experimental modelling of debris flow behaviour using a geotechnical centrifuge physical modelling of debris flows has been carried out in the geotechnical drum centrifuge at eth zurich a new apparatus to model debris flows in the centrifuge is described the apparatus permits the final reach of a typical debris flow to be modelled within the centrifuge with unconsolidated material flowing down a slope to deposit as a fan around the drum experiments are described for both fixed base conditions and erodible bases tests to examine the verification modelling of models show that debris flow behaviour is governed mainly by friction and consolidation processes although some resolution is required between flow behaviour downslope and flow arrest during runout the results are compared with bulk parameters determined for field scale debris flows it is found that some important flow mechanisms such as contact dominated behaviour and high pore pressures are developed that are closer to those developed at field scale than tests conducted at 1g velocity profiles for erodible beds are

structure of the north indian continental margin in the ladakh zanskar himalayas implications for the timing of obduction of the spontang ophiolite india asia collision and deformation events in the himalaya the collision of india and asia can be defined as a process that started with the closing of the tethyan ocean that during mesozoic and early tertiary times separated the two continental plates following initial contact of indian and asian continental crust the indian plate continued its northward drift into asia a process which continues to this day in the ladakh zanskar himalaya the youngest marine sediments both in the indus suture zone and along the northern continental margin of india are lowermost eocene nummulitic limestones dated at similar 54 ma along the north indian shelf margin southwest facing folded palaeocene lower eocene shallow marine limestones unconformably overlie highly deformed mesozoic shelf carbonates and allochthonous upper cretaceous shales indicating an initial deformation event during the latest cretaceous early palaeocene corresponding with the timing of obduction of the spontang ophiolite onto the indian margin it is suggested here that all the ophiolites from oman along western pakistan bela muslim bagh zhob and waziristan to the spontang and amlang la ophiolites in the himalaya were obducted during the late cretaceous and earliest palaeocene prior to the closing of tethys

interplay between detrital and diagenetic processes since the last glacial maximum on the northwest iberian continental shelf abstract integrated analyses of magnetic geochemical and textural data on six cores from the northwestern iberian continental shelf allowed the reconstruction of the paleoenvironmental evolution of this area since the last glacial maximum lgm four sedimentary units were identified representing a succession from fluvial and subaerial settings to high and finally low energy marine deposits subsequent to the post lgm sea level rise the uppermost unit was deposited during the holocene and its magnetic properties were controlled by the interplay between detrital input and early diagenetic reductive dissolution of magnetic minerals identification of a primary steady state early diagenetic signal allowed the recognition of periods of increased detrital input bounded by intervals of lower detrital input and intensified reductive diagenesis related to intensified upwelling in the area these paleoenvironmental alternations are consistent with the climatic evolution of the late holocene during the roman warm period and medieval warm period the combined effect of greater humidity and intense agricultural and mining activities led to a greater erosion and transport of detrital sediments to the shelf in contrast enhanced diagenetic reduction intervals caused by upwelling intensification were roughly coincident with the colder dark ages and the little ice age

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

evidence for changes in the north atlantic deep water linked to meltwater surges during the heinrich events abstract deep sea sediment records from north atlantic cores 40 n 55 n provide evidence of several massive iceberg discharges known as heinrich events during the last glacial period high resolution benthic 18 o and 13 c records from north atlantic sediment cores were used to monitor the impact of heinrich events on thermohaline circulation and to estimate the sensitivity of deep oceanic circulation to changes in freshwater input to the north atlantic surface waters our data indicate that major rearrangements of deep water masses were directly associated with these massive iceberg discharges to trace in detail the deep water conditions in the north atlantic benthic 13 c values in several cores were used to generate time slices before during and after heinrich event 4 dated at 35 ka bp although north atlantic deep water continued to form during the oxygen isotope stage 3 at 37 ka bp deep circulation was characterized by an increased incursion of deep waters of southern origin which reduced the 13 c composition of north atlantic deep waters particularly in the eastern atlantic basin north atlantic deep water production was reduced during heinrich layer 4 hl4 at 35 ka bp synchronously with the changes in the surface water hydrology deep convection processes may have occurred in areas not affected by the salinity decrease soon after hl4 33 ka bp the 13 c distribution was similar to that before the event similarly a rapid return to initial 13 c values was observed at the end of the most clearly defined heinrich events hl5 hl4 and hl1 comparison between deep circulation patterns corresponding to hl4 the last glacial maximum and heinrich event 1 indicates that each of these periods was characterized by a different circulation state associated with changes in convection sites

rapid changes of glacial climate simulated in a coupled climate model abrupt changes in climate termed dansgaard oeschger and heinrich events have punctuated the last glacial period approximately 100 10 kyr ago but not the holocene the past 10 kyr here we use an intermediate complexity climate model to investigate the stability of glacial climate and we find that only one mode of atlantic ocean circulation is stable a cold mode with deep water formation in the atlantic ocean south of iceland however a warm circulation mode similar to the present day atlantic ocean is only marginally unstable and temporary transitions to this warm mode can easily be triggered this leads to abrupt warm events in the model which share many characteristics of the observed dansgaard oeschger events for a large freshwater input such as a large release of icebergs the model s deep water formation is temporarily switched off causing no strong cooling in greenland but warming in antarctica as is observed for heinrich events our stability analysis provides an explanation why glacial climate is much more variable than holocene climate

centrifuge modelling of hillslope debris flow initiation physical modelling of hillslope debris flow initiation was undertaken using the geotechnical beam centrifuge at the university of dundee the tests were carried out on model slopes consisting of soils with known properties prepared with constant initial density and material thickness the results showed that soils with a higher silt fraction can sustain a higher increase in pore water pressure and thus a greater reduction in effective stress before failure is induced this suggests that sand rich soils with lower fines content are geotechnically more susceptible to slope failure and that observed higher spatial frequencies of debris flow on slopes with coarse grained bedrocks can be partially explained in terms of lower critical pore pressure failure thresholds amongst the sandier soil matrixes produced from such lithologies differences in rates of water ingress into the model soils required to trigger a critical rise in pore pressures during the tests provide insights into the varying synoptic conditions and antecedent rainfall characteristics that are likely to trigger debris flows in different soil types

an empirical statistical model for debris flow travel distance an empirical model is presented for analysis of debris flows based on field observations of landslides from clear cuts in the queen charlotte islands british columbia given an initial failure volume changes in event magnitude arising from entrainment and deposition along the path of movement are used to establish the point at which the cumulative flow volume diminishes to zero and therefore the total travel distance hillslope morphology is used to assign three types of flow behaviour unconfined confined and transition flow flow behaviour and slope angle determine the occurrence of entrainment or deposition in the model for every reach of the event path volume change in a reach is calculated from regression analysis of the queen charlotte islands field observations predictor variables are reach length width of entrainment and or deposition and slope angle together with a bend angle function and the incoming flow volume key words slope stability debris flow travel distance runout ris

turbidity of waters over the northwest iberian continental margin in omex ii ii 9 cruises gathered optical data principally by transmissometer the distribution of optical turbidity caused by concentration of particulate matter pmc in the water column over the northern iberianmargin shows several features related to hydrography it is concluded that a signal of pmc seen in mediterranean water mw found north of 42 n is not carried from its source at the gibraltar sill and gulf of cadiz because it is shown using intermediate stations that this turbid plume decays mainly by fall out but also partly by mixing to very low levels around southern portugal pmc maxima sometimes seen in mw on the northern iberianmargin are thus most likely to result from intermittent local resuspension by mw interacting with slope sediments the highest turbidity is found over the upper slope and is the result of i shelf edge resuspension and off shelf flow of turbid plumes mainly between 100 and 300 m depth and ii resuspension under the slope current aided by internal waves in the depth range 500 800 m where the density gradient between enacw and mw is maximal below the mw flows are generally slow and turbidity is low the bottom nepheloid layer in deep water is also weak with pmc values 100 mg m 3 the focus of resuspension activity on the upper slope means that the region is an efficient exporter to the ocean of sediment that either escapes from the shelf or sinks to the bed from surface production this accounts for upper slope sediments recorded in other studies as sandy or in places as rocky bottom

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

physical models of rock avalanche spreading behaviour with dynamic fragmentation the dynamic fragmentation of rock during avalanche motion has been postulated as a mechanism explaining the long runout of large rock avalanches or sturzstrome this paper investigates whether test

position of the polar front along the western iberian margin during key cold episodes of the last 45 ka 1 this paper documents the migration of the polar front pf over the iberian margin during some of the cold climatic extremes of the last 45 ka it is based on a compilation of robust and coherent paleohydrological proxies obtained from eleven cores distributed between 36 and 42 n planktonic 18o globigerina bulloides ice rafted detritus concentrations and the relative abundance of the polar foraminifera neogloboquadrina pachyderma sinistral were used to track the pf position these three data sets compared from core to core show a consistent evolution of the sea surface paleohydrology along the iberian margin over the last 45 ka we focused on five time slices representative of cold periods under distinct paleoenvironmental forcings the 8 2 ka event and the younger dryas two recent cold events occurring within high values of summer insolation heinrich events 1 and 4 reflecting major episodes of massive iceberg discharges into the north atlantic and the last glacial maximum typifying the highest ice volume accumulated in the northern hemisphere for each event we generated schematic maps mirroring past sea surface hydrological conditions the maps revealed that the polar front presence along the iberian margin was restricted to heinrich events the sea surface conditions during the last glacial maximum were close to those at present day except for the northern sites which briefly experienced subarctic conditions

productivity and paleoceanographic implications on the tore seamount iberian margin during the last 225 kyr foraminiferal evidence foraminifera counts and climatic assemblages from the tore seamount are used to approach the glacial and interglacial changes in temperature and productivity on the iberian margin over the last 225 kyr chronostratigraphy is based on globigerinoides ruber and globigerina bulloides oxygen isotopes and supported by foraminifera and carbonate stadial fluctuations foraminifera indicate cooling from late interglacial stage 5 to the beginning of termination i ti neogloboquadnna pachyderma s reflects cold conditions during glacial stages 4 2 in contrast glacial stage 6 is dominated by warmer n pachyderma d and dutertrei and a restricted arctic assemblage past sea surface temperatures confirm the general cooling reaching 4 3 c simmax 28 during stage 2 multiple productivity proxies such as organic carbon productivity related foraminifera and 13c constrain the changes observed a productivity increase occurs after interglacial stage 5 enhanced from late glacial stage 3 to ti present day satellite detected phytoplankton plumes off portugal would have accounted in the past glacial stages for the general productivity increase over the tore on top of this welldefined peaks of organic carbon and productivity related foraminifera correspond with heinrich events 1 4

