tertiary tectonics of the border ranges fault system chugach mountains alaska deformation and uplift in a forearc setting the border ranges fault system brfs locally separates supracrustal upper cretaceous tertiary rocks of the cook inlet matanuska valley forearc basin on the peninsular terrane from metamorphosed cretaceous subduction complex rocks of the chugach terrane to the south this 5 to 10 km wide zone of concentrated deformation along the inboard edge of southern alaska s accretionary prism has suffered a protracted history beginning with its inception as a megathrust by early cretaceous time and continuing into early tertiary time when it was transected by a system of steeply arcward dipping normal and dextral slip faults based on detailed geologic mapping structural analysis metamorphic mineral assemblage data and k ar and fission track geochronology the tertiary history of displacements along a central part of this forearc fault system has been divided into several phases of deformation these include a paleocene phase of regional uplift of the forearc basin together with block faulting along the brfs to rapidly uplift and subaerially expose low grade metamorphic rocks of the subduction complex upper cretaceous valdez group within 15 ma of their inferred underplating at deep structural levels of the accretionary prism continued normal separation faulting along the brfs in late paleocene early eocene time to further uplift the subduction complex was recorded by deposition of a syntectonic alluvial fan system chickaloon formation across the brfs and along the southern margin of the forearc basin a third mid eocene increment of normal separation faulting along the brfs juxtaposed greenschist facies fabrics of early eocene age in the subduction complex against the chickaloon formation this latter uplift event predated intrusion of early late eocene 43 48 ma zircon fission track minimum ages felsic dikes into the present terrane bounding fault and was accompanied by no more than a few tens of kilometers of dextral slip faulting along the brfs a conclusion that does not accord with recent suggestions for thousands of kilometers of displacement along that fault system in early middle tertiary time based on paleomagnetic data field observations in the study area indicate that the great oroclinal bend of southern alaska is postearly eocene and possibly prelate oligocene in age a final period of deformation in middle to late tertiary time was marked by periods of minor north south contraction of the forearc basin and by local reverse slip reactivation of earlier faults fission track age data on apatite indicate rapid cooling and probably uplift of both subduction complex and adjacent parts of the forearc basin in miocene time 17 24 ma episodic uplift of the subduction complex either locally by normal separation faulting along its backstop or by a more regional uplift also affecting the adjacent forearc basin overlapped in time or closely followed discrete pulses of large scale sediment underplating along the gulf of alaska subduction margin this coincidence suggests that major pulses of sediment underplating along southern alaska s convergent margin may have led to isostatic uplift of its critical taper accretionary prism an uplift that was in part accommodated by normal separation faulting along its mechanical backstop

the internal sediment architecture of a drumlin port byron new york state usa abstract an exposure within the central portion of a large drumlin at port byron new york state usa part of the large new york drumlin field reveals a sequence of steeply dipping cemented sands and gravels of proglacial ice contact deltaic origin overlain by a thin till veneer the sands and gravels appear to have been deposited within the proximal proglacial environment during a late retreat phase of the laurentide ice sheet sometime prior to being overridden by subsequent ice and drumlinized during deposition of the ice contact delta escaping subglacial regelation meltwater permeated the proximal deltaic sediment pile and calcium carbonate was released in a series of pulses to form pore occluding calcite cement within the sand and gravel porespaces the calcium carbonate precipitated into the sands and gravels due to a reduction in hydrostatic pressure and co2 outgassing of the meltwater as it exited from beneath the ice sheet once cemented these deltaic sediments were considerably stronger and acted afterward as an obstacle around which the future ice advance streamed and in turn produced the characteristic drumlin shape in overriding the ice contact deltaic sediments the ice sheet emplaced a thin layer of till which exhibits syndepositional deformation features indicative of being emplaced as a deforming bed layer beneath the advancing ice sheet micromorphological analysis of the overlying till shows that no interstitial or intraclastic calcite occurs within the till

new paleogene paleoclimate analysis of western washington using physiognomic characteristics from fossil leaves abstract the chuckanut and manastash formations were deposited in a lowland fluvial environment in western washington during the paleocene eocene we provide a thorough paleotemperature analysis using the physiognomic characteristics from the fossil dicotyledonous leaves from these formations using two techniques leaf margin analysis lma and climate leaf analysis multivariate program clamp this work differs from previous analyses by 1 analyzing more localities and including the assessment of the never before described taneum ridge body and manastash main body within the manastash formation and the maple falls member of the chuckanut formation and 2 using two different techniques to decipher mean annual temperatures through time in this study mean annual temperatures mat were determined from 125 distinct morphotypes and are several degrees higher at each locality than previously reported mat values derived from lma ranged from 17 0 to 28 8 c for the lowermost and 13 4 to 19 5 c for the uppermost chuckanut formation the manastash formation had mats ranging from 17 1 c to 29 1 c using clamp paleotemperatures ranged from 15 3 to 19 4 c for the lowermost and 12 3 to 15 6 c for the uppermost chuckanut formation and 15 8 to 21 3 c for the manastash formation these data are compared to other eocene paleocene formations in the western us the chuckanut and manastash formations record some of the warmest paleotemperatures in the paleogene in the western us because of their low elevation locations these paleotemperatures may reflect the terrestrial signal of paleoclimate optima defined in marine rocks during the paleocene eocene

