clast shape analysis and clast transport paths in glacial environments a critical review of methods and the role of lithology the reconstruction and tracing of transport paths in glaciated and other environments have a long tradition in the earth sciences we here present a dataset of clast shape samples from a worldwide selection of glaciated mountain environments in order to assess the reliability of this approach overall and the role of lithology on the performance of clast shape measurements in particular our findings demonstrate that the widely used ra c40 co variance approach is applicable to 63 of the 19 catchments investigated while the alternative rwr c40 approach is more widely applicable to 75 of these catchments a systematic assessment of mixing of lithologies at the catchment scale demonstrates that such mixing leads to pronounced overlaps between different control envelopes that had previously been separated thereby removing the discriminatory power of the method mixing of similar lithologies between different catchments shows an even more extreme loss of discriminatory power which strongly suggests that lithology plays a primary role in determining clast shape and that catchment specific processes are superimposed systematic analysis of the dataset also shows that nearly all catchments apart from two can be grouped into two types type i relates to sites in lesser mountain ranges and is characterised by dominantly blocky forms in the subglacial realm highlighting significant reworking processes type ii sites are dominantly in high mountain environments and characterised by a high similarity between subglacial and fluvial control envelopes this indicates that although reworking may be pronounced it is not necessarily effective enough to remove the platy shape that most likely results from extraglacial and supraglacial inputs our study highlights the potential of clast shape analysis as a tool that allows generic processes to be identified between catchments thereby enabling an understanding of debris cascades in glaciated mountain environments we finish with recommendations for ensuring that future clast shape studies are robust reproducible and comparable between different sites

the interrelation of glaciotectonic and glaciodepositional processes within the glacial environment abstract in recent years it has been recognised that ice sediment coupling occurred beneath the quaternary ice sheets that advanced over the soft sediments of lowland areas this paper looks in detail at the effects of this coupling on the sediments which results in glaciotectonic deformation and also discusses the interaction of deformation and deposition within the subglacial environment two types of glaciotectonic deformation are discussed that are produced by the active movement of ice 1 proglacial tectonics at the margin which include compressive fold styles such as listric thrusts and faults and open folding 2 subglacial tectonics formed beneath the glacier which include fold styles resulting from simple shear and represent a soft rock purely dynamic shear zone styles of deformation associated with stagnant ice are also investigated we argue that glaciotectonic deformation is a common phenomenon and an integral part of geological record from continental ice sheets it is suggested that zones of deformation within the sediment are related to similar zones of strain in the ice sheet and complex deformation sequences are produced by the superimposition of these differing styles upon one another as the ice sheet advances and retreats it is also argued that subglacial deposition and deformation are related and that on soft beds underformed till is rare whilst deformed till is very common

quaternary stratigraphy of the buried valleys of the lower red deer river alberta canada the quaternary fills of the buried valleys of southern alberta and saskatchewan have provided a wealth of information for the reconstruction of the glacial interglacial record of the western plains of canada and this paper reports on the previously unstudied stratigraphy of the buried calgary valley and its former tributaries in the lower red deer river area we attempt to differentiate empress group sediments which potentially relate to pre glacial interglacial interstadial and post glacial lake and river deposition using sedimentology stratigraphy and palaeoecology twenty nine stratigraphical logs indicate that empress group sediments have infilled a considerably large area of badlands and tributary coulees that once drained into the calgary valley located 15 km to the north of dinosaur provincial park radiocarbon dates of 52 4 ka 27 4 ka and 42 4 ka and glacially modified quartz grains suggest that at least some of the valley fills date to interglacial or interstadial periods and may be mid wisconsinan in age however outcrops of an older till overlying other valley fills suggest that the buried valleys were only partially excavated during interglacials interstadials and that older even pre glacial sediments could have survived subglacial channels recognisable on air photographs largely coincide with buried valley positions due to the preferential excavation of the quaternary sediment by meltwater and are filled with post glacial lake sediment from which a radiocarbon date of 16 ka bp was obtained pre glacial and glacial post glacial empress group sediments are lithologically indistinct but cover a large time span in southern alberta

late precambrian glacially related grooved and striated surfaces in the tillite group of central east greenland abstract the tillite group of central east greenland comprises five formations of which two are dominantly glacigenic the ulveso formation formerly lower tillite and the storeelv formation formerly upper tillite both of which embrace a wide range of facies including glaciomarine nearshore and terrestrial glacial sediments evidence of periodic terrestrial conditions is indicated especially by a variety of grooved and striated surfaces on the island ella o in the ulveso formation grooves of complex geometry 0 4 m wide and 0 3 m deep were cut into a cemented conglomerate horizon they are interpreted as having formed as a result of subglacial meltwater cavitation at the base of the storeelv formation boulders thought to have been dropped into partially cemented sandstone by floating glacier ice were largely planed off by a subsequent advance of grounded ice in the middle of the storeelv formation a striated boulder pavement occurs within diamictite on the basis of stone fabric striation orientation and cross bedding data this pavement is inferred to have formed by the packing of stones along a shear surface within an accumulating lodgement till such features have rarely been observed in pre pleistocene glacigenic sequences they imply that each glacigenic formation accumulated during a complex series of advances and retreats rather than just one

striated clast pavements products of deforming subglacial sediment studies of modern glaciers have recently drawn attention to the importance of subglacial sediment deformation to glacier dynamics and processes inferences regarding the probable shear strength of this sediment imply that large clasts may in some cases sink to underlying rigid sediment where abrasion by overlying deforming sediment could occur this scenario provides a formative mechanism for striated clast pavements commonly described from the base of fine grained massive diamictons associated with the late pleistocene laurentide ice sheet such a mechanism indicates that at the time of formation of clast pavements overlying diamictons associated with pavements had a low yield strength 0 5 kpa and were deforming mechanically like a debris flow clast pavements may therefore be an important criterion for recognition of sediments deposited by subglacial deformation transport

bolla bollana boulder beds a neoproterozoic trough mouth fan in south australia the bolla bollana formation is an exceptionally thick ca 1500 m rift related sedimentary succession cropping out in the northern flinders ranges south australia which was deposited during the sturtian mid cryogenian glaciation lithofacies analysis reveals three distinct facies associations which chart changing depositional styles on an ice sourced subaqueous fan system the diamictite facies association is dominant and comprises both massive and stratified varieties with a range of clast compositions and textures arranged into thick beds 1 to 20 m representing stacked ice proximal glaciogenic debris flow deposits a channel belt facies association most commonly consisting of normally graded conglomerates and sandstones displays scour and fill structure of ca 10 m width and 1 to 3 m depth these strata are interpreted as channelized turbidites rare mud filled channels in this facies association bear glacially striated lonestones finally a sheet heterolithics facies association contains a range of conglomerates through sandstones to silty shales arranged into clear normally graded cycles from the lamina to bed scale these record a variety of non channelized turbidites probably occupying distal and or inter channel locations on the subaqueous fan coarsening and thickening up cycles capped by dolomicrites or mudstones are indicative of lobe build out and abandonment potentially as a result of ice lobe advance and stagnation dropstones recognized by downwarped and punctured laminae beneath pebbles to boulders in shale or in delicate climbing ripple cross laminated siltstones are clearly indicative of ice rafting the co occurrence of ice rafted debris and striated lonestones strongly supports a glaciogenic sediment source for the diamictites comparison to pleistocene analogues enables an interpretation as a trough mouth fan most probably deposited leeward of a palaeo ice stream beyond emphasizing the highly dynamic nature of sturtian ice sheets these interpretations testify to the oldest trough mouth fan recorded to date

chemometric study of functional groups in different layers of trigonocarpus grandis ovules pennsylvanian seed fern canada abstract we examined four dispersed coalified ovules trigonocarpus grandis of medullosalean seed fern affinity from the late pennsylvanian age sydney coalfield canada which represent the larger type of the 7 8 cm trigonocarpalean form species at first glance it appears that the ovules are preserved like the usual carboniferous foliar compressions i e one coalified layer with one preserved anatomical tissue the cuticle however careful sample preparation uncovered at least three coalified layers and schulze s oxidative maceration process which dissolves the coalified material revealed several tissue layers altogether eight sample forms were defined i coalified layer ii cuticle a iii cupric vitrain iv vitrain v cupric vi cuticle b vii alkaline solution and viii added coal seam material the purpose of the study was twofold first to systematically analyze the forms by way of fourier transform infrared ftir spectrometry to fill a gap in chemical information that exits for coalified trigonocarpalean ovules of carboniferous seed ferns second to use principal component analysis to focus on groupings as a function of chemical structure functional groups and to assess the different fossil forms in terms of ftir chemical parameters based on a 8 49 data matrix results include distinction among the three coaly sample forms coalified layer i cupric vitrain iii and cupric v based mainly but not exclusively on differences in carbonyl content as well as length and branching of the polymethylenic chains important to note is the high aliphatic content of the cuticles as a signature of the biomacromolecules cutan cutin in particular new insights into the structure of the original ovule are presented and differences in chemistry are mainly a result of the complex structure of the precursor plant organ

