cross hole fracture connectivity assessed using hydraulic responses during liner installations in crystalline bedrock boreholes abstract in order to continually improve the current understanding of flow and transport in crystalline bedrock environments developing and improving fracture system characterization techniques is an important area of study the presented research examines the installation of flexible impermeable flute liners as a means for assessing cross hole fracture connectivity flute liners are used to generate a new style of hydraulic pulse with pressure response monitored in a nearby network of open boreholes drilled in gneissic rock of the canadian shield in eastern ontario canada borehole liners were installed in six existing 10 15 cm diameter boreholes located 10 35 m apart and drilled to depths ranging between 25 45 m liner installation tests were completed consecutively with the number of observation wells available for each test ranging between one and six the collected pressure response data have been analyzed to identify significant groundwater flow paths between source and observation boreholes as well as to estimate inter well transmissivity and storativity using a conventional type curve analysis while the applied solution relies on a number of general assumptions it has been found that reasonable comparison can be made to previously completed pulse interference and pumping tests results of this research indicate areas where method refinement is necessary but nonetheless highlight the potential for use in crystalline bedrock environments this method may provide value to future site characterization efforts given that it is complementary to and can be used in conjunction with other currently employed borehole liner applications such as the removal of cross connection at contaminated sites and the assessment of discrete fracture distributions when boreholes are sealed recreating natural hydraulic gradient conditions

reconstructing the environmental history of the last glacial interglacial transition evidence from the isle of skye inner hebrides scotland abstract a new interpretation is presented of the late devensian late weichselian wisconsinan lateglacial and early flandrian holocene environmental history of the isle of skye inner hebrides scotland this reconstruction based on pollen percentage pollen concentration pollen preservation and chemical data differs in a number of respects from previous explanations of the lateglacial environmental history of the island the evidence suggests that throughout the lateglacial and early flandrian variation in degree of exposure to prevailing westerly winds was the dominant factor influencing the development of regional vegetation patterns the data provide a proxy climatic record for western scotland during the last glacial interglacial transition and this is discussed in the context of both onshore and offshore evidence the results from skye demonstrate the importance of pollen preservation studies in the interpretation of pollen taphonomy and in the evaluation of lateglacial and early flandrian radiocarbon dates

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

evidence for two step deglaciation and its impact on north atlantic deep water circulation oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35 000 years in the northeastern atlantic the results support the idea that the last deglaci ation took place in two major steps1 4 and conflict with theories calling for a strong reduction in north atlantic deep water formation to explain the abrupt cooling of the younger dryas cold period5 7

the northern sector of the last british ice sheet maximum extent and demise abstract strongly divided opinion has led to competing apparently contradictory views on the timing extent flow configuration and decay mechanism of the last british ice sheet we review the existing literature and reconcile some of these differences using remarkable new sea bed imagery this bathymetric data provides unprecedented empirical evidence of confluence and subsequent separation of the last british and fennoscandian ice sheets critically it also allows a viable pattern of ice sheet disintegration to be proposed for the first time covering the continental shelf around the northern united kingdom extensive echosounder data reveals striking geomorphic evidence in the form of tunnel valleys and moraines relating to the former british and fennoscandian ice sheets the pattern of tunnel valleys in the northern north sea basin and the presence of large moraines on the west shetland shelf coupled with stratigraphic evidence from the witch ground basin all suggest that at its maximum extent a grounded ice sheet flowed from se to nw across the northern north sea basin terminating at the continental shelf edge the zone of confluence between the british and much larger fennoscandian ice sheets was probably across the northern orkney islands with fast flowing ice in the fair isle channel focusing sediment delivery to the rona and foula wedges this period of maximum confluent glaciation c 30 25 ka bp was followed by a remarkable period of large scale ice sheet re organisation we present evidence suggesting that as sea level rose a large marine embayment opened in the northern north sea basin as far south as the witch ground basin forcing the two ice sheets to decouple rapidly along a north south axis east of shetland as a result both ice sheets rapidly adjusted to new quasi stable margin positions forming a second distinct set of moraines c 24 18 ka bp the lobate overprinted morphology of these moraines on the mid shelf west of orkney and shetland indicates that the re organisation of the british ice sheet was extremely dynamic probably dominated by a series of internally forced readvances critically much of the ice in the low lying north sea basin may have disintegrated catastrophically as decoupling progressed in response to rising sea levels final stage deglaciation was marked by near shore ice streaming and increasing topographic control on ice flow direction punctuated retreat of the british ice sheet continued until c 16 ka bp when following the north atlantic iceberg discharge event heinrich 1 ice was situated at the present day coastline in nw scotland

local to regional scale structural controls on mineralisation and the importance of a major lineament in the eastern mount isa inlier australia review and analysis with autocorrelation and weights of evidence although major crustal lineaments may play an important role in mineralisation the relationship between lineaments and mineral deposits can be quite cryptic and structural controls may vary as a function of scale along lineaments major lineaments alone may be of limited use for detailed target generation the cloncurry lineament in the eastern part of the mount isa inlier is a crustal scale structure defined by potential field derived worms weights of evidence quantifies the association between mineral occurrences and this lineament autocorrelation is used to recognise structural controls on mineralisation at different scales by progressively limiting the lengths of the vectors between mineral occurrence points in the autocorrelation plot the weights of evidence analysis shows that au au cu cu au and cu deposits have a positive spatial correlation to the cloncurry lineament which suggests it that acted as a primary crustal scale control on the localisation of cu and au through focussing mineralisation systems on a broad scale however autocorrelation defines a variety of local structural controls which can be interpreted as shear zones variably oriented fault sets en echelon fault arrays and potentially the orientation of bedding and or iron formations which localise fluid flow and mineral deposition at finer scales the results suggest that major lineaments defined by geophysical contrasts can be used in conjunction with techniques of spatial analysis for targeting structurally controlled mineralisation in areas under thin cover adjacent to mineralised terrains such as the mt isa inlier

