paleogene igneous underplating and subsidence anomalies in the rockall faeroe shetland area abstract crustal thickening caused by igneous underplating related to continental break up in the northeast atlantic has been invoked as the cause of the apparent lack of thermal subsidence seen in many mesozoic basins in the northwest european area in this study we examine a set of commercial wells in the rockall faeroe shetland region and calculate tectonic subsidence histories the rate of post rift basement subsidence during the cretaceous cenozoic determined from backstripping calculations always implies a higher degree of extension than the total basement subsidence assuming uniform extension furthermore the size of this discrepancy increases northward along the rockall trough and westwards in the northern north sea towards scotland we interpret this depth anomaly to reflect the effect of igneous underplating rethickening the crust following mesozoic and cenozoic extension late paleocene extension is identified in subsidence reconstructions throughout the west of britain area and is greatest in the rockall trough assuming that the underplating is gabbroic in composition the subsidence depth anomalies indicate a regional pattern of 2 3 km underplated between the erris trough and porcupine basin increasing to 4 5 km in the west lewis basin and hebrides shelf area in the faeroe shetland basin underplating is 1 0 1 5 km in the east and increases to 4 5 km in the west the data support the hypothesis of a major asthenospheric thermal anomaly centered under the faeroes in the paleocene dynamic uplift of the region is often difficult to identify but is locally seen to develop rapidly around 63 ma implying rapid emplacement of the mantle anomaly the intrusion of gabbroic bodies to the base of the crust in the late paleocene may have had an impact on the thermal maturation of petroleum source rocks in the region however thermal maturity indicators show smaller peak heatflows than predicted from simple thermal models suggesting that underplating was a gradual process achieved through the accretion of several small rapidly cooled bodies

a unifying framework for particle entrainment 1 a new framework is presented that describes the hydrodynamic entrainment of sediments the framework is derived from the general equations of particle stability and fluid motion and covers a wide range of scales from that of the individual particle to en masse entrainment at the scale of the stream reach particle entrainment is explicitly shown to be driven by the combination of instantaneous fluid stress and pressure gradients particle surface contact forces particle submerged weight and the weight and motion of particle associated fluid of these factors bed shear stresses across particle differences in pressures and fluxes of momentum and sediment bed characteristics are found to be key factors in particle entrainment the conventional shields entrainment parameter is shown to be applicable to averaged en masse entrainment by steady uniform 2 d flows this nondimensionalized bed shear stress at threshold is further demonstrated to be a function of interparticle forces and bed normal hydrodynamic forces and thereby sediment size and other fluid sediment and bed characteristics observed shields parameter dependencies are discussed the presented framework which includes all relevant particle and fluid characteristics and flow dynamics may aid understanding of entrainment mechanics the design and analysis of further studies of entrainment the design of parameterizations that lead to the solution of entrainment problems and numerical modeling of combined fluid and sediment dynamics

predicting incipient motion including the effect of turbulent pressure fluctuations in the bed 1 incipient motion of particles on a river bed can in principle be understood and predicted from a balance of the forces acting on the particles on a natural river bed the exposure of particles to the flow is variable the effect of exposure on the initiation of motion including the case of deep embedding is studied in this paper so far the turbulence induced lifting force has been derived exclusively from examinations of the surface flow the understanding of destabilization processes of the riverbed is improved when turbulence induced vertical pressure gradients in the upper sediment layer are included this is particularly important for particles that lie in the lee of larger ones an analytical solution for the critical shields parameter of spherical particles is found including the effects of pressure fluctuations in the bed macroscale flow structures average bed slope and shallow flow existing laboratory data designed to test the effect of exposure and roughness conditions are in excellent agreement with the new model

processes of initiation of motion leading to bedload transport in gravel bed rivers 1 transport processes that lead to the initiation of bedload motion in gravel bed rivers have not yet been clarified we report patch and grain scale processes involved in the initiation of bedload motion in a natural gravel bed stream as observed through a series of video experiments with increasing flow strength the phases of initiation of motion that have been identified are 1 within patch grain instability grain vibration pivoting and grain scale rolling 2 within patch gyratory step and rest motion and 3 general sediment motion involving downstream transport from an individual patch and the throughput of grains inherited from upstream

mobility of bed material in harris creek 1 the mobility of bed material is investigated in a small gravel bed river in which the bed is weakly bimodal in texture and relatively stable the bed surface remained intact throughout the freshet and scour was limited to small areas of the bed observations of bedload caught in pit traps and displacement of magnetically tagged particles during two spring freshets permit analysis of the mobility of each size fraction fractional transport rates plot up to three orders of magnitude below the reference transport rate suggested in the literature at low flows no size fraction was fully mobile at intermediate flows shear stress 27 pa sand was fully mobile while larger material remained partially mobile at high flows 43 pa the division between the full and partial mobility regimes occurred around 16 mm which remains finer than the median size of the subsurface material the largest material scarcely moves at mean annual flood magnetic tracers confirmed results obtained from the pit traps three distinct zones of mobility can be defined in fractional transport plots partial mobility full mobility and overpassing suspended critical shear stress for incipient motion varied over an order of magnitude a qualitatively similar result for bimodal sediment was reported by wilcock and mcardell 1993 incipient motion analysis based on the largest grain observed to move yielded an upper envelope implying transport similarity for sizes found on the bed surface and a lower envelope that corresponds with our nonsimilar entrainment criterion

