imprints of himalayan thrust tectonics on the quaternary piedmont sediments of the neora jaldhaka valley darjeeling sikkim sub himalayas india abstract geological mapping in the neora jaldhaka valley of the darjeeling sikkim sub himalayan foothill region reveals the presence of discontinuous strands of tectonically active quaternary thrust faults the zones of active faulting coincide with occurrences of deeply incised piedmont deposits and river terraces along an e w trending corridor in order of younging the successive quaternary thrust faults delineated are the gorubathan matiali and chalsa thrusts unequivocal geological evidence of surface rupture faulting however is noted only along the gorubathan thrust where the precambrian daling group of rocks is thrust over the quaternary piedmont sediments along a low northerly dipping plane the presence of deformational features in the quaternary sediments such as anticlines bending moment faults and back tilting of both the piedmont and the incising river terraces along active fault scarps are interpreted to signify the presence of north dipping blind thrusts below the matiali and chalsa scarps radiocarbon dates of organic rich clay components indicate that the gorubathan thrust post dated 33 875 550 ybp and the lower bound age of the chalsa thrust is 22 030 130 ybp successive foreland ward development of these active strands and the increasing spacing between the successive thrust traces are interpreted to be due to foreland propagating blind thrusts of the himalayan ftb fold and thrust belt in the sub himalayan terrain evidences of backthrust movement are also presented along the thaljhora north fault the segmented and variable geometry of these thrusts imply that the mft main frontal thrust is still in its early stage of growth and the lateral linkages between the active fault strands are yet to be established

plant and insect fossils at norwood in south central minnesota a record of late glacial succession abstract the norwood site in sibley co minnesota contains 1 6 m of silt resting on till and overlain by peat the base of the peat has been radiocarbon dated at 12 400 60 and the top at 11 200 250 yr b p the pollen plant macrofossils and insect remains in the basal silt consist of boreal species inhabiting open environments but not tundra no modern analogue exists for the insect assemblage which includes elements of boreal forest tundra forest and western affinities the transition from an unstable open environment to a stable coniferous forest is reflected by both plant and insect fossils and is interpreted as a successional rather than a climatic event during this time of significant biologic change the climate is inferred to have been relatively uniform with temperatures similar to those presently existing in the boreal forest south of the tundra forest transition zone the geologic and ecologic succession at norwood is generally similar to that presently associated with ice stagnation of the klutlan glacier in the yukon territory localized successional sequences similar to those at norwood are conceived to have occurred repeatedly during the melting of the laurentide ice and thus the proposed model has potentially broad application to the interpretation of late glacial sequences

a model of late quaternary landscape development in the delaware valley new jersey and pennsylvania abstract in the delaware valley of new jersey and eastern pennsylvania the late quaternary history of colluviation fluvial adjustment and soil formation is based on the ages of pre wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid latitude climate changes indicated by marine oxygen isotope records the area is divided into four terranes characterized by sandstone gneiss slate and carbonate rocks since the last pre wisconsinan glaciation 130 ka inferred to be late illinoian each terrane responded differently to chemical and mechanical weathering during the sangamon interglacial stage 130 75 ka in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep highly weathered soil and saprolite and dissolution of carbonate rocks cold climatic conditions during the wisconsinan on the other hand induced erosion of the landscape at rates faster than soil development upland erosion during the wisconsinan removed pre wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium grezes litees and alluvial fans on footslopes fluvial gravel and overlying colluvium in the delaware valley both buried by late wisconsinan outwash are inferred to represent episodes of early and middle wisconsinan 75 25 ka upland erosion and river aggradiation followed by river degradation and colluvium deposition early middle wisconsinan colluvium is more voluminous than later colluvium despite colder possibly permafrost conditions during the late wisconsinan 25 10 ka extensive colluviation during the early and middle wisconsinan resulted from a longer 50 kyr generally cold interval of erosion with a greater availability of easily eroded pre wisconsinan surficial materials on uplands than during the late wisconsinan after recession of late wisconsinan ice from its terminal position soil formation and landscape stability were delayed until the holocene by a lingering cold climate slope erosion colluvium and alluvial fan deposition and eolian sedimentation late quaternary erosion in the delaware valley was dominated by glacial and periglacial processes during glacial stages during the warm interglacial stages soils developed on a more stable landscape these souls were easily colluviated by periglacial erosion during periods of intermittent cold climate

a full glacial biota from southeastern iowa usa wisconsinan full glacial silts filling a swale exposed in conklin quarry johnson co iowa contain a large and diverse biota that includes pollen bryophytes vascular plant macrofossils small mammals molluscs and insects radiocarbon dates on wood from the top middle and bottom of the swale fill respectively were 16710 270 17 170 205 and 18090 190 yr bp the pollen diagram is dominated by picea spruce pinus pine and cyperaceae sedge and it records low pollen accumulation rates plant macrofossils include a number of tundra species along with picea and larix larch needles and small pieces of wood the insect fauna contains many species now confined to the forest tundra transition zone of northwestern yukon and alaska small mammals include the tundra indicators dicrostonyx collared lemming and probably microtus miurus singing vole together with boreal forest taxa the molluscs include extinct and relict species and show the widest range in present geographic distribution but rocky mountain and especially northern elements predominate in the swale fill all these lines of evidence lead to consistent palaeoclimato logical interpretation and palaeoecological reconstruction the dominant habitats represented by the biota and sedimentary environment collectively included open calcareous silty to sandy or gravelly upland sites minerotrophic fens wetlands pond or stream side clayey to sandy shores and shallow possibly ephemeral cold clear water ponds mean july temperatures were probably 11 to 13 c cooler than at present the biota indicates that a picea larix krummholz with extensive tundra openings was present in southeastern iowa between 18090 and 16710 yr bp

application of geomorphic indices to address the foreland himalayan tectonics and landform deformation matiali chalsa baradighi recess west bengal india abstract in the himalayan foreland basin of the tista jaldhaka system of north bengal the presence of main boundary thrust mbt and himalayan frontal thrust hft along an e w direction has been reanalysed in the context of tectonic instability especially along the 17 93 km stretch of the kurti river it is a small rain fed stream that originated in the piedmont zone near the samsing scarp lineament trending e w this work discusses in detail the control of active matiali chalsa and baradighi faults that has been determined by the river morphometric aspects deformed landform as terraces and the valley incision mechanism over time we document not only the fault scarps as mbt near matiali and hft near chalsa but also decipher the baradighi fault as a local manifestation of tectonism with well exposed scarps a ramp anticline synformal zone i exists between the northernmost part of the matiali scarp mbt and towards the south near the chalsa scarp hft however to the south of chalsa lies another depression zone synformal zone ii that extends up to the baradighi scarp exposed in the left eastern side of kurti river changes in geomorphic indices such as long profile analysis drainage basin asymmetry hypsometric curve valley floor width to height ratio vfwh concavity index transverse topographic symmetry factor and sinuosity index along the kurti river have been evaluated uplift erosion cycle with valley incision between the mbt hft and hft baradighi fault scarp connotes that the foreland tectonics emerged to be the recent evolutionary phases in the tecto morphological study

the selection of sites for paleovegetational studies the judicious selection of sites for paleovegetational and paleoclimatic studies permits paleoecologists to answer specific research questions that go beyond primary descriptions of past vegetation we present a model that describes the relationship between basin size and pollen source area and predicts the proportions of local extralocal and regional pollen sampled by lake basins of different size the distinctive sampling properties of lakes peats and small hollows can be exploited to provide details of pattern in paleovegetation so long as attention is given to the limitations and problems of these types of sites combinations of site types in a single study most fully exploit the information contained in sediments

glacial and nonglacial sediment contributions to wisconsin episode loess in the central united states the relative contributions of various glacial and nonglacial sediments to wisconsin episode loess units along the lower illinois and central mississippi valleys are estimated on the basis of a comparison of magnetic susceptibility and silt and clay mineralogy a mathematical method of source area calculation using four compositional parameters was guided by current knowledge of the regional glacial history on the basis of this technique the roxana silt along the illinois and mississippi river valleys is composed of significant superior lobe sediment 35 40 as well as wadena or des moines lobe sediment about 35 this can account for its high magnetic susceptibility feldspar content kaolinite content and pink hue lower peoria silt contains about 25 35 lake michigan lobe sediment with reduced contributions of the other sources after the mississippi river s diversion 20 4 ka the supply of superior des moines and wadena lobe sediment was cut off from the illinois valley in favor of lake michigan lobe sediment 75 80 contribution this major source area shift accounts for higher dolomite and illite contents and a more yellow hue in approximately the upper two thirds of peoria silt in the study area in loess south of st louis less pronounced compositional shifts occur because superior lobe sediment was not cut off and because des moines lobe wadena lobe and missouri river sediments having more intermediate composition compose 40 50 of the loess thereby diluting other source area changes nonglacial sediment from fluvial and periglacial sources is estimated to compose 10 40 of loess in both regions

the geometry and kinematics of the main boundary thrust and related neotectonics in the darjiling himalayan fold and thrust belt west bengal india abstract the main boundary thrust mbt is well exposed in a section of the tista river valley in the darjiling himalayan fold and thrust belt the fault trace trends e w across the n s flowing tista and thrusts gondwana permian age sandstones over lower siwalik miocene age sandstones the mbt has been folded into a fault propagation synform antiform pair by tectonic activity along a younger south kalijhora thrust skt in its footwall that transports lower siwalik rocks over middle siwalik sandstones the skt cuts through the fault propagation structure preserving the mbt fault propagation fold pair in its hanging wall the motion along the skt rotated the bedding and the limbs of the folded mbt in its hanging wall footwall imbrication in front of the skt further rotated the folded mbt footwall imbrication continued to about 30 km south of the study area in the middle siwalik and younger section the region has been subsequently reactivated as evident from uplifted gravel beds and strath terraces along the folded trace of the mbt fault zone and also in the footwall of the skt the reactivation resulted in the formation of connective splays off the existing faults probably forming horses of a connecting splay duplex in the sub surface within the siwalik section the motion along these splays passively folded overlying beds and formed uplifted gravel beds and strath terraces along the local drainage the rotations resulting from footwall imbrication and reactivated splays probably caused the southern limb of the fault propagation synform to become overturned the duplexing also raised the river bed and arrested the flow of the river tista causing the river to pond and deposit its load resulting in the formation of a bar upstream of the mbt trace the tectonic reactivation of the area points to taper building activities in a subcritical wedge probably in response to monsoon induced excessive erosion in the middle of the darjiling sikkim tibet himalayan thrust wedge

seismotectonic model of the sikkim himalaya constraint from microearthquake surveys the seismotectonic model in the sikkim himalaya does not fit well with the proposed steady state or evolutionary models the main boundary thrust mbt is seismogenic and is a mantle reaching fault the earthquakes are not confined to shallower depths 25 km above the plane of detachment as proposed in the models the seismic activity continues from surface to the lower crust 0 45 km to the north of mbt and earthquakes are produced by a thrust mechanism the earthquakes to the east of sikkim in the bhutan himalaya on the other hand are produced along a 200 km long northwest southeast trending lineament by transverse tectonics the seismogenic lineament cuts across the himalayan major thrusts and extends to the goalpara wedge in the southeast the earthquakes occur by strike slip mechanism in the midcrust at a depth range of 10 25 km along this long active lineament

