crustal structure of the northern nova scotia rifted continental margin eastern canada 1 the nova scotia continental margin off eastern canada marks a transition from a volcanic to a nonvolcanic style of rifting the northern nonvolcanic segment of the margin was studied by a 490 km long refraction seismic line with dense air gun shots coincident with previous deep reflection profiles a p wave velocity model was developed from forward and inverse modeling of the wide angle data from 19 ocean bottom seismometers and coincident normal incidence reflection profiles the continental crust has a maximum thickness of 36 km and is divided into three layers with velocities of 5 7 6 9 km s crustal thinning down to 3 km occurs in a 180 km wide zone and the sediment cover in this area is up to 15 km thick farther seaward a 150 km wide transition zone is observed with a 5 km thick lower layer 7 2 7 6 km s interpreted as partially serpentinized mantle at the landward end this layer is overlain by highly altered continental crust 5 4 km s extending up to the seaward limit of the jurassic salt province farther seaward the upper layer is interpreted as exhumed and highly serpentinized mantle 5 1 km s separated from the lower layer by subhorizontal reflectivity which probably represents a serpentinization front oceanic crustal thickness is 4 km with layer 2 velocities of 4 6 5 0 km s layer 3 velocities of 6 4 6 55 km s are lower than typical lower oceanic crust velocities but consistent with a low magma supply and increased tectonism as observed on the reflection profile this reduced magma production might be related to the proximity of the newfoundland transform margin

dating the quaternary progress in luminescence dating of sediments abstract luminescence dating comprises a collection of numerical age techniques that are among the most significant chronological tools currently used in quaternary research this paper briefly reviews the key historical developments in luminescence dating from its roots in thermoluminescence dating of heated minerals to the development of optical dating methods for sunlight exposed sediments we describe the principles and practicalities of the various techniques commonly used in luminescence dating including multiple aliquot single aliquot and single grain procedures and we discuss some of the latest approaches to recognising and minimising potential errors in age estimation e g by means of component analysis and dose distribution methods in optical dating the overview also introduces the other papers in this special issue of quaternary science reviews which address a selection of important issues in basic research technique development and application of luminescence dating to critical questions in the geological and archaeological sciences illustrated with examples from around the world and the last million years of earth history

a deep seismic reflection profile across the nova scotia continental margin offshore eastern canada results from two deep seismic reflection lines are presented when combined these lines span the rifted continental margin off nova scotia from crust unaltered by rifting to the ocean basin these data provide crustal and upper mantle reflection geometry to depths of over 50 km and elucidate the rifting process on this margin which occurred during the mesozoic breakup of pangaea the continental crust below the continental shelf and slope becomes progressively thinner toward the ocean continent boundary in the upper crust normal faults accommodated mesozoic extension and these flatten and terminate at 5 6 s two way time in the lower crust and upper mantle mesozoic rifting may be reflected in dipping events which are interpreted to be normal faults all mesozoic extensional faulting could be controlled by the preexisting fabric of the crust which in this region would be related to appalachian compression within the meguma terrane below the continental rise there is some evidence for magmatic un

mesozoic and cenozoic stratigraphy eastern scotian shelf new interpretations a 320 km long deep seismic reflection line across the central part of the scotian basin provides new insight on the deep stratigraphy of the basin confirms the existence of up to 18 km of mesozoic and cenozoic sedimentary strata and provides additional control on the relationship of proximal and distal stratigraphic units within the basin detailed biostratigraphic and seismic correlation from three outer shelf upper slope wells yields important new information on late cretaceous and tertiary unconformities and identifies a number of third order sequence boundaries the dating of prominent unconformities and correlation with the oceanic seismic markers ac and au results in the reidentification of these horizons in the sohm abyssal plain

lithospheric structure of the labrador sea from constrained 3 d gravity inversion regional inversions of free air gravity data constrained by bathymetric and sediment thickness information were undertaken over the labrador sea and its margins to generate 3 d density anomaly models to investigate broad scale crustal structural variations across the extinct spreading centre benchmarked against independent seismic moho depth constraints a density anomaly isosurface within the inverted volumes was selected as a moho proxy and regional maps of moho structure were developed inversions using two different sources for depth to basement constraints revealed similar moho structures with a depth to moho of 12 km beneath the labrador sea which deepens to 20 km and greater towards davis strait and beneath the offshore extension of the grenville province density anomaly slices through the models corresponding to seismic lines show good agreement between the inverted moho proxy and the seismic moho with the only exceptions occurring where a high velocity lower crustal zone or underplate has been modelled from wide angle reflection refraction profiling studies the inverted depth to moho estimates were combined with depth to basement constraints to investigate crustal thickness both for the full crust and for individual crustal layers revealing that the crust of the labrador sea is generally 5 10 km thick but thickens to 20 25 km towards davis strait and beneath the offshore extension of the grenville province not taking into account high density underplates or anomalously high density lower crust sediment and crustal thickness variations were investigated to compute stretching factors across the labrador sea and to identify zones which deviate from local isostatic compensation assuming both an initial unstretched crustal thickness of 35 km and using a variable unstretched crustal thickness model much of the labrador sea has experienced 70 90 per cent thinning the derived values suggest that embrittlement of the entire crust and serpentinization of the upper mantle are likely to have occurred for large portions of the central and southern labrador sea inboard of known oceanic crust isostatic considerations reveal sediment excess and deficiency on the labrador and greenland margins respectively possibly reflecting fundamental rheological asymmetry with the greenland margin appearing weaker than the labrador margin a strong gradient from sediment deficiency to excess exclusive to the labrador margin may reveal the southwestern limit of a regional graben bounding listric detachment or of a zone of distributed faults and detachments

