numerical modeling of the emplacement of socompa rock avalanche chile 1 the 7 5 ka socompa sector collapse emplaced 25 km3 of fragmented rock as a thin but widespread 500 km2 avalanche deposit followed by late stage sliding of 11 km3 as toreva blocks most of the avalanche mass was emplaced dry although saturation of a basal shear layer cannot be excluded modeling was carried out using the depth averaged granular flow equations in order to provide information on the flow behavior of this well preserved long run out avalanche results were constrained using structures preserved on the surface of the deposit as well as by deposit outline and run up a proxy for velocity models assuming constant dynamic friction fail to produce realistic results because the low basal friction angles 1 to 3 5 necessary to generate observed run out permit neither adequate deposition on slopes nor preservation of significant morphology on the deposit surface a reasonable fit is obtained however if the avalanche is assumed simply to experience a constant retarding stress of 50 100 kpa during flow this permits long run out as well as deposition on slopes and preservation of realistic depositional morphology in particular the model explains a prominent topographic escarpment on the deposit surface as the frozen front of a huge wave of debris reflected off surrounding hills the result that socompa avalanche experienced a small approximately constant retarding stress during emplacement is consistent with a previously published analysis of avalanche data

the dynamics of the extratropical response to madden julian oscillation convection the rossby wave source rws and the corresponding extratropical wave response to tropical convection associated with different phases of the madden julian oscillation mjo is investigated with the dynamical core of a climate model the initial flow is specified to correspond to the boreal winter climatological flow and an imposed tropical heating that is derived from the observed precipitation for all eight mjo phases one key question addressed here is why does the extratropical rossby wave train depart the subtropics at a longitude well to the east of the rws for all eight mjo phases it is found that the extratropical response over the north pacific and north america is almost entirely due to the mjo convection over the western tropical pacific the rws is excited within the first 24 h after the model heating is turned on for mjo phases 1 3 and 8 the rws leads to the development of a cyclonic anomaly over southeast asia via advection of the climatological absolute vorticity by the anomalous divergent wind in the subtropics and by horizontal convergence in the tropics mjo phases 4 7 show opposite features the resulting anomaly is then advected eastward by the climatological zonal wind toward the central pacific after which dispersion into the extratropics and the excitation of a pacific north american teleconnection pattern takes place

catastrophic debris avalanche deposit of socompa volcano northern chile between 10 000 and 500 yr ago the socompa volcano in northern chile experienced a catastrophic collapse of a 70 deg sector of the original cone causing a debris avalanche that descended nearly 3000 m vertically and traveled more than 35 km from the volcano the deposits cover some 490 sq km and have a minimum volume of 15 cu km parts of the original cone slumped in a nearly coherent form and are now preserved as large blocks more than 400 m high the primary avalanche traveled northwestward over sloping ground before coming to rest transiently forming a prominent marginal ridge and then slid away northeastward to form a secondary flow overriding much of the primary avalanche deposit abundant prismatic jointed dacite blocks within the debris avalanche deposit and a thin fine grained pumiceous deposit beneath it suggest that the collapse was triggered by magmatic activity and may have been accompanied by a violent lateral blast collapse was followed by eruption of pumiceous pyroclastic flows and extrusion of voluminous dacite domes

changes in physical properties of a reservoir sandstone as a function of burial depth the etive formation northern north sea abstract rock physical properties like velocity and bulk density change as a response to compaction processes in sedimentary basins in this study it is shown that the velocity and density in a well defined lithology the shallow marine etive formation from the northern north sea increase with depth as a function of mechanical compaction and quartz cementation physical properties from well logs combined with experimental compaction and petrographic analysis of core samples shows that mechanical compaction is the dominant process at shallow depth while quartz cementation dominates as temperatures are increased during burial at shallow depths

on the rossby wave source and the steady linear response to tropical forcing abstract a two level spectral model with a zonally homogeneous climate is used to study the steady response of a spherical atmosphere to tropical heating solutions are obtained by both averaging the time integration of the model and solving for the linear steady response it is found that the rossby wave source rws from a simple tropical heat source exhibits a relatively complicated horizontal structure that extends from the tropics into extratropical regions the strong extratropical component of the rws is important for the steady response in middle and high latitudes a decomposition of the solution using separately the components of the rws in tropical and extratropical regions shows that the responses to the tropical and extratropical rwss tend to cancel in middle and high latitudes the extratropical component of the rws may be understood by quasigeostrophic dynamics

xanthones novel aromatic oxygen containing compounds in crude oils abstract xanthone and its alkylated homologues were determined to be present in 64 of 69 investigated oils from offshore norway central graben viking graben haltenbanken this is the first description of xanthones in crude oils these compounds were identified by comparison with authentic standards by coinjection based on mass spectra and relative retention times on two different gc columns the elution order of the four methylxanthones was established as 1 4 2 3 by using a bpx 5 column about 2 3 of the oils contain concentrations of xanthone lower than 5 g g oil but some oils are clearly enriched in the parent compound the highest amount of xanthone in the sample set was 38 g g oil the relative abundance of xanthone the sum of the methylxanthones and the sum of the c 2 xanthones is mainly controlled by maturity partitioning processes may effect changes in the distribution of methylxanthones as observed for a biodegradation sequence from the gullfaks field molecular dynamics calculations support the observation of a better preservation of the shielded isomers 1 and to a lesser extent 4 methylxanthone in the oil phase compared to the non shielded isomers 2 and 3 methylxanthone the ratio of these two different isomer groups may be useful as an indicator of secondary migration distances as demonstrated for an oil sequence from the tampen spur and haltenbanken oils however biodegradation could also cause an increase of the shielded isomers relative to the non shielded isomers due to sterical hindrance by the methyl groups restricting access to the oxygen functionalities the origin of xanthones in crude oils and source rocks is not known but they could be generated as diagenetic products formed by oxidation of xanthenes in the reservoir or originate by geosynthesis from aromatic precursors

relationship between petroleum generation migration and sandstone diagenesis middle jurassic gifhorn trough n germany abstract the gifhorn trough in north germany contains an interbedded succession of lower to middle jurassic source and reservoir rocks regional variations in the burial history made it possible to investigate different stages in the maturation history of source rocks and the diagenetic history of reservoir rocks this study focuses in particular on the temporal and spatial relation between secondary petroleum migration and diagenetic events in the reservoir sandstones reconstruction of the burial and geothermal history indicate the initiation of petroleum generation at the beginning of the upper cretaceous lower toarcian shales have been identified as the common source rock of all oils based on biomarker and stable isotope studies differences in the composition and maturity of reservoired oils are interpreted to be related to separated oil kitchens of different maximum source rock maturity rather than in reservoir alteration after migration and accumulation major diagenetic events in the shallow marine arenitic reservoir sandstones are linked to various processes operating during burial a fe calcite cement formation isotope analyses indicate that this is facies related from carbonate redistributed at shallow burial depth 800 1200 m b fe dolomite dolomitization of early formed fe calcite is discussed based on pore water and oxygen isotopic composition c late kaolinite two models are discussed to explain the observed simultaneous formation of kaolinite and the creation of minor amounts of secondary porosity d late quartz overgrowths diffusive silica transport from quartz grain dissolution in shales into adjacent sandstones is proposed as a formation mechanism geochemical analyses of carbonate cemented intervals suggest that early generated condensate was trapped during carbonate precipitation prior to the main phase of petroleum migration these early formed carbonate cemented horizons probably compartmentalized the reservoir controlled petroleum migration routes and promoted the formation of diagenetic traps

topographic reflection of the socompa debris avalanche chile one of the most remarkable features of the exceptionally well preserved 26 km3 socompa debris avalanche deposit is the evidence for topographically driven secondary flow the avalanche formed by sector collapse of socompa stratovolcano and spread 40 km across a pre existing basin forming a sheet of 50 m average thickness as the avalanche impinged on the western and northern margins of the basin it was reflected back forming a secondary flow that continued to travel 15 km down a gentle slope at an oblique angle to the primary flow the front of the return wave being preserved frozen on the surface of the deposit as a prominent escarpment satellite images aerial photos digital elevation models and field observations were used to reconstruct the sequence of events during avalanche emplacement and in particular during secondary flow the avalanche sheet was divided into distinct terrane groups each believed to have experienced a particular strain history during emplacement evidence for avalanche reflection includes clearly recognizable secondary slide masses sub parallel sets of curvilinear shear zones headwall scarps separating the primary levee from the secondary terranes extensional jigsaw breakup of surface lithologies during return flow and cross cutting or deflection of primary flow fabrics by secondary terranes reflection off the basin margin took place in an essentially continuous manner most major return motions being simultaneous with or shortly following primary flow the secondary flow occurred as a wave that swept obliquely across the primary avalanche direction remobilizing the primary material which was first compressed then stretched as it passed over and rearward of the wave front as return flow occurred surface lithologies were rifted in a brittle manner and the slabs were sheared pervasively as they glided and rotated back into the basin some sank into the more fluidal interior of the avalanche which drained out into a prominent distal lobe extension by factors of up to 1 8 took place during return flow secondary flow took place on slopes of only a few degrees and the distal lobe flowed 8 km on a slope of 1 overall the avalanche is inferred to have slid into place as a fast moving sheet of fragmental rock debris with a leading edge and crust with near normal friction and an almost frictionless fluidal interior and base the avalanche emplacement history deduced from field evidence is consistent with the results of a previously published numerical model of the socompa avalanche

early tertiary igneous activity west of the outer hebrides scotland evidence from magnetic anomalies and dredged basaltic rocks abstract much of the continental shelf off the outer hebrides northwest scotland is underlain by a basement platform which has not undergone the subsidence typical of many parts of the margin west of britain although seismic data suggest that the platform is largely an extension of the precambrian lewisian gneiss of the outer hebrides the pattern of magnetic anomalies indicates that other lithologies are present dredging operations in an area of basement outcrops between st kilda and the flannan isles have resulted in the recovery of a collection of basaltic rocks in addition to granitic gneisses analysis of the freshest basaltic samples reveals that they are olivine tholeiites typical of within plate basalts which are chemically distinct from basic intrusions on st kilda and other tertiary volcanic rocks nearby whole rock k ar dating yields a mean age of 43 4 1 0 ma the association of the basaltic material with one of several prominent linear belts of magnetic anomalies crossing the shelf points to an extensive invasion of the margin by basic igneous intrusions during the early tertiary the dredged basalts appear to represent a late stage volcanic episode in the evolution of the tertiary igneous province of britain one block of gneiss in the dredge haul has given ages of 404 9 and 431 7 ma perhaps indicating reworking of the precambrian basement by caledonian tectonic events on the lewisian foreland however further work is necessary to establish the provenance of this gneissic material