the geometry and kinematics of flow perturbation folds abstract minor folds formed synchronous with ductile deformation in high strain zones can preserve a record of the scale and kinematics of heterogeneous flow using structures associated with wnw directed caledonian thrusting in n scotland we show that localised perturbations in flow resulted in the generation of predominantly cylindrical minor folds with hinges lying at low angles to the transport direction these define a series of larger scale fold culminations reflecting surging flow or depressions reflecting slackening flow that are bisected by transport parallel culmination and depression surfaces the fold patterns suggest a dominance of layer normal differential shearing due to gradients in shear strain normal to transport culmination surfaces are marked by along strike reversals in the polarity of structural facing and vergence of minor folds which contrary to classic fold patterns define reverse asymmetric relationships culmination surfaces separate folding in to clockwise z folds and anticlockwise s folds domains relative to the transport lineation the dip of fold axial planes systematically increases as their strike becomes sub parallel to transport resulting in a 3d statistical fanning arrangement centred about the transport direction thus mean s and z fold axial planes intersect precisely parallel to the transport lineation and potentially provide a means of determining transport directions in cases where lineations are poorly preserved culminations display convergent fold patterns with fold hinges becoming sub parallel to transport towards the culmination surface and underlying detachment whilst axial planes define overall concave up listric geometries which are bisected by the culmination surface thus around culminations and depressions there are ordered scale independent relationships between transport direction shear sense fold facing vergence and hinge axial plane orientations the techniques described here can be applied and used predictively within any kinematically coherent system of ductile flow

late devensian to early holocene palaeoenvironmental changes in the viking bank area northern north sea abstract lithological and macrofaunal analysis of vibrocores collected from northwest of the viking bank enables the devensian to holocene strata to be subdivided into eight informal units three of which occur widely in the northern north sea for the viking bank area it is suggested that sea level was more than 100 110 m below that at present between 15 500 and 13 600 bp a time when some parts of the area were dry land and others covered by a shallow high arctic sea sea level may have been even lower more than 140 m below its present level prior to 15 500 bp during the windermere interstadial 13 000 11 000 bp polar water was replaced by atlantic water and the environment was low arctic with a regime of strong tidal currents sea level at approximately 12 000 bp had risen to some 80 100 m below present the loch lomond stadial and early holocene generally were characterised by high arctic followed by boreo arctic to boreal faunas relatively low energy conditions and probably rapidly rising sea level

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

new age constraints for the maximum extent of the last british irish ice sheet nw sector this paper presents the first terrestrial age constraints from the outer continental shelf for the maximum extent of the nw sector of the last british irish ice sheet cosmogenic 10be ages from eight glacially transported boulders on the island of north rona show that the late devensian late weichselian british irish ice sheet overrode the island at its maximal stage and retreated c 25 ka bp these new dates supported by other geological evidence indicate that the north western part of the ice sheet was most extensive between 27 and 25 ka bp reaching the outer continental shelf during the global eustatic sea level minimum at the last glacial maximum

the last ice sheet in north west scotland reconstruction and implications recent models of the last scottish ice sheet suggest that nunataks remained above the ice surface in areas peripheral to the main centres of accumulation this proposition has been investigated on 140 mountains over an area of 10 000 km2 in nw scotland outside the limits of the later loch lomond readvance in this area there is evidence for a single high level weathering limit that separates glacially eroded terrain from higher areas of in situ frost debris this limit occurs at altitudes ranging from 425 to 450 m in the outer hebrides to 950 m on the mainland and is best developed on lithologies that resisted breakdown after ice sheet downwastage interpretation of this weathering limit as a periglacial trimline cut by the last ice sheet at its maximum thickness is supported by 1 joint depth and schmidt hammer measurements that indicate significantly more advanced rock breakdown above the weathering limit 2 a much greater representation of gibbsite a pre late devensian weathering product in the clay fraction of soils above the limit 3 cosmogenic isotope dating of the exposure ages of rock outcrops above and below the limit 4 the sharpness of the limit at some sites and its regular decline along former ice flowlines and 5 shear stress calculations based on the inferred altitude and gradient of the former ice surface reconstruction of the ice surface based on trimline evidence indicates that the mainland ice shed lay near or slightly east of the present watershed and descended northwards from 900 m to ca 550 m at the north coast independent dispersion centres fed broad ice streams that occupied major troughs on skye an ice dome 800 m deflected the northwestwards movement of mainland ice but the mountains of rum were over ridden by mainland ice up to an altitude of ca 700 m the outer hebrides supported an independent ice cap that was confluent with mainland ice in the minches extrapolation of the trimline evidence indicates that most reconstructions of ice extent are too conservative and suggests that low gradient ice streams extended across the hebridean shelf offshore wider implications of this research are 1 that blockfields and other periglacial weathering covers are not all of the same age or significance depending on the resistance of different lithologies to frost weathering 2 that the contrasting degree of glacial modification in the western and eastern highlands of scotland may reflect a former cover of predominantly warm based ice in the former and predominantly cold based ice in the latter and 3 that the approach and techniques developed in this study have potential application for constraining ice sheet models not only in areas peripheral to the main centres of ice accumulation in britain and ireland but also in other mountain areas where nunataks protruded through warm based late pleistocene ice masses

new evidence from the south china sea for an abrupt termination of the last glacial period abrupt changes in climatic conditions have been seen at high latitudes in the north atlantic1 and the antarctic2 3 at 13 kyr bp it is important to determine whether this abrupt change was confined to high latitude regions or whether it was global here we present results demonstrating an abrupt change in the rate and character of sedimentation in the south china sea at the close of the last glacial period radiocarbon dating and its position in the oxygen isotope shift suggest that this change may be coincident with the changes found at high latitudes

