use of environmental magnetic measurements to validate the vertical extent of ice masses at the last glacial maximum analysis of soil samples from above and below trimlines representing the upper limit of glacial erosion at the last glacial maximum demonstrates that soils with prolonged weathering histories above such trimlines yield significantly different mineral magnetic signatures from soils below trimlines the nature of the contrast is conditioned by lithology basalt soils above the trimline yield significantly higher values of concentration dependent magnetic parameters arm irm3t soft irm and hard irm than those below the trimline due probably to transformation of non magnetic iron bearing minerals into magnetic forms conversely for sandstone soils most magnetic parameters yield significantly lower values for above trimline samples probably reflecting loss of ferrimagnetic minerals by dissolution and oxidation to aniferrimagnetic forms these significant contrasts represent a new approach to validating high level weathering limits as periglacial trimlines cut at the last glacial maximum copyright 2002 john wiley sons ltd

relict non glacial surfaces in formerly glaciated landscapes abstract relict non glacial surfaces occur within many formerly glaciated landscapes and contain important information on past surface processes and long term landscape evolution relict non glacial surfaces are distinguishable from glacial surfaces by large scale morphologies including rounded summits fluvial valleys and cryoplanation terraces and pediments and the presence of tors blockfields and or saprolites preservation during glaciation occurs either through coverage by non erosive cold based ice or as nunataks although surface morphologies and denudation rates indicate a continuous non glacial surface history since preglacial times relict non glacial surfaces are dynamic features that have evolved during the quaternary depending on spatial variables such as lithology slope regolith depth and the abundance of fine matrix and water some surfaces are denuding very slowly while others display more rapid denudation high spatial variability in denudation rates results in changing surface morphologies over time denudation rates also display high temporal variability with much surface evolution having perhaps occurred soon after the initial onset of glaciation or during paraglacial phases while some parts of non glacial landscapes are currently active others may be largely inactive relicts of past higher energy regimes although non glacial surfaces are dynamic much remains to be determined regarding surface denudation rates and the magnitude of morphological changes over time

c1c8 hydrocarbons in sediments from guaymas basin gulf of california comparison to peru margin japan trench and california borderlands surface seafloor sediments hydrothermal vent samples and deep sea drilling project sediments hole 481a from the guaymas basin were examined for c1c8 hydrocarbons the proportions of various classes of compounds were examined and compared to those from other geographic areas peru upwelling region and japan trench to gain insight into the relative importance of thermal generation migration and biodegradation concentrations of c2c7 hydrocarbons were about 10 10 000 times higher in geothermally warm estimated to have been exposed to maximum temperatures in the range of 30 150 c guaymas basin sediments in comparison to the low concentrations 0 1 10 ppb per compound typical of geothermally cold maximum thermal exposure less than 20 c seafloor and dsdp diatomaceous sediments however one sediment sample from dsdp site 477 estimated to have been exposed to temperatures of 300 c or higher in the past showed only a limited hydrocarbon composition consisting of c1c3 alkanes and aromatic hydrocarbons only alkene alkane ratios of 0 1 or greater were typical of both geothermally cold sediments and also of very hydrocarbon richalvin samples recovered from the seafloor because little or no alkene was generally detected in buried sediments exposed to geothermal temperatures greater than 30 c it is suggested that the alkenes are produced by biogenic processes normal alkenes predominated over cyclic and branched structures in geothermally cooler 20 c sediments with the proportion of cyclic and branched compounds increasing in hotter sediments concentrations ofgem dimethyl and aromatic compounds generally remained approximately constant or increased slightly with temperature in comparison with geothermally cold shallow sediments similarities in compositions of branched and cyclic compounds were observed in some pairs of bitumen rich guaymas seafloor samples recovered from different areas suggesting common mechanisms of light hydrocarbon generation and or migration localized increases in ratios of specific cycloalkane ratios were observed adjacent to sill intrusions