palliser s triangle reconstructing the central desert of the southwestern canadian prairies during the late 1850s between 1857 and 1860 the british north american expedition led by captain john palliser explored and surveyed the canadian prairies primarily to establish its suitability for agriculture and settlement historical and paleoclimate records indicate the expedition coincided with below normal precipitation leading to the perception of an arid or semi arid region that would forever be comparatively useless for agriculture today this part of the canadian prairies is known as the palliser triangle and is canada s productive dryland agricultural region here we present historic geomorphologic and chronometric evidence to reconstruct the landscape encountered by the expedition we contend that palliser s perception of the region was strongly influenced by his experience travelling through active sand dunes in the middle sand hills of southeastern alberta at present the dunes are entirely stabilized by vegetation in contrast to palliser s report of miles of burning sand archival aerial photographs

recent stabilization of active sand dunes on the canadian prairies and relation to recent climate variations the historical activity of sand dunes on the southern canadian prairies was investigated in order to determine the relation with recent climate variations changes in dune activity were determined from historical aerial photographs at seven sites with active parabolic dunes in saskatchewan and manitoba the methodology developed combines digital image processing and geographical information system gis analysis to measure changes in dune activity from the aerial photographs as well as correlation analysis to determine the relation between dune activity and climate variations overall dune activity has been decreasing since the early to mid 1900s as evidenced by greater vegetation colonization than sand dune migration or reactivation the decrease in dune activity is significantly correlated with decadal scale variations in aridity and is coincident with a decrease in annual wind speed evidence suggests that this response is superimposed on a longer trend towards stabilization possibly in place since the late 1700s taken together the effect of this complex response is that dune recovery on the southern canadian prairies is prolonged well after an initial disturbance and therefore gives the impression of anomalous levels of activity for extended periods thereafter for this reason dune mobility indices predicated on short term climate variations years to decades do not fully describe the present level of dune activity on the southern canadian prairies

biogeomorphic model of dunefield activation and stabilization on the northern great plains abstract a conceptual model is proposed for the activity of sand dune systems on the northern great plains that incorporates vegetation growth theory and geomorphic system theory dunefield activity is modeled as a cyclic phenomenon alternating between active and stable states with the latter as the system state attractor the model is divided into two constituent parts an activation model and a stabilization model the activation model is qualitative and describes the transition from stable to active dunes as the result of a climatic perturbation such as drought that decreases vegetation cover the intensity and duration of the climatic perturbation determines the rate of decline of vegetation cover the stabilization model is quantitative and describes the transition from active to stable dunes using a logistic model of vegetation growth small perturbations during stabilization can prolong the duration of recovery enabling dunes to remain active well after the initial perturbation despite the geographic focus of this study the model appears applicable to a variety of environments where dune activity is limited in part by vegetation cover

development history of the southern terminus of the central atlantic guyana suriname case study the study focuses on the offshore guyana suriname french guiana region it draws from seismic well gravimetric and magnetic data they indicate that the continental break up along the western margin of the demerara plateau took place during the callovian oxfordian associated with the central atlantic opening and accommodated by normal faults the continental break up in the se offshore guyana accommodated by strike slip faults was coeval the continental break up along the ne and eastern margins of the demerara plateau took place during the late aptian albian associated with the opening of the equatorial atlantic and accommodated by dextral strike slip and normal faults respectively different spreading vectors of the central and equatorial atlantic required development of the accommodation block during the late aptian albian paleocene in their contact region and in the region between the central atlantic and its southernmost portion represented by the offshore guyana block which were separated from each other by the opening equatorial atlantic its role was to accommodate for about 20 mismatch between the central and equatorial atlantic spreading vectors which has decreased from the late aptian albian to paleocene down to 0 differential movements between the central and equatorial atlantic oceans were also accommodated by strike slip faults of the guyana continental margin some active until the paleocene

caldera collapse and the generation of waves 1 the aim of this paper is to begin a study of the waves produced by the collapse of a caldera connected to the sea an example is the bronze age collapse of the caldera of santorini thera which is thought to have involved an area of approximately 70 km2 subsiding to a depth close to the present 390 m in this paper we concentrate on the purely mechanical aspects of the flow and adopt a simple geometry that replicates some of the features of the pre bronze age caldera of santorini by combining laboratory experiments with computer simulations we have been able to determine the amplitude of the waves for a wide range of cavity parameters for cavities with a width comparable to the depth of water entering the cavity we have determined a scaling relation for the amplitude in terms of the geometry of the system in the case of wider cavities the flow begins like a breaking dam flow it then becomes similar to a classical bore before breaking up into waves the computer simulations agree well with experiment and will allow us to simulate more complicated geometries