a mixing layer theory for flow resistance in shallow streams 1 a variety of surface roughness characterizations have emerged from nineteenth and twentieth century studies of channel hydraulics when the water depth h is much larger than the characteristic roughness height ks roughness formulations such as manning s n and the friction factor f can be explicitly related to the momentum roughness height zo in the log law formulation for turbulent boundary layers thereby unifying roughness definitions for a given surface however when h is comparable to or even smaller than ks the log law need not be valid using a newly proposed mixing layer analogy for the inflectional velocity profile within and just above the roughness layer a model for the flow resistance in shallow flows is developed the key model parameter is the characteristic length scale describing the depth of the kelvin helmholtz wave instability it is shown that the new theory originally developed for canopy turbulence recovers much of the earlier roughness results for flume experiments and shallow gravel streams this study is the first to provide such a unifying framework between canopy atmospheric turbulence and shallow gravel stream roughness characterization the broader implication of this study is to support the merger of a wealth of surface roughness characterizations independently developed in nineteenth and twentieth century hydraulics and atmospheric sciences and to establish a connection between roughness formulations across traditionally distinct boundary layer types

grain sorting processes grain sorting affects river bed aggradation through downstream fining and erosion processes through static and mobile armor formation a fractionwise sediment transport calculation procedure is presented it has been calibrated on rotational erosion tests and sediment feeding experiments under equilibrium conditions in the mobile armor case equal mobility must be reproduced to simulate the rotational erosion process application to flow ranges for which a static armor layer forms shows that transport under equilibrium conditions with identity of subsurface and bedload mixture is then not possible a unique sediment function exists only for higher flows

crustal structure of the faeroe shetland channel summary the deep structure of the faeroe shetland channel has been investigated as part of the north atlantic seismic project shot lines were fired along and across the axis of the channel with recording stations both at sea and on adjacent land areas at 61 n 1 7 km of tertiary sediments overlies a 3 9 4 5 km s 1 basement interpreted as the top of early tertiary volcanics a main 6 0 6 6 km s 1 crustal refractor interpreted as old oceanic crust occurs at about 9 km depth the moho 8 0 0 2 km s 1 is at about 15 17 km depth there is evidence that pn may be anisotropic beneath the faeroe shetland channel arrivals recorded at land stations show characteristics best explained by scattering at an intervening boundary which may be the continent ocean crustal contact or the edge of the volcanics the moho delay times at the shot points determined by time term analysis show considerable variation along the axis of the channel they correlate with the basement topography and the greatest delays occur over the buried extension of the faeroe ridge at about 60 15 n where they are nearly 1 s more than the delays at 61 n after correction for the sediments the large delays are attributed to thickening of the early tertiary volcanic layer with isostatic downsagging of the underlying crust and uppermost mantle in response to the load rather than to thickening of the main crustal ayer the new evidence is consistent with deeply buried oceanic crust beneath the faeroe shetland channel forming a northern extension of rockall trough the seabed morphology has been grossly modified by the thick and laterally variable pile of early tertiary volcanic rocks which swamped the region accounting for the anomalous shallow bathymetry the transverse ridges and the present narrowness of the channel

bed load transport flume experiments on steep slopes experiments were conducted over uniform gravel bed materials to obtain 143 friction factor values under bed load equilibrium flow conditions in an attempt to add to the scarce data available on slopes between 1 and 9 for shields numbers between 0 08 and 0 29 analyses showed that when only flows over flat beds are considered a distinction must be made between flows with and without bed load more particularly fitting flow resistance equations indicated that the roughness parameter increases by a factor of 2 5 from clear water flow to intense bed load transport between these two states the flow resistance can be approximated by a constant for a given slope

incipient sediment motion at high slopes in uniform flow condition 1 this paper reviews the problem of the incipient motion of cohesionless particles in a high sloping water stream a theoretical analysis of the equilibrium of a gravel particle is developed by a deterministic approach with the introduction of the relative degree of exposure of the particle itself to the stream flow the parameter relative degree of exposure relates the positioning of a particle with the upstream one the problem of velocity distribution and the definition of drag coefficient is also revised to better account for low submergence the results of the theory are compared with a series of ad hoc experiments performed by c gregoretti

feedback between bed load transport and flow resistance in gravel and cobble bed rivers 1 to calculate bed load engineers often use flow resistance equations that provide estimates of bed shear stress in these equations on the basis of the estimate of the appropriate hydraulic radius associated with the bed only the bed roughness ks is commonly set as a constant whatever the bed load intensity however several studies have confirmed the existence of feedback mechanisms between flow resistance and bed load suggesting that a flow dependent bed roughness should be used therefore using a data set composed of 2282 flume and field experimental values this study investigated the importance of these feedback effects new flow resistance equations were proposed for three flow domains domain 1 corresponds to no bed load and a constant bed roughness ks d where d is a representative grain diameter whereas domain 3 corresponds to a high bed load transport rate over a flat bed with a constant bed roughness ks 2 6d between these two domains a transitional domain 2 was identified for which the bed roughness evolved from d to 2 6d with increasing flow conditions in this domain the darcy weisbach resistance coefficient f can be approximated using a constant for a given slope the results using this new flow resistance equation proved to be more accurate than those using equations obtained from simple fittings of logarithmic laws to mean values the data set indicates that distinguishing domains 2 and 3 is still relevant for bed load in particular the data indicate a slope dependence in domain 2 but not in domain 3 a bed load model based on the tractive force concept is proposed finally flow resistance and bed load equations were used together to calculate both shear stress and bed load from the flow discharge the slope and the grain diameter for each run of the data set efficiency tests indicate that new equations implicitly taking a feedback mechanism into account can reduce the error by a factor of 2 when compared to other equations currently in use showing that feedback between flow resistance and bed load can improve field bed load modeling