exposure dating and validation of periglacial weathering limits northwest scotland periglacial weathering limits on two mountains in northwest scotland separate zones of contrasting exposure history exposure dating of bedrock below the weathering limits gives ages consistent with late devensian deglaciation but six out of seven samples from above the weathering limits give minimum exposure ages older than late devensian ice expansion these results suggest that mountain summits stood as nunataks above the last ice sheet surface and rule out formation of weathering limits by periglacial rock breakdown since deglaciation trimming of frost debris during an ice sheet readvance or enhanced weathering prior to climatic warming during ice sheet downwastage the dating results do not preclude the possibility that weathering limits mark a former englacial boundary between passive cold based ice on mountain summits and erosive warm based ice at lower elevations although 26 al 10 be ratios for high level bedrock surfaces provide no evidence of prolonged static ice cover

particle size related mineral magnetic source sediment linkages in the rhode river catchment maryland usa characterization of both the source materials and the bottom sediments of an estuary by magnetic characters on a particle size basis allows the source of the bottom sediments to be determined and indicates a shift in sediment sources corresponding to changing land use patterns the major source of the sediments in the lower part of cores from the middle of the estuary is eroding shorelines soil derived particulates from the uplands dominate the upper part of the cores this change in source occurred in the early part of the 19th century the magnetic character of the most recent sediments suggests a progressive depletion through time of the upland soils in the finest fractions

magnetic geochemical and pedological characterisation of soil profiles from different environments and geological backgrounds near coimbra portugal abstract this study presents an application of environmental magnetism techniques for the characterisation of the soils near coimbra central portugal magnetic measurements scanning electron microscopy and geochemical studies were carried out on samples collected in 6 soil profiles in order to find possible relationships and to interpret environmental implications magnetic susceptibility saturation isothermal remanent magnetisation and isothermal remanent magnetisation at the backfield of 100 mt and 300 mt were measured hardirm sirm and s ratios were also calculated polluted soils showed higher values of magnetic parameters in the superficial soil horizons closer to the roads plants and urban areas the lowest values were observed in the deeper horizons of the soil and in the areas least disturbed by human activity the magnetic results also suggested that the magnetic signal of these soils is mainly influenced by ferrimagnetic magnetite like minerals and with only a minor contribution from antiferromagnetic carriers such as hematite minerals in unpolluted soils lithogenic contribution is reflected by the enhancement of magnetic susceptibility near parental rock material scanning electron microscope images of the topsoil samples revealed the presence of magnetic spherules typical of vehicular exhaust and combustion processes this evidence suggests that the atmospheric deposition of fly ash is the main reason for the enhancement of the magnetic signal in the topsoil chemical analyses showed that the concentration of various heavy metals was higher than the mean background values for portuguese soils and higher in superficial soils heavy metals showed significant positive correlation with magnetic properties the conclusions highlight the importance of using environmental magnetism methods and techniques in the evaluation process of soil evolution and pollution history throughout time

combined rock magnetic and geochemical characterization of angangueo mining district central mexico results of a combined rock magnetic and geochemical investigation carried out at angangueo mining district are presented the different thickness and color of layers observed in field are also sketched from the magnetic susceptibility vertical ground profile accomplished additionally an area with enhanced magnetic susceptibility values is clearly outlined from a radial survey on the top of one of the biggest tailing the internal differentiation of the tailing was also supported by a full set of laboratory rock magnetic and physical chemical parameters geochemical results of matched samples reveal a complex relationship along the profile between some heavy metal concentrations i e cu and pb and magnetic susceptibility never reported in mining wastes nor in environmental studies contrary to environmental investigations of topsoils magnetic susceptibility enhancements zones in a tailing do not correspond necessarily to more heavy metal contaminated zones these outcomes evidence the intricate nature of mining wastes and the need for a better and intensive investigation of these barely studied objects