the sources of the glacial ird in the nw iberian continental margin over the last 40 ka abstract in this work the first results of ice rafted detritus ird provenance related to heinrich events in the nw iberian margin are presented and discussed this study is based on multi proxies namely on thorough analyses of sr and nd isotope ratios measured in the detrital fraction of the sediment core kc 024 19 from the galician continental slope ne atlantic aiming to unravel the sources of the terrigenous component of the sampled sediments in most of the core layers the isotope signatures are consistent with an origin ultimately in the nearby variscan continental crust however allochthonous contributions were also deposited namely during the last four heinrich events he the non carbonate detrital fraction of the sediments deposited during the he1 in its upper part he2 and he4 displays nd much lower than usual suggesting that those layers incorporate clasts dropped by icebergs ice rafted detritus ird whose sources must have been located in archaean cratons such as those of northeastern america and greenland the low nd values combined with dolomite peaks support the hypothesis that icebergs fed by the laurentide ice sheet and launched through hudson strait played a major role in the deposition of ird during he1 he2 and he4 the he1 layer seems to record a complex evolution of this event since at its base the coarse grained non carbonate fraction displays relatively high nd values pointing to european icelandic sources for the icebergs in the initial stages of he1 the ird content of the he3 contrasts significantly with the other he layers and the non ird layers because it has an isotope signature characterized by low 87 sr 86 sr ratios and high nd values this suggests that the most exotic components of the he3 layer may have come from east greenland fram strait and or result from a mixture of materials from western european and more juvenile iceland faeroes crustal sources

phase relationships of north atlantic ice rafted debris and surface deep climate proxies during the last glacial period we report stable isotope core scanning xrf and ice rafted detritus ird data in glacial aged sediments from piston core kn166 14 jpc 13 hereafter referred to as jpc 13 retrieved at 53 1 n 33 5 w on the southern gardar drift north atlantic a chronology was established by correlating millennial scale features in the benthic delta 18o record to portuguese margin core md95 2042 once the alignment of benthic delta 18o of jpc 13 to md95 2042 is fixed the relative timing of proxy variables is used to determine the phasing of changes in ird and surface deep hydrography each peak in north atlantic ird coincided with a decrease in benthic delta 18o that in turn has been linked to warming in antarctica events a1 a7 the ird pulses are followed shortly thereafter by abrupt decreases in planktonic delta 18o indicating warming and increased heat transport to the subpolar north atlantic associated with greenland interstadials gis 8 12 14 and 16 17 grain size and elemental k ti variations indicate that iceland scotland overflow water isow was stronger during these long warm interstadial periods of marine isotope stage mis 3 the results are consistent with interhemispheric phase relationships inferred from iberian margin sediment cores and with methane synchronization of greenland and antarctic ice cores

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

oxygen and carbon isotopes of detrital carbonate in north atlantic heinrich events abstract we report oxygen and carbon isotope results of detrital carbonate grains from heinrich layers at three sites in the north atlantic located along a transect from the labrador sea to the eastern north atlantic oxygen isotopic values of individual detrital carbonate grains from six heinrich layers at all sites average 5 6 1 5 1 n 166 reflecting values of dolomitic limestone derived from source areas in northeastern canada the 18o of bulk carbonate at integrated ocean drilling program iodp site u1308 re occupation of deep sea drilling project dsdp site 609 in the eastern north atlantic records the proportion of detrital to biogenic carbonate and 18o decreases to 5 during heinrich h events 1 2 4 and 5 relative to a background value of 1 to 2 for biogenic carbonate bulk 18o also decreases during h3 and h6 but only attains values of 1 indicating either a greater proportion of biogenic to detrital carbonate or a different source because the 18o of detrital carbonate is 9 lower than foraminifer carbonate any fine grained detrital carbonate not removed from the inner test chambers will lower foraminifer 18o we conclude bulk carbonate 18o is a sensitive proxy for detrital carbonate and may be useful for identifying heinrich layers in cores within and near the margins of the north atlantic ice rafted detritus ird belt

downstream evolution of turbiditic channel complexes in the pab range outcrops maastrichtian pakistan the pab formation consists of deltaic and turbiditic sediments which were deposited during the late maastrichtian on the indo pakistani passive margin the margin geometry has been restored in the pab range from a regional transect 120 km long two superposed turbiditic systems onlap the slope carbonates and completely pinch out southward the lowest turbiditic system lower pab is a sand rich basin floor fan which consists of sand rich channel complexes distally passing to lobes northward this basin floor fan is overlain by a mud rich slope fan formed during the subsequent sea level rise which drowned the shelf the upper turbiditic system upper pab is a sand rich slope fan formed during the progradation of a deltaic system in the shelf setting it consists of prograding tabular lobes passing upward to conglomeratic channels and thins out northwards the lower pab turbiditic system consists of three channel complexes lp1 2 3 organised in a backstepping succession each channel complex has a multi storey internal architecture resulting from the amalgamation of several individual turbiditic channels five major facies associations have been determined in the lp3 channel complex fa 1 corresponds to polygenic and monogenic debris flows fa 2 to high density gravelly or sandy turbidites fa 3 to by pass deposits fa 4 to thin bedded turbidites spill over lobes and levees and fa 5 to hemipelagites the downstream evolution of the lp3 channel complex can be studied from canyon to mid fan settings where it is confined in the canyon the channel complex is 50 m thick and 1 km large and shows a high sand shale ratio the development of overflow deposits is limited and occurs only at the top of the channel complex at the canyon mouth the channel complex is still deeply incised but overflow deposits start to expand laterally as a result of the decreased confinement by pass facies here are well developed and are related to hydraulic jump processes in the mid fan setting the channel complex widens and the sand shale ratio decreases erosion at the channel base is less developed whereas internal and external levees are well developed spill over lobes form the last stage of the channel complex infill the internal geometry of the channel complexes is a result of a complex interaction between lateral confinement by pass and lateral migration processes

the effects of diagenesis on the reservoir characters in sandstones of the late cretaceous pab formation kirthar fold belt southern pakistan abstract the maastrichtian pab formation in the southern part of pakistan is composed of fine to very coarse grained texturally mature quartz arenite and subordinate sublitharenite varieties the sandstones have undergone intense and complex diagenetic episodes due to burial and uplift diagenetic modifications were dependent mainly on the clastic composition of sandstone burial depth and thrust tectonics diagenetic events identified include compaction precipitation of calcite quartz clay minerals and iron oxide hydroxide dissolution and alteration of unstable clastic grains as feldspar and volcaniclithic fragments as well as tectonically induced grain fracturing the unstable clastic grains like feldspar and lithic volcanic fragments suffered considerable alteration to kaolinite and chlorite dissolution and alteration of feldspar and volcanic lithic fragments and pressure solution were the main sources of quartz cements mechanical compaction and authigenic cements like calcite quartz and iron oxide hydroxide reduced the primary porosity whereas dissolution of clastic grains and cements has produced secondary porosity chlorite coatings on clastic grains have prevented quartz cementation coarse grained thick bedded packages of fluviodeltaic shelf delta lobe and submarine channels facies have higher average porosity than fine grained thin bedded and bioturbated sandstone of deeper shelf and abyssal plain environments and these facies are concluded to be possible future hydrocarbon prospects

india eurasia collision chronology has implications for crustal shortening and driving mechanism of plates the motion of the indian plate is determined in an absolute frame of reference and compared with the position of the southern margin of eurasia deduced from palaeomagnetic data in tibet the 2 600 900 km of continental crust shortening observed is shown to have occurred in three different episodes subduction of continental crust intracontinental thrusting and internal deformation and lateral extrusion the detailed chronology of the collision and plate reorganizations in the indian and pacific oceans supports the hypothesis that slab pull is a dominant driving mechanism of plate tectonics

contourite processes associated with the mediterranean outflow water after its exit from the strait of gibraltar global and conceptual implications we characterize the eastern gulf of cadiz proximal to the strait of gibraltar using a multidisciplinary approach that combines oceanographic morphosedimentary and stratigraphic studies two terraces upper and lower were identified along the middle slope they are composed of several associated morphologic elements including two large erosive channels which allow us to determine a new and more detailed understanding of the mediterranean outflow water mow pathway and its deceleration upon exiting the strait of gibraltar there is evidence for along slope circulation and additional secondary circulation oblique to the main flow the present upper core of the mow flows along the upper terrace and the lower core flows along the lower terrace however the lower terrace shows larger and better defined erosive features on the seafloor than does the upper terrace we attribute this to a denser deeper and faster mow circulation that prevailed during past cold climates development of the present features started ca 3 8 3 9 ma but the present morphology was not established until the late pliocene early quaternary 3 2 to older than 2 0 ma when the mow was enhanced coeval with global cooling a sea level fall and an increase in thermohaline circulation we propose a direct link between the mow and the atlantic meridional overturning circulation and therefore between the mow and both the northern hemisphere and global climate our results have enabled a better understanding of a major overflow related to an oceanic gateway and are of broad interest to geologists climatologists oceanographers and petroleum geologists

erosional effects on runout of fast landslides debris flows and avalanches a numerical investigation the mechanism of mass changes in debris transportation process is an important topic in the study of fast landslides debris flows and avalanches basal erosion is recognised as a dynamic interaction between the original moving material and the entrained basal topsoil shearing along their non slip contact surface in this paper we propose a new concept of yield rate and establish the erosional relationship to bridge these two systems a pertinent mathematical model and numerical implementation are formulated parametric numerical experiments are conducted to compare the erosional effects the simulated results are consistent with available experimental and field observations the influence of the involvement of the erosive material on runout behaviour and the global mobility of the moving material are elucidated the proposed method is then employed to analyse a recent debris flow event in northern italy the excellent match to the field data gives it a plausible potential application to the analysis of this type of gravity driven flow with significant erosion defined in a dimensionless form the proposed yield rate can be estimated conveniently in general geotechnical practices