fossil wood in coal forming environments of the late paleocene early eocene chickaloon formation the early cenozoic chickaloon formation is the main coal bearing sequence in south central alaska coal and associated plant macrofossils are well exposed in the eska premier and jonesville coal groups in the wishbone hill district there is a striking variation in the degree and mode of preservation of fossil trees in a vertical sequence through these coal groups we examined the wood taxonomy mineralogy and geochemistry to elucidate potential cause s for these differences the wood anatomy indicates that the wood is all assignable to the cupressaceae taxodiaceae s str and assignable to the form genus taxodioxylon hartig emend gothan however we found no significant variation in the taxonomy of the wood between stratigraphic layers the wood generally becomes better preserved in the jonesville coal group wood from the stratigraphically lower premier coal group exhibits greater plastic deformation and contains less well preserved wood anatomical features the wood from the overlying jonesville coal group retains most of its original morphology but has suffered from brittle fracture the geochemistry and mineralogy of the wood follow a pattern that corresponds to the degree of preservation the less well preserved wood tends to have a higher concentration of iron carbonate minerals e g siderite and ankerite whereas the better preserved wood contains more calcium carbonate or silica all evidence points to rapid permineralization of the original wood although the least well preserved wood shows evidence of greater organic matter decomposition than the better preserved wood the wood taxonomy and mode of preservation of wood from the upper part of the chickaloon formation is similar to wood from coeval fossil forests that developed at higher polar paleolatitudes

the last glacial maximum in the north sea basin micromorphological evidence of extensive glaciation despite a long history of investigation critical issues regarding the last glacial cycle in northwest europe remain unresolved one of these refers to the extent timing and dynamics of late devensian weichselian glaciation of the north sea basin and whether the british and scandinavian ice sheets were confluent at any time during this period this has been the result of the lack of the detailed sedimentological data required to reconstruct processes and environment of sediments recovered through coring this study presents the results of seismic sedimentological and micromorphological evidence used to reconstruct the depositional processes of regionally extensive seismic units across the north sea basin thin section micromorphology is used here to provide an effective means of discriminating between subglacial and glacimarine sediments from cored samples and deriving process based interpretations from sediment cores on the basis of micromorphology critical formations from the basin have been reinterpreted with consequent stratigraphic implications within the current stratigraphic understanding of the north sea basin a complex reconstruction is suggested with a minimum of three major glacial episodes inferred on at least two occasions during the weichselian devensian the british and scandinavian ice sheets were confluent in the central north sea whilst micromorphology can provide much greater confidence in the interpretation of late quaternary offshore stratigraphic sequences it is noted that a much better geochronology is required to resolve key stratigraphic issues between the onshore and offshore stratigraphic records copyright 2006 john wiley sons ltd

micromorphology of iceberg scour in clays glacial lake agassiz manitoba canada abstract icebergs plough through unconsolidated lake sea sediments gouging out kilometre long grooves 100s of metres wide and tens of metres deep although the surface morphology of iceberg scours is well documented little is known about what scours look like in stratigraphic section particularly where surface characteristics are absent e g through decay or burial this investigation establishes a definitive suite of diagnostic criteria for identifying iceberg scours in clays by macroscopically and microscopically 2d thin sections examining sediment deformation below iceberg scours in former glacial lake agassiz manitoba canada structures unequivocally attributed to iceberg scour in this investigation include sub horizontal microfabrics folds sheath folds augen shapes normal faults reverse thrust faults discrete shears partially destroyed clasts intraclasts type iii multiple domains water escape structures flow structures unistrial plasmic fabric dropstones realigned bedding and specific structural sequences this research will be particularly valuable in palaeoenvironmental reconstruction and in predicting glacial dynamics in addition it may eventually aid structural engineering on polar shelves which could be of great value to oil and gas companies

a method for computing infiltration and redistribution in a discretized moisture content domain 1 a new one dimensional infiltration and redistribution method is proposed as an alternative to the richards equation re for coupled surface and subsurface models the proposed method discretizes soil water content into hypothetical hydraulically interacting bins the entry and propagation of displacement fronts in each bin are simulated by means of explicit infiltration and drainage approximations based on capillary and gravitational driving forces wetting front advances within bins create water deficits that are satisfied by capillary driven interbin flow the method inherently provides numerical stability by precluding the need to directly estimate nonlinear gradients through numerical schemes comparisons of the performance of this method against re solutions for theoretical laboratory and field data in both well drained and high water table conditions are presented the new method produces infiltration flux estimates with errors less than 10 compared to a widely used re solution in tests on multiple soil textures with and without high water table conditions while providing unconditionally guaranteed conservation of mass

