middle permian paleomagnetism of the sydney basin eastern gondwana testing pangea models and the timing of the end of the kiaman reverse superchron abstract paleomagnetic and geochronologic data from the eastern margin of gondwana have been obtained from the gerringong volcanics in the southern sydney basin australia the corresponding paleomagnetic pole at 56 9 s 154 8 e n 131 a95 9 1 has a 40ar 39ar plagioclase plateau age of 265 05 0 35 0 46 ma from the bumbo latite and overlaps with recent radio isotopic and paleomagnetic results published from western gondwana the long documented inconsistency between middle permian eastern and western gondwanan paleomagnetic datasets is most likely an artefact of a lack of reliable paleomagnetic data from eastern gondwana for this period a number of well dated and recently published ca 265 ma paleomagnetic results from gondwana and laurussia are shown to be consistent with the wegenerian pangea a configuration with a loose n s fit of the continents for the middle permian the lack of crustal overlap negates the need for a pangea b configuration which if valid must have been assembled to pangea a by ca 265 ma the reverse polarity bumbo latite was sampled from the kiaman type section located in the southern sydney basin three cases of normal polarity were detected in the overlying saddleback dapto and berkeley latites previously assigned to the kiaman reverse superchron krs we review krs aged magnetostratigraphic data and propose that an age assignment of 265 ma most likely represents the termination of the non reversing field with longer stable intervals of normal polarity recorded and able to be correlated globally

error analysis for the determination of tectonic rotation from paleomagnetic data appendix b is available with entire article on microfiche order from american geophysical union 2000 florida avenue n w washington d c 20009 document b83 001 2 50 payment must accompany order recent determinations of tectonic rotation and flattening from paleomagnetic data have exaggerated the size of the confidence limits or error bars by about 25 this has been caused by the misuse of conventional error propagation formulas to derive one degree of freedom error bars from a two dimensional cone of confidence 95 an analytical calculation which is valid when error bars are small shows that the correct error bars are 75 to 80 of the values derived in previous studies i have used numerical integration to check on the applicability of the analytical solution and to calculate error bars when the analytical approximation cannot be used the analytical approximation may be used whenever 95 is less than 10 and the mean inclination is not too close to vertical confidence limits given for tectonic rotation and flattening in recent literature are too large and should be reduced by 20 25 narrowing the error bars in this way permits a more accurate interpretation of paleomagnetic data

a scaling growth model for bubbles in basaltic lava flows abstract pahoehoe an and massive lavas from mount etna show common statistical properties from one sample to another which are independent of scale size over certain ranges the gas vesicle distribution shows two scale invariant regimes with number density n v v b 1 where v is the volume and empirically b 0 for small bubbles and b 1 for medium to large bubbles we introduce a bubble growth model which explains the b 1 range by a strongly non linear cascading growth regime dominated by a quasi steady state coalescence process the small bubble region is dominated by diffusion its role is to supply small bubbles to the coalescence regime the presence of measured dissolved gas in the matrix glass is consistent with the notion that bubbles generally grow in quasi steady state conditions the basic model assumptions are quite robust with respect to the action of a wide variety of processes since we only require that the dynamics are scaled over the relevant range of scales and that during the coalescence process bubble volumes are approximately conserved the model also predicts a decaying coalescence regime with b 1 associated with a depletion of the gas source or alternatively a loss of large vesicles through the surface of the flow our model thus explains the empirical evidence pointing to the coexistence of two different growth mechanisms in subsurface lava flows but acting over distinct ranges of scale with non linear coalescence as the primary growth process the total vesicularity of each sample can then be well estimated from the partial vesicularity of each growth regime without any outlier problems

final stages in the collapse of the laurentide ice sheet hudson strait canada nwt 14c ams dates seismics stratigraphy and magnetic susceptibility logs hudson strait is a key element in the history of ice sheet ocean interactions during the deglaciation of the laurentide ice sheet data from over 30 giant piston cores supplemented by ca 40 14c ams dates on foraminifers and shells from sites within and adjacent to hudson strait are used to describe the timing and sediment processes associated with the final complex phases of deglaciation in hudson strait each core is placed in a regional seismic architectural context through examination of deep tow huntec profiles most cores sample a thin postglacial unit and extend several meters into glacial marine sediment mainly silty clays 14c dates on cores from the adjacent shelf indicate that deglaciation occurred by 13 ka we have not been unable to confirm that hudson strait was ice free by 11 12 ka although this is a probable scenario whole core magnetic susceptibility wcms data are used as the primary signature of changes in the style of sedimentation and provenance and to correlate between cores wcms indicates that there is a regional differentiation in the ms signal associated with bedrock provenance changes in contribution of detrital carbonate and style of sedimentation one low wcms event is present in cores from both the western and eastern basins it dates from 8 0 ka and provides an important regional stratigraphic marker probably associated with the final deglaciation of hudson bay and hudson strait sediment from a southerly source ungava bay continued to be contributed into the 900 m deep eastern basin of hudson strait 8 and 7 ka and thick postglacial sequences were piled within ungava bay between 6 and 7 ka

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

late quaternary sediments and chronology of the northeast labrador shelf karlsefni trough saglek bank links to glacial history core hu87033 015 an 11 m long giant piston core from the western end of karlsefni trough was taken only 25 km from the coast of northernmost labrador the regional acoustic framework was established via a high resolution deep towed huntec dts seismic survey we recognized four acoustic facies that are associated with designated and recovered major lithologic units the ages of these units were determined from 13 accelerator mass spectrometry 14 c dates from marine biogenic carbonates these results suggest that glacial ice was present on the shelf from at least the mid wisconsinan and that the basal sequence contains reworked glacial marine diamicton furthermore our data provide the first evidence that the northern labrador inner shelf was ice free by ca 11 14 c ka the bulk of the postglacial deposition was around 8 2 ka and consists of increased detrital carbonate deposition the deposition of this detrital carbonate is age equivalent with dc 0 on the southeastern baffin shelf and in the north atlantic

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

bubble migration and coalescence during the solidification of basaltic lava flows the initial size distribution of gas bubbles in lava flows is modified by bubble rise and coalescence during post eruptive cooling and crystallization a simple model which computes the effects of rise and coalescence accounts for observed features and may provide a means whereby the initial bubble size distribution can be inferred a model lava flow of assumed thickness viscosity and volume percentage of gas bubbles is given an initial bubble size distribution bubbles coalesce due to differences in their relative rise velocities using a gravitational collection kernel the process may be modeled by numerical integration of the stochastic collection equation which yields the change in the number density spectrum of the population from the number densities of all pairs of bubbles and their probabilities of collision bubbles rise and coalesce within a fluid interior sandwiched between fronts of crystallization that advance inward from top and bottom bubbles that are overtaken by the crystallization f