reappraisal of the upper weichselian periglacial environment from danish frost wedge casts abstract in ditches dug for the oil and gas pipe line systems in jutland in 1983 many frost wedge casts were recorded sand wedge casts composite wedge casts and ice wedge casts were all common these phenomena indicate the former existence of continuous permafrost probably during the period of advance and presence of the weichselian ice cap the changes of environment which took place during the colder parts of the weichselian may have promoted relatively unstable soil surface and vegetation conditions when compared to present arctic areas where frost wedges form today it is suggested that even though primary sand infilling in wedges was common in denmark the climate need not have been very arid for their formation and further the environmental conditions in europe during the last ice age can not be readily compared with present arctic regions where frost wedges grow today

paleobiology of the sand beneath the valders diamicton at valders wisconsin abstract previously undescribed pollen plant macrofossils molluscs and ostracodes were recovered from a 2 5 m thick glaciolacustrine unit of silty sand and clay at valders wisconsin the interstadial sediment was deposited about 12 200 14 c yr b p after retreat of the green bay lobe that deposited diamicton of the horicon formation and before advance of the lake michigan lobe that deposited the red brown diamicton of the valders member of the kewaunee formation fluctuations of abundance of candona subtriangulata cytherissa lacustris and three other species define four ostracode biozones in the lower 1 7 m suggesting an open lake environment that oscillated in depth and proximity to glacial ice pollen is dominated by picea and artemisia but the low percentages of many other types of long distance origin suggest that the terrestrial vegetation was open and far from the forest border the upper part of the sediment a massive sand deposited in either a shallow pond or a sluggish stream contains a local concentration of plant macrofossils the interpretation of a cold open environment is supported by the plant macrofossils of more than 20 species dominated by those of open mineral soils arenaria rubella cerastium alpinum type silene acaulis sibbaldia procumbens dryas integrifolia vaccinium uliginosum var alpinum armeria maritima etc that in north america occur largely in the tundra and open tundra forest ecotone of northern canada ice wedge casts occur in the sand

sedimentologic evidence for outburst floods from the laurentide ice sheet margin in wisconsin usa implications for tunnel channel formation abstract clast supported boulder gravel in outwash fans along the glacial maximum margin of the laurentide ice sheet in wisconsin indicates the occurrence of outburst floods these sediments with clast intermediate axes of up to 2 m are located downstream of tunnel channels and were deposited shortly before cessation of glaciofluvial activity on each fan since tunnel channels with fans are widespread along the ice sheet margin in the western great lakes region these outburst floods were probably common paleodischarge estimates derived from the boulder deposits are poorly constrained but values of at least several hundred m3 s 1 are likely four potential water sources for the floods exist an extreme surface melt event an extreme precipitation event drainage of supraglacial lakes or drainage of stored subglacial meltwater we focus on the storage of subglacial meltwater behind the ice sheet margin as proglacial permafrost was present as ice advanced to its maximum extent and a frozen bed zone upstream from the margin probably impeded drainage through groundwater aquifers decay of this permafrost seal would have eventually allowed trapped water to drain through the tunnel channels we suggest that the 2 m boulders were entrained in an outburst of subglacial water that enlarged a pre existing channel cut by ablation derived flows

ideas about the surface runoff features on mars in their report evidence of recent groundwater seepage and surface runoff on mars 30 june p 2330 1 malin and edgett propose that the seepage and flow of water may have occurred on mars in the recent geologic past on the basis of the observation of a large number of channel features on

glacial landsystems and dynamics of the saginaw lobe of the laurentide ice sheet michigan usa the surficial terrain of the saginaw lobe in southern michigan is divided into 4 landsystems numbered sequentially from southwest to northeast containing related assemblages of sediments and landforms two of which appear to have a genetic relationship with the bedrock units over which they lie landsystem 1 consists of the sturgis moraine a terminal recessional moraine and an adjacent drumlin field the moraine is a high relief ridge with hummocky topography and ice walled lake plains at its crest and thick coarse outwash fans on its distal margin the drumlin field extends up glacier from the sturgis moraine across the subcrop of the mississippian coldwater shale to the subcrop of the overlying marshall sandstone the low permeability of the shale may have increased basal pore pressures into a range in which deformation of basal sediment into drumlins occurred landsystem 2 overlies the subcrop of the marshall sandstone stagnation of the lobe behind a discontinuous moraine in this area is indicated by high relief collapse topography composed of kames eskers and ice walled lake plains a system of tunnel valleys terminates and merges in this landsystem with large outwash fans and plains sloping away from the margin high basal drainage into the sandstone may have facilitated stagnation across a broad area to form this landsystem landsystem 3 may have also developed during stagnation of the lobe but it differs from landsystem 2 by its more subdued relief it contains a network of evenly spaced southwest trending open tunnel valleys that contain discontinuous esker segments landsystem 4 consists of till plains and low recessional moraines formed as the saginaw lobe retreated downslope into saginaw bay of the lake huron basin tunnel valleys are absent in this area

fracture networks in frozen ground fractures in frozen ground self organize into networks through interactions between sequentially emplaced fractures tensile stress and the developing fracture pattern from this viewpoint we model the development of networks on a lattice representing the ground surface on which fractures initiate propagate and arrest under a combination of uniform thermally induced tensile stress stress reduction near existing fractures and stochastic parameterization of heterogeneity in frozen ground and in insulating snow tensile stress from cooling tensile strength propagation threshold fracture depth and elastic properties are chosen to approximate properties of frozen ground using these parameters model networks assemble with properties similar to natural ice wedge networks including 1 individual fracture paths have lengths ranging from tens to hundreds of meters 2 fractures intersect to enclose regions with characteristic spacing between fractures of approximately 22 m 3 intersections between fractures are predominantly orthogonal with less common three way approximately equiangular intersections joint distributions of relative orientation and spacing between fractures from modeled networks and ice wedge networks at espenberg alaska are comparable at the level of variability in natural examples this similarity is consistent with the hypotheses that networks self organize by stress interactions between sequentially placed fractures in frozen ground and that networks are insensitive to the many details of fracture dynamics omitted from the model spacing between fractures in modeled networks is influenced by sub optimal placement of fractures during network development and increases nonlinearly with the length scale of stress reduction around a fracture three way approximately equiangular intersections form where modeled fractures arrest on the outside of bends in earlier fractures

relative rates of peoria loess accumulation and pedogenic processes implications for paleoclimatic inference abstract where it is thick enough to extend below the surface soil profile the late wisconsinan peoria loess in the midcontinent of north america has characteristics suggesting relatively little syndepositional pedogenesis in these thicker sections the peoria loess below the surface soil profile commonly displays massive macroscopic structure low organic carbon content and retention of detrital carbonate grains late wisconsinan climatic conditions provide one potential explanation for these observations this paper considers two other non climatic explanations 1 loess accumulation was more rapid than carbonate dissolution or oc accumulation and 2 post depositional diagenesis has removed evidence of syndepositional pedogenesis the approach used is comparison of potential rates for pedogenic processes and loess accumulation even when wide ranges of controlling factors precipitation evapotranspiration and soil carbon dioxide levels are considered loess accumulation was probably too rapid at many sites for carbonate mineral dissolution to keep pace on the other hand data from modern tundra and boreal forest environments suggest that soil oc accumulation could have kept pace with loess deposition in many cases low oc contents observed in the loess today probably reflect post depositional oxidation climatic factors may provide partial or local explanations for the apparent minor extent of syndepositional pedogenesis but loess accumulation rates and diagenesis are key factors as well

the application of radiocarbon age estimates to the dating of glacial sequences an example from the miami sublobe ohio u s a abstract despite the importance of dating glacial sequences little evidence has been available to highlight the stratigraphic issues associated with the interpretation of age analysis a compilation of radiocarbon data from the miami sublobe of the laurentide ice sheet provides a large enough data set more than 133 dates to identify at least two sources of error sample and unit variability and transportation problems analysis of different samples from the same stratigraphic level commonly differ by more than the reported one sigma error and 2 000 year differences do occur glacial entrainment and transportation emplace older organic material over younger in situ materials and this effect may also give age errors in the data set of up to 2 000 years at a minimum multiple radiocarbon ages from a sequence of units are necessary to assign a reliable age to events within a glacial sequence however representing multiple ages poses its own problems a graphical representation that combines the probability of each sample appears to be one solution

out of sequence reactivation of the munsiari thrust in the relli river basin darjiling himalaya india insights from shuttle radar topography mission digital elevation model based geomorphic indices abstract quantitative tectonic geomorphology has emerged as a powerful discipline for studying evolution of topography landscapes and neotectonics using geomorphic indices computed from digital elevation data such as the shuttle radar topography mission srtm data we computed srtm based geomorphic indices to study neotectonics in the relli river basin in the darjiling himalaya we also used real time kinematic global positioning system rtkgps independent checkpoints to assess the quality of the srtm data used to compute the geomorphic indices along with their uncertainties our analysis revealed that though the srtm c band 90 m resolution c90 digital elevation data has been used extensively for geomorphic studies the 30 m resolution c30 data were significantly more accurate moreover geomorphic indices computed using srtm c30 and c90 elevations in the relli basin indicate that normalized nondimensional indices such as the relief ratio rh hypsometric integral hi basin elongation re and valley floor width to height ratio vf are statistically indistinguishable with uncertainty 1 at least an order of magnitude below the index value the geomorphic indices in the relli basin reveal neotectonic activity in the munsiari thrust mt fault zone and intraformational faults in its footwall in the lesser himalayan rocks and also indicate that the basin is at an early mature stage close to equilibrium between tectonic and erosional process however analysis of the uncertainties associated with the indices suggest that the normalized or nondimensional geomorphic indices have the lowest uncertainties and that neotectonics in the relli basin may only be confined to reactivation in the mt the reactivation in the mt fault zone by out of sequence neotectonics implies the possibility of large earthquake events in the darjiling himalaya and significant seismic and landslide hazard for populations in large towns specifically located on the mt our new approach of looking at geomorphic indices and their uncertainties delivers a novel perspective for improved understanding of out of sequence neotectonics in river basins that may be applied more broadly across the himalaya and elsewhere

methane seeps and mud volcanoes in italy gas origin fractionation and emission to the atmosphere molecular composition ch 4 isotopes and gas flux of all main terrestrial mud volcanoes and other methane seeps in italy are being assessed for the first time whereas 74 of the italian gas reservoirs are biogenic about 80 of the seeps release thermogenic gas dry seep gas generally maintains the reservoir c 1 c 2 c 3 bernard ratio while mud volcanoes show molecular fractionation likely occurring during advective migration accordingly a simple and direct use of the bernard parameter might be misleading when applied to mud volcanoes as it could not always reflect the reservoir composition methane flux into the atmosphere from macro seep areas is in the order of 10 2 10 6 t km 2 y 1 microseepage is widespread throughout large areas and on a regional scale it provides the main methane output a first emission estimate for the total hydrocarbon prone area of italy suggests levels of 105 t y 1 comparable to national sources from fossil fuel industry

