330 m have been measured and modeling studies suggest that nontabular iceberg drafts of 500 m are possible we conclude that a modern ice keel turbate deposit in the form of a poorly stratified diamicton is probably widespread on that part 54 of the antarctic shelf less than 500 m deep

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

micromorphology of ice keel scour in pebbly sandy mud and fine grained sands scarborough bluffs ontario canada the keels of icebergs and ice pressure ridges plough through unconsolidated sea lake sediments gouging out long grooves known as ice keel scour marks although the surface and more recently subsurface morphology of scours are well documented little is known of the effect of grain size on the detectability style and intensity of sub scour deformation this investigation macroscopically and microscopically two dimensional thin sections examines suspected ice keel scour in i glaciolacustrine pebbly sandy mud and ii fine grained sands at scarborough bluffs ontario canada in this investigation there is an almost identical suite of deformation structures individual structures and overprinted structural patterns to those identified in icebergscoured clays from former glacial lake agassiz manitoba canada this confirms that deformation in the pebbly sandy mud and fine grained sands at scarborough bluffs is likely to be indicative of ice keel scour discrete differences in the detectability style and intensity of deformation between the scarborough bluffs and glacial lake agassiz sediments are probably a function of grain size in response to ice keel scour this research provides additional information on the types of structures that are associated with sediment deformation by processes of ice keel scour in a variety of grain sizes this information is particularly valuable to inform palaeoenvironmental reconstruction and offshore engineering in areas where ice keel scour occurs in a variety of grain sizes it also demonstrates the potential value of micromorphology where for example the study of cores is necessary

iceberg rafting and scouring in the early permian shoalhaven group of new south wales australia evidence of heinrich like events abstract this paper describes multiple layers of ice rafted debris and an ice scour structure in early permian marine strata within the shoalhaven group of the sydney basin new south wales australia strata were deposited on a high latitude glacially influenced continental margin during the final stages of late palaeozoic glaciation between 277 and 260 ma poorly sorted ice rafted debris forming layers up to 1 25 m thick is common within inner to outer shelf and continental slope facies of the shoalhaven group more than 120 layers can be identified these are argued to record the enhanced delivery of debris by icebergs drifting north from marine based antarctic ice margins deformation structures in associated sediments are interpreted as iceberg scours and ice keel turbates associated glendonites record early diagenesis of organic rich sediment and bottom water temperatures close to freezing a speculative hypothesis relates layers of ice rafted debris within the shoalhaven group to multiple episodes of accelerated calving at the margins of a marine based early permian ice sheet in east antarctica these events may be analogous to late pleistocene heinrich events when huge armadas of icebergs were released from the marine based laurentide ice sheet and triggered abrupt changes in ocean circulation and climate similar forcing may have characterized the early permian ice ocean system regardless of the climatic significance of ice rafted layers this is the first time such facies have been documented in the pre pleistocene literature to date few ice scour structures and no ice keel turbates have been reported

age of a eucrite clast from the bholghati howardite 39ar 40ar rb sr and sm nd investigations of the large eucrite clast 1 studied by the bholghati consortium show that it crystallized from a melt 4 51 ga ago the crystallization age is given most precisely by a sm nd internal isochron of 4 510 0 034 ga 2 error limits for 147sm 0 00654 ga 1 142nd144nd measurements show that the clast contained live 146sm at the time of crystallization a solar system initial 146sm144sm0 0 00431 0 0039 0 0026 at 4 555 ga ago can be calculated from a 146sm 142nd isochron and the age of the clast alternatively using 146sm144sm 0 0 0045 as previously reported in the literature a 146sm142nd formation interval of 0 05 0 12 0 08 ga can be calculated which is concordant with the 147sm 143nd isochron age and in agreement with pu u xe and pu nd xe formation intervals reported in a companion consortium paper the initial 143nd144nd ind of the clast was ind 0 505958 50 2 error limits normalized to 146nd 144nd 0 724140 and is consistent with the chur reference value for evolution in a source having chondritic relative ree abundances prior to magma generation however when interlaboratory bias is considered the data are also permissive of a lree depleted source as suggested in a companion consortium paper a primary rb sr isochron yields an age of 4 54 0 06 ga 2 error limits for 87rb 0 01402 ga 1 in agreement with the more precise sm nd age the initial 87sr86sr isr of the clast was isr 0 699006 21 and was the same within error limits as isr previously determined for a pristine eucrite clast from polymict eucrite y75011 compatible with a common parent body the 39ar 40ar data and some of the rb sr data show that bholghati was affected by a major thermal event 2 3 ga ago and also provide weak evidence for a minor thermal event 1 ga ago the age and isotopic systematics of the clast are consistent with those of other eucrites and support the widely held assumption of a common parent body for howardites and eucrites the isotopic investigations of polymict eucrites and howardites point to a prolonged cratering record on the howardite eucrite diogenite hed parent body and suggest that it survived the cataclysm affecting the moon 3 8 4 0 ga ago

