stratigraphic and sedimentological evidence for late wisconsinan sub glacial outburst floods to laurentian fan abstract sub glacial meltwater produces a distinctive stratigraphic and sedimentological response on the continental margin seismo stratigraphy of laurentian channel reveals thick till deposits at its seaward end that pass laterally into stratified sediment in deeper basins that may record periods of water build up beneath the ice two scales of meltwater discharge are recognised large scale that caused catastrophic erosion and transported large volumes of coarse sediment to the abyssal plain and smaller scale yielding principally muddy sediment sub glacial outburst floods from the laurentian channel ice stream delivered distinctive red sediment derived from permian carboniferous strata of the gulf of st lawrence directly to laurentian fan between ca 17 and 14 14 c ka separate from north atlantic heinrich events on levees of laurentian fan three major pulses of meltwater plume muds are separated by intervals dominated by hemipelagic sediments these meltwater intervals are recognised distally as periods of plume sedimentation on the scotian slope and ice rafting of hematite stained quartz to the north atlantic ocean in channels of laurentian fan at least one major sediment transport event is recognised that eroded the upper slope and the major fan valleys depositing a bed of gravel at least 3 m thick in the characteristically wide fan valleys and thick sand on the sohm abyssal plain the same event was probably responsible for giant flute like scours the age of the gravel bed is directly constrained only by the presence of local overlying holocene sediment much of the surface of the gravel bed was re worked by the 1929 grand banks turbidity current an erosional event on the upper slope likely correlative with the flood generated gravel bed has been dated at 16 5 14 c ka such large scale erosional flood events can be recognised back through several glacial cycles and have played an important role in the architectural evolution of laurentian fan

mobility and fractionation of rare earth elements in argillaceous sediments implications for dating diagenesis and low grade metamorphism abstract we report sm nd and rb sr data for the fine fractions of lower paleozoic argillaceous rocks from wales uk and new york usa spanning the range of low grade metamorphic conditions from the diagenetic zone zeolite facies to the epizone greenschist facies in all cases leaching of the fine fractions results in a high 147 sm 144 nd 0 09 0 29 acid soluble component and a complementary low 147 sm 144 nd 0 05 0 14 residual component the observed fractionation is an ancient feature related to diagenesis burial and metamorphism the magnitude of sm nd fractionation between leachates and residues as well as the resulting sm nd ages vary as a function of grain size and metamorphic grade uncleaved welsh mudrocks of the diagenetic zone yield sm nd leachate residue ages of 453 484 ma in agreement with their llanviian to caradocian biostratigraphic ages whereas higher grade rocks of the anchizone and epizone yield sm nd ages as young as 413 ma these ages are transitional between the time of deposition and the time of regional deformation related to the acadian orogeny at 390 ma distinct convex upward rare earth element ree patterns of the leachates suggest that the precipitation of early diagenetic apatite controls the trace element budget of the rock forcing a depletion of middle rees on the subsequently formed diagenetic phyllosilicates the amount of organic matter present and the extent of later prograde reactions are probable modifiers of this fractionation process ordovician and devonian clastic rocks associated with the trenton and onondaga limestones of new york yield single sample and multi sample sm nd isochron ages that agree well with their biostratigraphic ages of 454 ma and 390 ma respectively the ree fractionation observed in shale leachates of the ordovician utica formation is related to ca mg of the bulk rock and hence to the composition of the diagenetic carbonate cement in all cases the sm nd system remained closed subsequent to the peak of diagenesis or metamorphism including the north american rocks that show no evidence of being isotopically reset during widespread remagnetization of the subjacent limestone units in the late paleozoic

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

violent strombolian or not using ground penetrating radar to distinguish deposits of low and high energy scoria cone eruptions scoria cones often grow by the accumulation of individual particles transported ballistically in strombolian type eruptions alternative models of cone formation suggest that cones are built primarily of fallout from the eruption column in more explosive eruptions often termed violent strombolian currently the distinction between normal strombolian and violent strombolian is based on direct observations of eruptions or by inference of eruption characteristics from mapping of tephra fall deposits unfortunately medial to distal tephra fall deposits erode rapidly leaving behind only the near vent facies of scoria cones which are thicker and less easily eroded therefore a tool that is capable of delineating differences between low energy strombolian deposits and higher energy violent strombolian deposits from investigation of the preserved scoria edifice is necessary ground penetrating radar imaging of cerro negro an active basaltic scoria cone in nicaragua has revealed details of cone deposits at depths of up to 12 m the record of the 1992 eruption which was observed to be violent strombolian shows quantifiable differences from normal strombolian near vent facies including reflections in the downwind profile that are continuous for hundreds of meters and through the slope break the ability to differentiate between tephra fallout and ballistically emplaced deposits at cerro negro suggests ground penetrating radar imaging may be useful in distinguishing eruptive style in older scoria cones where the medial to distal tephra deposits are eroded or buried

slope water current over the laurentian fan on interannual to millennial time scales the strength and position of surface and deep currents in the slope water south of newfoundland are thought to vary as a coupled system in relation to the dipole in atmospheric sea level pressure known as the north atlantic oscillation nao paleoceanographic data from the laurentian fan used as a proxy for sea surface temperature reveal that surface slope waters north of the gulf stream experienced warming during the little ice age of the 16th to 19th centuries and support the notion of an nao driven coupled system the nao may be a useful model for millennial scale ocean variability during interglacial climate states

latest pleistocene ice rafting events on the scotian margin eastern canada and their relationship to heinrich events piston cores from the continental margin off nova scotia show up to four discrete intervals of brick red sandy mud which are up to 20 cm thick the ages of these intervals are bracketed by several radiocarbon dates and three fall in the range 12 5 14 1 ka radiocarbon years with 0 4 kyr reservoir correction the youngest dates from 10 4 ka placing it within the younger dryas the distribution of the beds and their petrographic character indicate a source in the gulf of saint lawrence the grain size of these beds suggests that they comprise a coarse component transported by ice rafting that diminishes distally and a fine component that represents suspension fallout from a surface plume and resulting nepheloid layers graded brick red beds in some cores were probably redeposited from turbidity currents the lowermost bed on the laurentian fan and east scotian rise is immediately overlain by a carbonate rich interval that can be identified all around the margin of the grand banks this interval is correlated with detrital carbonate bed dc 1 in the labrador sea and heinrich event h1 in the north atlantic the sequential occurrence of the two beds suggests that they may be a response to the same trigger probably sea level rise but that the gulf of saint lawrence source was more easily destabilized