survey of hydrothermally generated petroleums from the guaymas basin spreading center abstract the guaymas basin spreading center and hydrothermal system are generating an assortment of petroleum like bitumens by pyrolysis of organic matter in the overlying uncosolidated sediments samples collected by d s v alvin from hydrothermal fields in the southern trough exhibit large variations in the quantities and character of the solvent soluble organic materials various pyrolytic regimes combined with fluctuating thermal gradients and migration velocities may impart a compositional fractionation possibly by differential gaseous solubilization and hydrodynamic alteration of the multi component fluids the data suggest that differential condensation solidification biodegradation and water washing cause selective removal of components at the seabed many hydrothermal oils are unlike normal reservoir petroleums because they contain significant concentrations of polar material due to their rapid genesis and transport and probable solubilization or advection of polar immature components the biomarker distributions confirm high temperature pyrolysis at depth with variable entrainment of less thermally mature bitumens during transport data for shallow core samples from the northern trough indicate that those locations experienced variable influx predominantly volatiles of a low temperature pyrolysate

periglacial trimlines former nunataks and the altitude of the last ice sheet in wester ross northwest scotland high level weathering limits separating ice scoured topography from frost weathered detritus were identified on 28 mountains in wester ross at altitudes of 700 960 m and a further 22 peaks support evidence of ice scouring to summit level weathering limits are defined most clearly on sandstone and gneiss which have resisted frost shattering during the late devensian lateglacial but can also be distinguished on schists and quartzite schmidt hammer measurements and analyses of clay mineral assemblages indicate significantly more advanced rock and soil weathering above the weathering limits the persistence of gibbsite above weathering limits indicates that they represent the upper limit of late devensian glacial erosion the regular decline of weathering limit altitudes along former flowlines eliminates the possibility that the weathering limits represent former thermal boundaries between protective cold based and erosive warm based ice the weathering limits are therefore interpreted as periglacial trimlines that define the maximum surface altitude of the last ice sheet calculated basal shear stresses of 50 95 kpa are consistent with this interpretation reconstruction of ice sheet configuration indicates that the former ice shed lay above 900 m along the present watershed and that the ice surface descended northwestwards with broad depressions along major troughs and localised domes around independent centres of ice dispersal extrapolation of the ice surface gradient and altitude suggests that the ice sheet did not overrun the outer hebrides but was confluent with the independent outer hebrides ice cap in the north minch basin erratics located up to 140 m above the reconstructed ice surface are inferred to have been emplaced by a pre late devensian ice sheet or ice sheets of unknown age 1997 john wiley sons ltd

snow facies over ice sheets derived from envisat active and passive observations this paper aims to separate different snow regions over the terrestrial ice sheets based on their measured microwave signatures it takes advantage of coregistered data from passive and active sensors on the environmental satellite envisat to directly derive a snow facies indicator in a point by point basis this paper represents the first attempt of this kind in exploiting nadir viewing and dual frequency data from both altimeter and radiometer sensors the approach is based on a clustering method such representation of the data by means of fewer clusters necessarily loses fine details but achieves simplification in geographical representation and eases the description of the condition of the ice sheets in 2004 our approach broadens the description of the snow pack by taking into account characteristics such as surface roughness grain size stratification and snowmelt effects whereas the latter has often solely been considered in most previous work such partition of the ice sheets might help to better understand relationships between microwave signatures and snow morphology it could also be useful for estimating elevation uncertainty in altimeter data which in turn is essential to correctly interpret the significance of the rates of elevation change in a changing climate and to convert elevation change to snow mass change