acoustic fluidization and the extraordinary mobility of sturzstroms 1 sturzstroms are a rare category of rock avalanche that travel vast horizontal distances with only a comparatively small vertical drop in height their extraordinary mobility appears to be a consequence of sustained fluid like behavior during motion which persists even for driving stresses well below those normally associated with granular flows one mechanism that may explain this temporary increase in the mobility of rock debris is acoustic fluidization where transient high frequency pressure fluctuations generated during the initial collapse and subsequent flow of a mass of rock debris may locally relieve overburden stresses in the rock mass and thus reduce the frictional resistance to slip between fragments in this paper we develop the acoustic fluidization model for the mechanics of sturzstroms and discuss the conditions under which this process may sustain fluid like flow of large rock avalanches at low driving stresses

the deep seismic reflection marconi 3 profile role of extensional mesozoic structure during the pyrenean contractional deformation at the eastern part of the bay of biscay abstract the new marconi 3 deep seismic profile allows recognition of the upper crustal structure of the eastern part of the bay of biscay and the main features of its alpine geodynamic evolution it denotes that the easternmost part of the bay of biscay consists of a thick wedge of uppermost cretaceous to cenozoic synorogenic sediments lying unconformably on the top of a thinned continental crust with the mesozoic parentis basin to the north and the coeval landes high to the south the parentis basin appears as a major half graben bounded southwards by a north dipping planar fault it is filled by a thick sequence of jurassic upper cretaceous carbonates affected by salt domes and squeezed diapirs made up of triassic evaporites and mudstones these salt tectonic structures also affect the overlying uppermost cretaceous to lower miocene synorogenic deposits which are folded upon these structures the landes high includes a thin pre upper cretaceous cover tilted to the south in the basque shelf it is deformed by a basement involving thrust wedge emplaced during the late eocene miocene that constitutes the north pyrenean contractional front geometric relationships and thickness variations depict that this overall structure results from the following mesozoic extensional stage which includes a late jurassic late aptian syn rift stage in which the parentis basin formed and an albian early late cretaceous post rift stage in which diapirs of triassic evaporites grew close to this major fault compressive deformational stage coeval to the pyrenean orogeny which led to 1 the development of a latest cretaceous up to middle miocene foreland basin and 2 from late eocene the formation of a basement involving thrust wedge in the innermost foreland basin the squeezing of the diapiric structures formed previously in the parentis basin and later middle miocene the partial inversion of some pre existent faults located in the southern parentis basin margin this geodynamic evolution together with the structure of the area evidences that the extensional structure resulting from the opening of the bay of biscay played an important role both in the location of the north pyrenean front and in the north pyrenean foreland contractional deformation features specially the lack of significant inversion structures in the parentis basin despite that it belongs to a severely thinned crustal area before the alpine compression denotes that the mesozoic landes high acted as an important buffer for the propagation of the pyrenean contractional deformation to the north this deformational buffer was active until early miocene and probably vanished afterwards during the last stages of pyrenean orogen development when some basement faults reactivated in the parentis basin

geodynamic and hydrodynamic evolution of the broad fourteens basin the netherlands in relation to its petroleum systems abstract data analysis in combination with 2d basin modelling is used to study the hydrogeologic and hydrodynamic response of the basin fill of the broad fourteens basin to its geodynamic evolution and the significance of this response for the evolution of the petroleum systems in the basin data analysis resulted in the identification of the major mechanical processes involved in overpressure and fluid flow evolution in the basin sedimentary loading and unloading tectonic compression and extension topography of the groundwater table and provided a timeframework for the important permeability alterations in the basin and the distinct phases of fluid flow observed present day diagenetic features and fracture characteristics in the basin indicate permeability alterations and paleo fluid flow during distinct periods of tectonic activity in the basin e g during late jurassic rifting and late cretaceous inversion the basin boundary fault zones were repeatedly reactivated during the periods of tectonic activity the 2d basin modelling included sedimentary loading and unloading topography of the water table and petroleum generation as pressure and fluid flow influencing mechanisms in addition the influence of time dependent permeability of fault zones on the overpressure history and the evolution of petroleum systems was modelled and evaluated the favoured modelling scenario including a time dependent permeability of faults shows that syn rift and post rift sedimentation in combination with gas generation induced overpressured conditions in restricted parts of the basin that is mainly in the deeper low permeable carboniferous shales and zechstein evaporites the calculated pre inversion overpressured conditions disappear during subsequent inversion of the basin predicted present day pressures in the reservoir horizons are near hydrostatic and reasonably in accordance with observed pressures the favoured scenario also explains the known location of oil fields and the location and saturation characteristics of the gas occurrences the model results further show that the difference in timing of oil charging of the p9 and q1 lower cretaceous reservoirs explains the observed differences in geochemical composition of the accumulated oils the biodegraded and water washed nature of the late cretaceous charged q1 oil reservoir is consistent with the concentrated topography induced groundwater flow through lower cretaceous reservoir units during the late cretaceous inversion period late charging of the lower cretaceous oil reservoir in the p9 area explains the non biodegraded character of the accumulated oils in general this paper shows the importance of using data analysis to obtain an a priori characterization of the basin geofluid evolution and shows that paleohydrodynamic conditions and time dependent permeability of the hydrogeological framework have influenced significantly the petroleum systems in the basin

styles of positive inversion tectonics in the central apennines and in the adriatic foreland implications for the evolution of the apennine chain italy abstract integration of new field structural and geophysical data with existing information from the apennines chain in italy and its adjacent adriatic foreland indicates that the styles of positive inversion tectonics and the modes of interaction between the extensional and the subsequent compressive structures vary starting from the cretaceous the contractional deformation induced by the mainly north directed convergence of africa adria with respect to the european plate promoted the closure of various arms of the atlantic and the neo tethys oceans which opened in different times and with distinct orientations the mosaic of continental blocks carbonate platforms rift basins and oceanic domains with several geometries and orientations with respect to the axis of the subsequent compression and the resulting heterogeneities within the shallow sedimentary cover and the overall lithosphere strongly influenced both the structural evolution of the apennine orogenic belt and the intra continental deformation within the adriatic foreland field observations reveal that the steeply e and w dipping mesozoic cenozoic normal faults are systematically decapitated by sub horizontal or gently west dipping thrusts propagating with short cut trajectories pre thrusting normal faults were commonly deformed by later thrusts but little evidence seems to support their entire reactivation as high angle reverse faults this suggests that these shallow and steeply dipping discontinuities were not suitable to be reutilized by the superficial thin skinned thrust faults propagating within the sedimentary cover in contrast presumably late paleozoic and mesozoic w dipping normal faults appear moderately reactivated in the adriatic foreland and strong positive inversion tectonics affect the deeper and buried structural levels of the apennine chain within the latter the syn rift sediments in the hangingwall blocks of the fault bounded basins were totally extruded and generated the strong uplift of the thinned adria continental crust finally the contrasting styles of interactions of the pre existing normal faults with later thrusts i e passive truncation or positive reactivation strictly result from the different evolution of the apennine chain and the combined thin and thick skinned modes of deformation of the stretched lithosphere of the adria plate

velocity anisotropy of upper jurassic organic rich shales norwegian continental shelf abstractthis study investigates the seismic velocity anisotropy of two organic rich shales from the norwegian continental shelf the tested organic rich shale samples were from the upper jurassic draupne and hekkingen formations collected from two wells 16 8 3s and 7125 1 1 drilled in the central north sea and western barents sea respectively the two tested shales are different in organic matter richness and thermal maturation and they have experienced different burial histories the shale core plugs were tested in a triaxial cell under controlled pore pressure seismic velocities vp and vs were measured along different orientations with respect to layering to identify the complete tensor of the rock elastic moduli and to investigate the velocity anisotropy as a function of increasing effective stress the measured velocity values exhibit strong anisotropy for the two tested organic rich shales the anisotropy for both shales is strongest for vs seismic velocities follow an increasing trend as th

palaeogeographical evolution of the rattray volcanic province central north sea the rattray volcanics member at the triple junction of the north sea rift is here subdivided into two informal sub members based on analysis of core wireline and seismic data the lower and upper rattray volcanics were emplaced during two distinct phases of volcanism separated by a sustained volcanic hiatus the presence of hyaloclastite and abundant freshwater algae at the base of the lower rattray indicates that large lakes were present in the area prior to the volcanism possibly indicating that collapse of the regional jurassic central north sea dome began prior to volcanism pulsed subsidence probably occurred through the duration of the volcanism with lacustrine conditions becoming re established during the mid volcanic hiatus sediments were deposited across the rattray volcanic province in fluvial systems and floodplain coal swamps after the final cessation of volcanism with later marine transgression leading to drowning of the area in the callovian to oxfordian in terms of hydrocarbon prospectivity no evidence is currently found to confirm the presence of an intra basaltic play analogous to the rosebank field in the faroe shetland basin although post volcanic pentland formation sedimentary sequences in the fisher bank basin area indicate the possibility of supra basaltic prospectivity in the triple junction supplementary material a table containing the complete palynological record is available at https doi org 10 6084 m9 figshare c 4857195

the 1984 july 19 north wales earthquake a lower crustal continental event indicating brittle behaviour at an unusual depth summary attention has recently been focused on the structure and composition of the lower crust in continental areas it is generally believed that except in special circumstances ductile behaviour below mid crustal depths precludes the brittle processes that cause earthquakes the 1984 july 19 earthquake in north wales occurred at the unexpected depth of 23 km we report here the location of the larger aftershocks and the relocation of the main shock with respect to one of them the lower crustal depths of the events are confirmed by tests with a wide range of models the occurrence of earthquakes at these depths may be related to low heat flow in the region