δ13c values and radiocarbon dates of microbial biomarkers as tracers for carbon recycling in peat deposits this paper describes the first application of compound specific stable carbon isotope and radiocarbon isotope analyses to the investigation of microbial processes in peat deposits

morphology and origin of the fair oaks dunes in nw indiana usa abstract the fair oaks dunes fod of nw indiana usa is a large 4500 km 2 inland dune field associated with the late wisconsin deglaciation of the laurentide ice sheet meltwaters released by the michigan saginaw and huron erie lobes transported fluvioglacial sediment through the kankakee and tippecanoe valleys and their tributaries the texture and composition of the sand in the fod suggest a saginaw lobe origin of sediment with some huron erie lobe sediment sub mature sand with sub angular grains and a large feldspar content suggests relatively short distance of transport during two or possibly three dune building and dune reworking events we propose a model which explains the development of the dunes in three stages dune development began during the bolling allerod stage 1 15 13 ka interval during this stage anticyclonic easterly and north easterly winds deflated the sand from outwash deposits and built transverse and barchanoid dunes on the western sides of the tippecanoe valley and paleo channels further downwind on the western and southwestern windward margins of the fod loess was deposited during the early younger dryas stage 2 12 5 ka atmospheric circulation changed and westerly winds reworked the original dunes to create a great variety of parabolic dunes simple hemicyclic and lobate parabolic dunes developed in the western fod while further downwind in the eastern and the southern fod more elongated hairpin and windrift dunes developed on the upwind side of the dune field loess deposits remained stable and were not remobilized during the second stage dune development by the early holocene the fod dunes were stabilized until their minor remobilization during the middle holocene stage 3 minor disturbances caused by anthropogenic activities have occurred in last two centuries

geologic evidence for a large prehistoric earthquake in eastern connecticut postglacial wedges cutting stratified late quaternary glacial deposits have been widely reported throughout the northeastern us previous interpretations of these features as periglacial ice wedge casts have proved untenable for at least several of the reported localities this conclusion is also reached in the detailed study of 29 such wedges at a gravel quarry in eastern connecticut the wedges there are found to be planar vertical zones that widen upward from a few centimeters to as much as 150 cm and that contain material injected from below as well as collapsed from the sides these zones are interpreted as extension and collapse fissures that served as conduits for water and liquefied sediment during one or more prehistoric liquefaction events seismic excitation seems the most likely cause for the episode s of liquefaction and violent dewatering similar phenomena were reported to accompany large eighteenth century earthquakes in new england if the relation between large earthquakes and wedges is substantiated at their study locality and other localities these possibly contemporaneous features may provide an opportunity to determine the felt area magnitude of prehistoric earthquakes in the northeastern us 18 references 3 figures

landscape evolution alluvial architecture environmental history and the archaeological record of the upper mississippi river valley abstract the alluvial fill in the upper mississippi river valley umv is a palimpsest of past landscapes environments and physical evidence of human life ways the valley has undergone significant changes in fluvial style during the time humans have occupied its landscapes including changes in channel pattern location of depocenters and sediment lithology remnants of late glacial braidplains that predate human presence in the upper midwest occur as sandy terraces and terrace fills a subsequent major change in alluvial architecture resulted from fundamental changes in seasonal water and sediment input that marked the end of glacial meltwater input into the valley about 12 4 ka 10 500 14c yr b p a shift to net transport of sandy bedload and storage of fine grained overbank sediment on the floodplain accompanied the change to an island braided channel pattern at that time the holocene channel belt has been significantly narrower and the zone of sediment storage is reduced relative to that of the late glacial river major holocene depocenters include alluvial fans and colluvial slopes floodbasins natural levees and fluvial fans at the junction of large tributaries climate models and paleobotanical and isotopic studies indicate that shifts in large scale patterns of atmospheric circulation and moisture transport into the mid continent of north america induced hydrologic and vegetation changes that strongly influenced flood frequency and magnitude the delivery of sediment from tributary basins and the evolution of the umv landscape understanding the alluvial architecture of the valley and the temporal spatial distribution of biotic environments and processes that have buried mixed altered or destroyed archaeological deposits is essential to develop strategies for sampling the valley for evidence of past human activity and for properly interpreting the archaeological record

seismic activity at the mct in sikkim himalaya abstract a microearthquake survey in the sikkim himalaya raised a question whether the north south segment of the main central thrust mct in this part of the himalaya is seismically active fault plane solution of a cluster of events occurred below this segment of the mct shows right lateral strike slip motion the seismic observations and the geological evidences suggest that a nne ssw trending strike slip fault beneath this segment caused right lateral movement on the mct and is seismically active

estimates of motion and strain rates across active faults in the frontal part of eastern himalayas in north bengal from gps measurements within the 2500 km stretch of the himalayas a narrow window between longitudes 88 185e and 88 936e in the frontal himalayas in north bengal crisscrossed by several active fault traces presents an interesting region for crustal deformation study we have estimated velocities of 8 gps stations located in this area and the accumulating strain rate by two different methods a total shortening of 11 1 1 5 mm yr 1 is occurring across a set of four e w running faults gorubathan matiali chalsa and baradighi the strain rate becomes higher in the ne part of the network reaching 0 25 0 12 lstrain yr 1 with azimuth 21 a statistically significant extension of 10 9 1 6 mm yr 1 is estimated across the gish transverse fault with a maximum strain rate of 0 36 0 08 lstrain yr 1 with azimuth 103 the accumulating strain will be probably released through future earthquakes

subsidence rates in the po plain northern italy the relative impact of natural and anthropogenic causation abstract the central eastern po plain in northern italy is a rapidly subsiding sedimentary basin that hosts about 30 of the italian population and 40 of italy s total productive activities subsidence rates range from 0 to 70 mm year the maximum occurring in synclinal areas at the po delta and near bologna the minimum located at the top of buried probable tectonically active anticlines mirandola ferrara we show that modern subsidence is at least an order of magnitude higher than due solely to long term natural processes this implies that most subsidence in the po plain has been induced by human activities as previously noted we suggest that the main factor controlling modern subsidence is water withdrawal which was particularly intense during the second half of the 20th century coinciding with accelerating economic growth we also evaluate the impact of rapid subsidence on floods in low areas by comparing subsidence velocity maps with flood maps this shows that there is a clear cut correlation between flood frequency and rapid subsidence in contrast few floods occurred in low subsidence areas which generally correspond with the top of buried anticlines we finally note that the anthropic caused increase in subsidence has now greatly increased the potential for additional floodings

comment on geomorphology in relation to tectonics a case study from the eastern himalayan foothills of west bengal india by chandreyee chakrabarti goswami dhruba mukhopadhyay b c poddar quaternary international 298 80 92 abstract in a recent paper chakrabarti goswami et al 2013 discussed the geomorphology of matiali fan and the terraces formed along the rivers traversing this fan in the jalpaiguri district of west bengal eastern himalaya the area of their study is tectonically active with a couple of blind thrust traversing the quaternary fan deposits the authors have proposed that the tectonic movements along blind thrust faults of the area were the main control of formation and present disposition of the terraces in proposing this the authors have completely ignored the question of aggradation of the terraces sediment water ratio in the alluvial system and role of well known climatic fluctuations during the time span over which these geomorphic features formed in eastern himalaya they have reported fault propagation folds deforming the fan sediments but did not document any deformation or any other features within the younger terraces that could substantiate their claim of tectonics as the main agent for the development of the terraces in this comment we point out the inconsistencies in the tectonogeomorphic model proposed by them and suggest that the climate induced aggradation played a major role in the formation of the terraces in the river valleys in this area

evidence of possible enhanced peat burning by deep origin methane in the po river delta plain italy abstract a burning peat site in the po valley italy has been investigated for the first time beyond the smoke from the smoldering combustion of peat there are carbonatic concretions and huge amounts of methane in the soil 60 by vol leading to fluxes to the atmosphere of the order of 102 103 mg m 2 d 1 a wide range of analyses gas composition stable isotopes of ch4 and caco3 methane radiocarbon were performed in order to understand whether methane is produced by peat layers or seeps from deeper natural gas reservoirs the quasi fossil character of ch4 methane derived carbonates methane stable isotopic compositions related to marine carbonates reduction the presence of helium and a fault corresponding to the burning site all converge to indicate that the major part of the methane ascends from deep horizons such methane seepage is likely to feed the peat combustion explaining the observed phenomena and the large outbursts of historical gas emission events

glacial geomorphic study of the thajwas glacier valley kashmir himalayas india abstract glacial geomorphic studies provide vital information to make inferences about the effect of glacial advance and retreat on the geomorphology of an area in the present study glacial geomorphic landforms of the thajwas glacial valley in the upper reaches of the indus kashmir himalayas were mapped using geospatial technology validated with gps based field observations and ground photography the glacial geomorphic landforms were digitized using aster dem 30 m resolution landsat etm satellite imagery 30 m resolution and google earth 1 m resolution data results showed that google earth imagery supported by field validation is very useful for the interpretation of glacial geomorphic landscapes and relief features at micro and meso scales however morphometric characteristics of landforms are best obtained using dem overlaid onto the landsat etm satellite data glaciers in the valley are presently confined along the south and southwestern slopes however the significant role played by glaciers in shaping the geomorphic landforms and their subsequent preservation within the scenic landscape under the late quaternary climatic conditions are remarkably evident the glacial geomorphic landforms especially terminal moraine glacial trough and cirques observed in the valley aided the reconstruction of palaeo glacial setting of the area morphology shape and location of terminal and lateral moraine ridges were used to establish the palaeo glacial extents glacial volume and the number of glacial advances of the thajwas glacier the maximum elevation of the lateral moraines was used to define the former equilibrium line altitude ela the greater rock excavation to form a large valley during the last glacial maximum might have induced isostatic rock uplift exhumation in the glacier source area it is observed that the concomitant retreat of the north facing glacial cirques has played an important role in expanding the glacial valley and limiting the topographic relief

nonlinear dynamics of ice wedge networks and resulting sensitivity to severe cooling events patterns of subsurface wedges of ice that form along cooling induced tension fractures expressed at the ground surface by ridges or troughs spaced 10 30 m apart are ubiquitous in polar lowlands1 fossilized ice wedges which are widespread at lower latitudes have been used to infer the duration2 3 4 and mean temperature5 6 of cold periods within proterozoic2 and quaternary climates3 4 5 6 7 8 9 10 11 12 13 and recent climate trends have been inferred from fracture frequency in active ice wedges14 here we present simulations from a numerical model for the evolution of ice wedge networks over a range of climate scenarios based on the interactions between thermal tensile stress fracture and ice wedges we find that short lived periods of severe cooling permanently alter the spacing between ice wedges as well as their fracture frequency this affects the rate at which the widths of ice wedges increase as well as the network s response to subsequent climate change we conclude that wedge spacing and width in ice wedge networks mainly reflect infrequent episodes of rapidly falling ground temperatures rather than mean conditions

evidence for a great medieval earthquake 1100 a d in the central himalayas nepal the himalayan orogen has produced three thrust earthquakes with moment magnitude m w 7 8 to 8 5 during the past century yet no surface ruptures associated with these great earthquakes have been documented here we present paleoseismic evidence from east central nepal that since 700 a d a single earthquake ruptured the frontal thrust fault at 1100 a d with a surface displacement of 17 5 3 meters and a lateral extent and size that could have exceeded 240 kilometers and m w 8 8 respectively ruptures associated with m w