deep structure of the u s atlantic continental margin offshore south carolina from coincident ocean bottom and multichannel seismic data we present the results of a combined multichannel seismic reflection mcs and wide angle ocean bottom seismic profile collected in 1988 across the carolina trough on the u s atlantic continental margin inversion of vertical incidence and wide angle travel time data has produced a velocity model of the entire crust across the continent ocean transition the margin consists of three structural elements 1 rifted continental crust comprising 1 4 km of post rift sedimentary rocks overlying a 30 34 km thick subsedimentary crust 2 transitional crust a 70 to 80 km wide zone comprising up to 12 km of postrift sedimentary rocks overlying a 10 to 24 km thick subsedimentary crust and 3 oceanic crust comprising 8 km of sedimentary rocks overlying an 8 km thick crystalline crust the boundary between rifted continental and transitional crust marked by the brunswick magnetic anomaly represents an abrupt change in physical properties with strong lateral increases in seismic velocity density and magnetic susceptibility the transitional crust contains mid crustal seaward dipping reflections observed on the mcs section and has seismic velocities of 6 5 6 9 km s in the midcrust and 7 2 7 5 km s in the lower crust modeling of potential field data shows that transitional crust also produces the prominent margin parallel gravity anomaly and the brunswick and east coast magnetic anomalies these observations support the interpretation that the transitional crust was formed by magmatism during continental breakup the prodigious thickness up to 24 km of igneous material rivals that interpreted on continental margins of the north atlantic e g hatton bank and voring plateau which formed in the vicinity of the iceland hotspot these observations when combined with other transects across the margin confirm previous suggestions that the u s atlantic margin is strongly volcanic and further imply that the magmatism was not the result of a long lived mantle plume

crustal structure of the central nova scotia margin off eastern canada summary the central nova scotia margin off eastern canada is located at a transition from a volcanic margin in the south to a non volcanic margin in the north in order to study this transition a wide angle refraction seismic line with dense airgun shots was acquired across the central nova scotia margin the 500 km long transect is coincident with previous deep reflection profiles across the lahave platform and extending into the sohm abyssal plain a p wave velocity model was developed from forward and inverse modelling of the wide angle data from 21 ocean bottom seismometers and coincident normal incidence reflection profiles the velocity model shows that the continental crust is divided into three layers with velocities of 5 5 6 9 km s 1 the maximum thickness is 36 km a minor amount 5 km of thinning occurs beneath the outer shelf while the major thinning to a thickness of 8 km occurs over the slope region the seaward limit of the continental crust consists of 5 km thick highly faulted basement there is no evidence for magmatic underplating beneath the continental crust on the contrary a 4 km thick layer of partially serpentinized mantle 7 6 7 95 km s 1 begins beneath the highly faulted continental crust and extends 200 km seawards forming the lower part of the oceancontinent transition zone the upper part of the transition zone consists of the highly faulted continental crust and 4 to 5 km thick initial oceanic crust the continent ocean boundary is moved 50 km farther seawards compared to an earlier interpretation based only on reflection seismic data the oceanic crust in the transition zone consists of layer 2 and a high velocity lower crustal layer layer 2 is 1 3 km thick with velocities of 5 6 6 0 km s 1 the high velocity lower crustal layer is 1 2 km thick with velocities of 7 25 7 4 km s 1 suggesting a composite layer of serpentinized peridotite and gabbroic layer 3 oceanic crust with normal thickness of 5 7 km and more typical layer 3 with velocities of 6 95 7 3 km s 1 is observed at the seaward end of the profile

reactivation of supply limited dune fields from blowouts a conceptual framework for state characterization aeolian dune fields mantle the earth in both vegetated stable and unvegetated active states changes in state are poorly understood in particular little is known about reactivation devegetation from a vegetated state available evidence indicates that dune reactivation can be driven by changes in aridity increased wind speed fire biogenic disturbance human disturbance or a combination of the previous how these controls fit together and define the reactivation potential of dune fields is presently unknown here we develop a framework to describe reactivation potential for a specific case presently vegetated supply limited dune fields that develop blowouts under a unidirectional wind we first define a conceptual model of blowout expansion and then split the functions of vegetation in a stable dune field into i maintenance of a protective skin and ii blowout suppression we model reactivation as disturbance breaking through the protective skin which forms a blowout that is either i suppressed by colonizer species or ii capable of advancing downwind and reactivating part of the dune field the capacity for disturbance to break through the protective skin is a function of disturbance magnitude area and resistance of the skin the blowout suppression capacity of a dune field is a function of sediment flux blowout depth related to geomorphology and colonizer species vitality by plotting a given dune field with two variables protective skin breach rate and blowout suppression capacity we define four states i stable ii blowout dominated iii reactivating or iv stable but disturbance susceptible we reinforce the conceptual model with qualitative examples and discussion of experiments on grassland stabilized dunes in canada overall our framework provides a starting point for quantifying the reactivation potential of vegetated dune fields

generation mechanism of tsunamis from the 1883 krakatau eruption the 1883 eruption of krakatau generated a destructive tsunami which claimed about 34 000 lives we compute the generation and propagation of tsunamis from three models previously proposed they are 1 large scale caldera collapse of the northern part of krakatau island 2 emplacement of pyroclastic flow deposits 3 submarine explosion we numerically solve the non linear shallow water equations on actual bathymetry all three models displace the same volume 11 5 km 3 of water in different ways we compare the results of our computation with the observed tsunami waveforms at batavia and tsunami wave heights along the coasts of java and sumatra the comparison shows that the submarine explosion model of 1 to 5 min duration best explains the generation of the largest tsunami

a 10 000 year record of dune activity dust storms and severe drought in the central great plains dune fi elds and loess deposits of the great plains of north america contain stratigraphic records of eolian activity that can be used to extend the short observational record of drought we present a 10 000 yr reconstruction of dune activity and dust production in the central great plains region based on 95 optically stimulated luminescence ages the integration of data from both eolian sand and loess is an important new aspect of this record clusters of ages defi ne episodes of extensive eolian activity which we interpret as a response to frequent severe drought at 1 0 0 7 ka and 2 3 4 5 ka with peaks centered on 2 5 and 3 8 ka sustained eolian activity occurred from 9 6 to 6 5 ka parts of this record may be consistent with hypotheses linking holocene drought to sea surface temperature anomalies in the pacifi c or atlantic oceans or to the el nino southern oscillation phenomenon but the record as a whole is diffi cult to reconcile with any of these hypotheses