a comparison of different magnetic methods for determining the relative grain size of magnetite in natural materials some results from lake sediments abstract a new rapid method for identifying relative grain size variations in magnetic involves the parameter anhysteretic susceptibility arm i e specific arm obtained in a 1 oe steady field which is particularly sensitive to the single domain sd and small pseudo single domain psd grains of the finer magnetite fraction a second parameter low field susceptibility is relatively more sensitive to the coarser magnetite fraction larger psd and smaller multidomain md grains we can then obtain a measure of the ratio of coarse to fine grain magnetite for large numbers of samples by plotting arversus a simple idealized model based on sized magnetite samples is proposed to explain the use of the armversus plot for detecting relative grain size changes in the magnetic content of natural materials the sediments of three lakes that contain magnetite or a similar magnetic carrier and have a wide range of values of arm and are used to test the model the model is used to interpret the magnetic variations observed and the interpretations are supported by high field hysteresis measurements of the same sediments the combination of the high field hysteresis method of day et al 1 and the arm vs method is a powerful technique allowing the rapid identification of both the relative grain size and domain state for large numbers of samples containing magnetite the armvs method should be used as an intial means of identifying distinct groups of samples the high field hysteresis method should then be applied to a few representative samples from each group to confirm the initial interpretation

characterisation of soils by mineral magnetic measurements processes of iron mineral authigenesis diagenesis and dissolution in interaction with primary inputs of iron minerals act to produce vertical differentiation of soil magnetic properties thus magnetic iron oxides in common with other iron forms may both respond to and reflect soil forming processes investigation of the degree of detectable and persistent magnetic differentiation within different soil materials can provide insights into the nature and direction of distinct sets of soil processes evidence of clear association between magnetic variation and discrete types of soil environment also has applied significance in several areas of environmental study for example the observed magnetic variation can be used to discriminate between individual soils and soil horizons for the purposes of soil surveying sediment tagging and tracing and empirical modelling of source sediment linkages this paper reports the use of mineral magnetic techniques to characterise the iron oxide assemblages within soils of varying type and provenance the effect of different pedogenic regimes have been investigated through measurement of a range of magnetic parameters including magnetic susceptibility frequency dependent susceptibility and anhysteretic and saturation remanences contrary to current pedological thought but in accord with other magnetically based studies e g mullins the presence of magnetite maghemite typically of superparamagnetic single domain grain size within soils has been found to be an extremely widespread phenomenon its contemporary neoformation within the soil environment is inferred however the input of artificially generated ferrimagnetic material is indicated for one of the magnetically enhanced soils examined here and the possibility of extraneous sources of magnetite in topsoils should be considered before pedogenic processes of magnetic enhancement are inferred from the data presented discrimination of industrially derived magnetic particles appears possible on the basis of their very low levels of frequency dependent susceptibility fd low anhysteretic remanence arm and dissociation from the finer clay sized not the formation but the active dissolution of ferrimagnetic minerals is indicated for soils affected by the processes of gleying and podsolisation eluvial horizons of podsolised profiles demonstrate almost total loss of detectable magnetic content variations in the form of the iron reprecipitated in the underlying illuvial layers may reflect differences in the pedological characteristics of these horizons within gleyed waterlogged soils processes of magnetite dissolution appear to be grain size specific preferential reduction of those grains of ultrafine superparamagnetic and fine single domain magnetic grain size is indicated where soil forms a major contributor to catchment sediment loads this has significance in the area of source sediment modelling soil derived from permanently wet or highly leached catchment areas is unlikely to contribute to peaks in the magnetic content of deposited sediments further only those erosional processes that operate at a faster rate than those of magnetic depletion will have the capacity to produce peaks in sediment ferrimagnetic concentrations such as have been observed within the historical magnetic record

modelling of icecap glaciation of the northern rocky mountains of montana abstract the extent of the lastglacial icecap over the northern rocky mountains of montana has been inferred only from cursory correlation of its marginal deposits which leaves several significant unresolved controversies those controversies all involve the maximum altitude and shape of that interconnected ice mass and include 1 the source of the two medicine piedmont lobe local or cordilleran ice 2 correlation of terminal deposits of the flathead lobe late lastglacial early lastglacial or prelastglacial and 3 regional paleoclimate at last glacial maximum dominant westerlies or local easterlies theoretical reconstructions of the glacial surface along major flowlines constrained by ice marginal features nunataks and breached divides throughout the region tentatively resolve those issues the two medicine lobe was dominantly composed of northeast flowing local ice not ice of northwestern canadian cordillera origin flathead lobe deposits include lastglacial deposits both supported by and without a component from the swan valley there is evidence of only a regional westerly flow of moisture across the region in addition a proglacial lake 60 km long occupied the swan valley during the early stages of deglaciation although subject to revision from fieldwork glacial process modelling remains one of the few geological arenas in which rigorous process modelling can be used to predict the evolution of form