holocene strath terraces climate change and active tectonics the clearwater river basin olympic peninsula washington state the 400 km 2 clearwater river basin located on the pacific flank of the actively uplifting olympic mountains of western washington state contains a well preserved flight of holocene fluvial terraces we have collected a large data set of numeric ages from these terraces that is used to elucidate the geomorphic fluvial active tectonic and climatic processes that operate at holocene spatial and temporal scales detailed field mapping reveals three prominent holocene straths and their overlying terrace deposits terrace ages fall into three broad ranges ca 9000 11 000 yr b p qt4 4000 8000 yr b p qt5 and 0 3000 yr b p qt6 terrace deposit stratigraphy sedimentology and age distributions allow us to consider two alternative models for their genesis the favored model states that the terrace ages are coincident with lateral incision of the clearwater channel emplacement of the terrace alluvium and the carving of the straths vertical incision of the clearwater channel was primarily relegated to the brief 1000 yr intervals when we have no record of terraces alternatively the straths were carved as the channel incised vertically during the brief time periods between dated terrace deposits and the terrace ages record a subsequent long time of alluviation atop the straths and concomitant termination of vertical incision in both models we envision a clearwater river channel at or near capacity with a temporally variable rate of both lateral and vertical incision small deviations from this at capacity condition are driven by variations in the liberation and delivery of hillslope sediment to the channel we consider several causes for variable hillslope sediment flux in this tectonically active setting including holocene climate change and ground accelerations related to earthquakes holocene rates of vertical incision are reconstructed along nearly the entire clearwater valley from the wide distribution of dated terraces incision rates clearly increase upstream mimicking a pattern documented for pleistocene terraces in the same basin however the rates are 2 3 times those determined for the pleistocene terraces the faster holocene incision rates may be interpreted in terms of an increase in the rates of rock uplift however we favor an alternative explanation in which the holocene rates represent a channel rapidly reacquiring its stable graded concavity following protracted periods of time in the pleistocene when it could not accomplish any vertical incision into tectonically uplifted bedrock because the channel was raised above the bedrock valley bottom by climatically induced alluviation these results illustrate how even in tectonically active settings representative rates of rock uplift inferred from studies of river incision should be integrated over at least one glacial interglacial cycle

on the formation of the tunnel valleys of the southern laurentide ice sheet abstract catastrophic releases of meltwater produced by basal melting and stored for decades in subglacial reservoirs at high pressure may have been responsible for eroding the broad deep tunnel valleys that are common along the margins of some lobes of the southern laurentide ice sheet we surmise that these releases began when the high water pressure was transmitted to the margin through the substrate the water pressure in the substrate at the margin would then have been significantly above the overburden pressure leading to sapping failure headward erosion of a conduit in the substrate piping could then tap the stored water resulting in the outburst in some situations development of a siphon may have lowered the reservoir below its overflow level thus tapping additional water following the flood the seal could have reformed and the reservoir refilled setting up conditions for another outburst order of magnitude calculations suggest that once emptied a subglacial reservoir could refill in a matter of decades the amount of water released during several outbursts appears to be sufficient to erode a tunnel valley we think that tunnel valleys are most likely to have formed in this way where and when the glacier margin was frozen to the bed and permafrost extended from the glacier forefield several kilometers back under the glacier as reservoirs would then have been larger and more common and the seal more robust and more likely to reform after an outburst

methane emission from the mud volcanoes of sicily italy 1 mud volcanoes represent the largest expression of natural methane release into the atmosphere however the gas flux has never been investigated in detail methane output from vents and diffuse soil degassing is herewith reported for the first time measurements were carried out at 5 mud volcano fields around sicily italy each mud volcano is characterized by tens of vents and bubbling pools in the quiescent phase methane emission from single vents ranges between 0 01 and 6 8 kg day diffuse soil leakage around the vents is in the order of 102 104 mg m 2 d 1 an exceptional flux of 106 mg m 2 d 1 was recorded close to an everlasting fire soil ch4 flux is positive even at large distances from the mud volcano fields suggesting a diffuse microseepage over wider areas a total of at least 400 tons ch4 per year can be estimated over the area investigated alone 1 5 km2

paleoseismological evidence of surface faulting along the northeastern himalayan front india timing size and spatial extent of great earthquakes the similar to 2500 km long himalayan arc has experienced three large to great earthquakes of m w 7 8 to 8 4 during the past century but none produced surface rupture paleoseismic studies have been conducted during the last decade to begin understanding the timing size rupture extent return period and mechanics of the faulting associated with the occurrence of large surface rupturing earthquakes along the similar to 2500 km long himalayan frontal thrust hft system of india and nepal the previous studies have been limited to about nine sites along the western two thirds of the hft extending through northwest india and along the southern border of nepal we present here the results of paleoseismic investigations at three additional sites further to the northeast along the hft within the indian states of west bengal and assam the three sites reside between the meizoseismal areas of the 1934 bihar nepal and 1950 assam earthquakes the two westernmost of the sites near the village of chalsa and near the nameri tiger preserve show that offsets during the last surface rupture event were at minimum of about 14 m and 12 m respectively limits on the ages of surface rupture at chalsa site a and nameri site b though broad allow the possibility that the two sites record the same great historical rupture reported in nepal around a d 1100 the correlation between the two sites is supported by the observation that the large displacements as recorded at chalsa and nameri would most likely be associated with rupture lengths of hundreds of kilometers or more and are on the same order as reported for a surface rupture earthquake reported in nepal around a d 1100 assuming the offsets observed at chalsa and nameri occurred synchronously with reported offsets in nepal the rupture length of the event would approach 700 to 800 km the easternmost site is located within harmutty tea estate site c at the edges of the 1950 assam earthquake meizoseismal area here the most recent event offset is relatively much smaller 2 5 m and radiocarbon dating shows it to have occurred after a d 1100 after about a d 1270 the location of the site near the edge of the meizoseismal region of the 1950 assam earthquake and the relatively lesser offset allows speculation that the displacement records the 1950 m w 8 4 assam earthquake scatter in radiocarbon ages on detrital charcoal has not resulted in a firm bracket on the timing of events observed in the trenches nonetheless the observations collected here when taken together suggest that the largest of thrust earthquakes along the himalayan arc have rupture lengths and displacements of similar scale to the largest that have occurred historically along the world s subduction zones

structural evolution of a fold and thrust belt generated by multiple decollements analogue models and natural examples from the northern apennines italy this study analyses the role played by the mechanical proprieties of the rocks involved in a thrust system focusing on the problem of multiple decollements and of related compressional structures integration of geophysical seismic reflection profiles and geological data and scaled sandbox models are used to study the deformation style of two areas of the northern apennines italy the po plain and the umbria marche apennines both areas are characterised by a complex stratigraphy consisting of decollements located at different depths that influence the geometry and kinematics of the thrust system the main characteristic of the models presented here is the presence of two decollement horizons situated at the base and in an intermediate level of the models during deformation of the models these two decollement horizons generate two sets of structures with different geometrical characteristics and significance through the joint analysis of geophysical and geological data and model results wavelengths of the compressional structures analysed show that the structural style of the two analysed areas is almost similar moreover model results prove that the final configuration of the thrust system follows the general rules of evolution of a wedge deformed above a weak decollement and is largely governed by the larger deep seated structures

low slip rates and long term preservation of geomorphic features in central asia in order to understand the dynamics of the india asia collision zone it is important to know the strain distribution in central asia whose determination relies on the slip rates for active faults1 2 3 4 5 many previous slip rate estimates of faults in central asia were based on the assumption that offset landforms are younger than the last glacial maximum 20 kyr ago 6 7 8 9 10 11 in contrast here we present surface exposure ages of 40 to 170 kyr obtained using cosmogenic nuclide dating for a series of terraces near a thrust at the northern margin of the tibetan plateau combined with the tectonic offset the ages imply a long term slip rate of only about 0 35 mm yr 1 for the active thrust an order of magnitude lower than rates obtained from the assumption that the terraces formed after the last glacial maximum our data demonstrate that the preservation potential of geomorphic features in central asia is higher than commonly assumed

a numerical investigation of ice lobe permafrost interaction around the southern laurentide ice sheet permafrost existed around and under marginal parts of the southern laurentide ice sheet during the last glacial maximum the presence of permafrost was important in determining the extent form and dynamics of ice lobes and the landforms they produced because of influences on resistance to basal motion and subglacial hydrology we develop a two dimensional time dependent model of permafrost and glacier ice dynamics along a flowline to examine i the extent to which permafrost survives under an advancing ice lobe and how it influences landform development and hydrology and ii the influence of permafrost on ice motion and surface profile the model is applied to the green bay lobe which terminated near madison wisconsin during the last glacial maximum simulations of ice advance over permafrost indicate that the bed upstream of the ice sheet margin was frozen for 60 200 km at the glacial maximum permafrost remained for centuries to a few thousand years under advancing ice and penetrated sufficiently deep tens of meters into the underlying aquifer that drainage of basal meltwater became inefficient likely resulting in water storage beneath the glacier our results highlight the influence of permafrost on subglacial conditions even though uncertainties in boundary conditions such as climate exist

timing of recent out of sequence active deformation in the frontal himalayan wedge insights from the darjiling sub himalaya india recent studies of india eurasia convergence suggest that the entire convergence in the himalayan wedge is almost exclusively accommodated along its basal detachment fault main himalayan thrust mht and its near surface equivalent main frontal thrust mft using direct dating of fault zone gouge and strath terrace deposits we conclude the following 1 the present mountain front in the darjiling sub himalaya was emplaced by ca 40 ka 2 out of sequence deformation on surface breaking faults north of the mft in the darjiling sub himalaya began ca 20 ka and has probably continued since 3 the tista river responded to the ca 20 ka deformation by migrating 150 m eastward average rate 13 mm yr 1 and by incising 48 m vertically average rate 4 4 mm yr 1 creating unpaired disjointed strath terraces between 11 3 1 3 ka and 1 4 0 3 ka out of sequence surface breaking faults in the himalaya indicate partial accommodation of active convergence within the himalayan wedge using the results from the bhuj earthquake of 2001 we suggest that active deformation along the out of sequence faults is a potential seismic hazard in the himalaya and himalayan seismic hazard models must account for this we also propose a conceptual model for active deformation in the himalaya

the geological links of the ancient delphic oracle greece a reappraisal of natural gas occurrence and origin recent studies have speculated that the prophetic powers of pythia the woman of the delphic oracle at the temple of apollo in greece were induced by hydrocarbon vapors specifically ethylene rising from bedrock fissures at the intersection of the e w delphi fault with the nnw sse kerna fault and producing neurotoxic effects including trance and delirium new surveys including gas flux from soil gas in groundwater and isotopic analyses of spring scales provide the experimental confirmation of the gas release in the delphi area presently methane ethane and carbon dioxide are being released from a thermogenic catagenetic hydrocarbon prone environment this environment is not prone to biogenic production of ethylene in amounts inducing neurotoxic effects hundreds or thousands of ppmv a wnw ese trending subsidiary fault within the delphi fault zone extending for 2 km passes under the temple of apollo and shrine of athena the temple of apollo located above this fault may have been the site of enhanced degassing in the past if gas linked neurotoxic effects upon pythia need to be invoked they should be sought in the possibility of oxygen depletion due to co2 ch4 exhalation in the indoor temple alternatively a plausible geological explanation behind the natural presence of sweet scents could be the occurrence of aromatic hydrocarbons such as benzene dissolved in the groundwater spring

