undrained stress path of loose sand predicted from dry tests the constitutive properties of the soil skeleton of loose sand most relevant for predicting liquefaction flow slides are contraction and elastic compressibility they can be determined with dry triaxial tests a mathematical description of these idryi properties is presented and used to predict the specific stress path found in undrained triaxial tests a comparison between predicted and measured stress paths is discussed resume les propriotos de comportement du squelette de sable meuble les plus pertinentes pour prodire les couloes par liquofaction sont la contraction et la compessibilito olastique elles peuvent tre doterminoes par des essais triaxiaux secs une description mathomatique de ces propriotos sches est prosentoe et utilisoe pour prodire le cheminement de contraintes spocifique trouvo dans les essais triaxiaux une comparaison entre les cheminements mesuros et prodits est discutoe mots clos sable meuble liquofaction cheminement de contraintes non drainoes porosito mouilloe critique otat permanent traduit par la rodaction

triggering of liquefaction flow slides in coastal soil deposits abstract liquefaction flow slides have been observed in coastal soil deposits throughout the world the causes of many of these slides have never been well understood the materials involved in and circumstances surrounding eight reported liquefaction flow slides are reviewed and compared many of these slides have occurred in very similar materials shortly following small to moderate drawdowns of the adjacent water level liquefaction susceptibility of sands may be evaluated by steady state methods recent research indicates that liquefaction of loose sands similar to those typically involved in these slides may be triggered by very small changes in stress conditions if the sand is initially in equilibrium under high shear stresses the triggering of liquefaction may lead to flow sliding if the unbalanced driving stresses exceed the steady state strength of the liquefied soil elasticity methods are used to estimate the initial stress conditions in a gentle infinite slope and the effect of unloading due to drawdown it is shown that liquefaction flow slides in coastal soil deposits may be initiated by small to moderate drawdowns consistent with those observed in actual slides

antarctic marine temperatures late campanian through early paleocene an oxygen isotope paleotemperature study of benthic foraminifera from the upper campanian through lower paleocene section at seymour island near the coast of antarctica was done in conjunction with careful scanning electron microscope observations to monitor the state of foraminiferal preservation the isotopic compositions of those samples which were deemed to be well preserved were the basis of the conclusion that campanian through paleocene high latitude shelf waters near antarctica had temperatures between approximately 4 5 and 10 5 c temperatures during early and middle maastrichtian time were slightly higher than those of either the late campanian or late maastrichtian the inference of temperate climatic conditions in antarctica is in agreement with paleoclimatic conclusions drawn on the species composition of the planktonic foraminiferal assemblages and the character of the planktonic foraminifera as well as with published conclusions based upon paleobotanical evidence the maastrichtian and campanian water temperatures at seymour island are similar to those inferred from published isotope ratios of pacific late cretaceous benthic foraminifera from low latitudes indicating that campanian through early paleocene deep ocean waters at least in the pacific and perhaps elsewhere as well could have formed by sinking of surface waters in polar regions

did the rifting of the atlantic ocean cause the cretaceous thermal maximum the cretaceous thermal maximum was a major turning point in the history of earth s climate this interval of peak warmth in the turonian has been attributed to very high atmospheric pco2 resulting from rapid outgassing rates although crustal cycling rates peaked in the aptian albian interval on the basis of coupled ocean atmosphere model simulations of the middle cretaceous we hypothesize that the formation of an atlantic gateway could have contributed to the cretaceous thermal maximum differences between prerifting and postrifting climate experiments demonstrate substantial regional oceanographic changes in the north and south atlantic basins that are consistent with oxygen isotopic evidence used to infer a cretaceous thermal maximum the model results help reconcile the paleoclimate record inferred from foraminiferal d 18 o with our understanding of climate dynamics and cretaceous tectonism