cosmogenic nuclide exposure ages along a vertical transect in western norway implications for the height of the fennoscandian ice sheet 10 be and 26 al exposure ages for bedrock samples from a vertical transect at skala in western norway provide new constraints on the history of the fennoscandian ice sheet the weathered bedrock surface autochthonous block field mantling the summit of skala has an exposure age of 55 ka suggesting that this surface formed before the last glacial maximum 18 14 c ka or 21 calendar ka the block field is truncated by a glacial trimline at 1660 m above sea level glaciated bedrock below the trimline has an exposure age of 26 21 ka the range depends on assumptions about erosion rate ice therefore receded from this altitude at about the time of the last glacial maximum the 10 be age for bedrock immediately below a second lower trimline at skala suggests a glacial advance or stillstand at 18 13 ka consistent with previously documented readvances or stillstands at the western and southern margins of the ice sheet

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

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

hydrothermal petroleum in mineralized mounds at the seabed of guaymas basin petroleum has been dredged from an active hydrothermal mound area in the southern rift of guaymas basin gulf of california this organic matter is composed of gasoline range aliphatic and aromatic hydrocarbons and predominantly residual polar asphaltic material the aliphatic hydrocarbons of two bitumen samples have very different boiling range and composition both samples contain polynuclear aromatic hydrocarbons and olefins which indicate formation at pyrolytic temperatures the overall compositional data indicate an origin from biological detritus by thermal alteration and rapid quenching by hydrothermal removal followed by condensation at the seabed

the rate of iron oxide enrichment in arid zone alluvial fan soils tunisian southern atlas measured by mineral magnetic techniques abstract rates of iron oxide enrichment of soils on a segmented alluvial fan in southern tunisia are examined mineral magnetic and chemical characteristics of soils developed on two dated relict segments and on contemporary alluvium suggest that the rate of fe oxide enrichment was more rapid in the holocene 2 6 10 8 g g 1 yr 1 over the last 5000 years than in the pleistocene 1 91 10 9 g g 1 yr 1 over the previous 45 000 years thus fe oxide concentration may be used to determine an ordinal chronology of some geomorphological surfaces in drylands but rates of enrichment cannot be assumed to be uniform over time

secondary ferrimagnetic minerals in welsh soils a comparison of mineral magnetic detection methods and implications for mineral formation summary a range of low temperature and isothermal magnetic measurements are used to identify the secondary ferrimagnetic mineral sfm grain sizes in 10 representative soil samples from wales a comparison of percentage frequency dependent susceptibility fd percentage and low temperature remanence measurements shows that they are sensitive to different ranges of superparamagnetic sp grains the relative distributions of sp grains and stable single domain ssd grains are similar in nine of the samples typical distributions for soils dominated by sfms are 20 30 per cent ssd and 70 80 per cent sp multidomain md grains were not detected in the samples studied there is evidence that some soils contain significant numbers of ultrafine sp grains 0 010 m that are not detected by low temperature remanence measurements at 20 k and which will have the effect of depressing values of low field susceptibility lf and fd percentage a mixing model suggests that fd percentage may be used semi quantitatively to estimate the proportion of sp grains in a sample the positively skewed grain size distributions strongly suggest a mechanism of sfm formation that is driven by processes at the 10 8 m scale thus supporting weathering and fermentation as controlling processes rather than the degradation of ssd bacterial magnetosomes and primary minerals