millennial scale depositional cycles from the holocene of the po plain italy the holocene depositional history of southeastern po plain on time scales of 103 yr is reconstructed based upon integrated sedimentological and micropalaeontological analyses of nine continuously cored boreholes about 40 m deep major palaeoenvironmental changes include the rapid landward migration of a barrier estuary lagoon system during the early middle holocene transgressive systems tract tst followed by extensive delta progradation in the last 6000 yr highstand systems tract hst detailed facies analysis of cores combined with the identification of 12 microfossils benthic foraminifer and ostracod associations allow an ultra high resolution sequence stratigraphic framework to be reconstructed particularly eight small scale high frequency cycles about 3 5 m thick and spanning intervals of time of about 1000 yr can be physically traced throughout the study area interpretation of these cycles which are invariably bounded by sharp flooding surfaces and generally show internal shallowing upward trends parasequences indicates that relative sea level changes during the holocene were episodic and punctuated by rapid phases of sea level rise followed by periods of stillstand or decreasing sea level rise from seaward to landward locations parasequence boundaries document beach barrier migration bay head delta abandonment and increasing accommodation in the coastal plain the ensuing phases of sea level stillstands resulted in the progressive filling of the newly formed accommodation space through beach progradation extensive mud deposition in behind barrier lagoonal estuarine and marsh deposits and aggradation in bay head delta systems at the head of estuaries eustacy appears to be the major controlling factor of the retrogradational stacking pattern of parasequences within the tst by contrast a complex interplay of eustacy sediment supply and subsidence with an increasing influence of autocyclic mechanisms such as channel avulsion and delta lobe abandonment controlled facies architecture within the hst the maximum flooding surface cannot be assumed to be synchronous its timing being strongly dependent upon local variations in sediment influx and subsidence this study shows that the micropalaeontologic characterization of mud prone coastal plain and estuarine successions in terms of water depth and salinity can lead to very accurate sequence stratigraphic interpretations allowing identification of parasequence boundaries that may not be detected by conventional stratigraphic approach

carbon helium neon and argon isotopes in a po basin northern italy natural gas field the abundance and isotopic composition of he ne and ar have been determined in 19 gas samples taken from the dosso degli angeli hydrocarbon gas field between 3000 and 3750 m depth in the po basin carbon isotope ratios in these samples vary between 13c ch4 67 5 and 73 4 indicating a predominantly biogenic source for the methane c2 c2h6 c3h8 concentrations increase systematically from 0 04 to 0 17 by volume with depth suggesting that there is a small additional thermogenic or diagenetic hydrocarbon contribution to these gases ch4 36ar ratios in the dosso degli angeli gases are in the range predicted for a groundwater which has derived its rare gas by equilibration with the atmosphere and is ch4 saturated under reservoir conditions there is also up to 10 excess of ch4 which is not associated with the groundwater these results are consistent with 90 of the ch4 in the dosso degli angeli reservoir originating from ch4 saturated groundwater measured 20ne 36ar ratios depart from the predicted ratio in air equilibrated groundwater this fractionation is consistent with water gas phase equilibration under reservoir conditions and is similar to that observed in gas reservoirs in the vienna and pannonian basins austria and hungary respectively the he in the dosso degli angeli gases is almost entirely radiogenic and derived from the crust the concentration of 4he in the reservoir gases requires that he is mostly sourced from outside the reservoir volume radiogenic 4he 40ar ratios input into the reservoir gas must be much higher than averaged crustal production ratios as no shift from the atmospheric 40ar 36ar ratio is observed preferential release of 4he over 40ar from the sites of their production is the preferred explanation this observation contrasts with previous studies from active extensional basins in which radiogenic 4he and 40ar appear to have been stored released and transported at near production ratio on a regional scale the most obvious difference between these studies is the comparatively low thermal gradient of the po basin

tunnel valleys concepts and controversies a review abstract although erosion of valleys by subglacial meltwater was first proposed more than 100 years ago the processes that produced these valleys under past ice sheets have remained a topic of vigorous debate the most commonly hypothesized mechanisms have included gradual formation by sediment deformation into the incipient valleys under steady state conditions and subsequent transport by meltwater to the ice margin time transgressive formation along a retreating ice margin by drainage of surface meltwater to the bed or release of impounded meltwater behind a marginal permafrost wedge probably catastrophically and rapid erosion during widespread catastrophic basal sheetflood events recent application of new and enhanced imaging techniques has led to the identification of many new tunnel valleys both on land and offshore throughout the regions glaciated during former ice ages in addition new advances in understanding of subglacial hydrology both from modelling and field instrumentation have helped to constrain the drainage of meltwater from past ice sheet beds this work elucidates the role of subglacial groundwater flow systems in evacuating meltwater from the bed but also shows that groundwater flow alone was not enough to maintain ice bed meltwater pore pressures below the level of ice flotation both modelling and field observations indicate that subglacial conduits oriented parallel to glacial flow lines reorganize groundwater flow systems into basins containing lateral flow toward conduits cut upward into the ice or downward into the bed because of the inability of groundwater flow to account for all the meltwater produced by basal melting other drainage mechanisms involving both non channelized and channelized meltwater flow have been proposed the notion of catastrophic drainage of impounded basal meltwater is still favored by many and the discovery of hundreds of subglacial lakes beneath the antarctic ice sheet and the likelihood of similar lakes beneath pleistocene ice sheets provides a source of water for those advocating catastrophic formation for tunnel valleys proponents of catastrophic drainage consider the valleys to be channels reflecting the width and perhaps depths of flows that formed them tunnel valleys produced by the scandinavian ice sheet have been described and mapped on land as well as on the sea bed valleys and networks of valleys some of which are totally buried have been linked to 3 or more glaciations tunnel valley networks from the last weichselian glaciation in denmark can be related to specific ice margins developed during ice retreat in north america most research has focused on tunnel valleys associated with ice margins formed by the last wisconsin glaciation along the southern margin of the laurentide ice sheet

low altitude remote sensing and gis based analysis of cropmarks classification of past thermal contraction crack polygons in central western poland abstract the examination of low altitude aerial photographs reveals the presence of more than 400 polygonal nets in central western poland polygons range from 5 to almost 70 m in diameter based on the polygons diameter and intersection angles we identified seven main types of nets geometry based on ground verification we interpreted them as past thermal contraction cracks filled mostly with sand i e sand wedge casts as favourable weather conditions and a proper land cover i e cultivated land are necessary for identifying polygonal nets the observed number of polygons is probably much underestimated the broad occurrence of former thermal contraction cracks polygons indicates that continuous permafrost was widespread in central western poland after the termination of the last glacial maximum lgm preliminary dating of the cracks infilling as well as polygon geometry suggest that thermal contraction cracking occurred in several different phases and that a time frame of a few thousand years is sufficient to form complex mature nets

thaw modification of frost fissure wedges richards island pleistocene mackenzie delta western arctic canada thaw modification is the general process whereby frost fissure wedges are modified during thaw and by which frost fissure pseudomorphs may develop specific processes of thaw modification are inferred from ice wedge pseudomorphs composite wedge pseudomorphs and deformed sand wedges in the pleistocene mackenzie delta i e thermal erosion collapse subsidence refreezing loading buoyancy spreading folding and shearing thaw modification is believed to result in selective preservation of pseudomorphs and wedges sand wedges are more likely to be preserved than are ice wedge pseudomorphs or compositewedge pseudomorphs because only those sand wedges that penetrate massive ice or icy sediments are prone to thaw modification furthermore whereas ice wedges preferentially develop in ice rich fine grained sediments thaw sensitive their pseudomorphs appear to be selectively preserved in ice poor coarse grained sediments thaw stable

evidence and consequences of tilting of two alluvial fans in the pinjaur dun northwestern himalayan foothills abstract the pinjaur dun is a nw se trending intermontane valley in the foothills belt of the punjab sub himalaya in this dun the kiratpur and the balad rivers have formed fans with areas of 28 and 21 km 2 respectively a southwest tilt for the kiratpur and balad fans of 0 83 and 0 57 respectively has been determined based on these angles of tilt uplifts of 41 and 46 m at the fan head has been calculated for the kiratpur and balad fans respectively the incision by the kiratpur and balad rivers at the fan heads is also approximately 45 m

himalayan cross faults affect thrust sheet geometry an example from the munsiari thrust sheet near the gish transverse fault zone frontal darjiling himalaya india abstract the munsiari thrust mt sheet is a dominant thrust sheet in the himalaya and forms the frontal ridge in the gorubathan recess of the darjiling himalaya the geometry of the mt sheet in the recess was poorly constrained thereby inhibiting the understanding of how the geometry and kinematics of the sheet varied from the nepal to the bhutan himalaya we present new structural data and infer the deformation mechanisms and the geometry of the mt sheet in the gorubathan recess in the darjiling himalaya to fill this knowledge gap the mt sheet was dominated by large scale overturned antiforms and synforms the entire mt sheet was later folded to a north easterly plunging synformal fold with ne sw axial trend due to the effect of a himalayan cross fault in the region named the gish transverse fault a new brittle out of sequence and neotectonically active phaparkheti thrust was recognized in the mt sheet deformation microstructures indicate that the temperature of deformation in the mt fault zone and the sheet was 500 c to 700 c and 400 c respectively our approach of first mapping major and minor structures and then integrating these studies with deformation microstructure and tectonic geomorphology data resulted in an improved understanding of the structural characteristics of the mt sheet in the darjiling himalaya our study also suggests that there is considerable variation in the geometry and kinematics of frontal thrust sheets along the himalayan arc that must be studied systematically in the context of himalayan salients and recesses

numerical reconstruction of a soft bedded laurentide ice sheet during the last glacial maximum we used a numerical ice sheet model to reconstruct the north american laurentide ice sheet during the last glacial maximum our model simulates ice sheet conditions that can be specified experimentally as either a rigid substrate hard bed or a wet deformable till soft bed basal sliding is excluded we use geologic records of former basal ice sheet processes to prescribe the distribution of hard and soft beds our reconstruction of the laurentide ice sheet is significantly lower in ice surface height and contains less ice volume than the climap maximum reconstruction in contrast our reconstruction agrees well with the ice 4g reconstruction both in height and volume because the ice 4g reconstruction is based on the inversion of relative sea level data whereas our reconstruction is based on glacial geology and ice mechanics this agreement suggests that soft beds provide a glaciological mechanism to explain the shape and volume of the laurentide ice sheet that is most consistent with observations of relative sea level change and other geodynamic considerations

numerical modeling of subglacial sediment deformation implications for the behavior of the lake michigan lobe laurentide ice sheet we apply a numerical model of the late wisconsin circa 20 000 years b p lake michigan lobe lml laurentide ice sheet to investigate how fine grained subglacial sediment might influence lobe behavior particularly rapid millennial scale marginal oscillations observed in the geologic record over the canadian shield we assume a rigid bed hard bedded basal boundary condition in areas overlain by fine grained sediment soft bedded the base of the ice is coupled to a deformable sediment layer using a rate dependent stress strain law geotechnical tests of clay rich till deposited by the lml provide control for sediment rheologic parameters simulated cross sectional profiles are consistent with reconstructions from geologic evidence time dependent simulations suggest that a soft bedded lobe could have reached steady state in about 20 000 years or less in contrast to 50 000 to 60 000 years for an otherwise identical hard bedded lobe a soft bedded lobe with sediment viscosity at the experimentally determined value is about twice as responsive to millennial scale shifts in accumulation or ablation as a nonsliding hard bedded lobe but in both cases the response is slower than that indicated by the geologic record results suggest that while strong millennial scale changes in accumulation and ablation can produce responses in hard bedded or soft bedded ice that are consistent with the geologic record changes in subglacial sediment viscosity even relatively modest changes whether independent or in conjunction with climate change might more readily account for millennial and submillennial scale fluctuations of the lobe margin these observations do not exclude a role for sliding but they do provide some perspective from which to evaluate relative contributions of the various processes that influence lobe behavior