a new ice thickness and bed data set for the greenland ice sheet 1 measurement data reduction and errors ice thickness data collected between 1993 and 1999 using a coherent ice penetrating radar system developed at the university of kansas have been combined with data collected by the technical university of denmark in the 1970s to produce a new ice thickness grid for greenland crossover analysis was used to assess the relative accuracy of the two data sets and they were weighted accordingly and interpolated onto a regular 5 km spacing grid using a kriging interpolation procedure a high resolution land ice mask was used to help constrain the interpolation of the ice thickness data near the ice sheet margins where in the past the relative errors have been largest the ice thickness grid was combined with a new digital elevation model of the ice sheet and surrounding rock outcrops to produce a new bed elevation data set for the whole of greenland the ice thickness grid was compared with the currently available data set differences in the center of the ice sheet where the ice is thickest were of the order of a few percent near the margins however large differences of as much as a factor of 10 were found the total volume of ice contained in the ice sheet was reestimated and found to have a value of 2 93 x 10 6 km 3 the ice thickness grid was used to calculate the spatial pattern of gravitational driving stress over the ice sheet anomalous patterns of stress were found in areas that appeared to be associated with areas of rapid flow

functional groups and elemental analyses of cuticular morphotypes of cordaites principalis germar geinitz carboniferous maritimes basin canada well preserved cuticles were isolated from cordaites principalis germar geinitz leaf compressions i e foliage from extinct gymnosperm trees coniferophyta order cordaitales the specimens were collected from the sydney stellarton and bay st george subbasins of the once extensive carboniferous maritimes basin of atlantic canada fourier transformation of infrared spectra ftir and elemental analyses indicate that the ca 300 306 million year old fossil cuticles share many of the functional groups observed in modern cuticles the similarities of the functional groups in each of the three cuticular morphotypes studied support the inclusion into a single cordaite leaf taxon i e c principalis germar confirming previous morphological investigations vitrinite reflectance measurements on coal seams in close proximity to the fossil bearing sediments reveal that the bay st george sample site has the lowest thermal maturity whereas the sites in sydney and stellarton are more mature ir absorption and elemental analyses of the cordaite compressions corroborate this trend which suggests that the coalified mesophyll in the leaves follows a maturation path similar to that of vitrinite comparison of functional groups of the cordaite cuticles with those from certain pteridosperms previously studied from the y1 sydney subbasin shows that in the cordaite cuticles highly conjugated c o 1632 cm bands dominate over carbonyl stretch that characterizes the pteridosperm cuticles the differences demonstrate the potential of chemotaxonomy as a valuable tool to assist distinguishing between carboniferous plant fossil groups published by elsevier science b v

errata neogene fjordal sedimentation on the western margin of the lambert graben east antarctica the lambert graben is occupied by the world s largest fjord system through which flows the lambert glacier the amery ice shelf and their tributaries along the western margin of the graben in the northern prince charles mountains remnants of uplifted miocene and pliocene strata of the glacigenic fjordal pagodroma group total more than 800 m in thickness these sediments provide evidence for a dynamic east antarctic ice sheet during the neogene period each of the four pagodroma group formations defined from this region rests unconformably on either proterozoic or permo triassic rocks the unconformity surfaces represent parts of the walls and floors of neogene fjords for these surfaces to have been eroded the ice must have been grounded out as far as the continental shelf in prydz bay the pagodroma group was deposited by wet based glaciers discharging into a fjordal setting and includes lithofacies that are quite different from those produced by modern antarctic ice masses the principal lithofacies are massive diamicts and soulder gravels deposited both close to a calving grounded glacier terminus and from icebergs the few stratified diamicts are the product of more distal iceberg sedimentation an ice transported gravel lithofacies includes rockfall debris derived from palaeofjord walls and mixed with subglacially derived diamicts some lithofacies contain evidence of subaquatic slumping and gravity flowage volumetrically minor lithofacies include laminites with some exposures exhibiting large ice rafted clasts the laminites represent less proximal mainly ice free fjordal sediments resulting either from tidal current sorting of suspended sediment originating from subaquatic glaciofluvial discharge or from turbidity currents derived from unstable subaquatically deposited glacigenic sediment the pagodroma group provides a record of multiple glaciation by dynamic sliding glaciers carrying large amounts of both basal and supraglacial debris the closest modern analogues in terms of the thermal and dynamic characteristics of the neogene lambert glacier appear to be the fast flowing tidewater glaciers of east greenland these glaciers originate from the interior ice sheet and discharge large volumes of icebergs the resulting lithofacies are predominantly diamicts

the deforming bed debris rich basal ice continuum and its implications for the formation of glacial landforms flutes and sediments melt out till abstract there are two potentially important shear zones at the base of the glacier the deforming layer and or the debris rich basal ice layer these two layers have a significant effect on glacier motion and glacial erosional depositional and sedimentary processes however it is shown that most of the processes operating within these two layers are very similar this includes compression at the ice margin longitudinal extension and simple shear upglacier similar styles of shear zone and associated fabric development and similar incorporation transport and depositional processes in the past many criterion have been developed to identify distinct deposition from the deforming layer and the debris rich basal ice layer however if the processes within these layers are similar then it makes the distinct identification of these two separate layers in the geological record very difficult however it is also shown that the main differences between the two layers include rates of sediment movement processes and preservation potential the later is very important as it appears that the two layers are interconnected and that material is melted out from the debris rich basal ice to form a significant component of the deforming layer in this way the final depositional imprint is from the deforming layer and there is little likelihood of the debris rich basal ice layer being preserved undeformed this is demonstrated from modern glacial environments pleistocene flute studies and studies of pleistocene melt out tills from the u k u s a and germany

sand intraclasts as evidence of subglacial deformation of middle pleistocene permafrost north norfolk uk sand intraclasts are common within the bacton green till member a glacitectonic mlange subjected to polyphase deformation during the middle pleistocene in north norfolk uk the intraclasts range from a few tens of centimetres to 10 m in length and have sharp contacts with the surrounding till sand within the intraclasts is unconsolidated and contains well preserved primary stratification the wrapping of glacitectonic foliation around the intraclasts and the development of folds relating to mechanical instabilities indicate that the intraclasts acted as competent masses within a more easily deformable fine grained till that accommodated the majority of the strain sharp contacts and distinctive heavymineral assemblages indicate little intermixing between the sand and till five hypotheses about the entrainment and evolution of the intraclasts are tested against sedimentological structural and mineralogical observations the most reasonable hypothesis attributes the intraclasts to glacitectonic deformation of warm permafrost initial ice advance caused large scale thrusting of proglacial permafrost that led to the stacking of pre glacial and ice marginal sediments that were subsequently deformed sub marginally to generate the intraclasts preservation of primary stratification within the intraclasts is attributed to deformation at temperatures slightly below the pressure melting point when pore ice cemented the intraclasts as rigid bodies at the same time deformation was concentrated into the surrounding finer grained till because of its significant liquid water content and ductile rheology it is concluded that the intraclasts provide a criterion to identify past glacierepermafrost interactions and a potential means of differentiating between subglacial deformation under unfrozen and partially frozen conditions

magnetic fabrics of the douglas till of the superior lobe exploring bed deformation kinematics abstract the superior lobe of the laurentide ice sheet during its last advance into northwestern wisconsin may have moved and transported sediment primarily through deep widespread shear of its bed to high strains 100 to study the kinematics of this deformation we measured the anisotropy of magnetic susceptibility of 3750 intact samples of its basal till the douglas member of the miller creek formation collected from eight profiles at 0 2 m depth increments a benchmark for interpretations was provided by results of ring shear experiments conducted on the douglas till which provided fabric characteristics for the case of horizontal simple shear orientations of maximum susceptibility k1 were controlled by preferred orientations of silt sized magnetite grains and were similar to sand grain orientations measured in thin sections strengths of fabrics formed by orientations of k1 indicate that most of the till sampled was deformed but to variable strains deformation averaged over the 20 km spanned by the study approximated horizontal simple shear however large differences in k1 fabric azimuths 45 over lateral distances of meters to tens of meters indicate highly heterogeneous bed deformation perhaps focused in anastomosing zones with associated divergent and convergent till shear this interpretation is supported by orientations of principal susceptibilities that imply in many cases either that shear planes were steeply dipping particularly transverse to the shearing direction or that there were major components of pure shear variations in k1 fabric azimuth with depth indicate that most of the till thickness did not shear simultaneously rather till accumulated at the bed as shear direction changed in response to temporally shifting zones of shallow deformation