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

sedimentology of late glacial clays in lacustrine basins central ireland abstract distal bottom sediments of a large ice marginal interdomal lake that covered most of the central part midlands of ireland during the last deglaciation were poorly known recent work centred on two raised bog covered basins confirmed relatively thick distal glaciolacustrine sediments undisturbed samples taken in 100 mm cores enabled thin sectioning and micromorphological analysis to be carried out the upper part of the fine sediment mostly clay which is apparently homogenous at the macroscopic level is shown to have been bedded or laminated and subsequently homogenised by load casting with depth bedding or lamination becomes more common until the whole deposit is very finely and rhythmically laminated turbidites a consequence of density underflows together with coarse sediment rain out and dropstones confirm a likely ice marginal environment the finer sediment towards the top of the sequence reflects increasing distality synsedimentary folding and faulting load casting and water escape structures point to rapidly accumulating sediment in an unstable sedimentary environment the lack of bioturbation is not surprising and apparent minor traces towards the base of the rhythmites seems most likely to relate to synsedimentary faulting

color and albedo heterogeneity of vesta from dawn multispectral images 0 44 to 0 98 m of asteroid 4 vesta obtained by the dawn framing cameras reveal global color variations that uncover and help understand the north south hemispherical dichotomy the signature of deep lithologies excavated during the formation of the rheasilvia basin on the south pole has been preserved on the surface color variations band depth spectral slope and eucrite diogenite abundance clearly correlate with distinct compositional units vesta displays the greatest variation of geometric albedo 0 10 to 0 67 of any asteroid yet observed four distinct color units are recognized that chronicle processes including impact excavation mass wasting and space weathering that shaped the asteroid s surface vesta s color and photometric diversity are indicative of its status as a preserved differentiated protoplanet

microscopic evidence of subglacial deformation abstract subglacial deformation is by now a well established process however recognition of this process in pleistocene tills is not always clear studies of thin sections of pleistocene tills show that there are a variety of microscopic features caused by deformation this paper gives a review of microscopic evidence for subglacial deformation and starts with a case where deformation could be established macroscopically then traces the microscopic features through planar and rotational movements which are described and separated accordingly attention is also given to features caused by crushing of grains and sediment dewatering these studies indicate that almost all basal tills show evidence of subglacial deformation rather than sedimentary derivation this implies that if we want to understand subglacial processes such tills should be described in tectonic rather than sedimentary terminology

the micromorphology of unconsolidated sediments this paper aims to describe the use of thin sections micromorphology in the sedimentology of unconsolidated sediments it provides examples of the use of thin sections in a variety of sedimentary environments from fault gouge through caves and volcanics to aeolian fluviatile marine periglacial and glacial it demonstrates that in the latter three fields the use of micromorphology is relatively widespread and that in glacial sedimentology it has revolutionised our way of thinking about subglacial sediments although micromorphology has been mainly descriptive so far methods of quantification observations are demonstrated some of the important aspects of micromorphology are its use for microstratigraphy and the possibility of relating observations to documented processes thereby allowing a more robust sedimentological interpretation of modern and ancient sediments

petrologic and textural diversity among the pca 02 howardite group one of the largest pieces of the vestan surface abstract nine howardites and two diogenites were recovered from the pecora escarpment icefield pca in 2002 cosmogenic radionuclide abundances indicate that the samples are paired and that they constituted an approximately 1 m diameter meteoroid prior to atmospheric entry at about 1 m in diameter the pca 02 hed group represents one of the largest single pre atmospheric pieces of the vestan surface yet described mineral and textural variations were measured in six of the pca 02 howardites to investigate meter scale diversity of the vestan surface mineral compositions span the range of known eucrite and diogenite compositions additional non diogenitic groups of mg and fe rich olivine are observed and are interpreted to have been formed by exogenic contamination and impact melting respectively these howardites contain olivine rich impact melts that likely formed from dunite and harzburgite rich target rocks containing the first recognized olivine rich hed impact melts these samples provide meteoritic evidence that olivine rich lithologies have been exposed on the surface of vesta finally we present a new method for mapping distributions of lithologies in howardites using 8 elemental x ray maps proportions of diogenite and eucrite vary considerably among the pca 02 howardites suggesting they originated from a heterogeneous portion of the vestan surface while whole sample modes are dominated by diogenite the finer grain size fractions are consistently more eucritic this discrepancy has implications for near infrared spectral observations of portions of vesta s surface that are similar to the pca 02 howardites as the finer grained eucritic material will disproportionately dominate the spectra

the orientation of buried iceberg scours and other linear phenomena abstract the average orientations of surficial iceberg scours can be obtained from sidescan sonograms using certain assumptions the average orientation of similar buried phenomena can be estimated from a pattern of intersecting seismic profiles two possible solutions are generated at each intersection of two seismic profiles each of which is oriented at an angle i from the profile which encounters the fewer scours where i tan 1 sin i r cos i and r is the ratio of the number of scours observed on the two seismic lines several pairs of solutions are required to determine which solution of each pair is significant iceberg scours observed on aerial photographs of the floor of glacial lake agassiz demonstrate that the estimates provided by this technique correspond with the average orientation of the population applying this method to buried iceberg scours in emerald basin scotian shelf gives orientations which are parallel to paleo bathymetric contours