did the giant broken hill australia zn pb ag deposit melt abstract recent published research has proposed that some metamorphosed massive sulfide deposits including the broken hill deposit australia have partially melted here we discuss the evidence for and against this process the broken hill deposit is located in the curnamona craton within a rift in an apparent upward coarsening sequence of clastic metasediments into which paleoproterozoic mafic and felsic melts intruded the deposit was metamorphosed to granulite facies conditions 750 800 c and 5 6 kbar and was subjected to at least five periods of deformation at peak p t conditions a melt phase was produced in silicate rocks especially granitoids and psammopelites and in ore characterized by the systems cu as s ag pb s ag sb as s cu sb pb s sb as s cu sb s and fe as s however the proportion of minerals in these s bearing systems is insignificant 2 feo mno cao al 2 o 3 p 2 o 5 co 2 zns pbs fes feass feas 2 which is the most relevant system to broken hill ores p t conditions were never high enough to produce a melt phase in this system authors arguing for sulfide rock melting suggest that mn rich lithologies garnetite and quartz garnetite which are intimately associated with the pb rich ores at the broken hill deposit were produced by a reaction between mn rich sphalerite and aluminous wall rocks however to produce such rocks would require mn contents of sphalerite compositions that are unrealistically high and yet to be found in nature moreover the implication of the melt model is that wherever mn rich quartz garnetite and garnetite are found sphalerite should be located next to them this is clearly not the case the presence of polyphase sulfide inclusions within garnet in garnetite has also been considered by some in the literature to be sulfide melt inclusions with the implication that the enclosing garnet was a product of melting however we consider these sulfides to be products of hydrothermal processes during retrograde metamorphism it is impossible to form garnetite and quartz garnetite in rocks within the curnamona craton that formed at upper greenschist lower amphibolite facies conditions by partial melting p t conditions were too low we consider that the fe and mn component of garnetite and quartz garnetite are products of exhalation and inhalation at or near the sea floor and that these rocks are meta exhalites or meta inhalites some garnet rich rocks also formed by metasomatic processes throughout the protracted metamorphic history that affected the curnamona craton

a 9000 year old ash bed on the faroe islands abstract radiocarbon datings of the saksunarvatn ash bed on the faroe islands indicate an age of 9000 9100 yr b p the saksunarvatn ash bed differs geochemically from both ash zone 1 in the north atlantic and the vedde ash bed of norway and the norwegian sea all mentioned ashes are assumed to originate from iceland the vedde ash has been dated at 10 600 60 yr b p consequently the saksunarvatn and vedde ash beds provide an opportunity for precise dating of events around the pleistocene holocene boundary in marine cores especially from the region where the two plumes overlap

marine molluscs and late quaternary environmental studies with particular reference to the late glacial period in northwest europe a review abstract although it is now commonly thought that temperature is a minor factor in limiting the distribution of marine invertebrates particularly on a local scale there is evidence to suggest that some boreal molluscs particularly those which occur in similar environments on both sides of the north atlantic are valuable as oceanic temperature indicators this applies particularly to planktotrophic species whose northern limits of distribution are apparently controlled by summer surface temperature the oceanography of the eastern north atlantic is briefly considered in relation to zoogeographic subdivisions based on temperature and it is concluded that the latter are fairly crude and apply only to shelf seas most glaciomarine molluscan faunas are not specific to that environment an exception being that dominated by the bivalve portlandia arctica the role of marine molluscs in palaeoenvironmental research at the local level for the 13 11 ka bp period is illustrated by a site at inchinnan scotland it is concluded that a shell bed at this locality consists partly of a little modified life assemblage and partly of shells which have been gently reworked under conditions of generally rapid deposition during the same time interval the changing composition of molluscan faunas on the nw european seaboard suggests that a weak drift of north atlantic water replaced polar water at or a little later than 13 ka bp off scotland and a few hundred years later off northern norway evidence for relatively warm intervals early and late in the 13 11 ka bp period has been found particulary on the scottish coast and to a lesser extent more generally the later warm interval may be related to the southward movement of the polar front at the beginning of the younger dryas the value of the bivalve shell itself in the determination of temperature seasonality and calendar years is briefly discussed

late weichselian vegetation climate and floral migration at liastemmen north rogaland south western norway palynological results from liastemmen indicate a tripartite division of the late weichselian in the pleniglacial period from deglaciation ca 14000 bp to ca 13000 bp artemisia dominated pioneer vegetation on disturbed mineral soil was strongly influenced by cold winters and katabatic winds the late weichselian interstadial ca 13000 bp ca 11000 bp comprises a salix shrub consolidation phase and from ca 12700 bp a tree birch phase in the last 500 years of this period july and january means are estimated to about 16 c and between 2 c and 6 c respectively in the younger dryas stadial ca 11000 bp ca 10200 bp artemisia dominated vegetation returns three brief climatic deteriorations ca 12 250 bp 11 700 bp and 11 300 bp unfavourable to woody vegetation on humus soils are demonstrated within the interstadial critical climatic factors include cool winters and strong winds exposing vegetation and soil to frost drought and erosion the oldest and strongest oscillation probably involving local deforestation is correlated with the older dryas deterioration boreal circumpolar eurasiatic and arctic alpine plants dominated the late glacial flora for the majority of the late glacial taxa a northward migration is demonstrated this may also apply for papaver radicatum pinguicula alpina and primula scandinavica all with bicentric distributions in norway today

glaciology of the british isles ice sheet during the last glacial cycle form flow streams and lobes abstract the last ice sheet over the british isles together with other mid latitude pleistocene ice sheets and in contrast to the modern ice sheets of greenland and antarctica had a relatively low profile low summit elevation and extensive elongated lobes at its margin a thermo mechanically coupled numerical ice sheet model driven by a proxy climate has been used to explore the properties that would have permitted these characteristics to develop the approach the key to quantitative palaeoglaciology is to determine the boundary conditions that permit the simulated ice sheet to mimic the evolution of the real ice sheet through the last glacial cycle simulations show how a british ice sheet may have been confluent with a scandinavian ice sheet during some parts of its history and how unforced periodic and asynchronous oscillations could occur in different parts of its margins marginal lobes are a reflection of streaming within the ice sheet such streams can be ephemeral dynamic streams located because of ice sheet properties or fixed streams whose location is determined by bed properties the simulations that best satisfy constraints of extent elevation and relative sea levels are those with major fixed streams that strongly draw down the ice sheet surface in these the core upland areas of the ice sheet were cold based at the last glacial maximum basal streaming velocities were between 500 and 1000 ma 1 compared with surface velocities of 10 50 ma 1 in inter stream zones shear stresses were as low as 15 25 kpa in streams compared with 70 110 kpa in upland areas and 60 84 of the ice flux was delivered to the margin via streams

the submerged landforms of the st kilda archipelago western scotland abstract a detailed bathymetric map of the area around the st kilda archipelago has been prepared with a 10 m isobath vertical interval the map reveals two major submerged erosional surfaces that culminate in clifflines the lower surface at ca 120 m covers at least 40 km2 and is thought to have been produced during low sea levels coincident with periods of maximum northern hemisphere glaciation the upper surface is complex in origin varying between 80 and 40 m it is thought to have been produced during periods of partial northern hemisphere glaciation the last such period the loch lomond younger dryas stadial being responsible for the production of the ca 40 m cliff platform junction the last 40 m relative rise of sea level has been accompanied by very little marine erosion despite the very exposed situation of the islands and this sea level rise is thought to have taken place during the flandrian