characterization of the magnetic fabric of rocks abstract an inextensive system of magnetic susceptibility anisotropy factors is suggested which is sufficient in the majority of practical applications for characterizing the magnetic fabric of rocks the system involves three newly devised factors the corrected anisotropy degree the shape factor and the difference shape factor the first of these characterizes the quantity of anisotropy somewhat better than the commonly used anisotropy degree the shape factor characterizes the quality of anisotropy i e the shape of the susceptibility ellipsoid in a convenient way its definition is based on a certain analogy between the anisotropy ellipsoid and the strain ellipsoid the difference shape factor can replace the shape factor when only the differences between the principal susceptibilities are given while the mean susceptibility is unknown

subglacial drainage eskers and deforming beds beneath the laurentide and eurasian ice sheets glaciological theory predicts that the subglacial drainage network at the base of gently sloping ice sheets resting on deforming sediment should consist of many wide shallow probably braided canals distributed along the ice sediment interface rather than an arborescent network of relatively few large tunnels as would develop over a rigid substrate a corollary prediction examined here is that eskers which form in large subglacial tunnels should be rare where subglacial bed deformation occurred but they may be relatively common where the bed was rigid bed deformation would be most likely where subglacial till was relatively continuous fine grained and of low permeability that is in regions where till is derived primarily from underlying sedimentary bedrock but unlikely where discontinuous coarse grained high permeability till was derived from underlying crystalline bedrock the observed distribution of eskers in areas covered by the laurentide and eurasian british scandinavian and barents sea ice sheets during the last glaciation shows that most eskers occur over crystalline bedrock overlain by discontinuous high permeability till but are rare or absent over sedimentary bedrock overlain by fine grained low permeability till thus matching reasonably well our prediction glaciological theory and geologic evidence indicate that esker systems on a subcontinental scale are time transgressive sedimentological evidence for a canal drainage system appears to be present in fine grained tills where eskers are largely absent

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

till melange at amsdorf central germany sediment erosion transport and deposition in a complex soft bedded subglacial system abstract glacial melange in the open cast mine at amsdorf central germany consists of several square meters of large sorted sediment blocks embedded in till the blocks are composed of largely intact to slightly deformed glaciofluvial and glaciolacustrine sand silt and clay initially deposited in a proglacial lake 2 3 km up ice and subsequently overridden by a glacier the blocks typically have cuboid to subrounded outlines are randomly distributed in the till and the contacts with the surrounding till are distinctly sharp underneath the melange are varved clays which exhibit strong deformations occasionally intervening with entirely undisturbed areas it is suggested that the blocks were entrained into debris rich basal ice by bulk freeze on when the glacier sole was lowered onto the bottom of an overridden lake after entrainment the blocks were transported englacially and re deposited with far traveled till matrix as a melt out till from stagnant ice the glacier moved mainly by sliding enhanced by low permeability varved clays in the substratum the glacier is believed to have been of a polythermal type these results show that bulk freeze on can lead to entrainment of soft sediment blocks at least 20 m2 in size and that these blocks can be englacially transported with little or no deformation for several kilometers and more the occurrence of deformed and undeformed clays under the till melange indicates a possible mosaic of coupled and decoupled ice the latter caused by a thin transient subglacial water film separating the bed from the glacier

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

fabric signature of subglacial till deformation breidamerkurjokull iceland the foreland of breidamerkurjokull iceland is the only locality where tills known to have undergone subglacial deformation are exposed till on the foreland has a two tiered structure consisting of a dilatant upper horizon c 0 5 m thick and a compact lower till these horizons correspond to the ductile deforming a horizon and the brittle ductile b horizon observed below the glacier by g s boulton and co workers the relationship between known strain history and a variety of macrofabric elements is examined for these two genetic facies of deformation till the upper horizon exhibits variable a axis fabrics and abundant evidence for clast re alignment reflecting ductile flow and rapid clast response to transient strains in contrast the lower horizon has consistently well organized a axis fabrics with a narrow range of dip values recording clast rotation into parallel with strain axes during brittle or brittle ductile shear the data indicate that till strain history imparts identifiable macrofabric signatures providing important analogues to guide the interpretation of pleistocene tills

the vendian succession of northeastern spitsbergen petrogenesis of a dolomite tillite association abstract the sedimentary record of late precambrian time is magnificently displayed in the highland snowfields of northeastern spitsbergen svalbard vendian strata are represented essentially by the polarisbreen group which consists mostly of dolostone and includes two dolomitic glacial units the oldest sediments in the polarisbreen group compose the elbobreen formation c 400 m which is divided into four laterally persistent members the lower carbonate member e1 125 m contains a distinctive basal dark grey limestone with microspar filled synaeresis cracks suggested to be of lagoonal origin and associated with minor dolostone shale and chert higher parts of the member are dominantly dolostone partly stromatolitic with some shale and sandstone shallow subtidal to intertidal deposition is indicated by the dominance of intraclastic lithologies and relics of anhydrite penecontemporaneous dolomite is partially overprinted by microsparry dolomite thought to be of groundwater origin the redefined petrovbreen member e2 consists of diamictite and other detrital dolostone pronounced thickness variations 2 40 m are thought to be original depositional features the member represents the deposits of a short glacial period in which the following depositional processes are inferred lodgement massive diamictite subaqueous meltout massive and bedded diamictite ice rafting lithologies bearing dropstones and possibly also diamictite redeposition by sediment gravity flows some diamictite and conglomerate rhythmite and shale current winnowing thin tabular conglomerate subaerial or subaqueous meltwater action channelled conglomerate and sandstone periglacial shrinkage diamictite wedge fillings the macdonaldryggen member e3 230 m is a monotonous succession of shaly dolostone of lagoonal origin it grades up into the slangen member e4 25 m which consists of subtidal to intertidal dolarenite with anhydrite relics succeeded by fenestral dolostone that was fractured and cemented by saline groundwaters in an emergent environment the wilsonbreen formation 160 m represents a return to glacial deposition but this time longer lasting and with substantial extra basinal material represented the gropbreen member w1 28 107 m and the ormen member w3 44 139 m consist dominantly of dolomitic diamictite with subordinate conglomerate and sandstone and are separated by a middle carbonate member w2 3 30 m which contains distinctive rhythmitic and stromatolitic limestone as well as sandstone the same depositional processes can be recognised as in the petrovbreen member but the wilsonbreen formation is overall of somewhat more continental aspect lower proportion of rhythmite and dropstone structures in addition there are basal breccia and crack fillings formed by frost shattering of the underlying cemented dolostone tabular sandstone thought to be formed by wave reworking of outwash a striated terrestrial cobble pavement supraglacially derived breccia horizons periglacial wedges filled by sand and the w2 assemblage of possible lacustrine origin the dracoisen formation 525 m represents an abrupt return to non glacial conditions an upward deepening wave dominated succession of pure dolostone d1 20 m and impure dolostone d2 105 m is succeeded by offshore black shale d3 150 m and then by a very shallow water succession of evaporite lacustrine aspect with a dolostone containing evaporite relics d5 10 m separating dolomitic sandstone and shale d4 80 m and d6 150 m the contact with the transgressive cambrian sandstones above is poorly exposed deposition of the succession dominantly under marine conditions is inferred but it is difficult to rule out a lacustrine environment at any particular horizon this dolomite tillite association can be explained by penecontemporaneous and minor secondary dolomite formation in marginal environments with warm climatic indicators at some levels being sharply interrupted because of rapid climatic changes by glacial sediments containing abundant detrital dolomite since the latter sediments make up only 17 of the 1080m thick succession glacial conditions only occupied a small proportion of vendian time

classification of poorly sorted sedimentary rocks abstract the classification and nomenclature of sandstones has evolved over the years into a system which is now generally accepted as standard however no equivalent system exists for the poorly sorted sedimentary rocks which include grain sizes from clay to gravel a descriptive classification is proposed based on an earlier system but using updated nomenclature and lithological fields such a scheme is needed to clearly define lithological terms currently used in the description of sedimentary sequences

deformation of the batestown till of the lake michigan lobe laurentide ice sheet deep pervasive shear deformation of the bed to high strains 100 may have been primarily responsible for flow and sediment transport of the lake michigan lobe of the laurentide ice sheet to test this hypothesis we sampled at 0 2 m increments a basal till from one advance of the lobe batestown till along vertical profiles and measured fabrics due to both anisotropy of magnetic susceptibility and sand grain preferred orientation unlike past fabric studies interpretations were guided by results of laboratory experiments in which this till was deformed in simple shear to high strains fabric strengths indicate that more than half of the till sampled has a 5 probability of having been sheared to moderate strains 7 30 secular changes in fabric azimuth over the thickness of the till probably due to changing ice flow direction as the lobe receded indicate that the bed accreted with time and that the depth of deformation of the bed did not exceed a few decimeters orientations of principal magnetic susceptibilities show that the state of strain was commonly complex deviating from bed parallel simple shear deformation is inferred to have been focused in shallow temporally variable patches during till deposition from ice