ubiquity of anomalous fading in k feldspars and the measurement and correction for it in optical dating anomalous fading rates were measured in k feldspars separated from 49 sediment samples mainly from north america the intensity of the optically stimulated luminescence was found to decrease linea

triassic liassic western moroccan synrift basins in relation to the central atlantic opening abstract the upper triassic lower liassic sequence of the atlantic margin of morocco is primarily composed of fine grained detrital sedimentary rocks containing basaltic intercalations its age is carnian to hettangian well data outcrop observations and seismic sequence analysis suggest that rifting started earlier carnian in the eastern and southern parts of the margin and later proceeded towards the west and the north resulting in the formation of the central atlantic rift on the moroccan margin the rift was composed of i eastern basins relatively narrow and bounded by e dipping faults which are reactivated hercynian structures ii a central horst and iii western basins bounded by w dipping faults the 020 trending basins are separated by w dipping faults the 020 trending basins are separated by 070 striking transfer faults estimations of the amount of lithospheric extension along the moroccan external rift system show a thinning ratio decreasing northward and probably associated to a necking of the lithosphere rift evolution on the part of the moroccan margin shows good correlation to the conjugate north american margin

seaward dipping reflectors offshore the southeastern united states seismic evidence for extensive volcanism accompanying sequential formation of the carolina trough and blake plateau basin deep penetration multichannel seismic reflection profiles off the southeastern united states reveal widespread seaward dipping reflectors sdrs similar features have been imaged and sampled on other north atlantic rifted margins where voluminous volcanism has accompanied continental breakup beneath the carolina trough are two sets of sdrs one along a basement hinge zone and another seaward of the east coast magnetic anomaly axis the hinge sdrs lie beneath and apparently developed prior to a flood basalt that erupted at 184 3 ma and is marked by a prominent reflector j beneath the northern blake plateau basin only the hinge sdrs are observed but they developed after j we suggest that the inferred north to south age difference of sdr emplacement implies a heretofore unrecognized time transgressive breakup of northwest africa and north america during the early middle jurassic

effects of rifting and subsidence on thermal evolution of sediments in canada s east coast basins regional maps of lithospheric deformation and thermal history have been derived for the eastern continental margin of canada subsidence associated with the rifting and cooling stages of rifted margin formation was calculated from gridded maps of sediment thickness and bathymetry along the labrador grand banks and nova scotian margins a two layer lithospheric extension model was used to compute the deformation and thermal evolution of each region deformation results show that the crust and lower lithosphere have generally stretched by different amounts and that either crustal or subcrustal lithospheric stretching dominates beneath the various basins thermal modelling results for the older nova scotian and grand banks margins show a strong correlation between thermal gradient crustal stretching and sediment thickness and the predicted thermal gradient pattern for the younger labrador margin correlates extremely well with predicted stretching of the still cooling subcrustal lithosphere predictions

late 18th century drought induced sand dune activity great sand hills saskatchewan geomorphic evidence and optical ages from seven locations indicate that widespread dune activity occurred within the last 200 years in the great sand hills region of southwestern saskatchewan optical ages n 36 define an interval of dune activity bracketed by the earliest age of back ridges in the seward sand hills 185 8 years and the average age of stabilized dune heads about 105 years during this interval parabolic dunes were active in all areas studied these ages indicate that the most recent interval of activity was initiated about ad 1800 and continued at a level higher than present for approximately 80 years the most likely cause of dune activation was lower than average precipitation relative to 1960 1991 values through the 1700s culminating in drought in the late 1700s as evidenced in dendroclimatic records from the cypress hills and from the rocky mountain foothills dunes affected by such climatically induced regional activity require many decades to restabilize historical ob

interpretations and common challenges of aeolian records from north american dune fields abstract geomorphic and chronologic data for dune fields are evaluated for three contrasting areas of north america 1 the prairie parkland and boreal ecozones of the northern great plains in canada 2 the central great plains of the usa and 3 the deserts of southwestern usa and northern mexico luminescence and radiocarbon ages for periods of dune accumulation and stability are compared with palaeoenvironment proxies to provide an assessment of the boundary conditions of dune system response to changes in sediment supply availability and mobility dune fields in the northern great plains were formed from sediment originating from glaciofluvial or glaciolacustrine sediments deposited during deglaciation 16 11 ka subsequent aeolian deposition occurred in parkland and prairie dune fields as a result of mid holocene 8 5 ka and late holocene despite spatial and temporal gaps in chronometric data as a result of sampling biases the record from north american dune fields indicates the strong influence of sediment supply on dune construction with changes in sediment availability as a result of drought episodes resulting in dune field reactivation and reworking of pre existing sediment

