fault slip bed length and area variations in experimental rollover anticlines over listric normal faults influence in extension and depth to detachment estimations abstract to check the behaviour of physical experiments of simple rollover anticlines over listric normal faults several fault slip bed length and area parameters are measured for different beds in two stages of evolution of two physical experiments given a certain amount of extension the heave and dip of the displacement vary for different beds whereas the throw is approximately constant for small amounts of extension and the displacement remains constant for high amounts of extension neither bed lengths nor areas beneath beds remain constant with increasing extension a number of techniques allow amounts of extension and detachment depth to be estimated given one or more marker horizons the portion of the fault between hanging wall and footwall cut off points the depth to detachment and or the shear angle these techniques are applied to the physical experiments of listric normal faults analysed since many of these techniques rely on parameters measured on the physical experiments such as fault slip bed length and area the influence of these parameters on the different magnitudes of extension and detachment depths estimated using different techniques is discussed and the accuracy of the results is compared

structures caused by repeated freezing and thawing in various loamy sediments a comparison of active fossil and experimental data in this paper the authors present the results of both macroscopic and microscopic investigations on structure development created by repeated ice lensing in various loamy experiments experimental data are compared with observations performed on active forms in high arctic and alpine mountain environments those observations are also compared with phenomena observed in fossil periglacial formations of western europe platy and short prismatic structure formation is bonded to the hydraulic and thermal conditions during ice segregation when a long series of alternating freezing and thawing affects platy structures the fabric evolves also being influenced by slope and drainage conditions cryoturbations frostcreep and gelifluction can appear they are characterized by specific microfabrics which are better developed with an increasing number of cycles this is clear in experiments where hydraulic and thermal parameters are better controlled vesicles are also a prominent characteristic of the surface horizon in experiments and arctic soils the genesis of vesicles is discussed on the basis of new observations and is related to the mechanical collapse of frost created aggregates under the mechanical work of soil air escape during soil saturation by water at thaw

using multiple logistic regression and gis technology to predict landslide hazard in northeast kansas usa abstract landslides in the hilly terrain along the kansas and missouri rivers in northeastern kansas have caused millions of dollars in property damage during the last decade to address this problem a statistical method called multiple logistic regression has been used to create a landslide hazard map for atchison kansas and surrounding areas data included digitized geology slopes and landslides manipulated using arcview gis logistic regression relates predictor variables to the occurrence or nonoccurrence of landslides within geographic cells and uses the relationship to produce a map showing the probability of future landslides given local slopes and geologic units results indicated that slope is the most important variable for estimating landslide hazard in the study area geologic units consisting mostly of shale siltstone and sandstone were most susceptible to landslides soil type and aspect ratio were considered but excluded from the final analysis because these variables did not significantly add to the predictive power of the logistic regression soil types were highly correlated with the geologic units and no significant relationships existed between landslides and slope aspect

the importance of small scale faulting in regional extension a recurring observation in many studies of extensional basins has been that the amount of extension visible on normal faults for example on seismic reflection profiles is significantly less than the amount of extension indicated by crustal thickness and thermal subsidence1 5 one mechanism suggested to account for this discrepancy is small scale faulting with offsets too small to be resolved seismically6 7 but earthquake studies8 10 indicate that small faults are responsible for only a small fraction of the total seismic moment in an active area scholz and cowie11 have recently attempted to extend this approach to the total strain at the end of a finite deformation interval by combining scaling laws describing the distributions of fault lengths and displacements here we present fault displacement data that directly conflict with scholz and cowie s conclusions and imply that up to 40 of the extension may be missed by summing fault offsets on basin profiles the fault population at the end of a long deformation interval may differ substantially from that responsible for the earthquake population at any one time

lithospheric structures and possible processes in phanerozoic eastern australia from deep seismic investigations abstract the eromanga basin in eastern australia developed during four major episodes on the rifted eastern margin of the australian precambrian craton seismic reflection profiling together with coincident wide angle reflection refraction profiling indicates structures and compositions in the crust which are dominant in various depth ranges some structural features seem to be limited to the upper crust other deep reflection events and high crustal velocities predominate in the lower crust with mafic intrusion from upper mantle sources being one preferred interpretation these features emphasize the difference in structures and composition between the upper and lower parts of the crust yet other structural and deep reflection features are interpreted as being truly lithospheric in scale because they seem to have seismic expression right from the surface to the upper mantle similar interpretations are made for other continental regions indicating that lithospheric processes affect different depth ranges of the crust and upper mantle in a variety of ways any modelling of such processes in the lithosphere must lead to these quite different end results at appropriate depth ranges

middle to late pleistocene loess record in eastern nebraska usa and implications for the unique nature of oxygen isotope stage 2 abstract new subsurface data reveal a nearly continuous stratigraphic record of middle to late pleistocene loess sedimentation preserved beneath upland summits in eastern nebraska usa thickness and grain size trends as well as pedologic evidence indicate significant changes in loess sources accumulation rates and depositional environments the newly defined kennard formation accumulated in the middle pleistocene and may represent multiple thin increments of distal loess from nonglacial sources on the great plains the overlying loveland loess up to 18 m thick and deposited during oxygen isotope stage 6 ois 6 illinoian glaciation probably records the emergence of the missouri river valley as a major glaciogenic loess source the prominent sangamon geosol formed through long term pedogenic alteration of the upper loveland loess during ois 5 and 4 thin loess of the gilman canyon formation records slow loess accumulation and pedogenic alteration in ois 3 the peoria loess ois 2 is similar in thickness to loveland loess but may have accumulated more rapidly in an environment less favorable to bioturbation more importantly comparison of peoria and loveland loess thickness trends indicates much greater influx of nonglaciogenic loess from the great plains during ois 2 than in ois 6 suggesting colder and or drier conditions in the midcontinent during ois 2 than in earlier glacial stages

tectonic deformation by rotating parallel faults the bookshelf mechanism abstract in various tectonic environments extension of crustal parts and shear distortion has been accommodated by the rotation of an array of parallel faults because of its kinematic resemblance to the tilting of a row of books on a shelf the tectonic process may be referred to as a bookshelf mechanism its most important manifestions are cross faulting between normal faults or parallel wrench faults the extension of deltaic slope deposits and all forms of tilted block tectonics kinematically there are two basic modes of the mechanism a the dilational mode where rotating faults tend to open up and possibly become paths for fluid migration and b the domino style where reclining faults remain closed in both cases formation and rotation of the faults may take place in one tectonic event fault displacements may therefore often remain small and difficult to detect from the mechanical point of view bookshelf operations that accommodate shearing between parallel and predominantly parallel moving rock boundaries bookshelf mechanisms proper have to be differentiated from those operations responding to an imposed crustal extension or shortening after a review of geological evidence the process is addressed from a geomechanical point of view in order to determine the geological operating conditions and controlling parameters the crucial mechanical factor in the bookshelf mechanism is the component of normal stress that acts in the direction of the imposed displacement component parallel to the driving boundary plates in contrast to the usual assumption the driving shear stress on the boundary plates not only depends on the normal stress on the plates but it also varies with the value of the normal stress that acts inside the sheared material in the direction of the plate parallel displacement component it is the relationship between the two normal stresses that also determines the type of rotating parallel faults large scale rotation of parallel normal faults in domino style tilted block tectonics is primarily associated with the extension of ductile substrata from mechanical arguments and sand box experiments it has been inferred how the process and in particular the dip direction of the parallel faults is controlled by the way substratal extension progresses by means of the direction of a substratal squeeze flow the presence of a surface slope the strength anisotropy associated with fore set beds and by the configuration of competent boundaries of the extending overburden

some comments on two layer extensional models for the evolution of sedimentary basins simple extensional models that involve listric faulting in the brittle upper crust and plastic flow in the lower lithosphere have been shown to account for the subsidence history of various continental sedimentary basins and continental shelves in this paper we present structural evidence that extension in the continental lithosphere during rifting is not uniform we review evidence that the rifting process in major intracratonic rift basins is spasmodic rather than continuous that extension and subsidence within the rift during a tectonic phase is generally accompanied by uplift and erosion of the rift flanks that subcrustal heat input during rifting occurs over an area much broader than the rift proper and that there may be broad regional uplift before and or during rifting to explain the uplift of the flanks during rifting and their postrift subsidence we invoke two mechanisms subcrustal thinning by extension below the flanks and tilted major normal faults in the crust between graben and flanks the uplift and erosion of the flanks due to tilted faults probably do not significantly affect estimates of extension from subsidence analysis but uplift due to both sources can in certain cases be incorrectly attributed to regional uplift or doming we present a simplified analysis of the two layer extensional model for the elementary case in which extension is instantaneous and the crust is thinned by a different amount from the subcrustal lithosphere we provide a simple graphical method of data analysis to obtain the parameters that describe thinning of the crust and lithosphere during extension from the subsidence history application of this method to the central part of the pattani trough in the intracratonic gulf of thailand shows that extension and thinning of the lithosphere of a factor of 2 since late eocene can account for much of the subsidence history and the present day heat flow our analysis suggests that thinning of the crust in this area is 20 greater than thinning of the whole lithosphere assuming that none of the lithosphere is removed from the region of extension during rifting we show by simple geometric examples that a process of nonuniform extension implies that much greater thicknesses of sediment can be deposited in the center of a young basin than in the case of uniform extension of both crust and subcrustal lithosphere such an extensional process produces significant uplift of the flanks of the rift and as a result of erosion of the uplifted areas the effective cross sectional area of the basin can be increased by as much as 10 20 depending on the rate of erosion compared to the area that would have been created by a process of uniform extension finally we show that it may ultimately be possible to compute erosion rates from seismic cross sections of basins