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

the socompa collapse and avalanche event failure of the northwestern flank of the socompa volcano north chile about 7000 years ago created a 40 km long debris avalanche deposit the deposit is remarkably well exposed we have combined spectral reflectance data field observations and analysis of digital topographic surfaces to reconstruct the sequence of collapse events and to constrain the volumes and sources of materials comprising the avalanche collapse involved three principle components the debris avalanche deposit itself volume 26 km3 after 30 expansion large slide blocks 11 km3 and detached blocks 23 km3 which remained in the upper part of the amphitheatre the debris avalanche deposit comprised two main units and seven subunits landsat thematic mapper data enabled estimation of the proportions of spectrally distinct lithological components within these heterogeneous units about 35 of the deposit area is composed of ignimbrites and gravels derived from a 100 200 m thick slice of basement rock underlying the northwestern flank of the volcano dacite domes and lavas originally situated in the southern and western parts of the amphitheatre constitute much of the remainder of the deposit blocks composed largely of sequences of lavas and pyroclastic deposits originally located in the northern and eastern parts of the amphitheatre slid coherently 7 km northwestwards and accumulated near the mouth of the amphitheatre modelling of locations of centroids in the original cone and of displaced components shows that potential energy loss during collapse was 3 8 1017 j cf 0 7 1017 j for mount st helens 1980 significantly components of the avalanche with least potential energy travelled the furthest laterally perhaps demonstrating efficient transfer of momentum from rear to front of the avalanche retrogressive flank failures of the original cone contributed successive components to the avalanche most of these combined to form a single moving mass but some appear to have been emplaced separately

mechanisms for a pna like teleconnection pattern in response to the mjo abstractkinematic mechanisms of the pacific north america pna like teleconnection pattern induced by the madden julian oscillation mjo is examined using an atmospheric general circulation model gcm and a barotropic rossby wave theory observation shows that a negative pna like teleconnection pattern emerges in response to mjo phase 2 forcing with enhanced suppressed convection located over the indian western pacific ocean the gcm simulations show that both forcing anomalies contribute to creating the pna like pattern indian ocean forcing induces two major rossby wave source rws regions a negative region around southern asia and a positive region over the western north pacific wnp the negative rws to the north of the enhanced convection in the indian ocean arises from southerly mjo induced divergent wind crossing the asian jet unexpectedly another significant rws region develops over the wnp owing to refracted northerly divergent wind a ray tracing method demonstrates three different w

catastrophic debris avalanche from ancestral mount shasta volcano california a debris avalanche deposit extends 43 km northwestward from the base of mount shasta across the floor of shasta valley california where it covers an area of at least 450 km 2 the surface of the deposit is dotted with hundreds of mounds hills and ridges all formed of blocks of pyroxene andesite and unconsolidated volcaniclastic deposits derived from an ancestral mount shasta individual hills are separated by flat topped laharlike deposits that also form the matrix of the debris avalanche and slope northwestward about 5 m km radiometric ages of rocks in the deposit and of a postavalanche basalt flow indicate that the avalanche occurred between about 300 000 and 360 000 yr ago an inferred average thickness of the deposit plus a computed volume of about 4 km 3 for the hills and ridges indicate an estimated volume of about 26 km 3 making it the largest known quaternary landslide on earth

synoptic analysis of the pacific north american teleconnection pattern in this study we use various diagnostic techniques to investigate the synoptic evolution of the pacific north american teleconnection pattern pna national center for environment prediction national center for atmospheric research reanalysis data are used these data cover the years 1948 2008 for the months of november march it is found that the positive pna is initiated by enhanced convection over the western tropical pacific and weakened convection over the tropical indian ocean the excitation of the negative pna exhibits opposite features for both phases the response to tropical convection excites a small amplitude pna about 8 12 days prior to the pattern attaining its maximum amplitude this is followed by slow steady growth for about 5 days after which driving by synoptic scale waves via their eddy vorticity flux together with stationary eddy advection lead to much more rapid growth and the establishment of the full pna for the positive pna the synoptic scale waves propagate eastward into the midlatitude northeastern pacific where they are observed to undergo cyclonic wave breaking for the negative pna the synoptic scale waves first amplify over the midlatitude northeastern pacific and then propagate equatorward into the subtropics where they undergo anticyclonic wave breaking once established for both phases the pna appears to be maintained through a positive feedback that involves a succession of wave breakings these results suggest that preconditioning may play an important role in the formation of the pna for the positive pna in its early development the strengthening and eastward extension of the subtropical jet result in an increase in the cyclonic shear and a decrease in the meridional potential vorticity gradient features that are known to favour cyclonic wave breaking for the negative pna opposite changes were observed for the background flow which favour equatorward wave propagation and anticyclonic wave breaking the role of optimal growth is also discussed our results also suggest that the pna is potentially predictable 1 2 weeks in advance copyright 2011 royal meteorological society

the impact of the initial flow on the extratropical response to madden julian oscillation convective heating abstractthe response to the madden julian oscillation mjo over the pacific north american pna region is investigated in addition the sensitivity of this response to the interaction between madden julian oscillation forcing and the extratropical initial flow is explored first a simple dynamical model is run with an ensemble of 100 randomly selected initial conditions from era interim data with no heating mjo phase 1 like heating and mjo phase 5 like heating the 300 hpa geopotential height field is separated into a part that would evolve without an active mjo present and a part that is a consequence of the mjo heating a negative 300 hpa geopotential height anomaly centered over northeastern china bounded by positive anomalies on its equatorward and poleward flanks is found to be followed by a large amplitude negative pna like response for mjo phase 1 and a positive pna like response for phase 5 a similar study is carried out using observational data an analog approach using projections to det

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

early middle jurassic ostracod migration between the northern and southern hemispheres further evidence for a proto atlantic central america connection abstract early to middle jurassic marine ostracod assemblages from the southwestern part of the british isles north african continental margin and south america have yielded taxa which are not known from other parts of britain and europe we discuss the palaeogeographical and stratigraphical distribution of these taxa here arranged into ten informal groups from which we infer that benthonic podocopid ostracoda successfully migrated between northwest europe and the eastern part of tethys during the early and middle jurassic not through the main tethyan seaway but via a proto atlantic central america route supporting previous observations based on macrofossil evidence hispanic corridor of smith 1983 furthermore the fact that these taxa are absent from contemporary european sequences suggests the existence of physical and or chemical barriers limiting benthonic faunal exchange between the western part of the british isles and the rest of north western europe particularly during the late pliensbachian through to aalenian interval

the influence of the mjo on the intraseasonal variability of northern hemisphere spring snow depth abstractintraseasonal variability in springtime northern hemisphere daily snow depth change sd by phase of the mjo was explored in this study principal findings of the relationship between sd and the mjo included the following 1 statistically significant regions of lagged sd anomalies for multiple phases of the mjo were found in march april and may in both north america and eurasia 2 in each month lagged sd anomalies were physically supported by corresponding lagged anomalies of 500 hpa height z500 and surface air temperature sat spearman rank correlation coefficients indicated a moderate to strong relationship between both z500 and sd and sat and sd in both eurasia and north america for phases 5 and 7 in march in april a moderately strong relationship between z500 and sd was found over eurasia for phase 5 but the relationship between sat and sd was weak in may correlations between sd and both z500 and sat over a hemisphere wide latitude band from 60 to 75 n were close to 0

the llullaillaco volcano northwest argentina construction by pleistocene volcanism and destruction by sector collapse abstract llullaillaco is one of a chain of quaternary stratovolcanoes that defines the present andean central volcanic zone cvz and marks the border between chile and argentina bolivia the current edifice is constructed from a series of thick dacitic lava flows forming the second tallest active volcano in the world 6739 m k ar and new biotite laser 40ar 39ar step heating dates indicate that the volcano was constructed during the pleistocene 1 5 ma with a youngest date of 0 048 0 012 ma being recorded for a fresh dacite flow that descends the southern flank additional 40ar 39ar measurements for andesitic and dacitic lava flows from the surrounding volcanic terrain yield dates of between 11 94 0 13 ma and 5 48 0 07 ma corresponding to an extended period of miocene volcanism which defines much of the landscape in this region major and trace element compositions of lavas from llullaillaco are typical of miocene pleistocene volcanic rocks from the western margin of the cvz and are related to relatively shallow dipping subduction of the nazca plate beneath northern chile and argentina oversteepening of the edifice by stacking of thick viscous dacitic lava flows resulted in collapse of its southeastern flank to form a large volcanic debris avalanche biotite 40ar 39ar dating of lava blocks from the avalanche deposit indicate that collapse occurred at or after 0 15 ma and may have been triggered by extrusion of a dacitic flow similar to the one dated at 0 048 0 012 ma the avalanche deposits are exceptionally well preserved due to the arid climate and prominent levees longitudinal ridges and megablocks up to 20 m diameter are observed the avalanche descended 2 8 km vertically and bifurcated around an older volcano cerro rosado before debouching onto the salt flats of salina de llullaillaco the north and south limbs of the avalanche traveled 25 and 23 km respectively and together cover an area of approximately 165 km2 estimates of deposit volume are hampered by a lack of thickness information except at the edges but it is likely to be between 1 and 2 km3 equivalent coefficients of friction of 0 11 and 0 12 and excess travel distances of 20 5 and 18 5 km are calculated for the north and south limbs respectively the avalanche ascended 400 m where it broke against the western flank of cerro rosado and a minimum flow velocity of 90 m s 1 can be calculated at this point lower velocities of 45 m s 1 are calculated where distal toes ascend 200 m slopes it is suggested that the remaining precipitous edifice has a high probability for further avalanche collapse in the event of renewed volcanism