crustal architecture and moho topography beneath the eastern indian and bangladesh margins new insights on rift evolution and the continent ocean boundary the thick sedimentary cover 18 km along the eastern continental margin of india ecmi and over the bay of bengal has hindered understanding of the mechanisms of rifting that operated on the eastern indian and bangladesh margins analysis of multichannel seismic reflection data together with 3d gravity inversion and 2d gravity forward modelling illuminates basement configuration crustal thickness and moho topography thereby revealing the modes of rift evolution and the location of the continent ocean boundary cob along these margins the basement particularly in the shelf and slope regions of eastern peninsular india is traversed by nearly coast perpendicular graben and their seaward continuity is delineated up to 125 km from the coastline three different types of continental margin are present along the ecmi 1 sheared rift on the southern segment of the ecmi up to 14 n latitude offshore the southern granulite terrain 2 hyper extended rift in the central segment between 14 n and 17 n offshore the dharwar craton and 3 hypo extended rift on the northern segment between 17 n and 20 n offshore the eastern ghats mobile belt the graben terminations crustal thickness and moho topography of both the ecmi and offshore bengal basin clearly suggest that the cob runs nearly parallel to the coastline of peninsular india but takes an orthogonal turn offshore in the bengal basin and connects the palaeo continental shelf and the rajmahal sylhet line onshore in the bengal basin crustal thickness 8 10 km and depth to the moho discontinuity 28 km beneath the bangladesh margin are unusual because the crustal thickness increased through interaction of the kerguelen plume with the existing oceanic lithosphere the moho deepened largely due to the load of the bengal fan sediments the absence of rifted crustal blocks on the bangladesh margin and the continuity of the cob into the onshore bengal basin together imply that the present bangladesh region was under marine conditions at least until the beginning of bengal fan sedimentation i e no less than 23 ma

impact of the minoan tsunami of santorini simulated scenarios in the eastern mediterranean 1 we have simulated the impact of the tsunami generated by the late bronze age lba volcanic eruption of santorini on the eastern mediterranean two different tsunami triggering mechanisms were considered a caldera collapse and pyroclastic flows surges entering the sea simulations include the worst input conditions in order to evaluate the maximum possible impacts but also lighter input conditions compatible with the lack of any tsunami trace on the northern coasts of crete in all the simulations tsunami propagation is mainly confined to the southern aegean outside the aegean the tsunami impact was negligible and not responsible for the slide slumping of fine grained pelagic and or hemipelagic sediments considered the sources of the sporadically located sea deposits in the ionian sea and of the widespread megaturbidite deposits localized in the ionian and sirte abyssal plains

chronology and geochemistry of late holocene eolian deposits in the brandon sand hills manitoba canada abstract accelerator mass spectrometry and conventional radiocarbon age determinations of organic matter from paleosols indicate that the brandon sand hills area of southern manitoba has been subjected to recurrent intervals of eolian activity in the past 5000 years although precise regional correlations are precluded by dating uncertainties periods of most notable paleosol development occurred around 2300 to 2000 1400 to 1000 and 600 to 500 cal yr bp with eolian activity occurring before and after each of these periods episodes of eolian activity may correspond to periods of regional drought whereas paleosols mark periods of increased moisture availability and stabilization by vegetation the geochemistry of the eolian sands paleosols and source sediments indicates that partial leaching of carbonates occurs from pedogenesis during humid climatic phases and that this is probably the primary mechanism of carbonate depletion of eolian sands in this area recent trends in sand dune activity from historic aerial photography and early explorers accounts indicate that the few active dunes that presently exist have stabilized at a rate of 10 20 per decade despite several severe droughts in the 20th century this may be attributed to pre settlement droughts that were more severe than those in historic times although regional dune stabilization may also be related in part to the spread of forest cover in the past few hundred years

conjugate divergent margins an introduction the main objective of this book is to provide a global overview of divergent margins based on geological and geophysical interpretation of sedimentary basins along the south central and north atlantic conjugate margins from plate tectonics and crustal scales to a more detailed description of stratigraphical and structural elements that are responsible for petroleum plays these themes are complemented by geodynamic concepts based on physical and numerical models and by comparisons with present day embryonic margins which are succinctly discussed in some papers

optical dating studies of quaternary organic rich sediments from southwestern british columbia and northwestern washington state the suitability of optical dating using 1 4 ev infrared excitation for determining the time of deposition or compaction of organic rich sediments and peat is assessed with measurements on seven samples from six different lithostratigraphic units one is of zero age two have associated 14c ages three are known to have been deposited during an interglaciation and one is 1 ma old the samples yield satisfactory optical ages ranging from 0 to over 100 ka we conclude that the muir point formation southern vancouver island and the whidbey formation northwestern washington state were both deposited during 18o stage 5 as previously deduced from other evidence the age obtained from the 1 ma sample was significantly too low the optical dating method is simpler and more precise than thermoluminescence dating and is recommended for future work

barchan dunes stabilized under recent climate warming on the northern great plains we use light detection and ranging lidar imagery and optical stimulation luminescence dating to show that stable parabolic dunes on the canadian prairies originated from active barchan dunes 200 years ago residual dune ridges marking former lower stoss slope positions of migrating dunes record the transformation of barchan dunes to parabolic dunes between a d 1810 and 1880 parabolic dunes stabilized by ca a d 1910 with a few larger dunes and blowouts still active today a dry cool climate permitted sand transport to out compete vegetation stabilization and with lowered water tables maintain desert like barchan dunes with bare interdune sand sheets these findings explain why dune fields of the southern canadian prairies are currently more active than those of the united states great plains and the observation that dunes have stabilized under twentieth century warming our results emphasize the importance of viewing dune field responses to short term disturbances in the context of longer term system response particularly when relatively modest climatic changes can cause major shifts in dune activity