quaternary sedimentary processes and budgets in orphan basin southwestern labrador sea abstract the continental slope in orphan basin northeast of newfoundland is underlain by several seaward thinning debris flow wedges alternating with acoustically stratified regionally extensive mainly hemipelagic sediments 18o stratigraphy and volcanic ash layers in a 11 67 m core indicate that the uppermost debris flow wedge formed during the last of several sea level lowstands in isotopic stages 2 4 similarly seismic reflection correlation of dated levels at dsdp site 111 with the orphan basin succession suggests that two deeper debris flow wedges were deposited during oxygen isotopic stages 6 and 8 the oldest of the debris flow deposits in at least three of the wedges formed well into the corresponding glacial cycle after ice sheets had reached the edge of the continental shelf slower deposition by hemipelagic processes and ice rafting formed the acoustically stratified units including heinrich layers the youngest three debris flow wedges each have volumes of 1300 1650 km3 approximately two thirds of this material is attributed to glacial erosion of mesozoic and tertiary strata beneath the northeast newfoundland shelf the remainder is believed to have been derived by glacial erosion of older bedrock that now forms the island of newfoundland the observed sediment volumes and the inferred basal and upper ages of the debris flow wedges imply an average glacial denudation rate of about 0 13 mm yr for this older bedrock and an average of about 60 m of glacial bedrock erosion since oxygen isotope stage 22 this denudation rate is similar to estimates from the barents sea region off norway

climate instability during the penultimate glaciation evidence from two high resolution loess records china the xinzhuangyuan and lijiayuan loess sections in the northwestern part of the chinese loess plateau were studied down to paleosol unit s2 which probably formed during marine oxygen isotopic stage 7 200 000 years b p the thickness of the loess soil sequence above s2 is 63 m at xinzhuangyuan and 43 m at lijiayuan a 2 cm sample spacing yields a mean depositional resolution of 50 80 years for the last and penultimate glacial loess units l1 and l2 and 200 years for the last interglacial soil unit sl thus enabling us to reconstruct high resolution climatic changes during the last two glacial interglacial cycles the grain size records of the two sections are regarded as a proxy for changes in the monsoon desert system over northern china results show that frequent large amplitude climatic oscillations on millennial timescales occurred during the penultimate glaciation in a manner similar to that during the last glaciation suggesting that suborbital scale climatic variations may be a common feature of the climate system during glacial periods of the pleistocene the last interglacial soil s1 is composed of three individual soils and two thin intervening loess horizons in both of the sections short term variations in grain size are not prominent within the soil complex implying the absence of strong millennial scale climatic oscillations during the last interglaciation in northern china

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

late quaternary stratigraphy of laurentian fan a record of events off the eastern canadian continental margin during the last deglacial period abstract examination and correlation of 10 piston cores from laurentian fan off the eastern canadian continental margin revealed a high resolution stratigraphic record of events since the last glacial maximum lgm the five lithofacies identified in the cores are 1 bioturbated olive grey silty mud with varying amounts of biogenic carbonate 2 olive grey and reddish brown silt laminated mud with rare fine to very fine sand beds 3 poorly sorted light grey and brick red gravelly sandy mud 4 colour banded silty mud with colours alternating at a centimetre scale between olive grey and reddish brown and 5 brown silty mud commonly massive but occasionally silt laminated the dominant depositional processes include hemipelagic sedimentation turbidity currents and ice rafting in these sediments colour is diagnostic of the sediment source area with reddish sediment being delivered to the fan from the gulf of st lawrence and laurentian channel whereas greenish sediment arrives on the fan from st pierre bank through grand banks valley turbidites are the most volumetrically significant facies conversely ice rafted beds are volumetrically minor but they are the most chronostratigraphically significant facies and include heinrich layers h0 h1 and h2 the chronological control provided by radiocarbon dating and stable oxygen isotopes suggests that sedimentation rates for the reddish brown turbidites deposited between the lgm and 14 ka exceeded 10 m kyr 1 mapping of the units together with a simple sediment deposition model suggest that these beds resulted from deposition by turbidity currents over 1 km thick that lasted on the order of weeks less information can be ascertained from the olive grey turbidites that interbed with h2 and directly overlie h1 because of a lack of sampling except that they had a lower sedimentation rate and include sediment derived from newfoundland and the grand banks comparison of the stratigraphy on laurentian fan with that of other deep water areas further north southwest grand banks margin flemish pass and the labrador sea shows striking similarities over the late quaternary with the deglacial period characterized by rapid sediment accumulation however only on laurentian fan does sediment gravity flow deposition occur during the lgm reddish brown turbidites deposited on laurentian fan during the deglacial period have no equivalent facies further north these unique features suggest important glaciological differences between the ice stream occupying laurentian channel and ice streams farther north the onset of widespread hemipelagic deposition occurred after ca 12 ka on laurentian fan and in flemish pass but not until ca 8 2 ka in the labrador sea consistent with the earlier retreat of glacial ice out of laurentian channel as compared to hudson strait

short paper a note on rb sr whole rock ages from cleaved mudrocks in the welsh basin two cleaved epizone grade palaeozoic mudrock suites from snowdonia yield a mean rb sr whole rock age of 409 11 ma this is consistent with resetting of the rb sr whole rock isotope systems of the mudrocks during cleavage development in end silurian early devonian acadian deformation in contrast cleaved palaeozoic anchizone mudrocks from north and central wales give a silurian mean age of 430 9 ma this dates either a pre tectonic isotopic event preserved through acadian anchizone metamorphism or mid silurian deformation and metamorphism at anchizone grade unaffected by the acadian event the precise timing of the main caledonian deformation in wales has never been established firmly powell phillips 1985 suggest that it occurred in north and south wales in latest silurian time whereas ashgill and end llandovery tectonic events were dominant in central wales see also george 1963 however woodcock 1984 1987 and soper et al 1987 have argued in favour of a single tectonic event of early to middle devonian age this chronological study was undertaken to address this controversy the only previous attempt to define precisely the timing of cleavage development in wales was the k ar dating of cleavage parallel chlorite from a volcanic greywacke from north wales fitch et al 1969 when recalculated using modern decay constants these data give an age of 399 10 ma bath 1974 demonstrated the feasibility of obtaining rb sr ages from cleaved mudrocks of the welsh caledonides and this work produced caledonian ages of 409 20ma and 393 22ma from north wales and late

sedimentary facies of the nova scotian upper and middle continental slope offshore eastern canada a detailed survey of the upper and middle nova scotian continental slope at 42 50 n and 63 30 w indicates a complex morphology dominated by mass movements on various scales and an immature turbidity current channel the range of sediment facies is diverse including hemipelagic and turbidite muds turbidite sands and gravelly sandy muds of debris flow origin deformed units interpreted as slump deposits are also observed several facies associations related to discrete morphological environments are recognized thick turbidite sand units with minor intervening mud beds are characteristic of the high relief uppermost slope and channel margin thinner turbidite sands deformed slump beds and various mud facies are associated with small scale hummocky mid slope topography sand beds are more abundant in the depressions than on intervening hummocks indicating the preferred transport paths of small turbidity currents at the lower end of the main turbidity current channel frequent turbidite sand beds with relatively minor mud beds are deposited on a depositional lobe in areas unaffected by mass movements alternating bioturbated mud and sandy muds make up the core sequences a local model of sedimentation is proposed for this area and illustrates that simple models of continental slope sedimentation only apply to a limited range of settings