the structure of the rockall trough from seismic refraction and wide angle reflection measurements there are few detailed descriptions of the deep crustal structure of failed cratonic rifts and passive margins despite their import ance in constraining the variety of structural models invoked to account for their common structural symmetry or gross half graben form1 3 such deep crustal structure profiles also have considerable value in defining the continent ocean boundary con straining plate reconstructions and determining the overall setting of sedimentary basin development the rockall trough in the north atlantic ocean is a sinuous elongate bathymetric depression 200 km wide and more than 2 000 m deep lying between rockall plateau and the british isles and the structure nature and age of its underlying crust are disputed in the absence of deep crustal structure profiles the presence of oceanic crust has been assumed because the trough has to be accommodated in reconstructions of the north atlantic although stretched continental crust is equally plausible the nature of the crust is important for the precise reconstruction of the late jurassic early cretaceous plate history and setting of sedimentary basins of the north atlantic4 8 the nature of the crust beneath the trough as well as the structure thickness and composition of the sedimentary cover is also relevant to oil exploration here we report the first observations of deep crustal structure across the rockall trough and its margins from seismic refraction and wide angle reflection profiles our results show that the northern rockall trough is underlain by highly stretched continental crust and not by oceanic crust as previously postulated

analysis of flow competence in an alluvial gravel bed stream dupuyer creek montana 1 critical shear stress and unit discharge flow competence models were tested against coarse bed load data from dupuyer creek montana united states maximum particle sizes sampled dmax and d50 to d90 percentiles in the bed load grain size distribution were well correlated with both shear stress and unit discharge bed load grain sizes became coarser with increasing flow strength for the dmax curve shields dimensionless parameter for the surface d50 was estimated at 0 044 and the exponent for relative particle size di d50 was 0 59 in the unit discharge criterion the critical flow to entrain the surface d50 was poorly predicted flow competence relationships based on dmax are prone to the influence of outliers and sample mass variability the mean of the three largest particles dmax 3 is more sensitive to changes in flow strength than the d50 to d90 bed load grain sizes and may represent a good compromise

theoretical development on the effects of changing flow hydraulics on incipient bed load motion 1 several decades of flume and field measurements have indicated that in rough turbulent flows the critical shields stress increases with increasing slope and associated decreasing relative depth this result contradicts the usual consideration of a decreased critical shields value on very steep slopes because of increased gravitational effects however recent studies have demonstrated that these experimental results could be reproduced with a force balance model if the classical logarithmic velocity profile was replaced with a velocity profile that was more compatible with available velocity measurements over gravel beds these measurements indicate the existence of a roughness layer that is a zone of almost constant velocity close to the bed whose properties mean velocity and turbulence depended on the flow s relative depth unfortunately velocity profile measurements for low relative depth associated with steep slopes are scarce and it is still difficult to include such flow properties in a force balance model flow resistance data on the basis of depth average velocity measurements are very common and cover a wide range of slopes and relative depths in this paper these data are used to fit a velocity profile including a roughness layer when used in a force balance model for incipient motion it adequately reproduced a data set composed of 270 critical shields values measured in a flume with near uniform sediments the relevance of this research to field problems is discussed using a data set composed of 92 critical shields stresses obtained from field measurements finally a model is proposed for field applications taking into account the slope effect

multiple fluid migration events along the moine thrust zone scotland a palaeomagnetic study of different lithologies exposed along the moine thrust zone from skye to durness scotland has identified three chemical remanent magnetizations crms a potential fourth crm and one possible primary component that all reside in hematite local and regional fold tests suggest that the crms are post folding and post thrusting a contact test in the torridon group sandstone indicates that a permian crm is localized in and near the fault zone the permian crm which is also found in the durness group and associated alteration are direct evidence for post orogenic activity in which the thrusts vented excess heat during regional crustal extension on the isle of skye sandstones sleat torridon and eriboll groups in and around the fault zone contain a tertiary crm interpreted to be related to hydrothermal fluids associated with tertiary intrusions a possible mesozoic crm is also present but it could represent the vector addition of the permian and tertiary crms a devonian crm is interpreted to be related to hydrothermal fluids associated with devonian volcanic rocks or to fluids triggered by late stages of the caledonian orogeny geochemical and petrographical studies provide supporting evidence for multiple fluid flow events along the moine thrust zone these results show that palaeomagnetism can be used to date multiple fluid migration events and that dormant fault zones can act as conduits for flow

size selective entrainment of bed load in gravel bed streams entrainment of mixed size gravel bed material was studied in nine reaches of three high power streams in scotland and norway paired measurements of at a point shear stress estimated from velocity profiles and bed load transport by hand held sampler were made they extended to very high values 400 n m 2 3 5 kg m x s x analyses of maximum bed load diameter mean bed load diameter transport rates of individual size fractions and tracer pebble movements all show some dependence of threshold shear stress for entrainment on absolute particle size despite strong relative size effects precise equal mobility of all sizes was approached in the data set with the highest shear stresses and transport rates size selective transport in the streams studied is also indicated by clear downstream and downbar reductions in surface sediment size over distances too short for abrasion to be significant