footwall uplift associated with late jurassic normal faulting in the northern north sea tilted fault blocks in the north sea show varying degrees of erosion such footwall erosion is predicted by the domino model of extension in which rigid fault blocks rotate as extension proceeds profiles of three north sea fields snorre brent and heather are analysed to estimate the amount of uplift that accompanied late jurassic normal faulting and these estimates are compared with the footwall uplift predicted by the domino model agreement between observed and predicted uplift is excellent varying from 1 km at snorre to c 100 m at heather for a given amount of extension large fault blocks tend to be bounded by large faults and to show a greater degree of erosion the brent province of the northern north sea is an area of prolific hydrocarbon discoveries almost all of the major oil fields occur in tilted fault blocks which were formed by late jurassic extension and subsequently buried by cretaceous tertiary thermal subsidence badley et al 1988 marsden et al 1990 the crests of the tilted blocks are typically eroded or degraded with varying amounts of middle lower jurassic and upper triassic section removed this footwall erosion is commonly ascribed in the literature to pre rifting doming ziegler 1982 heterogeneous stretching coward 1986 local transpression beach 1985 or even regional compression frost 1987 the purpose of this paper is to show that the uplift and degradation is a direct consequence of the late jurassic normal faulting and fault block rotation the degree of uplift is related in a simple way to the size across strike of

gis techniques and statistical models in evaluating landslide hazard geographical information systems gis and numerical cartography may greatly facilitate the development and use of statistical models for the assessment of regional landslide hazard from a small drainage basin located in central italy relevant geological and geomorphological factors were collected and processed by applying gis technology in particular modules were used which both generate high fidelity digital terrain models and automatically partition the terrain into main slope units the resulting information was then analysed by discriminant analysis which enabled landslide hazard and risk to be evaluated in each slope unit although not lacking drawbacks the method proved to be a feasible and cost effective approach to landslide susceptibility assessment and mapping

the roermond earthquake of 13 april 1992 the netherlands geological aspects the epicentre of the roermond earthquake is located near the western boundary fault of the roer valley trough one of the deepest and the most active in the quaternary part of the lower rhine graben the late pleistocene and holocene activity of the trough is manifested by offsets of the main mindel and the lower riss and late pleistocene terraces along the boundary faults surface fractures have been observed in an area of more than 50 km2 2 5 3 5 km to the north of the town of roermond at 0 8 km to the south of the village of herkenbosch and in the southeastern part of the village of montfort three types of ruptures were differentiated scarps up to 50 cm high along open fractures near the maas river open fractures continued by scarps in some places and open fractures with a liquefaction of the quaternary alluvium sands the last type is predominant the location of the ruptures depends on the landscape and water table of the region while they could be produced solely by hydraulic shock during the earthquake increased by the wet spring season the majority of the ruptures strike n50 w 10 i e parallel to the main trough faults or n55 e 10 along neotectonic lines parallel to the maas valley and deduced from space imagery thus the ruptures could be the secondary surficial effect of the earthquake linked indirectly with the active tectonics of the region

collision induced rifting the grenville orogeny and the keweenawan rift of north america abstract we propose that the keweenawan rift formed as a result of convergence related to the synchronous grenville orogeny this proposal is based on 1 1 isotopic ages in the keweenawan rift and the grenville province are similar according to the best u pb and rb sr dates the grenville orogeny existed from 1150 to 1100 ma and keweenawan rifting occurred 1120 1100 ma 2 2 a similar modern orogenic belt and rift relationship in the middle east serves as an actualistic model the red sea gulf of aden rift system has formed as a continuous series of coalesced pull apart basins and is opening parallel to the orogenic front of the zagros and bitlis mountains rifting began in the early miocene while the collision began in the eocene suggesting that rifting is related to the collision 3 3 many other ancient rift collision pairs have a similar age relationship and geometrical configuration based on comparisons of these tectonic regimes we have derived a model whereby these rifts formed as a result of strike slip faults forming in either the foreland or the hinterland of orogenic zones

climate and paleo environmental change within the mannheim formation near heidelberg upper rhine valley germany a case study based upon microsedimentological analyses abstract microsedimentological analyses were used to examine the first 56 m of a 500 m core near heidelberg germany in the upper rhine valley this core chronostratigraphically stretches from present day to 450 ka and includes proxy evidence supporting the presence of wurmian eemian and likely components of the riss and ho kirch stages the sediment in the core reflects the geomorphic biotic pedogenic and climatic processes the sediments were deposited in a fluvial environment at times within a broad floodplain in the main channel and also at other times some distance from the main river these upper sediments act as indirect proxy evidence that indicate changes in climate over time illustrative of cool periglacial tundra like conditions and of milder forested temperate environments from ho kirch to present day times within the sediments evidence can be found of an interglacial fossil soil followed later by a holocene temperate climate up to present day a strong link can be ascertained between macro and micro stratigraphic evidence the latter revealing detailed and invaluable sources of information this analysis permits the reconstruction of past climate and paleoenvironmental conditions the application of microsedimentological analyses to the mannheim formation reveals a store of data that has been largely hidden when using only macro sedimentological methods

formation of afterflow silt loam deposits and structural modification due to drying under warm conditions an experimental and micromorphological approach in earlier papers the authors discussed several micromorphological and textural characteristics of loamy afterflow deposits derived from loess material and formed during overland flow without splash this discussion is completed by considering the critical load concentrations ccr for the start of sedimentation taking into account the hydraulic properties of laminar flow furthermore a remarkable combination of clayey and medium coarse sandy laminae was observed in the deposits produced under laboratory conditions mechanisms are proposed to explain the affinity of these fractions for simultaneous deposition when laminated silt loam deposits are found in the pleniglacial middle loess deposits in the southern part of the netherlands or in the belgian hesbayan loess showing structural modifications for example cracks formed after sedimentation it is not always clear whether these modifications were the results of cold or relatively warm conditions this paper describes micromorphological and laboratory investigations aimed at identifying criteria representative of warm conditions the experiments examined the effect of drying on the structure of laminated silt loam deposits produced by afterflow and enabled the characterization of the modifications formed drying could be done at room temperature with circulating warm air or at temperatures below 0 c elsewhere see coutard and mucher 1985 the influence of drying at temperatures below 0 c on the structures of an afterflow silt loam deposit will be discussed in comparison with the deformation in laminated silt loam deposits due to freeze drying these new formations are small and have only locally influenced the sedimentary structures these structure modifications are formations of cracks dominantly in clay layers and less about 25 per cent of the cracks in very fine silt layers consisting of grains smaller than 10 m in diameter with only very locally deformations of the laminated structure only incidentally the cracks are partly refilled by a subsequent overland flow deposit mostly only followed by sealing of cracks only incidentally the cracks are partly refilled by a subsequent overland flow deposit mostly only followed by sealing of cracks curling or argillaceous laminae maximum 5 mm in upward direction only very locally formations of the tiny waved laminae with a vertical amplitude between 100 and 400 m in combination with the occurrence of vesicles

topographic effects on the seismic response of steep slopes a frequency domain parametric study using generalized consistent transmitting boundaries has been performed to evaluate the significance of topographic effects on the seismic response of steep slopes the results show that the peak amplification of motion at the crest of a slope occurs at a normalized frequency h 0 2 where h is the slope height and is the wavelength of the motion the importance of the natural site frequency is illustrated by the analysis of a stepped layer over a half space it was found that the natural frequency of the region behind the crest can dominate the response relative to the topographic effect for the conditions studied moreover the effect of topography can be handled separately from the amplification due to the natural frequency of the deposit behind the crest of the slope this concept of separating the amplification caused by topography from that caused by the natural frequency is advantageous to the development of a simplified method to estimate topographic effects