early permian location of western north american terranes based on brachiopod fusulinid and coral biogeography abstract brachiopod rugose coral and fusulinid faunas present in early permian rocks along northern and western margins of north america in both cratonal localities and accreted terranes have been compared statistically allowing refinement in placement of these terranes relative to the north american continental margin at that time statistical tests including conventional and probabilistic indices of similarity as well as multivariate analysis show that the faunas of wrangellia alexander are most similar to those of stikinia and quesnellia and to the yukon canadian rocky mountains part of the continental margin they also show that faunas of the eastern klamath terrane are most similar to those of stikinia quesnellia and the central cordilleran part of the continental margin these results suggest that during the early permian wrangellia alexander was the northernmost of these terranes lying west of the yukon canadian rocky mountains region and the eastern klamath terrane was the southernmost lying west of the central cordillera stikinia and quesnellia were in intermediate positions these relative latitudes are compatible with latitudinal determinations based on paleomagnetic data faunal diversity in the eastern klamath and stikine terranes is similar to that at similar latitudes on the craton whereas diversity in the wrangellia alexander terrane is considerably lower than that of the latitudinally similar yukon canadian rocky mountains area as diversity is in part a function of temperature this may suggest water around the wrangellia alexander terrane was cooler than that along the continental margin therefore we suggest that warm water currents bathed the southern terranes and the southern and central parts of coastal north america whereas cool water currents influenced the northernmost terrane wrangellia alexander revised otsuka similarity coefficients for corals show higher similarities between western north american terranes and the western continental margin than previously published but they still are relatively low this and the overall patterns of similarity and limits on distribution of tethyan corals and fusulinids in the eastern panthalassa suggest that wrangellia alexander stikinia and the eastern klamath terranes were at approximately the same distance estimated at 2000 3000 km from their latitudinally equivalent segments of the north american craton

ice age paleotopography a gravitationally self consistent theory of postglacial relative sea level change is used to infer the variation of surface ice and water cover since the last glacial maximum lgm the results show that lgm ice volume was approximately 35 percent lower than suggested by the climap reconstruction and the maximum heights of the main laurentian and fennoscandian ice complexes are inferred to have been commensurately lower with respect to sea level use of these ice age boundary conditions in atmospheric general circulation models will yield climates that differ significantly from those previously inferred on the basis of the climap data set

marine evidence for the last glacial advance across eastern hudson strait eastern canadian arctic data from accelerator mass spectrometer radiocarbon dated sediment cores and huntec high resolution seismic profiles were used to investigate the age and origin of the sediments in the eastern basin of hudson strait the data indicate that the ice contact and glacial marine sediments on the basin flanks and much of the upper sequence in the deep floor of the basin were produced during the noble inlet advance 8 9 to 8 4 ka the last northward expansion of the labrador dome on to southeastern baffin island on the northern flank of eastern basin one sequence of ice contact sediments and glacial marine deposits overlies bedrock the glacial marine sediments are transitional upslope to ice contact sediments and form at least two successive ice sheet grounding zones the earliest abundance peaks of benthic foramininfera in glacial marine sediments date ca 8 6 and 8 4 ka and correlate to sediments near the base of the 58 m thick glacial marine section in the deepest part of eastern basin this correlation suggests that noble inlet ice was grounded throughout eastern basin during the early part of its advance in later stages the thinning ice produced grounding zones on the basin flanks while glacial marine sediments were deposited in the deep basin 1998 john wiley sons ltd

dynamics of the laurentide ice sheet in hudson bay canada abstract interpretation of sidescan sonar and high resolution sub bottom seismic data from hudson bay has led to the development of a model for final disintegration of the laurentide ice sheet the well preserved geomorphic features observed from the bay floor are similar to subaerially exposed glaciogenic features observed around the perimeter of hudson bay and can be related to the following three paleoenvironments subglacial erosion deposition ice margin deposition and reworking and post glacial reworking and burial subglacial features observed include fluted terrains with superimposed rogen moraines relief attributed to ice surging eskers subglacial channels and dead ice topography de geer moraines and recessional moraine complexes indicate the mechanism and orientation of ice breakup retreat the orientations of these features are locally consistent with regional trends indicating the overall direction of ice sheet flow and retreat during the last phase of the laurentide ice sheet subglacial channel complexes incised into the till and bedrock and high energy bedforms deposited on the till surface occur in present day water depths down to 160 m due to isostatic depression these could have been as much as 315 m deeper at the time of formation they indicate a wet based glacier with high energy subglacial drainage during the late phases of ice retreat the sidescan sonar data also reveal numerous zones of distinctive morphology attributed to ice breakup and post glacial processes cross cutting relationships allow the determination of the relative ages of these zones from oldest to youngest these zones are interpreted to represent scouring of the bedrock and overburden by the remnants of the ice sheet seafloor scouring by tabular icebergs which moved in a tidally induced arcuate pattern or under the influence of massive glacial lake outflows development of dead ice topography under residual ice masses and random iceberg scouring by smaller icebergs restricted to present day water depths of less than 180 m recently published reconstructions of the collapse of the laurentide ice sheet based on dated quaternary sections on land suggest that the bay was rapidly deglaciated in approximately 400 years the well preserved and distinctive glaciogenic and stratigraphic indicators observed from the bay floor suggest that they were formed by a succession of mechanisms which were too short lived to obliterate the underlying evidence of deglaciation this supports the interpretation of extremely rapid deglaciation of hudson bay and points out that subsequent marine processes have not been sufficient to obliterate the glacial features

paleomagnetic study of the eastern klamath terrane california and implications for the tectonic history of the klamath mountains province paleomagnetic study of permian through jurassic volcanic and sedimentary strata of the eastern klamath terrane has shown the remanent magnetization of many of these rocks to be prefolding and most likely primary similarities in magnetic declinations recorded by coeval strata over a broad area are consistent with the hypothesis that the terrane in general has behaved as a single rigid block paleomagnetic data indicate that the volcanic island arc represented by this terrane the nucleus of the province was facing toward the present southwest during late paleozoic time although its orientation during earlier periods is unknown whether the arc was separated from the north american craton by a small marginal basin or originated far offshore cannot be determined from paleomagnetic data the declination anomalies for both permian and triassic strata are similar average 106 12 so we infer that clockwise rotation of the late paleozoic arc did not begin until latest triassic or earliest jurassic time the arc may have completed its initial rotation with respect to stable north america by middle jurassic time after some retrograde motion the arc was again facing west by the late jurassic by which time some of the more westerly terranes of the province had become attached to the eastern klamath terrane the composite klamath mountains terranes continued to rotate until the final 60 of clockwise rotation was nearly complete by the early cretaceous coincidence of the waning stages of rotation at about 136 ma with the beginning of deposition of the basal great valley sequence onto the klamath basement probably represents the completion of accretion of the klamath mountains terranes to the north american continent nearly all the rotation occurred while the klamath mountains terranes were part of a converging oceanic plate with only about 20 of rotation in mid tertiary time during basin and range extension no data currently available show evidence for any significant latitudinal displacement of any klamath mountains terranes relative to cratonic north america