location and probability of shoal margin collapses in a sandy estuary channel bank failure collapses of shoal margins and beaches due to flow slides have been recorded in dutch estuaries for the past 200 years but have hardly been recognized elsewhere current predictions lack forecasting capabilities because they were validated and calibrated for historic data of cross sections in specific systems allowing local hindcast rather than location and probability forecasting the objectives of this study are to investigate where on shoal margins collapses typically occur and what shoal margin collapse geometries and volumes are such that we can predict their occurrence we identified shoal margin collapses generally completely submerged from bathymetry data by analyzing dems of difference dod of the western scheldt for the period 1959 2015 we used the bathymetry data to determine the conditions for occurrence specifically to obtain slope height and angle and applied these variables in a shoal margin collapse predictor we found 299 collapses along 300 km of shoal margin boundaries over 56 years meaning more than 5 collapses occur on average per year the average shoal margin collapse body is well approximated by a 1 3 ellipsoid shape covers on average an area of 34 000 m2 and has an average volume of 100 000 m3 shoal margin collapses occur mainly at locations where shoals take up a proportionally larger area than average in the cross section of the entire estuary and occur most frequently where lateral shoal margin displacement is low a receiver operating characteristic curve shows that the forecasting method predicts the shoal margin collapse location well we conclude that the locations of the shoal margin collapses are well predicted by the variation in conditions of the relative slope height and angle within the western scheldt and likely locations are at laterally relatively stable shoal margins this provides hypotheses aiding the recognition of these features in sandy estuaries worldwide

the importance of breaching as a mechanism of subaqueous slope failure in fine sand large bank failures comprising up to 10 6 m 3 of sediment are common features along steep channel banks in estuaries and large rivers that consist of clean fine sands and are mostly assumed to be generated by sudden liquefaction of large masses of very loosely packed sand another less commonly recognized type of failure is manifested by the gradual retrogression of a very steep wall steeper than the angle of repose instead of the voluminous surging plastic sediment water flow or hyperconcentrated density flow sensu mulder alexander 2001 generated by liquefaction this type of failure known as breaching by dredging companies and hydraulic engineers produces a sustained quasi steady turbidity current to date sedimentologists have not recognized the process of breaching as such in this paper it is suggested that breaching may be the origin of many thick massive sand layers known from ancient deposits from various environments notably in some turbidite successions possible differences in the sedimentary structure of the deposits produced by breach failures vs liquefaction slope failures liquefaction flow slides can be deduced from a knowledge of the sediment transport processes initiated by the failure a field study is presented on some poorly structured beds in the eocene vlierzele sands in belgium which are supposed to have originated from liquefaction failures but are reinterpreted to be the products of breaching it is postulated that the local steep slope disturbance required to initiate an active breach can be produced by a small liquefaction slope failure liquefaction flow slide failure or local erosion by river or tidal channel flow at the initial stage of the failure event

paleobotanical evidence for cool north polar climates in middle cretaceous albian cenomanian time mid cretaceous albian cenomanian floras are abundant and diverse on the north slope of alaska the older floras consist of conifers cycadophytes ferns ginkgophytes and sphenophytes horsetails angiosperms appeared in latest albian time and rapidly diversified the preserved floras consist entirely of deciduous plants with the exception of a microphyllous conifer ferns and sphenophytes deciduousness is evidence for strong seasonality which for these floras might be variations in either light or temperature or both cool temperatures are suggested by the prevalence of toothed leaves among the angiosperms and the presence of large leaved conifers the paleobotanical evidence points to a mid cretaceous climate that was no warmer than cool temperate on the north slope of alaska

state boundary surface for very loose sand and its practical implications a state boundary surface defines a boundary in stress void ratio space above which no stress state can exist the applicability of the state boundary surface for sand has not gained widespread attention primarily because sand is not generally considered to be a difficult soil from a design point of view apart from liquefaction liquefaction is a phenomenon usually encountered in very loose cohesionless materials an experimental study relating the drained and undrained behavior of very loose saturated sand is presented it is shown that the post peak portion of undrained stress paths travels along the state boundary and that the state boundary can be approximated by a straight line the slope of this straight line appears to stay constant for very loose sand there are potentially an infinite number of these lines which form a three dimensional surface in deviator stress effective mean normal stress void ratio space previously published results by various researchers are used to confirm the existe

flow slide prediction method influence of slope geometry a quasi two dimensional method is presented for predicting liquefaction flow slides in a slope with saturated loose sand the initial stresses at the start of the actual flow slide process are predicted assuming completely drained conditions during the gradual change in slope geometry caused by erosion or sedimentation the condition for a flow slide is considered to be the presence of at least one sand element in a metastable stress state i e a state in which the undrained response to any quick change in load however small it may be consists of a sudden large increase in pore pressure the metastability of any sand element is predicted as a function of its constitutive properties its location in the slope and the slope geometry the constitutive properties are derived from dry triaxial tests and basically describe the liquefiability brittleness of the sand the metastability criterion for a soil element in a slope is different from that under triaxial loading flow slides observed in large scale

strength of undisturbed versus reconstituted silt and silty sand specimens the differences in undrained stress strain strength behavior between undisturbed and reconstituted silt and silty sand specimens tested at the same void ratio and initial stress state may be dramatic in all tests reported herein the undisturbed specimens showed dilative and ductile behavior whereas in all but a very few cases the accompanying reconstituted specimens at the same or lower density showed contraction much lower undrained strength and brittle behavior the test series included samples from a natural fluvial silt deposit as well as from silty sand hydraulically placed in a tailings dam when reconstituting specimens for laboratory testing it is not sufficient to only satisfy the criteria of correct density and grain size distribution but somehow the same fabric also must be reproduced otherwise deformation and stability analyses based on the results of reconstituted specimens or on in situ tests calibrated against such results may be misleading most of the reconstituted specimens

the liquefaction of sands a collapse surface approach recent large scale slides occurring during the hydraulic placement of an artificial island berm in the beaufort sea resulted from the liquefaction of the berm sand subsequent laboratory tests and

a crossbeam co ordinate caliper for the morphometric analysis of lithic nuclei a description test and empirical examples of application over the last four decades there has been surprisingly little advance in the quantitative morphometric analysis of palaeolithic stone tools especially compared to that which has taken place in biological morphometrics over a comparable time frame in palaeolithic archaeology s sister discipline of palaeoanthropology detailed quantitative morphometric geometric morphometric and even 3d geometric morphometric analyses are now seen almost as routine this period of relative methodological stasis may have been influenced by the lack of homologous landmarks on many lithic tools essential for any comparative analysis especially core based technologies of the lower palaeolithic archaeological field conditions may also prohibit the use of expensive and delicate precision instruments in certain cases here we present a crossbeam co ordinate caliper that e crucially e both geometrically locates and measures distances between morphologically homologous landmarks upon lithic nuclei via a single protocol intra and inter observer error tests provide evidence that error levels associated with the instrument fall within acceptable ranges in addition we present empirical examples of application in the form of a multivariate analysis of 55 discrete morphometric variables and a 3d geometric morphometric analysis of co ordinate landmark configurations derived from pleistocene lithic nuclei i e cores sensu lato we also introduce to lithic studies some techniques for the study of shape variation that have previously been used with success in biological morphometric analyses we conclude that use of an instrument such as the crossbeam co ordinate caliper may provide a useful adjunct to traditional techniques of lithic analysis particularly in developing a quantitative morphometric approach 2005 elsevier ltd all rights reserved

paleogeographic and tectonic evolution of southern tibet since middle cretaceous time new paleomagnetic data and synthesis during the second french chinese paleomagnetic campaign in tibet in the summer of 1981 we sampled the middle cretaceous red beds of the takena formation and the cenozoic volcanics of the lingzizong formation a detailed analysis of about 400 specimens of red beds reveals a stable component of normal magnetization n in the north of the lhasa block north of the nyainqentanglha range and two stable components in the south lt ht where the red beds are more strongly folded and are unconformably overlain by the lingzizong volcanics all three components are carried by hematite blocking temperatures range from 400 to 600 c for lt and up to the neel temperature of hematite for both n and ht lt is shown to postdate part of the folding of the takena whereas n and ht both indicate a positive fold test at the 99 probability level in addition a small less than 10 of the natural remanent magnetization antiparallel component is superimposed in most samples and may be consistent with a model of long term acquisition of a chemical remanent magnetization for the red beds analysis of the volcanics reveals a single stable component with mixed polarities carried either by hematite or magnetite the paleomagnetic directions indicate that 1 the lhasa block stood at 12 5 3 n by upper cretaceous and at 13 5 6 5 n in the paleocene eocene thus confirming the limited displacement of the margin of eurasia between albian aptian deposition of the red beds and eocene onset of the india asia collision these values imply crustal shortening by as much as 1900 850 km north of the block since the upper cretaceous and by 1400 1200 km south of the block since the onset of the collision 2 southern tibet formed a single tectonic unit by middle cretaceous time and 3 differential rotations are observed within the block and are related to the collision these rotations are discussed in the frame of a recent propagating extrusion tectonics model this study confirms the close paleogeographic relationship between indochina khorat plateau and southern tibet prior to the india asia collision

critical density of sand although hardly used in theoretical soil mechanics nowadays critical density still is an important parameter in cases where the flow slide susceptibility of sand deposits has to be investigated in this paper two types of triaxial tests in which the critical porosity of sand is measured are described during the first type of test on dry sand the volume change is measured in the second type of test undrained and stress controlled on saturated sand the sudden collapse and liquefaction of the loose samples is observed the results of the two tests are related to each other by means of calculations and a more safe criterion is derived in the wet critical porosity the unsafe influences of membrane penetration and of insufficient saturation are removed with this method the sudden failure and liquefaction of saturated samples under stress controlled but completely drained conditions could be explained quoique rarement utilisee a l heure actuelle dans les travaux theoriques relatifs a la mecanique du

did the indo asian collision alone create the tibetan plateau it is widely believed that the tibetan plateau is a late cenozoic feature produced by the indo asian collision however because tibet was the locus of continental accretion and subduction throughout the mesozoic crustal thickening during that time may also have contributed to growth of the plateau this portion of the geologic history was investigated in a traverse through the central lhasa block southern tibet together with earlier studies our mapping and geochronological results show that the lhasa block underwent little north south shortening during the cenozoic rather our mapping shows that 60 crustal shortening perhaps due to the collision between the lhasa and qiangtang blocks occurred during the early cretaceous this observation implies that a significant portion of southern tibet was raised to perhaps 3 4 km elevation prior to the indo asian collision

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

impacts of palaeogeography and sea level changes on mid cretaceous climate climate is often depicted as globally warm during the middle part of the cretaceous however major tectonic events such as the break up of gondwana or sea level changes inducing the flooding of vast continental areas occurred from 120 to 95 ma resulting in drastic climatic re organisations in order to investigate the impact of plate tectonics and sea level change on climate we performed climatic simulations during the cenomanian 95 ma and aptian 120 ma using an atmospheric general circulation model problems with models lie in our knowledge of a few key factors for examples the middle cretaceous sea surface temperature gradient from equator to pole remains an open question and it is not clear yet how flat it was two sensitivity experiments for each period prescribing a flatter sst gradient based on oxygen isotopic data have been done in order to test its climatic consequences we discuss separately the effect of palaeogeography and meridional sst gradient impacts in the northern hemisphere the flooding of large continental areas due to sea level rise leads to a more equable climate in the mid latitudes however the impact of epicontinental seas varies seasonally from site to site due to local feedbacks in the southern hemisphere the breakup of gondwana deeply affects the climate of this region moderating the seasonal thermal variations in addition we test the impact of a flatter sst gradient on climate and we show that simulations with flat sst gradients compare well with field data we analyse the remaining model data discrepancies in terms of missing feedbacks co2 vegetation but also of new measurements that enable to infer a better meridional variation of sea surface temperature

flow slides in the netherlands experience and engineering practice this paper deals with flow slide experience in the netherlands it gives an extensive survey of empirical field data concerning the geological characteristics of the region the profiles just before the flow slides and the damage that flow slides can cause the traditional dutch procedure for analyzing the flow slide potential of underwater sand slopes is described this is an engineering approach that is mainly based on the empirical field data together with geological surveys and soil investigations performed at the relevant site key words sand collapse flow slides liquefaction slope stability

palaeobiogeography of the early cretaceous corals abstract a compilation of the geographical distribution of about 1000 species of corals from the early cretaceous valanginian to cenomanian is presented after the reefal regression during the latest jurassic no corals appear in the berriasian and only a few species are known from the valanginian and hauterivian in many regions it is impossible to distinguish pre barremian stages many of the pre barremian corals reported are hauterivian in age the pre barremian displays an explosion of the scleractinia more than 300 species extended through europe africa and north and south america during the aptian and albian coral distribution was about the same as during the pre barremian but during the albian the number of species decreased and the proportion of ahermatypic forms increased because of pronounced endemism during the albian faunal similarity no longer existed between the americas and europe during the cenomanian the madreporaria nearly disappeared from north america but were still well represented in europe half of the known cenomanian coral species are ahermatypic and they appear to be distributed on the two sides of the hermatypic buildup along the tethyan realm