magnetic susceptibility mapping of the sudbury area ontario canada evaluating pollution distributions decades later this study evaluates the use of magnetic susceptibility and magnetic parameter measurements in assessing spatial and temporal variations of pollutants that emanated from mining industries in and around sudbury ontario canada for this purpose in situ magnetic susceptibility in situ was measured at 106 sites on a grid of 10 km 10 km and 5 km 5 km the in situ values ranged from 2 10 5 to 149 10 5 si and the highest in situ values were observed near the active copper cliff and inactive coniston mining sites the lowest in situ values were measured at increased distances from possible pollution sources therefore mapping of in situ magnetic susceptibility values is a proxy to polluted areas in and around sudbury to evaluate potential anthropogenic and or lithogenic input to in situ low frequency mass specific magnetic susceptibility lf variations with depth were classified into four different types of profiles for further investigation of magnetic minerals in the samples labo

mapping soil magnetic properties in bosnia and herzegovina for landmine clearance operations electromagnetic properties of soils have negative impacts on metal detector performance during landmine clearance operations in particular topsoils with high concentrations of pedogenic viscous superparamagnetic minerals magnetite maghemite as shown by high values of magnetic susceptibility and frequency dependent susceptibility limit the detector capability of identifying buried landmines thus a priori knowledge of the spatial extent of soils that may be problematic for landmine detection would aid strategic planning of clearance operations and ensure appropriate equipment is deployed here we compare two approaches for estimating the broad magnetic properties of soils in bosnia and herzegovina 1 an analogue approach using data for magnetic susceptibility and frequency dependent susceptibility available for soil types from other temperate and mediterranean regions 2 magnetic measurements of a stratified sample of soil samples taken from the bosnian national soil archive the national soil magnetic maps produced estimate that the area of land inferred as problematic for metal detectors is 4 and 30 according to the analogue and measurement methods respectively combining soil type with soil parent material and climate explains the spatial variability of soil magnetic properties in terms of mechanisms of secondary ferrimagnetic mineral production and accumulation the resulting maps indicate that the magnetic properties of dominant soils in northern bosnia tend to be unproblematic for detectors while in central bosnia there is likely to be moderate detector interference however there is a high likelihood of dominant soils affecting detectors in southern and western bosnia and herzegovina equivalent to 30 of the total land area the mapped outputs of susceptibility and frequency dependent susceptibility provide demining end users with an indication of the likelihood of encountering problem soils in areas selected for clearance operations

periglacial trimlines in the scottish highlands abstract two periglacial weathering limits have been identified on mountains in the highlands of scotland the lower has been interpreted as a periglacial trimline marking the upper limits of loch lomond younger dryas stade glaciers and has been employed to reconstruct the dimensions of parts of the main west highland icefield and certain smaller glaciers and icefields interpretation of the upper weathering limit has been more contentious but recent research has demonstrated 1 significant contrasts in the degree of bedrock weathering above and below this limit 2 that gibbsite a pre devensian weathering product is abundant above the limit but rare in soils farther downslope 3 that the isotopic 26al age of bedrock exposures above the limit greatly exceeds that at lower altitudes and 4 that the altitude of the weathering limit descends regularly along former ice sheet flowlines collectively these attributes suggest that the upper weathering limit is a periglacial trimline defining the maximum altitude of the last ice sheet calculated basal shear stress values are consistent with this interpretation which implies that the mainland ice shed lay at ca 900 m in wester ross and descended gently northwards whilst harris and lewis in the outer hebrides supported an independent ice cap that achieved a maximum altitude of ca 700 m wider implications of this interpretation and the future potential for ice sheet reconstruction are explored