explained and unexplained spatial and temporal variability in rates of marine sediment accumulation along the northeast margin of the laurentide ice sheet 14 ka abstract changes in sediment accumulation rate sar cm ky for fifteen ams 14c dated late quaternary sites from along the ne margin of canada between 66 and 54 n are examined these 15 cores cover the last deglacial cycle of sediment input from the decaying laurentide ice sheet and subsequent postglacial marine sedimentation on these arctic and subarctic shelves and basins it is shown that the spatial and temporal variability of the 15 sar time series do not simply parallel the known glacial chronology deglaciation of the shelves initially occurred after heinrich event 1 h 1 14 5 ka all dates are in 14c yr subsequently there were major ice advances during the younger dryas yd h 0 10 11 ka and the noble inlet glacial events 8 6 ka with final collapse of the ice sheet ca 8 0 ka a total of 73 radiocarbon dates were used which led to 58 sar estimates the median sar is 69 cm ky however the distribution is strongly positively skewed because of short lived intervals of very high sar 5000 cm ky ca 5000 kg m 2 ky 1 on the labrador shelf high sar are associated with ice retreat from the noble inlet maximum 8 6 ka whereas on the se baffin shelf there is little response in the sediment system to this event conversely during the younger dryas heinrich 0 yd h 0 event high sars occur on the se baffin shelf but along the labrador shelf the interval 10 11 ka is marked by modest sars both the 11 10 and 8 6 8 ka rapid sediment accumulation events are marked by considerable increases in the detrital carbonate content hence bear similarities to the major heinrich events in the nw labrador sea these unexpected spatial and temporal differences in sediment deposition probably reflect changes in sediment transport trajectories associated with differences in ice glacial or sea ice extent and atmospheric oceanic circulations

effects of compressibility on the flow of lava lava contains gas bubbles and hence is a compressible liquid whose density increases as a function of pressure after eruption at the earth s surface it spreads at a rate which is a function of its thickness and it is compressed under its own weight therefore both thickness and spreading rate are determined by a balance between viscous and compressible effects theoretical equations are derived for the shape and velocity of a compressible liquid spreading on a horizontal surface solutions are obtained for a fixed eruption rate q the radial extent of the flow increases proportional to t1 2 a dimensionless number c is defined which characterizes the importance of flow compression c rho 0 beta g left frac mu q rho 0 2 g right 1 mathord left vphantom 1 4 right kern nulldelimiterspace 4 where 0 is bubbly lava density at atmospheric pressure compressibility viscosity and g the acceleration of gravity c can be thought of as the ratio of two characteristic length scales one for compression effects and one for viscous effects the larger c is the more important compressibility effects are as c is increased the flow becomes thinner because the liquid is compressed more and more efficiently compressibility acts to smooth out variations of flow thickness which provide the driving force thus all else being equal a compressible liquid flows less rapidly than an incompressible one when trying to infer the effective viscosity of a flow from its spreading rate the neglect of compressibility leads to an overestimate the various factors which act to determine the distribution of gas bubbles in lava flows are reviewed and discussed quantitatively comparison with data from obsidian dome eastern california shows that disequilibrium effects are important and that bubble resorption during burial in a thick flow is not a pervasive phenomenon the analysis is applied to the 1979 dome of soufriere de saint vincent w i an effective value of compressibility for this 100 m thick dome is 1 5x10 6 pa 1 this implies that all else being equal the viscosity of this lava may be overestimated by a factor of 5 if no account is taken of the compressible nature of the flow

tectonic rotations and translations in western canada new evidence from jurassic rocks of vancouver island the lower jurassic bonanza group sinemurian and pliensbachian lavas and tuffs about 205 to 195 ma on northwestern vancouver island possesses a stable remanent magnetization with a mean direction d i of 276 42 13 sites distributed through 1800 m of section 128 specimens kb 50 95 6 palaeopole 22 n 154 e dm dp 9 6 reversals are present but one polarity is dominant and most directions are westerly the palaeolatitude is 24 6 with the usual ambiguity as to whether it is north or south of the palaeoequator to determine the relative motions between ancestral north america and vancouver island these data are compared with determinations from peri atlantic igneous rocks dated radiometrically in the same time interval the use of model apparent polar wander paths for this purpose is criticized a net post jurassic northerly motion of 9 7 or 57 7 is indicated depending on the chosen hemisphere of origin the net post jurassic rotations relative to cratonic north america are 66 7 anticlockwise or 114 7 clockwise for the northern and southern hemispheres respectively such large rotations are apparently a common feature of early mesozoic rocks of the canadian cordillera it is suggested that these large and variable rotations characterize the deformation occurring during the pre mid cretaceous amalgamation of the various terranes of british columbia

cache creek terrane entrapment oroclinal paradox within the canadian cordillera exotic and far traveled oceanic crustal rocks of the cache creek terrane cc are bordered by less exotic quesnel qn and stikine st arc terranes to the east north and west all of these terranes are enveloped by an arcuate belt of displaced continental margin rocks the kootenay ko nisling ns and parts of the yukon tanana ytt terranes that have indirect ties to ancestral north america na initial 87sr 86sr isopleths conform to this arcuate pattern such a pattern of concentric belts presents a geological conundrum how did the qn st and cc come to be virtually enveloped by terranes with ties to na past and current models that explain assembly of the canadian cordillera are deficient in their treatment of this problem we propose that early mesozoic qn and st were joined through their northern ends as two adjacent arc festoons that faced south toward the cache creek ocean panthalassa oceanic plateau remnants within the cc today were transported from the tethyan realm and collided with these arcs during subduction of the cache creek ocean counterclockwise oroclinal rotation of st and ns terranes in the late triassic to early jurassic caused enclosure of the cc rotation continued until these terranes collided with qn in the middle jurassic paleomagnetic declination data provide support for this model in the form of large average anticlockwise rotations for permian to early jurassic sites in st but moderate clockwise rotations for sites in qn specific modern analogues for the cordilleran orocline include the yap trench where the caroline rise is colliding end on with the mariana arc and the banda arc located on the southeastern tail of the asian plate which is being deformed into a tight loop by interactions with the australian and pacific plates

evidence from neodymium isotopes for mantle contributions to phanerozoic crustal genesis in the canadian cordillera sm nd and rb sr isotopic studies of several phanerozoic orogenic belts have shown that much of the crust in these belts is composed of reworked pre existing continental crust in contrast isotopic data collected from two of the largest terranes in the canadian cordilleran orogenic belt the alexander and stikine terranes show that these tectonic fragments are composed of mantle derived continental crust in many respects the style and rate of crustal accretion of these and related terranes appear similar to those of some proterozoic crustal regions