accounting for uncertainty in cumulative sediment transport using bayesian statistics abstract that sediment transport estimates have large uncertainty is widely acknowledged when these estimates are used as the basis for a subsequent analysis such as cumulative sediment loads or budgets treatment of uncertainty requires careful consideration the propagation of uncertainty is a problem that has been studied in many other scientific disciplines in recent years bayesian statistical methods have been successfully used to this end in hydrology ecology climate science and other disciplines where uncertainty plays a major role their applications in sediment transport however have been few previous work demonstrated how deterministic sediment transport equations can be brought into a probabilistic framework using bayesian methods in this paper we extend this basic model and apply it to sediment transport observations collected on the snake river in wyoming usa these data were used previously to develop a 50 year sediment budget below jackson lake dam we revisit this example to demonstrate how viewing sediment transport probabilistically can help better characterize the propagation of uncertainty in the calculation of cumulative sediment transport we present the development of probabilistic sediment rating curves that rely on deterministic sediment transport equations and then show how these can be used to compute the distribution of sediment input and output for each year from 1958 to 2007 the bayesian approach described provides a robust way to quantify uncertainty and then propagate it through to subsequent analyses results show that transport uncertainty is quantified naturally in the bayesian approach making it unnecessary for modelers to assume some specified error rate e g 5 when developing estimates of cumulative transport further we demonstrate that a bayesian approach better constrains uncertainty and allows sediment deficit and surplus to be examined in terms of quantified risk

a pollen based pseudobiomisation approach to anthropogenic land cover change the degree of anthropogenic modification of land cover through the mid to late holocene is of significant interest for archaeologists climate modellers and conservation ecologists amongst others spatially extensive pollen data provide an appropriate resource for the reconstruction of land cover change however traditional simple methods e g the ap nap ratio do not provide the degree of detail required for these user groups a range of more sophisticated methods have been developed e g mechanistic model based methods but they require a high degree of understanding of the pollen vegetation relationship which is resource and time consuming this paper proposes a method of intermediate complexity by which major land cover changes can be assessed for individual sites and regions a pseudobiomisation approach is used in which pollen taxa are assigned to different land cover classes lcc and the sum of adjusted pollen proportions for each class used to determine an lcc affinity score for individu

bed load at low shields stress on arbitrarily sloping beds alternative entrainment formulation 1 according to the bagnold hypothesis for equilibrium bed load transport a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains it was shown in a companion paper seminara et al 2002 however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose an investigation of this failure resulted in a demonstration of its lack of validity even for nearly horizontal beds the constraint is here replaced with an entrainment formulation according to which a dynamic equilibrium is maintained by a balance between entrainment of bed grains into the bed load layer and deposition of bed load grains onto the bed the entrainment function is formulated so that the entrainment rate is an increasing function of the excess of the fluid shear stress at the bed over the threshold value the formulation is implemented with the aid of a unique set of laboratory data that characterizes equilibrium bed load transport at relatively low shear stresses for streamwise angles of bed inclination varying from nearly 0 to 22 the formulation is shown to provide a description of bed load transport on nearly horizontal beds that fits the data as well as that resulting from the bagnold constraint the entrainment formulation has the added advantage of not requiring the unrealistically high dynamic coefficient of coulomb friction resulting from the bagnold constraint finally the entrainment formulation provides reasonable and consistent results on finite streamwise and transverse bed slopes even those at which the bagnold formulation breaks down completely

comment on the permian triassic transition and the onset of mesozoic sedimentation at the northwestern peri tethyan domain scale palaeogeographic maps and geodynamic implications by s bourquin a bercovici j lopez gomez j b diez j broutin a ronchi m durand a arche b linol and f amour palaeogeography palaeoclimatology palaeoecology 299 2011 265 280 abstract the recent paper by bourquin et al 2011 describes the regional palaeogeographic evolution of the late permian to middle triassic on a pan european scale whilst useful data and interpretations are provided for their southern and intra variscan belt domains additional well and seismic data from the central and northern north sea and the atlantic margin region together with results from recent publications allow us to refine and improve their interpretation of their northern domain the presence of a regional unconformity at the permian triassic boundary with only localised induan sedimentation is less clear in the northern region where multiple extensional events through late permian and triassic time led to the development of localised footwall and rift flank unconformities as arctic rifting propagated southwards and entered the north sea and the atlantic margin regions the hardegsen unconformity may be locally identifiable in the southern portion of the northern domain but again forms one of a number of unconformities marking the onset of rifting data from the northern domain suggest that early triassic aeolian activity was ubiquitous on the distal fringes of terminal fluvial systems but with no evidence of the discrete episode of increased aridity in the smithian identified in the south the onset of vegetation cover in the northern domain was also more diachronous in this region appearing in the central north sea at approximately the same time as muschelkalk flooding of the adjacent southern permian basin and later in basins further to the north in most cases the middle triassic fluvial systems in the north were terminal in nature failed to discharge into marine basins and were not exorheic in character their advance and retreat was independent of sea level fluctuations or the presence of a marine water body and fluvial expansion and retreat aeolian reworking and vegetation cover appear to have been linked to catchment runoff the disconnect with the observations to the south may be in part a product of the more northern latitudinal position of these systems or at least that of the headwaters of the fluvial drainage

the structure and subsidence of rockall trough from two ship seismic experiments coincident multichannel seismic reflection and refraction profiles acquired northwest of britain during a two ship seismic experiment in the southern rockall trough provide evidence for a thin 6 km syn rift crust below rockall trough the variation of seismic velocity with depth is consistent with either oceanic crust similar to that found in other parts of the north atlantic or with thinned continental crust heavily intruded by syn rift igneous rocks the syn rift crust beneath rockall trough is now buried by nearly 5 km of sediments that are intruded by tertiary volcanics varying in extent from isolated sills to a large sill complex extending 100 km laterally the basement imaged on seismic profiles exhibits a band of subhorizontal reflectors that extend laterally over distances of up to 40 km which they interpret as sediments intercalated with submarine lava flow generated during the opening of the trough estimates of stretching from crustal thinning and from subsidence indicate that rockall trough has undergone extensive rifting beta 6 upwelling asthenosphere beneath the thinned lithosphere generated at least 1 3 km thickness of melt as it decompressed the molten rock rose upward from the mantle until it was in part extruded as lava flows and in partmore intruded into the crust less