green ampt infiltration parameters from soils data the analysis of approx 5 000 soil horizons indicated that green and ampt parameters effective porosity wetting front capillary pressure and hydraulic conductivity could not be developed based on phases of soil order or suborder however sets of average parameters are developed based on soil horizon or soil texture class or both a procedure for determining the green and ampt parameters based on soil properties utilizing the full spectrum of soil survey information is outlined

progressive soft sediment deformation within a subglacial shear zone a hybrid mosaic pervasive deformation model for middle pleistocene glaciotectonised sediments from eastern england this paper presents a hybrid pervasive and mosaic model for the progressive deformation of a stratified diamicton complex in eastern england within an active subglacial shear zone sedimentary evidence from undeformed low strain zones towards the base of the sediment pile indicates that the tectonised sediments were originally deposited as a series of subaqueous flows in a glaciolacustrine basin these sediments have subsequently been deformed during a progressive subglacial shearing event this event is divided into three stages ductile folding and sediment remobilisation d1 brittle faulting in the form of reidel shears d2 and hydrofracturing and sediment remobilisation d3 the dominant control on the pattern and style of deformation appears to relate to the rate of thrust induced till accretion and the aquifer properties and pore water content and or pressure of the deforming sediments

moving multi front mmf a generalized green ampt approach for vertical unsaturated flows abstract a moving multi front mmf method is developed and tested for solving the richards equation governing unsaturated flow in vertical homogeneous porous columns the mmf model is a gridless method it can be viewed as a generalization of the green ampt piston flow approach which models flow as a single abrupt moving front separating saturated and dry regions during infiltration the mmf model further generalizes this concept using a parametrization of unsaturated water retention and conductivity pressure curves it reduces the richards pde to an ode system governing m moving front positions different tests are developed to validate this approach for 1d transient downwards upwards flows submitted to constant and time varying pressure boundary conditions they include i infiltration to deep water tables ii infiltration to shallow water tables iii capillary rise from fixed water tables iv gradual water table rise partially saturated column with evolving pressure condition at bottom the mmf results are compared favorably to finely discretized fixed grid solutions of richards pde analyses of error and accuracy show satisfactory results in terms of water content profiles and boundary fluxes e g infiltration rate

ponded infiltration into soils bounded by a water table a simple model of ponded infiltration into homogenous soils bounded by and at steady state equilibrium with a water table is presented the model parameterizes the wetting front profile as a tension saturated zone above a zone in which the moisture content decreases linearly with depth application of the model requires numerical evaluation of an integral relating the time since the onset of ponding to the infiltration rate or wetting front position wetting fronts predicted by the simplified model compare favorably with laboratory measurements of vachaud and thony 1971 and for a wide range of soil types with those predicted by finite element integration of the governing flow equations the presence of a shallow water table causes the infiltration rate to decrease faster than it would under semi infinite conditions with uniform initial moisture content infiltration equations for soils bounded by water table may be used in distributed hydrologie models and other applications where the shallow position of the water table significantly affects the partitioning of precipitation forcing during storms

stable carbon isotopes of c3 plant resins and ambers record changes in atmospheric oxygen since the triassic estimating the partial pressure of atmospheric oxygen po2 in the geological past has been challenging because of the lack of reliable proxies here we develop a technique to estimate paleo po2 using the stable carbon isotope composition d 13 c of plant resins including amber copal and resinite from a wide range of localities and ages triassic to modern plant resins are particularly suitable as proxies because their highly cross linked terpenoid structures allow the preservation of pristine d 13 cs ignatures over geological timescales the distribution of d 13 c values of modern resins n 126 indicates that a resin producing plant families generally have a similar fractionation behavior during resin biosynthesis and b the fractionation observed in resins is similar to that of bulk plant matter resins exhibit a natural variability in d 13 c of around 8 d 13 cr ange 31 to 23 m ean 27 which is caused by local environmental and ecological factors e g water availability water composition light exposure temperature nutrient availability to minimize the effects of local conditions and to determine long term changes in the d 13 co f resins we used mean d 13 c values d 13 c resin for each geological resin deposit fossil resins n 412 are generally enriched in 13 c compared to their modern counterparts with shifts in d 13 c resin of up to 6 these isotopic shifts follow distinctive trends through time which are unrelated to post depositional processes including polymerization and diagenesis the most enriched fossil resin samples with a d 13 c resin between 22 and 21 formed during the triassic the mid cretaceous and the early eocene experimental evidence and theoretical considerations suggest that neither change in pco2 nor in the d 13 c of atmospheric co2 can account for the observed shifts in d 13 c resin the fractionation of 13 c in resin producing plants d 13 c instead is primarily influenced by atmospheric po2 with more fractionation occurring at higher po2 the enriched d 13 c resin values suggest that atmospheric po2 during most of the mesozoic and cenozoic was considerably lower po2 10 20 than today po2 21 in addition a correlation between the d 13 c resin and the marine d 18 o record implies that po2 pco2 and global temperatures were inversely linked which suggests that intervals of low po2 were generally accompanied by high pco2 and elevated global temperatures intervals with the lowest inferred po2 including the mid cretaceous and the early eocene were preceded by large scale volcanism during the emplacement of large igneous provinces lips this suggests that the influx of mantle derived volcanic co2 triggered an initial phase of warming which led to an increase in oxidative weathering thereby further increasing greenhouse forcing this process resulted in the rapid decline of atmospheric po2 during the mid cretaceous and the early eocene greenhouse periods after the cessation in lip volcanism and the decrease in oxidative weathering rates atmospheric po2 levels continuously increased over tens of millions of years whereas co2 levels and temperatures continuously declined these findings suggest that atmospheric po2 had a considerable impact on the evolution of the climate on earth and that the d 13 c of fossil resins can be used as a novel tool to assess the changes of atmospheric compositions since the emergence of resin producing plants in the paleozoic