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

late glacial flow patterns deglaciation and postglacial emergence of south central baffin island and the north central coast of hudson strait eastern canadian arctic new georaorphic sedimentologic and chronologic data are used to reconstruct late quaternary ice sheet flow patterns deglaciation and isostatic uplift along the largest marine trough connecting the laurentide ice sheet with the north atlantic ocean the lake harbour region was targeted for study given its potential to record flow from several ice dispersal centers striations and sediment provenance indicators define flow patterns thirty four radiocarbon dates constrain a chronology of events centuries or millennia before deglaciation a southeast flowing ice stream impinged on southernmost big island as recorded by a single striation site and delimited in extent by geomorphic evidence of cold based ice during the cockburn substagc 9000 8000 bp the region was scoured by southward to southwestward flow from an ice cap on meta incognita peninsula as recorded by 60 striation sites along 200 km of coastline carbonate erratics are uncommon in till above the marine limit where present they sugg

sediment thicknesses and holocene glacial marine sedimentation rates in three east greenland fjords ca 68 n we compared measured and estimated sediment budgets in heavily glaciated fjords in east greenland mass balance calculations and regional glacio climatic conditions suggest that the sediment flux to the seafloor in kangerdlugssuaq and nansen fjords should be dominated by iceberg rafting and not by the rain out of suspended particulates in meltwater as the glacier calving flux is estimated at 15 and 2 km 3 yr compared to meltwater volumes of 4 4 and 1 7 km 3 yr respectively gravity cores in the three fjords indicate that the uppermost 1 2 5 m of sediment consists of diamictons or fine grained laminated muds ams radiocarbon dates on calcareous foramininfera or shells 16 total indicate sedimentation rates of 110 to 340 cm ka within the fjords over the last 1 ka and 10 20 cm ka during the holecene on the inner and middle shelf annual sediment discharge is around 0 67 times 10 6 tonnes yr within the kangerdlugssuaq fjord and trough system which translates into an average basin wide rate

paleomagnetism of the late paleozoic slide mountain terrane northern and central british columbia paleomagnetic samples were collected from mid pennsylvanian to lower permian red argillaceous cherts at two localities of the slide mountain terrane 18 sites from the sylvester allochthon in northern british columbia and 11 sites from sliding mountain in central british columbia a secondary component of natural remanent magnetization in the sylvester samples yields a paleomagnetic pole that can be brought into coincidence with the jurassic portion of the north american apparent polar wander path by inferring vertical axis rotation during obduction of the allochthon both localities yield a characteristic component chrm with unblocking temperatures from 650 to 680 c after structural correction for bedding tilt all inclinations of chrm are negative consistent with magnetization during a reversed polarity interval in the northern hemisphere site mean chrm directions show consistent inclinations but distinct stratigraphic groupings of declinations inclination only statistics indicate that the chrm p

postglacial sequence stratigraphy of lake melville labrador abstract in lake melville labrador the quaternary glacimarine sediments reflect a single retreat phase of the laurentide ice sheet during the early holocene based on extensive airgun and high resolution seismic surveys sediment deposits are subdivided into thirteen units that are associated with glacial paraglacial and postglacial styles of deposition their distribution patterns reflect paleo positions of a retreating ice margin during the period between 10 000 and 9000 years before present formation of paraglacial deltas during the early to mid holocene 6 9 ka and postglacial tidal influenced deposition during the late holocene

lava flows are fractals we have conducted a preliminary investigation of the fractal nature of the plan view shapes of lava flows in hawaii based on field measurements and aerial photographs as well as in idaho and the galapagos islands using aerial photographs only our results indicate that the shapes of lava flow margins are fractals in other words lava flow shape is scale invariant at least within the range of scale measured 0 5m to 2 4km this observation has important implications for understanding the fluid dynamics of lava flows it suggests that nonlinear forces are operating in them because nonlinear systems frequently produce fractals furthermore a a and pahoehoe flows can be distinguished by their fractal dimensions d the majority of the a a flows we measured have d between 1 05 and 1 09 whereas the pahoehoe flows generally have higher d 1 14 1 23 we have extended our analysis to other planetary bodies by measuring flows from orbital images of venus mars and the moon all are fractal and have d consistent with the range of terrestrial a a and pahoehoe values combining the terrestrial and extraterrestrial data the fractal nature of lava flow outlines holds for over five orders of magnitude in scale 0 5m to 60km

p type and s type pahoehoe a study of vesicle distribution patterns in hawaiian lava flows abstract two main types of hawaiian pahoehoe lava p type pipe vesicle bearing and s type spongy are characterized their origin is inferred from features of the vesicle sizes and abundances particularly in their chilled margins which record frozen in the vesicle population at the time and place of solidification s type margins are distinctly more vesicular than p type porosity and vesicle size and range in s type margins are highest at the vent vesicle size reaches a minimum in medial areas and then increases while porosity decreases onto the flatter ground of the coastal terrace the vesicles are inferred to be part of the complement of bubbles that was present at the vent modified by loss and coalescence during travel in lava tubes the minimum porosity occurs on the coastal terrace and is the result of degassing during a longer residence time in lava tubes there the systematically lower porosity of p type margins than s type is attributed to a still longer residence allowing more time for bubble coalescence and loss p type pahoehoe is common only on flatter ground such as the coastal terrace it is found where tumuli and lava rises are widespread and where extensive networks of lava expansion clefts occur through which lava moving below the surface crust can lose gas without significant cooling additionally p type pahoehoe shows clear evidence that a strong inward movement and growth of bubbles took place from the outermost selvage into an inner selvage concentration zone a mechanism that might cause this inward movement is surface tension operating against deforming forces in the steep viscosity gradient of flow margins causing down gradient bubble translation inward movement does not usually occur in the upper crust of thick 2 m flow units because of the absence of strong deforming forces in the shallow velocity gradient there many of the larger bubbles that entered the inner selvage rose buoyantly to form pipe vesicles p type pahoehoe is characterized by sampled profiles across 20 flow units continued gas loss through surface clefts caused a general overall reduction in vesicle content within each flow unit to less than that in the upper crust and the pronounced depletion of vesicles from its lower half is attributed to scavenging by ascending pipe bubbles in a small proportion of flow units overall gas loss was small and a median gas blister fed by pipe bubbles developed instead

northern labrador shelf glacial chronology and depositional environments huntec deep tow records 3 5 and 12 khz echo sounder profiles backed by airgun reflection cores and 14c dates delineate 10 mappable acoustic morphologic units between 57 n and 61 n on the northern labrador shelf these include i section composed of numerous horizontal reflectors with minimal scattering and smooth microrelief ii acoustically transparent section with numerous subparallel draped reflectors at its base it underlies unit i in basin centers iii section marked by intense scattering point reflectors and a rough microrelief iv section exhibiting strong scattering as in iii but with smooth microrelief and obvious terraces v a b outcropping portions of ii type sediments variably dissected vi outcrops of ii exhibiting warping acutely intersecting reflectors and undulating mesorelief vii a b areas of strong macrorelief with ridges and wedge or lens shaped reflectors and strong scattering vii section exhibiting strong macrorelief as in vii a b but with somewhat rougher microrelief a

paleomagnetic evidence for motions of parts of the canadian cordillera abstract paleomagnetic evidence from major terranes of the western cordillera in canada referred to collectively as baja british columbia indicates that they have moved as a whole about 2300 km from the south and rotated 60 clockwise relative to north america in the late cretaceous and earliest tertiary 85 50 ma sometime between the early jurassic and the mid cretaceous 190 100 ma these same terranes moved south over 1000 km and underwent irregular but where well constrained counter clockwise rotations the terranes amongst themselves seem to have shared much the same paleolatitude during and since the late triassic although they may have undergone relative rotations in the later jurassic and early cretaceous these motions are now known to be broadly consistent with the motions of oceanic plates to the west as calculated by independent procedures and indicate that the terranes of the western cordillera were for part of their existence coupled to oceanic plates first to the farallon plate during the late jurassic and early cretaceous and then to the kula plate during the late cretaceous and early tertiary it was this change of allegiance from farallon to kula that caused first the southerly and then the northerly motion the paleomagnetic evidence despite claims to the contrary is consistent with geologically inferred displacements along major faults in the canadian cordillera when due account is taken of the age constraints on those motions