paleomagnetic dating of fracturing using breccia veins in durness group carbonates nw scotland abstract a paleomagnetic study of red fault related breccia veins in the cambro ordovician durness group in nw scotland was conducted to determine the time of brecciation the origin of the veins and the nature and timing of associated fluid related diagenetic alteration the veins contain brecciated fragments of the host durness group and strike either east west or north south clasts of breccia cemented by calcite suggest multiple brecciation events the host durness limestone is a gray dolomite and contains a devonian chemical remanent magnetization crm that resides in magnetite the veins contain magnetizations that reside in hematite and are interpreted as crms the breccias in north south veins contain a triassic crm whereas the veins with east west strikes contain a jurassic crm authigenic hematite is common in the breccias along growth planes in the calcite cements the two crms within the veins are interpreted as dating two separate brecciation and fluid flow events that precipitated authigenic hematite the brecciation and fluid flow events are interpreted to be related to extension in the mesozoic which is consistent with the extensional history of the northern atlantic margins

river loads and modern denudation of the alps a review this paper presents the first comprehensive analysis of sediment and dissolved load across an entire mountain range we investigate patterns and rates of modern denudation of the european alps based on a compilation of data about river loads and reservoir sedimentation from 202 drainage basins that are between ca 1 to 10 000 km2 large the study basins cover about 50 of the total area of the alps modern glaciated basins have the highest sediment yields of up to 7000 t km 2 a 1 which are on average 5 to 10 times higher than in non glaciated basins likewise sediment yield and glacial cover are positively correlated instead relief is a relatively weak predictor of sediment yield the strong glacial impact in the correlations is due to glacier recession since the 19th century as well as due to glacial conditioning during repeated quaternary glaciations which have produced the strong transient state of the alpine landscape we suggest that this is the major cause for ca 3 fold enhanced denudation of the western compared to the eastern alps chemical denudation rates are highest in the external alps dominated by carbonate sedimentary rocks where they make up about one third of total denudation the high rates cannot be explained without anhydrite dissolution we estimated that only 45 of the sediments mobilized in headwaters are exported out off the alps most sediments being trapped in artificial reservoirs the total amount of sediment annually trapped within the alps equates to 43 mt when corrected for sediment storage we obtain an area weighted mean total denudation rate for the alps of about 0 32 mm a 1 the pre dam rate might be as high as 0 42 mm a 1 in total ca 35 plus 23 mt of mass are exported each year out of the alps as solids and solutes respectively these rates are not enough to out pace modern rock uplift nevertheless pattern of sediment yield across the alps coincides roughly with the intensity of glacial conditioning and modern rock uplift supporting the hypothesis of an erosion driven uplift of the alps

mesozoic rocks from the hebrides shelf and implications for hydrocarbon prospectivity in the northern rockall trough abstract shallow boreholes drilled in the west lewis and west flannan basins outer hebrides shelf have proved rocks of probable latest bajocian bathonian to barremian age where previously a mainly permo triassic infill has been assumed the full geological succession of the basins remains unproved although the permo triassic history of the basins may be similar the rocks encountered suggest that the basins may have dissimilar geological histories during the jurassic and early cretaceous lithologies are mainly fine grained poorly sorted sandstones or organic rich mudstones some correlation can be made with the isle of skye and the west shetland area the sandstones are poor hydrocarbon reservoirs but the middle jurassic and ryazanian mudstones although immature where drilled have excellent oil source rock potential and may have generated large amounts of hydrocarbons if they are present at depth in the adjacent northern rockall trough

the social connectivity of urban rivers abstract by social connectivity we refer to the communication and movement of people goods ideas and culture along and across rivers recognizing longitudinal lateral and vertical connectivity much as has been described for other rivers for hydrology and ecology we focus on rivers as they pass through cities and the relationships between these rivers and city dwellers historically the most important longitudinal connectivity function of rivers was their role as major transport routes and the simplification of formerly complex irregular banks and beds into straight uniform shipping channels has resulted in a loss of lateral and vertical connectivity notably the quotidian uses such as fishing washing clothes water supply swimming and other recreation the scale of the river itself and its scale in comparison to the scale of the city largely determine the river s social function and the degree to which it influences city form river width affects the perception of closeness of the other bank ease of bridging the river influence of the river on the city s street pattern and type of waterfront uses that occur up to 15 m wide people can converse whereas across rivers 50 to 200 m wide people are not recognizable but still clearly visible instilling the banks with a lively atmosphere at widths over 200 m people blur yet moving vehicles and trees branches shaking in wind may still provide some dynamic elements to an otherwise static landscape composed of building facades in exceptionally wide rivers the city on the opposite bank is little more than a skyline which often becomes a signature and symbol of regional identity in contemplating how people use rivers we can define a range of human activities in relation to height above the water i e instream to banktop a vertical dimension of human connectivity with rivers many uses occur on the top of the bank such as quiet contemplation walking or cycling along a riverside trail while others depend on contact with the water itself such as wading diving and canoeing which presupposes adequate water quality many of these relationships are illustrated by the challenge of reconnecting cairo with the nile