shear zone versus fold geometries at the cannington ag pb zn deposit implications for the genesis of bht deposits existing structural analysis of drill core and sulphide zonation were taken as evidence for a large scale synform that dominates the geometry of the cannington ag pb zn deposit a broken hill type bht deposit underground mapping in this study has found that northwesterly directed thrusting took place during peak temperature d1 and that s1 gneissosity is continuous around an amphibolite mega boudin d2 sillimanite biotite shear zones contain asymmetric folds previously interpreted to be parasitic folds but in this study they are interpreted as due to easterly directed extension of s1 s1 and s2 indicate that shear zones were continuous and not folded into the current deposit geometry d2 is associated with garnet pyroxene alteration that proved to be a favourable host for low temperature sulphide precipitation retrograde deformation post d2 controlled lode geometry such a concept of high temperature shear zone formation can be applied to other bht deposits such as the broken hill main lode and the aggeneys gamsberg base metal deposits in south africa in the shear zone model cannington and other bht deposits are situated within high temperature thrust shear zones that formed in conjunction with regional large scale folding

maramungee a proterozoic zn skarn in the cloncurry district mount isa inlier queensland australia the significant but subeconomic 1 8 mt4 4 zn maramungee deposit is 90 km south southeast of cloncurry in northwest queensland it lies in the eastern fold belt of the proterozoic mount isa inlier within rocks of the maronan supergroup that also hosts the large pb zn ag deposits at cannington and pegmont the maramungee deposit is a product of a series of processes that occurred during the metamorphic evolution of the eastern fold belt and the brittle structures that host sulfide mineralization are likely to have been active after the emplacement of the late to post tectonic granites of the williams batholith maramungee is hosted by upper amphibolite sillimanite k feldspar zone gneisses exceptionally iron rich metabasites and foliated granite mineralization was restricted to an elongate embayment in the margin of the maramungee granite pluton created by the antiformal part of a steeply inclined parasitic f 2 fold a major photolinear feature lies immediately west of the hinge in both the granite and its host rocks this structure was initiated by fabric intensification during attenuation of the adjacent fold limb mineralization was further localized by a heterogeneous altered rock package including 1 potassic rocks generally foliated with large amounts of microcline and or biotite 2 skarns partly discordant including both manganoan hedenbergite fe mn rich grossularite quartz apatite rocks and ca rich almandine or clinopyroxene bearing metabasites and 3 a range of compositionally intermediate assemblages distinguished by the coexistence of fe mn ca and k bearing metamorphic silicates graphite commonly occurs at levels of several modal percent in the altered rocks but magnetite and zincian spinel are absent the most strongly altered rocks have a chemical component derived from the metasedimentary gneisses and possibly reflect alteration of a unit which previously contained carbonates this alteration would have involved reduction producing graphite coupled with differential addition of k fe mn p and f the potassic and skarnoid rocks are distinctive components of a regional pattern of metasomatism that exploited steeply inclined d 2 structures early metasomatic fluids in equilibrium with graphite at maramungee are unlikely to have been evolved from the magnetite bearing pluton sulfides mainly sphalerite pyrrhotite and pyrite occur in veinlets and microbreccia matrices that overprint all the earlier rock types and alteration assemblages they are associated with the development of retrograde hydrous and comparatively oxidized secondary minerals including cl and fe rich amphiboles chlorite scapolite calcite albite epidote and muscovite hematite is present in the youngest alteration assemblages retrograde phase relationships suggest that sulfide deposition was induced by reduction of the infiltrating fluid initially occurred at temperatures of 450 degrees to 500 degrees c and may have continued through a significant cooling interval zn is the only economically significant metal present although pb ag cu cd and sb are commonly anomalous and there are sporadically elevated amounts of au as and mo molybdenite is associated with fluorite and enrichments of rb ba u th and light ree in the early potassic alteration with the exception of zn and cd there is little overall correlation among the chalcophile elements there is a crude zoning toward higher cu zn ratios in the southern part of the prospect and there are sporadic occurrences of cu fe sulfide mineralization that have no clear relationship to the main zn zone associated with silicification muscovite chlorite alteration and variably anomalous au ag se co ree and u

late quaternary stratigraphy of the northern rockall trough and faeroe shetland channel northeast atlantic ocean a late quaternary deep water stratigraphic framework has been established for the deep water areas 450m of the northern rockall trough and faeroe shetland channel four stratigraphic units 1 4 are identified these are primarily biostratigraphic units based on dinoflagellate cyst evidence unit 1 represents the late weichselian glacial pre 13 000 yr bp unit 2 the late glacial interstadial 11 000 13 000 yr bp unit 3 is of younger dryas age 10 000 11 000 yr bp and unit 4 represents the holocene interglacial post 10 000 yr bp this stratigraphy is supported by the discovery of the mixed vedde ash 10 600 yr bp and north atlantic ash zone 1 and the saksunarvatn ash 9000 9100 yr bp concentrated in units 3 and 4 respectively the sedimentology indicates that the oceanographic regime underwent a major change between the glacial and interglacial stages this is marked by the onset of strong bottom current activity allied to the restoration of overflow of the norwegian sea deep water into the north atlantic towards the end of the younger dryas stadial despite intense bioturbation and bottom current reworking the basic stratigraphic framework is maintained recognition of two volcanic ash markers enables correlation with established onshore and offshore sequences of marine and non marine environments

millennial scale depositional cycles related to british ice sheet variability and north atlantic paleocirculation since 45 kyr b p barra fan u k margin lithology lithic petrology planktonic foraminiferal abundances and clastic grain sizes have been determined in a 30 m long core recovered from the barra fan off northwest scotland the record extends back to around 45 kyr b p with sedimentation rates ranging between 50 and 200 cm kyr the abundance of ice rafted debris indicates 16 glacimarine events including temporal equivalents to heinrich events 1 4 enhanced concentrations of basaltic material derived from the british tertiary province suggest that the glacimarine sediments record variations in a glacial source on the hebrides shelf margin glacimarine zones are separated by silty intervals with high planktonic foraminifera concentrations that reflect an interstadial circulation regime in the rockall trough the results suggest that the last british ice sheet fluctuated with a periodicity of 2000 3000 years in common with the dansgaard oeschger climate cycle