depositional facies of late pleistocene heinrich events in the labrador sea late pleistocene heinrich ice rafting events produced layers rich in ice rafted debris in major parts of the north atlantic north of 40 n a high detrital carbonate content points to the hudson strait outlet of the laurentide ice sheet as a dominant source of the icebergs heinrich events were coupled with short term climate fluctuations during the last and penultimate glaciations and provide evidence for cryosphere hydrosphere atmosphere interaction in pleistocene climate change an unsolved problem with heinrich layers has been their high concentration of fine grained detrital carbonate 80 of the total detrital carbonate which cannot have been delivered by icebergs alone we propose combinations of different processes that deposited four sedimentologically different types of heinrich layers ice rafting alone for the coarser sand to gravel sized fractions and the fine fractions in distal regions type iv heinrich layers whereas nepheloid flows deposited the bulk of the fine sediment in regions proximal to the hudson strait type i heinrich layers on the labrador slope turbidity currents spilling over from canyons were also involved in transporting the fine grained carbonate rich material causing an alternation of mud turbidites and thin laminae of ice rafted debris in type ii heinrich layers on the levees of the northwest atlantic mid ocean channel the thickness relationship is reversed mud turbidites deposited by occasional spillover of currents from the channel are thin and alternate with thicker laminae of ice rafted debris type iii heinrich layers

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

measurement of bubble size distributions in vesiculated rocks with implications for quantitative estimation of eruption processes abstract this paper outlines methods for determining a bubble size distribution bsd and the moments of the bsd function in vesiculated clasts produced by volcanic eruptions it reports the results of applications of the methods to 11 natural samples and discusses the implications for quantitative estimates of eruption processes the analysis is based on a quantitative morphological stereological method for 2 dimensional imaging of cross sections of samples one method determines with some assumptions the complete shape of the bsd function from the chord lengths cut by bubbles the other determines the 1st 2nd and 3rd moments of distribution functions by measurement of the number of bubbles per unit area the surface area per unit volume and the volume fraction of bubbles comparison of procedures and results of these two distinct methods shows that the latter yields rather more reliable results than the former though the results coincide in absolute and relative magnitudes results of the analysis for vesiculated rocks from eleven subplinian to plinian eruptions show some interesting systematic correlations both between moments of the bsd and between a moment and the eruption column height or the sio2 content of magma these correlations are successfully interpreted in terms of the nucleation and growth processes of bubbles in ascending magmas this suggests that bubble coalescence does not predominate in sub plinian to plinian explosive eruptions the moment moment correlations put constraints on the style of the nucleation and growth process of bubbles the scaling argument suggests that a single nucleation event and subsequent growth with any kind of bubble interaction under continuous depressurization which leads to an intermediate growth law between the diffusional growth r m t 2 3 at a constant depressurization rate and the ostwald ripening r m t 1 3 under a constant pressure where rm and t are the mean radius of bubble and the effective time of diffusion respectively occurred in the eruptions it is emphasized that the bsd in vesiculated rocks from terrestrial volcanoes can be used to estimate quantitatively eruption processes such as the initial saturation pressure and magma ascent velocity in a volcanic conduit

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

late quaternary stage 2 and 3 meltwater and heinrich events northwest labrador sea two major meltwater events are documented in cores from the nw labrador sea one occurred ca 20 000 14c yr b p in association with deposition of a major detrital carbonate unit both prior to and after this event 18o values of near surface planktonic foraminifera were 4 5 indicating fully enriched glacial values a younger event ca 14 000 14 c yr b p is characterized by a dramatic change in 18o from 4 5 to 2 0 and coincided with the retreat of ice from the outer se baffin shelf possibly into hudson strait these meltwater events coincide with heinrich h layers 1 and 2 from north atlantic sediments the 14 000 14c yr b p meltwater event indicates that the eastern margin of the laurentide ice sheet also underwent rapid retreat at approximately the same time as other ice sheet margins around the ne north atlantic a third major detrital carbonate event at the base of hu87 033 009 possibly correlative with heinrich layer 3 occurred ca 33 960 675 14 c yr b p however this is older than the accepted date for h 3 of 27 000 14c yr b p and may be h 4

sediments sedimentation rates and environments southeast baffin shelf and northwest labrador sea 8 26 ka ten 14c dated cores are described from the labrador sea continental slope and hatton and resolution basins on the southeast baffin shelf based on sharply defined detrital carbonate layers in the labrador sea cores we propose that the laurentide ice sheet reached the shelf break at both 20 and 15 14c ka 24 3 and 18 2 sidereal ka and contributed significant sediment to the northwest labrador sea both times the flux was 720 kg m2 ka during these periods of maximum ice extent the laurentide ice sheet retreated from its 15 ka position at the shelf break to the inner shelf between 14 and 12 14c ka ice proximal conditions recognized by relatively light 18o on near surface planktonic foraminifera high detrital carbonate and benthic foraminiferal faunas dominated by elphidium excavatum forma clavata cassidulina reniforme prevailed until at least 10 14c ka the ice readvanced toward resolution basin and across part of hatton basin at 11 14c ka accelerator mass spectrometry dates on core tops i

preliminary paleomagnetic results from the permian asitka group british columbia tuffs rhyolites and basalts collected at seven sites 25 samples in the early permian asitka group of stikinia have similar paleomagnetic inclinations and corresponding paleolatitudes of 23 6 21 4 and 23 5 respectively both polarities occur so the paleolatitudes could be either north or south of the paleoequator although the polarity bias favours the former option the paleolatitude expected for the sampling region is 27 4 n adopting the paleomagnetically more probable northern option the mean displacement relative to the north american craton is 5 6 indicating that stikinia was in much the same latitudinal position relative to the craton during the early permian as it is at present although possibly somewhat to the south the declinations are in poor agreement indicating that relative rotations occurred in this faulted terrane

numerical modeling of late glacial laurentide advance of ice across hudson strait insights into terrestrial and marine geology mass balance and calving flux a time dependent finite element model was used to reconstruct the advance of ice from a late glacial dome on northern quebec labrador across hudson strait to meta incognita peninsula baffin island and subsequently to the 9 9 9 6 ka 14c gold cove position on hall peninsula terrestrial geological and geophysical information from quebec and labrador was used to constrain initial and boundary conditions and the model results are compared with terrestrial geological information from baffin island and considered in the context of the marine event dc 0 and the younger dryas cooling we conclude that advance across hudson strait from ungava bay to baffin island is possible using realistic glacier physics under a variety of reasonable boundary conditions production of ice flux from a dome centered on northeastern quebec and labrador sufficient to deliver geologically inferred ice thickness at gold cove hall peninsula appears to require extensive penetration of sliding south from ungava bay the discharge of ice into the ocean associated with advance and retreat across hudson strait does not peak at a time coincident with the start of the younger dryas and is less than minimum values proposed to influence north atlantic thermohaline circulation nevertheless a significant fraction of freshwater input to the north atlantic may have been provided abruptly and at a critical time by this event