the transition from a volcanic to a nonvolcanic rifted margin off eastern canada three multichannel seismic reflection profiles were collected on the rifted continental margin southeast of nova scotia eastern canada the profiles cross the east coast magnetic anomaly ecma which parallels much of the margin of eastern north america south of the grand banks and which is usually associated with the transition from continental to oceanic crust studies to the south of the work reported here suggest that the ecma may be related to the emplacement of large thicknesses of late rift stage or early drift stage igneous material which is characterized by seaward dipping reflections in basement and a high velocity lower crustal layer the seismic data show that seaward dipping reflections sdr continue northward into the study area and support the correlation between the sdr unit and the presence of a well developed ecma magnetic modeling confirms this association although it does not rule out an additional contribution to the magnetic anomaly from an edge effect or suture just north of the study area the ecma diminishes and is no longer well developed the sdr unit also terminates and it is not observed over most of the nova scotian margin if our understanding of the origin of these features is correct then their disappearance marks a transition from a volcanic margin in the south to a nonvolcanic margin in the north the association of the transition with significant changes in the prerift fabric of the adjacent continental crust in the trend of synrift extensional structures and in the width of the zone of thinned continental crust below the margins must be clues to the deeper processes controlling the amount of volcanism produced we suggest that these clues are consistent with small scale convection as a mechanism for delivering large melt volumes to crustal depths during rifting

extreme inundation flows during the hokkaido nansei oki tsunami the tsunami generated by the july 12 1993 hokkaido nansei oki mw 7 8 earthquake produced in japan the worst local tsunami related death toll in fifty years with estimated 10 18m sec overland flow velocities and 30m runup these extreme values are the largest recorded in japan this century and are among the highest ever documented for non landslide generated tsunamis we model this event to confirm the estimated overland flow velocities and we find that given reasonable ground deformation data current state of the art shallow water wave models can predict tsunami inundation correctly including extreme runup current velocities and overland flow we find that even small local topographic structures affect the runup to first order and that the resolution of the bathymetric data is more important than the grid resolution our results qualitatively suggest that for this event coastal inundation is more correlated with inundation velocities than with inundation heights explaining also why threshold type modeling has substantially underpredicted coastal inundation for this and other recent events

holocene dune activity and environmental change in the prairie parki and and boreal forest central saskatchewan canada past aeolian activity was reconstructed at four dunefields in the prairie parkland and boreal forest of central saskatchewan to elucidate landscape response to environmental change optical ages from stabilized dunes in the boreal transition ecoregion indicate two episodes of activity the first at about 11 ka corresponds to a period of early holocene parkland and grassland cover following deglaciation and drainage after about 13 0 ka and brief establishment of boreal forest the second between about 7 5 and 5 ka corresponds to a period of mid holocene parkland grassland cover optical ages from dunefields in the prairie parkland primarily record mid holocene activity between about 7 5 and 4 7 ka corresponding to a period of grassland cover with some reworking continuing into the late holocene although this area was deglaciated by about 13 5 ka there is no evidence of early holocene dune activity suggesting that mid holocene activity may have reworked earlier deposits here consequently much of the morphology and stratigraphy observed in these dunefields are associated with mid holocene activity likely associated with increased aridity and reduced vegetation cover at that time this study provides the most northerly evidence of mid holocene dune reactivation on the great plains lending support to the assertion that aeolian activity was widespread at that time

some observations on tunnelling of trapped electrons in feldspars and their implications for optical dating abstract anomalous fading in feldspars is now understood to be caused by the tunnelling of electrons from one defect site to another here we present some experimental observations concerning the phenomenon the fading rates of a variety of feldspar crystals and k feldspar separates from sediments are reported it is found that 1 the fading rates of 77 k feldspar extracts from sediments range from 1 to 10 decade with an average value of about 5 decade 2 the fading rates of k feldspars extracted from sediments derived largely from volcanic bedrock are not higher than those from non volcanic bedrock as is widely thought 3 the fading rates of 31 individual feldspars range from 1 to 35 decade 4 in plagioclase feldspars the fading rate increases with increasing ca and or fe content 5 the fading rate increases with laboratory radiation dose at large doses 6 for samples for which the time elapsed since burial is long enough for their luminescence to be in saturation the fading rate is correlated with the ratio of the field saturation intensity to the laboratory saturation intensity extrapolation to zero fading rate shows that trap emptying as a result of thermal eviction is not significant and that the mean thermal lifetime in temperate environments of electrons in traps relevant to dating is 4 ma and 7 different aliquots of a sample can have fading rates that differ by a factor as large as two even if the aliquots contain several thousands of grains thus it is necessary to ensure when correcting ages for anomalous fading that the fading rate used is that applicable to the aliquots on which the equivalent dose is measured

holocene eolian sand deposition linked to climatic variability northern great plains canada the bigstick and seward sand hills are possibly two of the oldest dune fields within the late wisconsin glaciated regions of the northern great plains as with most northern great plains dune fields source sediments are former proglacial outwash sands thus holocene dune construction is primarily related to spatial temporal variations in surface cover and transport capacity rather than renewed sediment input however eolian landscape reconstructions on the northern great plains have been temporally constrained to recent periods of activity as older episodes of deposition are typically reworked by younger events in this study sediment cores from shallow lacustrine basins and interdune areas provide an improved record of holocene eolian sand deposition eolian sand accumulation in the interdunes and basins occurred between 150 and 270 years ago 1 9 and 3 0 ka 5 4 and 8 6 ka and prior to ca 10 8 ka these episodes of sand accumulation were bracketed by lacustrine deposition and soil formation whi