k th ti systematics and new three component mixing model of hed meteorites prospective study for interpretation of gamma ray and neutron spectra for the dawn mission abstract the dawn spacecraft carries a gamma ray and neutron detector grand which will measure and map the abundances of selected elements on the surface of asteroid 4 vesta we compare the variability of moderately volatile refractory incompatible element ratios k th and k ti in howardite eucrite and diogenite hed meteorites with those in other achondrite suites that represent asteroidal crusts because these ratios may be accurately measured by grand and likely reflect initial chemical compositions of the hed parent body the k th and k ti variations can differentiate hed meteorites from angrites and some unique eucrite like lithologies the results suggest that k th and ti abundances determined from grand data could not only confirm that vesta is the parent body of hed meteorites but might also allow recognition of as yet unsampled compositional terranes on vesta besides the k th ti systematics study we propose a new three component mixing model for interpretation of grand spectra required because the spatial resolution of grand is coarser than the spectral compositional heterogeneity of vesta s surface the mixing model uses abundances of k ti fe and mg that will be analyzed more accurately than other prospective grand analyzed elements we examine propagated errors due to grand analytical uncertainties and intrinsic errors that stem from an assumption introduced into the mixing model the error investigation suggests that the mixing model can adequately estimate not only the diogenite eucrite mixing ratio but also the abundances of most major and minor elements within the grand propagated errors

thin section production of diamicts problems and solutions abstract thin section production of diamict samples presents many problems primarily as a result of incomplete impregnation this problem is investigated in diamicts of known glacial glaciomarine and subaerial origin the inherent sedimentological characteristics rather than particular mode of deposition appears to influence resin impregnation of diamicts a technique of surface impregnation is presented to overcome this problem when samples fail to impregnate fully during initial preparation and is incorporated into current techniques within a flowchart in the majority of cases this technique results in successful production of a useful thin section

relative chronology of crust formation on asteroid vesta insights from the geochemistry of diogenites abstract the eucrites and diogenites are meteorites that probably originate from asteroid 4 vesta the upper part of the crust of this body is certainly composed of eucrites which are basaltic or gabbroic rocks diogenites are ultramafic cumulates whose relationships with eucritic lithologies are unknown here we show that the orthopyroxenes of some diogenites display very deep negative eu anomalies eu eu close to 0 1 or lower the contamination of the parental magmas of diogenites by melts derived by partial melting of the eucritic crust can satisfactorily explain the range of the eu anomalies displayed by diogenites thus these anomalies are the first firm indication that parental melts of diogenites have intruded the eucritic crust and consequently are younger than eucrites

microstructures in subglacial and proglacial sediments understanding faults folds and fabrics and the influence of water on the style of deformation abstract macroscopic field and micromorphological studies have been carried out on subglacially and proglacially deformed glacigenic sequences at a number of sites throughout scotland uk examination of microstructures folds faults hydrofractures plasmic fabrics aided understanding of the deformation histories preserved in the sediments but a similar range of structures were developed in both subglacial and proglacial settings discrimination between subglacial and proglacial deformation was only possible when micromorphological data was used in conjunction with larger scale field observations variations in lithology and water content were controlling factors influencing the style and apparent intensity of deformation recorded changes in pore water content and pressure during deformation can lead to liquefaction and hydrofracturing with early formed structures locally controlling the pattern of water escape liquefaction can also lead to homogenisation of the sediments and the destruction of earlier deformation structures even at relatively low strains beds or zones of liquefied sand and silt may form highly lubricated detachments within the sediment pile resulting in a marked reduction in the amount of shear transmitted to underlying units a multidisciplinary approach involving sedimentological geomorphological stratigraphical and structural field observations combined with micromorphological analysis is recommended to confidently unravel the glacitectonic history and depositional environment of most deformed glacigenic sedimentary sequences

ibitira a basaltic achondrite from a distinct parent asteroid and implications for the dawn mission i have done a detailed petrologic study of ibitira a meteorite that has been classified as a basaltic eucrite since 1957 the mean fe mn ratio of pyroxenes in ibitira with 10 mole wollastonite component is 36 4 0 4 this value is well resolved from those of similar pyroxenes in five basaltic eucrites studied for comparison which range from 31 2 to 32 2 data for the latter five eucrites completely overlap ibitira pyroxenes have lower fe mg than the basaltic eucrite pyroxenes thus the higher fe mn ratio does not reflect a simple difference in oxidation state ibitira also has an oxygen isotopic composition alkali element contents and a ti hf ratio that distinguish it from basaltic eucrites these differences support derivation from a distinct parent asteroid thus ibitira is the first recognized representative of the fifth known asteroidal basaltic crust the others being the hed mesosiderite angrite and nwa 011 parent asteroids 4 vesta is generally assumed to be the hed parent asteroid the dawn mission will orbit 4 vesta and will perform detailed mapping and mineralogical compositional and geophysical studies of the asteroid ibitira is only subtly different from eucritic basalts a challenge for the dawn mission will be to distinguish different basalt types on the surface and to attempt to determine whether 4 vesta is indeed the hed parent asteroid