numerical modelling of the response to variable stretching rate of a domino fault block system abstract using a numerical model of domino fault block development the effects of a variable stretching rate during rifting were investigated it is shown that a varable stretching rate can have an important influence on synrift sequence geometries this can lead to complex synrift sequences composed of wedge shaped units formed during periods of high stretching rate and more symmetrical units formed during periods of relative tectonic quiescence at the fault block crest increases in stretching rate can produce offlapping synrift sequences whereas decreases in stretching rate allow onlap onto the fault block crest if the rifting period contains multiple pulses of stretching complex intra synrift unconformities can be formed the initial bathymetry is also shown to have an important influence on the modelled synrift stratigraphy the modelled stratigraphies are similar to those thought to result from variations in absolute sea level pseudo facies markers based on the combined initial depth and slope of deposition of the modelled sediments are shown to be a useful tool and graphically illustrate the response of the system to pulses of tectonic activity

quantitative analysis of north sea subsidence stratigraphic and geophysical maps of the northern and southern north sea basin are used to study mechanisms of intracratonic basin formation these maps include 1 tectonic subsidence for ten stratigraphic units 2 predicted and observed sediment overpressure 3 geographic variation of compaction constants 4 net basement fault extension 5 free air gravity 6 flexural rigidity 7 heat flow and 8 predicted hydrocarbon maturation in northern areas of the north sea observed basement fault extension crustal thinning present day flexural rigidity and tectonic subsidence are predicted reasonably well by a simple stretching model of basin formation with rifting phases during the triassic and mid jurassic early cretaceous in southern areas of the north sea however a similar analysis suggests that other non extensional rift related processes dominated basin evolution the effects of anomalously active aesthenospheric convection coupled with basalt eclogite and deep crustal dewatering reactions are considered as possible additional mechanisms the troughlike form of quaternary tectonic subsidence suggests a new phase of rifting may be starting in the north sea the importance of such thermal rejuvenation is borne out by the association of areas of differential subsidence with high heat flow and low flexural rigidity one component of tectonic reactivation during this period may be due to thermally induced isostatic reequilibration of older tectonic loads

tectonic analysis of a viking graben border fault the viking graben has been proven to be an aulacogen on a passive continental margin the rifting started in the late permian and had numerous episodes throughout the mesozoic the strongest tectonic events occurred in the late jurassic and in the early cretaceous namely in the late cimmerian phases toward the end of the cretaceous the taphrogeny ceased and the graben became part of a rigid continental margin a laramian phase however did occur the tertiary basins had their depocenters close to the viking and the central graben axes but the outline of these smooth and rounded basins were independent of the graben border faults however in one area in the central part of the north sea a viking graben border fault was reactivated in the paleocene eocene this rejuvenation has resulted in such structural features as flower structures and normal faults along the old cimmerian viking graben border fault the tensional features are found along one border fault dogleg trend and the compressive features are found along another this is explained as a response to strike slip reactivation of the old fault the transient movements coincide with the incipient sea floor spreading in the norwegian greenland sea area and may be related to consequent rotation of the shetland platform relative to the fennoscandian shield

low temperature effects of the skye tertiary intrusions on mesozoic sediments in the sea of hebrides basin fission track analysis of samples from the sea of hebrides basin and surrounding regions demonstrates two very distinct age groups around 50 ma and 300 ma regardless of the stratigraphic age apatite fission track results from sediments within 8 km of the tertiary igneous complex on skye were totally reset by temperatures 110 c during intrusion of the centres but now yield ages younger than the granites zircon fission track results from the granites also demonstrate ages significantly younger than their hosts mean track lengths in apatites of 13 5 m and reduced apatite and zircon ages suggest that temperatures remained elevated throughout the 6 ma during which intrusive activity occurred but were hotter within the granite bodies than the surrounding sediments prior to intrusion of the complex temperatures in the basin sediments presently at outcrop were unlikely to have been higher than 50 c and beyond the effects of the tertiary intrusions age and track length distributions from northern skye the isle of lewis and the west coast of scotland illustrate that the area is unlikely to have been buried beneath more than 2 km of sediment at any one time since the end of the devonian north of the highland boundary fault tertiary uplift and erosion in scotland is considered to have been between 1 1 5 km this is consistent with a regional pattern of tertiary erosion identified across the british isles but considerably less than that recognised in northern england the geological society 1992

boreal winter links between the madden julian oscillation and the arctic oscillation abstract there is increasing evidence that the madden julian oscillation mjo modifies the mid to high latitude circulation and in particular appears to have a relationship to the leading mode of extratropical variability the arctic oscillation ao in this study new insights into the observed similarities between the mjo and the ao are explored it is shown that the eastward progression of the convectively active phase of the mjo is associated with a corresponding shift in the tendency and sign of the ao index moreover the ao and the mjo share several analogous features not only in the global circulation but also in surface temperature fields also the ao is linked to a pattern of eastward propagating mjo like variability in the tropics that is partially reproduced in free runs of the ncep climate forecast system cfs model finally it is shown that the structure of the ao as defined by the leading mode in the 1000 hpa geopotential height field is significantly altered based on the phase o

in situ stress from breakouts in the danish sector of the north sea abstract borehole breakouts from 26 wells situated in the danish central graben and one well situated in the northwestern section of the ringkobing fyn high have been studied the data provide information on the orientation of the contemporary principal horizontal stresses down to depths of 4 7 km statistics were used to obtain a mean azimuth of breakouts for each well and each individual breakout was weighted by its length data quality of breakouts is assigned according to the world stress map quality ranking scheme the breakout data reveal that s h orientations in the danish central graben are extremely scattered no regional trend in mean s h orientation can be identified as a result of the large standard deviation 77 similar scatterings of s h orientations have been reported from adjacent regions of the north sea the results indicate that the state of stress in the sedimentary cover of the danish central graben is influenced by a local stress generating mechanism rather than platewide stress transmissions mechanisms three units with different states of stress have been identified and found to correspond somewhat with the lithostratigraphic divisions of the post chalk group chalk group and pre chalk group

discovery of lower cretaceous hydrothermal vent complexes in a late rifting setting southern north sea insights from 3d imaging we present data for 31 kilometre scale hydrothermal vent complexes and associated sand remobilization that have formed as a consequence of magmatic intrusions within salt strata southern north sea dutch sector this study uses 3d seismic data tied to three wells and artificial neural networks to describe conical and cylindrical vent structures located in the ne part of the broad fourteens basin the structures are composites of 58 subvertical pipes that form complexes and are 951 364 m in height and 487 426 m in diameter interactions of magma and fluids at depth triggered successive fluid pressure build ups in triassic sandstones resulting in upward propagated ruptures followed by the collapse of overlying deposits and the injection and extrusion of fluidized sand the relationship between vent tops and their overlying deposits indicates a mid hauterivian age unusual for volcanic activity in the north sea area this event could have a significant impact on hydrocarbon exploration as the hydrothermal vent complexes bypass a regional source rock and seal offering new migration routes and connectivity between potential reservoirs the intrusions also raise questions about the influence of transform tectonics on the focusing of volcanic activity during the late rifting phase of the north sea supplementary material tables of seismic attributes and the geometry of the vent complexes as well as a 3d visualisation of the vents are available at https doi org 10 6084 m9 figshare c 3571593

a sedimentological approach to refining reservoir architecture in a mature hydrocarbon province the brent province uk north sea improved reservoir characterisation in the mature brent province of the north sea aimed at maximising both in field and near field hydrocarbon potential requires a clearer understanding of sub seismic stratigraphy and facies distributions in this context we present a regional high resolution sequence stratigraphic framework for the brent group uk north sea based on extensive sedimentological re interpretation of core and wireline log data combined with palynostratigraphy and published literature this framework is used to place individual reservoirs in an appropriate regional context thus resulting in the identification of subtle sedimentological and tectono stratigraphic features of reservoir architecture that have been previously overlooked we emphasise the following insights gained from our regional high resolution sequence stratigraphic synthesis 1 improved definition of temporal and spatial trends in deposition both within and between individual reservoirs 2 development of regionally consistent predictive sedimentological models for two enigmatic reservoir intervals the broom and tarbert formations and 3 recognition of subtle local tectono stratigraphic controls on reservoir architecture and their links to the regional middle jurassic structural evolution of the northern north sea we discuss the potential applications of these insights to the identification of additional exploration potential and to improved ultimate recovery

geochemical insights into the internal dynamics of debris avalanches a case study the socompa avalanche chile one way to infer the internal dynamics of debris avalanches is to characterize the heterogeneity of their deposits here we present high precision sr nd isotope compositions plus major and trace element concentrations of matrix samples and rock fragments from the socompa debris avalanche deposit chile the socompa blocks are easily identifiable in the field but distinguishing substrate debris from disaggregated material formed at the volcano is difficult to do with only field criteria combining isotope data with field observations can help with this measured sr and nd isotope ratios show significant variations defining a binary mixing array where matrix and rock deposits overlap this testifies to the mixing of crushed rocks during collapse and or movement assimilation of socompa basement appears to be variable overall it is far lower than was previously proposed comparison between matrix and block samples in contact over the whole surface area of the deposit shows that the isotopic heterogeneity increases from source to front close to the socompa matrices are resulting from simple crushing of adjacent rocks at the front rock samples with distinct compositions are found in a close relationship with matrices that result either from mixing of these or some of these rocks or from crushing of basement material between the source and the front the efficient mixing of socompa rocks and basement rocks generates matrices with isotopic compositions distinct from those of the blocks they are in contact with we interpret these results as being due to more efficient vertical mixing during the avalanche emplacement

why do similar patterns of tropical convection yield extratropical circulation anomalies of opposite sign abstracttropical precipitation anomalies associated with el nino and madden julian oscillation mjo phase 1 la nina and mjo phase 5 are characterized by a tripole with positive negative centers over the indian ocean and central pacific and a negative positive center over the warm pool region however their midlatitude circulation responses over the north pacific and north america tend to be of opposite sign to investigate these differences in the extratropical response to tropical convection the dynamical core of a climate model is used with boreal winter climatology as the initial flow the model is run using the full heating field for the above four cases and with heating restricted to each of seven small domains located near or over the equator to investigate which convective anomalies may be responsible for the different extratropical responses an analogous observational study is also performed for both studies it is found that despite having a similar tropical convective anomaly spa