ftir microspectroscopy of particular liptinite lopinite rich late permian coals from southern china abstract the late permian coals from southern china are unique in their high content of lopinite liptinite and elemental hydrogen and typically produce high yields of tar typical of the late permian coals of southern china the coals used in this study show special petrographic and chemical characteristics as well as significant oil producing potential studies of these coals and of their content of the lopinite maceral will help to explain the genesis of both the lopinite maceral and of the oil producing potential of the coals in this study an ftir spectrometer was used in the standard transmission mode to generate the ir spectra of the whole coal an ftir spectrometer equipped with a microscope in the reflectance mode was used to analyze the chemical structure of individual coal macerals including lopinite vitrinite semifusinite and inertinite the chemical structure of lopinite is characterized by its higher content of longer and less branched aliphatic side chains and distinct c 0 groups the oil producing potential of the coals is attributed to their higher content of lopinite

the origins of glacially related soft sediment deformation structures in upper ordovician glaciogenic rocks implication for ice sheet dynamics in the upper ordovician glaciogenic rocks of west gondwana many soft sediment deformation structures are attributed to glaciotectonic processes however little is known about the subglacial and ice marginal processes associated with this ice sheet a systematic description and interpretation of these soft sediment deformation structures is supplemented by a comparison with late quaternary and modern glacial settings to provide qualitative constraints on the character of ancient subglacial thermal regimes soft sediment striations were formed by discontinuous shear induced deformation beneath an ice sheet that oscillated between warm and cold based thermal regimes beneath warm based ice coupling across the ice bed interface was poor with sliding and loading occurring at this surface loading of soft waterlogged sediments allowed the development of fluted surfaces which are also associated with the formation of truncated folded zones during times of cold thermal regimes coupling across the ice bed interface was enhanced by freezing which caused changes in the position of the freezing front these discontinuous changes coupled with sustained subglacial shearing resulted in the development of stacked soft sediment striated surfaces in areas where the subglacial substrate had an irregular topography complex shear zones formed that comprised stacked duplex systems interlayered with highly strained units preserving pervasive folded lineations at the ice front large glaciotectonic deformation structures comparable with push moraines developed during sustained periods of re advance that created composite thrust and fold systems deformation was transmitted for up to 1 km from the ice front and reduced in intensity with distance other deformation structures include dome like folds that consist of central anticlines 30 to 70 m in width with tight rim synclines that formed by the load induced diapiric intrusion of muds an ice sheet surging mechanism is inferred for the development of composite thrust and fold systems and the coeval sediment diapirs these surges potentially caused the widespread reorganisation of a glacial load resulting in the pro to subglacial extrusion of soft sediments

glacimarine processes at grounding line fans and their growth to ice contact deltas abstract grounding line fans originate from subglacial and basal stream tunnels at grounding lines of glaciers terminating in a marine environment during melt seasons discharge forms a turbulent jet beyond the efflux over the initial zone of flow establishment in the jet it may remain in contact with the sea floor for up to 13 4 d d tunnel diameter along a runout distance if velocity is constant plug flow in this zone deposits marine outwash sediment commonly having chaotic texture and graded and welded contacts texture may vary rapidly because of discharge pulses and the jet may move laterally to produce sheet or cut and fill geometries imbricate gravel is deposited near the efflux then farther out are sheet or weakly channelized finer grained gravels and sands in some instances a migrating barchanoid bar forms at the detachment zone and forms large scale trough cross beds beyond the detachment zone the turbulent jet becomes vertical and sediment cascades from it in a veil this sediment is added to by flows from continuous failures of bed load sediment in the detachment zone resulting deposits are interstratified sediment gravity flows and thick coarse end members of cyclopsams the jet changes to a plume when inertial forces become less than buoyancy forces turbulent vorticies within the jet can re entrain particles into a buoyant plume the plume remains vertical although continuously spreading until reaching neutral buoyancy fan depocentres have been observed to accumulate at over 10 6 m 3 a 1 in temperate glacial areas eventually at quasi stable grounding lines fans may aggrade to sea level to form ice contact deltas at incipient deltas when the delta plain is intertidal coarse sediment is redistributed to the prodelta with each tidal cycle intense prodelta rhythmites mark the transition of a fan into a delta

the interpretation and classification of subglacially deformed materials abstract a general classification of subglacially deformed materials is proposed based on sediment properties and their relationship to styles of subglacial strain deformation till is defined as homogenized usually diamictic material formed by glacially induced shear of subsole materials three types are recognized type a formed by pervasive ductile deformation type b formed by brittle shear and comminution till produced by the reduction of void space by in situ crushing and abrasion the term glacitectonite is adopted for materials that have undergone subglacial shear but retain some of the structural characteristics of the parent material original structures may be truncated by glacitectonic fabric elements type a or distorted but not truncated type b the principles of strain and material response particle orientation mechanisms fabric development and drainage conditions are reviewed examples of deformation tills and glacitectonites from breidamerkurjokull iceland slettmarkbreen norway loch lomond scotland and east yorkshire england are used to illustrate the nature of subglacially deformed materials and their relationship to former subglacial strain and drainage conditions the geologic evidence suggests a continuum of bed strengths can be recognized in deforming substrata ranging from high strength low strain type b deformation till and comminution till to low strength high strain type a deformation till

the experimental basis for interpreting particle and magnetic fabrics of sheared till particle fabrics of basal tills may allow testing of the bed deformation model of glacier flow which requires high bed shear strains 100 field studies however have not yielded a systematic relationship between shear strain magnitude and fabric development to isolate this relationship four basal tills and viscous putty were sheared in a ring shear device to strains as high as 714 fabric was characterized within a zone of shear deformation using the long axis orientations of fine gravel and sand particles and the anisotropy of magnetic susceptibility ams of small 5 8 cm3 intact samples results indicate that till particles rotate toward the plane of shearing with long axis orientations that become tightly clustered in the direction of shear 0 78 s1 0 94 for three dimensional data these strong steady state fabrics are attained at shear strains of 7 30 with no evidence of fabric weakening with further strain regardless of the specific till or particle size fraction under consideration these results do not support the jeffery model of particle rotation which correctly describes particle rotation in the viscous putty but not in the tills owing to fluid mechanical assumptions of the model that are violated in till the sensitivity of fabric development to shear strain magnitude indicates that for most till units where shear strain magnitude is poorly known attributing fabric variations to spatial differences in other variables such as till thickness or water content will be inherently speculative attributing fabric characteristics to particular basal till facies is uncertain because shear strain magnitude is unlikely to be closely correlated to till facies weak or spatially variable fabrics in the absence of post depositional disturbance or major deviations from unidirectional simple shear indicate that till has not been pervasively sheared to the high strains required by the bed deformation model strong flow parallel fabrics are a necessary but insufficient criterion for confirming the model copyright 2008 john wiley sons ltd

icesat antarctic elevation data preliminary precision and accuracy assessment 1 since first light on february 20th 2003 nasa s ice cloud and land elevation satellite icesat has derived surface elevations from 86 n to 86 s latitude these unique altimetry data have been acquired in a series of observation periods in repeated track patterns using all three geoscience laser altimeter system glas lasers here we focus on antarctic ice sheet elevation data that were obtained in 2003 2004 we present preliminary precision and accuracy assessments of selected elevation data and discuss factors impacting elevation change detection we show that for low slope and clear sky conditions the precision of gla12 laser 2a release 21 data is 2 1 cm and the relative accuracy of icesat elevations is 14 cm based on crossover differences

neogene fjordal sedimentation on the western margin of the lambert graben east antarctica neogene glacial sedimentation east antarctica