mid wisconsin laurentide ice sheet growth and decay implications for heinrich events 3 and 4 a close look at the sedimentology of heinrich event 4 from the northwest labrador sea indicates that an extended ice margin perhaps greater than before heinrich events 1 or 2 h 1 and h 2 existed in the hudson strait region pre heinrich event 4 h 4 and that on the basis of characteristics of the sediment unit heinrich event 4 was different than heinrich events 1 or 2 i e larger ice sheet collapse longer duration dirtier icebergs other data from across the southern and eastern margin of the laurentide ice sheet as well as greenland and the north atlantic support this interpretation possibly indicating a relative mid wisconsin glacial maximum pre heinrich event 4 many of these data also indicate that heinrich event 4 35 ka resulted in serious climatic and oceanographic reorganizations we suggest that heinrich event 4 gutted the hudson strait leaving it devoid of ice for heinrich event 3 we further hypothesize that heinrich event 3 did not originate from axial ice transport along the hudson strait thus heinrich event 3 may be more analogous to the proposed northward advancing ice from ungava bay during heinrich event 0 than to the more typical down the strait flow during h 1 h 2 and h 4 consequently the climatic and oceanographic impacts resulting from heinrich events are highly susceptible to the type origin and magnitude of ice sheet collapse something which varied per heinrich event during the last glacial period

rapid fluctuations of the laurentide ice sheet at the mouth of hudson strait new evidence for ocean ice sheet interactions as a control on the younger dryas ice directional features and erratic lithologies of the last glaciation demonstrate that a major outlet glacier of the laurentide ice sheet flowed nne across outer hudson strait rather than se down the strait as previously hypothesized ice advanced more than 600 km from a labradorean source crossing hudson strait and outer frobisher bay and advancing onto hall peninsula the highest summits on loks land circa 400 m asl a large island at the se tip of hall peninsula were inundated by labradorean ice three distinct late wisconsin advances have been recognized the earliest most extensive advance crossed frobisher about 11 5 kyr b p and was maintained for circa 1 kyr differences in the extent of amino acid racemization in shells from interstadial and deglacial sites on eastern loks land limit the duration of the most extensive late wisconsin advance s to a brief interval of no more than 2 kyr radiocarbon dates on in situ shells and on shells incorporated in till indicate that frobisher bay was ice free from at least 10 5 to 10 2 kyr b p after which a second labradorean advance the gold cove readvance attained nearly the same extent as the earlier advance the readvance was short lived and the bay was deglaciated before 9 5 kyr b p a final readvance occurred during the cockburn substage 9 to 8 kyr b p but ice failed to cross frobisher bay the maximum extent of the labradorean advance coincides with the onset of younger dryas cooling based on a minimum cross sectional area and reasonable estimates of ice velocity the iceberg flux to the north atlantic ocean at this time was between 300 to 2400 km year 1 about the same as the freshwater influx from the diversion of lake agassiz drainage to the st lawrence the input of a significant volume of ice into the north atlantic via the labrador sea would have cooled sea surface and air temperatures increased sea surface albedo and diminished the effectiveness of wind mixing of surface waters thereby reducing the volume of water required to effectively cap the north atlantic we suggest that a combination of a massive iceberg flux and increased st lawrence discharge may have been required to initiate younger dryas cooling when the outflow of lake agassiz was again routed down the st lawrence at 9 5 kyr b p a second younger dryas event failed to occur because by that time labradorean ice had retreated within hudson strait and was unable to generate a substantial climate altering volume of icebergs the possibility of an iceberg flood in the north atlantic could be tested by measuring the concentration of ice rafted detritus ird traditionally defined as quartz feldspar grains 125 m in deep sea cores however sediment entrained by the labradorean ice is dominated by detrital carbonate and only a small fraction of the noncarbonate component is 125 m hence a revised definition of ird is required to evaluate the iceberg flood hypothesis

a geomagnetic polarity timescale for the permian calibrated to stage boundaries the reverse polarity kiaman superchron has strong evidence for at least three or prob ably four normal magnetochrons during the early permian normal magnetochrons are during the early asselian base ci1r 1n at 297 94 0 33 ma late artinskian ci2n at 281 24 2 3 ma mid kungurian ci3n at 275 86 2 0 ma and roadian ci3r an at 269 54 1 6 ma the mixed polarity illawarra superchron begins in the early wordian at 266 66 0 76 ma the wordian capitanian interval is biased to normal polarity but the basal wuchiapingian begins the beginning of a significant reverse polarity magnetochron lp0r with an overlying mixed polarity interval through the later lopingian no significant magnetostratigraphic data gaps exist in the permian geomagnetic polarity record the early cisuralian magnetochrons are calibrated to a succession of fusulinid zones the later cisuralian and guadalupian to a conodont and fusulinid biostratigraphy and lopingian magnetochrons to conodont zonations age calibration of the magnetochrons is obtained through a bayesian approach using 35 radiometric dates and 95 confidence intervals on the ages and chron durations are obtained the dating control points are most numerous in the gzhelian asselian wordian and changhsingian intervals this significant advance should provide a framework for better correlation and dating of the marine and non marine permian

paleomagnetism of late paleozoic rocks in the northern cache creek terrane near atlin british columbia the cache creek terrane is exposed along the length of the canadian cordillera and is composed of oceanic strata that are probably at least in part exotic to north america in the northern portion of the cache creek terrane near atlin british columbia paleomagnetic samples were collected from layered paleozoic rocks at 22 sites 6 samples site on alfred butte principal component analysis of detailed thermal demagnetization data allowed clear isolation of a characteristic remanent magnetization chrm from 17 of these sites blocking temperatures to 680 c indicate that this magnetization is carried by hematite and site mean chrm directions are determined with 95 10 for the majority of sites on sentinel mountain samples were collected from 16 sites in layered paleozoic volcanic and chert rocks and from a diabase sill thermal demagnetization revealed a chrm in the chert and volcanic rocks with blocking temperatures to 680 c whereas alternating field demagnetization to 40 mt successfully is