assessing the formation of valley networks on a cold early mars predictions for erosion rates and channel morphology abstract the ancient noachian highlands of mars host an extensive population of valley networks which formed predominantly during the early geologic history of the planet morphologic characteristics of the valley networks have been interpreted to indicate the formation of these features through precipitation derived fluvial activity and therefore as evidence for a relatively warm and wet noachian mars climate however these interpretations conflict with the results of sophisticated global climate modeling studies which suggest that early mars was dominated by a cold and icy climate with conditions characterized by adiabatic cooling and regional ice sheets within the highlands difficulties in replicating the warm and wet early climate conditions interpreted from the valley networks has served as the basis for alternative suggestions for the formation of valley networks by transient heating and snowmelt in an otherwise cold and icy climate here we test a conceptual model for valley network formation and incision under cold and icy conditions with a substrate characterized by the presence of an ice free desiccated surface regolith and subjacent ice cemented regolith similar to that found in the antarctic mcmurdo dry valleys on earth we implement numerical thermal models quantitative erosion and transport estimates and morphometric analyses in order to outline and test predictions for 1 the nature and structure of the cold and icy noachian substrate 2 valley network fluvial erosion and incision rates and 3 resulting channel valley morphology morphologic predictions are compared against observational data to determine if the valley networks characteristics are consistent with formation in a cold and icy climate through this approach we present and develop the underlying conceptual model identify and generate the fundamental data inputs required to evaluate it and perform a preliminary first order assessment to serve as a basis for further investigation while these analyses have been performed over a broad parameter space to address relative uncertainties we report findings with a specific emphasis on the nominal results we find that under cold conditions the substrate is characterized by a kilometers thick globally continuous cryosphere with a 50 100 m thick ice free surface layer in diffusive equilibrium with the atmosphere and underlying ice cemented regolith the top of which forms the ice table estimates of the potential infiltration capacity of the ice free surface regolith layer indicate that surface runoff generation does not require excessively large precipitation rates and thus does not preclude fluvial activity sourced by rainfall additionally due to the predicted thicknesses of the ice free surface regolith any transient period of warming would need to be sustained in duration 2 kyr to induce melting of ground ice to initiate solifluction gelifluction activity the predicted range of ice table depths is exceeded by the incised depths of a majority of the valley network population therefore suggesting interactions were possible evaluation of the rates of mechanical substrate erosion and thermal ice cement erosion by valley network fluvial activity are subject to large uncertainties due to several poorly constrained parameters i e the substrate erodibility factor and the valley network fluvial water temperature but generally indicate that at low water temperatures consistent with a cold and icy surface environment thermal erosion of the ice cement can be outpaced by mechanical erosion of the substrate in this scenario the relative efficiency of lateral erosion is predicted to be enhanced during incision below the ice table causing preferential channel valley widening and increased width to depth ratios assessment of this prediction through a morphometric analysis of valley network width to depth ratios and occurrence of u shaped cross sections indicates no significant correlation to ice table depths this result suggests that either 1 permafrost was not present in the noachian mars substrate indicating a warmer climate 2 the permafrost ice table did not significantly influence valley network width to depth ratios possibly owing to more rapid thermal erosion rates than mechanical or 3 additional factors not accounted for in this analysis are involved potential additional factors which could influence the results of this analysis include variable surface geothermal heat flux substrate thermal conductivity substrate composition and physical state as well as valley network preservation state and morphometric sampling biases due to data availability constraints these factors represent areas for future investigation to refine assessments of valley network formation under cold early mars conditions