direct radiometric age determination of carbonate diagenesis using u pb in secondary calcite abstract carbonate rocks and corals from the middle devonian lucas formation ontario have 238 u 204 pb values ranging from 132 to 559 and give concordant apparent 206 pb 238 u and 207 pb 235 u ages in approximate agreement with the primary age of sedimentation a carbonate rock from one part of the section gives an anomalously young age and contains patches of secondary calcite spar this spar is predominantly pale purple under cathodoluminescence cl and contains 250 600 ppb u and 15 22 ppb pb the values range from 2 10 3 10 4 making the pb very radiogenic apparent 206 pb 238 u ages range from 208 to 249 ma and 232 th 238 u values are from 0 005 to 0 040 the younger ages are correlated with an increase in orange cl and higher apparent values the age scatter is attributed to mixing of a subordinate calcite spar which infiltrated the older spar the young calcite is bright orange under cl has 7200 ppb u of 6 2 10 4 a of 0 23 and is dated at 45 ma the age of the older spar has been determined by a sequential dissolution technique the resulting u pb data can be plotted as u pb age spectra and yield lplateau dates ranging from 231 5 1 4 to 244 9 1 6 ma and an integrated 206 pb 238 u age of 238 2 1 1 ma also the sequential dissolution increases the values progressively to a5 10 4 making these ages independent of the initial pb correction the occurrence of two young ages of diagenetic calcite in these strata is consistent with the idea of recurrent fluid activity along fracture zones in subsurface sediments in the michigan basin this study shows that it is now possible to date secondary carbonate diagenesis by u pb and by inference to determine precisely the timing of activity on ancient fracture zones in carbonate rocks

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

impact of melting of the laurentide ice sheet on sediments from the upper continental slope off southeastern canada evidence from sm nd isotopesthis article is one of a series of papers published in this special issue on the theme polar climate stability network we present new sm nd isotope data for sediments from a core located on the continental slope of the st pierre bank of canada s east coast the nd analyses indicate that the sediments were derived from two principal sources the north american shield that yields an average early proterozoic isotopic signature and a younger proterozoic signature attributed to appalachian crustal sources the appalachian sourced sediments predominated during the last glacial maximum lgm and were associated with low sedimentation rates 30 cm ka with the exception of a strong north american shield signature present in a detrital carbonate layer that corresponds to heinrich layer 1 h1 the dominance of the appalachian signature decreased subsequent to h1 the appalachian signatures closely follow the distribution of sediments interpreted as locally derived glacial tills while the north american shield signatures follow the distribution of hemipelagic mud that was likely deposited by the labrador current the nd data a

the deglaciation over laurentian fan history of diatoms ird ice and fresh water abstract a high resolution diatom census coupled with other proxy data from laurentian fan lf provides a detailed description of the last deglaciation bringing new insight to that period by revealing directly the timing of sea ice formation and melting cold events heinrich event 1 h1 and the younger dryas yd were multiphase events h1 16 8 15 7 cal kyr bp was defined by a two pulse release of icebergs promoting sea ice formation melting of sea ice after h1 corresponds to a cold and fresh anomaly that may have kept the bolling colder than the allerod at 13 6 cal kyr bp a cooling trend culminated with sea ice formation marking the yd onset 12 8 cal kyr bp the decrease in sea ice 12 2 cal kyr bp led to a yd second phase characterized by very cold winters however the contribution of warm water diatoms tends to increase at the same time and the yd gradual end 11 6 cal kyr bp contrasts with its abrupt end in greenland ice cores the yd cannot be regarded as an event triggered by a fresh water input through the laurentian channel since only one weak brief input nearly 1000 yrs after its onset is recorded very cold and cool conditions without ice mark the following preboreal a northward heat flux between 10 8 and 10 2 cal kyr bp was interrupted by the increased influence of coastal waters likely fed by inland melting there was no further development of sea ice or ice drift then

down canyon evolution of turbidity currents at a late glacial ice margin halibut canyon offshore southeastern canada abstract submarine canyons are the principal conduit for turbidity currents transporting sediment to the deep sea this study examines the interplay between ice margin conditions and the style of turbidity currents during deglaciation from 19 to 11 ka we investigated 7 cores from halibut canyon located seaward of a small ice stream draining the newfoundland ice dome cores were x radiographed for sedimentary structures sediment provenance was assessed from x ray fluorescence geochemistry and age was determined by ams c 14 dating high resolution seismic profiles and cores show three phases of canyon evolution 1 canyon erosion by plunging hyperpycnal meltwater from shelf edge ice at maximum ice extent 2 during deglaciation active deposition of an inner levee by turbidity currents adjacent to an erosional talweg system recorded in cores from the younger dryas 12 ka to before h1 16 5 ka 3 passive canyon fill during the holocene by the alongslope labrador current with only minor down canyon sediment supply in the active canyon depositional phase turbidity currents were of variable size reaching thicknesses 390 m at 40 km down canyon numbers of sand beds and mean grain size decrease down canyon which is inferred to result from rapid entrainment of ambient seawater on the steep gradient and a downflow thinning of the lower part of the current with fine sand in suspension silt becomes increasingly segregated from muds downcanyon as a result of floc break up and re formation the processes inferred from halibut canyon are representative of other canyons on formerly glaciated margins

inferring the mass fraction of floc deposited mud application to fine grained turbidites fine sediment deposition in the ocean is complicated by the cohesive nature of muds and their tendency to flocculate the result is disaggregated inorganic grain size digs distributions of bottom sediment that are influenced by single grain and floc deposition this study outlines a parametric model that characterizes bottom sediment digs distributions modelled parameters are then used to infer depositional conditions that account for the regional variation in the grain sizes deposited by turbidity currents on the laurentian fan sohm abyssal plain offshore south eastern canada results indicate that on the channellized laurentian fan the mass fraction of floc deposited mud increases only slightly downslope the small evolution in this fraction arises because sediment concentration and turbulent energy are associated in turbidity currents on the sohm abyssal plain however the mass fraction of floc deposited mud decreases probably as a result of lower sediment concentration at this source distal site estimates of the mass fraction of mud deposited as flocs suggest that floc deposition is the dominant mode by which sediment is lost from suspension although single grain deposition contributes more to the depositional flux in proximal areas where high energy breaks flocs and in distal areas where low sediment concentration limits floc formation it is concluded that throughout the dispersal system changes in the fraction of flocculated mud deposited from turbidity currents reflect changes in sediment concentration and energy downslope

evidence for wisconsinan glaciations in the verrill canyon area scotian slope a composite thickness of about 25 m of sediment has been cored from the verrill canyon on the scotian slope it is interpreted that the majority of this sequence was deposited in a glaciomarine environment during oxygen isotopic stage 2 and the top of stage 3 these sediments as seen in high resolution seismic reflection profiles are well stratified become thicker upslope are laterally variable in thickness and pass upslope into possible outer shelf tills three wedge shaped units of incoherent reflections interfinger with the parallel reflections and terminate in water depths greater than 700 m these wedge shaped units are interpreted as slumped diamict and outwash deposits the age of the uppermost wedge shaped unit is 26 000 21 000 yr based on extrapolation of radiocarbon dates this unit documents a late wisconsinan glacier readvance on the outer scotian shelf the underlying wedge shaped unit estimated to be 70 000 yrs old extends further west along the continental slope and may represent a more extensive early wisconsinan ice advance a third wedge shaped unit inferred to have formed during isotopic stage 6 is possibly a remnant of the first glaciation in the study area