canadian cordilleran displacement palaeomagnetic results from the early jurassic hazelton group terrane i british columbia canada summary the early jurassic telkwa formation comprising the base of the hazelton group was sampled at three areas in the central part of the stikine terrane british columbia detailed alternating field and thermal step demagnetization on samples from nine sites from the red canyon area and 10 sites from the zymoetz river area both of which are in the bulkley ranges and eight sites from the telkwa range area isolate stable remanence magnetization components the components are interpreted to be primary magnetizations because of the presence of two polarities and the much improved agreement of their inclinations after full tilt correction of the sites from the bulkley ranges within locality declinations agree well between locality declinations are discordant the expected cratonic declination is 340 whereas declinations from this study are 265 227 and 328 for the red canyon zymoetz river and telkwa range areas respectively these results are similar to those of monger irving 1980 and we concur that the discordant declinations are the result of differential rotation about vertical axes between sample localities our observed mean inclination of 52 is in good agreement with monger irving s 1980 result of 54 they interpreted this to indicate 1300 km of northward displacement since the early jurassic and their interpretation was substantiated by several later studies however with revisions to the geologic time scale and the early jurassic reference pole for north america the early jurassic canadian cordillera palaeomagnetic data base appears latitudinally concordant this indicates that terrane i and southern wrangellia were in much the same latitudinal position relative to the north american craton as they are now tectonic displacement models developed in view of discordant cretaceous palaeomagnetic data from the canadian cordillera must now consider latitudinally concordant permian to early jurassic data and middle eocene to recent data this tectonic senario appears more reconcilable with the regional tilt hypothesis however this hypothesis cannot account for discordant cretaceous data from bedded volcanic rocks in terrane i it is therefore probable that cretaceous cordilleran tectonics were characterized by both regional tilting and moderate latitudinal displacement

the timing of initiation of fast flowing ice streams during a glacial cycle inferred from glacimarine sedimentation fast flowing ice streams drain huge basins within modern ice sheets and are a mechanism for rapid iceberg production and mass loss some ice streams are known to be unstable and to switch between fast flow and stagnation numerical ice sheet models and geophysical observations of large scale streamlined glacial landforms and large glacier derived sedimentary fans along high latitude continental margins indicate the presence of ice streams in quaternary ice sheets high resolution ams dated sedimentary records from an inter fan area on the svalbard continental margin yield evidence on the timing of initiation of fast glacier flow during a glacial cycle of ice sheet growth and decay sedimentation rates and iceberg rafted debris influx show that debris delivery to the svalbard margin was relatively high during the period of late weichselian ice sheet growth from about 30 000 18 000 yr bp both parameters fell dramatically in inter fan areas when full glacial conditions with ice at the continental shelf edge were established at about 18 000 yr bp this shift is interpreted to mark the initiation of a fast flowing ice stream the convergence of flow from the surrounding ice sheet into this ice stream and the consequent slowing of ice flow and sediment delivery to the inter fan area beyond the ice stream margins this provides a constraint on the timing of icestream initiation during the cycle of ice sheet growth and decay 4 2002 elsevier science b v all rights reserved

new time constraints on lithospheric scale oroclinal bending of the ibero armorican arc a palaeomagnetic study of earliest permian rocks from iberia abstract the palaeozoic variscan orogeny was a large scale collisional event that involved amalgamation of multiple continents and microcontinents previous palaeomagnetic and structural analyses of the western variscan orogen notably the ibero armorican arc suggest that this region underwent oroclinal bending of an originally near linear orogen during the latest stages of variscan deformation in the late palaeozoic these analyses necessitate a two stage tectonic history with east west compression forming a linear belt in the carboniferous followed by a change in regional compression directions resulting in crustal block rotation and formation of the present day arc this study presents new palaeomagnetic analyses of early permian samples from the sotres and cabranes formations 41 3 n 222 5 w 95 13 1 in the northern inner limb and the viar basin 51 8 n 199 2 w 95 6 7 in the southern outer limb of the arc both locations yield expected early permian palaeomagnetic pole positions for stable iberia implying that measured magnetizations have undergone no significant vertical axis rotation since acquisition and thus were acquired subsequent to oroclinal bending this new result places a time constraint of about 10 ma for oroclinal bending of the ibero armorican arc which agrees well with recent geodynamical models that relate oroclinal bending to lithospheric delamination in this region

late glacial ice margins and deglacial chronology for southeastern baffin island and hudson strait eastern canadian arctic radiocarbon dates from marine piston cores and from onshore raised marine stratigraphic sections in the hudson strait region were used to reconstruct deglacial isochrons for 9900 9500 8800 8500 and 8000 bp at the culmination of the gold cove readvance 9900 bp labrador ungava ice flowed northeastward across hudson strait and outer frobisher bay and stood for the last time on the baffin island continental shelf subsequent retreat by calving was rapid and profound opening the entire hudson strait marine trough by 9500 bp at this time ice dispersal from foxe basin labrador ungava and local ice on meta incognita peninsula supported tidewater margins along much of the coastline with the exception of northernmost ungava peninsula where the ice margin stabilized onshore this onshore margin remained in place throughout the cockburn substage while a major northeastward readvance of ungava bay ice the noble inlet readvance from 8800 to 8500 bp crossed outer hudson strait grounding on the hudson st

a heinrich like event h 0 dc 0 source s for detrital carbonate in the north atlantic during the younger dryas chronozone in the north atlantic we define h 0 as a heinrich like event which occurred during the younger dryas chron on the se baffin shelf prior to 11 ka surface water productivity was reasonably high as measured by the numbers of diatom and planktic foraminifera per gram but an abrupt increase in detrital carbonate dc 0 event from approximately 15 up to 50 carbonate by weight occurred at 11 14c ka and continued to circa 10 ka these deposits 2 6 m thick are dominated by detrital calcite and silt and clay sized sediments during this event dc 0 h 0 ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over labrador ungava as a consequence the pattern of ice rafted debris and sediment provenance shown by h o in the north atlantic is different from that during h 1 14 5 ka or h 2 20 ka when the ice sheet extended along the axis of hudson strait and may have reached the shelf break for example there is no concrete evidence for dc o is cores on the floor of the labrador sea due east of hudson strait hu75 55 56 but h o has been noted in cores off newfoundland and west of ireland a coeval carbonate event to dc 0 but this one dominated by dolomite occurs in hu82 su5 on the west side of davis strait with a source either from northern baffin bay or cumberland sound although other sources for north atlantic detrital carbonate cannot be totally excluded our evidence suggests that h 0 represents the expression of glaciological instability of the laurentide ice sheet within the general region of hudson strait and probably to the north cumberland sound and northernmost baffin bay there is one younger dc event dated circa 8 4 ka present in sediments along the labrador margin and in hudson strait which represents the final collapse of the ice sheet within hudson strait and hudson bay

deformation of foamed rhyolites under internal and external stresses an experimental investigation the style of magma eruption depends strongly on the character of melt degassing and foaming depending on the kinetics of these processes the result can be either explosive or effusive volcanism in this study the kinetics of foaming due to the internal stresses of gas expansion of two types of obsidian have been investigated in time series experiments 2 min 24 h followed by quenching the samples the volumetric gas melt ratio has been estimated through the density measurements of foamed samples

the north atlantic atmosphere sea surface 14c gradient during the younger dryas climatic event abstract we attempt to quantify the 14c difference between the atmosphere and the north atlantic surface during a prominent climatic period of the last deglaciation the younger dryas event yd our working hypothesis is that the north atlantic may have experienced a measurable change in 14c reservoir age due to large changes of the polar front position and variations in the mode and rate of north atlantic deep water nadw production we dated contemporaneous samples of terrestrial plant remains and sea surface carbonates in order to evaluate the past atmosphere sea surface 14c gradient we selected terrestrial vegetal macrofossils and planktonic foraminifera neogloboquadrina pachyderma left coiling mixed with the same volcanic tephra the vedde ash bed which occurred during the yd and which can be recognized in north european lake sediments and north atlantic deep sea sediments based on ams ages from two norwegian sites we obtained about 10 300 yr bp for the atmospheric 14c age of the volcanic eruption foraminifera from four north atlantic deep sea cores selected for their high sedimentation rates 10 cm kyr 1 were dated by ams 21 samples for each core the raw 14c ages assigned to the ash layer peak is significantly older than the 14c age obtained on land part of this discrepancy is due to bioturbation which is shown by numerical modelling nevertheless after correction of a bioturbation bias the mean 14c age obtained on the planktonic foraminifera is still about 11 000 11 100 yr bp the atmosphere sea surface 14c difference was roughly 700 800 yr during the yd whereas today it is 400 500 yr a reduced advection of surface waters to the north atlantic and the presence of sea ice are identified as potential causes of the high 14c reservoir age during the yd