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

glacimarine processes and inductive lithofacies modelling of ice shelf and tidewater glacier sediments based on quaternary examples abstract three variables control the type of glacial debris source and where and when debris is introduced to an ocean 1 type of glacial ice source ice sheet or valley glacier 2 condition of a grounded glacier melting freezing or frozen base and cold or warm internal ice and 3 type of glacier front ice shelf or tidewater using these variables in different combinations eight glacimarine regimes are postulated to exist by integrating information from holocene sediment and pleistocene glacimarine sequences with the eight inductive regimes lithofacies relationships are predicted and modelled the models show a complexity of glacimarine lithofacies the importance of recognizing this complexity lies in realistic interpretations of ancient sequences ice shelf sediment may be limited in the geologic record because of tectonic and climatic constraints required for ice shelf formation alternatively in some tidewater glacier regimes larger volumes of glacimarine sediment are produced than in ice shelf regimes ice proximal sediment is distinctive especially near subglacial meltwater stream effluxes ice shelves and tidewater glaciers may produce similar ice proximal lithofacies e g morainal bank associations and laminites in certain regimes however details of lithofacies may aid in distinguishing ice shelf from tidewater regimes ice shelf and tidewater iceberg zone sediment can be distinguished from each other if basal and high level englacial debris can be distinguished ice shelf zone sediment out from the grounding line has a basal debris source high level englacial debris is deposited in more distal ice shelf zones resulting in sediment by pass in corresponding positions of a tidewater glacier regime iceberg rafted debris comprises mixed basal and high level englacial debris deeper water zones receive large volumes of sediment when a melting freezing base grounding line is at the edge of a continental shelf when the grounding line retreats sediment supply may be drastically reduced because of a back sloping continental shelf and trapping by morainal banks cool water bioclastic carbonates may accumulate once a grounding line has retreated although ice shelf iceberg zones are more extensive than those in tidewater regimes ice shelf icebergs have low debris content and resulting ice rafted debris may be scarce the smallest volume of sediment is produced by a frozen base ice sheet ending as a tidewater front and the largest volume by a melting freezing base valley tidewater glacier glacimarine sediment has a relatively high preservation potential near continental interiors or margins however at continental margins mass flow olistostrome and tectonic melange deposits may be preserved with glacimarine diamictites these deposits may be difficult to distinguish from each other especially if metamorphosed such as at a convergent margin the models presented do not fully represent the glacimarine environment because many other variables are omitted however the principal concepts of generating glacimarine lithofacies associations are considered continued research will verify if each regime exists and will provide data on those regimes that exist today to compare and modify these models

a comparison of clast fabric and shape in late precambrian and modern glacigenic sediments abstract northeastern svalbard contains a well preserved glacigenic sequence of vendian late precambrian age in which terrestrial lacustrine intertidal and marine glacial facies are represented diamictite facies are of two main types massive and weakly to strongly bedded diamictite field appearance and relationships with other facies however provide insufficient information to allow a clear interpretation of the precise mode of glacial deposition by combining this information with data concerning the fabric of clasts in modern glacigenic sediments where the mode of glacial deposition is better known a wider understanding of the processes of glacial deposition in vendian time is obtained several diamictite samples were interpreted to be of lodgement tillite facies and material o water laid and glacigenic sediment flow origin was also recorded clast shape analyses indicate that most glacial debris was transported at least for a time at the glacier bed little angular supraglacial debris was present implying that the ice mass was of ice cap or ice sheet dimensions with few subaerial rock exposures clast shape in the late precambrian deposits was not useful in distinguishing between the variety of lithofacies derived from basally transported glacial material too few systematic studies of clast striation in modern glacigenic sediments are yet available for this criterion to be helpful in distinguishing between tillite facies lithofacies analysis together with clast fabric and shape studies provide useful and complementary lines of evidence concerning the ode of deposition of ancient diamictite sequences an understanding of the depositional processes and patterns of modern glacial sedimentation provides a fundamental framework for such studies

subaqueous mass flow origin for lower permian diamictites and associated facies of the grant group barbwire terrace canning basin western australia the intracratonic canning basin is western australia s largest sedimentary basin 400 000 km2 and has experienced repeated episodes of phanerozoic extension and subsidence resulting in deposition of a number of first order megasequences a major phase of basin extension and sedimentation grant group occurred in the late carboniferous early permian when australia lay at high palaeolatitudes facies analysis of 5000 m of drill core from 25 continuously cored wells in grant group strata on the fault bounded barbwire terrace in the northern canning basin identified three facies associations fas these record the predominance of fault generated subaqueous mass flow and sediment reworking the lowest association fa i up to 355 m thick rests unconformably on tilted older strata and consists of coarse grained subaqueously deposited sediment gravity flow facies these include fault generated breccias massive and graded sandstones and conglomerates deposited by turbidity currents and diamictites generated by mixing of different textural populations during downslope remobilization fa i is overlain abruptly by relatively fine grained deposits of fa ii up to 140 m thick which consist of laminated to thin bedded mudstone and sandstone turbidites recording an abrupt increase in relative water depths in turn these facies coarsen upwards and are transitional into shallow water swaley cross stratified and rippled sandstones of fa iii up to 125 m thick the overall stratigraphic succession probably records an initial phase of faulting and accommodation of coarse sediment fa i a subsequent phase of rapid subsidence increasing water depths and sediment underfilling fa ii and finally a regressive phase of shoreface progradation the occurrence of rare striated clasts in fa i suggests reworking of glacial sediment but no direct glacial influence on sedimentation can be identified

fabric shape and the interpretation of sedimentary fabric data abstract the concept of fabric shape provides a powerful means of visualizing and analyzing data on sedimentary fabric the shape of a fabric is defined in terms of the ratios between eigenvalues s1 s2 and s3 derived using the orientation tensor method a continuum of all possible orthorhombic fabric shapes can be clearly represented on equilateral ternary diagrams originally developed for the presentation of particle shape data two indices are of particular value in scaling these diagrams fabric isotropy i s3 s1 and fabric elongation e 1 s2 s1 together these indices uniquely define the shape of any orthorhombic fabric and provide a rational and quantitative basis for reconstructing depositional and de ormational processes equilateral ternary diagrams provide a more versatile and powerful basis for analyzing fabric data than other eigenvalue diagrams now in use use of the diagrams in reconstructing processes of sediment transport and deposition is illustrated using fabric data from subglacial tills and a variety of slope deposits

magnetic fabric of sheared till a strain indicator for evaluating the bed deformation model of glacier flow wet based portions of ice sheets may move primarily by shearing their till beds resulting in high sediment fluxes and the development of subglacial landforms this model of glacier movement which requires high bed shear strains can be tested using till microstructural characteristics that evolve during till deformation here we examine the development of magnetic fabric using a ring shear device to deform two wisconsin age basal tills to shear strains as high as 70 hysteresis experiments and the dependence of magnetic susceptibility of these tills on temperature demonstrate that anisotropy of magnetic susceptibility ams develops during shear due to the rotation of primarily magnetite particles that are silt sized or smaller at moderate shear strains 6 25 principal axes of maximum magnetic susceptibility develop a strong fabric s 1 eignevalues of 0 83 0 96 without further strengthening at higher strains during deformation directions of maximum susceptibility cluster strongly in the direction of shear and plunge up glacier consistent with the behavior of pebbles and sand particles studied in earlier experiments in contrast the magnitude of ams does not vary systematically with strain and is small relative to its variability among samples this is because most magnetite grains are contained as inclusions in larger particles and hence do not align during shear although processes other than pervasive bed deformation may result in strong flow parallel fabrics ams fabrics provide a rapid and objective means of identifying basal tills that have not been sheared sufficiently to be compatible with the bed deformation model

architectural element analysis applied to glacial deposits internal geometry of a late pleistocene till sheet ontario canada deposits left by continental ice sheets are characterized by sedimentological complexity and stratigraphic heterogeneity but stratigraphic descriptions of such deposits and resulting first generation facies models are still based primarily on one or two dimensional borehole or outcrop data reconstruction of depositional environments hydrogeological investigations of pleistocene glacial deposits and hydrocarbon exploration in pre pleistocene glaciated basin fills require a more detailed understanding of the form and heterogeneity of lithofacies sequences in three dimensions architectural element analysis is used widely by sedimentologists for categorizing internal stratigraphic heterogeneity in sandstones particularly those of fluvial origin this paper demonstrates the first application of architectural element analysis to glacial deposits such as tills outcrop borehole and a broad range of subsurface geophysical data were collected from a thick 60 m till sheet present across an 80 km 2 study area near toronto canada the till sheet is not homogeneous but is composed of three distinct architectural elements and associated lithofacies viz diamict elements interbeds of subglaciofluvial sediments and glaciotectonically deformed zones application of architectural element analysis to these subglacial strata provides insights into the origin of drumlin bedforms and subglacial processes below the laurentide ice sheet and creates a framework for understanding ground water and contaminant movement in underlying aquifers