constraining ecological and biological bias in planktonic foraminiferal mg ca and δ18occ a multispecies approach to proxy calibration testing 1 parallel stable isotope 18occ and mg ca measurements performed in three planktonic foraminifer species provide multiple perspectives on past temperature change and thus allow published calibrations for these geochemical proxies to be tested against each other the comparison of simultaneous temperature records as recorded by both the 18occ and mg ca signature of each species reveals very clearly the nonpassive character of foraminifera as proxy carriers and allows the systematic temperature response of 18occ and mg ca in different foraminifer species to be explored on the basis of their mg ca signatures neogloboquadrina pachyderma right globigerina bulloides and globigerinoides ruber white are each found to exhibit a specific and narrow range of temperature variability however the interspecies offsets in optimum temperature habitat that are suggested in this way are not expressed by similarly scaled 18occ offsets hence it is demonstrated that the temperature modes variations that are recorded by each species cannot be calibrated to mg ca and 18occ variations via a single pair of calibrations for all three species species specific 18occ and or mg ca temperature calibrations are required on the basis of the average 18occ and mg ca offsets observed between the three species it appears that many of the temperature calibrations that are currently proposed for both of these proxies are inconsistent the data presented here cannot provide species specific mg ca and 18occ temperature calibrations however they do provide a simple method for testing our calibrations in application and clearly indicate that further calibration work using paired mg ca and 18occ is required before the full potential of these proxies may be realized

crustal structure beneath north west iberia imaged using receiver functions abstract in the last years the deep crustal structure of the north western part of the iberian peninsula has been explored using teleseismic receiver function rf analysis of p to s conversions at main crustal interfaces this area has been previously investigated by seismic reflection and refraction experiments and therefore provides an excellent opportunity to compare the results of both approaches the region shows the imprint of two orogenic events the variscan and alpine ones that exhibit different reverse intensities from west to east in a first stage a n s transect across the cantabrian mountains was instrumented to study the area affected by the alpine compressional tectonics later on the limit between the undisturbed variscan units and the reworked alpine zones was explored by n s and e w transects finally an array was deployed in the nw edge of iberia over the variscan hinterland zone the receiver functions are calculated by inverse filtering deconvolution of the l component from the q component and the resulting rf are processed using a simple form of migration to obtain images in depth of the lithosphere that can be compared to the 2 d velocity depth models from active seismic experiments the deep crustal structure constrained by both techniques is remarkably consistent and provides further evidence on the crustal doubling and wedging between the iberian and european crusts throughout the northern part of the iberian peninsula affected by the alpine tectonics the undisturbed variscan domains characterized by a clear subhorizontal moho and few intracrustal convertors show up at the southern edge of the n s transects southward of the alpine deformation front and over the variscan hinterland in the e w transect the crust resulting from alpine reworking presents a complex structure with short and frequently dipping convertors which in some cases seem to image preserved variscan structures

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

latest cretaceous himalayan tectonics obduction collision or deccan related uplift abstract diverging interpretations and incompatible scenarios have been proposed for the early stages of himalayan history numerous researchers have postulated that northern india was involved in ophiolite obduction arc continent or continent continent collision during the late cretaceous or early paleocene but firm geological evidence was never produced in this article we argue against orogenic events predating the late paleocene when the neotethys ocean was still open the tethys himalayan sedimentary record testifies to anorogenic evolution primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of deccan lavas and eventually followed by thermal subsidence major stratigraphic gaps in pelagic sediments suggest that such tectono magmatic episode started to affect the base of the indian plate in the campanian or possibly even in the santonian 10 to 20 ma before the climax of deccan flood basalt eruptions the abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the indian subcontinent during the maastrichtian was followed by progradation of coastal quartzarenites along the northern indian margin in the early paleocene sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose felsitic volcanic rock fragments and cr spinels many of which with the same geochemical fingerprint as deccan spinels and newly found throughout the maastrichtian to danian succession resisted the combined effect of subequatorial weathering and subsequent diagenesis and testify that detritus from deccan basalts reached the indian passive margin as far as south tibet at the close of the early paleocene india drifted away from the seychelles block and thermal subsidence led to widespread carbonate deposition along the tethys himalaya this article illustrates how mega events of magmatic upwelling followed by lithospheric cooling may control passive margin sedimentation and stratigraphic patterns as occurred in northern india first in the early cretaceous and next in the latest cretaceous paleocene

sequence stratigraphic distribution of coaly rocks fundamental controls and paralic examples significant volumes of terrigenous organic matter can be preserved to form coals only when and where the overall increase in accommodation approximately equals the production rate of peat accommodation is a function of subsidence and base level for mires base level is very specifically the groundwater table in paralic settings the groundwater table is strongly controlled by sea level and the precipitation evaporation ratio peat accumulates over a range of rates but always with a definite maximum rate set by original organic productivity and space available below depositional base level groundwater table below a threshold accommodation rate nonzero no continuous peats accumulate due to falling or low groundwater table sedimentary bypass and extensive erosion by fluvial channels this is typical of upper highstand lowstand fan and basal lowstand wedge systems tracts higher accommodation rates provide relatively stable conditions with rising groundwater tables mires initiate and copyright 1997 the american association of petroleum geologists all rights reserved 1manuscript received september 7 1995 revised manuscript received november 25 1996 final acceptance may 5 1997 2exxon production research company 3120 buffalo speedway houston texas 77096 3exxon production research company 3120 buffalo speedway houston texas 77096 present address conoco inc p o box 2197 houston texas 77252 we benefited from the input and assistance of many people of special assistance were the teams involved in collaborative studies with esso australia and esso malaysia p moore m sloan j emmett b burns a partridge s creaney hanif hussein r hill r lovell and m feeley we also thank the rock springs team r beauboeuf p mclaughlin w devlin a carroll y y chen g grabowski jr k miskell gerhardt m farley r webster and j schwalbach group members d curry and j yeakel were always helpful we also enjoyed and profited from many discussions of these concepts with our colleagues outside exxon c diessel r boyd k shanley b zaitlin p mccabe m hendricks a cohen and m kirschbaum we thank the reviewers of company reports whose careful comments on several generations of this work improved it s creaney m feeley j van wagoner f wehr j yeakel and a young f weber and j zullig provided extensive management support k linke translated our sketches into the fine figures herein we value all the help

oceanic density fronts steering bottom current induced sedimentation deduced from a 50 ka contourite drift record and numerical modeling off nw spain abstract how the various bottom near hydrographic and sedimentary processes control the formation of contourite drifts i e of bottom current related confined deep sea depocenters usually remains widely speculative this study uses a transect of six sediment cores and a sediment echosounder profile across a whole contourite system off nw spain to address the sediment dynamics responsible for the depositional pattern this mounded patch type contourite drift 18 km long 20 km wide with a 150 m deep channel moat has formed around an 800 m high structural obstacle deposition on the contourite drift in the past was characterized by alternating calm and high energy bottom flow conditions calm conditions last glacial period 27 17 cal ka bp late holocene times process based numerical modeling demonstrates that pulse like oceanic density fronts traveling within the transition zone of two water masses labrador sea water mediterranean outflow water provide a powerful mechanism for contouritic deposition rather than the core of a water mass itself these gravity driven density fronts lead to local re suspension of sands stored inside the drift s moat and to subsequent upward transport towards the drift s crest here the oceanic density fronts produce additional km scale eddies these migrating eddies provide an efficient mechanism for further widespread sediment re distribution in comparison with paleoceanographic reconstructions a downward migration or expansion of the mediterranean outflow water by about 300 m led most probably to such temporary contouritic sand deposition we finally propose a conceptual model to explain how seafloor obstacles redirect and perturbate bottom currents this model proposes not only a sharp contact between two water masses but also the transition zone between those as an important high energy regime offering oceanic density fronts a travel medium these fronts are strong enough to distribute fine sands across highly pronounced seabed topography on the respective time scale the moat itself seems to act as the main source for those sands making a remote source and a long distance sediment transport unnecessary

a multiproxy approach of the holocene evolution of shelf slope circulation on the nw iberian continental shelf abstract textural mineralogical geochemical and microfaunal data benthic foraminifera were studied along the omex core ksgx 40 recovered in the galicia mud deposit of the nw iberian outer continental shelf off the ria de vigo north of spain this core included the records of the last ca 4 8 ka cal bp and consists from the base to the top of a sedimentary sequence exhibiting gradual upward decrease in grain size sediments of this core are mainly siliciclastic largely composed of quartz k feldspars plagioclases and phyllosilicates mica illite kaolinite and chlorite showing a great continental influence in this zone two periods of deposition of finer sediments are registered between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp since the last 2 2 ka bp but mainly during both muddy intervals the galicia mud deposit was nourished with a lower and finer supply of detrital minerals compensated by higher amounts of organic matter as it is suggested by a benthic foraminifera high productivity bfhp proxy processes involved in organic matter degradation by aerobic organisms led to depressed levels of oxygen in the sediments as shown by a benthic foraminiferal oxygen index bfoi peaks of redox sensitive elements like mn fe cu ni cr co zn ni and pb as well as the presence of diagenetic minerals such as pyrite suggest the development of anoxic conditions beneath the sedimentary surface and early diagenetic changes due to high organic matter flux in both muddy intervals two different hydrodynamic regimes were inferred through the analysis of the different proxies textural mineralogical geochemical and benthic foraminifera 1 a strong hydrodynamic regime between 4 8 and 2 2 ka cal bp characterized by the prevalence of winter storms which gave rise to a deep mixed layer on the shelf 2 weak hydrodynamic regime between 2 2 1 2 ka cal bp and 0 5 0 ka cal bp with a high predominance of upwelling and an increase in oceanic stratification

stratigraphic uncertainty in sparse versus rich data sets in a fluvial deltaic outcrop analog ferron notom delta in the henry mountains region southern utah the turonian notom delta is one of the ferron fluvial deltaic wedges deposited in the cretaceous foreland basin of north america and is well exposed in the henry mountains region utah this article uses variable sampling of measured sections of the fluvial deltaic wedge along a 19 mi 30 km outcrop belt to address correlation uncertainties in sparse data sets such as are common in subsurface studies a high resolution sequence stratigraphic analysis based on 58 measured sections extensive walking out of beds and field photomosaics shows that the wedge is composed of 43 parasequences 18 parasequence sets and six depositional sequences resampling the outcrop belt with 13 sections provides a sparse data set correlations using the data set show considerable uncertainties fluvial complexity is greatly underestimated and in the extreme case only 40 of the fluvial bodies are identified overcorrelation results in as much as 400 exaggeration of sandstone width and thickness some of the uncertainties can be reduced by incorporating nonmarine sequence stratigraphic models and various techniques that allow a more reasonable evaluation of fluvial body geometry with sparse data uncertainties also arise in marine successions a key challenge is to identify and correlate the small scale units particularly forced regressive deposits many of their diagnostic features that can be easily recognized from outcrops and cores may not be as easily detected from well logs and on seismic data in subsurface studies where sparse data are observed integrating detailed facies analysis cores and sequence stratigraphic concepts is critical to predict the occurrence and understand the architecture of such deposits