last glacial maximum surface water properties and circulation over laurentian fan western north atlantic abstract millennial scale events marked by the contribution of detrital sand are recorded in north atlantic sediments during the last glacial maximum lgm between heinrich events he 1 and 2 and left their imprint on laurentian fan lf 43 n sediments off eastern canada the lf counterpart of the well known detrital events consist of glacial red brick sediments resulting from subglacial flows separated by olive grey sediments appears at 21 4 19 9 and 19 5 18 65 cal kyr bp high resolution analyses of diatom assemblages and lithic grains coupled with planktonic oxygen isotopic records reveal that while the red sediment is almost barren of diatoms foraminifera and lithics 150 m they are abundant in the olive grey sediment diatom assemblages reveal three phases during these events 1 initial relatively warm temperate conditions followed by 2 very cold surface water and drifting ice and 3 a final phase characterized by relatively warmer waters and the appearance of detrital carbonate although these events possibly reflect the variability specific to the slope water region they are likely the response to atlantic meridional overturning circulation perturbations and ice sheet instability through a chain of mechanisms meltwater inputs into the north atlantic led ultimately to an increased volume of tropical waters and part of the heat stored in the subsurface was flushed by a brief convective episode that was not sustained accounting for the return of cold conditions after the events the sequence of mechanisms deduced from the paleo data here and elsewhere is consistent with previous modeling results these data suggest that the detrital events between heinrich event 1 and 2 may be synchronous across the north atlantic and that the lgm was probably not a time of prolonged steady state in the climate system

radar imaging of glaciovolcanic stratigraphy mount wrangell caldera alaska interpretation model and results glaciological measurements and an airborne radar sounding survey of the glacier lying in mount wrangell caldera raise many questions concerning the glacier thermal regime and volcanic history of mount wrangell an interpretation model has been developed that allows the depth variation of temperature heat flux pressure density ice velocity depositional age and thermal and dielectric properties to be calculated some predictions of the interpretation model are that the basal ice melting rate is 0 64m yr 1 and the volcanic heat flux is 7 0 w m 2 by using the interpretation model to calculate two way travel time and propagation losses radar sounding traces can be transformed to give estimates of the variation of power reflection coefficient as a function of depth and depositional age prominent internal reflecting zones are located at depths of approximately 59 91 m 150 m 203 m and 230 m we attribute these internal reflectors to buried horizons of acidic ice possibly intermixed with volcanic ash that were deposited during past eruptions of mount wrangell the depositional dates corresponding to these reflecting zones are 1950 1924 1853 1770 and 1728 a d and we use this information to propose a volcanic history for mount wrangell

submarine moraines in newfoundland coastal waters implications for the deglaciation of newfoundland and adjacent areas abstract submarine moraines near modern coasts of newfoundland show regional variations in architecture off the west coast arcuate moraines in shallow water were altered to varying degrees by postglacial sea level lowering off the southwest coast arcuate moraines on deep fiord mouth sills interdigitate with glaciomarine deposits whose maximum age is 14 17 ka bp off the northeast coast submarine moraines are absent at the mouths of the deep fiords morainal ridges outside the fiords are coast parallel it is proposed that the moraines formed during deglaciation of the region the late wisconsinan ice sheet extended to the edge of the continental shelf and was divided into catchments with fast flow concentrated in deep channels ice calved back along channels isolating the newfoundland ice cap and ice caps on the offshore banks ca 14 ka drawdown from the interior was localized in fiords and ice margins stabilized just offshore forming the submarine moraines described here off the southwest coasts the ice margin was maintained for up to 1 5 ka at fiord mouths off the northeast coast many of the deep wide fiords are without sills and retreat was nearly continual until the margin stabilized at fiord heads just before 13 ka

evolution of iceberg melting biological productivity and the record of icelandic volcanism in the irminger basin since 630 ka abstract planktic 18 o and 13 c records and point count records of biogenic volcanic and nonvolcanic terrigenous ice rafted debris ird sediment components from hole 919a in the irminger basin northern north atlantic provide a comprehensive dataset from which a paleoceanographic reconstruction for the last 630 kyr has been developed the paleoceanographic evolution of the irminger basin during this time contains both long term patterns and significant developmental steps one long term pattern observed is the persistent deposition of hematite stained ice rafted debris this record suggests that the modern and late pleistocene discharges of icebergs from northern redbed regions to the irminger sea lie in the low end of the range observed over the last 630 kyr in addition arctic front fluctuations appear to have been the main controlling factor on the long term accumulation patterns of ird and planktic biogenic groups the hole 919a sediment record also contains a long term association between felsic volcanic ash abundances and light 18 o excursions in both interglacial and glacial stages which suggests a causal link between deglaciations and explosive icelandic eruptions a significant developmental step in the paleoceanographic reconstruction based on benthic evidence was for diminished supply of denmark strait overflow water dsow beginning at 380 ka possibly initiated by the influx of meltwater from broad scale iceberg discharges along the east greenland coast there is also planktic evidence of a two step cooling of sea surface conditions in the irminger basin first at 338 309 ka and later at 211 190 ka after which both glacials and interglacials were colder as the arctic front migrated southeast of site 919 in addition to offering these findings this reconstruction provides a longer term geologic context for the interpretation of more recent paleoceanographic events and patterns of deposition from this region

the deglaciation of the americas during the last glacial termination this paper reviews current understanding of deglaciation in north central and south america from the last glacial maximum to the beginning of the holocene together with paleoclimatic and paleoceanographic data we compare and contrast the pace of deglaciation and the response of glaciers to major climate events during the global last glacial maximum glgm 26 5 19 ka average temperatures decreased 4 to 8 c in the americas but precipitation varied strongly throughout this large region many glaciers in north and central america achieved their maximum extent during the glgm whereas others advanced even farther during the subsequent heinrich stadial 1 hs 1 glaciers in the andes also expanded during the glgm but that advance was not the largest except on tierra del fuego hs 1 17 5 14 6 ka was a time of general glacier thickening and advance throughout most of north and central america and in the tropical andes however glaciers in the temperate and subpolar andes thinned and retreated during this period during the bolling allerod interstadial b a 14 6 12 9 ka glaciers retreated throughout north and central america and in some cases completely disappeared many glaciers advanced during the antarctic cold reversal acr 14 6 12 9 ka in the tropical andes and patagonia there were small advances of glaciers in north america central america and in northern

mechanisms of argon retention in clays revealed by laser 40ar 39ar dating a method for dating clays is important for studies of weathering diagenesis hydrocarbon migration and the formation of major metalliferous deposits however many attempts have produced imprecise or inaccurate results data from shales show that contrary to expectations the 40ar 39ar dating technique can be successfully used to determine the diagenetic age of ancient sediments because 39ar losses during irradiation are controlled by release from low retentivity sites in illite equivalent to those that have lost radiogenic 40ar in nature rather than by direct recoil as is generally assumed

ice rafted evidence of long term north atlantic circulation abstract the absolute and relative rates of deposition of ice rafted volcanic and terrigenous clastic material were determined for the interval from the base of oxygen isotope stage 5 127 000 yrs b p to the lower part of stage 3 50 000 yrs b p in five subpolar north atlantic deep sea cores during this time interval global climate changed from a full interglaciation to nearly a full glaciation for the sediment derived from the continents dominantly quartz and feldspar the eastward decrease in deposition rates during interglacial intervals and eastward increase during glacial intervals is best explained by a southeastward jump in the locus of iceberg melting during climates colder than that of today a similar model may explain the eastward increase in volcanogenic debris during glacial time intervals however the eastward increase of volcanogenic debris during interglacial stage 5 requires a stronger southeastward component of flow from greenland than is evident in the modern circulation