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

oil generation capacity of coals as a function of coal age and aliphatic structure abstract the relative proportions of aliphatic ch2 ch3 aliphatic hydrogen hali together with the aliphatic chain length in a series of carboniferous permian jurassic and cenozoic humic coals have been analysed using ftir and ruthenium tetroxide catalysed oxidation rtco followed by gc ms analysis of the n monocarboxylic acids esterified to assess their ability to generate oil most of the coals contain 2 11 vol liptinite only coals with almost similar hydrogen indices his were compared as they were considered to possess comparable hydrocarbon generation potentials all contain isolated aromatic hydrogen haro in the coal structure and a considerable proportion of aliphatic chains in the range c16 18 hi values cannot alone explain the proportion of aliphatic ch2 implying that for coals haro contributes to the measured hi cenozoic coals contain the highest proportion of aliphatic ch2 and hali and the content of longer chain aliphatics c18 increases considerably from palaeozoic to cenozoic coals aliphatic chains c18 are absent from or very restricted in the carboniferous coals and most of the permian coals indicate no or a negligible ability to generate oil jurassic coals show a slightly better potential whereas cenozoic coals contain aliphatic chains up to at least c35 demonstrating the greatest capacity to generate oil in addition to significant gas potential multivariate data analysis suggests that the aliphatic chains c24 are related to the collodetrinite liptodetrinite matrix which is a prominent constituent of cenozoic coals with regard to oil potential the coals from the major coal forming periods may be ranked carboniferous permian

subglacial and proglacial glacitectonic deformation in the neoproterozoic port askaig formation scotland abstract the recognition and interpretation of glacigenic sediments in the ancient rock record has important implications for understanding processes and patterns of climate change diamictite facies from the neoproterozoic port askaig formation scotland have been variously interpreted as evidence for grounded glacier ice mass movements on a glacially influenced submarine slope and subaqueous mass movements in a non glacial environment these contrasting interpretations imply widely differing degrees of ice cover and have contrasting implications for neoproterozoic snowball glaciations in this paper we focus on the great breccia and the disrupted beds two controversial units in the port askaig formation we present evidence that they were formed by the proglacial and subglacial deformation respectively of pre existing shallow marine facies during an advance of grounded ice quaternary examples provide remarkably exact analogues for the great breccia and disrupted beds illustrating the potential value of applying litho and tectono facies models to ancient sedimentary successions

magnetic fabrics in the basal ice of a surge type glacier 1 anisotropy of magnetic susceptibility ams has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments here we present results from debris rich basal glacier ice to examine deformation associated with glacier motion basal ice samples were collected from tunabreen a polythermal surge type glacier in svalbard the magnetic fabrics recorded show strong correlation with structures within the ice such as sheath folds and macroscopic stretching lineations thermomagnetic low temperature susceptibility varying field susceptibility and isothermal remanent magnetism acquisition experiments reveal that the debris rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier an up glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation the results suggest that ams can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed

kerogen origin evolution and structure kerogen commonly defined as the insoluble macromolecular organic matter om dispersed in sedimentary rocks is by far the most abundant form of om on earth this fossil material is of prime importance as the source of oil and natural gas moreover kerogen can provide essential information on major topics such as past environments climates and biota this review reports the main advances in kerogen studies since the comprehensive synthesis edited by durand durand b ed kerogen insoluble organic matter from sedimentary rocks editions technip paris 1980 it is organized into eight sections the first two are concerned with the successive definitions of kerogen and the definition used here the different techniques used for kerogen isolation without loss or degradation and basic kerogen analysis the third and fourth focus on sedimentary om sources and preservation processes in relation to depositional environment including sedimentation conditions favourable for kerogen accumulation and extrapolation to past geological time great strides have been made in the latter topics over the last 25 years owing to a combination of classical studies in organic geochemistry and studies in other domains such as biogeochemistry oceanography hydrology and soil science along with the development of powerful analytical tools the next two sections deal with the different kerogen classifications by type and kerogen evolution and maturation upon burial in sediments structural modelling of coal and kerogen based on physical and or chemical structural analysis is described in the following section although only statistical the models thus derived provide a synthetic view of the main structural resemblances and differences among various samples in relation to source maturity or physicochemical properties finally the last section explores some of the advances in kerogen understanding expected for the near future the review includes a list containing about 500 references

theory of glacial erosion transport and deposition as a consequence of subglacial sediment deformation a theory of erosion transport and deposition of unlithified sediments by glaciers is presented it predicts the large scale areal distribution of zones and rates of erosion and deposition in time and space through a complete glacial cycle together with the resultant intensity of large scale lincations drumlins which will be incised in the landscape the theory also predicts the dispersal patterns of subglacial lithologies together with the form of dispersal trains derived from distinctive sources and the vertical and horizontal distribution of lithologies within a till it predicts major erosional discontinuities within tills and the formation of boulder pavements it suggests that the dominant proportion of the lowland tills produced by pleistocene mid latitude ice sheets was generated by subglacial deformation and explains why they are predominantly fine grained the theory is based on an analysis of glacier dynamic processes and therefore can be used to infer the dynamic behaviour of former ice sheets from the distribution of tills and their lithologic composition

orbitally forced ice sheet fluctuations during the marinoan snowball earth glaciation the presence of dynamic ice sheets during snowball earth glaciations is controversial geological evidence and ice sheet modelling suggest that ice sheets may have responded to orbital forcing when pco2 reached a certain threshold

chemotaxonomy for naturally macerated tree fern cuticles medullosales and marattiales carboniferous sydney and mabou sub basins nova scotia canada abstract naturally macerated cuticles nmc and one synangium representing medullosalean and marattialean tree fern species from two carboniferous coalfields in nova scotia canada are investigated the samples were analyzed by infrared spectroscopy ftir and by pyrolysis gas chromatograph mass spectrometry py gc ms techniques in search for chemical signatures that would help in developing a chemotaxonomic classification of carboniferous fern species assuming genetically dependent make up of cuticles ftir derived ch 2 ch 3 ratios in conjunction with contributions from carboxyl groups demonstrated a better potential for discriminating between medullosalean genera and species than molecular signatures obtained by py gc ms however the latter provided better data for differentiating medullosalean from marattialean tree ferns as a group changes in the chemical make up of naturally macerated cuticles due to sample preparation are discussed

upper paleozoic glacigenic deposits of gondwana stratigraphy and paleoenvironmental significance of a tillite succession in northern victoria land antarctica abstract late paleozoic glacial deposits are widespread in gondwana in antarctica the best outcrops occur in the central transantarctic mountains ellsworth mountains pensacola mountains and in southern victoria land whereas they are rare and very scattered in northern victoria land which represents a linkage sector with tasmania and eastern australia the aim of the present research is to define the stratigraphic setting and the environmental interpretation of a poorly studied lower permian glacigenic succession located near orr glacier in the lanterman range in northern victoria land it has great importance because it represents the only significant glacigenic succession for this wide area marking and defining time and modality of a glacial postglacial transition during the early permian a critical time interval in the paleoenvironmental evolution of southern gondwana this succession named here as the lanterman formation lies directly on to crystalline basement and is overlain by a thick permian fluvial succession takrouna formation the results provided by sedimentological facies analysis and palynological analysis integrated with a limited petrographic characterization show a correlation framework between two isolated successions outlining their stratigraphic architecture and subdivided into a lower glacial portion and an upper postglacial portion the former asselian in age is dominated by diamictite sandstone mudstone with lonestones and carbonate deposits suggesting repeated advance and retreat of a terrestrial glacier with facies associations indicating environmental changes from subglacial to glaciofluvial to glaciolacustrine the latter is dominated by lacustrine mudstone with decreasing lonestones upward thin bedded sandstone conglomerate and a thick fluvial sandstone and pebbly sandstone succession at the top signalling the transition to a fluvial system through time the overall dataset suggests that the late paleozoic glacigenic deposits of northern victoria land record the evolution from a setting characterized by a terrestrial small ice cap that underwent repeated advances and retreats due to climate cycles in a lacustrine setting into a postglacial paleoenvironmental scenario with a wide fluvial system draining northwards from victoria land towards the tasmanian basin the results contribute to increasing knowledge of the timing and modalities of the late paleozoic ice age in gondwana particularly for polar regions such as antarctica

compression cuticle relationship of seed ferns insights from liquid solid states ftir late palaeozoic early mesozoic canada spain argentina abstract cuticles have been macerated from suitably preserved compressed fossil foliage by schulze s process for the past 150 years whereas the physical biochemical relationship between the coalified layer with preserved cuticle as a unit has hardly been investigated although they provide complementary information this relationship is conceptualized by an analogue model of the anatomy of an extant leaf vitrinite mesophyll cuticle biomacropolymer compression alkaline solutions from schulze s process as a proxy for the vitrinite are studied by means of liquid solid states fourier transform infrared spectroscopy ftir in addition cuticle free coalified layers and fossilized cuticles of seed ferns mainly from canada spain and argentina of late pennsylvanian late triassic age are included in the study sample infrared data of cuticle and alkaline solutions differ which is primarily contingent on the mesophyll biomacropolymer characteristics the compression records two pathways of organic matter transformation one is the vitrinized component that reflects the diagenetic post diagenetic coalification history parallel with the evolution of the associated coal seam the other is the cuticle that reflects the sum total of evolutionary pathway of the biomacropolymer its monomeric or polymeric fragmentation though factors promoting preservation include entombing clay minerals and lower ph conditions caution is advised when interpreting liquid state based ftir data as some ir signals may have resulted from the interaction of schulze s process with the cuticular biochemistry a biochemical study course for taphonomy is suggested as fossilized cuticles cuticle free coalified layers and compressions are responses to shared physicogeochemical factors

glacitectonism subglacial and glacilacustrine processes during a neoproterozoic panglaciation north east svalbard