study of fracture induced anisotropy from discrete fracture network simulation of well test responses different conceptualizations of fracture networks have been generated in order to simulate well tests in fractured reservoirs these models have two purposes firstly to investigate whether the behaviour of realistic fracture networks can be emulated with more simple models and secondly to assess whether different sources of anisotropy have characteristic and recognizable influences on the pressure derivative the anisotropy of the fracture networks was increased by decreasing the angle between two originally orthogonal fracture sets and by increasing the permeability contrast between two orthogonal fracture sets results indicate that simple models can capture the first order behaviour of more realistic examples however because early time data are strongly influenced by the connectivity of the fracture network the degree of anisotropy can only be assessed at later times in a test increasing anisotropy results in increasing heterogeneity and compartmentalization and permeability anisotropy in an orthogonal system can only partially replicate the behaviour of a geometrically anisotropic system

freshwater influx hydrographic reorganization and the dispersal of ice rafted detritus in the sub polar north atlantic ocean during the last deglaciation a sediment core from the north east north atlantic contains high resolution co registered foraminiferal 18o and ice rafted detritus ird records for the last deglaciation these reveal a distinct ice rafting event that occurred at the time of greenland interstade 1d gi 1d a feature also seen in other high resolution cores from the north atlantic the occurrence of a geographically widespread peak in ird at ice distal sites at a time when increased freshwater flux to the surface ocean is inferred to have caused rapid cooling suggests a mechanistic link between the processes analogous to the younger dryas gs 1 cooling episode the general absence of ird at southern locations at other times during gi 1 when the flux of icebergs from surviving ice sheets to northern locations continued suggests that the gi 1d ird peak represents a time of hyrdrographic reorganization which changed ird dispersal while numerous studies have suggested freshwater flux as a major driver of rapid climate oscillations observed around the north atlantic during the last deglaciation the evidence presented here both supports that mechanism and highlights the potential for rapid and major reorganization of the north atlantic s surface hydrography to explain changes in ird flux independently of ice sheet calving dynamics

late devensian and flandrian palaeoenvironmental changes on the scottish continental shelf west of the outer hebrides examination of two radiocarbon dated vibrocores taken from south of st kilda at a water depth of about 155 m a short distance within the maximum position of the late devensian dimlington stadial ice sheet suggests that the st kilda basin became free of glacier ice after 15250 yr bp sedimentation in a shallow low energy high arctic muddy environment continued until after 13500 yr bp there followed a higher energy temperate episode during which water depths were roughly about 40 m this is correlated with the latter part of the windermere interstadial and with the warmer interval known in shallow scottish seas about or a little before 11 000 yr bp the loch lomond younger dryas stadial is marked in the vibrocores by the return of muddy sediments and a cold water fauna relatively shallow water conditions seem to have persisted into the earliest flandrian when the water depth was still roughly 60 m corresponding to a sea level in the area 90 100 m below present it is suggested that pack ice was widespread in the northeast atlantic before the windermere interstadial and also during the loch lomond stadial when it transported shards of icelandic volcanic ash into the st kilda basin estimates of sea surface temperature for the last part of the windermere interstadial are close to those derived from the deep sea record for the same period

evidence for heinrich event 1 in the british isles in the north irish sea basin isb sedimentary successions constrained by ams 14c dates obtained from marine microfaunas record three major palaeoenvironmental shifts during the last deglacial cycle i marine muds cooley point interstadial dated to between 16 7 and 14 7 14c kyr bp record a major deglaciation of the isb following the late glacial maximum lgm ii terminal outwash and ice contact landforms killard point stadial were deposited during an extensive ice readvance which occurred after 14 7 14c kyr bp and reached a maximum extent at ca 14 14c kyr bp at this time the lowlands surrounding the north isb were drumlinised coeval flowlines reconstructed from these bedforms end at prominent moraines killard point bride st bees and indicate contemporaneity of drumlinisation from separate ice dispersal centres substrate erosion by fast ice flow and subglacial sediment transfer to ice sheet margins in north central ireland bed reorganisation associated with this fast ice flow phase involved overprinting and drumlinisation of earlier transverse ridges rogen type moraines by headward erosion along ice streams that exited through tidewater ice margins this is the first direct terrestrial evidence that the british ice sheet bis participated in heinrich event 1 h1 iii regional mud drapes directly overlying drumlins record high relative sea level rsl with stagnation zone retreat after 13 7 14c kyr bp rough island interstadial elsewhere in lowland areas of northern britain ice marginal sediments and morainic belts record millennial scale oscillations of the bis which post date the lgm advance on to the continental shelf and pre date the loch lomond stadial younger dryas advance in the highlands of western scotland ca 11 10 14c kyr bp in western northwestern and northern ireland killard point stadial h1 ice limits are reconstructed from ice flow lines that are coeval with those in the north isb and end at prominent moraines on the scottish continental shelf possible h1 age ice limits are reconstructed from dated marine muds and associated ice marginal moraines it is argued that the last major offshore ice expansion from the scottish mountains post dated ca 15 14c kyr bp and is therefore part of the h1 event in eastern england the stratigraphic significance of the dimlington silts is re evaluated because evidence shows that there was only one major ice oscillation post dating ca 18 14c kyr bp in these lowlands in a wider context the sequence of deglacial events in the isb widespread deglaciation of southern part of the bis major readvance during h1 ice sheet collapse is similar to records of ice sheet variability from the southern margins of the laurentide ice sheet lis well dated ice marginal records however show that during the killard point readvance the bis was at its maximum position when retreat of the lis was well underway this phasing relationship supports the idea that the bis readvance was a response to north atlantic cooling induced by collapse of the lis 1998 john wiley sons ltd