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

palaeohydrodynamics of fluids in the brent group oseberg field norwegian north sea from chemical and isotopic compositions of formation waters generally the history of past sub surface fluid movements is difficult to reconstruct however the composition of oil field waters characterizes the origins and mixing processes that allow such a reconstruction we have investigated present day formation waters from brent group sedimentary rocks of the oseberg field in order to assess both their geochemical variations and their origin s water samples sampled at the separator produced from immediately above the oil water contact and from the aquifer water saturated zone below the oil water contact were taken from 11 wells across the field in addition 3 trace water samples were extracted from oil produced from higher up in the oil column the water samples were analysed for their chemical components and isotopic compositions conservative tracers such as cl br deltad and delta o 18 were used to evaluate the origin of the waters all formation waters can be characterised as na cl brines the separator samples are of aquifer origin indicating that aquifer water drawn up by the pressure reduction near the well is produced from the lower few tens of metres of the oil zone by defining plausible endmembers the waters can be described as mixtures of seawater 60 90 meteoric water 10 30 evaporated seawater primary brines 3 5 and possibly waters which have dissolved evaporites secondary brines alternatively using multidimensional scaling the waters can be described as mixtures of only 3 endmembers without presupposing their compositions in fact they are seawater very dilute brine and a secondary brine confirming the power of this approach meteoric water was introduced into the reservoir during the end brent and early cretaceous periods of emergence and erosion and partially replaced the marine pore fluids lateral chemical variations across the oseberg field are extremely small the waters from closer to the erosion surfaces show slightly stronger meteoric water isotopic signatures the primary and secondary brines are believed to come from permian and triassic evaporitic rocks in the deeply buried viking graben to the west and to have been modified by water rock interactions along their migration path these primary basinal brines have not been detected in the oil zone waters suggesting that the brines entered the reservoir after the main phase of oil migration there are indications that these external fluids were introduced into the reservoir along faults present day aquifer waters are mixtures of waters from different origins and hardly vary at a field scale they are different in composition to the water trapped in the present oil zone one of the oil zone samples is a very dilute brine it is thought to represent a simple mixture of seawater and meteoric water due to oil emplacement this geochemical signature was preserved in the waters trapped within the oil zone another oil zone water shows a very similar chemical signature to the aquifer waters but the chlorine isotopic signature is similar to that of the dilute oil zone water this water is interpreted to represent a palaeo aquifer water that is it was within the aquifer zone in the past but was trapped by subsequent emplacement of more oil these vertical differences can be explained by two features i emergence of the brent group sedimentary rocks in the early cretaceous allowed ingress of meteoric water ii subsequent rapid burial of viking graben rocks caused migration of petroleum and aqueous fluids into the adjacent less deeply buried oseberg field c 2001 elsevier science ltd all rights reserved

giant debris avalanches from the colima volcanic complex mexico implications for long runout landslides 100 km and hazard assessment at least two giant volcanic debris avalanche deposits are associated with the colima volcanic complex located in the western part of the trans mexican volcanic belt one avalanche originated from volcan de colima 3820 m probably 4300 yr ago a much larger avalanche originated from nevado de colima 4240 m 18500 yr ago it traveled more than 120 km from its source and covered an area of at least 2200 km 2 almost twice the area of any previously described avalanche deposit this older debris avalanche is the second largest by volume known has the longest travel distance yet reported and has one of the lowest height length ratios 0 04 the avalanche material was probably hot during emplacement and after initial slope failure may have behaved similarly to a pyroclastic flow such large long runout landslides from volcanic or nonvolcanic constructs present a serious geologic hazard that must be considered in risk assessment

3d seismic analysis of an upper palaeozoic carbonate succession of the eastern finnmark platform area norwegian barents sea abstract this paper presents 3d seismic data to enhance our understanding of the seismic stratigraphy and buildup developments of the finnmark platform we focus on carbonate buildup distributions and platform geometry in space and upper palaeozoic time multi attribute analysis neural network techniques and the use of inverted impedance data reveal seismic anomalies that can be linked with significant geological geometries such as buildups subtle prograding clinoforms karstified surfaces or platform breaks the seismic expressions show a platform development mainly driven by climatic changes and differential subsidence seismic data indicate the first progradation of a low angle warm water carbonate ramp during mid carboniferous times a gradual change from a low angle mixed carbonate ramp to a more restricted carbonate shelf with a marked break and slope occurs during upper carboniferous lower permian gipsdalen group large buildups on the platform are identified both as individual mounds and unique continuous complexes e g network of polygonal ridges as well as a 30 km long barrier complex multi attribute analysis reveals a distinct karst event on top of the gipsdalen group climatic cooling during the lower permian bjarmeland group resulted in an even more restricted platform as seen in the seismic data with developments of 200 m high bryozoan mounds in deeper waters of the platform slope further cooling during mid permian tempelfjorden group resulted in a major chert event with development of a series of spiculitic chert mounds

crustal structure along the egt profile across the tornquist fan interpreted from seismic gravity and magnetic data abstract the tornquist fan is a northwestward widening splay of late carboniferous to early permian fault zones in the danish area which emanates from the teisseyre tornquist zone in the baltic sea it is located over an area of deep sedimentary basins around denmark in the southwestern corner of the former baltica plate this paper presents an integrated model of seismic velocity density and magnetic properties along the egt profile across the tornquist fan between southern sweden and northern germany the model shows distinct features that may be related to the main tectonic events in the area the caledonian crustal suture between baltica and eastern avalonia is interpreted from changes in physical parameters at all crustal levels most noticeable as an abrupt lateral change in seismic velocity in the lowest crust at moho level from 6 9 km s in baltica to only 6 4 km s in eastern avalonia thick sedimentary successions beneath the mesozoic sequence are interpreted as palaeozoic sedimentary rocks which may have been deposited on the southern margin of the baltica plate in a deep caledonian foreland basin and in late carboniferous early permian rifts and extensional basins rift related magmatism is indicated by the presence of zones of high velocity density and magnetic susceptibility as well as strong remanent magnetization thermal subsidence following the emplacement of these bodies may be the origin of regional subsidence of the danish and north german basins of late paleozoic and mesozoic age late cretaceous to early cenozoic inversion of basin structures is detected at the sorgenfrei tornquist zone stz in the transition between shield and basin areas the stz coincides with a pronounced change in crustal thickness and the southwestern edge of a major magmatic intra crustal body significant abrupt changes in moho depth exist along the profile 26 30 km beneath the deep basins ca 35 km beneath the ringkobing fyn basement high and 48 km beneath the baltic shield around the sorgenfrei tornquist inversion zone the basement in the tornquist fan area is of proterozoic age the moho topography indicates strong thinning of the crust during its phanerozoic evolution the model supports the hypothesis that existing tectonic structures and weakness zones are continuously being reactivated during subsequent tectonic activity

volcanic dry avalanche deposits identification and comparison with nonvolcanic debris stream deposits abstract a volcanic dry avalanche deposit is defined as a volcaniclastic deposit formed as a result of a large scale sector collapse of a volcanic cone associated with some form of volcanic activity avalanche transport occurred in response to the gravitational field in a manner similar to the transport of nonvolcanic debris streams e g hsu 1975 such deposits are characterized by megablock structure deformed and fractured large blocks up to several hundreds meters in diameter a megablock preserves original layering intrusive contacts or weathered surfaces of the source volcanic edifice surface topography of the deposit is characterised with hummocky relief ratios of fell height to travel distance for volcanic dry avalanche deposits are between 0 18 and 0 06 this range is similar but smaller than the value of 0 58 to 0 08 for nonvolcanic debris stream deposit this similarity suggests similar transportation mechanisms excessive travel distances as defined by hsu 1975 calculated for volcanic dry avalanche deposits give values larger than for debris stream deposits of the same volume the difference is explained by lower rigidity of the collapsing mass due to the existence of soft pyroclastic layers alteration around the vent development of fractures owing to new cryptodome intrusion and boiling of supercritical fluid contained within the collapsed mass

the global atmospheric circulation response to tropical diabatic heating associated with the madden julian oscillation during northern winter abstractthe detailed dynamical mechanisms of the upper tropospheric circulation response to the madden julian oscillation mjo convection are examined by integrating a primitive equation model a series of initial value calculations with the climatological boreal winter background flow forced by the mjo like thermal forcing successfully capture the key aspects of the observed circulation response to the mjo convection this suggests that a large fraction of mjo related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics it is found that mjo like dipole heatings not only intensify tropical upper tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial kelvin and rossby waves the rossby wave train primarily excited by horizontal divergence of upper level perturbation flow propagates northeastward and then heads back to the equator in this way rossby wave act

seismic images of caledonian lithosphere scale collision structures in the southeastern north sea along mona lisa profile 2 abstract the unexposed suture between baltica and eastern avalonia is imaged by coincident normal incidence reflection and wide angle reflection refraction seismic data of the mona lisa project we present new results of the upper lithospheric seismic structure from the n s striking profile 2 across the caledonian deformation front which represents the crustal collision suture between baltica and eastern avalonia that formed after closure of the tornquist sea during the caledonian orogeny in late ordovician times three different crustal types are identified with great similarities to the nearby profile 1 1 a three layered crust typical of shields to the north 2 a transitional crust suture zone in the central part and 3 a two layered crust of caledonian origin to the south characterized by very low velocities throughout the crust the crustal thickness varies from 38 35 km under the northern margin of the ringkobing fyn high baltica crust to 28 27 km beneath the north german basin in the caledonian crust to the south the suture zone is imaged by s dipping crustal reflections from 1 9 to 10 6 s two way travel time twt over a horizontal distance of 70 km within the transitional crust the reflection suture zone terminates in a 60 km wide reflective lens with velocities of 6 6 6 8 km s in the lowermost crust the reflective lens may be interpreted as a remnant of oceanic or island arc crust that was accreted to the leading edge of baltica during closure of the tornquist sea alternatively the reflective lens may represent an indentor of baltica crust into the avalonian terrane the change in lower crustal reflectivity and the abrupt transition from a three to a two layered crust further south suggest that the trans european fault and the elbe lineament continue into the north sea the upper mantle reflectivity is dominated by bands of strong amplitude s dipping reflections from 13 5 to 21 8 s twt and a weaker band of n dipping reflections from 12 to 16 s twt reversed wide angle refractions and reflections indicate the presence of a s dipping high velocity layer 8 65 8 8 km s in the uppermost mantle the sub moho high velocity layer partially coincides with the strong s dipping normal incidence mantle reflections we propose that the s dipping mantle structure may represent a late caledonian or late carboniferous to early permian mantle shear zone