loess and palaeoenvironment some results of a european joint programme of research in 1985 a programme of research on the sedimentology and diagenesis of the loess and loessic silts of western europe was initiated jointly by laboratories in leicester meudon caen milan cardiff and southampton involving a limited amount of comparative work on the loess from types sites in the loess plateau of central china preliminary results include the following 1 experimental procedures in particle size analysis clay sample preparation and microscopy have been standardised in all cooperating groups distinctive fabrics indicative of depositional mechanisms have been recognised 2 comparison of aeolian colluvial and alluvial silt by laser scanning and bulk magnetic susceptibility anisotropy methods appears to differentiate aeolian silt from loessic silts re deposited by slope processes and flowing water 3 the variability in the anisotropy of the limon a doublet facies has been assessed by image analysis of scanning electron microscopy sem and optical microscopy strong anisotropy has also been measured in thin section imagery of loess from normandy and poland as the product of freezing and thawing this is confirmed by scanning electron microscopy and by experimental freezing of some silts 4 the clay fabric and mineralogy in western european loess differ from those in chinese loess especially in the case of semi arid deposits 5 distribution of caco3 using thin sections and sem analysis has been determined for loess from normandy and the rh ne valley in france and for some chinese loess at saint vallier zones of caco3 concentration occur masking much of the original loess sedimentary skeleton which is a locally reworked loessic silt with some laminations despite considerable scatter the palaeomagnetic results indicate a reversed polarity throughout placing the whole saint vallier sequence in the matuyama chron these preliminary results suggest the existence of two different palaeoenvironments one typified by central china with arid glacials and humid interglacials and the other represented by western europe with generally high humidities there was stronger weathering and soil development and fewer freezing effects on the lossic succession in northern italy than in western littoral europe

a rhaetian 40 ar 39 ar age for the rochechouart impact structure france and implications for the latest triassic sedimentary record ar 39 ar dating of potassium feldspar primary spherulitic blocky and secondary idiomorphic k feldspar separated from impact metamorphosed gneiss found near videix in the western central part of the rochechouart impact structure nw massif central france yielded a rhaetian combined age of 201 2 ma 2r indistinguishable within uncertainty from the age of the triassic jurassic boundary ballen quartz intergrown with the primary k feldspar indicates post shock temperatures exceeding approximately 1000 c that affected the precursor gneiss geochemically both feldspar types represent essentially pure potassium end members apart from the approximately 15 km diameter impact deposit area the youngest crystallization age known for basement rocks in this part of the massif central is approximately 300 ma no endogenic magmatic thermal events are known to have occurred later in this region the k feldspar recrystallized from local feldspar melts and superimposed post shock hydrothermal crystallization probably within some thousands of years after the impact it is therefore suggested that the 40 ar 39 ar age for the videix gneiss as a potassic impact metasomatite dates the rochechouart impact in consistence with evidence for k metasomatism in the rochechouart impactites the new age value is distinctly younger than the previously obtained karnian norian age for rochechouart and thus contradicts the late triassic multiple impact theory postulated some years ago in agreement with the paleogeographic conditions in the western tethys domain around the triassic jurassic boundary the near coastal to shallow marine rochechouart impact is compatible with the formation of seismites and tsunami deposits in the latest triassic of the british isles and possible related deposits in other parts of europe

niveo aeolian sedimentation of loess and sand an experimental and micromorphological approach the concept of a niveo aeolian influence on the genesis of northwest european pleistocene aeolian sand and loess deposits has been advocated in the past both to explain the presence and the absence of lamination field experiments were carried out on artificially deposited alternating layers of sand and snow and of loess and snow to investigate the role of a niveo aeolian mode of deposition on resulting sedimentary structures field observations of sand plots revealed minor changes in surface morphology typical of denivation surfaces the thin sections showed a characteristic porous structure deformations of the depositional structure and indications for erosion and redeposition were limited however the originally smooth aeolian sedimentary surface of the loess changed considerably the thin sections showed also a porous spongy structure indications were found for disturbances by frost action liquefaction during melting of the snow and ice and redeposition of loess by meltwater the experimental results strongly suggest that sand and loess deposited as niveo aeolian material are characterized both by a porous structure and that the original sedimentary structure of the sand is not affected by snowmelt whereas loess becomes non laminated thus the intercalation of snow during sedimentation of sand and loess does not in itself induce a laminated structure

vistulian loess deposits in western poland and their palaeoenvironmental implications the loess deposits of western poland are a periglacial facies having been deposited in the plenivistulian so far western poland is the onlypart of the countryin which vistulian loess deposits occurring as small patches on di erent glacial and glacio uvial landfoms have been found the diagnostic features of these sediments provide a tool for the sub division of the main lithofacies loess deposits occur in two main lithofacies massive loess lm and laminated loess ll there are three sub lithofacies within the laminated loess cryptolaminated sl laminated loess sensu stricto ll and banded loess sm loess lithofacies are associated with a varied topographyand are distributed in the end moraines till plains and outwash plains there is a signi cant correlation with the periglacial zone and aeolian processes active during the vistulian in western poland 2001 elsevier science ltd and inqua all rights reserved

a micromorphological and chemical study of a buried saalian till deposit in the northern part of the netherlands abstract macro and micromorphological characteristics as well as textural chemical and mineralogical properties of a reddish brown saalian till deposit covered by a 50 cm aeolian sand layer are discussed morphological observations show an interaction between pedogenetic processes and frost effects the glacial origin of the till resulted in a very dense fabric mechanical action of ice lense growth has further enhanced this compaction the occurrence of alternating freezing and thawing conditions was indicated by sorted platy structures superimposed on these frost effects and therefore younger are features of biological activity brunification and clay illuviation these originated from interglacial pedogenesis under more temperate conditions the occurrence of an aeolian deposit on top of the till indicated a subsequent cold and dry period disrupted clay illuviation coatings in the 2btg horizon and the absence of these clay coatins in situ in a network of frost cracks and sandy involutions in the 2btg horizon provide evidence of more recent periglacial conditions silt and impure clay coatings dominantly present in frost cracks are typical sorting and accumulation products due to micro erosion enhanced by snow meltwater under cold conditions surface water gley features like iron and manganese compounds overlay periglacial structures and clay illuviation and are therefore younger ferrolysis occurring predominantly in the e horizon and in frost fissures favoured textural heterogeneity of the soil

unraveling multiple thermotectonic events accommodated by crustal scale faults in northern iberia spain insights from k ar dating of clay gouges

geodynamic evolution of the proterozoic mount isa terrain the proterozoic mount isa terrain records the effects of four periods of intraplate tectonism the c 1870 ma barramundi orogeny was characterized by a massive felsic magmatic event and global correlations suggest a physical link between australia and laurentia at this time thereafter the terrain underwent an extensional history spanning 200 ma involving repeated episoded of rifting post rift subsidence and associated depositional and magmatic phases this protracted rifting history resulted in a cumulative stratigraphic thickness of up to 25km above attenuated continental crust rifting was interrupted prior to the formation of ocean crust by the compressional isan orogeny 1590 1500 ma the isan orogeny was synchronous with low pressure high temperature metamorphism and widespread metasomatism in the waning stages of shortening the mount isa terrain evolved into a wrench system characterized by an extensive network of strike slip faults the current level of exposure in this terrain provides spectacular examples of superimposed rifts basin inversion and wrench geometries developed at middle to upper crustal levels

diagenesis of ferriferous phases in the northampton ironstone in the cowthick quarry near corby england berthierine siderite and pyrite are the major ferriferous phases in the northampton ironstone nis mineralogical and chemical data suggest a formation of these phases in a diagenetic marine environment changing from post oxic to sulphidic conditions berthierine was formed first when the fe 2 activity in the diagenetic system increased later this phase was partially replaced by siderite and or pyrite a second stage of the diagenetic development in the nis with increasing co 2 partial pressure p co 2 is documented by siderite the isotopic composition 18 o mean value 1 7 pdb 13 c mean value 8 6 pdb points to siderite precipitation from a marine porewater environment with a microbial co 2 source the shift from post oxic to sulphidic conditions is indicated by the occurrence of pyrite and can be considered as a final stage the diagenetic processes in the marine environment and the formation of the ferriferous phases were stopped by the influx of brackish or fresh water when the midland shelf turned estuarine

inversion tectonics and magnetic fabrics in mesozoic basins of the western tethys a review abstract positive tectonic inversion of sedimentary basins has been recognized as one of the primary mechanisms of mountain building and intraplate deformation reconstructing the tectonic history of basins is relatively easy for the inversion stage but becomes more difficult for the basinal stage especially when strong deformation involving cleavage development is associated with the subsequent compressional tectonics since tectonic markers for the extensional episodes are not commonly well developed anisotropy of magnetic susceptibility ams has provided recently a tool for analyzing early stages in the evolution of sedimentary basins even in the absence of other outcrop scale mesostructures here we expose and discuss the applicability of magnetic fabrics by means of ams to different types of intra plate sedimentary basins in the western tethys region formed under extensional or transtensional regimes and which underwent different inversion styles total or partial inversion with or without cleavage development forming part of compressional thrust sheets etc owing to specific particular p t conditions and structural controls factors such as lithology magnetic mineralogy position within the sedimentary pile and deformation intensity are key to interpret the obtained magnetic fabrics in terms of tectonic evolution a basin classification is proposed according to inversion styles and magnetic fabrics where inversion did not involve cleavage development magnetic lineation is parallel to the stretching direction corresponding to the extensional stage the transition between non cleaved to inversion related cleaved units is marked by the switch of magnetic lineations from parallel to extension to parallel to the intersection lineation between cleavage and bedding these relationships are enhanced when extension and compression are roughly coaxial then favoring the clustering of axes of the magnetic ellipsoid even when extreme inversion occurs and the early extensional fabric is obliterated magnetic fabrics provide information about the interaction between preferred deformation directions associated with the main stages in basin evolution