structure of the isan orogeny under cover to the east of the mount isa inlier revealed by multiscale edge analysis and forward and inverse modelling of aeromagnetic data aeromagnetic data reveals the presence of three north south orientated tens of kilometre scale elliptical structures under cover to the east of the mount isa inlier in queensland australia the holy joe creek boot creek and nora creek structures are typically defined by three narrow continuous magnetic ridges highly magnetically susceptible amphibolite bodies similar to those exposed in the inlier are probably the source of most of these magnetic anomalies multiscale edge analysis 2d forward modelling and 3d inverse modelling methods have been used to resolve the geometry and near surface dip of the structures these techniques indicate that the structures dip moderately to steeply around their edges the holy joe creek structure exhibits sub vertical to steeply west dipping sides and a moderate plunge around the northern closure the boot creek and nora creek structures are more complex magnetically but their eastern edges also have sub vertical to steep westerly dips diapirism and domes in an egg box style type 1 fold interference pattern are considered as possible origins for the elliptical structures however disparity between the shape of the structures and possible diapiric bodies and the lack of complementary basin structures to the domes makes these two explanations unlikely a more plausible alternative is that the structures are the result of deformation in a single phase producing folds with a variable hinge line plunge these results indicate that east west shortening during the d2 event of the isan orogeny was the major deformation in the buried rocks of the study area suggesting a shared structural history with the mount isa inlier to the west

evolution of seasonal stratification in the celtic sea during the holocene seasonal thermocline development in the shelf seas of nw europe results in the formation of pronounced frontal regions which separate stratified from well mixed water numerical m 2 palaeotidal modelling of the nw european continental shelf during successive stages of the holocene transgression indicates that seasonal stratification started to develop in the central celtic sea once a critical threshold water depth had been exceeded at around 9000 years bp this hypothesis has been tested through faunal isotopic and geochemical analysis of an ams 14 c dated british geological survey vibrocore from the celtic deep bathymetric basin a record which spans the last 12 000 years marked positive trends in the stable oxygen isotopic data from the benthic foraminifera ammonia batavus and quinqueloculina seminulum between 9000 and about 5000 years bp represent a 4 5 c cooling in summer bottom water temperature caused by the progressive replacement of tidally well mixed by stratified water stable carbon isotopic data from the same species measured through the same core intervals show a negative trend consistent with net oxygen utilization and decomposition of organic matter beneath the productive frontal zone these geological data indicate the progressive evolution of seasonally stratified water in the celtic sea during the earlier part of the holocene modern shelf sea frontal and thermocline development are known to influence biological productivity sedimentation rates the organic content of shelf sediments and the climate of surrounding landmasses hence these palaeodata have significance in defining the role of shelf sea environments in the climate system

vergence and facing patterns in large scale sheath folds the careful geometric analysis of minor structural detail elucidates the relationships and evolution of associated large scale curvilinear hinge geometries developed during wnw directed caledonian thrusting exposed in neoproterozoic moine psammites of the moine nappe reversals in the polarity of structural facing associated with minor folding mark the position of major sheath folds which parallel transport upwardly convex sheaths closing in the direction of thrust transport cored by older gneissose basement inliers are termed culminations whilst those opening in the transport direction and cored by moine psammites are termed depressions sheath folds are bisected by transport parallel and foliation normal culmination depression surfaces which separate not only the reversals in facing but also delineate zones of minor fold hinge obliquity into clockwise and anticlockwise domains relative to the transport direction the sense of obliquity of minor z and s folds is thus dependent on position with respect to the surfaces of culmination and depression and not the fold axial surfaces surfaces of culmination and depression may be superimposed on original overturned antiformal and synformal folds to produce a variety of dome culmination on antiform saddle depression on antiform inverted saddle culmination on synform and basin depression on synform configurations the curvilinear hinges of minor folds may also be asymmetrical about the transport direction and within the plane of the regional foliation to define patterns of fold hinge line vergence classical concepts of fold limb vergence may thus relate to larger antiformal and synformal hinges whilst the fold hinge line vergence defines major curvilinear hinges associated with culminations and depressions major sheath folds may therefore be interpreted in terms of both minor fold hinge line and limb vergence coupled with fold axis obliquity and reversals in the polarity of structural facing the ability to recognise consistent and reliable structural relationships between facing and hinge obliquity at small scales indicates that the regional deformation process forms a linked and coherent system through several orders of magnitude 1999 elsevier science ltd all rights reserved

proterozoic transpressive deformation in the northern marginal zone limpopo belt zimbabwe a major tectono metamorphic event affected the southern half of the northern marginal zone of the limpopo belt at 2 0 ga structural analysis along a 43 km long profile perpendicular to strike shows extension inclined toward the northeast extension parallel to axes of folds that uplift the southeast of the section i e the central zone of the limpopo belt and dextral shear these deformation patterns developed coevally the lineations form distinct tightly clustered groups that occur together in the profile there is no evidence for superimposed deformation or deformed lineations nor are lineations observed cross cutting each other this single episode of deformation can therefore be called transpression petrographic and thermobarometric evidence support this kinematic picture in that decreases of both pressure 2 5 kb and temperature 150 c are documented from southeast to northwest across strike 39 ar 40 ar step heating of metamorphic hornblende from amphibolites has yielded ages of

autochthonous block fields in southern norway implications for the geometry thickness and isostatic loading of the late weichselian scandinavian ice sheet the consistent geographical and altitudinal distribution of autochthonous block fields mantle of bedrock weathered in situ and trimlines in southern norway suggests a multi domed and asymmetric late weichselian ice sheet low gradient ice sheet profiles in the southern baltic region in the north sea and along the outer fjord areas of southern norway are best explained by movement of ice on a bed of deforming sediment although water lubricated sliding or a combination of the two may not be excluded the ice thickness distribution of the late weichselian scandinavian ice sheet is not in correspondence with the modern uplift pattern of fennoscandia early holocene crustal rebound was apparently determined by an exponential glacio isostatic rise later however crustal movements appear to have been dominated by large scale tectonic uplift of the fennoscandian shield centred on the gulf of bothnia the region of maximum lithosphere thickness

a younger dryas ash bed in western norway and its possible correlations with tephra in cores from the norwegian sea and the north atlantic abstract a bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western norway it is formally mamed the vedde ash bed and its age is approximately 10 600 yr b p i e mid younger dryas the bed consits of pure glass having a bimodal basaltic and rhyolitic somposition the geochemistry of the glass shards suggests an icelandic source by means of stratigraphic position and geochemistry the ash is correlated with ash zones found in cores from the continental shelf the norwegian sea and the north atlatic