contemporary tectonics of the himalayan frontal fault system folds blind thrusts and the 1905 kangra earthquake the sub himalayan fold thrust belt consists of deformed late cenozoic and older deposits south of the main boundary thrust mbt in pakistan east of the indus river the sub himalaya comprises the potwar plateau and the salt range which is thrust southward over the jhelum river floodplain along the salt range thrust although an estimated 9 14 mm a 1 shortening has been taken up on the salt range thrust during the last 2 ma the range front scarp does not show signs of recent faulting shortening may be shifting southward to the lilla overpressured anticline which rises from the jhelum floodplain as a fault propagation fold farther east shortening is partitioned among several anticlines underlain by foreland and hinterland dipping blind thrusts southeast of the main deformation zone the pabbi hills overpressured anticline is best explained as a fault propagation fold throughout the potwar plateau and salt range thrusts and folds rise from a basal decollement horizon in eocambrian evaporites the pakistani part of the decollement horizon could generate large earthquakes only if these evaporites die out northward at seismogenic depths in india and nepal the sub himalaya is narrower reflecting the absence of evaporites and a steeper slope of the basement towards the hinterland the southern boundary of the sub himalaya is the himalayan front fault discontinuous because part of the shortening is expressed at the surface by folding broad alluvial synclinal valleys dun valleys are bounded on the south by rising barrier anticlines of siwalik molasse the 1905 kangra earthquake m8 produced uplift on the mohand anticline and the dehra dun valley suggesting that this earthquake occurred on a decollement horizon above basement downdip from the fold if so the kangra event is the largest known earthquake on a blind thrust expressed at the surface as a fold

the fox permafrost tunnel a late quaternary geologic record in central alaska the fox permafrost tunnel which penetrates 110 m into frozen sediments of gold stream valley provides a continuous exposure of fossiliferous silt and alluvium above schistose bedrock deposition of fluvial gravel was followed by a long interval of loess accretion and permafrost aggradation that was punctuated by episodes of thaw and of gullying and redeposition of silt imbricated sandy gravel above the bedrock contains lenses of finer alluvium that contain wood fragments and some rooted stumps radiocarbon dates indicate that the gravel is older than 40 ka but absence of mature soil and weathering profiles at its upper contact indicates that fluvial activity must have continued until shortly before loess accretion began at the tunnel site silt is the most widespread depositional unit in the tunnel this deposit is of eolian origin loess but some has been redeposited by slope processes the silt units contain abundant ground ice as pore filings lenses wedges and buried pond ice loess accretion was interrupted by a period when little loess accumulated and when large ice wedges formed in the lower loess unit and subsequently were truncated by thaw loess began forming sometime before 40 ka and was rapidly accreting by 39 ka under xeric conditions with open vegetation a sharply decreased rate of loess accretion associated with local erosion and thaw between about 36 and 30 ka is marked by anomalous cation concentration values lenses of buried sod fossils indicative of moist to wet substrates and truncated ice wedges beneath small frozen ponds or streamlets that occupied ice wedge troughs a later episode of rapid loess influx under drier conditions began after 30 ka and coincided with glacial advances of late wisconsin age in the adjoining alaska range large ice wedges also formed in the upper loess unit but only their bases are exposed in the tunnel and their history of development is uncertain fanlike deposits of poorly sorted debris near the tunnel portal formed between about 12 5 and 11 ka during deep erosion of loess slopes under moister conditions the deposits locally form two subunits the younger over whelmed a stand of tall willows on the floor of goldstream valley between about 11 3 and 11 1 ka the older may have formed about 1 000 yr earlier stratigraphic records elsewhere in central alaska indicate variable middle wisconsin environments followed by colder and drier conditions that began between 30 and 25 ka and persisted until perhaps 12 5 ka widespread loess erosion and redeposition subsequently occurred under moister and probably warmer conditions renewed early holocene loess deposition may have been widespread but its exact environmental controls are uncertain our data challenge three generally accepted concepts of late quaternary periglacial processes in central alaska we contend that 1 many ice wedge systems may have formed under interstadial conditions rather than full glacial conditions 2 episodes of rapid loess influx may have been partly out of phase with episodes of glacier expansion and 3 redeposition of loess by solifluction sheetwash and gully formation may have been episodic and required conditions moister than those under which the loess initially accreted

late quaternary evolution of tista river terraces in darjeeling sikkim tibet wedge implications to climate and tectonics abstract terraces in the himalayas are important geomorphic archives which preserve the signature of tectonics and past environment terraces in eastern part of the himalayan fold and thrust belt have not received much attention of the geologists a geochemical approach using luminescence dating has been applied to understand the evolution of paired and deformed terraces between major thrust boundaries of the eastern himalayas on the either banks of the tista river in darjeeling sikkim tibet wedge these terraces are located at the confluence of tum thang khola and the tista river three levels of terraces are present in general and also in the study area the terrace t3 was formed during last interglacial period and the t2 terrace during last glacial maximum lgm and in the humid phases after lgm the top section of t2 terrace 2 5 m thick was formed in the transition phase arid to humid after younger dryas event the region has experienced several deformational events i one after 45 ka which raised the t3 terrace to its present level ii another one after 11 9 ka which raised the t2 to its present level and this event is also associated with the shifting of the tum thang khola and iii the region is still tectonically active as shown by the warping of the t1 and t0 surfaces which are of recent origin these terraces have complex input of sediments from higher himalayan crystalline hhc rocks and from locally present lingtse granites

episodic deposition of illinois valley peoria silt in association with lake michigan lobe fluctuations during the last glacial maximum the chronology and cause of millennial depositional oscillations within last glacial loess of the central lowlands of the united states are uncertain here we present a new age model that indicates the peoria silt along the illinois river valley accumulated episodically from 28 500 to 16 000 cal yr bp as the lake michigan lobe margin fluctuated within northeastern illinois the age model indicates accelerated loess deposition coincident with regional glacial advances during the local last glacial maximum a weakly developed paleosol the jules geosol represents a period of significantly slower deposition from 23 700 to 22 000 cal yr bp a gastropod assemblage based reconstruction of mean july temperature shows temperatures 6 10 c cooler than modern during peoria silt deposition stable oxygen and carbon isotope values 18 o and 13 c of gastropod carbonate do not vary significantly across the pedostratigraphic boundary of the jules geosol suggesting slower loess accumulation was a result of reduced glacial sediment supply rather than direct climatic factors however a decrease in 18 o values occurred between 26 000 and 24 000 cal yr bp synchronous with the lake michigan lobe s southernmost advance this 18 o decrease suggests a coupling of regional summer hydroclimate and ice lobe position during the late glacial period

methane emission from mud volcanoes in eastern azerbaijan methane ch4 flux to the atmosphere was measured from gas vents and for the first time from soil microseepage at four quiescent mud volcanoes and one everlasting fire in eastern azerbaijan mud volcanoes show different activity of venting craters gryphons and bubbling pools with ch4 fluxes ranging from less than one to hundreds of tons per year microseepage ch4 flux is generally on the order of hundreds of milligrams per square meter per day even far away from the active centers the ch4 flux near the everlasting fires on the order of 105 mg m 2 d 1 represents the highest natural ch4 emission from soil ever measured the specific ch4 flux to the atmosphere between 102 and 103 t km 2 yr 1 was similar to specific flux from other mud volcanoes in europe at least 1400 tons of ch4 per year are released from the investigated areas it is conservatively estimated that all onshore mud volcanoes of azerbaijan during quiescent activity may still emit 0 3 0 9 106 t of ch4 per year into the atmosphere the new data fill a significant gap in the worldwide data set and confirm the importance of geologic sources of greenhouse ch4 although they are not yet considered in the climate study budgets of atmospheric ch4 sources and sinks

constraining the timing of microbial methane generation in an organic rich shale using noble gases illinois basin usa abstract at least 20 of the world s natural gas originates from methanogens subsisting on organic rich coals and shales however in situ microbial methane production rates are unknown methanogens in the upper devonian new albany shale in the illinois basin extract hydrogen from low salinity formation water to form economic quantities of natural gas because of this association constraining the source and timing of groundwater recharge will enable estimation of minimum in situ metabolic rates thirty four formation water and gas samples were analyzed for stable isotopes oxygen and hydrogen chloride tritium 14 c and noble gases chloride and 18 o spatial patterns reveal a plume of water with low salinity 0 7 to 2154 mm and 18 o values 0 14 to 7 25 penetrating 1 km depth into evapo concentrated brines parallel to terminal moraines of the laurentide ice sheet suggesting glacial mediated recharge however isotopic mixing trends indicate that the recharge endmember 7 18 o is higher than the assumed bulk ice sheet value 18 o and similar to modern local precipitation 7 5 to 4 5 18 o continental paleoprecipitation records reveal that throughout the pleistocene 18 o of precipitation in the region ranged from 10 to 5 suggesting that the dilute groundwater was primarily sourced from paleoprecipitation with minor contributions from glacial meltwater for the majority of samples the atmosphere derived 4 he contribution is negligible and the 4 he is dominated by a crustal radiogenic source with near complete transfer of dissolved noble gases to the gas phase in addition mantle derived helium is negligible for all samples 18 o data however all groundwater in the study area was influenced by pleistocene recharge estimated in situ microbial methane production rates range from 10 to 1000 tcf ma 10 4 to 10 6 times slower than average laboratory rates from coals findings from this study have implications for targeting undeveloped microbial gas accumulations improving natural gas reservoir estimates the potential of in situ methanogen stimulation and understanding biologic cycling of carbon in subsurface reservoirs

the frequency of ice wedge cracking 1967 1987 at garry island western arctic coast canada the frequency of ice wedge cracking has been studied at garry island northwest territories for the 1967 1987 period sites have included low centre polygons intermediate centre polygons and polygons that do not fit any classification system analyses of crack frequency have included trough characteristics polygon characteristics and ice wedge types the results show that crack frequencies are highly variable within one site and also between two adjacent sites the correlation between crack frequency and a low air temperature is poor crack frequencies for a site with 59 wedges ranged from 8 to 42 between 1967 and 1979 and for a nearby site with 32 wedges from 22 to 75 between 1967 and 1987 in view of the wide range in crack frequencies at a given site the use of mean ice wedge growth rates for estimating ages of ice wedges and their casts in environmental reconstruction may be hazardous the data show that the common twofold classification into active and inactive wedges is difficult to apply be

ice wedge casts and relict patterned ground in central illinois and their environmental significance abstract sediment features and soil patterns indicate that permafrost developed beyond the late wisconsinan woodfordian ice margin in illinois vertical wedge shaped bodies in woodfordian glacigenic deposits and buried by woodfordian loess are interpreted to be ice wedge casts large scale patterned ground common on the late wisconsinan drift plain and on the illinoian drift plain to the south and west also is interpreted to be the result of ice wedge formation permafrost extended to about 38 30 n latitude and formed during the interval from about 21 000 to 16 000 yr b p formation and degradation of permafrost was time transgressive directly related to the ice marginal climate and probably restricted temporally to less than 1000 years at a site the following environmental conditions are suggested near the ice margin mean annual ground temperature 3 c mean annual air temperature 6 2 c less precipitation than modern particularly in winter strong and likely dry wind systems and relatively open vegetation with few woody plants

sequence stratigraphy and the resolution of the fossil record sequence stratigraphy a major theoretical achievement of earth sciences integrates facies associations and stratal architecture within a chronological framework of the geological record the sequence stratigraphic model implies that sediment supply to the basin preservation potential of individual horizons and the resolution of paleontological data co vary with base level fluctuations especially for siliciclastic depositional systems using holocene transgressive regressive successions of the po plain italy we assessed the model s hypotheses by analyzing 249 marine mollusk shells dated individually using 14 c calibrated amino acid racemization methods as postulated by the model the temporal resolution of the fossil record frequency of depositional events and net accumulation rates decreased upward concomitantly through the transgressive systems tract reaching minima in the condensed section maximum flooding zone the reverse trend with increasingly frequent thicker and less time averaged beds was observed throughout the overlying highstand systems tract the results quantify the postulated sequence stratigraphic asymmetry in temporal resolution of the fossil and sedimentary records