eocene underplating along the kodiak shelf alaska implications and regional correlations structural geology and geophysical data from the kodiak shelf suggest that the mesozoic rocks exposed on the shelf are structurally underlain at about 12 km depth by several kms of eocene age strata kinematic data from the late cretaceous to paleocene ghost rocks formation indicate that this formation and probably all of the kodiak islands were uplifted vertically to nearly their present elevations landward tilting and imbrication are not indicated the age of uplift is indicated by a regional angular unconformity of early eocene to early oligocene age that separates deep sea rocks from shallow water to non marine rocks the uplift of the accretionary prism is believed to have been caused by underplating of an eocene sedimentary sequence because 1 a band of seismic reflections that occur 12 to 20 km beneath the shelf is interpreted as the top of the underplated material and 2 an obductively offscraped sequence of eocene deep sea rocks crops out on the seaward side of the kodiak shelf suggesting that a thick trench fill sequence may have been present prior to uplift of the prism the underplated material is interpreted to be part of either a previously unrecognized turbidite fan of early eocene age or a proximal equivalent of the zodiac fan of late eocene to early oligocene age other possible on land remnants of the underplated material may be present in prince william sound the montague belt the gulf of alaska lower sections of the yakutat block and in the coast ranges of oregon and washington the large volume of underplated material beneath the kodiak shelf suggests that underplating may be the dominant process in the growth of convergent margins

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

an mis 3 age organic deposit from balglass burn central scotland palaeoenvironmental significance and implications for the timing of the onset of the lgm ice sheet in the vicinity of the british isles this paper reports the analysis of a glaciotectonised organic deposit located between a lower weathered till and an upper unweathered till at balglass burn north of the campsie fells in central scotland uk close to the centre of ice accumulation in scotland sedimentology pollen macroscopic plant remains and coleoptera indicate accumulation in a small pond as part of an open tundra landscape with low floral diversity mcr palaeotemperature reconstructions for the coleoptera give a mean temperature for the warmest and the coldest months of 8 to 10 c and 26 to 10 c respectively indicating the presence of at least discontinuous permafrost six ams dates on carex fruit and coleoptera fragments give ages between 34 480 and 28 050 14c yr bp ca 39 8 to ca 32 8 cal yr bp fairbanks et al 2005 the upper till and the glaciotectonism are attributed to glaciation during the lgm glaciotectonic deformation means that the ages do not indicate sequential development and it is not possible to relate this palaeo evidence to the fine resolution palaeoclimatic signature for mis 3 however the fact that this part of central scotland was ice free at this time means that some recent proposals suggesting that the british ice sheet began to accumulate around the middle of mis 3 are unlikely to be correct copyright 2006 john wiley sons ltd

an investigation of subglacial processes at the microscale from briksdalsbreen norway the subglacial processes at briksdalsbreen norway are examined by a combination of sedimentology thin section and scanning electron microscope sem analysis of till samples from an exposed subglacial surface and from beneath the glacier studies of a fluted surface indicate that subglacial deformation is occurring on a field scale with flutes forming behind most clasts 0 6 m high at the thin section scale 0 014 2 0 mm it is seen that deformation is by rotation and attenuation and is dependent on till texture at the sem scale 0 1 0 4 mm it is seen that erosion is controlled by abrasion and percussion which produces distinct grain styles as part of an erosional continuum overall it is shown that rotation and attenuation is a dominant process at all scales and that the clast interactions associated with different scale perturbations within the shear zone control erosion and deposition as well as landform and fabric production

radiometric age of the chickaloon formation of south central alaska location of the paleocene eocene boundary k ar and fission track ages from two volcanic ash partings in upper chickaloon formation coals range from 53 3 1 5 m y to 55 8 1 7 m y these ages establish that the paleocene eocene boundary 55 m y occurs within the dated upper part of this formation

a case study in the new york drumlin field an investigation using microsedimentology resulting in the refinement of a theory of drumlin formation abstract the formation of drumlins remains a major enigma it is accepted that drumlins form under active temperate ice most likely within a soft sediment deforming bed at ephemeral sticky points these sticky points likely lead to the causative mechanism around which sediment nucleation occurs the critical question is under what conditions and where and how do sticky spots form a comparative investigation of a drumlin and mega flute in the new york drumlin field as a case study demonstrates that rheological and sedimentological tills from these different forms are similar it is not therefore rheological change alone that must account for drumlin shape and form but likely the advective subglacial basal sediment flux rate at the ice bed the rate of sediment motion between the upper interface at the ice sediment bed boundary and the lower immobile sediment at depth is crucial at the lower decollement between the mobile and immobile sediment units within the deforming sediment package proto drumlin nucleation is likely to occur and develop into a streamlined form the trigger mechanism for such a perturbation is a derivative of sediment rheology and sediment flux rate driven by the overlying ice stresses recent evidence from antarctica lends credence to this new hypothesis that can be related to all drumlins formed under temperate soft sediment deforming bed conditions