volcanic ash deposits of early eocene age from the rockall trough the stratigraphy of the rockall trough fig 1 has proved difficult to elucidate because a mantle of recent sediments usually prevents piston corers and dredges from sampling older accumulations although a seismic stratigraphy has been erected1 2 considerable uncertainty surrounds the history of sedimentation and consequently the petroleum potential of the region the upper 500 1 000 m of the succession are clearly cenozoic deposits whose distribution has been strongly influenced by movements of norwegian sea overflow water1 deeper in the section major current controlled accumulations are absent a feature observed elsewhere in the atlantic1 in view of the paucity of samples from these older deposits3 we report here the recovery of sediments that were laid down in the northern rockall trough before polar waters radically changed the depositional regime the sediments record a period of explosive volcanicity during the early eocene in the vicinity of the wyville thomson ridge

the effect of the madden julian oscillation on the north atlantic oscillation using idealized numerical experiments abstractthe aim of the paper is to investigate the influence of the madden julian oscillation mjo on the north atlantic oscillation nao using a quasigeostrophic model on the sphere a simplifie

formation mechanisms of the pacific north american teleconnection with and without its canonical tropical convection pattern abstractthe mechanisms that drive the pacific north american pna teleconnection pattern with and without its canonical tropical convection pattern are investigated with daily era interim and noaa olr data the former pattern is referred to as the convective pna and the latter pattern is referred to as the nonconvective pna both the convective and nonconvective positive pna are found to be preceded by wave activity fluxes associated with a eurasian wave train these wave activity fluxes enter the central subtropical pacific a location that is favorable for barotropic wave amplification just prior to the rapid growth of the pna the wave activity fluxes are stronger for the positive nonconvective pna suggesting that barotropic amplification plays a greater role in its development the negative convective pna is also preceded by a eurasian wave train whereas the negative nonconvective pna grows from the north pacific contribution to a circumglobal teleconnection pattern driving by high frequency ed

the modulation of the subtropical and extratropical atmosphere in the pacific basin in response to the madden julian oscillation abstract the 40 yr ecmwf re analysis era 40 data are combined with a number of novel climatologies to conduct a comprehensive examination of the response of the subtropical and extratropical atmosphere over the pacific basin to an evolving madden julian oscillation mjo event the adopted approach constitutes a symbiosis of a climatological analysis during the northern hemisphere winter from 1979 to 2002 and a case study analysis of a distinct mjo event that occurred in january february 1993 the former is designed to obtain the general characteristics observed during a composite mjo life cycle while the latter is used to provide insight into the instantaneous mechanisms responsible for the observed composite evolution a primary component of the study involves the diagnosis of anomalous wave breaking activity in response to mjo forcing in the form of tropical convection and or upper level divergence wave breaking events are separated by their characteristic life cycles lc1 anticyclonic and lc2 c

pre permian sedimentary basins in the north sea images from reprocessed and pre stack depth migrated mona lisa data pre permian sedimentary basins in the southeastern north sea have been previously interpreted from potential field data but only poorly imaged on seismic sections due to the presence of salt layers and a thick mesozoic and cenozoic cover furthermore potentially low prospectivity for hydrocarbon resources has resulted in sparse penetration of pre permian sediments in the southeastern north sea we present images of large palaeozoic basins obtained through reprocessing and pre stack depth migration of seismic data from the mona lisa project the depth images show in detail the structure of pre permian basins beneath the danish basin and the ringkobing fyn high providing new insights into upper palaeozoic basin formation in the north sea

a gravitational spreading origin for the socompa debris avalanche abstract socompa volcano arguably provides the world s best exposed example of a sector collapse derived debris avalanche deposit new observations lead us to re interpret the origin of the sector collapse we show that it was triggered by failure of active thrust anticlines in sediments and ignimbrites underlying the volcano the thrust anticlines were a result of gravitational spreading of substrata under the volcano load about 80 of the resulting avalanche deposit is composed of substrata formerly residing under the volcano and in the anticlines the collapse scar can be traced up to 5 km from the edifice truncating two spreading related anticlines which collapsed in the event outcrops near the volcano preserve evidence of edifice material being carried along on top of mobilised substrata on the north side of the scar the avalanche motion was initially at right angles to the failure edge structural relations indicate that immediately prior to collapse the substrata disintegrated became effectively liquidised and were ejected from beneath the edifice catastrophic mobilisation of substrata probably resulted from breakdown of ignimbrite clasts and cement it may have occurred through progressive rock fracture by high shear strain during spreading material ejected from under socompa formed a layer on which volcanic edifice debris was transported this interpretation of events explains the puzzling observation that avalanche units with the lowest gravitational potential energy moved the furthest it can also account for avalanche motion normal to the collapse scar walls ignimbrites and other rock types probably capable of similar behaviour underlie many other volcanoes identification of spreading at other sites could therefore be a first step towards assessment of the potential for this style of catastrophic sector collapse

a magnus opus helium neon and argon isotopes in a north sea oilfield this study of the magnus oilfield located in the east shetland basin northern north sea represents the most detailed investigation of noble gas isotope systematics in a liquid hydrocarbon reservoir yet undertaken samples from nine producing wells across this middle jurassic field were taken and the helium neon and argon isotopic ratios and abundances in the oil were determined both the helium and the neon isotope systematics require a contribution from a mantle source if the mantle endmember is modeled using mid ocean ridge mor values 2 3 4 5 of the 4he and 4 3 6 2 of the 21ne is mantle derived the remainder of the 4he and 9 0 12 0 of the 21ne is crustal radiogenic and the remaining 21ne is atmosphere derived the resolved mantle derived he ne ratio is quite distinct from upper mantle values estimated from mor samples but indistinguishable from values resolved in other regions of continental extension this result provides strong evidence that the subcontinental lithospheric mantle not only has a different noble gas inventory to the convecting mantle under mors but also has a near uniform composition the quantity of radiogenic noble gas associated with the magnus oil groundwater system can only be accounted for by production predominantly from outside the volume of the magnus sandstone aquifer reservoir drainage area and the associated kimmeridge clay source rock formation and together with the mantle derived noble gases provides strong evidence for cross formational communication with deeper regions of the crust the 20ne and 36ar must have been input into the oil phase by interaction with an air equilibrated groundwater noble gas partitioning between a seawater derived groundwater and the oil phase at the average magnus sandstone aquifer temperature requires a subsurface seawater oil volume ratio of 110 40 to account for both the 20ne and 36ar concentrations in the central and southern magnus samples the volume of groundwater which has equilibrated with the magnus oil is indistinguishable from the static volume of water estimated to be in the down dip magnus aquifer reservoir drainage volume this suggests that the magnus oil has obtained complete equilibrium with the groundwater in the reservoir drainage volume probably during secondary migration and further suggests that concurrent cementation of the magnus sandstone aquifer has occurred with little or no large scale movement of air equilibrated groundwater through the aquifer system higher concentrations of 20ne and 36ar in the n magnus oil cannot be accounted for by equilibration with a seawater derived groundwater this is qualitatively consistent with the earlier and more mature oil in this section equilibrating with freshwater which is known to have been trapped in the crest of the reservoir structure

internal structure of the erlend tertiary volcanic complex north of shetland revealed by seismic reflection detailed seismic reflection mapping 100 km n of shetland has revealed a large subcrop of palaeocene basalts proved by exploration drilling the geometry of internal reflectors within the buried basalt suggests the existence of two partially eroded volcanoes a vent of about 2 km in diameter surrounded by radially outward dipping basalts is centred over the erlend igneous complex whose existence had been postulated previously on gravity and magnetic evidence alone a new volcano the more deeply eroded west erlend centre is postulated by interpretation of seismic data and by gravity modelling an approximately cylindrical mafic or ultramafic pluton is inferred from the gravity modelling to underlie each of the two centres the diameter of the erlend pluton is about 14 km and that of west erlend about 5 7 km the seismic stratigraphy of volcanic rocks can now be recognized as a valid new field of study with particular relevance to hydrocarbon exploration

petroleum geochemistry of the lower and middle jurassic in atlantic margin basins of ireland and the uk potential hydrocarbon source rocks of lower and middle jurassic age have been reported from outcrop shallow boreholes and exploration wells in atlantic margin basins of the uk hebrides west of shetlands and flanking the ne rockall trough and recently in the continuation of this trend offshore ireland slyne erris and porcupine basins previously these organic rich mudrocks were considered to be of little economic importance due largely to their perceived limited areal distribution and low maturity however recent geochemical studies of oils and shales from exploration drilling of these basins shows the lower and middle jurassic to have considerable potential as effective hydrocarbon source rocks supplanting the late jurassic early cretaceous kimmeridge clay formation equivalents as the only viable oil source rock in the region flanking the atlantic margin in the irish and uk sectors rich oil source potential occurs in two transgressive mudrock cycles of lower jurassic age these are the sinemurian pliensbachian interval and the overlying toarcian section present in basins such as the solan minch hebrides slyne north celtic sea st george s channel and central english channel the middle jurassic source rocks have a more limited areal distribution and occur in the faroe shetland solan west lewis west flannan hebrides slyne and north porcupine basins with oil source potential in regressive marginal marine to lacustrine facies mudrocks geochemical studies were undertaken on mudrocks from the lower and middle jurassic sections in atlantic margin basins outcrop shallow borehole core and exploration well cores and cuttings samples and on oils from drill stem test and shows core and cuttings extracts detailed analyses using gc gc ms and carbon isotopes allowed both characterization of the source rocks and oil to source correlation biomarker and carbon isotope studies of oils from the faroe shetland basin foinaven and schiehallion fields the porcupine basin connemara accumulation the wessex basin wytch farm and kimmeridge oil fields and wells in the slyne basin show strong correlations to the various source rock developments in the lower and middle jurassic the mixed biodegraded foinaven and schiehallion oils have a major waxy component and correlate with lacustrine middle jurassic source rocks in the solan and west lewis west flannan basins middle jurassic sourcing of the connemara oils is also suggested while oils in the slyne basin appear to have been largely sourced by the lower jurassic pabba shale formation oils in the wessex basin wytch farm and kimmeridge appear to have been sourced by hettangian sinemurian mudrocks and those in the north celtic sea basin by toarcian source rocks the results from this study in combination with previously published data show that rich effective oil prone source rocks occur in both the lower and middle jurassic of the atlantic margin basins offshore ireland and the uk these source rocks can be correlated with indigenous oils indicating the existence of a previously under evaluated petroleum system