storm induced sediment gravity flows at the head of the eel submarine canyon northern california margin 1 as part of the strataform program a bottom boundary layer bbl tripod was deployed at 120 m depth in the northern thalweg of the eel canyon during winter 2000 increases of the near bottom suspended sediment concentrations ssc recorded at the canyon head were not directly related to the eel river discharge but were clearly linked to the occurrence of storms bbl measurements revealed that during intensifications of the wave orbital velocity sediment transport at the head of the canyon occurred as sediment gravity flows directed down canyon observational evidence for near bed sediment gravity flow transport included an increase toward the bed of the down canyon component of wave averaged velocity and high estimated ssc at higher sampling frequencies 1 hz the current components during these events fluctuated at the same periodicity as the pressure reflecting a clear influence of the surface wave activity on the generation and maintenance of the sediment gravity flows the origin of such flows is not related to the formation of fluid muds on the shelf or to intense wave current sediment resuspension around the canyon head region rather liquefaction of sediment deposited at the head of the canyon induced by wave load excess pore water pressures during storms combined with elevated slopes around the canyon head appear to be the mechanisms initiating sediment transport the resulting fluidized sediment layer can easily be eroded entrained into the water column and transported down canyon as a sediment gravity flow results from this study reveal that storm induced sediment gravity flows occur periodically in the eel canyon head and suggest that this kind of sediment transport process can occur in other submarine canyons more frequently than previously expected

dune stabilization in central and southern yukon in relation to early holocene environmental change northwestern north america abstract eolian deposits of central and southern yukon northwestern canada consist of loess mantles small areas of active dunes and larger stabilized dune fields dune fields in valley settings within the region are situated both within and beyond the limit of the last glaciation infrared stimulation luminescence irsl dating in central and southern yukon reveals that these dune fields stabilized as late as 9 8 5 ka well after the retreat of cordilleran glaciers these findings are comparable to other valley setting dune fields and loess from central alaska which record activity during the period from the lateglacial to the holocene thermal maximum htm and reduced or altered activity after 9 8 ka post glacial dune activity was most likely related to warm dry conditions during the htm under predominantly shrub tundra vegetation early holocene stabilization of these dunes probably occurred in response to cooler moister conditions and replacement of predominantly tundra by boreal forest cover dominated by spruce stabilization of dune fields in southern yukon and alaska most likely represented an extension of the time transgressive stabilization of dune fields that occurred across northwestern north america with the post glacial expansion of the boreal forest

deep seismic reflection data of edge u s mid atlantic continental margin experiment implications for appalachian sutures and mesozoic rifting and magmatic underplating the edge seismic experiment across the virginia continental margin delineated a paleozoic suture buried appalachian terranes and mesozoic rifting and magmatic events the seismic grid revealed that the mesozoic norfolk rift basin exists only in the northern one third of the previously mapped area the north striking listric border fault of the norfolk basin half graben parallels seismic laminations in the basement the jurassic volcanic wedge pinches out just landward of the baltimore canyon trough hinge zone and downlaps on the hummocky oceanic basement under the continental rise under the continental slope the volcanic wedgereaches depths 9 s 20 km two distinct intracrustal reflections at 4 0 5 0 s and at 7 0 s twit two way traveltime dip southeastward at low angles 15 the moho reflection is disrupted where it is intersected by the 7 0 s reflection northwest of this point the moho dips landward seaward it is horizontal seaward of this point the lower crustal boundary laminations exist in a narrow interval 10 5 11 0 s and are of strong amplitude these changes in the moho and lower crust represent the seaward edge of the grenville age north american crust and the landward edge of jurassic magmatic underplating a northwest dipping reflection observed for the first time on the u s atlantic margin may be the top of the jurassic magmatic underplating layer the northwest dipping reflection truncates the southeast dipping 7 0 s twtt reflection landward projection of the 7 0 s reflection yields a north south trace on the postrift unconformity under the center of lower chesapeake bay this trace is near a basement fault between low grade metamorphic rocks carolina slate avalonia on the east and high grade rocks goochland terrane on the west this fault boundary and the southeastdipping 7 0 s reflection probably represent the taconic suture

discovery of minoan tsunami deposits the hellenic arc is a terrane of extensive quaternary volcanism one of the main centers of explosive eruptions is located on thera santorini and the eruption of the thera volcano in late minoan time 1600 1300 b c is considered to have been the most significant aegean explosive volcanism during the late holocene the last eruptive phase of thera resulted in an enormous submarine caldera which is believed to have produced tsunamis on a large scale evidence suggesting seawater inundation was found previously at some archaeological sites on the coast of crete however the cause of the tsunami and its effects on the area have not been well understood on the aegean sea coast of western turkey didim and fethye and crete gouves we have found traces of tsunami deposits related to the thera eruption the sedimentological consequences and the hydraulics of a thera caused tsunami indicate that the eruption of thera volcano was earlier than the previous estimates and the tsunami did not have disruptive influence on minoan civilization

formation and evolution of the nova scotian rifted margin evidence from deep seismic reflection data a deep marine seismic reflection profile was obtained across the mesozoic rifted continental margin off nova scotia eastern canada this profile crosses the seotian basin one of the deepest basins on the margin of eastern north america and it complements other deep crustal seismic data on this margin the seismic data have been interpreted in conjunction with gravity anomaly and subsidence data they show significant thinning of the continental crust over a zone about 200 km wide the mode of extensional deformation is probably a combination of pure and simple shear there is evidence for simple shear in the crust the continent ocean boundary lies near the seaward edge of synrift salt below the continental rise a 100 km wide zone of very thin approximately 9 km or less continental or transitional crust extends seaward from the outer shelf to this boundary reflectivity of the oceanic crust adjacent to the margin shows evidence of progressive igneous construction perhaps modified by extensional faulting this margin is nonvolcanic and the transition to the volcanic margin off the eastern united states occurs about 500 km southwest of the seismic line the width of the zone of crustal extension is much greater on this nonvolcanic margin segment than it is on the volcanic margin to the south it seems likely that the prerift fabric of the continental lithosphere controls this width a narrow rift may be prone to vigorous asthenospheric convection and therefore to more voluminous volcanism however significantly narrower zones of crustal extension occur on other nonvolcanic margins so factors in addition to rift width such as the rate of rifting may also be important