sediment instability on the portuguese continental margin under abrupt glacial climate changes last 60 kyr abstract it is well established that orbital scale sea level changes generated larger transport of sediments into the deep sea during the last glacial maximum than the holocene however the response of sedimentary processes to abrupt millennial scale climate variability is rather unknown frequency of distal turbidites and amounts of advected detrital carbonate are estimated off the lisbon setubal canyons core md03 2698 at 4602 mwd within a chronostratigraphy based on radiometric ages oxygen isotopes and paleomagnetic key global anomalies we found that 1 higher frequency of turbidites concurred with northern hemisphere coldest temperatures greenland stadials gs including heinrich h events but more than that an escalating frequency of turbidites starts with the onset of global sea level rising and warming in antarctica and culminates during h events at the time when rising is still in its early mid stage and the atlantic meridional overturning circulation amoc is re starting this short time span coincides with maximum gradients of ocean surface and bottom temperatures between gs and antarctic warmings antarctic isotope maximum aim 17 14 12 8 4 2 and rapid sea level rises 2 trigger of turbidity currents is not the only sedimentary process responding to millennial variability land detrital carbonate with a very negative bulk 18o signature enters the deep sea by density driven slope lateral advection accordingly during gs 3 possible mechanisms to create slope instability on the portuguese continental margin are sea level variations as small as 20 m and slope friction by rapid deep and intermediate re accommodation of water masses circulation 4 common forcing mechanisms appear to drive slope instability at both millennial and orbital scales

sediment distribution patterns on the galicia minho continental shelf abstract a sedimentological and bathymetric study of the minho galicia shelf shows a strong contrast between a southern shelf region with a thin partially relict cover of sands and gravel and a northern region where fine grained sediments predominate this contrast is explained through differences in the sediment supply the oceanographic environment storms and ocean currents and the morphology of the shelf which results from its underlying tectonic framework most sediment is supplied to the galicia minho shelf by river discharges onto the minho shelf particularly that from the douro river in the northern part of the shelf the galician rias act as sediment traps rather than sediment suppliers the bulk of the sediment washes out of the rivers during episodic storm events while most of the coarse sediments remain deposited close to the coast the fine grained material is exported to the outer areas of the shelf subsequently coarse sediments close to the coast are transported southwards by the littoral drift whereas the fine grained material is frequently resuspended through the action of the large swells who influence reaches deep into the water this frequent resuspension has a long term sorting effect on the sediments furthermore resuspended sediments on the middle and outer regions of the shelf are transported northwards by a poleward flowing bottom current as a consequence of the differential transport of coarse sediments to the south and of the fine grained sediments to the north the outer reaches of the minho shelf are relatively poor in recent sediments in many areas relict sediments as well as features associated with ancient coastlines and river mouths still appear as seabed features in contrast the northern regions of the shelf are covered by a thin veneer of fine grained material that smooth other most of these fossil features the fine grained sediment fractions mostly very fine sands to coarse silts are deposited in two large mud patches the douro and the galicia mud patches which are situated at water depths of around 100 120 m these two mud patches are both controlled by the local hydrodynamics and morphology the beiral de viana to the west of the douro mud patch is a plateau up to 20 m high lying parallel to the shelf break and is a morphological expression of an underlying horst system this plateau acts as a barrier that prevents the drift of some of the fine grained material to the west out over the shelf break and the continental slope the galicia mud patch is situated on the eastern part of the galician shelf to the north of the douro mud patch it is situated near the extension of the porto tomar fault which results in the shelf being usually steep in this region down to a depth of about 100 m west of this area the slope is much more gentle northward transport of the sediment is strongly reduced by the e w trending outcrops of plutonic and metamorphic rocks

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

centennial scale surface hydrology off portugal during marine isotope stage 3 insights from planktonic foraminiferal fauna variability 1 the marine isotopic stage 3 mis3 at ocean drilling program odp site 1060 gulf stream shows both sharp onset and end of interstadials the existence of very short lived warm events during stadials and points to differences in detail between the sea surface temperature sst record from the western north atlantic and the atmospheric temperature record inferred from 18o in greenland ice investigating mis3 and obtaining comparable data from other locations appears crucial the eastern atlantic provides well documented records of climate changes we have selected a core from off portugal and use it to examine dansgaard oeschger events d o at centennial scale resolution 139 years on average between two data points we have obtained a faunal data set for core md01 2444 37 n 10 w 2600 m water depth and use a group of species globigerina bulloides globigerinita glutinata as a proxy of upwelling intensity driven by trade winds intensity changes we tentatively relate the variation of this group to a north atlantic oscillation like phenomenon nao off portugal we observe that it resembles the rainfall index in the caribbean as recorded at odp site 1002 cariaco basin which traces the intertropical convergence zone itcz location through changes of terrigenous inputs the driest intervals itzc to the south at site 1002 correspond to intervals of increased upwelling in md01 2444 as well as the driest periods identified during stadials on similar cores in the area because the itzc to the south is consistent with an el nino southern oscillation enso situation our study suggests a positive correlation between enso like conditions and nao like conditions at a millennial timescale during interstadial intervals when increased wetness over cariaco is recorded itcz to the north and the upwelling in md01 2444 is decreased we see from both ssts and faunal tropical indicators that md01 2444 site is warm in addition interstadials are equally warm through each so called bond cycle this contrasts with the greenland ice core project grip record where interstadial peaks are successively cooler through each bond cycle this record confirms a link between tropical climate linked to itcz position and the climate of southern europe at millennial timescales in spite of showing a very good correlation with polar latitudes grip through 18o on globigerina bulloides in addition because the warmest ssts and the 18o on g bulloides are so remarkably different our work points to changes in seasonality as a strong control over the climatic pattern of the north atlantic area and the marked influence of winter conditions

palaeocurrent reconstruction sediment and thorium focussing on the iberian margin over the last 140 ka sedimentological data in particular sediment grain size from core md95 2040 2465 m water depth and a nearby core omii 9k 1833 m water depth presently under the influence of lower north atlantic deep water and deep intermediate water respectively have been used to reconstruct changes in the vigour of near bottom water flow on the iberian margin the pattern of the palaeocurrent index indicates faster flow during the warm periods and slower in cold this also holds in the younger dryas but there is an added effect of brief collapse of the circulation in termination 1b due to meltwater input the cold periods are generally characterised by elevated clay percentage terrigenous material 2 m diameter and overall sediment accumulation fluxes in comparison warm periods of higher flow have lower depositional flux and a tendency to silt terrigenous material 2 63 m dominance consistent with the higher flow speed and suppression of clay deposition this is in contrast with a recent 230thxs based study of two cores md95 2040 and 2039 j thomson et al earth planet sci lett 165 1999 255 270 which concluded that increased glacial sediment and th focussing was caused by stronger currents the crucial factor is that the controlling speed is that of the flow at the depositional site rather than that of the erosional or transporting flow to the site high glacial maximum fluxes of carbonate 6 g cm 2 ka 1 are largely composed of fine 63 m non coccolith material suggesting a significant detrital component it is proposed that the sediment and th arrive on the lower slope via different routes sediment down slope in bottom nepheloid layers and turbidity currents th scavenged from the water column by organic matter and are rapidly mixed on the bed removal of this material from a large area and its deposition in a small one adjacent to oporto seamount together with a small amount of direct down slope supply accounts for the properties of the deposits allowance for erroneous fluxes due to possible coring expansion stretching of the upper part of md95 2040 does not invalidate these conclusions

downslope volume enlargement of a debris slide debris flow in the 1999 hiroshima japan rainstorm abstract following a heavy rainstorm on 29 june 1999 hundreds of slope failures occurred in granitic mountains in hiroshima prefecture japan among these events a highly mobile landslide termed the kameyama landslide in this paper which occurred in kameyama area of hiroshima city was the most catastrophic and was investigated in detail the displaced soil mass from the source area of this landslide traveled about 300 m and deposited a volume more than 10 times as great as that in the source area the landslide originated in and traversed a valley shaped concave slope covered by pre existing colluvial debris deposits in addition a spring was visible in the source area and very shallow ground water was observed in an observation pit dug in the source area thus it is inferred that the ground water table rose quickly during the rainfall and that this rise triggered the slope failure in the source area based on a field survey along the landslide cross section a possible explanation for the mechanism of the landslide was obtained the displaced soil mass from the source area impacted the debris deposit in the path of the landslide thus triggering liquefaction failure of the saturated part of debris the original landslide and the liquefied debris then moved downslope as a single mass to examine this assumption ring shear tests were performed on samples taken from the source area undrained ring shear tests on the saturated samples showed that the sample is highly liquefiable and liquefaction failure could have been triggered in the debris deposits by a very small impact from the displaced soil mass of the initial failure in addition laboratory tests simulating the impacts on the debris deposits at natural water content i e unsaturated at the survey time 2 days after the failure showed that although shear failure could be caused by the assumed impact force the displaced soils stopped after a few centimeters displacement indicating that existence of a saturated zone in debris deposits is prerequisite for this kind of failure

hydrographic conditions along the western iberian margin during marine isotope stage 2 the surface water hydrography along the western iberian margin as part of the north atlantic s eastern boundary upwelling system consists of a complex seasonally variable system of equatorward and poleward surface and subsurface currents and seasonal upwelling not much information exists to ascertain if the modern current and productivity patterns subsisted under glacial climate conditions such as during marine isotope stage mis 2 and how north atlantic meltwater events especially heinrich events affected them to help answer these questions we are combining stable isotope records of surface to subsurface dwelling planktonic foraminifer species with sea surface temperature and export productivity data for four cores distributed along the western and southwestern iberian margin md95 2040 md95 2041 md99 2336 and md99 2339 the records reveals that with the exception of the heinrich events and greenland stadial gs 4 hydrographic conditions along the western iberian margin were not much different from the present during the last glacial maximum lgm subtropical surface and subsurface waters penetrated poleward to at least 40 6 n site md95 2040 export productivity was in general high on the western margin during the lgm and low in the central gulf of cadiz in agreement with the modern situation during the heinrich events and gs 4 on the other hand productivity was high in the gulf of cadiz and suppressed in the upwelling regions along the western margin where a strong halocline inhibited upwelling heinrich event 1 had the strongest impact on the hydrography and productivity off iberia and was the only period when subarctic surface waters were recorded in the central gulf of cadiz south of lisbon 39 n the impact of the other heinrich events was diminished and not all of them led to a significant cooling in the surface waters thus climatic impacts of heinrich events highly varied with latitude and the prevailing hydrographic conditions in this region