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

characterization of pyroclastic fall and flow deposits from the 1815 eruption of tambora volcano indonesia using ground penetrating radar abstract ground penetrating radar gpr is used to image and characterize fall and pyroclastic flow deposits from the 1815 eruption of tambora volcano in indonesia analysis of gpr common mid point cmp data indicate that the velocity of radar in the sub surface is 0 1 m ns and this is used to establish a preliminary traveltime to depth conversion for common offset reflection profiles common offset radar profiles were collected along the edge of an erosional gully that exposed approximately 1 2 m of volcanic stratigraphy additional trenching at select locations in the gully exposed the contact between the pre 1815 eruption surface and overlying pyroclastic deposit from the 1815 eruption the deepest continuous prominent reflection is shown to correspond to the interface between pre eruption clay rich soil and pyroclastics that reach a maximum thickness of 4 m along our profiles this soil surface is distinctly terraced and is interpreted as the ground surface augmented for agriculture and buildings by people from the kingdom of tambora the correlation of volcanic stratigraphy and radar data at this location indicates that reflections are produced by the soil pyroclastic deposit interface and the interface between pyroclastic flows including pyroclastic surge and the pumice rich fall deposits in the thickest deposits an additional reflection marks the interface between two pyroclastic flow units

laurentian fan morphology sediments processes and growth pattern thick sediment accumulations in deep water provide a new target in the search for oil and require an innovative approach to hydrocarbon exploration the laurentian fan is a large deep sea 2 000 to 5 000 m fan in the western north atlantic and has been the major depocenter off nova scotia since at least the early tertiary the main development of the present depositional and erosional fan morphology in the past 2 to 3 m y was closely related to onshore glacial history the slope above the fan has been the site of rapid sedimentation and consequent slumping a network of tributaries on the upper fan appears to feed three main channel systems incised up to 800 m between broad asymmetric levees these channels meander widely across the lower fan then die out abruptly and pass into a lobate suprafan differences between the laurentian fan and typical fan models result in part from the muddy nature of the sediment and the supply system the channels contain thick coarse gravels which probably grade distally into sandy lobes both should produce good reservoir bodies with suitable source and trapping mechanisms fine grained sediments were more important in fan construction interbedded turbidites contourites and hemipelagites are present in the late quaternary holocene sequence the distribution of these sediments and in particular the recognition of structural sequences textural trends and fabric types in the fine grained turbidites can be used to characterize particular parts of the fan environment the development of this approach should prove useful in future hydrocarbon exploration

late quaternary sediment sediment mass flow processes and slope stability on the scotian slope canada the study area just to the west of the verrill canyon on the scotian slope eastern canada exhibits both large and small scale sediment mass movement features study of high resolution seismic reflection and sidescan sonar data shows that a large portion approximately 70 of the near surface sediment 20 m in the area has undergone erosion rotational slumping and internal deformation remoulded sediment observed in physical properties profiles of piston cores and sediment deformation structures are further evidence of slumping small scale mass flow events are recorded by abundant turbidites and debris flow deposits noted in piston cores sediment physical properties are highly dependent on sediment type lithofacies frequent facies changes both temporally and spatially make correlation between cores difficult although the small scale mass movement events correlate with glacial recession on the continental shelf and lower relative sea levels the triggering mechanisms for the large scale events are less obvious slope stability analyses indicate that at present the seabed is stable the most plausible explanation for large scale slope failures in this region are ground accelerations related to earthquake shock our analyses demonstrate that it is unlikely that large magnitude distant earthquakes such as those previously proposed in the laurentian slope seismic zone lsp model could initiate failure of sediment in the study region our data support the interpretation that more frequent lower magnitude earthquakes closer to the study region as previously proposed in the eastern slope experimental source zone esx model are the likely causes of large scale slope failures furthermore excess pore pressures resulting from shallow gas and or high sedimentation rates during deglaciation contribute to slope failure

late glacial stratigraphy and history of the gulf of st lawrence reply the three dimensional configuration of the quaternary sediments in the gulf of st lawrence is described based on analysis of 8000 km of high resolution seismic reflection data complemented by anal

anatomy of a bioclastic grainstone megashoal middle silurian southern ontario revealed by ground penetrating radar porous grainstones deposited as offshore carbonate sand shoals are important hydrocarbon reservoirs but little is known about their internal architecture and its effect on reservoir heterogeneity the middle silurian amabel formation exposed along the niagara escarpment of southern ontario provides an unparalleled opportunity to examine such a deposit in three dimensions with photomosaics and ground penetrating radar the amabel is a dolomitized bioclastic grainstone unit up to 25 m thick composed mainly of crinoid ossicles it thins and grades westward to thin bedded argillaceous dolostones although previously assumed to be reefal the undulating and oblique bedding that dominates the internal geometry was caused by vertical and lateral accretion on hummocky topography and scour surfaces some scours are huge as much as 15 m deep and attest to the dramatic nature of sediment movement by storms and hurricanes ground penetrating radar successfully detects the large scale bedding pattern and in conjunction with outcrop observations has potential for mapping the three dimensional architecture of ancient lithified deposits

the impact of diagenesis on high precision upb dating of ancient carbonates an example from the late permian of new mexico we have applied upb trace element and sr isotopic analyses to subsamples of a single specimen of the capitan formation from the permian reef complex of new mexico with the goal of calibrating the late permian time scale and understanding the factors that set and later alter the initial u pb ratio and pb isotopic composition of the limestone the data indicate a limestone upb isochron age of 249 8 4 7 ma 2 and a pbpb age of 249 18 ma in addition with values 238u 204pb ranging up to 4200 among the highest ever recorded for a limestone we also obtain precise single sample 206pb 238u 207pb 235u and 207pb 206pb ages indicating averages of 250 2 3 2 ma 250 0 2 8 ma and 256 3 3 5 ma respectively comparison of the average pb u age of 250 3 ma for the latest guadalupian with published radiometric constraints for the late permian suggests preservation of essentially the depositional age trace element and sr isotopic analyses highlight four samples that preserve a chemical signature expected for primary marine aragonite including high sr 3000 g g high u 2900 ng g low initial pb 26 g g and 87sr 86sr 0 7073 as well as the lower u and higher pb mg and fe expected for a diagenetically altered carbonate these data clearly delineate the diagenetic alteration of the limestone and allow us to demonstrate the critical importance of diagenesis in controlling the spread in values primarily through the expulsion of u but with some incorporation of pb the high are simply a function of preservation of original carbonate chemistry and not of u scavenging by fe oxyhydroxides or phosphates although it has long been suspected that limestone upb and pbpb isochron ages reflect the timing of early diagenesis as opposed to a strictly depositional age this is the first study in which this is conclusively demonstrated to be the case the upb data also suggest a late stage neogene alteration that disturbed the system mainly via the redistribution of u intriguingly the four samples that best retain their primary marine aragonitic geochemistry also best maintained a closed upb system most of the subsamples with comparably high values but clearly altered trace element compositions showed upb systematics indicating late disturbance unfortunately it is not yet possible to determine which processes are responsible for this late stage alteration and it is unclear exactly how to avoid such alteration in future work