earthquake recurrence and rupture dynamics of himalayan frontal thrust india the black mango fault is a structural discontinuity that transforms motion between two segments of the active himalayan frontal thrust hft in northwestern india the black mango fault displays evidence of two large surface rupture earthquakes during the past 650 years subsequent to 1294 a d and 1423 a d and possibly another rupture at about 260 a d displacement during the last two earthquakes was at minimum 4 6 meters and 2 4 to 4 0 meters respectively and possibly larger for the 260 a d event abandoned terraces of the adjacent markanda river record uplift due to slip on the underlying hft of 4 8 0 9 millimeters per year or greater since the mid holocene the uplift rate is equivalent to rates of fault slip and crustal shortening of 9 6 3 5 7 0 millimeters per year and 8 4 3 6 7 3 millimeters per year respectively when it is assumed that the hft dips 30 10

north american ice sheet reconstructions at the last glacial maximum abstract the areal extent of the last glacial maximum lgm ice sheets is well known in north america but there is no direct geological proxy for ice sheet thickness or volume uncertainties associated with glaciological and geophysical reconstructions give widely varying estimates of north american ice sheet nais volume at lgm in an effort to quantify the uncertainty associated with glaciological reconstructions we conducted a suite of 190 numerical simulations of the last glacial cycle in north america prescribing different climatic mass balance glaciologic and isostatic treatments for the least constrained model variables lgm ice sheet reconstructions were evaluated using the well established geologic record of ice sheet area and southern extent at lgm dyke and prest 1987 these constraints give a subset of 33 simulations that produce reasonable lgm ice cover in north america ice sheet dispositions and the associated parameter settings in this subset of tests provide insight into the plausible range of nais thickness form and mass balance regime at lgm ice volume in this subset of tests spans a range of 28 5 38 9 10 15 m 3 at lgm with a predominant cluster at 32 36 10 15 m 3 taking floating ice and displaced continental water into account this corresponds to 69 94 m eustatic sea level msl more than 75 of the accepted tests fall in the range 78 88 msl we argue that this is a plausible estimate of the volume of water locked up in the nais at lgm

subsurface combustion in mali refutation of the active volcanism hypothesis in west africa surface heat anomalies have been known in the timbuktu region in northern mali for more than a century since about 1960 several authors have argued that these heat anomalies are caused by incipient volcanic and hydrothermal activity surface temperatures as high as 765 c were measured locally in january 2002 and smoke emanated from holes and fractures in the ground we demonstrate that subsurface combustion of organic material is the source of the heat and the gases several square kilometers are currently active or have been affected by subsurface fires since 2001 self ignition during biological degradation of organic rich layers in the lacustrine deposits is the most likely mechanism that started the subsurface combustion that caused the heat anomalies in the area an important consequence of this conclusion is that west africa should still be regarded as volcanologically inactive and that possible reactivations of the major ew trending guinean nubian lineament are not associated with volcanism we suggest that the subsurface combustion in the timbuktu region today represents a phenomenon with a very long record in the trans saharan region

geomorphology in relation to tectonics a case study from the eastern himalayan foothills of west bengal india abstract the effects of neotectonic activity on geomorphic features have been studied in a large alluvial fan in the foothills area of the eastern himalayas the interfluve area between the rivers mal and murti is an alluvial fan composed of quaternary sediments characterized by clay sand pebble and boulder beds most of the river valleys in this area show well developed terraces there are four major terrace surfaces named as t 1 t 2 t 3 and t 4 according to increasing height from the river bed two e w scarps named as matiali and chalsa scarps that cut across the fan represent traces of the main boundary thrust mbt and the himalayan frontal thrust hft respectively there are two other nnw sse and nne ssw lineaments which have partially guided the courses of the neora and murti rivers these are interpreted as conjugate sets of normal faults transverse to the orogenic trend the e w scarps are the manifestation of the frontal limbs of the ramp anticlines over two blind thrusts fault propagation folding has affected the fan surface recurrent movements on the thrusts and consequent downcutting of the rivers have led to the formation of the raised terraces on the banks of these rivers the terraces are formed by cut and fill process later transverse normal faulting has given rise to a horst of the neora mal interfluve block

timing and origin for sand dunes in the green river lowland of illinois upper mississippi river valley usa abstract the recent increase in dune studies in north america has been heavily focused in the great plains while less attention has historically been given to the dune fields east of the mississippi river here we report ages and suggest a potential sediment source for sand dunes in the green river lowland illinois which may provide a better understanding of the dynamic interactions between eolian glacial lacustrine and fluvial processes that shaped the landscapes of the upper midwest seven coherent optically stimulated luminescence ages osl or optical ages obtained from four sites suggest that major dune construction in the green river lowland occurred within a narrow time window around 17 500 ago this implies either an enhanced aridity or an episodic increase of sediment supply at 17 500 years ago or combination of the both contrary to previous assertions that dune sand was sourced from the deflation of the underlying outwash sand deposited when the lake michigan lobe retreated from the area we propose that green river lowland dunes sand originated from the green bay lobe through the rock river specifically sediment supply increased in the rock river valley during drainage of glacial lake scuppernong which formed between 18 000 and 17 000 years ago when the green bay lobe retreated from its terminal moraine the lake drained catastrophically through the rock river valley providing glacial sediment and water to erode the preexisting sandy sediments throughout the remainder of the late pleistocene the laurentide ice sheet drained into larger more northerly glacial lakes that in turn drained through other river valleys therefore the dunes in the green river lowland formed only during the catastrophic drainage of glacial lake scuppernong but were stabilized through the remainder of the pleistocene this scenario explains the abrupt dune construction around 17 500 years ago and explains the lack of later dune activity up to the pleistocene holocene transition osl and radiocarbon ages also indicate that dunes were reactivated during the early middle and late holocene some eolian activation occurred within well defined dry intervals in the upper midwest suggesting that increased aridity may have been the primary driver in mobilizing sand however many ages do not correspond to drier periods in contrast to the relative coherency of the pleistocene osl ages from multiple study sites the holocene osl ages do not overlap from one site to another suggesting that increased aridity alone cannot explain the multiple phases of dune reactivation in the holocene therefore we conclude that the combined effect of localized disturbances and greater aridity acted in concert to increase eolian sand activity in the holocene the multiple periods of eolian activity during the holocene suggest a high potential for future sand activation in the region and these results are informative for environmental prediction and potential future mitigation

pattern of active tectonic deformation across the churachandpur mao thrust zone of manipur hills indo myanmar range ne india inferences from geomorphic features and indices abstract the churachandpur mao thrust cmt in indo myanmar range imr is known to be tectonically active but nevertheless the extent and pattern of activities on it and effects thereof on the surrounding region has not been determined as yet we herein present the results of our tectonic geomorphological investigations on these aspects across a long stretch of cmt zone spanning western imphal intermontane valley and enclosing frontal mountains the nne ssw trending cmt and nw se trending sekmai fault have subdivided the area into four tectonic blocks geomorphic features in conjunction with statistically analyzed mountain front sinuosity index smf stream length gradient index sl hypsometric integral hi drainage basin asymmetry factor af and transverse topography symmetry factor t reveal variations in nature and extent of tectonic activities and thus the pattern of surface deformation in these tectonic blocks tectonic blocks to the north of sekmai fault are experiencing more intense activities than the tectonic blocks to the south of sekmai fault north of the sekmai fault the cmt s footwall is experiencing the most intense activity and thus severe surface deformation in the area whereas the tectonic activity in the cmt s hanging wall here is only intense in the northern part to the south of sekmai fault while the hanging wall of the cmt is experiencing relatively moderate tectonic activities the footwall of the cmt is experiencing moderate to intense tectonic activities in different parts being most intense close to the sekmai fault tectonic activities have caused an overall southward down tilting of the cmt s footwall to the north of sekmai fault and overall northward down tilting of the remaining three tectonic blocks evidently the tectonic activities and thus the pattern of active surface deformation in the cmt zone of the area is significantly influenced by the transverse sekmai fault

modeling the subglacial hydrology of the late pleistocene lake michigan lobe laurentide ice sheet the fast ice flow characteristic of the low gradient lake michigan lobe of the southern laurentide ice sheet during the last glaciation likely resulted from some combination of subglacial sediment deformation and sliding at the ice bed interface both mechanisms require high basal water pressure relative to overlying ice pressure to evaluate the basal water pressures of the lake michigan lobe we used the groundwater model modflow to simulate groundwater flow along a 1040 km long flow line corresponding to the flow path taken by the ice lobe our simulations show that groundwater flow directions and velocities were substantially different than modern conditions simulations also indicate that subglacial aquifers were not capable of evacuating the estimated basal meltwater but that excess water draining through a basal drainage system such as one that may underlie ice stream b west antarctic ice sheet would prevent basal water pressure from exceeding the ice overburden pressure the buried mahomet bedrock valley system near the distal end of the lake michigan lobe could have drained enough subglacial water to substantially lower basal water pressure and thus affect the dynamics of the lobe by draining basal meltwater away from the lake michigan lobe the buried mahomet bedrock valley system may have attenuated the effect of permafrost on basal water pressure during the last glacial maximum groundwater flow patterns and velocities were altered or reversed relative to present conditions

shallow gas and flood deposition on the po delta abstract sediment cores acquired on the po delta northwestern adriatic sea in water depths of 10 to 25 m yielded anomalous concentrations of methane up to 41 300 ppm of the 19 unique sites analyzed 5 sites 9 cores had more than 90 ppm of ch 4 and of those 3 sites 4 cores had more than 13 800 ppm methane compositional and isotopic analyses of the gas support a bacterial origin anomalous methane concentrations were found in kasten gravity and box cores where more than one core type was acquired at a single location all cores contained anomalous methane despite the regional high productivity in the adriatic all of the highest gas concentrations were found in the region associated with the thickest accumulation of recent flood deposits off the most active channel of the po delta po di pila cores acquired in this region contain primary sedimentary structures that indicate rapid burial of thick 10 cm flood deposits and a relative lack of bioturbation down to the base of the flood layer we propose that in the po delta flood deposits deliver significant amounts of terrigenous organic matter that can be rapidly buried on the prodelta effectively removing this organic matter from aerobic oxidation and biological uptake and leading to the potential for methanogenesis with burial in areas unaffected by this high flux of organic matter and rapid thick flood deposition or in between flood events our data indicate that the conditions for methanogenesis and gas accumulation have not been met we suggest that in these areas the physical and biological reworking of the surficial sediment between flood events may effectively oxidize and mineralize organic matter derived from both marine and terrestrial sources and limit bacterial methanogenesis in the subsurface