the quaternary deposits and landforms of scotland and the neighbouring shelves a review abstract a thick sequence of quaternary sediments up to 1000 m has been deposited in the north sea basin and perhaps five major glacial episodes the first occurring prior to ca 1 8 2 1 ma bp and the last during the late devensian can be recognised between the glacial events periods of low salinity arctic marine or glacio marine sedimentation have been dominant although episodes of ameliorated climate when north atlantic drift waters had access to the north sea have been identified a number of horizons in separate boreholes have been correlated with the last interglacial oxygen isotope stage 5e and a sequence of water mass movements around the scottish coasts can be reconstructed for the last ca 125 ka on land sequences of quaternary deposits relating to several glacial and non glacial terrestrial and marine events occur in different areas but due to poor dating correlation between these sequences cannot yet be achieved in particular north east scotland has a complex glacial history with evidence for ice sheet glaciation on at least four occasions evidence from the outer hebrides north east scotland and the north sea basin indicates that the late devensian scottish ice sheet had a rather restricted extent only reaching a short distance offshore along much of the east and west coasts at this time ice free areas existed in north east scotland on the isle of lewis and probably in caithness and orkney whilst part of the outer shelf around st kilda was dry land a marine embayment extended down the east coast of scotland between the scottish and scandinavian ice sheets and independent ice caps existed on the outer hebrides and probably on shetland deglaciation of the greater part of the country took place prior to ca 13 ka bp whilst the climate was still very cold the ice retreat appears to have been orderly with stagnant ice masses being trapped only in topographically suitable locations a number of retreat stages or minor readvances occurred during the general deglaciation the firth of clyde was one of the last areas outside the highlands to be deglaciated and this occurred in a rapid possibly catastrophic fashion shortly prior to ca 13 ka bp despite the mild climate at the start of the lateglacial interstadial it is not known if there was complete deglaciation prior to the loch lomond readvance the readvance glaciers however may have started to advance during the latter part of the interstadial when declining terrestrial temperatures coincided with a period of mild marine conditions the loch lomond readvance maximum can only be dated to some time after ca 10 9 ka bp and it is likely that final ice free conditions were not achieved until the earliest holocene

extent and deglacial chronology of the last british irish ice sheet implications of exposure dating using cosmogenic isotopes over 160 10be and 36cl exposure ages pertaining to the extent and chronology of the last british irish ice sheet biis are critically reviewed despite uncertainties inherent in the use of exposure ages this approach has demonstrated that at the last glacial maximum lgm ca 26 21 ka the biis extended over all low ground in scotland and all or almost all of ireland consistent with recent models depicting extension of the last biis to the atlantic shelf edge all exposure ages obtained for high level sites above trimlines on the mountains of northwestern scotland and ireland pre date the lgm this finding confirms that high plateaux in these areas escaped significant glacial erosion probably under a protective cover of cold based glacier ice that remained frozen to the underlying substrate in terms of deglaciation chronology the southern irish sea basin was probably deglaciated by 19 18 ka with extensive deglaciation of low ground in ireland and northeastern scotland prior to ca 14 5 ka ice cover on low ground in northwestern scotland apparently persisted after 14 0 ka suggesting survival of ice in favourable locations during the lateglacial interstade ca 14 5 12 9 ka attempts to date readvances have had mixed success the wester ross readvance in northwestern scotland was initially dated to ca 16 3 ka but more recent research implies a much younger age ca 14 0 13 5 ka exposure ages indicating a prolonged stillstand during ice sheet retreat in the cairngorms at ca 14 5 14 0 ka conflict with ages obtained on postglacial rockslides and basal radiocarbon dates which indicate deglaciation before ca 15 5 15 0 ka exposure dating has been successfully employed to confirm a loch lomond stadial ca 12 9 11 5 ka age for moraines in several mountain areas and to constrain the minimum altitude of the ice cap that extended over the western grampians at that time copyright 2009 john wiley sons ltd

long range transport of volcanic ash to the greenland ice sheet betzer et al 1 reported the surprising discovery of giant 75 m mineral particles transported more than 10 000 km from their source we have found volcanic ash containing glass shards as large as 300 m in a section of wisconsinian ice from the dye 3 core in greenland which is similarly unexpected and raises interesting questions concerning the long range aeolian transport of particulate matter as the volcanic ash correlates well with similar ash in deep sea sediment cores from the atlantic it also allows us to date the ice with some confidence

multiple foliations defined by different sillimanite crystal habits partial melting and the late metamorphic development of the cannington ag pb zn deposit northeast australia a succession of foliations defined by different sillimanite bearing structural fabrics suggests that the macroscopic isoclinal synform that dominates the geometry of the cannington ag pb zn deposit northwest queensland australia formed during d2 the five foliations in this succession s1 to s5 are defined by aligned sillimanite with habits ranging from individual crystals in s1 through s4 to clusters of fibrolite in s5 in both the matrix and as inclusion trails within garnet and gahnite zn rich spinel porphyroblasts s1 s3 and s5 formed as sub horizontal foliations whereas s1a s2 and s4 formed sub vertically foliation intersection inflexion axes fias within garnet and gahnite porphyroblasts preserve a succession of trends that shifts from w e to n s this succession indicates that this region experienced n s followed by w e bulk crustal shortening n s shortening occurred during d1and d1a and w e shortening occurred from d2 to d5 prismatic and rhombic sillimanite produced during d1 d4 accompanied prograde metamorphism to ca 634 62 c and 4 8 1 3 kbar the coexistence of fibrous prismatic and rhombic sillimanite resulted from post peak metamorphic reactivation of the early foliations during d5 the synformal d2 fold was intensified during d4 by w e bulk shortening local partial melting occurred after d1 in the appropriate bulk rock compositions based on calculation of p t pseudosections in the chemical systems kfmash kfmashto nckfmash and mnnckfmash zn mineralization related to gahnite growth occurred during d3 through d4 and was redistributed by partial melting into structural and rheological sites during d4 and d5shearing

a late devensian ice free area and possible interglacial site on the isle of lewis scotland at the time of the last glacial maximum the last scottish ice sheet has been considered by some1 2 to have extended to the continental shelf edge fig 1a whilst others3 4 have suggested that there were ice free areas in northern scotland no radiocarbon dated strati graphical evidence has been published to support either interpretation we present here data from the isle of lewis establishing that the shelly deposits from the north of that island are of late devensian age but which also show that a late devensian ice margin lay across northern lewis leaving part of the island ice free a peat possibly of interglacial status has been found in the ice free area the last scottish ice sheet therefore did not pass beyond the outer hebrides and may not even have reached the north of the island chain this evidence is also of interest to the debate on the relative expansions of the northern and southern margins of the laurentide and scandinavian ice sheets at the last glacial maximum5 6 for it suggests a restricted glacial expansion of the northern margin of the last british ice sheet at the time of its greatest southerly extent