an efficient and guaranteed stable numerical method for continuous modeling of infiltration and redistribution with a shallow dynamic water table we have developed a one dimensional numerical method to simulate infiltration and redistribution in the presence of a shallow dynamic water table this method builds upon the green ampt infiltration with redistribution gar model and incorporates features from the talbot ogden t o infiltration and redistribution method in a discretized moisture content domain the redistribution scheme is more physically meaningful than the capillary weighted redistribution scheme in the t o method groundwater dynamics are considered in this new method instead of hydrostatic groundwater front it is also computationally more efficient than the t o method motion of water in the vadose zone due to infiltration redistribution and interactions with capillary groundwater are described by ordinary differential equations numerical solutions to these equations are computationally less expensive than solutions of the highly nonlinear richards 1931 partial differential equation we present results from numerical tests on 11 soil types using multiple rain pulses with different boundary conditions with and without a shallow water table and compare against the numerical solution of richards equation re results from the new method are in satisfactory agreement with re solutions in term of ponding time deponding time infiltration rate and cumulative infiltrated depth the new method which we call garto can be used as an alternative to the re for 1 d coupled surface and groundwater models in general situations with homogeneous soils with dynamic water table the garto method represents a significant advance in simulating groundwater surface water interactions because it very closely matches the re solution while being computationally efficient with guaranteed mass conservation and no stability limitations that can affect re solvers in the case of a near surface water table

subglacial till formation microscale processes within the subglacial shear zone abstract this was a study of subglacial deformation till genesis from a modern temperate glacier at skalafellsjokull iceland detailed microscale properties of till samples from scanning electron microscope sem and thin section analysis were examined from a glacial site with in situ subglacial process monitoring and an exposed subglacial surface in the foreland two lithofacies were examined a grey sandy till derived from the ash and basalt and a silty reddish brown till derived from oxidized paleosols and or tephra layers these also represented a clay content continuum from low 0 3 to high 22 3 the evolution from debris to subglacial till was investigated this included a reduction in grain size 21 for grey lithology 13 reddish brown lithology and reduction in rounding ra 32 for the grey lithology 26 for the reddish brown lithology and the quantification and analysis of the different grain erosion comminution processes in the resultant till it was shown that the microstructures within a till were dependent on shear strain and glaciological conditions deformation history the low clay content tills were dominated by linear structures lineations and boudins and anisotropic microfabric whilst the higher clay content tills were dominated by rotational structures turbates and plaster and isotropic microfabric these results are important in our understanding of the formation of both modern and quaternary tills and informs our reconstruction of past glacial dynamics

preparation of polished thin sections from poorly consolidated regolith and sediment materials abstract good quality polished thin sections can be prepared from poorly consolidated wet fragile and friable regolith and sediment materials in a standard earth science thin section laboratory with only minor additional equipment materials are dried over an acetone bath impregnated with a polyester resin mix and cut and polished using minor modifications of standard hard rock thin sectioning equipment and techniques the sections produced are suitable for both optical and electron microscopy and electron probe microanalysis

thin section production of diamicts problems and solutions abstract thin section production of diamict samples presents many problems primarily as a result of incomplete impregnation this problem is investigated in diamicts of known glacial glaciomarine and subaerial origin the inherent sedimentological characteristics rather than particular mode of deposition appears to influence resin impregnation of diamicts a technique of surface impregnation is presented to overcome this problem when samples fail to impregnate fully during initial preparation and is incorporated into current techniques within a flowchart in the majority of cases this technique results in successful production of a useful thin section