modeling the complexity of different recently deglaciated soil landscapes as a function of map scale the scale at which a soil landscape soilscape is viewed has a significant impact on soil pattern and interpretations made from those patterns recently deglaciated soilscapes are particularly spatially complex in order to understand how scale impacts pattern on complex soilscapes we used a gis to examine soil maps for 13 counties in the northern united states all affected by late wisconsinan glaciation we used an arck macro language script to change the map scale and when the change was to a smaller scale group dissolve soil map units based on similarities to a prescribed list of neighboring map unit characteristics similarity criteria included drainage class taxonomic great group parent material and slope soilscape complexity was measured at nine different scales and is based on various pattern metrics number of punctate soil units km 2 map unit polygons km 2 map unit boundary length km 2 and boundary length polygon 1 km 2 soilscape complexity as a function of scale was then examined by regressing pattern metric data against the size of the minimum map unit for each of the nine scales extrapolation of the regression lines to 1 10 000 a scale larger than is typically mapped illustrated how much additional information might accrue if these counties were to be mapped at that larger scale in most cases 2 10 times more map units would have been recognized and delineated at the two times larger map scale but map unit boundary lengths would have increased by only about 1 5 times whether this additional information is of such a magnitude that it could justify remapping some of these complex landscapes at larger scales is an economic decision our study provides much needed data on the magnitude of information gained by mapping soilscapes at larger scales d 2004 elsevier b v all rights reserved

up in the refrigerator geomorphic response to periglacial environments in the upper mississippi river basin usa abstract james c knox was best known for his work on holocene and historical changes in fluvial systems but he also had a long standing interest in the effects of late pleistocene periglacial environments on landscape evolution in parts of the upper mississippi river basin that were just outside the laurentide ice sheet margin or as knox put it up in the refrigerator knox and others in the quaternary community of the midwestern u s often suggested that hillslope erosion was accelerated under periglacial conditions so that glacial periods have had a dominant effect on the landscape we see today this paper reviews the evidence and reasoning supporting that view in a study area of the upper mississippi basin bordered on three sides by ice margins of the last glaciation including the wisconsin driftless area and adjacent landscapes sparse but compelling paleoecological data and relict ice or sand wedge polygons provide clear evidence for a cold climate and widespread permafrost around the peak of the last glaciation in highly dissected relatively high relief parts of the study area the loess and soil stratigraphy on ridgetops and the colluvial mantles on steeper slopes are best explained by highly effective hillslope erosion including solifluction during and just after the last glacial maximum knox used the post depositional truncation of a loess unit to quantify contrasting late pleistocene and holocene sediment yields from a small driftless area watershed while the late pleistocene yield indicates accelerated erosion it is still lower than modern sediment yields in many tectonically active or semiarid landscapes and it may reflect deposition of highly erodible loess as well as effects of periglacial conditions the views of knox and other midwestern geomorphologists on landscape evolution through glacial interglacial cycles were highly influenced by the work of robert v ruhe ruhe proposed that an episode of widespread erosion during and just after the last glacial maximum can explain enigmatic aspects of quaternary stratigraphy and the soil landscape on the iowan erosion surface a very low relief landscape of the study area ruhe s key evidence is still valid though it needs to be separated from an implausible model of landscape evolution interpretation of the iowan erosion surface and other low relief landscapes just outside the ice margin also requires recognition of the profound effect of eolian processes on those landscapes under periglacial conditions many new insights on landscape evolution in the study area could result from wider application of cosmogenic nuclide based methods to assess glacial interglacial changes in basinwide rates of erosion and residence time of soils just as important a need exists for much more field based characterization of hillslope fluvial and eolian sediments for comparison with those of modern permafrost regions and past periglacial environments in europe

use of liquefaction induced features for paleoseismic analysis an overview of how seismic liquefaction features can be distinguished from other features and how their regional distribution and properties of source sediment can be used to infer the location and strength of holocene paleo earthquakes abstract liquefaction features can be used in many field settings to estimate the recurrence interval and magnitude of strong earthquakes through much of the holocene these features include dikes craters vented sand sills and laterally spreading landslides the relatively high seismic shaking level required for their formation makes them particularly valuable as records of strong paleo earthquakes this state of the art summary for using liquefaction induced features for paleoseismic interpretation and analysis takes into account both geological and geotechnical engineering perspectives the driving mechanism for formation of the features is primarily the increased pore water pressure associated with liquefaction of sand rich sediment the role of this mechanism is often supplemented greatly by the direct action of seismic shaking at the ground surface which strains and breaks the clay rich cap that lies immediately above the sediment that liquefied discussed in the text are the processes involved in formation of the features as well as their morphology and characteristics in field settings whether liquefaction occurs is controlled mainly by sediment grain size sediment packing depth to the water table and strength and duration of seismic shaking formation of recognizable features in the field generally requires a low permeability cap above the sediment that liquefied field manifestations are controlled largely by the severity of liquefaction and the thickness and properties of the low permeability cap criteria are presented for determining whether observed sediment deformation in the field originated by seismically induced liquefaction these criteria have been developed mainly by observing historic effects of liquefaction in varied field settings the most important criterion is that a seismic liquefaction origin requires widespread regional development of features around a core area where the effects are most severe in addition the features must have a morphology that is consistent with a very sudden application of a large hydraulic force this article discusses case studies in widely separated and different geological settings coastal south carolina the new madrid seismic zone the wabash valley seismic zone and coastal washington state these studies encompass most of the range of settings and the types of liquefaction induced features likely to be encountered anywhere the case studies describe the observed features and the logic for assigning a seismic liquefaction origin to them also discussed are some types of sediment deformations that can be misinterpreted as having a seismic origin two independent methods for estimating prehistoric magnitude are discussed briefly one method is based on determination of the maximum distance from the epicenter over which liquefaction induced effects have formed the other method is based on use of geotechnical engineering techniques at sites of marginal liquefaction in order to bracket the peak accelerations as a function of epicentral distance these accelerations can then be compared with predictions from seismological models

land snails from the last glacial maximum on andikithira southern greece and their palaeoclimatic implications an assemblage of land snails from an aeolianite deposit on the coast of the southern greek island of andikithira is shown to date to 16 000 yr bp and thus represents the period of the last glacial maximum lgm oxygen isotope stage 2 the assemblage has no modern analogue five of the ten species are extinct on the island and some of these now live only at high elevations 950 m significantly cooler temperatures some 5 8 c below present and slightly drier moisture conditions lower rainfall partially offset by reduced evapotranspiration at the lower temperature are inferred the large temperature depression at the lgm well documented in northern and central europe extended also to the mediterranean climate of southern europe late quaternary climatic changes had a considerable impact on the fauna of this isolated island

himalayan seismic hazard the devastating earthquake in bhuj on 26 january 2001 highlighted the high earthquake risk in the indian region of gujarat in their perspective bilham et al warn that major earthquakes may be expected in another part of india the himalayan arc an analysis of historic earthquakes suggests that several major earthquakes are overdue in this region but that recent low activity has focused attention away from the himalayan arc projections from earlier earthquakes suggest that just one of the possibly overdue himalayan earthquakes may lead to 200 000 predictable fatalities

the pattern and style of deglaciation at the late wisconsinan laurentide and cordilleran ice sheet limits in northeastern british columbia this paper reports on the landform assemblages at the northern confluence of the late wisconsinan laurentide and cordilleran ice sheets with montane and piedmont glaciers in the northern rockies and southern mackenzie mountains recent observations in northeastern british columbia refine our knowledge of the pattern and style of ice sheet retreat glacial lake formation and meltwater drainage at the onset of deglaciation confluent laurentide and cordilleran terminal ice margins lay between 59 n 124 30 w and 60 n 125 15 w from this terminal limit ice sheets retreated into north central british columbia and yukon territory with remnant cordilleran ice and montane glaciers confined to mountain valleys and the liard plateau distinctive end moraines are not associated with the retreat of cordilleran ice in these areas laurentide ice retreated northeastward from uplands and the plateaus then separated into lobes occupying the fort nelson and petitot river valleys ice retreat landforms include recessional end moraines sometimes overridden and drumlinized hill hole pairs crevasse fill deposits de geer like ribbed till ridges hummocky moraines kames meltwater features and glacial lake deposits that fall within the elevation range of glacial lake liard and glacial lake fort nelson ca 840 380 m meltwater and sediment transport into glacial lakes fort nelson liard nahanni and mackenzie was sustained by remnant ice in the liard river and fort nelson river drainage basins until the end of glaciation optical dating of sand from stabilized parabolic dunes on the liard plateau indicates that proglacial conditions lake formation and drainage began before 13 0 0 5 ka calendar years the petitot fort nelson and liard rivers all occupy spillways incised into glacial deposits and bedrock by meltwater overflow from glacial lakes peace and hay

periglacial climate at the 2 5 ma onset of northern hemisphere glaciation inferred from the whippoorwill formation northern missouri usa the whippoorwill formation is a gleyed diamicton that is present locally within bedrock depressions beneath the oldest glacial till in northern missouri usa stratigraphy paleomagnetism and cosmogenic nuclide burial ages show that it was deposited between the matuyama gauss magnetostratigraphic boundary at 2 58 ma and the first advance of the laurentide ice sheet into missouri at 2 47 0 19 ma high cosmogenic nuclide concentrations also show that the constituents of the whippoorwill formation experienced long exposure at a stable landscape surface with erosion rates of 1 2 m ma however cosmogenic nuclide concentrations are invariant with depth below the whippoorwill formation surface indicating active mixing of the soil profile shortly before burial by till the whippoorwill formation retains numerous features indicative of cryoturbation therefore we interpret it as a buried gelisol a soil formed under periglacial conditions in the presence of permafrost at the onset of northern hemisphere glaciation climate cooling established permafrost conditions and accelerated erosion by inducing landscape instability thus weathered regolith materials were mobilized and redeposited by gelifluction shortly before the ice sheet overrode the landscape

simulation of the climate of 18 000 years bp results for the north american north atlantic european sector and comparison with the geologic record of north america abstract the large ice sheets in north america and europe and the extensive sea ice cover in the north atlantic at the time of the last glacial maximum must have greatly modified the surface temperature patterns and in turn the location and intensity of the surface winds and jet streams a general circulation model was used to simulate the january and july patterns of temperature precipitation and wind for 18 ka bp boundary conditions for the model consisting of ice sheet location and height sea ice location and sea surface temperature were prescribed from climap 1981 the model results are illustrated and described for the north american north atlantic european sector the jet stream splits around the north american ice sheet and the southern branch strengthens considerably compared to present over the southern portion of the united states the sea ice margin of the north atlantic and the southern edge of the european ice sheet geologic evidence principally from north america of wind temperature and moisture conditions is assessed from sand dune and loess records estimates of snowline depression pollen records and lake level studies the geologic evidence is generally compatible with the model simulation

evidence at lomax illinois for mid wisconsin 40 000 yr b p position of the des moines lobe and for diversion of the mississippi river by the lake michigan lobe 20 350 yr b p abstract an abrupt change in environment from a wetland to a deeper slackwater lake at 20 345 85 yr b p occurred in a second order valley tributary to the mississippi river near lomax illinois the age of this shift is associated with the overflow of glacial lake milan and diversion of the mississippi river from the princeton valley rock island to peoria to its present course rock island to st louis the diversion occurred due to blockage of the princeton valley segment of the ancient mississippi river by the lake michigan lobe impoundment of glacial lake milan and eventual overflow of the lake southwest of rock island across a former drainage divide near andalusia illinois fossil ostracode assemblages in the slackwater sediment at lomax indicate changes in the post diversion full glacial paleohydrology and based on multivariate analysis hint at the area s paleoclimate an older part of the succession at lomax is consistent with glaciation in the upper iowa river basin about 40 000 yr b p aggradation of sediment rich in coarse silt is attributed to a response of the ancient iowa river basin associated with deposition of the glacigenic sheldon creek formation by the des moines lobe