passive roof duplex geometry in the frontal structures of the kirthar and sulaiman mountain belts pakistan abstract exploration for hydrocarbons over the past few years has greatly improved our understanding of the geometry of frontal mountain belt structures in this study we introduce and discuss the concept of the passive roof duplex using as the main example the kirthar and sulaiman ranges in the baluchistan province of pakistan structures similar to those described here have been recognized previously in other mountain belts and they appear to exist as a common feature in many more frontal regions of mountain belts our example of a passive roof duplex which we describe from pakistan is compared briefly with similar structures reported by others the passive roof duplex is here defined as a duplex whose roof thrust has backthrust sense passive roof thrust and whose roof sequence those rocks lying above the roof thrust remains relatively stationary during foreland directed piggy back style propagation of horses within the duplex

tectonic geomorphology and structural architecture of eastern sulaiman fold thrust belt sftb and adjacent sulaiman foredeep sf northwest pakistan abstract this investigation combines a number of datasets to provide an enhanced and improved tectono geomorphological framework with which to identify new possible structural lineaments in northwest pakistan the dataset includes satellite images and geographic information system gis methods the present study was carried out using the usgs aster dem 30 m landsat 8 oli tirs and surface field geology of the study area different band combinations directional filters and principle component analysis pca methods were used to identify the major structural styles and tectonic geomorphological pattern the panchromatic band band 8 was applied to the landsat 8 satellite images in order to increase the spatial resolution from 30 m to 15 m which aided in the investigation and comparative analysis of tectonic geomorphology and structural styles drainage patterns of zindapir anticline za sakhi sarwar ss sulaiman foredeep sf and kingri fault kf areas were generated using strahler order of streams the results suggested a combination of the dendritic network with a minor component of trellis pattern for zp and sf areas hence proposing a combined structural and stratigraphic lithological control whereas the kf area indicated an element of a rectangular pattern suggesting a more structural influence in the western part in comparison to the eastern region the presence of water gaps wags and active drainage network indicate lateral growth and propagation directions of the zp and ss frontal anticlines following the paleocene epoch the geomorphic evidence coupled with satellite data show that the sftb is tectonically active along with the adjacent sf the stream courses are deflected or guided due to active folds and tectonics in the area characterized by the distinct fluvial erosional pattern on the flanks limbs of za evidence from the study suggests that compressional deformation uplift and erosion played a significant role in the shaping of the structural and depositional architecture of the basin it is proposed that the deformation in the sftb during the late paleogene is related to the indian eurasian oblique collision while the subsequent late tertiary collision of indian plate with the afghan block an accreted part of southern eurasia further ensued compressive deformation the results from this study elucidate the possible models proposed for this compressional regime with prevailing wrenching by presenting new data the findings from this research reveal new tectono geomorphological features and lineaments in the area that were not documented previously

the role of outcrop geology in predicting reservoir presence in the cretaceous and paleocene successions of the sulaiman range pakistan hydrocarbon exploration in remote mountainous regions commonly creates a logistical challenge remote sensing methods are used to gain an understanding of the geologic evolution of an area however over reliance on these techniques has commonly precluded finer scale observations made in the field which can significantly reduce exploration risk the sulaiman concession lies in the sulaiman range which forms part of the himalayan fold and thrust belt in the baluchistan province of northwest pakistan rugged exposures developed in this semiarid area provide excellent outcrops of the principal stratigraphy of interest in the concession to reduce uncertainty associated with reservoir presence the upper cretaceous to lower paleocene mughal kot pab and ranikot formations were studied detailed centimeter scale sedimentological observations enabled the depositional context of these units to be resolved by recognizing abrupt dislocations in facies tracts and changes in depositional architecture a low order stratigraphic framework was established furthermore local candidate high frequency surfaces were recognized which gave an insight into the processes active in the individual facies tracts during periods of relative base level change these observations resulted in an integrated model that was used to predict reservoir presence in the mirawah structure

changes in paleocurrents during the development of an obliquely convergent plate boundary sulaiman fold belt southwestern himalayas west central pakistan abstract pre orogenic cretaceous shelf sandstones at the northern and southern ends of the sulaiman range in west central pakistan show basically westward dispersal which is off the craton however paleocene marine sandstones in the south spread east southeast and early eocene deltaic sandstones in the north spread southeast and north these are mostly onto the craton and indicate slope reversal of the cretaceous shelf post oligocene fluvial molasse shows mostly southward drainage a 3852 m section of molasse in the northern sulaiman range comprises a lower 2378 m of claystones and upwardly fining sandstones that represent meandering rivers and an upper 1474 m that are dominated by conglomerates that represent gravelly braided rivers paleocurrents in the lower meandering part of the section were generally southward but very variable whereas those in the upper braided part were more uniform and show eastward flow a 3146 m section of molasse in the southern sulaiman range comprises 1 a basal 1160 m sequence of claystones and sandstones meandering streams with very diverse flow directions overall to the southwest 2 a middle 1603 m sequence dominated by pebbly sandstone with large bedforms big sandy braided rivers with less diverse flow to the southwest and 3 an upper 383 m conglomeratic sequence gravelly braided streams that still flow uniformly southwest rivers in the early molasse paralleled the modern sulaiman range in the north and flowed obliquely into it in the south which suggests no uplift of the modern front of the range until the onset of modern transverse eastward drainage and the associated influx of conglomerates in present and admittedly uncertain lithostratigraphic terms uplift of the modern front of the range apparently began about 700 m lower in the north than in the south the northern and southern molasse sections otherwise show broadly similar histories of river development

contrasting late cretaceous palaeocene lithostratigraphic successions across the bibai thrust western sulaiman fold thrust belt pakistan their significance in deciphering the early collisional history of the nw indian plate margin abstract the sulaiman fold thrust belt is a significant tectonic element in northwest pakistan located on the nw margin of the indian plate having a rift drift collision plate tectonic history late cretaceous palaeocene successions in the western sector of this belt conventionally comprise strata above the widespread pelagic parh limestone albian campanian and below the fluvio deltaic ghazij formation early eocene these successions display marked lithostratigraphic variations across the bibai thrust long known to be an important structural feature in the western sulaiman belt the successions on the foot wall to the east and southeast of the bibai thrust quetta spera ragha and chinjun areas exhibit the most variable lithostratigraphy were deposited exclusively in shallow marine conditions and include volcanics associated with a local submarine edifice they also display several internal disconformities locally accompanied by oxidised units that attest to intermittent emergence by contrast coeval successions on the hanging wall to the north and northwest of the bibai thrust urghargai mazu ghar and kach ziarat areas are the products of deposition in deeper marine conditions and also include important volcanigenic contributions these contrasting lithofacies accumulated respectively in widely separated proximal and distal sectors of the north western margin of the indian plate and their current proximity is attributed to tectonic juxtaposition by relative southward translation of the distal facies along the bibai and related thrusts involvement of late eocene limestones in these thrusts and their sealing by mio pliocene fluvial sediments demonstrates that active translation on these thrusts continued at least into late eocene or oligocene times

predicting deposition of debris flows in mountain channels an empirical model for predicting deposition of coarse textured debris flows in confined mountain channels is developed based on field measurements of 14 debris flows in the pacific northwest u s a the model uses two criteria for deposition channel slope less than 3 5 and tributary junction angle greater than 70 the model is tested by predicting travel distances of 15 debris flows in the oregon coast range and six debris flows in the washington cascades u s a the model is further tested on 44 debris flows in two lithological types in the oregon coast range using aerial photos and topographic maps on these flows only the approximate travel distance is known the model can be used by resource professionals to identify the potential for impacts from debris flows key words debris flow deposition travel erosion

experimental study on gully shaped mud flow in the loess area vast expanse of land in northwest china is covered by loess because of the characteristics of loess mud flow disasters can be induced in this area easily worse still due to the mud flow gully transformation and the environmental changes in recent decades mud flow disasters are increasing in order to know more about gully shaped mud flow the field investigation of more than 60 gullies and the similarity principle were applied to determine the test parameters and a physical model of gully was made for mud flow during the tests the motion characteristics velocity acceleration and intermittent debris flow and deposition parameters length width area aspect ratio distribution shape and thickness of mud flow in the model were collected and analyzed the instantaneous velocities of the mud flow fluctuated discharge exerts a maximum impact on the velocity second is unit weight and minimum slope angle in the transportation zone the mud flow flows and forms the bed firstly then the intermittent debris flow occurs which is affected by discharge and unit weight the length width and area of deposition have a certain linear rule and distribution pattern greatly relates to the first accumulation the stacking thickness is decreasing from the center to the edge

sedimentary architecture of a low accumulation shelf since the late pleistocene nw iberia abstract continental shelves represent areas of highest economical and ecological importance nevertheless these sedimentary systems remain poorly understood due to a complex interplay of various factors and processes which results in highly individual construction schemes previous studies of sedimentary shelf systems have mainly focused on a limited number of cores retrieved from holocene fine grained depocentres as such the relation between shelf architecture and sedimentary history remains largely obscure here we present new data from the nw iberian shelf comprising shallow seismic profiles a large number of sediment cores and an extended set of radiocarbon dates to reveal the late quaternary evolution of a low accumulation shelf system in detail on the nw iberian shelf three main seismic units are identified these overly a prominent erosional unconformity on top of the basement the lowermost unit 1 is composed of maximal 75 m thick late tertiary to pleistocene deposits the youngest sediments of this unit are related to the last glacial sea level fall unit 2 was controlled by the deglacial sea level rise and shows a maximum thickness of 15 m finally unit 3 comprises deposits related to the late stage of sea level rise and the modern sea level highstand with a thickness of 4 m in mid shelf position two pronounced seismic reflectors separate these main units from each other their origin is related to 1 exposure and ravinement processes during lower sea level and 2 to reworking and re deposition of coarse sediments during subsequent sea level rise according to the sediment core ground truthing sediments of the late tertiary to pleistocene unit predominantly display homogenous fine sands with exceptional occurrences of palaeosols that indicate an ancient exposure surface fine sands which were deposited in the run of the last sea level rise show a time transgressive retrogradational development the seismic reflectors bounding the individual units appear in the cores as 0 1 to 1 m thick deposits consisting either of shell gravels or siliceous coarse sands with gravels the modern sea level highstand stage is characterised by zonal deposition of mud forming a mud belt in mid shelf position and sediment starvation on outer shelf zones radiocarbon ages indicate that this mud belt was the main depocentre for river supplied fine material on the nw iberian shelf at least over the past 5 32 ka bp the initial onset of this depocentre is proposed to be related to a shift in the balance between rate of sea level rise and amount of terrigenous sediment supply various other stratigraphical shelf reconstructions reveal analogies in architecture which indicate that timing and shaping of the individual units on low accumulation shelves is fundamentally controlled by eustatic sea level changes other factors of local importance such as differential elevation of the basement and the presence of morphological barriers formed by rocky outcrops on the seafloor have additionally modifying influence on the sedimentary processes