palaeozoic mesozoic and contemporaneous megaspores from the tertiary of southern england indicators of sedimentary provenance and ancient vegetation megaspores are recorded from several localities in the thanet and reading beds upper palaeocene of southern england evidence from their taxonomic affinity colour compression and state of preservation indicates three separate groups two reworked from lower westphalian coal measures and lower cretaceous sequences respectively and one of contemporaneous forms mesozoic megaspores redeposited in the british tertiary have not previously been recorded isolated carboniferous forms have been found before but their possible value in provenance studies has not been fully explored the new material includes a diverse assemblage of numerous westphalian and lower cretaceous forms from a single horizon in the thanet beds of possible source areas it seems most likely that these spores were reworked from the moray firth basin and elsewhere near the present eastern coast of scotland by means of longshore drift following a roughly n s palaeocoastline evidence from other studies of heavy mineral assemblages and palaeogeography also indicates derivation of thanet beds sediments by this means the cenozoic megaspores include an azolla water fern and two distinct lycopsid forms one probably of selaginellalean and one of isoetalean affinity these latter provide the first clear evidence of lycopsids in british tertiary floras and expand our knowledge of freshwater macrophytes of that time the assemblages of minerisporites show morphological trends which may prove to be of biostratigraphic value

deformation of laminated silt loam due to repeated freezing and thawing cycles the effect of repeated freezing and thawing cycles on an experimentally produced laminated silt loam was studied with the purpose of obtaining more insight into the genesis of macro and microstructures observed in the loessic formations of northwestern europe the laminated silt loam was subsequently subjected to 18 cycles of alternate freezing and thawing the minimum temperature recorded after 11 days of frost was 7 c at a depth of 5 cm and 4 c at 29 cm the underlying sediments compact loam except its upper part and sand always remained unfrozen the experiment reproduced a seasonal superficially frozen ground new structures and microfabrics in the form of vesicles platy structures shear planes and micro undulations were created by ice segregation and thawing mechanical stress and subsequent frost creep the impact of the freezing and thawing cycles is very strong all the laminae being deformed or broken judging by the abundance and the diversity of the structures created freezing is a more important process than simple drying without frost as is evidenced by the range in temperature chosen for the experiment and the low number of cycles these structures do not necessarily require severe climatic conditions to develop unlike frost cracks or ice wedge casts they could develop in winter conditions similar to those present today in the french southern alps

gis modelling of slope stability in phewa tal watershed nepal abstract hazards are an inherent but dangerous and costly element of mountainous environments conventional maps of mountain hazards provide useful inventories of hazardous sites but provide little insight into the operation of the hazards furthermore this approach tends to rely heavily on subjective interpretation of the landscape which means that the results can not be replicated or transferred to other areas thus alternative approaches employing the quantitative capabilities of geographic information systems gis to model and predict slope stability are receiving increasing attention this paper reports on the use of a diverse gis database compiled primarily from existing maps and aerial photographs to construct a regional model of slope stability in phewa tal watershed nepal an integral part of the research was to explore an alternative approach to the commonly used grid cell approach by employing geomorphometrically significant terrain units the terrain units employed were created by generating line networks representing local maxima and minima extracted from elevation and curvature surfaces one of the chief benefits of applying gis technology in this research was the ability to georeference all of the attribute data to these terrain units in doing so it allowed the database to be exported into an external statistical package where the terrain units could be statistically explored as the basic analytical unit the application of a variety of statistical techniques resulted in logistic regression being selected as the most useful logistic regression successfully predicted terrain units as being either stable or unstable at a rate of approximately 90 concordance with a conventionally produced map of slope stability the statistical probabilities of terrain unit stability were imported back into the gis to produce a map of predicted slope stability that compared well with the conventional map of slope stability the findings of this research suggest that the use of geomorphometrically significant terrain units extracted from a digital elevation model dem are an efficient alternative to approaches using regular grid cells in particular the terrain units facilitated the use of logistic regression and significantly decreased the amount of computing costs finally this research also suggests that important information can be gathered from existing information sources such as maps aerial photographs and written documents thereby limiting the need for costly and time consuming field work at the reconnaissance level based on this latter finding other information sources such as satellite imagery should be examined

the micromorphology of paraglacial and periglacial slope deposits a case study from morfa bychan west wales uk micromorphological analysis of the crudely stratified diamictons exposed in coastal sections at morfa bychan west wales is presented and discussed three major units yellow head blue head and brown head have been recognised and their crudely stratified nature plus clast orientations indicate that they were all subject to mass movement down the flanks of the adjacent coastal hills earlier workers have suggested a periglacial environment for this mass movement but recently it has been proposed that the blue head at least may have accumulated in a paraglacial environment through gravitational redistribution of recently deposited unstable till it is shown here that the yellow head contains occasional dense silt rich coatings on the upper surfaces of sand and gravel grains although other cryogenic micromorphological phenomena were not observed the blue head however contains no clear cryogenic micromorphological features although there is abundant evidence for sediment shearing and grain rotation within the matrix the brown head contains diffuse grain coatings and lenticular aggregates very similar to those observed elsewhere in periglacial solifluction deposits thus it is concluded that accumulation of the blue head was rapid and took place in a paraglacial environment as a result of mudflow the yellow head may represent periglacial solifluction immediately prior to glaciation whereas the brown head accumulated above the blue head as a result of periglacial weathering of the adjacent exposed hill tops and subsequent downslope solifluction of the weathering product 1998 john wiley sons ltd

crustal structure of the celtic sea and western approaches from gravity data and deep seismic profiles constraints on the formation of continental basins a free air anomaly map of the celtic sea and the western approaches is presented including all available marine gravimetric data and bouguer anomalies on land n60 features are predominant in the area they correspond to the n60 so called caledonian grain which played a major role in the variscan orogeny and in the formation of the permo triassic sedimentary basins the fundamental new point which comes out from this gravimetric map is the existence of a closely spaced pattern of n105 features which we regard as late carboniferous transpressional structures in the eastern pan of the celtic sea thrusts are in the same n105 direction west of 6 w longitude however folds and thrusts trend preferentially in a n60 direction following the older grain there the n105 lineaments may be regarded as dextral shear structures with a possible compressive component the hercynian shortening of the celtic sea domain located between the variscan front and the lizard suture resulted from the displacement along the n160 direction of the two adjacent rigid domains north of the variscan front the n105 and n135 features were possibly active in more recent times then both the n60 and n105 trends controlled the formation of permo triassic basins the n105 directions being transfer faults two dimensional gravity modelling of the swat profiles in the celtic sea shows that the base of the reflective lower crust may be associated with the moho discontinuity everywhere in the celtic sea except below the saint george s channel basin the lower crust does not change significantly in depth and thickness beneath the permo triassic basins none of the available models simply satisfies such conditions they all require at least a modification of the geometry of the lower crust after the formation of the celtic sea basins nevertheless if the simple shear model can be ruled out mainly from structural arguments the uniform stretching and to a lesser degree the thermomechanical models seem to be more relevant models however two additional conditions are necessary 1 the preservation of crustal seismic features formed before the creation of basins must be explained and 2 a significant portion of the volume of the stretched lower crust about 40 of this volume for the north celtic sea basin must be added below or perhaps partly above the lower crust by lateral flow of the crust or at the expense of the upper mantle

devonian carboniferous sedimentary evolution of the clair area offshore north western uk impact of changing provenance abstract the clair group was deposited in a devonian carboniferous rift basin at the edge of the present day north west european shelf west of the shetland islands the west shetland basin in which the clair area lies therefore provides the most westerly record of devonian carboniferous environments in northern britain and allows comparison with the orcadian basin to the east palaeogeographical time slices are presented based on sedimentological studies of core electrical logs and heavy mineral assemblages the basin underwent two cycles of increasing endorheism internal drainage in a devonian continental rift followed by a cycle of increasing humidity as high sinuosity streams were succeeded by marginal marine environments in the carboniferous the two lower cycles of increasing endorheism are separated from the upper cycle by an important field wide unconformity this stratigraphic break is accompanied by a major change in provenance from small intra rift drainage networks and deserts depositing polycyclic minerals to much enlarged drainage systems transporting first cycle unstable minerals from catchments reaching far beyond the devonian rift

seventeen years of the la clapiere landslide evolution analysed from ortho rectified aerial photographs we present a new method of digital elevation model dem calculation from aerial photographs and apply this method to the la clapiere landslide in the mercantour massif in eastern france the method uses new techniques of image correlation and of restitution of camera parameters the calculated dems are used to ortho rectify three aerial photographs acquired between 1983 and 1999 measurements made from these ortho rectified images show that the average velocity of the landslide was of 1 7 cm day with the rate of the headscarp retreat of 4 1 cm day and the toe of the landslide advancing at 1 7 cm day between 1983 and 1999 within the landslide the velocity field is are relatively homogeneous although their directions are locally heterogeneous scree slopes and scarps develop in an heterogeneous way within the landslide because the headscarp moves faster than the front of the landslide material spreads laterally at the scree slopes and or is eroded at the front of the landslide by the river and or is accumulated within the landslide on a low slope area located above a competent bar called igliere bar d 2002 elsevier science b v all rights reserved