sediment dynamics during heinrich event h1 inferred from grain size abstract throughout the last glacial period massive volumes of icebergs were discharged periodically through hudson strait during so called heinrich h events these icebergs transported sediments that were subsequently deposited in distinct layers across the north atlantic as they melted the objective of this research was to measure and describe sedimentation associated with a meltwater plume discharged during the h1 ice rafting event at about 17 ka by examining sediment texture the h1 layer was sampled in 11 piston cores that cover about 4000 km of the slope between hudson strait and the gulf of maine disaggregated inorganic grain size digs distributions were determined using a coulter counter additionally the caco 3 content and the 63 m fraction were measured and digs distributions were sorted using entropy analysis entropy analysis proved to be a useful tool for distinguishing between sediment delivery mechanisms textural interpretation of sediment dynamics during the h1 event was broadly consistent with facies interpretations h1 layer sediments were mainly delivered by plume and ice rafting with some samples showing higher energy sorting in general plume deposition was dominant within 1000 km of hudson strait and distal sediments were mainly delivered by ice rafting entropy analysis of digs distributions provides a robust means of understanding fine fraction

the magnetic signature of rapidly deposited detrital layers from the deep labrador sea relationship to north atlantic heinrich layers rock magnetic parameters from deep labrador sea piston core p 094 are useful for recognizing rapidly deposited detrital layers some of which correlate with north atlantic heinrich layers variations in magnetic properties and lithology distinguish two classes of rapidly deposited detrital layers during the last ice age 1 seven detrital carbonate dc layers have high carbonate content and mean magnetite grain diameters about 4 times greater than the background sediments 2 six low detrital carbonate ldc layers have very similar magnetic properties to dc layers but low carbonate content similar to the background sediments the magnetite associated with dc and ldc layers is well sorted and relatively uniform within and between layers ice rafted detritus ird recognized by increased percentage of the 125 micron grain size fraction and by high magnetic susceptibility is associated with most dc and ldc layers but is not the dominant detrital constituent the correspondence of dc and ldc layers with increased grain size of well sorted magnetite but not with coarse fraction content precludes ice rafting as the primary depositional mechanism dc and ldc layers may have been deposited from suspended sediment derived from turbidite activity in the nearby northwest atlantic mid ocean channel namoc this interpretation is supported by a piston core p 013 from a greenland rise site largely but not completely outside the influence of the namoc the association of dc layers with ird and the apparent age correlation of dc layers to north atlantic heinrich layers suggest that the ice advances which produced the ird in p 094 and in correlative north atlantic heinrich layers also triggered turbiditic flows down the namoc several dc and ldc layers however do not correlate with recognized heinrich layers but appear to be coeval with recently discovered high frequency ird rich layers in the north atlantic

in situ geotechnical characterization of sediments on the nova scotian slope eastern canadian continental margin abstract a seabed 2 m long cone penetrometer and coring system geotechnical module has been used at 17 stations in four transects on the scotian slope to characterise in situ shear strength and induced pore pressure on several different types of late pleistocene and early holocene failure study sites were selected using the sar high resolution deep towed acoustic system equipped with a digital 160 190 khz sidescan sonar and a 3 5 khz subbottom profiler several distinctive types of geotechnical signature were recognised from plots of cone resistance and induced pore pressure with depth in the sediment normally consolidated sediments show a progressive increase in cone resistance with depth to about 75 kpa at 2 m subbottom holocene surficial muds show spectacular apparent overconsolidation reaching a peak of 250 kpa at about 50 cm subbottom and then decreasing down to 1 5 m this overconsolidation is associated with zoophycos burrows late pleistocene sediments exhumed by bedding plane slides show strong true overconsolidation consistent with the original depth of burial inferred from high resolution seismic stratigraphy debris flows show only a slight shear stress gradient with depth 40 45 kpa over 0 5 1 m subbottom with under consolidation due to remoulding of sediment

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

late quaternary slumps and debris flows on the scotian slope the scotian slope just west of verrill canyon was surveyed using the sea marc i deep towed sidescan sonar system high resolution seismic reflection profiles and 25 piston cores the generally smooth continental slope has a gradient of 2 5 it is crossed by 2 small valleys that are 1 km wide and 100 m deep much of the sea bed shows evidence of surficial sliding that removed 10 20 m of sediment and the slide scars give the sea bed a steplike morphology from the 600 m isobath to 1 800 m there extend 2 zones of disturbed sediment these disturbed zones have the rough surface and transparent acoustic character previously regarded as characteristic of debris flows but sidescan sonar images and cores suggest that they are principally rotational slide deposits with true debris flows at their distal limits streamlined erosional depressions near the downslope edge of the debris flows cut both the flow and sediment farther down slope these may have been produced by a turbidity current associated with the debris flows sorted coarse sand in piston cores provides further evidence of current activity this widespread sediment failure on relatively low slopes was probably the result of a large earthquake that can be dated from cores as occurring between 5000 and 12000 yr b p

paleoceanographic significance of sediment color on western north atlantic drifts i origin of color reflectance spectra collected during odp leg 172 were used in concert with solid phase iron chemistry carbonate content and organic carbon content measurements to evaluate the agents responsible for setting the color in sediments factor analysis has proved a valuable and rapid technique to detect the local and regional primary factors that influence sediment color on the western north atlantic drifts sediment color is the result of primary mineralogy as well as diagenetic changes sediment lightness is controlled by the carbonate content while the hue is primarily due to the presence of hematite and fe 2 fe 3 changes in clay minerals hematite most likely derived from the permo carboniferous red beds of the canadian maritimes is differentially preserved at various sites due to differences in reductive diagenesis and dilution by other sedimentary components various intensities for diagenesis result from changes in organic carbon content sedimentation rates and h2s production via anaerobic methane oxidation iron monosulfides occur extensively at all high sedimentation sites especially in glacial periods suggesting increased high terrigenous flux and or increased reactive iron flux in glacials 7 2002 elsevier science b v all rights reserved