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

high resolution palynological record off the iberian margin direct land sea correlation for the last interglacial complex abstract we present high resolution pollen dinocyst and isotopic data for the last interglacial complex from marine core md952042 southwestern margin of the iberian peninsula 37 48 n 10 10 w 3148 m direct land sea correlation from this core indicates that during this period north atlantic sea surface temperatures were in phase with iberian climate our palynological analysis suggests a younger dryas like event at the marine isotope stage mis 6 5 transition the analysis also indicates that the eemian spans from the lightest isotopic values of mis 5e ca 126 ky bp to the heavier isotopic values towards the mis 5e 5d transition therefore the eemian is not entirely equivalent to mis 5e pollen analysis identifies four climatic phases of low amplitude during the eemian a mediterranean climate in southwestern europe is gradually replaced by oceanic conditions the middle of the eemian is characterized by an increase in precipitation on the land and ocean associated with a slight cooling this seems to be the result of a displacement of the polar front as far south as southern europe during this period after the eemian three relatively short climatic phases on land melisey i st germain ia and montaigu cold event occurred contemporaneously with three shifts of sea surface temperatures the montaigu event first identified in terrestrial pollen sequences is therefore also recorded in core md952042 on the basis of pollen dinocyst and planktonic isotopic data our results also show that the warm periods of mis 5 are not characterized by similar climatic conditions on land

temperature and productivity changes off the western iberian margin during the last 150 ky abstract present day hydrographic conditions along the western iberian margin are characterized by seasonal upwelling with filaments that can penetrate more than 200 km into the open ocean and constitute areas of cold and highly productive waters in order to investigate spatial and temporal gradients in temperature and productivity conditions during the last 150 ky high resolution proxy records were generated in 3 cores su92 03 md95 2040 md95 2042 located along the iberian coast between 43 12 n and 37 48 n and forming a n s profile in all cores planktonic foraminifera census counts are used to reconstruct summer sea surface temperature sstsu and export productivity pexpsu using the modern analog technique simmax 28 sstsu and pexpsu values similar to the present are observed throughout the holocene and mis 5e periods for each site respectively indicating fairly stable conditions equivalent to the modern ones on glacial interglacial timescales sstsu increases by 2 3 c from the northern to southernmost site pexpsu on the other hand shows a decrease of 30 40 gc m2 yr from north to south at present time and during interglacial periods and no significant variation 90 100 gc m2 yr during glacial periods the northernmost core su92 03 reveals the coldest conditions with records more similar to md95 2040 than to md95 2042 the later of which is as at present more affected by subtropical waters core su92 03 shows higher interglacial productivity similar to open ocean mid to high latitude sites while the other two cores monitor higher glacial productivity conform with other upwelling sites off nw africa a boundary between differences in glacial interglacial productivity appears to be present in our study between 43 12 n and 40 35 n especially north of 40 n coldest sstsu and lowest pexpsu are found during heinrich events h 1 h8 and h10 h11 in contrast lowest pexpsu do not coincide with these events at site md95 2042 but appear to be related to the presence of relatively warm and nutrient poor subtropical eastern north atlantic central water advected with the azores current

past circulation along the western iberian margin a time slice vision from the last glacial to the holocene abstract fifteen iberian margin sediment cores distributed between 43 12 n and 35 53 n have been used to reconstruct spatial and temporal sub surface circulation along the iberian margin since the last glacial period time slice maps of planktonic foraminiferal derived summer sea surface temperature sst and export productivity pexp were established for specific time intervals within the last 35 ky the holocene recent and last 8 ky younger dryas yd heinrich stadials hs 1 2a 2b 3 and the last glacial maximum lgm the sst during the holocene shows the same latitudinal gradient along the western iberian margin as present day with cold but productive areas that reflect the influence of coastal upwelling centers the lgm appears as a slightly less warm but more productive period relative to the holocene and present day conditions suggesting that sea level minima forced a westward displacement of the coastal upwelling centers possibly accompanied by a strengthening of northward winds during the yd a longitudinal thermal front is depicted at 10 w with cold polar waters offshore and warmer subtropical waters inshore suggesting that the subtropical paleo iberian poleward current more likely flowed at a more inshore location masking the local sst signal and amplitude of variation a substantial cooling and drop in productivity is observed during all hs in particular hs1 and hs3 reflecting the penetration of icebergs derived meltwater these most extreme southward extensions of very cold waters define a strong sst gradient that marks a possible paleo azores front higher production south of this front was likely fed by frontal nutrient advection

late pleistocene and holocene sedimentary facies on the sw galicia bank atlantic nw iberian peninsula abstract five main pleistocene holocene lithofacies are defined in three different sedimentary environments fault scarp sedimentary lobe and inter lobe channel of the sw galicia bank 1 turbidites biogenous and terrigenous 2 hemipelagites 3 pelagites 4 debrites and 5 heinrich sediments in the sedimentary lobe and inter lobe channel the stratigraphic record consists mainly of turbidites interbedded with debrites and heinrich sediments and hemipelagites that are covered by hemipelagites or pelagites in the fault scarp the stratigraphy comprises hemipelagites and turbidites covered by pelagites frequency of turbidite events has varied between 1 1 2 ka and 1 3 1 ka since 31 3 ka bp at least four turbidite events 1 to 4 between 9 1 and 31 3 ka bp have been correlated between the different sedimentary environments the downslope of turbidity flows prevailed until 9 1 ka after which vertical settling and slow lateral advection have controlled sedimentation the source area of turbidites and debrites is the fault scarp erosion of the slope near surface pelagites hemipelagites and ancient outcropping deposits could explain the presence of biogenous turbidites and terrigenous turbidites respectively the rhythmic development of turbidites interrupted by hemipelagites could represent the manifestation of different pulses of sedimentary instability induced by a combination of oversteepening up to 29 and occurrence of earthquakes

the application of high resolution sequence stratigraphy to fluvial systems a case study from the upper carboniferous breathitt group eastern kentucky usa the pennsylvanian pikeville hyden and four corners formations of the breathitt group in eastern kentucky usa contain six major facies associations along with a number of subassociations these facies associations are offshore siltstone rhythmically bedded mouthbar heteroliths predominantly fine grained floodplain deposits minor channel fills major distributary channels and major stacked fluvial bodies the stacked fluvial bodies are incised into a variety of open marine and delta plain deposits have widths of several kilometres and exhibit a range of sandy fill types these fluvial complexes are interpreted as incised valley fills parasequences and parasequence sets are not identifiable nonetheless it is possible to identify systems tracts on the basis of sequential position facies associations and systematic changes in architectural style and sediment body geometries the studied portion of the breathitt group comprises stacked 4th order sequences which occur in lowstand transgressive and highstand sequence sets related to the development of a lower frequency base level cycle in the lowstand sequence set incision associated with successive 4th order sequence boundaries has commonly removed all the hst and tst of the underlying sequences such that succeeding 4th order incised valley fills are amalgamated within the transgressive sequence set incision is at a minimum and incised valley fills tend to stack discretely with the maximum amount of fine grained tst and hst between them the highstand sequence set is transitional between the lowstand and transgressive sequence sets in terms of the amount of transgressive and highstand deposits preserved incised valley fills tend to stack discretely

geological characterization of the galicia bank region atlantic ocean nw iberia the marine geology community s response to the prestige disaster abstract the geological characterization of the galicia bank region in the nw iberian continental margin atlantic ocean was the marine geology community s response to the environmental risk posed by the sinking and oil spill of the prestige tanker this special volume of marine geology is a collection of papers that address themes of general interest for marine geohazard determination and assessment a variety of topics associated with morphology stratigraphy sedimentology tectonism and seismicity were considered in order to define the geohazards at the location of the prestige wreck which still has oil in its tanks these studies have also served to provide greater detail and high resolution datasets on the geological evolution of the galicia bank region in general and particularly its sw flank

physical and numerical modelling of dry granular flows under coriolis conditions in this paper quantitative observations of dry granular flows subject to varying magnitude and direction of coriolis acceleration are presented in order to assess the robustness of the savage hutt

drained principal stress rotation in saturated sand an investigation into the effects of drained principal stress rotation on the behaviour of a saturated medium loose sand is described using a hollow cylinder apparatus the principal stress directions were rotated both at a constant shear stress and under an increasing shear stress during drained monotonic loading to failure the experimental results are presented the findings are used to support the notion that a bounding surface defined by tests with fixed principal stress orientations can be used to make a qualitative prediction of drained and undrained behaviour during monotonic loading to failure which includes rotation of principal stress directions the bounding surface conveys the importance of both anisotropy in determining strength and the direction of principal stress rotation in determining the magnitude of volumetric strains or pore pressures which develop the findings concerning the bounding surface apply to a medium loose sand which has a well defined con tractant region strains which

occurrence of pockmarks on the ortegal spur continental margin northwestern iberian peninsula a total of 445 pockmarks were observed on the upper continental slope of the northwest corner of the iberian peninsula the ortegal spur area by swath bathymetric and ultrahigh resolution seismic data the pockmarks are u v and w shaped and have terraces or indentations in cross section and are dish shaped circular to oval in plan view they occur on the surface of the seabed and buried within the plio quaternary and neogene sediments four types of pockmarks were identified and mapped on the basis of their plan view and cross section morphology regular irregular asymmetric and composite the concentration of pockmarks is attributed to seepage of fluids migrating up dip from deeper parts of the sedimentary basin a linear high density concentration with a nnw to n ne and ese trend of pockmarks is observed above inferred basement faults that do not affect the quaternary succession these pockmarks are thus caused by seepage of thermogenic gas and or other pore fluids from deeper late cretaceous units and their distribution may help to improve our understanding of the fluid system and migration regime in this part of the galicia continental margin