the origin of the west spitsbergen fold belt from geological constraints and plate kinematics implications for the arctic abstract the west spitsbergen fold belt which extends for 300 km along the western margin of svalbard and is up to 80 km wide has much in common with foreland fold and thrust belts the near foreland segment of the fold belt exhibits ramp flat thrust trajectories whilst structurally higher nappes are typified by more listric thrusts higher nappes to the west contain imbricated carboniferous and basement rocks showing that the latter were actively involved in the fold belt deformation and a minimum of 80 km total shortening perpendicular to the western margin of svalbard is estimated the early stages of the eurekan deformation in north greenland can be linked to that of the west spitsbergen fold belt and the combined shortening across the two fold belts may exceed 80 km in ellesmere island eurekan structures are distributed in an arc like belt which records between 50 to 100 km of shortening since the late cretaceous kinematic reconstructions suggest that before the opening of the eurasian basin and norwegian greenland sea chron 25 svalbard was linked to north america in the late cretaceous palaeocene interval the motion across the greenland svalbard margin was mainly convergent giving rise to the west spitsbergen fold belt and the eurekan structures of north greenland the dextral separation of greenland and svalbard in post chron 24 time was accompanied by extension followed by pure extension in post chron 13 time

effects of glacial transport and neomorphism on precambrian dolomite crystal sizes late precambrian glacial rocks are notable for their association with dolostones1 and this has been regarded as a palaeoclimatological paradox2 5 however little detailed work has been carried out to determine the mode of origin of the dolomite in north east spitsbergen svalbard the vendian6 7 succession contains two glacial stratigraphical units8 9 which are dolomitic and are underlain and overlain by dolostones evidence from sedimentary structures and gross textures indicates that dolomite within the glacial units is detrital whereas at other levels it is a precipitate10 accordingly dolomite crystal sizes were analysed to determine whether evidence of glacial erosion and transport rock flour has been preserved allowing for the effects of later crystal enlargement aggrading neomorphism which vary within and between samples the results show a markedly higher proportion of very fine crystals in the inferred detrital dolostones compared with the precipitated dolostones the very fine crystals are interpreted as relics of rock flour the preservation of which demonstrates a novel means of testing the origin of dolostones associated with glacial sequences inorganic precipitation of dolomite during glaciation or secondary dolomitization of till are not required to explain the dolomite tillite association but pronounced climatic changes at the onset and close of glacial periods are indicated

depositional controls on the magnetic characteristics of lodgement tills and other glacial diamict facies genetic interpretation of massive unstructured diamict and diamictite facies is a commonly encountered problem faced by sedimentologists data are presented concerning the magnetic characteristics namely anisotropy of magnetic susceptibility ams and natural remanent magnetism nrm of facies deposited by 1 lodgement processes at a glacier base lodgement till and 2 subaqueously by pelagic mud deposition and ice rafting rain out diamicts lodgement tills have an nrm that is distorted around the geomagnetic pole position to form a girdle approximately 90 in length either transverse or parallel to ice flow direction this distension appears to be the result of subglacial shear processes because other diamicts deposited passively by melt out below stagnant ice and modelled by a laboratory experiment show a nondeformed nrm clustering around the geomagnetic pole the ams data show that lodgement tills have only a weakly orientated magnetic microfabric glaciolacustrine rain out diamicts show

discriminating glacier thermal and dynamic regimes in the sedimentary record abstract this paper provides a description and evaluation of the sedimentary facies and environments associated with a range of glacier thermal and dynamic regimes with additional consideration given to the tectonic context new and previously published data are evaluated together and are presented from modern terrestrial and marine glacial sedimentary environments in order to identify a set of criteria that can be used to discriminate between different glacier thermal regimes and dynamic styles in the sedimentary record sedimentological data are presented from a total of 28 glaciers in 11 geographical areas that represent a wide range of contemporary thermal dynamic and topographic regimes in the context of landsystems representatives from terrestrial environments include temperate glaciers in the european alps patagonia new zealand the cordillera blanca peru cold glaciers in the dry valleys of antarctica and the antarctic peninsula region and polythermal valley glaciers in svalbard northern sweden the yukon and the khumbu himal nepal the glaciomarine environment is illustrated by data from cold and polythermal glacier margins on the east antarctic continental shelf and from a polythermal tidewater glacier in svalbard along with general observations from temperate glaciers in alaska these data show that temperate glacial systems particularly in high relief areas are dominated by rockfall and avalanche processes although sediments are largely reworked by glaciofluvial processes debris in polythermal glaciers is both thermally and topographically influenced in areas of moderate relief debris is mainly of basal glacial origin and the resulting facies association is dominated by diamicton in high relief areas such as the himalaya the debris load in polythermal glaciers is dominated by rockfall and avalanche inputs resulting in extensive accumulations of sandy boulder gravel cold glaciers are dominated by basal debris entrainment but sediments are little modified from the source materials which are typically sandy boulder gravel from older till and sand from glaciofluvial glaciolacustrine and aeolian sources similar facies associations but with different facies geometry and thickness occur in equivalent glaciomarine settings application of these concepts can aid the interpretation of glacier thermal regime and hence palaeoclimate in quaternary and ancient glacial systems

polyphase deformation at an oscillating ice margin following the loch lomond readvance central scotland uk the sequence of glacitectonic disturbance of an ice contact delta during the initial stages of deglaciation following the loch lomond readvance is examined an ice marginal gilbert type deltaic sequence exposed in drumbeg quarry drymen scotland displays a polyphase deformation history that is punctuated by periods of erosion and deposition progradation of the delta into ice dammed lake blane led to a temporary stabilisation of the loch lomond glacier during recession from its loch lomond readvance maximum position this was followed by a ne directed readvance into the ice contact slope of the delta resulting in proglacial deformation d1 and the formation of a thrust block ridge in the middle to outer parts of the delta complex sedimentation continued uninterrupted subsequent retreat of the ice was accompanied by erosion and deposition as the ice contact slope was re established a second phase of readvance resulted in subglacial ductile shearing d2 and deposition of a diamicton during ne directed over riding of the delta sediments by the ice the direction of ice flow subsequently changed towards the se this was followed by a further retreat of the ice and re establishment of the fan delta complex the complexity of the glacitectonic sequence at drumbeg records the impact of an oscillating ice margin responding to either relative deepening of the lake waters in contact with the receding snout or climatic controls it provides further evidence that many of the scottish highland glaciers were subject to active recession rather than stagnation at the end of the loch lomond readvance

chemometric study of functional groups in pennsylvanian gymnosperm plant organs sydney coalfield canada implications for chemotaxonomy and assessment of kerogen formation abstract the samples comprise the foliage of four pteridosperm medullosalean plant fossil species of differing preservation states and one of a cordaitean species from two canadian maritime sub basins of carboniferous age 300 ma sydney and stellarton coalfields nova scotia respectively included in the sample set were some coal samples from sydney coalfield along with published data for coal macerals for comparison by applying schulze s maceration process to the fossil foliage to obtain the cuticles five sample forms evolved viz compressions cuticles and fossilized cuticles and acidic and alkaline solutions from schulze s process to which was added the sydney coal samples as the sixth form area integration of the absorbance spectra from solid and liquid state fourier transform infrared ftir spectroscopy produced functional chemical parameters which were organized into a data matrix of eight variables and 62 samples 8 62 matrix since we were interested in grouping the sample forms as a function of phytochemistry functional groups to assess primarily the palaeophytotaxonomic potential as a general approach to carboniferous taxonomy principal components were extracted from the matrix and a subset of 4 33 samples in order to refine the grouping results from the initial component analysis in each case a two component model resulted accounting for least 80 of the cumulative variance overall the results are encouraging in offering increasing support for fossil leaf chemotaxonomy but bearing in mind the limited sampling number 56 and restricted sampling of genera 5 apart from this general conclusion which supports our previous ftir work vis a vis chemotaxonomy we noted functional group similarities in our ftir data with types of kerogen and coal macerals on this basis we hypothesize that in combination with the different preservation states of our fossil specimens these factors have a bearing on kerogen genesis from plant material i e the oil and gas prone types i and ii

phyto and chronostratigraphical correlations between the late pennsylvanian morien group sydney nova scotia and the silesian pennant measures south wales three macrofloral interval zones lobatopteris vestita l micromiltoni and linopteris bunburii recognized in the westphalian d and the cantabrica biozone in the stephanian of europe are also present in the morien group pictou group of sydney coalfield nova scotia these zones allow a more refined correlation to be made between sequences of the same age in the sydney and south wales coalfields and thus between western europe and north america in general