magnetic characterisation of present day deep sea sediments and sources in the north atlantic the north atlantic plays a key role in global climate through formation of north atlantic deep water which drives the thermohaline circulation to understand past and future climate change it is essential to understand the processes occurring within the present day north atlantic but ocean wide studies of present day sediment distribution and sources are relatively sparse here we use magnetic measurements to characterise the surface sediments of the north atlantic and identify the major climatic and oceanographic controls on their magnetic signatures the magnetic data and subsequent cluster analysis identify distinct spatial patterns of sediment sources and transport pathways much of the sedimentary magnetic signal appears to be controlled by detrital inputs especially of windblown dust and ice rafted debris ird with a range of different sources these sediment transport pathways can be validated by making direct comparison of the sediment magnetic properties with source rocks and soils and with iceberg trajectory and observation data the spatial distributions of the ird dominated sediments substantiate those mapped previously using lithological tracers provide additional spatial information on sediment sources and pathways and suggest that deep water currents are less significant than proposed in controlling present day sediment mineralogy and distribution the data form a present day basis for comparison with glacial stage ird and dust distributions and modes of ocean circulation

the marine record of deglaciation from the continental margin off nova scotia continental margin sediments off nova scotia accumulate at high rates up to 360 cm kyr 1 and contain a history of millennial scale environmental changes which are dominated by the proximity of the laurentide ice sheet during the latest quaternary using stable isotope ratios of oxygen accelerator mass spectrometer radiocarbon dating micropaleontology and sedimentology we document these changes in six piston cores ranging in water depth from 450 to 4300 m we find that maximum 18o in n pachyderma occurred about 15 ka and preceded the maximum abundance of this species in these cores by 1000 years between 13 and 14 ka we find a second peak in abundance of n pachyderma minimum 18o and two pulses of ice rafting the sediment lithology supports terrestrial studies which indicate that there was a general withdrawal of ice beyond the upper paleozoic and mesozoic red beds by 14 ka in southeastern canada so the ice rafting events between 13 and 14 ka probably reflect ice stream activity in the st lawrence valley the younger dry as event is recognized as a peak in abundance of n pachyderma and ice rafting dated as 11 3 ka but meltwater discharge to the gulf of st lawrence was either too small or occurred over too long a time to leave a distinct 18o minimum off nova scotia at 7 1 ka in the middle of holocene warming we find a third peak in abundance of n pachyderma and another 18o minimum but no ice rafting we interpret these data as evidence of a late occurring meltwater event which if correct could have originated in the great lakes in the labrador ungava region or in both the final millennial scale phenomenon off nova scotia is the onset of neoglaciation marked by increased ice rafting and increased n pachyderma beginning about 5 kyr ago

late quaternary sedimentation on the southwestern scotian slope eastern canada relationship to glaciationgeological survey of canada contribution 20070176 the sedimentary record on continental slopes has the potential to preserve a record of glacial retreat on the adjacent continental shelf the glacial history of the southwestern part of the scotian shelf is poorly known air gun and high resolution sparker profiles and numerous sediment cores up to 10 m long have been used to determine the character of sedimentation on the southwestern scotian slope since the last glacial maximum lgm seismic reflection profiles show that glacial till was deposited at shallow depths on the upper continental slope and correlation to dated piston cores farther downslope show that this till dates from the lgm slope sedimentation at this time was dominated by local ice and deposited as plume fallout and turbidites progressively increasing importance of red brown sediment derived from glacial supply to laurentian channel indicates retreat of ice from the shelf edge and diminishing supply of proglacial sediment from the calving embayment in the mid scotian shelf with the

late quaternary sedimentation in central flemish pass flemish pass is a basin in 1000 m water depth on the continental slope off the grand banks of newfoundland and has a quaternary fill principally of turbidites the late quaternary history of the pass has been investigated using mid range side scan sonargraphs high resolution seismic profiles and cores dated using c 14 the sequence of facies in the cores reveals six lithostratigraphic units deposited in the past 40 ka at 15 19 ka and 25 30 ka sedimentation was dominated by debris flow and turbidite deposits together with hemipelagic deposits of similar clay size mineralogy derived from the grand banks at other times ice rafting and hemipelagic sedimentation principally of carbonate rich sediment transported by the labrador current predominated a late quaternary regional unconformity on the slope may reflect the effects of ice sheets reaching the shelf break probably in the early wisconsinan late wisconsinan resedimentation was not related to ice marginal processes and probably resulted from

late carboniferous and early permian drainage patterns in atlantic canada paleoflow data have been compiled for late carboniferous late westphalian a to early permian alluvial deposits over a large area of atlantic canada the data which include more than 36 000 measurements of large scale trough cross strata indicate a predominantly northeasterly paleoflow and suggest that a major source area lay to the southwest of the region throughout the 30 ma period represented uplands within the basin deflected paleoflow and probably formed important local drainage and sediment sources tectonostratigraphic analysis suggests that the drainage originated in the fold and thrust belt of the central appalachians and parts of the northern appalachians rivers probably followed northeast oriented structural lineaments through the older acadian mountains of the northern appalachians a considerable proportion of the rising orogen s drainage and probably detritus may have traversed basins along the strike of the mountain belt a situation analogous to that of the modern himalayas

large scale internal structure of the sanbongi fan towada volcano japan putting the theory to the test using gpr on volcaniclastic deposits abstract the towada caldera volcano is located between the prefectures of aomori and akita northeast honshu island japan the caldera today filled by a lake has produced 15 000 years ago a complex eruption emplacing an ignimbrite topped by the lake outburst flood deposit through which the present oirase river erodes this flood deposit has shaped the geomorphologic feature named sanbongi fan on which towada city extends this flood event hypothesis is mainly based on sedimentological and geomorphological evidences of floods mainly from outcrops retrieved from the sanbongi fan area because of the lack of extended outcrops typical of the japanese environment the present paper has therefore put the theory to the test using gpr ground penetrating radar radargram extending along a 640 m length the gpr used for the survey was a pulse ekko pro with 50 mhz antennas and the software reflex was used to process the data the radargrams have displayed a sole unit which the gpr could not penetrate it can be interpreted as the ignimbrite on top of this deposit a series of subhorizontal layers with the alternation between a backset and a foreset extends between 5 m and 3 m depth above 3 m the units are regular and subhorizontal the deposit is also characterized by the extensive presence of boulders which are located along three bands 1 on top of the ignimbrite 2 in the units deposited by the outburst flood between 3 and 5 m depths 3 and in the units close to the surface although part of these punctual elements are most certainly anthropogenic compared with the outcrops the present research confirms that the material located above the ignimbrite material have been deposited by the outburst flood creating large sheet patterns which have transported boulders these sheets display backset and foreset patterns depending on the position of the deposit indicating flow pulsation or surges under a high energy flow condition

the influence of meltwater on the labrador current in heinrich event 1 and the younger dryas abstract the labrador current transports freshwater from the arctic regions to the northern atlantic and the freshwater flux can influence the meridional overturning circulation the response of the labrador current to meltwater processes is unclear during the deglaciation of the ice sheets around the northwest atlantic this study utilized cores from flemish pass to monitor variations in the strength of the labrador current by using the sortable silt proxy the carbonate content the amount of ice rafted detritus and xrf chemical data were measured to identify the main meltwater events during the last deglaciation this study observed a clear enhancement of the flow strength of the labrador current in heinrich event 1 and the younger dryas with the greatest flow strength during the younger dryas event the onset of the current enhancement was dated at ca 13 cal ka bp which preceded the enhanced ice rafted deposition in hudson strait by about one thousand years the current enhancement in flemish pass during the younger dryas event corresponds to the freshening of the surface water thus meltwater preceding significant iceberg supply has an important effect on the labrador current in heinrich events on the laurentide ice sheet margin