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

millennial scale iceberg discharges in the irminger basin during the last glacial period relationship with the heinrich events and environmental settings high resolution records of coarse lithic content and oxygen isotope have been obtained in a piston core from the irminger basin the last glacial period is characterized by numerous periods of increased iceberg discharges originating partly from iceland and corresponding to millennial scale instabilities of the coastal ice sheets and ice shelves in the nordic area a comparison with midlatitude sediment cores shows that ice rafted material corresponding to the heinrich events was deposited synchronously from 40 to 60 n there are thus two oscillating systems every 5 10 kyr massive iceberg armadas are released from large continental ice caps whereas more frequent instabilities of the coastal ice sheets in the high latitude regions occur every 1 2 3 8 kyr at the time of the heinrich events the synchroneity of the response from all the northern hemisphere ice sheets attests the existence of strong interactions between the two systems

evidence of abrupt changes in western mediterranean deep water circulation during the last 50kyr a high resolution marine record from the balearic sea abstract the images core md99 2343 recovered from a sediment drift north of the island of minorca in the north western mediterranean sea holds a high resolution sequence that is perfectly suited to study the oscillations of the overturning system of the western mediterranean deep water wmdw detailed analysis of grain size and bulk geochemical composition reveals the sensitivity of this region to climate changes at both orbital and centennial millennial temporal scales during the last 50 kyr the dominant orbital pattern in the k al record indicates that sediment supply to the basin was controlled by the insolation evolution at 40 n which forced changes in the fluvial regime with more efficient sediment transport during insolation maxima this orbital control also modulated the long term pattern of the wmdw intensity as illustrated by the silt clay ratio however deep convection was particularly sensitive to climatic changes at shorter time scales i e to centennial millennial glacial and holocene oscillations that are well documented by all the paleocurrent intensity proxies si al ti al and silt clay ratios benthic isotopic records 13c and 18o show a dansgaard oeschger d o pattern of variability of wmdw properties which can be associated with changing intensities of the deep currents system the most prominent reduction on the wmdw overturning was caused by the post glacial sea level rise three main scenarios of wmdw overturning are revealed a strong mode during d o stadials a weak mode during d o interstadials and an intermediate mode during cooling transitions in addition d o stadials associated with heinrich events hes have a very distinct signature as the strong mode of circulation typical for the other d o stadials was never reached during he due to the surface freshening induced by the inflowing polar waters consequently the wmdw overturning system oscillated around the intermediate mode of circulation during he though surface conditions were more stable during the holocene the wmdw overturning cell still reacted synchronously to short lived events as shown by increments in the planktonic 18o record triggering quick reinforcements of the deep water circulation overall these results highlight the sensitivity of the wmdw to rapid climate change which in the recent past were likely induced by oceanographic and atmospheric reorganizations in the north atlantic region

formation and fate of sedimentary depocentres on southeast asia s sunda shelf over the past sea level cycle and biogeographic implications abstract sea level variations are the major factor controlling sedimentation as well as the biogeographic patterns at continental margins over late quaternary times fluctuations on millennial time scales produce locally complex deposits in coasts and on shelves associated with short term influence on species development this article reviews the sedimentary and biogeographic history of the tropical siliciclastic sunda shelf as an end member of continental shelves regarding extreme width an enormous sediment supply and highest biodiversity in response to rapid sea level fluctuations we describe particular depositional segments as part of a genetic succession of zones from land to the deep sea based on literature data field observations and calculation of hydro isostatic adjustment effects on changing relative sea level these segments are characterized by individual sedimentary processes and deposits and by a specific potential for material storage and re mobilization long term regressive intervals led to overall sigmoidal promoting extremely thick and wide succeeding units in contrast rapid lateral shifts of defined depocentres over long distances took place in response to short term sea level fluctuations fully isolated small scale sediment bodies formed when sea level changed at exceptionally high rates as a result of the high availability of organic rich sediments mangrove and freshwater peats formed frequently over late quaternary times the appearance of thick massive and widespread peats is mainly linked to time intervals of a sea level rise at slow rates whilst organic matter appears much more dispersely in the sediments during episodes of rapidly changing sea level the preservation potential of the regressive units is generally high due to highest initial sediment supply stabilizing soil formation during exposure and rapid subsidence preservation of depositional elements from other periods is more exceptional and either restricted to local morphological depressions or to episodes of rapid sea level change besides complex channel incision an overall lowering of the sediment surface related to erosion as deep as 20 m or more over wide areas took place mainly during sea level lowering the final export of shelf material is documented by enormous mass wasting packages on the associated continental slope from a palaeogeographic perspective the rapid formation or disappearance of special habitat zones such as mangrove fringes and extended mud flats led to species establishment or truncation in distribution in addition the opening or closure of ocean passages as narrow bridges allowing limited species crossing or as fully colonized corridors had severe impact on eco fragmentation and the expansion or contraction of species independent of such particular conditions sea level changes have been too rapid over the past climatic cycle to allow full regeneration and mature development of coast related ecosystems

paleogeographic maps of the continents bordering the indian ocean since the early jurassic paleomagnetic data from the african plate from the early jurassic onward are critically re evaluated and updated resulting in a set of 30 paleopoles from which an apparent polar wander path is derived using 20 ma intervals this path is then used in conjunction with kinematic models of the indian and atlantic oceans to place other continents bordering the indian ocean eurasia india islands and plateaus madagascar seychelles mascarene and blocks involved in the collision of india with eurasia south tibet indochina in an absolute paleogeographic frame fixed with respect to africa paleogeographic maps are presented for the early jurassic pre breakup the jurassic cretaceous boundary anomaly ml5 the early cretaceous m2 the late cretaceous a 34 the cretaceous tertiary boundary a 29 the early eocene a 24 the middle eocene a 21 and the oligocene miocene boundary a 6 observed and predicted paleomagnetic directions for landmasses other than africa i e for western europe china korea india and australia which are not used in deriving the maps are found to be in very satisfactory agreement the quality of reconstructions as measured by rms discrepancies between observed and predicted paleolatitudes is of the order of 5 the main features of the paleogeographic maps are discussed with the aim of relating oceanic and on land geodynamic events the constraints provided by tibetan data on the india asia collision and the 20 ma reorganization of geology and plate boundaries in a band extending from the south china sea through tibet to the red sea system are discussed in more detail we emphasize the episodic nature of the breakup of gondwanaland and formation of the indian ocean and subsequent interaction with eurasia in which six major discrete events are identified separated by 30 ma phases of rather uniform plate motion

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

mediterranean outflow strengthening during northern hemisphere coolings a salt source for the glacial atlantic abstract high resolution grain size and magnetic susceptibility records from the eastern gulf of cadiz site md99 2339 1170 m water depth reveal contourites formed by the mediterranean outflow mow during the last 47 kyr bp oscillations in the mow s intensity occurred in phase with greenland temperature variations with a stronger outflow during northern hemisphere coolings such as dansgaard oeschger stadials heinrich events and the younger dryas benthic 13c data implies the western mediterranean deep water as one of the main sources feeding the outflow current while differential changes in the properties of the mediterranean source and entrained north atlantic central water largely control the mow s strength detailed studies for heinrich events 1 4 and 5 show that the flow strength peaked only when subtropical surface waters prevailed in the eastern gulf of cadiz while incursions of icebergs and subpolar surface water were not favorable for the mow s intensification as the mow was strong when the atlantic s thermohaline circulation thc was weakened the heat and salt injected by the mow into the intermediate north atlantic waters might have preconditioned the thc to switch from the stadial to the interstadial mode

late glacial to holocene history of the mediterranean outflow evidence from benthic foraminiferal assemblages and stable isotopes at the portuguese margin records of benthic foraminiferal assemblage variations and benthic 13c along 12 sediment cores from the western iberian margin between 36 and 42 n at water depths from 820 to 3580 m are used to monitor fluctuations of the mediterranean outflow water mow during the past 30 ka the chronostratigraphy of the cores is based on planktonic 18o records 14c ams dating and the recognition of heinrich events h1 through h4 increased abundances of suspension feeding benthic foraminifers denoted as epibenthos group closely match areas where the recent mow core layers impinge on the continental slope at 800 and 1300 m water depth and near bottom current velocities are enhanced elevated epibenthos group abundances increased benthic 13c and sedimentological evidence for winnowing and erosion are found in glacial sections up to the earliest termination i in cores at water depths between 1600 and 2200 m off southern portugal the combined evidence reveals enhanced current activity at these depths due to a deep glacial mow the mow advection at the portuguese margin during the last glacial was about 700 m deeper than today conceivably forced by increased mow density due to higher salinity and colder temperatures of mediterranean waters the deep mow current gradually decreased in strength and shoaled to 1300 m water depth during the termination and early holocene a shallow mow core layer became active with the onset of termination i at depths between 600 and 1000 m both the shallow and deep mow current culminated during the younger dryas period the present flow pattern with two mow core layers centred at 800 and 1300 m water depth was established between 7 5 and 5 5 ka

perspectives on the sequence stratigraphy of continental strata this report is the result of a working group on continental sequence stratigraphy that was set up at the 1991 nuna conference in banff canada to date sequence stratigraphic concepts have been applied mainly to the marine realm but unconformity bounded units have long been recognized in nonmarine strata successful application of sequence stratigraphic concepts to continental strata requires careful consideration of controls on base level and sediment supply as with shallow marine environments relative sea level can be considered as the stratigraphic as well as the geomorphic base level for coastal nonmarine settings farther inland stratigraphic base level which determines accommodation space is more complex and takes various forms such as the graded profile for fluvial strata groundwater tables for some eolian strata and lake level for some intermontane sediments sediment supply is also generally a more complex variable for nonmarine environments than in the marine realm because of the proximity to the source area the influence of climate and tectonism on sediment supply can clearly be seen in many continental sediments the fact that the major controls of climate tectonism and eustasy are somewhat interdependent and that a change in one parameter will most likely be reflected in others is also more readily apparent in continental strata although in its infancy sequence stratigraphic concepts have been applied to a wide variety of continental settings in attempts to explain variations in facies architecture of particular interest are studies that have linked fluvial architecture on coastal plains to variations in relative sea level as indicated by coeval marine strata and studies of lacustrine environments that show marked variation in facies between highstand and lowstand deposits the application of sequence stratigraphy to continental strata will likely result in the development of better correlation techniques and models that better predict the location and nature of fluvial and eolian reservoirs