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

porphyroblast rotation eppur si muove in a number of recent papers the theory has been postulated that porphyroblasts as a rule do not rotate with respect to geographical coordinates and can be used to determine the original orientation of older foliations complex inclusion patterns in spiral garnets have even been used to advocate a new model of orogenesis involving several alternating phases of horizontal shortening and extension critical assessment of the assumptions and data used to support the theory of irrotational porphyroblasts reveals numerous flaws millipede structures used as proof for flow partitioning can also form by other flow geometries evidence quoted to support irrotational behaviour of porphyroblasts is unsound porphyrobl asts do occur in sets with a preferred orientation of the internal foliation trace but these cannot be shown to represent original orientations microstructures which resemble truncation planes in spiral garnets are used as evidence that these structures developed by several phases of deformation and as proof for periodic extension and horizontal shortening in orogenesis they can however also be explained by intermittent growth of a rotating porphyroblast during a single phase of deformation finally porphyroblast sets in which orientation is a function of aspect ratio indicate that porphyroblast rotation with respect to kinematic axes does occur in at least some situations

constraints of deep crustal structures on large deposits in the cloncurry district australia evidence from spatial analysis abstract deep structures are commonly recognized as critical factors for controlling the formation of large hydrothermal deposits it is of great importance for the metallogenic studies to quantitatively describe the spatial associations of deep structures with mineral deposits in the cloncurry district of the mt isa province australia many large deposits have been discovered and district scale deep structures have also been recognized from the magnetic gravity seismic and magnetotelluric data in this paper we delineate the 3d configuration of the deep structures by 3d geometric modeling and gaussian curvature analysis and quantify spatial associations of the deep structures with the large deposits by the weights of evidence method the results demonstrate that the configuration of deep structures has a positive spatial constraint on the distribution of deposits many deposits are located close to the high curvature portion of the deep structures according to this rule there are some potential target areas where curvature of the deep structural surfaces is high but no deposits have been discovered such results can be used to identify targets with potential for finding undiscovered deposits

a progressive ductile shear model for the proterozoic aggeneys terrane namaqua mobile belt south africa abstract recent structural and stratigraphic study results indicate that the namaqua orogenesis ca 1 2 ga involved relative movement of lozenge shaped suspect terranes detailed study of one of the terranes the aggeneys terrane provided important information concerning the deformation process the principal process was differential shear which produced complex structures such as interference folds and thrust faults all the observed deformational structures can be explained by a single long lived compressional event

deformational behaviour of migmatites and problems of structural analysis in migmatite terrains an understanding of the response of migmatites to deformation is crucial to an interpretation of their structures and in anatectic and intrusive migmatite terrains due consideration must be given to the modification of deformation processes imposed by melts in partially molten systems containing more than 30 melt the classical theories of fold formation are inapplicable the folds produced are of the viscous fold type their geometry is unpredictable and may mimic structures due to refolding this is particularly true at very high degrees of melting where flow of melt carrying rafts of solids begins failure to distinguish viscous folds from the products of refolding will lead to errors in interpreting the structural and metamorphic history of an area and to consequent misinterpretation of the true structural relations between geometrically complex high grade and more regularly deformed low grade areas

late weichselian environmental history in southeastern sweden during the deglaciation of the scandinavian ice sheet abstract late weichselian litho bio and chronostratigraphy 14 c and varves in southeastern sweden provide a detailed picture of the deglaciation pattern and dynamics shore displacement late glacial sedimentation and history of the landscape vegetation and climate two plausible glacial models were tested against lithologic chronologic and climatic data permafrost at and outside the ice margin and topographic conditions beneath the ice apparently caused inward spread of frozen glacier bed conditions this led to a buildup of a large zone of debris rich basal ice a climatic amelioration about 12 700 yr b p changed the temperature profile in the ice sheet deposition of basal melt out till began at the previously frozen glacier bed and a rapid recession of the clean ice set in thin exposed debris rich basal ice which was separated from the active ice margin about 150 yr later in this zone of stagnant ice there followed a 200 300 yr period marked by subglacial and supraglacial melt out and resedimentation forming a large hummocky transverse moraine the mild climate favored rapid plant immigration and a park tundra was established the gradual closing of the landscape was interrupted by a 100 to 150 yr period of tundra vegetation and a cool dry climate with local vegetational differences caused by differences in soil moisture about 12 000 yr b p a second climatic amelioration set in and during the next 1000 yr a birch and pine woodland gradually developed soils stabilized and empetrum heaths became abundant as the climate gradually deteriorated at the end of this period by 11 000 yr b p the area had become a tundra again with scattered birch stands dominated by herbs such as artemisia chenopodiaceae grasses and sedges some 500 yr later a birch pine woodland again succeeded and within about 500 yr the vegetation changed to a rather closed woodland as the climate ameliorated further however the time lag between climatic and vegetation change was considerable

migmatite structures in the central gneiss complex boca de quadra alaska migmatite structures in the coast plutonic metamorphic complex are well exposed in the inlet of boca de quadra southeast alaska two types of anatectic migmatites are present patch migmatites formed by in situ melting and subsequent crystallization of melt diktyonitic migmatites comprise a discontinuous veined network of leucocratic material in which leucosomes enclose boudins of host rock the margins of these boudins show the development of both melanosomes and shear band fabrics strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 20 27 this volume decrease is attributed to melt extraction into the adjacent fracture filling leucosomes thus diktyonitic migmatites formed by shear induced segregation of partial melt whereas in patch migmatites the lack of shear stresses inhibited melt segregation the variable structural style of anatectic migmatites in boca de quadra is not related to host rock composition but may be due to differences in the amount of differential stress during migmatization these in turn may be controlled by host rock strength and or diachroneity of migmatization and deformation determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels