early diageneitc isotopic signal at the cretaceous tertiary boundary israel abstract carbon and oxygen isotope records from carbonate fractions in marls overlying the k t boundary in southern israel are used to interpret paleoenvironmental changes and the history of early diagenetic events in the earliest tertiary the 13c record of the whole rock does not significantly depart from the original values and reflects the global productivity drop shortly after the k t boundary and the subsequent recovery fine fraction oxygen isotope values reflect the addition of carbonate cement highly depleted in 18o throughout the profile the 18o record demonstrates two main episodes in which contact with fresh water affected the sediments one is below a short hiatus at planktic foraminiferal subzone transition po p1a guembelitria cretacea parvularugoglobigerina eugubina and the other at an pyrite rich clay layer near the top to planktic foraminiferal subzone p1b globigerina taurica the latter event suggests introduction of sapropelic bottom conditions in the oceanic paleoenvironment

multiple impacts across the cretaceous tertiary boundary abstract the stratigraphy and age of altered impact glass microtektites microkrystites ejecta layers from the chicxulub crater are documented in late maastrichtian and early danian sediments in mexico guatemala belize and haiti in northeastern mexico two to four ejecta layers are present in zone cf1 which spans the last 300 ky of the maastrichtian the oldest ejecta layer is dated at 65 27 0 03 ma based on sediment accumulation rates and extrapolated magnetostratigraphy all younger ejecta layers from the maastrichtian and early danian parvularugoglobigerina eugubina zone pla l may represent repeated episodes of reworking of the oldest layer at times of sea level changes and tectonic activity the k t boundary impact event 65 0 ma is not well represented in this area due to widespread erosion an early danian pla l ir anomaly is present in five localities bochil actela coxquihui trinitaria and haiti and is tentatively identified as a third impact event at about 64 9 ma a multiimpact scenario is most consistent with the impact ejecta evidence the first impact is associated with major deccan volcanism and likely contributed to the rapid global warming of 3 4 c in intermediate waters between 65 4 and 65 2 ma decrease in primary productivity and onset of terminal decline in planktic foraminiferal populations the k t boundary impact marks a major drop in primary productivity and the extinction of all tropical and subtropical species the early danian impact may have contributed to the delayed recovery in productivity and evolutionary diversity

secondary flow deflection in the lee of transverse dunes with implications for dune morphodynamics and migration measurements of lee side airflow response from an extensive array of meteorological instruments combined with smoke and flow streamer visualization is used to examine the development and morphodynamic significance of the lee side separation vortex over closely spaced transverse dune ridges a differential deflection mechanism is presented that explains the three dimensional pattern of lee side airflow structure for a variety of incident flow angles these flow patterns produce reversed along dune and deflected surface flow vectors in the lee that are inferred to result in net lateral diversion of sand transport over one dune wavelength for incident angles as small as 10 from crest transverse i e 80 from the crest line this lateral displacement increases markedly with incident flow angle when expressed as the absolute value of the total deflection in degrees reversed and multi directional flow occurs for incident angles between 90 and 50 these results document the three dimensional nature of flow and sand transport over transverse dunes and provide empirical evidence for an oblique migration model copyright 2013 john wiley sons ltd

the cretaceous tertiary boundary transition in the antarctic ocean and its global implications abstract three antarctic ocean k t boundary sequences from odp site 738c on the kerguelen plateau odp site 752b on broken ridge and odp site 690c on maud rise weddell sea have been analyzed for stratigraphic completeness and faunal turnover based on quantitative planktic foraminiferal studies results show that site 738c which has a laminated clay layer spanning the k t boundary is biostratigraphically complete with the earliest tertiary zones p0 and p1a present but with short intrazonal hiatuses site 752b may be biostratigraphically complete and site 690c has a hiatus at the k t boundary with zones p0 and p1a missing latest cretaceous to earliest tertiary planktic foraminiferal faunas from the antarctic ocean are cosmopolitan and similar to coeval faunas dominating in low middle and northern high latitudes although a few endemic species are present this allows application of the current low and middle latitude zonation to antarctic k t boundary sequences the most abundant endemic species is chiloguembelina waiparaensis which was believed to have evolved in the early tertiary but which apparently evolved as early as chron 30n at site 738c since this species is only rare in sediments of site 690c in the weddell sea this suggests that a watermass oceanographic barrier may have existed between the indian and atlantic antarctic oceans the cosmopolitan nature of the dominant fauna began during the last 200 000 to 300 000 years of the cretaceous and continued at least 300 000 years into the tertiary this indicates a long term environmental crisis that led to gradual elimination of specialized forms and takeover by generalists tolerant of wide ranging temperature oxygen salinity and nutrient conditions a few thousand years before the k t boundary these generalists gradually declined in abundance and species became generally dwarfed due to increased environmental stress there is no evidence of a sudden mass killing of the cretaceous fauna associated with a bolide impact at the k t boundary instead the already declining cretaceous taxa gradually disappear in the early danian and the opportunistic survivor taxa ch waiparaensis and guembelitria cretacea increase in relative abundance coincident with the evolution of the first new tertiary species

paleoenvironmental changes across the cretaceous tertiary boundary at koshak kazakhstan based on planktic foraminifera and clay mineralogy abstract the koshak section of the mangyshlack peninsula kazakhstan is one of the most complete cretaceous tertiary k t transitions known from the boreal paratethys cretaceous species richness is low 11 to 13 species except for a peak of 20 species near the k t boundary in the uppermost maastrichtian top 50 cm that represents the temporary incursion of low latitude taxa this maximum species richness occurred during climatic warming associated with increased humidity as suggested by clay mineral analyses biofacies analysis suggests external platform conditions at this time followed by a more humid climate a sea level transgression and deepening basinal facies in the lower danian subzone p1a shallower platform conditions resumed in danian subzones p1b and p1c accompanied by a cooler and probably more arid climate no abrupt mass extinction occurred at the koshak k t boundary which is marked by an ir anomaly a clay layer and the first appearance of tertiary planktic foraminifera the influx of lower latitude species ends at or before the k t boundary whereas the majority of the indigenous cretaceous assemblage survived into the danian these data suggest that long term climatic changes may have been the principal factors in the progressive demise of the cretaceous planktic foraminifera in the eastern boreal paratethys

elongation and migration of sand dunes two distinct processes are known to act on dynamic dunes the process of migration by erosion on the windward side and deposition on the lee side typical for transverse dunes and the process of elongation typical for linear dunes these two processes are determined by wind direction relative to the dune alignment this article reviews the assertion that linear dunes experience lateral displacement in addition to elongation fieldwork on vegetated linear dunes vlds and gis work on seif dunes indicates no lateral migration for these dunes linear dunes can shift laterally only when a slip face formed on the lee side reaches the plinth of the dune the winds from both sides of the seif dune are never symmetric usually winds from one direction are more dominant and effective the outcome is the formation of peaks and saddles along the dune the strongest winds create a slip face on the lee side of the peak segments of the dune oblique to the dune alignment which reaches the base of the dune and displaces the peak downwind along the dune alignment the internal structure of the seif dune is formed mostly by this dominant wind direction and gives the impression that the dune has shifted laterally on the other hand there are cases in which the wind directions relative to dune alignment fall between those of transverse and seif dunes in such cases both processes act on the dune which subsequently experiences migration as well as elongation

storm controlled oblique dunes of the oregon coast discussion and reply no abstract available the article discussed appeared in the bulletin v 94 p 1450 1465

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

physical modelling of rainfall and snowmelt induced erosion of stony slope underlain by permafrost physical modelling experiments have been carried out in a cold room to test on a small scale the effects of water supply during the thaw of an experimental slope with permafrost permafrost was maintained at depth and a thin active layer was frozen and thawed from the surface data from the experiments relate to two different conditions first with moderate rainfall and second with heavy rainfall during the thaw period when moderate rainfall is applied during thaw phases the experimental slope is slightly degraded at the scale of the experiment erosion processes involve frost jacking of the coarse blocks frost creep and gelifluction that induce slow and gradual down slope displacements of the active layer but also small landslides leading to large but slow mass movements with short displacements changes in experimental slope morphology are marked by the initiation of a small scale drainage network and the development of a little crest line which shows a progressive upslope migration with such boundary conditions there is not enough water supply to evacuate downslope the whole of the eroded material and a topographic smoothing is observed when heavy rainfall is applied during thaw periods rapid mass wasting small mud flows and debris flows become prominent slope failures are largely controlled by the water saturation of the active layer and by the occurrence of steeper slopes at the scale of the experiment rates of erosion and maximum incision increase by about 100 leading to significant slope degradation with marked and specific scars comparable to gullying these morphological changes are dependant on both the size and the frequency of catastrophic events these experiments provide detailed data that could improve the knowledge of the physical parameters that control the initiation at a small scale of erosion processes on periglacial slopes with a thin active layer and or with thin cover of mobilizable slope deposits copyright 2010 john wiley sons ltd

age and paleoenvironment of the maastrichtian to paleocene of the mahajanga basin madagascar a multidisciplinary approach abstract lithology geochemistry stable isotopes and integrated high resolution biostratigraphy of the berivotra and amboanio sections provide new insights into the age faunal turnovers climate sea level and environmental changes of the maastrichtian to early paleocene of the mahajanga basin of madagascar in the berivotra type area the dinosaur rich fluvial lowland sediments of the anembalemba member prevailed into the earliest maastrichtian these are overlain by marginal marine and near shore clastics that deepen upwards to hemipelagic middle neritic marls by 69 6 ma accompanied by arid to seasonally cool temperate climates through the early and late maastrichtian an unconformity between the berivotra formation and betsiboka limestone marks the k t boundary and juxtaposes early danian zone plc or pld and latest maastrichtian zones cf2 cf1 micula prinsii sediments seasonally humid warm climates began near the end of the maastrichtian and prevailed into the early danian accompanied by increased volcanic activity during the late danian zones p1d p2 a change to seasonally arid climates was accompanied by deepening from middle to outer neritic depths

bedrock fracture by ice segregation in cold regions the volumetric expansion of freezing pore water is widely assumed to be a major cause of rock fracture in cold humid regions data from experiments simulating natural freezing regimes indicate that bedrock fracture results instead from ice segregation fracture depth and timing are also numerically simulated by coupling heat and mass transfer with a fracture model the depth and geometry of fractures match those in arctic permafrost and ice age weathering profiles this agreement supports a conceptual model in which ice segregation in near surface permafrost leads progressively to rock fracture and heave whereas permafrost degradation leads episodically to melt of segregated ice and rock settlement

benthic foraminiferal turnover across the cretaceous paleogene boundary at agost southeastern spain paleoenvironmental inferences abstract we studied upper cretaceous and lower paleogene benthic foraminifera from the agost section southeastern spain to infer paleobathymetrical changes and paleoenvironmental turnover across the cretaceous paleogene k p transition benthic foraminifera indicate uppermost bathyal depths at agost during the abathomphalus mayaroensis biochron from about 400 kyr before the k p boundary through the early plummerita hantkeninoides biochron about 120 150 kyr before that boundary the depth increased to middle bathyal for the remainder of the cretaceous and remained so for the danian part of the studied section parasubbotina pseudobulloides biochron at least 200 kyr after the k p boundary there were no perceivable bathymetrical changes at the k p boundary where 5 of the species became extinct and the species composition of the benthic foraminiferal fauna changed considerably below the boundary infaunal morphogroups constitute up to 65 73 of the faunas directly above the boundary in the black clays of the lower guembelitria cretacea biozone benthic foraminifera are rare several opportunistic taxa e g the agglutinant haplophragmoides sp have short peaks in relative abundance possibly reflecting low oxygen conditions as well as environmental instability with benthos receiving food from short lived local blooms of primary producers above the clays through the end of the studied interval epifaunal morphogroups dominate up to 70 of the assemblages or there is an even mixture or epifaunal and infaunal morphogroups infaunal groups do not recover to pre extinction relative abundances indicating that the food supply to the benthos did not recover fully over the studied interval about 200 kyr after the k p boundary the benthic foraminiferal faunal changes are compatible with the direct and indirect effects of an asteroid impact which severely destabilized primary producers and the oceanic food web that was dependent upon them

stable isotope toc and caco3 record across the cretaceous tertiary boundary at el kef tunisia we report the results of stable oxygen and carbon isotope analysis of carbonate fine fraction and benthic and planktic foraminifers caco3 and toc determinations of sediments across the cretaceous tertiary k t boundary at el kef tunisia we used grain size analysis of the fine fraction carbonate to determine possible compositional effects and smearslide and scanning electron microscope examinations to evaluate possible diagenetic alteration and microfossil preservation the data suggests the following sequence of events upper maastrichtian oxygen and carbon isotope signals indicate relatively warm temperatures a decreasing thermal gradient possibly related to a shallowing sea and relatively high surface water productivity a sharp cooling appears to begin just below the k t boundary the k t boundary is characterized by a sudden 2 negative shift in fine fraction 13c a slight 0 6 enrichment in benthic 13c and a reduction of about 40 in caco3 sedimentation these data imply strongly reduced surface water productivity as also observed in numerous deep sea sequences worldwide the lower danian planktic foraminiferal zones p0 p1a is marked by generally low productivity and unstable environmental conditions as indicated by generally low but fluctuating fine fraction 13c values and low 5 15 carbonate deposition at the base of subzone p1b caco3 benthic and fine fraction 13c values increase gradually and reach near pre k t boundary levels in subzone p1c indicating initial recovery after the k t boundary event about 300 000 400 000 years after the k t boundary the prolonged low productivity episode after the k t crisis and the pre k t boundary cooling associated with a major reduction in planktic foraminiferal diversity are difficult to explain by a single k t boundary bolide impact

new links between the chicxulub impact structure and the cretaceous tertiary boundary the 200 km diameter chicxulub structure1 3 in northern yucatan mexico has emerged as the prime candidate for the cretaceous tertiary k t boundary impact crater3 6 concentric geophysical anomalies associated with enigmatic occurrences of upper cretaceous breccias and andesitic rocks led penfield and camargo1 to suspect that this structure was a buried impact basin more recently the discovery of shocked quartz grains in a chicxulub breccia3 and chemical similarities between chicxulub rocks and k t tektite like glasses3 6 have been advanced as evidence that the chicxulub structure is a k t impact site here we present evidence from core samples that chicxulub is indeed a k t source crater and can apparently account for all the evidence of impact distributed globally at the k t boundary without the need for simultaneous multiple impacts or comet showers shocked breccia clasts found in the cores are similar to shocked lithic fragments found worldwide in the k t boundary ejecta layer7 8 the chicxulub melt rocks that we studied contain anomalously high levels of iridium up to 13 5 parts per 109 also consistent with the iridium enriched k t boundary layer9 our best estimate of the crystallization age of these melt rocks as determined by 40ar 39ar analyses is 65 2 0 4 1 myr in good agreement with the mean plateau age of 64 98 0 05 myr recently reported10 furthermore these melt rocks acquired a remanent magnetization indicating that they cooled during an episode of reversed geomagnetic polarity the only such episode consistent with40ar 39ar constraints is chron 29r which includes the k t boundary

guembelitria dominated late maastrichtian planktic foraminiferal assemblages mimic early danian in central egypt abstract during the late maastrichtian 66 8 65 5 ma the asyut basin in central egypt experienced a breakdown of the surface to bottom gradient of the 13c 12c ratio with planktic 13c values 0 2 0 8 lighter than benthic values planktic foraminiferal species diversity was reduced by more than 50 with assemblages dominated 60 90 by the opportunistic blooms of the disaster species guembelitria cretacea which mimic the early danian the prolonged breakdown in productivity occurred during a time of tectonic activity and increased terrestrial runoff that may have resulted in highly eutrophic waters coupled with a sea level regression 65 5 ma that led to restricted circulation increased productivity during the short climate warming between 65 4 and 65 2 ma is associated with increased species diversity abundant rugoglobigerinids and common heterohelicids at the end of the maastrichtian decreased productivity coincided with the k t impact and mass extinction followed by characteristically early danian low diversity assemblages the similarity of the late maastrichtian and post k t impact guembelitria dominated assemblages reveals that the planktic foraminiferal response to the k t catastrophe was not unique but followed a predictable pattern of response to severe environmental perturbations

gelifluction viscous flow or plastic creep this paper reports results from two scaled centrifuge modelling experiments designed to simulate thaw related gelifluction a planar 12 prototype slope was modelled in each experiment using the same natural fine sandy silt soil however two different scales were used in experiment 1 the model scale was 1 10 tested in the centrifuge at 10 gravities g and in experiment 2 the scale was 1 30 tested at 30 g centrifuge scaling laws indicate that the time scaling factor for thaw consolidation between model and prototype is n2 where n is the number of gravities under which the model was tested however the equivalent time scaling for viscous flow is 1 1 if gelifluction is a viscosity controlled flow process scaling conflicts will therefore arise during centrifuge modelling of thawing slopes and rates of displacement will not scale accurately to the prototype if however no such scaling conflicts are observed we may conclude that gelifluction is not controlled by viscosity but rather by elasto plastic soil deformation in which frictional shear strength depends on effective stress itself a function of the thaw consolidation process models were saturated consolidated and frozen from the surface downwards on the laboratory floor the frozen models were then placed in the geotechnical centrifuge and thawed from the surface down each model was subjected to four freeze thaw cycles soil temperatures and pore water pressures were monitored and frost heave thaw settlement and downslope displacements measured pore water pressures displacement rates and displacement profiles reflecting accumulated shear strain were all similar at the two model scales and volumetric soil transport per freeze thaw cycle when scaled to prototype were virtually identical displacement rates and profiles were also similar to those observed in earlier full scale laboratory floor experiments it is concluded therefore that the modelled gelifluction was not a time dependent viscosity controlled flow phenomenon but rather elasto plastic in nature a first approximation flow law is proposed based on the cam clay constitutive model for soils

mass failure of the north atlantic margin triggered by the cretaceous paleogene bolide impact the 65 ma chicxulub impact is known to have triggered large submarine slope failures near the crater in the gulf of mexico and caribbean here we show that the impact also precipitated massive submarine failure of the continental margin around the western north atlantic we have identified mass flow deposits containing impact ejecta of cretaceous paleogene boundary age in two deep sea cores more than 700 km from the continental margin the mass flows must have originated from the continental margin because they contain microfossils typical of shallow water environments and sedimentary features indicative of deposition by gravity currents geophysical data suggest that the mass wasting deposits may be present over the entire western north atlantic from puerto rico to the grand banks of canada and that much of the eastern margin of north america catastrophically failed during the cretaceous paleogene impact

stable isotope and foraminiferal changes across the cretaceous tertiary boundary at stevns klint denmark arguments for long term oceanic instability before and after bolide impact event abstract stable isotope and planktic and benthic foraminiferal analyses of the k t boundary transition at stevens klint denmark indicate a 100 500 kyr long period of instability in oceanic bottom water temperature and sea level during the latest maastrichtian from 2 7 m below and up to the k t boundary bottom water temperatures gradually cooled about 1 5 c as surface water temperatures remained constant at the k t boundary bottom water temperatures decreased additionally 3 c and then returned to pre boundary values just above the boundary interval coincident with the onset of the first temperature decrease there was a prominent sea level fall estimated between 50 100 m as observed in benthic and planktic foraminiferal assemblages as well as in a decreasing surface to bottom 13 c gradient about 40 cm below the iridium rich k t boundary clay sea level began to rise poor preservation of foraminifera above the k t boundary allows only tentative interpretation of danian events at stevns klint however sea level generally continued to rise interrupted by short sea level falls associated with the observed sea level changes are three important hiatuses at the contact between the white chalk and overlying grey white bryozoan chalk about 2 7 m below the k t boundary at or near the top of the fish clay zone pla parvularugoglobigerina eugubina missing and at the contact of the cerithium limestone and overlying bryozoan limestone about 60 cm above the k t boundary part of zone plc missing these unconformities are coeval with hiatuses observed in many continental shelf sections and indicate a global eustatic rather than regional isostatic response notable is that at stevns klint the episode of oceanic instability is registered over approximately the same stratigraphic interval in which supposed extraterrestrial amino acids occur a circumstance that may indicate a connection a gradual positive shift in 13 c is registered in both benthic and planktic foraminiferal assemblages in the upper maastrichtian at stevns klint the positive shift is followed by a prominent negative 13 c shift 1 3 at the k t boundary an upper maastrichtian positive 13 c excursion followed by a negative 13 c anomaly at or near the k t boundary has previously been observed in deep sea cores from the pacific ocean and the weddell sea antarctica implying a global event previous suggestions of a relation between the uppermost maastrichtian positive 13 c excursion and sea level variation are not supported by the data for stevns klint

rates and processes of periglacial solifluction an experimental approach cold room physical modelling of periglacial solifluction processes on an experimental slope of 12 is described and data on soil temperatures surface frost heave thaw consolidation downslope soil movement and porewater pressures over seven freeze thaw cycles are presented these data are analyzed in the context of laboratory determination of the rheometry of the experimental soils at high moisture contents it is concluded that the observed thaw induced solifluction represents pre failure soil shear strain and results from loss of strength due to the combined effects of raised porewater pressures during thaw consolidation and upward seepage pressures as water flows towards the surface away from the thaw front an investigation of the rheometry of thawing soils offers the prospect of an analytical model to predict rates and depths of periglacial solifluction 1997 by john wiley sons ltd

calcareous nannofossil biostratigraphy and paleoecology of the cretaceous tertiary transition in the central eastern desert of egypt abstract the gebel qreiya and nearby wadi hamama sections of the central eastern desert are among the most complete k t boundary sequences known from egypt the two sections were analyzed spanning an interval from l 83 myr below to about 3 myr above the k t boundary a 1 cm thick red clay layer at the k t boundary at gebel qreiya contains an ir anomaly of 5 4 ppb the high resolution study and well preserved nannoflora provide good age control and the first quantitative records of calcareous nannofossil assemblages for paleoecological interpretations across the k t transition in egypt four zones micula murus micula prinsii np1 and np2 were distinguished and correlated with other nannofossil and planktonic foraminiferal zonations that are broadly applicable for the eastern tethys region latest maastrichtian assemblages are abundant and diverse though cretaceous species richness progressively decreased across the k t boundary dominant species include arkhangelskiella cymbiformis micula decussata and watznaueria barnesae with high abundance of dissolution resistant m decussata reflecting periods of high environmental stress thoracosphaera blooms mark the k t boundary and are followed by an acme of the opportunistic survivor braarudosphaera bigelowii the first appearance of the new tertiary species cruciplacolithus primus and an acme of coccolithus cavus pelagicus these successive abundance peaks provide the basis for subdivision of the early danian zones np1 and np2 into five subzones correlation of selected nannofossil taxa from the egyptian sections with those from various onshore marine and deep sea sections provides insights into their paleoenvironmental and paleoecological affinities

decline of the maastrichtian pelagic ecosystem based on planktic foraminifera assemblage change implication for the terminal cretaceous faunal crisis an outer shelf upper slope tropical tethyan pelagic environment existed over southern israel during maastrichtian time planktic foraminifera in the 63 and 149 m size fractions from four sections in this area were studied quantitatively for a high resolution ecostratigraphic analysis of the pre cretaceous tertiary k t paleoenvironment during the maastrichtian 41 of the planktic foraminifera species became extinct mostly keeled globotruncanidae which also became quantitatively reduced near the end of the maastrichtian from as much as 35 to only 5 of the planktic foraminifera population evolutionary replacement of extinct species by new forms nearly ceased in that interval two major opportunistic blooms of guembelitria took place associated with reduced abundances of keeled forms and the dominant species heterohelix globulosa the first bloom occurred within the upper gansserina gansseri to lower abathomphalus mayaroensis zones and the second within the plummerita hantkeninoides zone the extinctions concomitant changes in faunal dominance and opportunist blooms indicate that the pelagic ecosystem in the negev area experienced multiple stresses during the maastrichtian the planktic foraminiferal assemblages were taxonomically impoverished and in decline prior to the k t boundary crisis

tektite bearing deep water clastic unit at the cretaceous tertiary boundary in northeastern mexico the hypothesis of cretaceous tertiary k t boundary impact on yucatan mexico predicts that nearby sites should show evidence of proximal impact ejecta and disturbance by giant waves an outcrop along the arroyo el mimbral in northeastern mexico contains a layered clastic unit up to 3 m thick that interrupts a biostratigraphically complete pelagic marl sequence deposited at more than 400 m water depth the marls were found to be unsuitable for determining magnetostratigraphy but foraminiferal biostratigraphy places the clastic unit precisely at the k t boundary we interpret this clastic unit as the deposit of a megawave or tsunami produced by an extraterrestrial impact the elastic unit comprises three main subunits 1 the basal spherule bed contains glass in the form of tektites and microtektites glass spherules replaced by chlorite smectite and calcite and quartz grains showing probable shock features this bed is interpreted as a channelized deposit of proximal ejects 2 a set of lenticular massive graded laminated beds contains intraclasts and abundant plant debris and may be the result of megawave backwash that carried coarse debris from shallow parts of the continental margin into deeper water 3 at the top several thin ripple beds composed of fine sand are separated by clay drapes they are interpreted as deposits of oscillating currents perhaps a seiche an iridium anomaly 921 23 pg g is observed at the top of the ripple beds our observations at the mimbral locality support the hypothesis of a k t impact on nearby yucatan

physical modelling of fault scarp degradation under freeze thaw cycles physical modelling has been developed in order to simulate the effects of periglacial erosion processes on the degradation of slopes and scarps data from 41 experimental freeze thaw cycles are presented they attest to the efficiency of periglacial processes that control both erosion and changes in scarp morphology i cryoexpulsion leads to an increase of scarp surface roughness and modifies significantly the internal structure of the active layer ii combined effects of frost creep and gelifluction lead to slow and gradual downslope displacements of the active layer 0 3 cm cycle iii debris flows are associated with the most significant changes in scarp morphology and are responsible for the highest rate of scarp erosion iv quantification of the erosion rate gives values close to 1 cm3 cm 2 for 41 freeze thaw cycles these experimental results are consistent with field data acquired along the la hague fault scarp normandy france where an erosion rate of 4 6 1 m3 m 2 per glacial stage has been computed from the volume of natural slope deposits stored during the weichselian glacial stage these results show that moist periglacial erosion processes could lead to an underestimation of plio quaternary deformation in the mid latitudes copyright 2006 john wiley sons ltd

disaster opportunists guembelitrinidae index for environmental catastrophes blooms of the disaster opportunist guembelitria species are proxies for environmental catastrophes whether impact or volcanism leading to severe biotic stress crises that may range from temporary exclusion of ecological specialists and generalists to mass extinctions during the late maastrichtian and early danian zones p0 and pla guembelitria blooms show global distributions but with the largest blooms 40 80 guembelitria in low and middle latitudes and only minor blooms 10 20 in high latitudes late maastrichtian guembelitria blooms are so far known from the indian ocean and eastern tethys the most intense guembelitria blooms 60 guembelitria occurred in shallow continental shelf areas slope shelf margins and volcanic provinces of the indian ocean what these environments have in common is high nutrient influx eutrophication either from continental runoff upwelling along continental margins or volcanic input at times of biotic crises guembelitria blooms may have spread rapidly to the exclusion of most or all other species much like today s red tides but with near global distributions a simple model can explain the ecological succession and recovery phases that follow major biotic perturbations caused by impacts or volcanism that lead to exclusion of specialist and most generalist species within such highly stressed environments guembelitria is the only genus to thrive and without competition rapidly reproduce and exponentially increase their populations when nutrients are depleted populations rapidly decrease leading to ecologic niches for other generalists and ecosystem recovery small low o2 tolerant heterohelicid populations mark this second stage followed by small trochospiral and planispiral species with further environmental recovery increasing competition niche development and restoration of a well stratified water mass oligotrophic conditions are restored opening habitats for the highly specialized and diverse species and a return to normal diverse assemblages this ecological succession is observed in association with mantle plume volcanism in the indian ocean and eastern tethys during the late maastrichtian and in association with the k t impact and volcanism during the early tertiary d 2004 elsevier b v all rights reserved

geomorphological characteristics of small debris flows on junior s kop marion island maritime sub antarctic the geomorphological characteristics of small debris flows in a maritime sub antarctic environment are described the morphological and sedimentological characteristics of the debris flows are comparable to debris flows documented for other parts of the world their initiation appears closely linked to the unusual environment in which they are found sediment supply is generated by diurnal frost heave of loamy sediment associated with azorella selago the debris flows are triggered by sediment mobilization upon saturation of the frost heaved surface gravel and overland flow over the low permeability and frost susceptible slope materials morphological effects of the flows are short lived due to obliteration by subsequent frost heave activity copyright 2000 john wiley sons ltd

an overview of recent large catastrophic landslides in northern british columbia canada at least thirty eight large catastrophic landslides each either larger than 0 5 m m 3 or longer than 1 km have occurred in northern british columbia in the last three decades the landslides include low gradient flowslides in cohesive sediments long runout rock slides rock avalanches and complex rock slide flows the flowslides have occurred in a variety of sediments including glaciolacustrine silt clay rich till and clay rich colluvium the rock failures have happened in weak shale overlain by sandstone and volcanic rocks the frequency of large landslides in northern british columbia appears to be increasing suggesting a link to climate change d 2005 elsevier b v all rights reserved

solifluction rates processes and landforms a global review abstract field data on the rates of solifluction and associated parameters are compiled from the literature in an attempt to evaluate factors controlling the spatial variability in solifluction processes and landforms with special attention on the climate solifluction relationship the analyzed data originate from 46 sites over a wide range of periglacial environments from antarctic nunataks to tropical high mountains solifluction broadly defined as slow mass wasting resulting from freeze thaw action in fine textured soils involves several components needle ice creep and diurnal frost creep originating from diurnal freeze thaw action annual frost creep gelifluction and plug like flow originating from annual freeze thaw action and retrograde movement caused by soil cohesion the depth and thickness of ice lenses and freeze thaw frequency are the major controls on the spatial variation in solifluction processes near the warm margin of the solifluction affected environment diurnal freeze thaw action induces shallow but relatively rapid movement of a superficial layer 5 10 cm thick on average often creating the thin stone banked lobes typically seen on tropical high mountains in addition to diurnal movement annual frost creep and gelifluction may occur on slopes with soil climates of seasonal frost to warm permafrost dislocating a soil layer shallower than 60 cm at a rate of centimeters per year and eventually producing medium size solifluction lobes in high arctic cold permafrost regions two sided freezing can induce plug like flow of a soil mass 60 cm or thicker the correlation between process and landform suggests that the riser height of lobes is indicative of the maximum depth of movement and prevailing freeze thaw type climate change may result in new different ground freezing conditions thereby influencing the surface velocity and maximum depth of soil movement soil moisture and topography also control solifluction high moisture availability in the seasonal freezing period enhances diurnal freeze thaw action and subsequent seasonal frost heaving the latter contributes to raising the moisture content of the thawed layer and promotes gelifluction during the thawing period the slope angle defines the upper limit of the surface velocity of solifluction a diagram correlating the potential frost creep with the actual surface velocity permits an inter site comparison of the relative magnitude of solifluction components physically based modelling of periglacial slope evolution requires synthetic and more detailed field monitoring and laboratory simulations of solifluction processes

gradual mass extinction species survivorship and long term environmental changes across the cretaceous tertiary boundary in high latitudes stable isotope and planktic foraminiferal analyses across the cretaceous tertiary k t boundary transition at nye klov indicate longterm oceanic instability associated with global sea level fluctuations a gradual mass extinction and decreased magnitude of the 13 c shift in high latitudes oceanic instability which began at least 100 kyr before the k t boundary and continued for about 300 kyr into the tertiary was accompanied by a gradual faunal turnover the maximum sea level lowstand during latest maastrichtian is recorded about 75 cm below the k t boundary a sea level rise first in evidence at 20 cm to 40 cm below the boundary continued into zone p0 boundary clay this sea level rise was accompanied by 2 c of cooling in surface and bottom waters prior to the k t boundary 13 c values remained relatively stable up to 10 cm below the k t boundary a negative shift of 0 5 to 1 0 per mil occurred in the boundary clay in both planktic and benthic foraminifera the surface to deep 13 c gradient remained nearly unchanged in contrast to low latitudes where this gradient is virtually eliminated no sudden mass extinction occurred in this cosmopolitan high latitude fauna and nearly all cretaceous taxa thrived well into the tertiary when they gradually disappeared shallow seas dominated by cretaceous survivor taxa and a well developed oxygen minimum zone prevailed during the earliest tertiary short term sea level lowstands are marked by hiatuses at the top of zones p0 and p1a about 50 kyr and 230 kyr after the k t boundary respectively rising sea level reestablished normal marine conditions about 300 kyr to 350 kyr after the k t boundary coincident with the first post k t boundary recovery of the tertiary fauna and extinction of cretaceous survivors during this time high latitude regions temporarily acted as centers of origin and dispersal for planktic foraminifera long term oceanic instability gradual faunal turnover absence of a sudden mass extinction and greatly diminished 13 c shift in high latitudes suggest that a k t boundary bolide impact was not the primary cause for the k t boundary faunal transition moreover these data strongly imply that the destructive effects of the bolide impact would have been greatest in low latitudes and negligible in high latitudes

multiple microtektite horizons in upper eocene marine sediments no evidence for mass extinctions microtektites have been recovered from three horizons in eight middle eocene to middle oligocene marine sediment sequences five of these occurrences are coeval and of latest eocene age 37 5 to 38 0 million years ago three are coeval and of early late eocene age 38 5 to 39 5 million years ago and three are of middle oligocene age 31 to 32 million years ago in addition rare probable microtektites have been found in sediments with ages of about 36 0 to 36 5 million years the microtektite horizon at 37 5 to 38 0 million years can be correlated with the north american tektite strewn field which has a fission track age minimum of 34 to 35 million years and a paleomagnetic age of 37 5 to 38 0 million years there is no evidence for mass faunal extinctions at any of the microtektite horizons many of the distinct faunal changes that occurred in the middle eocene to middle oligocene can be related to the formation of the antarctic ice sheet and the associated cooling phenomena and intensification of bottom currents that led to large scale dissolution of calcium carbonate and erosion which created areally extensive hiatuses in the deep sea sediment records the occurrence of microtektite horizons of several ages and the lack of evidence for faunal extinctions suggest that the effects of extraterrestrial bolide impacts may be unimportant in the biologic realm during middle eocene to middle oligocene time

paleoecology of the cretaceous tertiary mass extinction in planktonic foraminifera abstract paleobiogeographic patterns of the cretaceous tertiary k t mass extinction in planktonic foraminifera in tunisia spanning environments from open marine upper bathyal to shelf and shallow marginal settings indicate a surprisingly selective and environmentally mediated mass extinction this selectivity is apparent in all of the environmental proxies used to evaluate the mass extinction including species richness ecological generalists ecological specialists surface and subsurface dwellers whether based on the number of species or the relative percent abundances of species the following conclusions can be reached for shallow to deep environments about three quarters of the species disappeared at or near the k t boundary and only ecological generalists able to tolerate wide variations in temperature nutrients salinity and oxygen survived among the ecological generalists heterohelicids guembelitrids hedbergellids and globigerinellids only surface dwellers survived ecological generalists which largely consisted of two morphogroups of opportunistic biserial and triserial species also suffered selectively biserials thrived during the latest maastrichtian in well stratified open marine settings and dramatically declined in relative abundances in the early danian triserials thrived only in shallow marginal marine environments or similarly stressed ecosystems during the latest maastrichtian but dominated both open marine and restricted marginal settings in the early danian this highly selective mass extinction pattern reflects dramatic changes in temperature salinity oxygen and nutrients across the k t boundary in the low latitude tethys ocean which appear to be the result of both long term environmental changes e g climate sea level volcanism and short term effects bolide impact

fifty years of coastal erosion and retrogressive thaw slump activity on herschel island southern beaufort sea yukon territory canada abstract patterns of coastal erosion in the arctic differ dramatically from those coasts in more temperate environments thick sea ice and shore fast ice limit wave based erosional processes to a brief open water season however despite this permafrost coasts containing massive ice ice wedges and ice bonded sediments tend to experience high rates of erosion these high rates of erosion reflect the combined thermal mechanical processes of thawing permafrost melting ground ice and wave action climate change in the arctic is expected to result in increased rates of coastal erosion due to warming permafrost increasing active layer depths and thermokarst rising sea levels reduction in sea ice extent and duration and increasing storm impacts with the most ice rich permafrost in the canadian arctic the southern beaufort sea coast between the tuktoyaktuk peninsula and the alaskan border is subject to high rates of erosion and retrogressive thaw slump activity under many climate change scenarios this area is also predicted to experience the greatest warming in the canadian arctic this paper presents results of a remote sensing study on the long term patterns of coastal erosion and retrogressive thaw slump activity for herschel island in the northern yukon territory using orthorectified airphotos from 1952 and 1970 and an ikonos image from 2000 corrected with control points collected by kinematic differential global positioning system and processed using softcopy photogrammetric tools mean coastal retreat rates of 0 61 m yr and 0 45 m yr were calculated for the periods 1952 1970 and 1970 2000 respectively the highest coastal retreat rates are on north west facing shorelines which correspond to the main direction of storm related wave attack during the period 1970 2000 coastal retreat rates for south to south east facing shorelines displayed a distinct increase even though these are the most sheltered orientations however south to south east facing shorelines correspond to the orientations where the highest densities of retrogressive thaw slumps are observed differences in rates of headwall retreat of retrogressive thaw slumps and coastal erosion results in the formation of larger thermokarst scars and the development of polycyclic thaw slumps on south to south east exposures the number and the total area of retrogressive thaw slumps increased by 125 and 160 respectively between 1952 and 2000 as well the proportion of active retrogressive thaw slumps increased dramatically polycyclic retrogressive thaw slumps appear to develop in a periodic fashion related to retrogressive thaw slump stage and maximum inland extent

biotic turnover in benthic foraminifera across the cretaceous tertiary boundary at el kef tunisia abstract the cretaceous tertiary boundary section exposed near el kef tunisia is the most complete boundary sequence known to date it contains nearly 1 m of black and gray boundary clay containing planktic foraminiferal zone poa b 2 m of clayey shales of p1a globigerina eugubina zone and 4 m of shales and marls of p1b g taurica zone quantitative analysis of the benthic foraminiferal fauna suggests that deposition during the latest cretaceous occurred in an upper slope to outer shelf environment which shallowed at the k t boundary to an outer to middle shelf depth and shallowed further by p1b time to mid shelf depth a major reduction in benthic diversity occurred near the k t boundary with about 50 of the fauna disappearing diversity remained an average of 37 lower during deposition of the first 3 m of sediment above the boundary poa b p1a and productivity was very low surviving and thriving foraminifers during this interval were primarily low oxygen tolerant epifaunal and infaunal species a sharp decrease in the low oxygen tolerant fauna and appearance of a shallow mid shelf fauna at about 4 m above the boundary p1b zone signals a second regression return to higher oxygen levels and higher productivity although the environmental effects of the k t boundary event can be inferred from benthic faunas the ultimate cause remains elusive faunal changes prior to and the long recovery period after the k t boundary are difficult to explain by a single impact hypothesis

physical modelling of gelifluction and frost creep some results of a large scale laboratory experiment an experimental slope was constructed in a 5 m 5 m square refrigerated tank the slope was formed of four sections each consisting of regolith soil collected from a distinct bedrock lithology the four lithologies utilized were granite limestone mudstone and slate the slope was subjected to freezing and thawing from the surface downwards water was supplied at the base of the soil during freezing frost heaving and surface downslope soil movement were determined after each of 15 freezing cycles and the profiles of soil movement with depth for each soil type were measured at the end of the 15th cycle the experimental soils were non cohesive those derived from granite and limestone were respectively sandy and gravelly in texture while those derived from mudstone and slate were silt rich mass movement in the granite and limestone soils was due mainly to frost creep and was associated with the growth of needle ice in the mudstone and slate soils gelifluction was dominant as a result of high moisture contents caused by the melting of segregation ice mean per cycle rates of downslope soil transport for the granite limestone mudstone and slate soils were 5 8 cm3 cm 1 6 9 cm3 cm 1 21 2 cm3 cm 1 and 31 2 cm3 cm 1 respectively units referring to the volume of soil passing a unit width of slope per cycle mass movement rates were shown to be strongly related to the silt content of the soils