solving a conundrum of a steady state hilltop with variable soil depths and production rates bodmin moor uk the common wisdom is that steady state hilltops should display convex shape with both uniform soil thickness and uniform rates of lowering of the soil bedrock interface a 120 m hilltop transect on bodmin moor southwest uk displays a parabolic hilltop form which implies it is in geomorphic steady state yet the measured depths to bedrock range almost 6 fold from 14 to 80 cm and the soil production rates derived from 10be concentrations in rock at the soil interface range by 2 fold from 10 to 20 m my we address this conundrum by developing a theory to explain the scatter in soil depths that would result from block by block lowering of the soil bedrock boundary and support our theory with a simple model involving block release and diffusive transport we show that over long timescales a hilltop can indeed be in geomorphic steady state while at any point in time exhibiting a broad range of depths to bedrock variable depth to bedrock results in variable 10be concentrations in the rock sampled at the base of regolith which yields calculated soil production rates that vary about the long term average hence scatter in plots of soil production as a function of soil depth are to be expected in many landscapes and if the landscape is in geomorphic steady state this scatter reflects the stochastic nature of the block release mechanism by which the bedrock interface is lowering we find in our models that the commonly observed humped and exponentially declining soil production functions are only preserved during the transient approach toward geomorphic steady state

late palaeozoic mesozoic tectonostratigraphic development of the eastern faroe shetland basin new insights from high resolution 3d seismic and well data abstract the faroe shetland basin fsb belongs to the sedimentary basins that encompass outer parts of the ne atlantic continental margin the fsb contains several kilometres thick cenozoic and cretaceous strata which overlie poorly understood pre cretaceous strata regional high resolution 3d seismic reflection data used in this study covers the eastern half of the basin generally devoid of thick basaltic successions the pre cretaceous successions are preserved as erosional remnants of originally more extensive deposits throughout the fsb devono carboniferous and permo triassic rifting probably took place in the fsb but the magnitude and regional extent of each phase is less constrained than in the neighbouring inner hebrides shetland rift basins major rifting took place in jurassic times and generated a fault controlled marine basin during the apto albian and cenomanian distributed extension occurred throughout the fsb suggesting wide rift mode of extension the subsequent campanian maastrichtian extensional phase on the contrary was localized in the flett sub basin controlled by the westray and corona faults along its western margin and oppositely dipping faults along the eastern basin margin the fault controlled cretaceous deposition in the fsb is a distinct feature that is documented in the basins along the mid norwegian margin but rarely recorded in other large cretaceous basins along the ne atlantic margin in the fsb late cretaceous faults frequently reactivated earlier structures suggesting that a structural inheritance played an important role in basin development the existence of permo triassic evaporites is postulated to explain geometries of jurassic and lower cretaceous strata and fault patterns in the foula sub basin a partial mantle serpentinization during early cretaceous times proposed for other outer basins along the ne atlantic margin is unlikely to have occurred in the fsb

a systematic analysis of eight decades of incipient motion studies with special reference to gravel bedded rivers data compiled from eight decades of incipient motion studies were used to calculate dimensionless critical shear stress values of the median grain size t c 50 calculated t c 50 values were stratified by initial motion definition median grain size type surface subsurface or laboratory mixture relative roughness and flow regime a traditional shields plot constructed from data that represent initial motion of the bed surface material reveals systematic methodological biases of incipient motion definition t c 50 values determined from reference bed load transport rates and from visual observation of grain motion define subparallel shields curves with the latter generally underlying the former values derived from competence functions define a separate but poorly developed field while theoretical values predict a wide range of generally higher stresses that likely represent instantaneous rather than time averaged critical shear stresses the available data indicate that for high critical boundary reynolds numbers and low relative roughnesses typical of gravel bedded rivers reference based and visually based studies have t c50 ranges of 0 052 0 086 and 0 030 0 073 respectively the apparent lack of a universal t 50 for gravel bedded rivers warrants great care in choosing defendable t c50 values for particular applications

triassic sand supply to the slyne basin offshore western ireland new insights from a multi proxy provenance approach to assess provenance data and derive basin infill models with a higher level of certainty it is vital to understand how minerals used in sedimentary provenance behave in the sedimentary system a multi proxy approach helps ensure rigour in how provenance data are interpreted u pb geochronology of refractory zircon and relatively less stable apatite and pb isotopic analysis of labile k feldspar are employed in this study to reassess the provenance of triassic sandstones in the slyne basin offshore western ireland this approach aims at reducing the potential bias in each method producing a complementary dataset u pb zircon and apatite geochronology yields archean paleoproterozoic ages caledonian ages and previously unrecognized permo triassic ages pb isotopic analysis of k feldspar does not identify the permo triassic as a source the detection of permo triassic aged detritus may suggest that volcanism was more widespread than previously recognized these results support the hypothesis of a triassic drainage divide between the basins offshore western ireland and those onshore britain and in the irish sea sand supply was dominantly from the north with significant input from the flanks of the basin and previously unrecorded sources such as permian aged rocks playing an important role the provenance signal is consistent and homogenized throughout the sampled sequence indicating that the drainage system was long lived supplementary material details of laboratory and sample preparation data tables and summary pie charts for each sample are available at https doi org 10 6084 m9 figshare c 4571096

flow velocity profiles in gravel bed rivers velocity measurements carried out in a rectangular laboratory flume having a gravel bed are presented the measurements are carried out for four different bed shapes characterized from different concentrations of coarser elements and for the two conditions of small and large scale roughness the analysis showed that the dean profile is usable to establish the velocity profile for both hydraulic conditions for small scale hydraulic condition an indirect estimate procedure of the coefficients of dean profile is proposed