tectonics global changes in sea level and their relationship to stratigraphical sequences at the us atlantic continental margin of geological the principal factors that control the extent of seas through geological time are vertical movements of the lithosphere and global changes in sea level the relative height of the sea surface determines the facies and the thickness of sediments that can accumulate in a sedimentary basin backstripping studies show that the primary factors affecting the subsidence of rifted sedimentary basins are thermal contraction following heating and thinning of the lithosphere at the time of rifting and sedimentary loading factors such as compaction palaeobathymetry erosion and global sea level changes also contribute but their combined affects are small compared to those of thermal contraction and sedimentary loading simple models have been constructed which combine the effects of sedimentary loading and thermal contraction with those of compaction sub aerial erosion and global changes in sea level in the models it was assumed that the lithosphere was heated and thinned by stretching at the time of rifting sedimentary loading occurs by flexure of a lithosphere that progressively increases its flexural rigidity with age following rifting and that sediment compaction and bathymetry change across a basin but do not vary significantly with geological time furthermore different assumptions were made on the magnitude of curves of global sea level changes and the relationship between denudation rate and regional elevation the models show that tectonics in the form of thermal contraction of the lithosphere and flexure and slowly varying global changes in sea level can explain a number of the stratigraphic features of the us atlantic continental margin in this paper some of the implications of these results are examined for studies of a sea level changes through geological time and b the maturation history of continental margin basins

evidence for kilometre scale neogene exhumation driven by compressional deformation in the irish sea basin system simon p holford paul f green jonathan p turner gareth a williams richard r hillis david r tappin ian r duddy

the transition between the erris and the rockall basins new evidence from wide angle seismic data abstract the rockall trough is a deep water basin west of britain and ireland the origin of the basin and the nature of the crust beneath it is controversial a series of seismic wide angle experiments carried out during 1988 and 1990 help to clarify the crustal and upper mantle structure in the region results for the crustal structure from a profile which straddles the shelf break between the basin and the irish shelf are discussed here these data together with the available geological information indicate that the basin probably formed in the late palaeozoic to early mesozoic as part of a regionally linked basin assemblage which includes the hatton basin and the shallow sea basins surrounding ireland and britain good data quality has allowed the transition between the relatively unstretched crust of the irish and british mainland defined by previous onshore seismic refraction experiments to be well resolved the erris trough one of the small late palaeozoic to early mesozoic basins which fringe the mainland shelf region north of the porcupine basin is a half graben its major bounding fault is located on its western margin and the basin is divided from the rockall trough by a narrow horst the erris ridge the shelf trajectory along the western flank of the horst deepens smoothly towards the trough centre where the crust thins to 5 km near the trough margin below a sedimentary and water column 8 km thick surprisingly the crustal thickness is slightly greater over a 150 km broad zone at the trough centre i e ca 6 km this change in crustal thickness may be due to lateral strain migration to the warmer basin margins as its centre cooled during the deformation the crustal structure beneath the sediment pile at the trough centre is two layered as opposed to the three layered seismic refraction structure found onshore however the basic character of the lower crust present in onshore ireland in particular the presence of a gradient zone defining the crust mantle transition is still preserved in the trough this similarity in structure precludes the presence of magmatic underplating the crustal structure observed in the rockall trough can be formed by differential stretching of the lithosphere in this model the lower ductile crust and mantle lithosphere are stretched over a wide region by 2 2 3 strain focusing into a much narrower region of brittle upper crust generates severe amounts of crustal thinning 1 8 10 and is responsible for the fusing of the upper and mid crustal seismic refraction layers found beneath onshore ireland and britain mediating detachment surfaces sited at the brittle ductile transition at any time served to relay the strain from the lower lithosphere into the upper crust syntectonic heat loss plays an important role in controlling the deformation pattern

an observed connection between the north atlantic oscillation and the madden julian oscillation abstract based on the bivariate madden julian oscillation mjo index defined by wheeler and hendon and 25 yr 1979 2004 of pentad data the association between the north atlantic oscillation nao and the mjo on the intraseasonal time scale during the northern hemisphere winter season is analyzed time lagged composites and probability analysis of the nao index for different phases of the mjo reveal a statistically significant two way connection between the nao and the tropical convection of the mjo a significant increase of the nao amplitude happens about 5 15 days after the mjo related convection anomaly reaches the tropical indian ocean and western pacific region the development of the nao is associated with a rossby wave train in the upstream pacific and north american region in the atlantic and african sector there is an extratropical influence on the tropical intraseasonal variability certain phases of the mjo are preceded by the occurrence of strong naos a significant change of upper zonal

tectonic subsidence flexure and global changes of sea level tectonic models for the evolution of passive continental margins predict that following rifting sediments should progressively onlap basement at the edge of a margin as the lithosphere cools and increases its flexural rigidity with age the pattern of modelled onlap is strikingly similar to that used by vail and colleagues to estimate sea level rise through geological time this similarity suggests that major portions of stratigraphical sequences at margins may have a tectonic rather than eustatic control the patterns of onlap used by vail and colleagues may be widespread however because several widely separated passive margins rifted at similar times but they are unlikely to be worldwide

the cretaceous opening of the northeast atlantic abstract a continuous rift system from the rockall trough through the faeroe shetland channel and the more and voring basins up to the tromso and bear island basins is inferred to have developed during the cretaceous oceanic crust was generated in its southern part but its width presumably decreases toward the northeast and probably ends in the more basin this rift spreading system requires a clockwise rotation of greenland and the rockall plateau during the cretaceous around a rotation pole at its northern end at about 74 n 21 e north of the pole of rotation crustal shortening must have occurred this compression is interpreted to have taken place on west spitsbergen the orogeny there is reinterpreted as 1 1 a cretaceous folding phase 2 2 a phase of overthrusting at the paleocene eocene boundary and 3 3 an extensional faulting phase during the oligocene this plate tectonic model can resolve a series of problems in the northeast atlantic region the connection of the caledonian fronts of scotland and greenland can be easily established the northern ends of the west shetland basin and the north sea graben the unusual depth of the more and voring basins the marked obliqueness of structural trends between the northeast greenland shelf and the norwegian shelf the fact that the western hammerfest basin was intersected by a younger north south trending graben which formed the deep tromso basin all these enigmatic observations can be explained by the cretaceous rift system

testing the sensitivity of the extratropical response to the location amplitude and propagation speed of tropical convection abstractthe dynamical core of a dry global model is used to investigate the role of central pacific versus warm pool tropical convection on the extratropical response over the north pacific and north america a series of model runs is performed in which the amplitude of the warm pool wp and central pacific cp heating anomalies associated with the mjo and el nino southern oscillation enso is systematically varied in addition model calculations based on each of the eight mjo phases are performed first using stationary heating and then with heating corresponding to a 48 day mjo cycle and to a 32 day mjo cycle in all model runs the extratropical response to tropical convection occurs within 7 10 days of the convective heating the response is very sensitive to the relative amplitude of the heating anomalies for example when heating anomalies in the wp and cp have similar amplitude but opposite sign the amplitude of the extratropical response is much weaker than is typical for the mjo and enso f

the generation of global rotational flow by steady idealized tropical divergence abstract tropical convective heating is balanced on the large scale by the adiabatic cooling of ascent the horizontal divergence of the wind above this heating may be viewed as driving the upper tropospheric rotational wind field a vorticity equation model is used to diagnose this relationship it is shown that because of the advection of vorticity by the divergent component of the flow the rossby wave source can be very different from the simple fd source often used in particular an equatorial region of divergence situated in easterly winds can lead to a rossby wave source in the subtropical westerlies where it is extremely effective this part of the source can be relatively insensitive to the longitudinal position of the equatorial divergence a divergence field which is asymmetric about the equator can lead to a quite symmetric rossby wave source for a steady frictionless flow the rossby wave source averaged over regions within closed streamfunction or absolute vorticity contours is under cert

planktic foraminifera from the mid cretaceous barremian early albian of the north sea basin palaeoecological and palaeoceanographic implications abstract a marine cretaceous succession barremian albian of a cored borehole bgs 81 40 located in the central north sea basin has been examined with respect to its planktic and benthic foraminiferal content as well as for calcareous nannofossils the distribution patterns of foraminifera and calcareous nannofossils allow for a two fold division of the investigated interval 1 the barremian earliest aptian interval which reflects a marine temporary restricted setting this is indicated by sporadic occurrences of planktic foraminifera with very rare planispiral forms suggesting short term connections of the boreal and tethyan realms the benthic foraminiferal assemblages indicate aerobic sometimes dysaerobic bottom water conditions high abundances of nannoconids in the barremian suggest enhanced stratification and or warm oligotrophic surface water 2 the late aptian early albian interval which was characterised by an open oceanic environment with cool and aerobic surface water conditions planktic foraminifera are more abundant and diverse than in the lower interval trochospiral hedbergellids dominate the foraminiferal assemblages the episodic occurrences of planispiral clavate and trochospiral flattened planktic morphotypes indicate the existence of a seaway between the boreal and the tethyan realms aerobic to dysaerobic bottom water conditions are suggested by the composition of the benthic foraminiferal assemblages high abundances of cool water taxa within the calcareous nannofossil assemblages indicate a cooling trend across the latest aptian and earliest albian