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

permo carboniferous climate early pennsylvanian to late permian climate development of central europe in a regional and global context a well justified stratigraphical correlation of continental successions and new palaeogeographic reconstruction of pangaea reveal new insights into the northern pangaean climate development influenced by palaeogeography palaeotopography glacio eustatic sealevel changes and ocean currents the overall permo carboniferous aridization trend was interrupted by five wet phases these are linked to the gondwana icecap the aridization and weakening of wet phases over time were not only caused by the drift of northern pangaea to the arid climatic belt but also by the successive closure of the rheic ocean which caused the expansion of arid semi arid environments in the lower middle permian the end of the gondwana glaciation rearranged ocean circulation leading to a cold coast parallel ocean current west of northern pangaea blocking moisture coming with westerly winds the maximum of aridity was reached during the roadian wordian the trans pangaean mountain belt was non existent its single diachronous parts never exceeded an average elevation of 2000 m the maximum elevation shifted during time from east to west the hercynian orogen never acted as an orographic east west barrier and the inter tropical convergence zone was widely displaced causing four seasons dry summer winter wet spring autumn at the equator and a strong monsoon system the climate history of the european realm during the late carboniferous pennsylvanian and permian is stored in many solitary basins fig 1 within the hercynian orogen and the foreland basin the story of westphalian climate is well known because of the numerous investigations of the coal bearing variscan foredeep the younger westphalian is characterized by a slight aridization abbink van kronijnenburgvan cittert 2003 oplustil 2004 which was accompanied by an increase of seasonality nevertheless the environment was strongly influenced by the ocean and epi continental seas with multiple transgression events the last extensive marine ingression was the aegir mansfield band westphalian b c the post westphalian climate development is more differentiated and

intraplate lithosphere deformation and the strength of the lithosphere summary the intraplate deformation of continental lithosphere in response to applied stress has been investigated using a mathematical model which incorporates the elastic ductile and brittle response of lithosphere material ductile deformation is assumed to be controlled in the crust by dislocation creep in quartz and in the mantle by dislocation creep and plasticity in olivine brittle failure is predicted using modified griffith theory a fundamental feature of the model is the redistribution of stress within the lithosphere following stress release by both ductile and brittle deformation this redistribution produces high levels of stress in the middle or lower crust immediately above the elastic ductile or brittle ductile transition lithosphere deformation is shown to be critically dependent on the temperature structure of which surface heat flow is a convenient indicator for higher geothermal gradients the release of stress in the lower lithosphere by ductile deformation is more rapid and complete and results in large stress levels in the upper lithosphere for sufficiently large applied stresses or steep geothermal gradients the stress levels in the upper and middle crust will cause complete fracture of the upper lithosphere whole lithosphere failure wlf then results by continued brittle and ductile deformation causing geologically significant strains the critical value of applied stress required to give wlf has been calculated for both tensional and compressional deformation as a function of surface heat flow the predicted lithosphere bulk strength is then compared with expected levels of intraplate stress arising from plate boundary forces and isostatically compensated loads which are thought to give net stress levels in the continental lithosphere in the range 0 25 to 0 25 kb using these expected maximum stress levels the model predicts significant extensional deformation in regions of moderate heat flow with q c 60mwm e g central europe as well as for areas of high heat flow like the basinand range province significant compressional deformation is predicted for areas of high heat flow with q c 75 mwm 2 but only for restricted conditions of stress combination these results are in good agreement with

tectonic evolution of the north sea basin crustal stretching and subsidence summary the lithospheric stretching model for the formation of sedimentary basins was tested in the central north sea by a combined study of crustal thinning and basement subsidence patterns a profile of crustal structure was obtained by shooting a long range seismic experiment across the central graben the main axis of subsidence a seabed array of 12 seismometers in the graben was used to record shots fired in a line 530 km long across the basin the data collected during the experiment were interpreted by modelling synthetic seismograms from a laterally varying structure and the final model showed substantial crustal thinning beneath the graben subsidence data from 19 exploration wells were analysed to obtain subsidence patterns in the central north sea since jurassic times changes in water depth were quantified using foraminiferal assemblages where possible and observed basement subsidence paths were corrected for sediment loading compaction and changes in water depth through time the seismic model is shown to be compatible with the observed gravity field and the small size of observed gravity anomalies is used to argue that the basin is in local isostatic equilibrium both crustal thinning and basement subsidence studies indicate about 70 km of stretching across the central graben during the mid jurassic to early cretaceous extensional event this extension appears to have occurred over crust already slightly thinned beneath the graben and the seismic data suggest that total extension since the early permian may have been more than 100km the data presented here may all be explained using a simple model of uniform extension of the lithosphere

basin analysis predictions of known hydrocarbon occurrences the north sea viking graben as a test case abstract basin analysis can assimilate structural burial and thermal histories to predict hydrocarbon prone zones in speculative areas the validity of the modelling approach was field tested in the north sea viking graben an area for which good data are available a recent birps deep seismic reflection profile across tectonic strike of the graben was interpreted and depth converted with good well control the burial and structural histories were determined by backstripping the chronostratigraphic layers using a one dimensional fluid flow compaction model on pseudo wells after removal of each sequence the section was manually reconstructed the thermal history was examined using thermal indicator tomography extensional models and calculations of depth to detachment lack of resolution required that three different paleo heat flow trends be tested to encompass the range in variability a gradual warming trend a constant heat flow through time and a low heat flow until the cretaceous tertiary boundary where a heat pulse occurred basement subsidence extension depth to detachment calculations and thermal indicator inversions all suggest that the uk side of the graben has developed differently to the norwegian section the generation modelling predicts the position of the oil window in the cross section the areas where this window enveloped the draupne formation kimmeridge clay source rock broadly correlate with the positions of the gullfaks statfjord and thistle oilfields of the uk sector however in the norwegian sector the draupne formation was generally overmature except in the area around the troll oilfield predicted middle to late cretaceous generation in the rift axis may have caused updip oil migration towards the horda platform the correct prediction of oil prone zones validates the use of quantitative basin analysis as a tool for evaluating frontier areas where data are limited

shear angle and amount of extension calculations for normal faults emanating from a detachment implications on mechanisms to generate rollovers abstract the reconstruction restoration modelling of normal faults both listric and planar emanating from a detachment at depth and their associated rollover folds using the vertical or inclined shear method is widely utilized because its simplicity and the information it can provide however it has a rather serious issue derived from the uncertainty about the shear angle the type of shear and the amount of extension that should be employed in each situation here we describe a new methodology that using easily acquired input data allows estimation of whether the shear was vertical antithetic or synthetic and the values for both the shear dip and the amount of extension these calculations rely on the use of graphs of throw versus heave for different horizons affected by the normal fault and the associated rollover and are checked using an area based method which permits the determination of whether these values are correct these graphs may be used as a predictive tool or as a guide to show how the assumptions deviate such as distinguishing quickly whether other mechanisms apart from vertical inclined shear took place the effects of syn extension sedimentation and reverse fault reactivation on the proposed method are also examined the analysis of experimental and natural examples shows that the initiation of some rollovers with a component of fault propagation and or drag folding and or development of a crestal collapse graben cause the estimated shear dips to be smaller than the actual values and the amounts of extension to be greater in addition these analyses show that the shear dip may increase with increasing extension

a two level concept of plate tectonics application to geodynamics abstract a two level plate tectonics concept is developed on the basis of data on lithosphere rheological stratification this approach differentiates between crust and subcrust plate ensembles separated by a lower crust viscoplastic asthenolayer similarly to classical plate tectonics three types of boundaries are distinguished in the lower layer which do not always coincide with crust plate boundaries especially for continents applications of this concept to geodynamics are considered and a corresponding quantitative analysis for several important processes is carried out a quantitative model of mountain formation and collision plateau origins is proposed also a geodynamic model of the evolution of passive margins taking into account a lower crust viscous flow is considered and its geological consequences are discussed a mechanism of rifting taking into consideration rheological lithospheric layering and its vertical movements caused by extension is developed both a qualitative scheme and quantitative analysis of the slow evolution of intracraton structures of shield basin type taking into account erosion and sedimentation processes are worked through also historical aspects of plate tectonics are discussed from the point of view of the proposed concept