late permian to early mesozoic rifting and sedimentation offshore nw ireland abstract a late permian triassic and early lias rift succession up to 1 km thick is revealed from offshore nw ireland sediments are preserved in deep narrow grabens from the donegal basin in the north southwestwards through the erris and slyne troughs to a series of newly defined basins collectively forming the north porcupine basin with a further structure the galway graben on the porcupine bank this line of basins superimposed on a caledonoid fractured basement underwent a complex structural evolution but since the late permian they developed primarily as a wrench modified rift system during the latest lias crustal doming west of britain may have produced a regional angular unconformity and created a source for thick middle jurassic alluvial clastics deposited in the main porcupine basin to the south early tertiary transpression of the north porcupine area caused late stage fragmentation of the basin the rift succession consists of continental red beds bounded by two dateable transgressive intervals these intervals provide valuable stratigraphic control for constraining the timing and scale of seaways propagating across the fracturing pangean supercontinent from the late permian to the early jurassic evidence is also presented for an episode of syn rift volcanism temporally unique to western britain and ireland

a new look at the rockall region offshore ireland abstract a 700 km wide angle reflection refraction profile carried out in the central north atlantic west of ireland crossed the erris trough rockall trough and rockall bank and terminated in the western hatton rockall basin the results reveal the presence of a number of sedimentary basins separated by basement highs the rockall trough with a sedimentary pile up to 5 km thick is underlain by thinned continental crust 8 10 km thick some major fault block structures are identified especially on the eastern margin of the rockall trough and in the adjacent erris trough the hatton rockall basin is underlain by westward thinning continental crust 22 10 km thick sedimentary strata are up to 5 km thick the strata in the rockall trough and hatton rockall basin probably range in age from late palaeozoic to cenozoic however the basins have different sedimentation histories and differ in structural style the geometry of the crust and sediments suggests that the rockall trough originated by pure shear crustal stretching associated with rift deposits and cenozoic thermal sag strata in contrast the development of the erris trough located on unthinned continental crust was facilitated by shallow brittle extension with little deep crustal attenuation a two layered crust occurs throughout the region the lower crustal velocity in the hatton rockall basin is higher than that in the rockall trough the velocity structure shows no indication of crustal underplating by upper mantle material in the region

palaeoecological evidence for the prehistoric settlement of bodmin moor cornwall southwest england part ii land use changes from the neolithic to the present abstract radiocarbon dated pollen sequences from two areas of bodmin moor rough tor in the north west and the east moor are presented and the evidence for settlement in the prehistoric period on the moor considered the nature and extent of human impact in the two areas are compared and the evidence for anthropogenic activity in the environmental record is related to that deduced from the archaeology a tentative model of settlement and land use from the neolithic to the iron age is proposed with early activity in the neolithic leading to a peak of settlement in the bronze age and continuing activity on the moor during the iron age and into the romano british period human activity may have begun in the earliest neolithic and was possibly associated with construction of the hill top enclosure at rough tor the bronze age peak of activity that is apparent in the archaeology is also represented in the palynological record activity in the iron age and later shows that the moorland was intensively used for grazing and probably hay production until settlement expanded back onto the uplands in the medieval period this last phase resulted in the impoverishment of the soils and development of the current acid grassland and heath dominated vegetation of the moor finally various suggestions are made for future research into the palaeoecology of bodmin moor

historical context and chronology of bronze age land enclosure on dartmoor uk the upland of dartmoor southwest england is one of the flagship prehistoric landscapes within britain owing to the excellent survival of extensive prehistoric coaxial field systems archaeological surveys and rescue excavations during the 1970s and 1980s did much to further the understanding of this landscape however much remains to be explored in particular the chronology of enclosure the nature of the pre enclosure landscape and the relationship between bronze age communities and their environment reconsideration of this landscape is important given the place it holds in our understanding of subdivision of the landscape across northwest europe during prehistory this paper presents new palaeoecological data recovered as part of an integrated archaeological and palaeoecological project on northeast dartmoor the sequences detailed here include the first dated neolithic period palaeoenvironmental data from within the prehistoric enclosed land on the moor providing a longer term context for enclosure neolithic groups are implicated in the first establishment of heathland in the study area at around 3630 3370 cal bc during the early bronze age reestablishment of hazel scrub in the study area implies reduced use of the upland although it is not clear whether this is local or indicative of the wider landscape a combination of pollen and fungal spore data indicates a substantial shift to species rich grassland with grazing animals at c 1480 cal bc in a phase that lasted 400 years the later bronze age and early iron age are characterised by low intensity use of the upland these data provide new chronological data for land cover change on dartmoor and whilst they broadly confirm existing models of upland land use in later prehistory their proximity to the standing archaeology affords a more nuanced interpretation of local change

later holocene vegetation history of the isles of scilly uk coastal influence and human land use in a small island context small islands tend to experience exacerbated environmental social vulnerabilities due to isolation size and a small resource base the response of social communities to environmental stress can be addressed by compiling palaeoecological proxies for land management alongside archaeological records this paper presents pollen data from four new late holocene sequences that lie around sea level on the isles of scilly south west england to understand the impact of coastal change on island communities interpretation of sequences near the coastal zone can be confounded by problems in disentangling human impact from maritime and wetland influence multivariate analysis is used to separate samples influenced by maritime conditions and wetland development from inland human land management practices during the bronze age clearance of woodland resulted in an intensively managed pastoral system and archaeological datasets indicate that maritime resources formed an important part of the subsistence economy despite coastal change that resulted in loss of land area and reduced the extent of the intertidal zone the pollen data and evidence from existing archaeological data show continuity through later prehistory and into the medieval period the archaeological data and pollen evidence point towards a highly resilient community that employed a mixed and varied subsistence base copyright c 2015 john wiley sons ltd