statistical empirical index of chemical weathering in igneous rocks a new tool for evaluating the degree of weathering abstract chemical weathering indices are useful tools in characterizing weathering profiles and determining the extent of weathering however the predictive performance of the conventional indices is critically dependent on the composition of the unweathered parent rock to overcome this limitation the present paper introduces an alternative statistical empirical index of chemical weathering that is extracted by the principal component analysis pca of a large dataset derived from unweathered igneous rocks and their weathering profiles the pca analysis yields two principal components pc1 and pc2 which capture 39 23 and 35 17 of total variability respectively the extent of weathering is reflected by variation along pc1 primarily due to the loss of na 2 o and cao during weathering in contrast pc2 is the direction along which the projections of unweathered felsic intermediate and mafic igneous rocks appear to be best discriminated therefore pc1 and pc2 represent independent latent variables that correspond to the extent of weathering and the chemistry of the unweathered parent rock subsequently pc1 and pc2 were then mapped onto a ternary diagram mfw diagram the m and f vertices characterize mafic and felsic rock source respectively while the w vertex identifies the degree of weathering of these sources independent of the chemistry of the unweathered parent rock the w index has a number of significant properties that are not found in conventional weathering indices first the w index is sensitive to chemical changes that occur during weathering because it is based on eight major oxides whereas most conventional indices are defined by between two and four oxides second the w index provides robust results even for highly weathered sesquioxide rich samples third the w index is applicable to a wide range of felsic intermediate and mafic igneous rock types finally the mfw diagram is expected to facilitate provenance analysis of sedimentary rocks by identifying their weathering trends and thereby enabling a backward estimate of the composition of the unweathered source rock

runout of dry granular avalanches laboratory experiments on granular avalanching of dry sands and gravels reveal a consistent pattern of runout distance varying with fall height fall slope and volume of material for volumes rangi

dynamics and physical parameters of the lastarria debris avalanche central andes abstract volcanic debris avalanches are extremely destructive phenomena with the potential to travel many kilometers from their source region either as rockslides or as mass flows given that they may even be triggered at inactive volcanoes their hazard is often underestimated understanding the dynamics of such mass movements is essential for evaluating and mitigating hazards a number of case studies have been carried out around the world but there is still a need for further studies of flow dominated avalanches which remain poorly constrained these studies would have high educational value providing striking examples to teach decision makers and at risk populations about the hazard in this study we investigate the 7500 cal year b p lastarria debris avalanche it is a 7 km long deposit with exceptional preservation of both the flow structures and the collapse scar detailed fieldwork morphometric mapping of over 600 surface features and numerical modelling was carried out to constrain the avalanche s trigger and flow parameters numerical models and field scaling relationships are in good agreement suggesting maximum velocities of 210 to 270 km h 1 negligible basal friction low cohesion 50 kpa and an intermediate friction coefficient structures are dominantly oriented parallel to transport direction suggesting minimal influence from a smooth paleotopography lastarria provides an example of a shallow flank failure initiated along stratigraphic planes that allowed low strength pyroclastic strata to disaggregate rapidly and then quickly accelerate to flow as a granular material at high velocity beyond the base of the volcano overall lastarria provides excellent constraints on granular avalanche initiation and flow which are valuable for hazard assessments and for the study of less well preserved flow deposits elsewhere the question of which precursory signs may warn of such a flank failure remains open and is important to address in future studies

the continuum of north pacific sea level pressure patterns intraseasonal interannual and interdecadal variability this study combines k means cluster analysis with linear unidimensional scaling to illustrate the spatial and temporal variability of the wintertime north pacific sea level pressure slp field daily wintertime slp data derived from the ncep ncar reanalysis are used to produce 16 slp anomaly patterns that represent a discretized approximation of the continuum of north pacific slp patterns this study adopts the continuum perspective for teleconnection patterns which provides a much simpler framework for understanding north pacific variability than the more commonly used discrete modal approach the primary focus of this research is to show that variability in the north pacific on intraseasonal interannual and interdecadal time scales can be understood in terms of changes in the frequency distribution of the cluster patterns that compose the continuum each of which has a time scale of about 10 days this analysis reveals 5 6 pacific north american like pna like patterns for each phase as well as dipoles and wave trains a self organizing map som analysis of coupled slp and outgoing longwave radiation data shows that many of these patterns are associated with convection in the tropical indo pacific region on intraseasonal time scales the frequency distribution of these patterns in particular the pna like patterns is

discrete element simulations of gravitational volcanic deformation 1 deformation structures and geometries 1 we have carried out two dimensional particle dynamics simulations of granular piles subject to frictional coulomb failure criteria to gain a first order understanding of different modes of gravitational deformation within volcanoes under uniform basal and internal strength conditions granular piles grow self similarly developing distinctive stratigraphies morphologies and structures piles constructed upon cohesive substrates exhibit particle avalanching forming outward dipping strata and angle of repose slopes systematic decreases in basal strength lead to progressively deeper and steeper internal detachment faults and slip along a basal decollement landslide forms grade from shallow slumps to deep seated landslide and finally to axial subsidence and outward flank displacements or volcanic spreading surface slopes decrease and develop concave up morphologies with decreasing decollement strength depositional layers tilt progressively inward spatial variations in basal strength cause lateral transitions in pile structure stratigraphy and morphology this approximation of volcanoes as coulomb granular piles reproduces the richness of deformational structures and surface morphologies in many volcanic settings the gentle slopes of hawaiian volcanoes and olympus mons on mars suggest weak basal decollements that enable volcanic spreading high angle normal faults favored above weak decollements are interpreted in both settings and may explain catastrophic sector collapse in hawaii and broad aureole deposits surrounding olympus mons in contrast steeper slopes and shallow detachment faults predominate in the canary islands thought to lack a weak decollement favoring smaller more frequent slope failures than predicted for hawaii the numerical results provide a useful predictive tool for interpreting dynamic behavior and associated geologic hazards of active volcanoes

seismic structure across the caledonian deformation front along mona lisa profile 1 in the southeastern north sea abstract seismic data from the mona lisa marine and onshore north sea acquisition for lithospheric seismic analysis project in the southeastern north sea image the caledonian deformation front cdf which is the collisional suture between baltica to the north and east and avalonia to the south and west the n s trending mona lisa normal incidence reflection profile 1 was recorded to 26 s twt coincident wide angle data were acquired on nine ocean bottom hydrophones and several onshore mobile seismographs along and off the profile the model of compressional seismic velocity shows three different crustal types a a typical three layered shield type crust below the ringkobing fyn high to the north b a highly complex transitional crust in the central part and c a two layered crust of caledonian origin to the south sharp and strong normal incidence and wide angle reflections from moho were recorded south of the caledonian deformation front in contrast to less distinct reflections further north s dipping crustal reflections from 4 to 11 s twt over 70 km horizontal distance terminate at moho and coincide with a change in the seismic velocity structure this indicates northward obduction of avalonian crust non migrated normal incidence seismic sections show crossing weak n dipping and stronger s dipping reflections to 20 s twt from the uppermost mantle we propose a tectonic model where the closure of the tornquist sea took place along a n dipping subduction zone which was later overprinted by a late or post caledonian s dipping shear zone sub moho velocities are 7 8 7 9 km s under 34 35 km thick baltica crust and 8 1 8 3 km s under 25 26 km thick caledonian crust the sub horizontal moho across the caledonian collision zone implies late or post caledonian re equilibration of the seismological moho we interpret the low velocity upper mantle 7 8 8 1 km s to the north as former baltica lower crust in eclogite facies after pressure induced metamorphism as a result of lithospheric flexure during the caledonian orogeny these rocks today appear as upper mantle that was uplifted to their present position during the middle devonian collapse of the north german polish caledonides

effects of an oceanic anoxic event on the stable carbon isotopic composition of early toarcian carbon the early toarcian transgression is marked by the occurrence of organic carbon rich shales in large parts of western europe and in other parts of the world as well based on the positive carbon isotope excursion of pelagic limestones in the middle to upper part of the falciferum zone in several of the tethyan sections the widespread occurrence of the early toarcian shales was explained by an oceanic anoxic event oae jenkyns 1988 jenkyns and clayton 1997 the rapid burial of large amounts of organic carbon which is rich in 12 c would have led to a relative enrichment in 13 c of the global carbon reservoir and hence to an increase in delta 13 c of the limestones in southwest germany and a number of other locations both organic and inorganic carbon display a negative isotope excursion in the upper part of the tenuicostatum zone and the lower part of the falciferum zone synchronous to black shale deposition and predating the positive isotopic excursion kuspert 1982 1983 it is presently unclear what the exact cause for this widespread negative isotopic excursion is jenkyns and clayton 1997 the objective of our study was to examine if the negative carbon isotope excursion of organic matter om in the southwest german toarcian shales can be attributed to compositional changes of the om or if the excursion is related to variations in delta 13 c sub co2 aq in the photic zone to this end we analyzed the molecular and stable carbon isotope composition of om in ten samples spanning the early toarcian toc 2 5 10 5 percent hi 350 700 biomarker distributions and kerogen pyrolysates differ only slightly among the samples and delta 13 c values of primary production markers follow closely those of associated carbonate and kerogen delta 13 c sub carb toc this strongly suggests that differences in delta 13 c toc are related to differences in delta 13 c of co 2 aq in the photic zone supporting kuspert9s model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters evidence for euxinic conditions extending into the photic zone was found by the presence of derivatives of carotenoids such as isorenieratane from anoxygenic phototrophic sulfur bacteria their concentrations are extremely low in black shales from the tenuicostatum zone but are significant in the falciferum and bifrons zone with a maximum in the exaratum subzone suggesting that photic zone euxinia pze was a common feature of the early toarcian sea in southwest germany our data therefore support the kuspert model of advection of isotopically light organic matter derived co 2 from anoxic bottom waters to the upper part of the photic zone resulting in a negative isotope spike the enrichment in 13 c in the middle of the falciferum zone which followed the negative spike may be attributed to the burial of isotopically light organic matter through worldwide black shale deposition