dependence of stress state on the histories of burial erosion mechanical properties pore pressure and faulting abstract most onshore basins have experienced one or more phases of burial and erosion the geomechanical evolution of simplified and idealised fault bounded mudrock basins on crystalline basement subject to burial and erosion cycles is examined numerically the changes in strains and stress state and the displacements including bedding slip which occur with changes of the overlying load are tracked changes of mechanical properties to represent diagenesis are included development of the widely reported high horizontal normal stresses results from the changes of vertical load and does not rely directly on applied horizontal tectonic shortening strains lateral gradients of normal stress associated with faults are described the final basin stress state is related to the magnitudes of the burial and erosion diagenetic or otherwise changes of mechanical properties and pore pressure changes during burial and at depth the magnitudes of the horizontal stress developed for the 1 km and 2 km burial and erosion cycles tested here exceed the magnitude of the vertical stress for a range of depths extending downwards from the surface unless the horizontal stress is reduced at shallow depths by failure during erosion bedding shear instability during erosion around faults and otherwise may influence the response to engineering disturbance

faulting and graben formation in western and central europe rifts and rift related basins play a pre eminent role among the sedimentary basins of western and central europe through time grabens developed in a number of different megatectonic settings whereby the principal mechanisms governing their subsidence was crustal stretching and subcrustal erosion the level of volcanic activity associated with rifting is highly variable and can change significantly during the development history of a rift some rifts are totally non volcanic the development of rift domes is generally associated with volcanic activity uplifting of a rift dome can induce a reversal in the subsidence pattern of a rift intracontinental rifts with their thinned crust are prone to inversion when the respective craton is subjected to tangential stresses in the process of inversion the crust of rifts is mechanically thickened again

the application of gis based logistic regression for landslide susceptibility mapping in the kakuda yahiko mountains central japan as a first step forward in regional hazard management multivariate statistical analysis in the form of logistic regression was used to produce a landslide susceptibility map in the kakuda yahiko mountains of central japan there are different methods to prepare landslide susceptibility maps the use of logistic regression in this study stemmed not only from the fact that this approach relaxes the strict assumptions required by other multivariate statistical methods but also to demonstrate that it can be combined with bivariate statistical analyses bsa to simplify the interpretation of the model obtained at the end in susceptibility mapping the use of logistic regression is to find the best fitting function to describe the relationship between the presence or absence of landslides dependent variable and a set of independent parameters such as slope angle and lithology here an inventory map of 87 landslides was used to produce a dependent variable which takes a value of 0 for the absence and 1 for the presence of slope failures lithology bed rock slope relationship lineaments slope gradient aspect elevation and road network were taken as independent parameters the effect of each parameter on landslide occurrence was assessed from the corresponding coefficient that appears in the logistic regression function the interpretations of the coefficients showed that road network plays a major role in determining landslide occurrence and distribution among the geomorphological parameters aspect and slope gradient have a more significant contribution than elevation although field observations showed that the latter is a good estimator of the approximate location of slope cuts using a predicted map of probability the study area was classified into five categories of landslide susceptibility extremely low very low low medium and high the medium and high susceptibility zones make up 8 87 of the total study area and involve mid altitude slopes in the eastern part of kakuda mountain and the central and southern parts of yahiko mountain

assessment of landslide susceptibility on the natural terrain of lantau island hong kong steep terrain and the high frequency of tropical rainstorms make landslide occurrence on natural terrain a common phenomenon in hong kong for example more than 800 slope failures were triggered by a rainstorm in november 1993 on lantau island hong kong maps of recent landslides interpreted from aerial photographs in combination with a geographical information system were used to evaluate the frequency and distribution of landslides with particular reference to such physical parameters as lithology slope gradient slope aspect elevation vegetation cover and proximity to drainage line all of which are considered to be influential in the occurrence of landslides a stepwise logistic regression model was obtained between landslide susceptibility and the above mentioned physical parameters the study area has been classified into five classes of relative landslide susceptibility namely very low low moderate high and very high based on this methodology

susceptibility assessment of earthquake triggered landslides in el salvador using logistic regression abstract this work has evaluated the probability of earthquake triggered landslide occurrence in the whole of el salvador with a geographic information system gis and a logistic regression model slope gradient elevation aspect mean annual precipitation lithology land use and terrain roughness are the predictor variables used to determine the dependent variable of occurrence or non occurrence of landslides within an individual grid cell the results illustrate the importance of terrain roughness and soil type as key factors within the model using only these two variables the analysis returned a significance level of 89 4 the results obtained from the model within the gis were then used to produce a map of relative landslide susceptibility

correlation between fragipans and permafrost with special reference to silty weichselian deposits in belgium and northern france abstract a comparison is made between the properties of permafrost and those of fragipans the permafrost characteristics are summarized from published data on active permafrost and from personal observations on fossil permafrost the study of the fragipans mainly concerns the silty sediments of weichselian age which occur in belgium and northern france the distribution and the physical macromorphological and micromorphological properties of fragipans can all satisfactorely be explained by the growth of segregated ice during permafrost aggradation particularly striking is the relationship of both permafrost and fragipans to drainage conditions the quantity of segregated ice is highest in moist or poorly drained soil and it is at such places that the best developed fragipans are observed certain arguments that can be stated against the hypothesis of fragipan genesis by permafrost are discussed 1 the development of a platy structure by freeze thaw or by wet dry cycles 2 the discontinuous distribution of the fragipan 3 the development of the fragipan by pedogenetic weathering and migration processes it is concluded that only the permafrost hypothesis can explain the complete set of properties of the fragipan

a spatiotemporal probabilistic modelling of storm induced shallow landsliding using aerial photographs and logistic regression landslides constitute one of the major natural hazards that could cause significant losses of life and property mapping or delineating areas prone to landsliding is therefore essential for land use activities and management decision making in hilly or mountainous regions a landslide hazard map can be constructed by a qualitative combination of maps of site conditions including geology topography and geomorphology by statistical methods through correlating landslide occurrence with geologic and geomorphic factors or by using safety factors from stability analysis a landslide hazard map should provide information on both the spatial and temporal probabilities of landsliding in a certain area however most previous studies have focused on susceptibility mapping rather than on hazard mapping in a spatiotemporal context this study aims at developing a predictive model based on both quasi static and dynamic variables to determine the probability of landsliding in terms of space and time the study area selected is about 13 km 2 in north lantau hong kong the source areas of the landslides caused by the rainstorms of 18 july 1992 and 4 5 november 1993 were interpreted from multi temporal aerial photographs landslide data lithology digital elevation model data land cover and rainfall data were digitized into a geographic information system database a logistic regression model was developed using lithology slope gradient slope aspect elevation slope shape land cover and rolling 24 it rainfall as independent variables since the dependent variable could be expressed in a dichotomous way this model achieved an overall accuracy of 87 2 with 89 5 of landslide grid cells correctly classified and found to be performing satisfactorily the model was then applied to rainfalls of a variety of periods of return to predict the probability of landsliding on natural slopes in space and time it is observed that the modelling techniques described here are useful for predicting the spatiotemporal probability of landsliding and can be used by land use planners to develop effective management strategies copyright 0 2003 john wiley sons ltd

prediction of landslide susceptibility using rare events logistic regression a case study in the flemish ardennes belgium abstract in this article a statistical multivariate method i e rare events logistic regression is evaluated for the creation of a landslide susceptibility map in a 200 km2 study area of the flemish ardennes belgium the methodology is based on the hypothesis that future landslides will have the same causal factors as the landslides initiated in the past the information on the past landslides comes from a landslide inventory map obtained by detailed field surveys and by the analysis of lidar light detection and ranging derived hillshade maps information on the causal factors e g slope gradient aspect lithology and soil drainage was extracted from digital elevation models derived from lidar and from topographical lithological and soil maps in landslide affected areas however we did not use the present day hillslope gradient in order to reflect the hillslope condition prior to landsliding the pre landslide hillslope was reconstructed and its gradient was used in the analysis because of their limited spatial occurrence the landslides in the study area can be regarded as rare events rare events logistic regression differs from ordinary logistic regression because it takes into account the low proportion of 1s landslides to 0s no landslides in the study area by incorporating three correction measures the endogenous stratified sampling of the dataset the prior correction of the intercept and the correction of the probabilities to include the estimation uncertainty for the study area significant model results were obtained with pre landslide hillslope gradient and three different clayey lithologies being important predictor variables receiver operating characteristic roc curves and the kappa index were used to validate the model both show a good agreement between the observed and predicted values of the validation dataset based on a qualified judgement the created landslide susceptibility map was classified into four classes i e very high high moderate and low susceptibility if interpreted correctly this classified susceptibility map is an important tool for the delineation of zones where prevention measures are needed and human interference should be limited in order to avoid property damage due to landslides