eocene volcanism above a depleted mantle slab window in southern alaska the caribou creek volcanic fi eld lies along the continent side edge of forearc basin rocks in south central alaska and consists of over 1000 m of shallow dipping basalt and andesite lavas with minor mafi c pyroclastic deposits dacite and rhyolite lavas along with shallow intrusions form dome complexes with associated pyroclastic deposits that overlie and crosscut the basalt and intermediate lavas the basalts are tholeiitic and strongly depleted in the light rare earth elements la yb 0 18 1 5 with concentrations of high fi eld strength elements e g zr hf ti y similar to mid ocean ridge basalt and with variable enrichment in fl uid mobile elements e g cs ba and pb intermediate and felsic rocks show enrichment in the rare earth elements and fl uid mobile elements plus rb and k but retain low la yb ratios 0 48 3 6 a few andesite and dacite samples are strongly depleted in the heavy rare earth elements and are geochemically similar to adakites e g sr y up to 52 ten 40 ar 39 ar ages for the caribou creek volcanic rocks range from 49 4 2 2 to 35 6 0 2 ma an adakite like tuff beneath the other volcanic rocks yields an age of 59 0 0 4 ma caribou creek basalts were derived from mid ocean ridge like depleted mantle that was emplaced beneath the southern margin of alaska through a slab window following spreading ridge subduction caribou creek volcanism was coeval with oblique subduction oroclinal bending and right lateral strike slip faulting in south central alaska all of which could have induced crustal extension to allow adiabatic melting of the depleted mantle reservoir to form basaltic magmas the basalts then evolved by fractional crystallization with moderate to high degrees of assimilation of jurassic arc basement rocks to form the intermediate and felsic magmas enrichment of the basaltic parent magmas in fl uid mobile elements occurred by contamination from the jurassic arc rocks and or by contamination with metasomatic mantle remnant from preceding subduction high heat fl ow through the slab window induced partial melting of garnet bearing mafi c parts of the jurassic arc basement to form the adakite like rocks the caribou creek volcanic rocks demonstrate that slab windows can directly infl uence magmatism inboard of accretionary prism and forearc basin settings given a suitable deformation regime e g crustal extension and that the infl uence of a slab window on continental margin magmatism can be long lived 20 m y

subglacial emplacement of tills and meltwater deposits at the base of overdeepened bedrock troughs the sedimentary infill of subglacially eroded bedrock troughs in the alps are underexplored archives for the timing extent and character of pleistocene glaciations but may contain excellent records of the quaternary landscape evolution over several glacial interglacial cycles the onset of sedimentation in these bedrock troughs is often reflected by diamicts and gravels directly overlying bedrock in the deepest basin segments subglacial or proglacial depositional environments have been proposed for these coarse grained basal units but their characteristics and origin remain controversial this article presents results from drill cores that recovered a coarse grained basal unit in a major buried bedrock trough system in the lower glatt valley northern switzerland the excellent core recovery allowed a detailed study combining macroscopic microscopic and geochemical methods and gives unprecedented insights into the transition from erosion to deposition in overdeepened bedrock troughs these results show that the basal infill comprises diamicts interpreted as subglacial tills separated by thin sorted interbeds originating from subglacial cavity deposition the stacking may thus represent repeated switching between a coupled and decoupled ice bed interface indicating an ever transforming mosaic of subglacial bed conditions decoupling in response to high basal water pressures is probably promoted by the confined subglacial hydraulic conditions resulting from the bedrock acting as aquitard the narrow reverse sloping outlet and a large catchment area while stratigraphic and lithological evidence suggests that erosion and the onset of basal sedimentation occurred during the same glaciation different scenarios for the relative timing of infilling in relation to formation and glaciation of the bedrock trough are discussed overlying deltaic and glaciolacustrine sediments suggest deposition during subsequent deglaciation of the bedrock trough the basal sediment characteristics are in agreement with previous reports in hydrogeological and seismic exploration and suggest the occurrence of similar basal successions in other subglacially overdeepened basin in the alps and elsewhere

an investigation of subglacial shear zone processes from weybourne norfolk uk abstract the glacial sediments of north norfolk are a type site for subglacial deforming bed sediments this investigation focussed on subglacial shear zone process at the field and thin section scale in order to understand subglacial processes as well as considering the implications for regional stratigraphies the sandy and chalky tills from three sites within 1 km at weybourne norfolk showed evidence for subglacial deformation associated with simple shear producing extension compression and rotation it was demonstrated how these processes interacted to cause chalk fragmentation and predictable fabric strengths dependant on sorting and grain size it is suggested that the marly drift is a diachronous unit and the resultant stratigraphy at weybourne reflects one deformation till resulting from a series of ice advances but with a lithology derived from the local chalk bed rock with some far travelled erratics which have undergone different degrees of chalk fragmentation reflecting the nature and duration of the subglacial deformation

till fabric patterns and significance particle response to subglacial stress abstract the analysis of particle arrangements within glacial sediments fabric has long been considered to reflect the behaviour of the ice that transported and deposited or deformed the sediment particles can develop specific fabric arrangements as a response to bulk sediment strain driven by effective stress at the bed of a glacier as such fabric analysis has been used to try and understand the complex relationship between glacier and ice sheet dynamics and the geological evidence of former glaciation developments have focused on the use of stereonet patterns and statistical measures vector and eigenvector analysis of clast fabric to infer the process of sediment deposition deformation and consequent ice flow directions and dynamics however as this study identifies fundamental processes of particle orientation march jeffery and taylor rotation mechanisms would suggest more complex explanations than have been previously reported this study reports the results of a detailed field and laboratory investigation of macro scale clast and microfabrics from a till sequence in central scotland the results suggest a systematic behaviour of different particle size fractions which may be interpreted in terms of the strain response of sediment three fabric patterns are identified that illustrate consistent progressively shifting and more complex particle behaviour it is suggested these orientation patterns indicate the degree to which subglacial sediment has undergone strain and the nature of the deforming bed erosional or accretionary it is concluded that this approach may yield fundamental information about the strain conditions underlying different ice masses providing critical data linking glaciological modelling with the sedimentary evidence of glaciation