late pleistocene dune activity in the central great plains usa abstract stabilized dunes of the central great plains especially the megabarchans and large barchanoid ridges of the nebraska sand hills provide dramatic evidence of late quaternary environmental change episodic holocene dune activity in this region is now well documented but late pleistocene dune mobility has remained poorly documented despite early interpretations of the sand hills dunes as pleistocene relicts new optically stimulated luminescence osl ages from drill cores and outcrops provide evidence of late pleistocene dune activity at sites distributed across the central great plains in addition late pleistocene eolian sands deposited at 20 25 ka are interbedded with loess south of the sand hills several of the large dunes sampled in the sand hills clearly contain a substantial core of late pleistocene sand thus they had developed by the late pleistocene and were fully mobile at that time although substantial sand deposition and extensive longitudinal dune construction occurred during the holocene many of the late pleistocene osl ages fall between 17 and 14 ka but it is likely that these ages represent only the later part of a longer period of dune construction and migration at several sites significant late pleistocene or holocene large dune migration also probably occurred after the time represented by the pleistocene osl ages sedimentary structures in late pleistocene eolian sand and the forms of large dunes potentially constructed in the late pleistocene both indicate sand transport dominated by northerly to westerly winds consistent with late pleistocene loess transport directions numerical modeling of the climate of the last glacial maximum has often yielded mean monthly surface winds southwest of the laurentide ice sheet that are consistent with this geologic evidence despite strengthened anticyclonic circulation over the ice sheet mobility of large dunes during the late pleistocene on the central great plains may have been the result of cold short growing seasons with relatively low precipitation and low atmospheric co 2 that increased plant moisture stress limiting the ability of vegetation to stabilize active dune sand the apparent coexistence of large mobile dunes with boreal forest taxa suggests a late pleistocene environment with few modern analogs

deep crustal structure of the rhine graben from dekorp ecors seismic reflection data a summary abstract results of two deep reflection seismic lines crossing the northern and southern part of the rhine graben which were recorded in 1988 by the french ecors and the german dekorp teams indicate that the asymmetry of this rift persists to the base of the crust the brittle ductile transition zone approximately coincides with the top of the lower crust ductile shear zones appear to affect the crust mantle boundary upper crustal extension by faulting accounts for a divergence of the graben flanks by 5 7 km whereas the crustal configuration of the rhine graben suggest an extension value of some 17 km

evidence of active dune sand on the great plains in the 19th century from accounts of early explorers eolian sand is extensive over the great plains of north america but is at present mostly stabilized by vegetation accounts published by early explorers however indicate that at least parts of dune fields in nebraska colorado kansas new mexico and texas were active in the 19th century based on an index of dune mobility and a regional tree ring record the probable causes for these periods of greater eolian activity are droughts accompanied by higher temperatures which greatly lowered the precipitation to evapotranspiration ratio and diminished the cover of stabilizing vegetation in addition observations by several explorers and previous historical studies indicate that rivers upwind of great plains dune fields had shallow braided sandy channels as well as intermittent flow in the 19th century wide braided sandy rivers that were frequently dry would have increased sand supplies to active dune fields we conclude that dune fields in the great plains are extremely sensitive to climate change and that the potential for reactivation of stabilized dunes in the future is high with or without greenhouse warming

syn and postrift evolution of the el jadida agadir basin morocco constraints for the rifting models of the central atlantic the el jadida agadir basin shows an evolution related to that of the central atlantic rifting history the synrift period late early triassic to earliest jurassic is dominated by deposition of red clastic sediments and evaporites which are overlain by or intercalated with basalt flows two intense extensional phases are recognized the first probably in middle triassic times is oriented north northwest south southeast and resulted in the formation of east northeast west southwest oriented grabens and half grabens the second a widespread northwest southeast trending extension is ladinian to earliest liassic and induced the formation of westward dipping half grabens extensional tectonics initiated in the southern part of the basin and migrated northwards contrary to classical ideas proposing rifting from north to south the postrift evolution is characterized by jurassic to eocene subsidence tectonism appears to have been restricted to a narrow area close to the present day coast subsidence h

crustal structure of the southeast georgia embayment carolina trough preliminary results of a composite seismic image of a continental suture and a volcanic passive margin new deep penetration multichannel seismic reflection data combined with refraction results and magnetics modeling support a hypothesis that the carolina trough is a mesozoic volcanic passive margin exhibiting a seaward dipping wedge and associated underplating the structure of carolina platform continental crust is consistent with the late paleozoic continental collision that produced the appalachians but imbrication has had no obvious effect on shallower structures produced by mesozoic extension and volcanism the origin of prominent magnetic anomalies crossing the southeast georgia embayment can be explained by processes attending mesozoic separation of africa and north america and is not related to a paleozoic continental suture as previously postulated

crustal structure of the newfoundland rifted continental margin from constrained 3 d gravity inversion the rifting history of the atlantic continental margin of newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2 d seismic surveys while informative the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin a 3 d gravity inversion of the free air data over the newfoundland margin allows us to generate a 3 d density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage results of the gravity inversion show good correspondence with moho depths from seismic results a shallowing of the moho to 12 km depth is resolved on the shelf at the northern edge of the grand banks in a region poorly sampled by other methods comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends such insights must act as constraints for future palaeoreconstructions of north atlantic rifting