the opening of the atlantic the mesozoic new england igneous province and mechanisms of continental breakup abstract plume and tensionally induced rifting models have been proposed as causes of continental rifting and breakup mantle plumes should produce early lithospheric doming events associated with alkaline magmatism however the triassic alkaline rocks on the east north american e n a margin are structurally localized the uplifts are mostly jurassic in age and voluminous plateau magmatism post dates the initiation of taphrogenesis by 10 to 20 ma in addition there are no chains of anorogenic igneous rocks leading to any of the postulated triassic plumes these facts argue against the plume generated rifting model for the e n a margin but are consistent with the predicted effects of the tensionally induced rifting model the genesis of linear chains of alkaline rocks has been attributed to passage of a lithospheric plate over a mantle plume this explanation has been proposed for the cretaceous monteregian and white mountain intrusive series and the kelvin seamount chain however these rocks are distributed along structurally controlled e w trending lineaments the monteregians are localized by the presence of a paleorift ottawa bonnechere graben in the underlying grenvillian basement and the kelvin seamounts are emplaced along the early jurassic kelvin fracture zone the structures localizing the southern white mountain lineament are less well defined the spatial temporal and geochemical relationships along and between these lineaments are consistent with an origin as a southeastward propagating tensional event the intra plate stresses are probably the result of shifts in the pole of rotation of the north american plate due to irregular northward extensions of seafloor spreading during the cretaceous

weathering mantles and their significance for geomorphological evolution of central and northern europe since the mesozoic abstract weathering mantles saprolites are very widespread in central western and northern europe where they form thick near surface residual deposits often in excess of 50 m they vary in the type of weathering the bedrock lithology involved the topographic setting and the age and stratigraphic context this review paper provides information about the distribution and major characteristics of weathering mantles from a number of key areas including the british isles the central european belt of mid mountains and uplands the scandinavian mountains and the fennoscandian shield it also examines the evidence for weathering etched origin of various landforms including boulders tors inselbergs basins and some regional landforms assemblages major types of regionally important weathering mantles include ferrallitic lateritic saprolites kaolinite rich saprolites sandy to grus mantles and various residuals left after partial dissolution of carbonate rocks although dating of weathering mantles is often circumstantial it appears sufficiently precise to argue for various ages of deep weathering mesozoic pre late cretaceous mantles are particularly widespread but there are also early tertiary and miocene saprolites widely present whilst most grus weathering is likely to be of miocene to pleistocene age individual upland areas have been subjected to multiple episodes of weathering whose legacy is the present day co existence of different weathering products continental and shallow marine deposits around the uplands particularly in the north sea and intra continental graben structures are often dominated by quartz and kaolinite pointing to deeply weathered land surfaces as the source areas and extending the record of weathering on the geological time scale they demonstrate that weathering mantles repeatedly formed and were subjected to erosion and new cycles of weathering were initiated we suggest that deep unroofing of basement structures in many parts of europe has been mainly accomplished by deep weathering and stripping of pre weathered rock the phenomenon of deep weathering has been very important for geomorphology etched landforms vary in size from small residual boulders up to regional characteristic landscapes etchsurfaces such as joint valley landscapes of southern sweden or undulating multi convex and multi concave landscapes of many uplands in central europe deep weathering has played a major part in the geomorphological evolution of europe since at least the late triassic and the concept involving long term etching and stripping provides an appropriate framework to describe and explain both erosional landscapes and sediment features

permian climate development in the northern peri tethys area the lodeve basin french massif central compared in a european and global context abstract the lodeve basin which contains an exceptional long and nearly uninterrupted profile of early to late permian continental red beds is well correlated to the other european permocarboniferous basins together they cover the time span from the late pennsylvanian to the permian triassic boundary although these basins were placed within the equatorial belt for the whole permian several climatic changes are recorded in the sediments terrestrial sedimentation is governed by the interaction of climate and tectonics as well as by volcanism to a variable degree therefore small scale climatic variations of the milankovitch band are hardly discernable and if so they could not be correlated between different basins indeed larger scale climatic shifts could be identified it is shown that the shift from the carboniferous icehouse to the mesozoic warmhouse was a multi stage process this global warming resulted in a general aridisation of northern pangea indicated by outspreading playa and sabkha red beds aeolianites and evaporites several short phases of increased humidity interrupted this trend indicated by wet red beds lake sediments and coal deposits in central and southern europe these wet periods are traceable within the late stephanian lower rotliegend gzhelian asselian topmost lower rotliegend asselian sakmarian upper rotliegend i late artinskian early kungurian and upper rotliegend ii zechstein wuchiapingian the aridisation of the northern pangea which accelerated near the sakmarian artinskian transition is attributed to a reorganisation of the major ocean currents cold water currents along the western flank of the pangea indicated by the permian chert event blocks moisture transport from west onto the continent during roadian and wordian the onset of an additional cold water current along the cimmerian continents blocks moisture transport from the east both phenomena together are responsible for the maximum of aridity at the early to middle permian transition additionally the equatorial climate has been affected by an increasing seasonality within the late pennsylvanian and permian caused by the wide shifting of the zone of inter tropical convergence itc over the equator based on a new reconstruction of the pangean assembly in this paper climatic changes in the permian are interpreted and causes of the arid humid arid shifts are examined phases of higher humidity are often related to events of global impact like the waxing and waning of the gondwanan glaciation obtained in the south african karoo basin dwyka group but also regional events had strong climatic influence the zechstein transgression in the northern and southern permian basin as well as the bellerophon transgression of the southern alps caused the wet phase in the wuchiapingian

a consistency index and rainwash mechanisms on belgian loamy soils the effects of soil crusting in belgium are particularly conspicuous on the loamy plateaus and hill regions of southern flanders brabant and hesbaye field observations made at the end of rainy winter seasons permitted the making of a simple distinction between a stable soils showing crusting on less than 50 per cent of their total surface without any evident slope wash and b unstable soils crusting over more than 50 per cent of the total surface with evident rainwash and basal colluviation the atterberg limits have been examined for both soil types it was found that the upslope part of the liquid limit curves in the range of low consistencies high water contents is steeper for stable than for unstable soils so a distinctive consistency index c2 10 was deduced from the liquid limit curves which may be used for prediction of the relative sensitivity of topsoils for crusting stable well structured clods are more hydrophobic than unstable material this was made clear by wettability tests under a rain simulator therefore more water must be added to remolded stable material to lower its consistency as is shown by the liquid limit curves crustability decreases and c5 10 values increase with increasing clay and organic matter contents as one would expect stable soils are well aggregated but rain simulator tests also showed that the detachment of this material by raindrop impact is high therefore crumbs and clods of stable soils are relatively more sensitive to splash erosion their erosion results from the ejection of stable aggregates clods of unstable topsoils are compacted and flattened by raindrop impact which causes internal liquefaction micromorphological analysis indicates that typical stable topsoils originate from well structured ap horizons and from bt horizons of grey brown podzolic soils alfisols laminated silt and mudcrust fragments characterize unstable topsoils which originate at least partly from slopewash deposits the external stability of both stable and unstable clods is increased by compaction and by surficial concentration of gravel coarse sands root and other plant fragments thin sections of unstable material show the internal collapse of structures due to liquefaction a clear distinction must be made between the structural stability and the erodability of topsoils

structural styles and basin evolution in eromanga region eastern australia the eromanga region of eastern australia has undergone at least four major tectonic cycles the results of which are recognized in the structures seen on seismic sections the late proterozoic early phanerozoic cycle ended with the formation of the thomson foldbelt which forms basement in the region the subsequent reactivations of the fault systems within this basement and deeper lithosphere have produced the structural styles now important as exploration targets most reactivations are interpreted as resulting from crustal shortening events affecting sedimentary strata deposited in an epicontinental shallow water environment with small strike slip adjustments affecting some structures the dominant style of deformation evident from the seismic sections is that seen across high angle thrust faults in other parts of the world with the amount of overthrusting being comparatively small generally the maximum throw on faults in the devonian strata can be measured in thousands of meters whereas those in the permian triassic and jurassic cretaceous strata are a few hundred meters at most the devonian sequences of the adavale basin and associated troughs were deformed during two carboniferous events the first with crustal shortening in a north south direction and the second in an east west direction associated small strike slip movements were accommodated along a number of faults including the warrego grenfield warbreccan and canaway faults southwest of our study area in the permian triassic cooper basin other workers have interpreted a northwest southeast crustal shortening event during the late permian and another wrench induced northeast southwest crustal shortening during the triassic during the middle tertiary a crustal shortening event regionally affected the jurassic cretaceous eromanga basin sequence and older sedimentary rocks this event is seen pro inently in a deformation zone between the canaway and cunnavalla faults with the direction of crustal shortening being northeast southwest small strike slip movements are interpreted as partially decoupling events from neighboring provinces the adavale basin and cheepie shelf to the east and southeast and the cooper basin and warbreccan dome to the southwest and northwest respectively in this partial decoupling the canaway cunnavalla warrego and warbreccan faults are interpreted as playing an important role the basin modifying tectonic episodes within the lithosphere control structural style these relatively small scale events have resulted in structures that provide attractive petroleum prospects