moist and the continuity of crustal reflector geometry along the caledonian appalachian orogen new aspects of the deep structure of the scottish caledonides are revealed by the moine and outer isles deep seismic reflection traverse moist the caledonian foreland is underlain by an easterly dipping strongly reflecting surface cutting through the moho and traceable to more than 45 km depth thrusts within the foreland basement and caledonian orogen have been reactivated as normal faults bounding half grabens filled with sediments of late palaeozoic to mesozoic age the moine thrust which carries rocks of the orogen over lewisian foreland dips at 20 25 to the e on moist and is either a the westernmost of a series of easterly dipping reflections thrusts which flatten or terminate at 17 20 km depth or b a thrust lying further e which structurally overlies these easterly dipping reflectors by comparison with easterly dipping reflections on cocorp lines in the northern and southern appalachians the latter interpretation is preferred implying that many of the easterly dipping reflections on moist correspond to off shelf metasedimentary rocks with slivers of basement stacked and imbricated against the lewisian basement edge regional seismic refraction and conductivity data from northern scotland suggest that regions of the caledonian orogen have lower mid crustal velocity gradients and higher conductivities than the foreland which might be explained by this interpretation of the easterly dipping reflections despite similarities in crustal reflector geometries there are important differences between the moist and cocorp lines including 1 a remarkably continuous relatively horizontal moho seen on moist data at about 25 km depth and 2 the sedimentary basins offshore from northern scotland which have formed by reactivation under crustal extension of the easterly dipping thrusts furthermore it is probable that the easterly dipping reflectors in these areas of the moist and cocorp lines were formed at different times in the early palaeozoic

variation in the reference shields stress for bed load transport in gravel bed streams and rivers 1 the present study examines variations in the reference shear stress for bed load transport r using coupled measurements of flow and bed load transport in 45 gravel bed streams and rivers the study streams encompass a wide range in bank full discharge 1 2600 m3 s average channel gradient 0 0003 0 05 and median surface grain size 0 027 0 21 m a bed load transport relation was formed for each site by plotting individual values of the dimensionless transport rate w versus the reach average dimensionless shear stress the reference dimensionless shear stress r was then estimated by selecting the value of corresponding to a reference transport rate of w 0 002 the results indicate that the discharge corresponding to r averages 67 of the bank full discharge with the variation independent of reach scale morphologic and sediment properties however values of r increase systematically with average channel gradient ranging from 0 025 0 035 at sites with slopes of 0 001 0 006 to values greater than 0 10 at sites with slopes greater than 0 02 a corresponding relation for the bank full dimensionless shear stress bf formulated with data from 159 sites in north america and england mirrors the relation between r and channel gradient suggesting that the bank full channel geometry of gravel and cobble bedded streams is adjusted to a relatively constant excess shear stress bf r across a wide range of slopes

diachronous variscan late orogenic collapse as a response to multiple detachments a view from the internides in france to the foreland in the irish sea

bed load at low shields stress on arbitrarily sloping beds failure of the bagnold hypothesis 1 the bagnold hypothesis has been a major tool in the development of mechanistic models of bed load transport according to the hypothesis a necessary constraint for the maintenance of equilibrium bed load transport is that the fluid shear stress at the bed must be reduced to the critical or threshold value associated with incipient motion of grains the constraint determines a functional form for the areal concentration of bed load grains as a function of flow parameters it is shown here however that the bagnold hypothesis breaks down when applied to equilibrium bed load transport on beds with transverse slopes above a relatively modest value that is well below the angle of repose in particular under such conditions it is shown that no areal concentration no matter how large is sufficient to reduce the fluid shear stress at the bed to the critical value this failure motivates the abandonment of the bagnold constraint even for nearly horizontal beds the framework presented here however provides a natural basis for an entrainment based model of sediment transport that neither satisfies nor suffers from the drawbacks of the bagnold constraint

the incidence and nature of bedload transport during flood flows in coarse grained alluvial channels a continuous record reveals that the incidence of bedload in a coarse grained river channel changes from flood to flood long periods of inactivity encourage the channel bed to consolidate sufficiently so that bedload is largely confined to the recession limb of the next flood wave but when floods follow each other closely the bed material is comparatively loose and offers less resistance to entrainment in this case substantial amounts of bedload are generated on the rising limb this is confirmed by values of bed shear stress or stream power at the threshold of initial motion which can be up to five times the overall mean in the case of isolated floods or those which are the first of the season this produces a complicated relationship between flow parameters and bedload and explains some of the difficulties in establishing bedload rating curves for coarse grained channels besides this the threshold of initial motion is shown to occur at levels of bed shear stress three times those at the thresholds of final motion this adds further confusion to attempts at developing predictive bedload equations and clearly indicates at least one reason why equations currently in use are unsatisfactory bedload is shown to be characterized by a series of pulses with a mean periodicity of 1 7 hours in the absence of migrating bedforms it is speculated that this well documented pattern reflects the passage of kinematic waves of particles in a slow moving traction carpet the general pattern of bedload including pulsations is shown to occur more or less synchronously at different points across the stream channel

incipient motion of sand particles on side slopes several criteria have been theoretically proposed for the critical shear stress of noncohesive sediment on side slopes however no laboratory work has ever been done on this problem a theoretical study of the incipient motion of sediment particles on side slopes is presented including the effects of viscous sublayer turbulence and lift force as a special case of level beds the theory describes the experimental values reported by several workers a specially designed rotary wind tunnel permits the evaluation of the critical shear stress on side slopes and the experiment supports the theory these works reveal that the lift force can be neglected in estimating the critical shear stress using the proposed theory if the averaged experimental values are concerned but inclusion of the lift force in the theory is recommended for safety and for describing the lower limit of the possibility of incipient motion