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

quantifying the effect of rheology on lava flow margins using fractal geometry this study aims at quantifying the effect of rheology on plan view shapes of lava flows using fractal geometry plan view shapes of lava flows are important because they reflect the processes governing flow emplacement and may provide insight into lava flow rheology and dynamics in our earlier investigation bruno et al 1992 we reported that flow margins of basalts are fractal having a characteristic shape regardless of scale we also found we could use fractal dimension d a parameter which quantifies flow margin convolution to distinguish between the two endmember types of basalts a a d 1 05 1 09 and pahoehoe d 1 13 1 23 in this work we confirm those earlier results for basalts based on a larger database and over a wider range of scale 0 125 m 2 4 km additionally we analyze ten silicic flows sio2 52 74 over a similar scale range 10 m 4 5 km we note that silicic flows tend to exhibit scale dependent or non fractal behavior we attribute this breakdown of fractal behavior at increased silica contents to the suppression of small scale features in the flow margin due to the higher viscosities and yield strengths of silicic flows these results suggest we can use the fractal properties of flow margins as a remote sensing tool to distinguish flow types our evaluation of the nonlinear aspects of flow dynamics indicates a tendency toward fractal behavior for basaltic lavas whose flow is controlled by internal fluid dynamic processes for silicic flows or basaltic flows whose flow is controlled by steep slopes our evaluation indicates non fractal behavior consistent with our observations

glaciomarine environments in canada an overview the present understanding of canada s glaciomarine environments owes much to the remarkable role played by the scientists of the geological survey of canada their efforts have led to the review and partial revision of three scientific paradigms 1 there is a mechanical rather than a climatic control of the collapse of a tidewater ice sheet 2 ice sheets were mostly grounded on canada s continental shelves rather than with floating ice shelves 3 ice loaded glaciomarine sediments are sometimes indistinguishable from deposits of till a proposed stratigraphic framework for canadian glaciogenic sequences can be quantified allowing insights into ice sheet dynamics for instance the arctic margin of the wisconsinan ice complex appears to have generated comparatively little meltwater ice margin retreat being principally by iceberg calving surprisingly the atlantic margin of the wisconsinan ice complex appears to have transported larger quantities than its pacific counterpart this is contrary to t

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

heinrich event 0 dc 0 in sediment cores from the northwest labrador sea recording events in cumberland sound layers of ice rafted limestone debris rich sediment were deposited in the northwest labrador sea and the north atlantic during the last glacial period 10 80 ka these sediments were deposited by heinrich events h events which record catastrophic collapses of the laurentide ice sheet in the region of the hudson strait these intervals of detrital carbonate rich sediments are referred to as detrital carbonate layers dc in the northwest labrador sea accelerator mass spectrometry ams 14c dates provide a strong constraint on the timing for these events h 1 dc 1 and h 2 dc 2 dc 0 also known as h 0 correlative to the younger dryas cooling event is not as distinct a sediment unit in the northwest labrador sea as dc 1 and dc 2 an analysis of sediments from two cores hu75009 iv 055 and hu75009 iv 056 off the mouth of the hudson strait in the northwest labrador sea basin sheds new light on the missing dc 0 sediment unit timing for the dc 0 event in cores 055 and 056 is bracketed between 11

distribution sediment magnetism and geochemistry of the saksunarvatn 10 180 60 cal yr bp tephra in marine lake and terrestrial sediments northwest iceland in 1997 seismic surveys in the troughs off northwest and north iceland indicated the presence of a major regional sub bottom reflector that can be traced over large areas of the shelf cores taken in 1997 and later in 1999 on the images v cruise penetrated through the reflector in core md99 2269 in hunafloaall this reflector is shown to be represented by a basaltic tephra with a geochemical signature and radiocarbon age correlative with the north atlantic wide saksunarvatn tephra we trace this tephra throughout northwest iceland in a series of marine and lake cores as well as in terrestrial sediments it forms a layer 1 to 25 cm thick of fine to medium grained basaltic volcanic shards the base of the tephra unit is always sharp but visual inspection and other measurements carbonate and total organic carbon weight indicate a more diffuse upper boundary associated with bioturbation and with sediment reworking off northwest iceland the saksunarvatn tephra has distinct sediment magnetic properties this is evident as a dramatic reduction in magnetic susceptibility an increase in the frequency dependant magnetic susceptibility and hard magnetisation in a 0 1t irm backfield geochemical analyses from 11 sites indicate a tholeiitic basalt composition similar to the geochemistry of a tephra found in the greenland ice core that dates to 10 180 60 cal yr bp and which was correlated with the 9000 14c yr bp saksunarvatn tephra we present accelerator mass spectrometry 14c dates from the marine sites which indicate that the ocean reservoir correction is close to ca 400 yr at 9000 14c yr bp off northwest iceland copyright 2002 john wiley sons ltd

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

late quaternary seismic stratigraphy and geological development of the south voring margin norwegian sea abstract high resolution seismic data and sediment cores show that an up to 280 m thick sedimentary sequence has been deposited on the south voring margin off mid norway the last ca 250 ka the sedimentary succession has been divided into six seismic units dominated by hemipelagic sediments five wedge shaped massive sequences of marine isotope stages 8 6 and 2 interfinger the hemipelagic deposits on the upper slope the wedge shaped sequences represent glacigenic debris flows that have been fed by till transported to the shelf edge by grounded ice sheets during maximum glaciations the hemipelagic units show well defined depocentres of various thicknesses on the upper continental slope seismic facies interpretation indicates that the sediment distribution locally has been controlled by currents commonly the hemipelagic units are characterised by parallel and continuous reflectors however the second youngest unit identified deposited between 15 7 and 15 0 14 c ka bp is acoustic transparent we suggest that this unit has been sourced by along slope transported meltwater plume deposits released during the initial stage of the last deglaciation of the norwegian channel the hemipelagic sedimentation rates have varied considerably throughout the studied time period until ca 21 14 c ka bp the rates did not exceed 1 4 m kyr whereas during the last glacial maximum the rates increased and reached values of about 36 m kyr before decreasing again at ca 15 14 c ka bp observation of iceberg scourings of mis 8 age about 800 m below the present day sea level suggest that the south voring margin has subsided by a rate of 1 2 m kyr in the late quaternary