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

a novel sedimentological method based on ct scanning use for tomographic characterization of the galicia interior basin abstract non destructive techniques of core analysis especially of marine cores are being broadly employed for sedimentary paleoceanographic and paleoclimate research in particular computed tomography scanning ct scanning allows acquisition of 3d and 2d images according to desired planes and thus the identification of sedimentary structures large grains and their distributions as well as direct measurements of material densities the most significant contribution of this technique is the possibility of getting results before opening the core in this work ct scan data obtained for five cores from the galicia interior basin gib nw peninsula iberia are presented and discussed focussing on 1 methodology of the ct scan use 2 tomographic description of sedimentary facies identified in the gib 3 treatment of the numeric data obtained with ct scanning using specific software anidoc and 4 comparison of tomographic data with data obtained by conventional methodologies of core analysis the most singular feature of gib cores is the presence of ice rafted debris ird deposited during late pleistocene heinrich events he which can be easily recognized using the ct scan by the presence of high radio density grains immersed in a low radio density matrix comparison of ct scan data with analytical sedimentary data and he proxies performed on the cores validates the ct scanning method as a powerful tool to improve correlations identify well constrained events and make more accurate basin reconstructions without opening all the cores in an oceanographic study

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

millennial scale oceanic climate variability off the western iberian margin during the last two glacial periods high resolution palaeoclimate records recovered from the iberian margin in core md95 2040 exhibit large fluctuations in oceanographic conditions over the last 190 ka large scale cooling of the surface ocean is indicated by the presence of the polar planktonic foraminifer neogloboquadrina pachyderma sinistral and in some instances the occurrence of ice rafted debris ird ice rafting episodes were prevalent in both of the last two glacials with greater intensity in stages 2 through 4 than in stage 6 the six youngest heinrich events are well defined during the last glacial but detrital carbonate is absent from heinrich layers hl6 hl5 and hl3 dansgaard oeschger stadial equivalent sub millennial ird deposition events have been detected in particular during stage 3 allowing a good match with the cooling displayed in the greenland ice core gisp2 sea surface temperature off portugal in stage 6 was in general warmer than during the last glacial pointing towards a weaker southward influence of polar water masses ice rafting occurred mainly in mid mis marine isotope stage 6 between 173 and 153 kyr as a group of poorly differentiated short duration quasi continuous events mainly marked by the high abundance of sinistral n pachyderma differences exist in ird composition relative to the last glacial with a reduced canadian derived detrital carbonate component combined with an important contribution of volcanic particles the lower magnitude and higher frequency of these events suggest that the higher temperatures would have induced iceberg waning closer to the source areas

phase relationship between sea level and abrupt climate change direct traces of past sea levels are based on the elevation of old coral reefs at times of sea level high stands however these measurements are discontinuous and cannot be easily correlated with climate records from ice cores in this study we show a new approach to recognizing the imprint of sea level changes in continuous sediment records taken from the continental slope at locations that were continuously submerged even during periods of sea level lowstand by using a sediment core precisely synchronized with greenland ice cores we were able to recognize major floods of the mediterranean continental shelf over the past 270 kyr during the last glacial period five flooding events were observed at the onset of the warmest greenland interstadials consistent correspondence between warm climate episodes and eustatic sea level rises shows that these global flooding events were generated by pronounced melting of the northern hemisphere ice sheets due to rapid intensification of atlantic meridional overturning circulation the method described in this study opens a new perspective for inter hemi spheric synchronization of marine climate records if applied in other continental margins from the southern hemisphere or the equatorial regions c 2009 elsevier ltd all rights reserved

the origin of heinrich layers evidence from h2 for european precursor events recent well dated isotopic sr nd fingerprinting of heinrich layer ice rafted detritus ird on the european margin indicates supply from european ice sheets as precursors to laurentide ice sheet lis supply f e grousset et al geology 28 2000 123 126 h snoeckx et al mar geol 158 1999 197 208 these precursorevents lead lis input by up to 1 5 ka f e grousset et al geology 28 2000 123 126 and have been interpreted to indicate lis collapse during heinrichevents stimulated by events originating on the european side of the atlantic f e grousset et al geology 28 2000 123 126 such phasing of ird supply from different sources within heinrich layers therefore has implications for the origin and mechanics of heinrichevents we present evidence here that the ird comprising heinrich layer 2 h2 20 21 14c ka bp on the european continental margin contains detrital campanian upper chalk deriving from bedrock sources eroded on the celtic shelf by the british ice sheet bis in addition to lithic material sourced from the lis high resolution radiocarbon chronology indicates chalk grain deposition as discrete pulses both before and coincident with supply of lis sourced detritus the specificity of the chalk fingerprint to the bis enables a 700 1000 yr lag between the bis and lis events to be identified this phasing indicates a more rapid response of the outlet lobes draining the smaller bis than those draining the lis and implicates external climatic forcing of heinrichevents it is unlikely that this precursorevent represents ird event 18 the recently identified 1 2 ka ird cycle event which immediately precedes h2 because the lag between precursor and main event is here less than 1 5 ka and because such pervasive periodicity is not apparent in european continental margin ird records the later synchroneity between the bis and lis input in h2 identifies glacio eustatic sea level rise associated with lis discharges as a possible feedback mechanism causing destabilisation of ice streams elsewhere during heinrichevents

a review of the physical oceanography of the mediterranean outflow abstract the physical oceanography of the mediterranean sea is reviewed with particular emphasis on the mediterranean outflow in the gulf of cadiz in this region the dense mediterranean water forms a high velocity bottom current that interacts strongly with the sea floor the major energy source for the plume comes from the release of potential energy as the plume descends the continental slope and the major energy sink is work against bottom stress which is as large as 4 pa where the plume begins to descend the continental slope in this region the current makes a nearly inertial turn that would otherwise appear to be steered by the underlying topography the mediterranean plume entrains the overlying north atlantic central water and thereby loses much of its density anomaly the mixed mediterranean water becomes neutrally buoyant in the lower portion of the north atlantic thermocline near cape st vincent there are then two preferred transport modes having somewhat different temperature and salinity whose distinct characteristics can be found far into the open north atlantic the temperature salinity and volume of the mediterranean water in the strait of gibraltar and in the gulf of cadiz appear to be roughly constant since modern measurements have been made the estimated westward transport of mediterranean water has gone down considerably as direct measurement techniques have been applied a recent estimate is that the westward transport of pure mediterranean water is only about a half a sv 1 sv 106 m3 s 1 the transport of mixed mediterranean water in the western gulf of cadiz is larger by about a factor of three or four because of the entrainment of north atlantic water

heinrich events massive late pleistocene detritus layers of the north atlantic and their global climate imprint 1 millennial climate oscillations of the glacial interval are interrupted by extreme events the so called heinrich events of the north atlantic their near global footprint is a testament to coherent interactions among earth s atmosphere oceans and cryosphere on millennial timescales heinrich detritus appears to have been derived from the region around hudson strait it was deposited over approximately 500 250 years several mechanisms have been proposed for the origin of the layers binge purge cycle of the laurentide ice sheet jokulhlaup activity from a hudson bay lake and an ice shelf buildup collapse fed by hudson strait to determine the origin of the heinrich events i recommend 1 further studies of the timing and duration of the events 2 further sedimentology study near the hudson strait and 3 greater spatial and temporal resolution studies of the layers as well as their precursory intervals studies of previous glacial intervals may also provide important constraints

winter dynamics on the northern portuguese shelf part 2 bottom boundary layers and sediment dispersal abstract the northern portuguese shelf between 41 n and 42 n is characterised by the presence of a mid shelf mud deposit the douro mud patch dmp observations conducted between july 1996 and june 1999 under the framework of project omex ii ii are used to examine the impact of the dynamic processes in the lower water column particularly on the dmp the typical wave conditions observed during the winter maintain a highly energetic environment capable of promoting the erosion of fine sediments at mid shelf depths however the bottom nepheloid layers generated beneath these waves only extend a few meters above the bottom and are contained within rocky outcrops with similar heights that fringe the outer shelf each year there are about ten storms mostly associated with southerly winds that create downwelling conditions over the shelf the waves associated with these storms produce shear velocities over 3 cm s at mid shelf and bottom nepheloid layers which extend a few tens of meters above the bottom and spread offshore over the outer shelf and upper slope a rough estimate suggests that these events account for an offshore export of about 20 10 6 kg of fine sediments each year equivalent to 1 2 of sediments trapped at dmp

distribution thickness and origin of heinrich layer 3 in the labrador sea abstract the presence of heinrich layer 3 hl 3 in the northwest labrador sea has been debated in the literature calypso giant piston core md99 2233 five new standard piston cores and re interpretation of 34 cores from previous cruises confirm the presence of hl 3 in the labrador sea it is identified by high total carbonate concentration up to 45 an increase in coarse fraction content and lighter 18o values in polar species planktonic foraminifer neogloboquadrina pachyderma left coiling as low as 3 1 the age of hl 3 of 27 ka was bracketed in the various cores by about 50 14c accelerator mass spectrometer dates where it is present in ice proximal regions it consists of nepheloid flow deposits at the base and mud turbidites at the top the thickness of hl 3 varies between 4 8 m proximal to hudson strait and 0 9 m distal decreasing rapidly seaward on the upper continental slope hl 3 was too deeply buried to be sampled elsewhere hl 3 is absent in some cores probably due to slumping or erosion associated with sandy turbidity currents or debris flows

zooming in on heinrich layers theories explaining the origin of the abrupt massive discharges of ice rafted detritus ird into the glacial north atlantic the heinrich layers hls generally point to the laurentide ice sheet as the sole source of these events until it was found that the irds also originated from icelandic and european ice sheets bond and lotti 1995 snoeckx et al 1999 grousset et al 2000 this apparent contradiction must be reconciled as it raises fundamental questions about the mechanism s of hl origin we have analyzed two 12 cm thick hls in an ultrahigh resolution mode 1 2 century intervals in a mid atlantic ridge piston core the 18o record n pachyderma left coiling reveals strong excursions induced by the melting of the icebergs these excursions are associated with a strong decrease in the amount of planktic foraminafersand with a 3 c cooling of the surface waters counts of coarse detrital grains reveal that ird are deposited according to a typical sequence 1 volcanic glass 2 quartz and feldspars 3 detrital carbonate that implies a chronology in the melting of the differentpan atlantic ice sheets sr and nd isotopic composition confirm that in both heinrich layers h1 and h2 precursor ird came from first europe iceland followed then by laurentide derived ird an internal cyclicity can be identified during h1 and h2 about four to six major abrupt discharges occurred roughly on a century timescale the 13c and 15n records reveal that dominant inputs of continent derived organic matter are associated with ird within the hls hiding the plankton productivity signal