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

late proterozoic glacial carbonates in northeast spitsbergen new insights into the carbonate tillite association carbonate rich glacial deposits from two discrete vendian glacial periods are described the older is represented by the 24 40 m thick petrovbreen member e2 of the elbobreen formation which contains abundant detrital dolomite clasts in e2 and their possible source rocks have positive 13 c and negative 18 o pdb values in contrast the carbonate mud fraction of e2 sediments has different cathodoluminescence characteristics from clasts slightly negative 13 c values and higher fe and mn concentrations than clasts oxygen isotopes vary from 2 5 to 4 5 pdb thought to be related to various seawater meltwater mixtures in the depositional environment preservation of information about glacial sedimentary environments is attributed to early diagenetic recrystallization forced by excess surface free energy ostwald s ripening and coinciding with sulphate reduction the younger glaciation is represented by the wilsonbreen formation 170 m which has a distinctive glaciolacustrine middle carbonate member w2 w2 contains precipitated periglacial carbonates with high mn fe ratio both limestone rhythmitic and stromatolitic and dolostone rhythmites stromatolites and dolomite rich sandstones which are compared with carbonates in modern antarctic lakes evaporitic environments for dolomitic sandstones and stromatolitic dolostones are indicated by heavy oxygen isotope values up to 10 5 pdb high na concentration and evidence for dissolved evaporites high mn concentration in detrital dolostones in w2 is suggestive of syn sedimentary dolomite recrystallization in freshwater diamictites and haematitic siltstones the carbonate tillite association ultimately arises from the erosion of underlying carbonates which originated in this case under radically different climatic conditions glacial depositional waters then became carbonate saturated as a result of dissolution of detrital carbonate massive recrystallization of glacially transported carbonate is proposed as a geologically significant process with considerable potential for palaeoenvironmental analysis in glacial lakes carbonate precipitated in response to evaporation or photosynthesis carbonate precipitation as the result of seawater freezing or in warm interglacial conditions is not yet established oxygen isotope value are inconsistent too heavy with the presence of high latitude meltwaters implying that glaciation extended to low latitudes as proposed by harland

reconstructing the transport history of glacigenic sediments a new approach based on the co variance of clast form indices abstract two indices are used to describe the aggregate shape and roundness characteristics of glacially transported clasts the c40 index the percentage of clasts with c a ratios 0 4 and the ra index the percentage of very angular and angular clasts in a sample analysis of the between and within sample co variance of these indices provides a powerful tool for discriminating actively and passively transported clasts in glacigenic deposits use of these indices is illustrated in an analysis of the form characteristics of clasts from lateral and frontal moraines at storbreen jotunheimen these fall between those of actively transported clasts in basal till low c40 and ra values and those of unmodified frost weathered clasts high c40 and ra values both indices decline down moraine within sample analyses of clast shape demonstrates that these aggregate clast form gradients reflect changes in the relative proportions of actively and passively transported debris on the moraines rather than progressive modification of actively transported clasts these analyses also indicate that actively transported clasts form the dominant component of the moraines particularly near the former glacier terminus further applications of the approach developed here are suggested

functional groups in a single pteridosperm species variability and circumscription pennsylvanian nova scotia canada abstract multiple foliar specimens of the late pennsylvanian fossil pteridosperm gymnosperm alethopteris zeilleri ragot wagner were collected from one restricted stratigraphical horizon in the canadian sydney coalfield variability of functional group distribution using ftir technique was studied in compressions adaxial versus abaxial cuticles and in unseparated cuticles as a function of maceration time from 48 to 168 h the results obtained document spectral variability that could be expected within specimens of one species for example ch 2 ch 3 and al ox ratios can differ by as much as 20 of the values moreover the experiments performed confirm that by using a previously established maceration protocol long maceration periods do not bias ftir spectra in terms of oxygenation overprinting the inference that this cuticle is robust under the given diagenetic level probably reflects a reassuring degree of chemical fidelity of the pennsylvanian plant to support carboniferous chemotaxonomic observations

subglacial till formation sedimentary characteristics and classification we review the major subglacial till forming processes as presently understood by glacial researchers and define the parameters within which tills are produced and reconcile them with sedimentary end members processes of deformation flow sliding lodgement and ploughing coexist at the base of temperate glacier ice and act to mobilize and transport sediment and deposit it as various end members ranging from glacitectonically folded and faulted stratified material to texturally homogeneous diamicton the dominance of any one subglacial process varies both spatially and temporally giving rise to the possibility that a till or complex till sequence contains a superimposed signature of former transportation deposition at the ice bed interface we recommend that while glacial geologists and geomorphologists should be able to recognize the sedimentary imprints of various subglacial processes genetic fingerprinting of subglacial tills should be less process specific and till classification must reflect the range of products encompassed by the subglacial till production continuum glacial geologists can presently unequivocally identify a glacitectonite rock or sediment that has been deformed by subglacial shearing deformation but retains some of the structural characteristics of the parent material b subglacial traction till sediment deposited by a glacier sole either sliding over and or deforming its bed the sediment having been released directly from the ice by pressure melting and or liberated from the substrate and then disaggregated and completely or largely homogenised by shearing and support the theoretical case for c melt out till sediment released by the melting of stagnant or slowly moving debris rich glacier ice and directly deposited without subsequent transport or deformation because observations on contemporary glaciers reveal that their beds are most likely to be mosaics of deformation and sliding and warm based and cold based conditions the patterns of which change temporally and spatially it is extremely unlikely that subglacial till end members in the geological record will be anything but hybrids produced by the range of processes operative in the subglacial traction zone

criteria to distinguish between subglacial glaciotectonic and glaciomarine sedimentation i deformation styles and sedimentology abstract this paper compares and contrasts the sedimentology and structural geology of a quaternary glaciomarine site melabakkar asbakkar iceland and a quaternary subglacial glaciotectonic site west runton uk research suggests that the glaciomarine environment is dominated by sedimentary processes related to sediment supply water content and distance from the glacier margin glaciotectonic deformation however is dominated by deformational processes related to effective pressure shear strain nature of the subglacial material and distance from the glacier margin from this study a series of criteria are suggested to distinguish both quaternary and contemporary glaciotectonic and glaciomarine environments in addition the paper also discusses the subsequent effects of glaciotectonic deformation on a primary glaciomarine site due to a glacial readvance

icesat observations of arctic sea ice a first look 1 analysis of near coincident icesat and radarsat imagery shows that the retrieved elevations from the laser altimeter are sensitive to new openings containing thin ice or open water in the sea ice cover as well as to surface relief of old and first year ice the precision of the elevation estimates measured over relatively flat sea ice is 2 cm using the thickness of thin ice in recent openings to estimate sea level references we obtain the sea ice freeboard along the altimeter tracks this step is necessitated by the large uncertainties in the sea surface topography compared to that required for accurate determination of freeboard unknown snow depth introduces the largest uncertainty in the conversion of freeboard to ice thickness surface roughness is also derived for the first time from the variability of successive elevation estimates along the altimeter track overall these icesat measurements provide an unprecedented view of the arctic ocean ice cover at length scales at and above the spatial dimension of the altimeter footprint of 70 m

geomorphology of sand dunes in the northeast taklimakan desert three types of sand dunes exist in the taklimakan desert namely compound complex crescent dunes and crescent chains compound dome dunes and compound complex linear dunes besides these three compound complex types single simple dunes are also distributed throughout the sand sea the compound complex linear dunes are developed under acute bimodal wind regimes though the ratios of the resultant drift potential rdp and the drift potential dp are the same as that near the border and adjacent area of the sand sea the compound complex crescent and dome dunes are developed respectively because of divergence of the sand available the stress of the sand moving winds and the time scales of dune formation the sand supply for the dunes is not from lopo nor in the east as previous studies suggested but mainly from local alluvial or lacustrine deposits the grain size component does not correlate evidently to the morphology parameters of the sand dunes analyses of the dp and drift direction suggest that the northeast taklimakan is an area of low wind energy and the resultant drift direction rdd coincides well with the distribution morphology and scales of the dunes

application of reflectance micro fourier transform infrared analysis to the study of coal macerals an example from the late jurassic to early cretaceous coals of the mist mountain formation british columbia canada abstract the applicability of the reflectance micro fourier transform infra red spectroscopy ftir technique for analyzing the distribution of functional groups in coal macerals is discussed high quality of spectra comparable to those obtained using other ftir techniques kbr pellet and transmission micro ftir indicate this technique can be applied to characterizing functional groups under most conditions the ease of sample preparation the potential to analyze large intact samples and ability to characterize organic matter in areas as small as 20 m are the main advantages of reflectance micro ftir the quantitative aspects of reflectance micro ftir require further study the exaples from the coal seams of the mist mountain formation british columbia show that at high volatile bituminous rank reflectance micro ftir provides valuable information on the character of aliphatic chains of vitrinite and liptinite macerals because the character of aliphatic chains influences bond disassociation energies such information is useful from a hydrocarbon generation viewpoint in medium volatile bituminous coal liptinite macerals are usually not detectable but this technique can be used to study the degree of oxidation and reactivity of vitrinite and semifusinite