thermal alteration of cretaceous black shale by diabase intrusions in the eastern atlantic ii effects on bitumen and kerogen abstract the thermal effects of three one major and two minor miocene diabase intrusions on cretaceous black shales from dsdp site 41 368 have been analyzed a concentration gradient was observed especially for the hydrocarbons decreasing towards the major intrusion and between the three sills the thermally altered samples in the proximity of and between the sills contained elemental sulfur and an excess of thermally derived pristane over phytane whereas the unaltered sediments contained no elemental sulfur and more phytane than pristane a maximum yield of the extractable hydrocarbons was observed at a depth of 7 m below the major sill two classes of molecular markers were present in this bitumen suite the first was sesqui di and triterpenoids and steranes which could be correlated with both terrigenous and autochthonous sources they were geologically mature and showed no significant changes due to the thermal stress the second class was found in the altered samples which contained only polynuclear aromatic hydrocarbons with low alkyl substitution and sulfur and oxygen heterocyclic aromatic compounds these compounds were derived from pyrolytic reactions during the thermal event kerogen was isolated from all of these samples but only traces of humic substances were present the h c n c 13 c 34 s and d all exhibit the expected effects of thermal stress the kerogen becomes more aromatized and richer in 13c 34s and d in the proximity of and between the sills maturation trends were also measured by the vitrinite reflectance and electron spin resonance where the thermal stress could be correlated with an elevated country rock temperature and an increased degree of aromaticity the effects of in situ thermal stress on the organic rich shales resulted in the generation and expulsion of petroliferous material from the vicinity of the sills

characterization of diamictons on the basis of their mineral magnetic properties in murchisonfjorden nordaustlandet svalbard abstract different grain size fractions of 12 lithologically defined and 2 non defined weichselian glacial stage diamicton units from nordaustlandet svalbard were studied for their mineral magnetic properties the applied measurements included magnetic susceptibility anhysteretic remanent magnetization arm saturation isothermal remanent magnetization sirm backfield isothermal remanent magnetization irm and several of their parametric ratios the results indicated a poor correlation between the magnetic fingerprint of dry sieved and wet sieved diamicton samples the dry sieved samples had higher arm and sirm values suggesting a higher concentration of ferrimagnetic grains this was probably because washing of the samples resulted in the loss of the most fine grained ferrimagnetic material both sieving methods seem to be capable of discriminating different diamictons but they cannot be used contemporaneously the results only partially support previous findings of the chronostratigraphic correlation of diamictons they indicate that in suitable conditions and within a limited area it is possible to discriminate and group glacigenic sequences based on the magnetic signature of their fine grained fractions in the sample for example and based on the mineral magnetic fingerprint a diamicton unit that was described from the marine core mur 09 sor1 125 150 obtained from isvika region most probably represents diamicton material that were derived from provenance areas related to the middle weichselian glacial stage it was also noted that certain mineral magnetic parameters such as sirm and sirm arm ratio had greater potential in discriminating diamicton units than others

gibbsitic soils on former nunataks implications for ice sheet reconstruction x ray diffraction analyses of soils above and below a periglacial trimline developed across the basalts of the trotternish escarpment isle of skye scotland demonstrate that gibbsite is restricted to soils above the trimline this suggests that the gibbsite is a relict of pre late devensian weathering and that the trimline did not develop after the last ice sheet achieved its maximum thickness the sharpness of the boundary between frost weathered regolith and gibbsitic soils upslope and ice scoured bedrock associated with gibbsite free soils downslope suggests that the trimline represents the altitude of the last ice sheet at its maximum thickness rather than a former boundary between passive cold based ice and erosive warm based ice these findings illustrate how identification of high level periglacial trimlines and associated contrasts in clay mineralogy provide a means for constraining reconstructions of the form of the last ice sheets

glacial trimlines to identify former ice margins and subglacial thermal boundaries a review and classification scheme for trimline expression abstract reconstructions of former ice sheets and glaciers provide important palaeoglaciological information about their behaviour in response to climate changes glacial trimlines record both the margin positions and palaeo ice thickness enabling the production of empirically constrained 3 dimensional reconstructions however the literature review into the characteristics interpretation and use of glacial trimlines here presented shows that these features have been under utilised and are poorly described in the existing literature with a confusing terminology currently in use a new classification scheme and terminology for trimline identification and interpretation is developed to better facilitate further research into these common features of glacierised and formerly glaciated landscapes