validation of finite water content vadose zone dynamics method using column experiments with a moving water table and applied surface flux data from laboratory experiments on a 143 cm tall and 14 5 cm diameter column packed with wedron sand with varied constant upper boundary fluxes and water table velocities for both falling and rising water tables are used to validate a finite water content vadose zone simulation methodology the one dimensional finite water content talbot and ogden 2008 t o infiltration and redistribution method was improved to simulate groundwater table dynamic effects and compared against the numerical solution of the richards equation using hydrus 1d both numerical solutions agreed satisfactorily with time series measurements of water content results showed similar performance for both methods with the t o method on average having higher nash sutcliffe efficiencies and smaller absolute biases hydrus 1d was more accurate in predicting deponding times in the case of a falling water table while hydrus 1d and the t o method had similar errors in predicted ponding times in the case of a rising water table in six of nine tests the improved t o method was able to predict general features of vadose zone moisture dynamics with moving water table and surface infiltration using an explicit mass conservative formulation the advantage of an explicit formulation is that it is numerically simple using forward euler solution methodology and is guaranteed to converge and to conserve mass these properties make the improved t o method presented in this paper a robust and computationally efficient alternative to the numerical solution of the richards equation in hydrological modeling applications involving groundwater table dynamic effects on vadose zone soil moistures

coupled surface subsurface hydrologic measurements reveal infiltration recharge and discharge dynamics across the swash zone of a sandy beach swash groundwater interactions affect the biogeochemistry of beach aquifers and the transport of solutes and sediment across the beachface improved understanding of the complex coupled dynamics of surface and subsurface flow processes in the swash zone is required to better estimate chemical fluxes to the sea and predict the morphological evolution of beaches simultaneous high frequency measurements of saturation water table elevation and the cross shore locations of runup and the boundary between the saturated and unsaturated beachface surface saturation boundary were collected on a sandy beach to link groundwater flow dynamics with swash zone forcing saturation and lysimeter measurements showed the dynamic response of subsurface saturation to swash events and permitted estimation of infiltration rates surface and subsurface observations revealed a decoupling of the surface saturation boundary and the intersection between the water table and the beachface surface measurements alone were insufficient to delineate the infiltration and discharge zones which moved independently of the surface saturation boundary results show for the first time the motion and areal extent of infiltration and recharge zones and constrain the maximum size of the subaerial discharge zone over swash and tidal time scales the width of the infiltration zone was controlled by swash processes and subaerial discharge was controlled primarily by tidal processes these dynamics reveal the tightly coupled nature of surface and subsurface processes over multiple time scales with implications for sediment transport and fluid and solute fluxes through the hydrologically and biogeochemically active intertidal zone of sandy beaches

sedimentology facies architecture and chemostratigraphy of a continental high latitude paleocene eocene succession the chickaloon formation alaska abstract the paleocene eocene chickaloon formation of southern alaska represents rapid deposition in a floodbasin setting contains abundant and diverse fossil plant material and spans the paleocene eocene thermal maximum petm sedimentologic lithofacies and chemostratigraphic analyses of exposures of the chickaloon formation were conducted in order to provide a contextual framework for this late paleocene early eocene high latitude sedimentary succession and to test if hyperthermal conditions are recorded in the unit at the main study area in the evan jones coal mine strata represent an alluvial sequence dominated by floodplain channel sandstone crevasse lobe crevasse channel and mire deposition floodplain environments are represented by medium gray commonly nodular and or carbonate cemented shaly siltstone and centimeter scale thick sheet sandstone interbeds most channel sandstone deposits are interpreted to be crevasse channels and are generally small 2 5 m thick rarely coarser than medium grained sandstone and sand grains are commonly coated with fe oxides carbonaceous shale and coal are localized and indicate a high rate of organic carbon accumulation in the area 13c analyses of bulk organic carbon from the succession at the evan jones mine are internally consistent with this interpretation they yield uniformly negative values that are typical of continental organic matter 21 7 to 28 5 x 25 4 fossil plant material is also very common and includes leaves wood seeds and resins from broad leaf angiosperms conifers ferns and sphenopsids considered together lithologic and paleontologic data suggest that these strata represent a floodbasin environment the observed crevasse channels probably originate from a main channel located within several kilometers of the depocenter ash fall tuffs punctuate the studied sequence and contain abundant reworked or recycled zircons indicating that the depocenter was proximal to a volcanic source across all of these chickaloon depositional environments a significant negative isotopic shift 5 8 occurs which we hypothesize to represent a short lived perturbation associated with a global hyperthermal event