a possible mechanism for epeirogenic uplift continental geology is dominated by vertical movements some of these are the result of crustal shortening and extension associated with large horizontal displacements involving processes which are now understood at least in outline however both uplift and subsidence can occur without associated shortening or extension of the continental crust most investigations of such epeirogenic movements have been concerned with subsidence partly because of the economic importance of the resulting sedimentary basins and partly because of the existence of a simple model for the process1 which can account for the development of several basins in some detail2 4 however uplift has been relatively neglected and cannot be produced by the same mechanism the purpose of this paper is to examine whether epeirogenic uplift can result from the intrusion of large thicknesses of basic magma into the lower part of continental crust this suggestion was considered as a possible mechanism for the regional uplift of the colorado plateau by gilbert5 more than 100 years ago and also by holmes6 though both rejected the idea however a recent discussion of no less than 14 different mechanisms for generating uplift7 did not include this process even though it seems able to produce the observed vertical motions and also to account for some of the features of the evolution of sedimentary basins that cannot be explained by the uniform stretching model3 8 9 although the suggestion is not new the argument used here to support it is and depends on an understanding of the relationship between ocean island volcanoes and mantle circulation

the hydrological response of soil surfaces to rainfall as affected by cover and position of rock fragments in the top layer rainfall experiments have been conducted in the laboratory in order to assess the hydrological response of top soils very susceptible to surface sealing and containing rock fragments in different positions with respect to the soil surface for a given cover level rock fragment position in the top soil has an ambivalent effect on water intake and runoff generation compared to a bare soil surface rock fragments increase water intake rates as well as time of runoff concentration and decrease runoff volume if they rest on the soil surface for the same cover level rock fragments reduce infiltration rate and enhance runoff generation if they are well embedded in the top layer the effects of rock fragment position on infiltration rate and runoff generation are proportional to cover percentage micromorphological analysis and measurements of the saturated hydraulic conductivity of bare top soils and of the top layer underneath rock fragments resting on the soil surface reveal significant differences supporting the mechanism proposed by poesen 1986 i e runoff generated as rock flow or as horton overland flow can partly infiltrate into the unsealed soil surface under the rock fragments provided that they are not completely embedded in the top layer hence rock fragment position beside other rock fragment properties should be taken into account when assessing the hydrological response of soils susceptible to surface sealing and containing rock fragments in their surface layers a simple model based on the proportions of bare soil surface soil surface occupied by embedded rock fragments and soil surface covered with rock fragments resting on the soil surface describes the runoff coefficient data relatively well

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

statistical analysis of landslide susceptibility at yongin korea the aim of this study is to evaluate the susceptibility of landslides at yongin korea using a geographic information system gis landslide locations were identified in the yongin area from interpretation of aerial photographs field surveys and maps of the topography soil type timber cover and geology these data were collected and constructed into a spatial database using gis the factors that influence landslide occurrence such as slope aspect and curvature of topography were calculated from the topographic database texture material drainage and effective soil thickness were extracted from the soil database and type age diameter and density of timber were extracted from the forest database lithology was extracted from the geological database and land use was classified from the landsat tm satellite image landslide susceptibility was analyzed using the landslide occurrence factors by probability and logistic regression methods the results of the analysis were verified using the landslide location data the validation results showed satisfactory agreement between the susceptibility map and the existing data on landslide location the gis was used to analyze the vast amount of data efficiently and statistical programs were used to maintain specificity and accuracy the results can be used to reduce associated hazards and to plan land use and construction

recognition and palaeoclimatic implications of late quaternary niche glaciation in eastern lesotho geomorphic evidence of former glaciation in the high drakensberg of southern africa has proven controversial with conflicting glacial and non glacial interpretations suggested for many landforms this paper presents new geomorphological sedimentological and micromorphological data and glacier mass balance modelling for a site in the leqooa valley eastern lesotho preserving what are considered to be moraines of a former niche glacier that existed during the last glacial maximum lgm the geomorphology and macro sedimentology of the deposits display characteristics of both active and passive transport by glacial processes however micromorphological analyses indicate a more complex history of glacial deposition and subsequent reworking by mass movement processes the application of a glacier reconstruction technique to determine whether this site could have supported a glacier indicates a reconstructed glacier equilibrium line altitude ela of 3136 m a s l and palaeoglacier mass balance characteristics comparable with modern analogues reflecting viable if marginal glaciation radiocarbon dates obtained from organic sediment within the moraines indicate that these are of lgm age the reconstructed palaeoclimatic conditions during the lgm suggest that snow accumulation in the drakensberg was significantly higher than considered by other studies and has substantial relevance for tuning regional climate models for southern africa during the last glacial cycle copyright 2009 john wiley sons ltd

effects of strain gradients on asymmetry of experimental normal fault systems abstract sandbox experiments were carried out to investigate the influence of horizontal strain gradients on the asymmetry of normal fault systems in regions of crustal extension during the experiments faults facing in the direction of higher strain were preferentially developed the results show that the horizontal strain gradient is an important factor in controlling the asymmetry of normal fault systems the experiments also relate the degree of asymmetry to the horizontal strain gradient the results may be applicable to the formation of asymmetric normal fault systems on either side of the axes of mid oceanic ridges extensional back arc regions and continental rifts

evolution of permafrost on the qinghai xizang tibet plateau since the end of the late pleistocene 1 the present distribution of permafrost on the qinghai xizang tibet plateau qtp is largely a relict of the permafrost formed during the late pleistocene it has been degrading and shrinking in areal extent under the fluctuating climates with a general trend of warming during the holocene the major criteria for the occurrence of relict permafrost include the remnants of ancient buried permafrost relict permafrost tables thawed sandwiches taliks thick layered ground ice and periglacial phenomena such as pingo scars cryoturbations primary sand and clayey silt wedges ice wedge casts aeolian sand dunes and loesses thick layers of peat and humic soils on the basis of 14c dating of soils comprehensive analyses and comparisons of the spatiotemporal distribution of relict and modern permafrost and periglacial phenomena the evolution of permafrost and periglacial environments since the late pleistocene was divided into seven stages 1 the cold period at the end of the late pleistocene 35 000 to 10 800 years b p 2 the period of significant climatic change during the early holocene 10 800 to 8500 7000 years b p 3 the megathermal period in the middle holocene 8500 7000 to 4000 3000 years b p 4 the cold period in the late holocene 4000 3000 to 1000 years b p 5 the warm period in the later holocene 1000 to 500 years b p 6 the little ice age 500 to 100 years b p and 7 the recent warming period 100 years b p to present the conditions for permafrost development distribution and the paleoclimates and paleoenvironments are discussed for each stage

a multidisciplinary approach to the evaluation of the mechanism that triggered the cerda landslide sicily italy abstract the present paper describes a multidisciplinary approach to the evaluation of a seismically triggered landslide that occurred in the cerda area italy on september 6 2002 about 1 h after an earthquake took place in the south tyrrhenian sea the study was focused on an analysis of the role of the seismic input in triggering the landslide in view of the evidence that no other mass movement was recorded in the adjacent areas despite geological and geomorphological spatial homogeneity the studied area is located on a slope of the western flank of the fiume imera settentrionale northern sicily which is made up of clayey arenitic rocks the slope inclines gently but is not uniform due to fluvial gravitative and rainwash processes field data dealing with global positioning system gps geology geomorphology geophysics vertical electrical sounding or ves and geochemistry soil gas fluxes and composition were acquired and analysed in order to investigate the cause effect relationships between the earthquake and the mass movement the gps survey allowed us to map the ground failures that have also been classified on the basis of their kinematical meaning i e compressive distensive or transcurrent structures the geological analysis revealed outcropping rocks and tectonic structures the geomorphologic survey highlighted the presence of preexisting landslide bodies the geophysical survey detected a buried surface located at a depth of about 100 m finally the geochemical survey showed that the gas released from the displaced mass came from a shallow depth and was not related to any active fault system the abovementioned information allowed us to interpret the landslide event as a partial reactivation of a preexisting landslide body that was triggered by the earthquake

frost and soils implications for paleosols paleoclimates and stratigraphy abstract frost is a pedogenetic agent this paper describes the use of frost features in soil for paleoclimatic and stratigraphic interpretation it is possible to differentiate periods of frost activity from those of temperate pedogenesis by macroscopic and microscopic criteria and to distinguish between soils with pre syn and epigenetic frost effects an experimental approach is necessary to determine initial frost effects because they are usually difficult to observe at natural active sites work with ecologists also clarifies the evolution of frost affected soils under climatic and vegetational constraints vegetation has important effects on the thermal and hydraulic regimes of soils and on erosion susceptibility the recognition of fossil cryosoils often allows the reconstruction of sequences of paleoclimatic events in periods or environments with little or no micropaleontological evidence the interrelations between frost and other pedogenetic processes allow a better understanding of climatic evolution and deterioration throughout the neogene and especially during the quaternary and the holocene most of the inherited frost features in european soils are younger than 480 ka bp the differentiation between frost and tectonic perturbations is very important for calculation of soil erosional budgets