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

low latitude sea surface temperatures for the mid cretaceous and the evolution of planktic foraminifera isotopic data from exceptionally well preserved foraminifera show that the subtropical north atlantic had sea surface temperatures ssts between 30 and 31 c during the late albian and early cenomanian these temperatures were warmer than average modern temperatures in the tropical western atlantic and support previous inferences based on diagenetically suspect material of albian tropical ssts of 30 c this finding is consistent with basic theories of oceanic thermal response in the tropics to the high atmospheric carbon dioxide levels during the middle cretaceous greenhouse however our data do not support the concept of a super tethyan region of hypersaline waters in the western north atlantic during late albian and early cenomanian time because seawater salinities substantially higher than modern ones would require significantly higher ssts than those reported here isotopic analysis of mid cretaceous planktic foraminifera shows that planomalina ticinella and biticinella grew in surface waters and provide isotopic proxies for sst whereas deeper growing species include hedbergella rotalipora and praeglobotruncana none of these taxa display isotopic indications of photosymbiosis suggesting that this ecology did not evolve in planktic foraminifera before the late cretaceous contrary to previous hypotheses none of these species increased their depth habitat during their life cycles unlike many extant planktic foraminifera the rotaliporids may have been preferentially susceptible to extinction during oceanic anoxic events because they lived within or below the thermocline for most of their life cycles

thermal evolution of cretaceous tethyan marine waters inferred from oxygen isotope composition of fish tooth enamels 1 the evolution of subtropical 30 35 n upper ocean temperatures through the cretaceous is inferred from the oxygen isotope compositions of 64 fish teeth enamel coming from the western tethyan platform mean 18o values of 22 at the berriasian valanginian boundary decrease with oscillations to 18 5 around the cenomanian turonian boundary and progressively increase to 21 5 by the end of the cretaceous the similarity of this oxygen isotope curve for bioapatites from platform environments with those for foraminifera and bulk carbonates that were deposited in deeper waters and at other paleolatitudes indicates that they record global climatic signals major cooling events at the million year scale can be distinguished 1 at the berriasian valanginian boundary and 2 during the earliest late valanginian a third cooling event is detected during the earliest aptian these events already proposed as icehouse interludes during the lower cretaceous are also recorded at subtropical latitudes a progressive warming is identified from the aptian to the cenomanian turonian interval that corresponds to a thermal optimum and then upper ocean temperatures decreased to the maastrichtian minimum isotopic temperatures range from 15 c to 28 c assuming a 18oseawater of 1 for an ice free world taking more realistic 18oseawater values of 0 for tropical waters during glacial periods within the berriasian valanginian interval and earliest aptian or with above average salinities possibly the maastrichtian temperatures are increased by 4 5 c temperature differences between climatic extremes of the valanginian and cenomanian turonian are estimated to have been 10 c latitudinal thermal gradients for the albian cenomanian turonian and maastrichtian were 0 2 0 3 c latitude and thus weaker than modern oceanic values at about 0 4 c latitude

evidence for glacial control of rapid sea level changes in the early cretaceous lower cretaceous bulk carbonate from deep sea sediments records sudden inputs of strontium resulting from the exposure of continental shelves strontium data from an interval spanning 7 million years in the berriasian valanginian imply that global sea level fluctuated about 50 meters over time scales of 200 000 to 500 000 years which is in agreement with the exxon sea level curve oxygen isotope measurements indicate that the growth of continental ice sheets caused these rapid sea level changes if glaciation caused all the rapid sea level changes in the cretaceous that are indicated by the exxon curve then an antarctic ice sheet may have existed despite overall climatic warmth

late cretaceous chronology of large rapid sea level changes glacioeustasy during the greenhouse world we provide a record of global sea level eustatic variations of the late cretaceous 99 65 ma greenhouse world ocean drilling program leg 174ax provided a record of 11 14 upper cretaceous sequences in the new jersey coastal plain that were dated by in tegrating sr isotopic stratigraphy and biostratigraphy backstripping yielded a late cre taceous eustatic estimate for these sequences taking into account sediment loading com paction paleowater depth and basin subsidence we show that late cretaceous sea level changes were large 25 m and rapid k1 m y suggesting a glacioeustatic control three large d 18 o increases are linked to sequence boundaries others lack sufficient d 18 o data consistent with a glacioeustatic cause and with the development of small 10 6 km 3 ephemeral ice sheets in antarctica our sequence boundaries correlate with sea level falls recorded by exxon production research and sections from northwest europe and russia indicating a global cause although the exxon record differs from backstripped estimates in amplitude and shape