characterization of volcanic deposits with ground penetrating radar field based studies of surficial volcanic deposits are commonly complicated by a combination of poor exposure and rapid lateral variations controlled by unknown paleotopography the potential of ground penetrating radar gpr as an aid to volcanological studies is shown using data collected from traverses over four well exposed recent volcanic deposits in western canada the deposits comprise a pumice airfall deposit 3 4 m thick a basalt lava flow 3 6 m thick a pyroclastic flow deposit 15 m thick and an internally stratified pumice talus deposit 60 m thick results show that gpr is effective in delineating major stratigraphic contacts and hence can be used to map unexposed deposits different volcanic deposits also exhibit different radar stratigraphic character suggesting that deposit type may be determined from radar images in addition large blocks within the pyroclastic deposits are detected as distinctive point diffractor patterns in the profiles showing that the technique has potential for providing important grain size information in coarse poorly sorted deposits laboratory measurements of dielectric constant k are reported for samples of the main rock types and are compared with values of k for the bulk deposit as inferred from the field data the laboratory values differ significantly from the field values of k these results suggest that the effectiveness of gpr at any site can be substantially improved by initial calibration of well exposed locations

continental slope sedimentation adjacent to an ice margin iii the upper labrador slope abstract the upper labrador slope is the key area for sediment transfer from the northeastern margin of the pleistocene laurentide ice sheets lis to the deep basin it is subdivided from north to south into 8 sectors based on relief differences and echo character on 750 line km of continuous sleeve gun and 3 5 khz seismic profiles high to moderate relief sectors 2 and 4 and in part 6 and 8 are seismically transparent and well stratified with continuous individual high amplitude reflections and deep penetration low relief sectors 1 3 5 and 7 show strong bottom reflections and with the exception of sector 1 low seismic penetration poor stratification and low amplitude if any subbottom reflections the lateral distribution of these alternating high to moderate and low relief sectors reflects fundamental differences in the sediment transfer mechanisms through outlets from the lis onto the slope low relief slope sectors represent debrite and turbidite slopes and are located in front of ice outlets on the slope and adjacent regions to the north they originate from mass wasting on the upper slope of glacial detritus with a significant coarse component originally delivered as englacial or subglacial material and deposited in end moraines or as bedload by subglacial or supraglacial rivers high to moderate relief sectors originate from fall out of suspended sediment from turbid surface plumes tsp and preferentially occur off the southern half of outlets and south of major outlets as exemplified by sector 2 south of the hudson strait outlet this asymmetry is caused by the south flowing labrador current which entrains the buoyantly rising turbid meltwater plumes at the glacier front the present high relief topography which shows a dendritic pattern of upslope canyon branching is the result of retrograde headward canyon erosion by mass wasting processes of an originally much smoother mud blanket surface the sediment is remobilized by slumping and entrained in debris flows and turbidity currents the occurrence of tsp deposits on the high to moderate relief upper slope sectors requires a summer sea surface not frozen over during major parts of the pleistocene including glacial maxima tps deposition on the upper slope ice rafting and a plethora of ice margin depositional phenomena many of which give rise to mass wasting and mass flow phenomena are the main features that make high latitude continental slopes adjacent to continental ice sheets different from their lower latitude counterparts

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

gpr investigation of tephra fallout cerro negro volcano nicaragua a method for constraining parameters used in tephra sedimentation models most tephra fallout models rely on the advection diffusion equation to forecast sedimentation and hence volcanic hazards here we test the application of the advection diffusion equation to tephra sedimentation using data collected on the proximal 350 to 1 200 m from the vent to medial greater than 1 200 m from the vent tephra blanket of a basaltic cinder cone cerro negro volcano located in nicaragua our understanding of tephra depositional processes at this volcano is significantly improved by combination of sample pit data in the medial zone and high resolution ground penetrating radar gpr data collected in the near vent and proximal zones if the advection diffusion equation applies then the thickness of individual tephra deposits should have gaussian crosswind profiles and exponential decay with distance away from the vent at cerro negro steady trade winds coupled with brief eruptions of relatively low energy vei 2 3 create relatively simple deposits gpr data were collected along three crosswind profiles at distances of 700 1 600 m from the vent sample pits were used to estimate thickness of the 1992 tephra deposit up to 13 km from the vent horizons identified in proximal gpr profiles exhibit gaussian distributions with a high degree of statistical confidence with diffusion coefficients of 500 m2 s 1 estimated for the deposits confirming that the advection diffusion equation is capable of modeling sedimentation in the proximal zone the thinning trend downwind of the vent decreases exponentially from the cone base 350 m to 1 200 m from the vent beyond this distance deposit overthickening occurs identified in both gpr and sample pit datasets the combined data reveal three depositional regimes 1 a near vent region on the cone itself where fallout remobilizes in granular flows upon deposition 2 a proximal zone in which particles fall from a height of less than 2 km and 3 a medial zone in which particles fall from 4 to 7 km and the deposit is thicker than expected based on thinning trends observed in the proximal zone of the deposit this overthickening of the tephra blanket defining the transition from proximal to medial depositional facies is indicative of transition from sedimentation dominated by fallout from plume margins to that dominated by fallout from the buoyant eruption cloud a feature of deposits previously identified in larger volume eruptions we interpret this change to represent a change in diffusion law occurring at total particle fall times the fall time threshold of numerical models of 400 s thus the detailed gpr profiles and pit data collected at cerro negro help to validate current numerical models of tephra sedimentation

compositional changes in deglacial red mud event beds off the laurentian channel reveal source mixing grain size partitioning and ice retreat abstract between 22 and 17 cal ka bp five large meltwater events from within the laurentian channel ice stream deposited mud beds meters thick across a large area of the laurentian fan and adjacent continental slopes this study determines the sources of these event beds and relates them to the glaciological evolution of the retreating laurentian ice stream we analyzed major element and magnetic mineral contents of these event beds and compare them with a new collection of 80 source reference samples from the gulf of st lawrence area element ratios suggest a steady compositional change from older to younger outburst event beds while element specific offsets from reference sample compositions indicate grain size and mineral element partitioning during suspension transport their magnetic properties place event beds on the source mixing trend of four reference samples groups which represent two magnetite rich sources canadian shield and or southern newfoundland and two hematite rich sources appalachian red beds using a deterministic linear source mixing model based on irm100mt hirm and ca we find that the earlier two outburst events had higher contributions from granitic and calcareous sources than the later three events combining materials timing and scenarios of the outburst events with ice sheet retreat and ice stream dynamics we argue that the subglacial sediment depocenter of the earlier two event beds was located in the lower laurentian channel while that of the later three events was upstream from cabot strait

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

petrographic evidence from the eastern canadian margin of shelf crossing glaciations abstract it is difficult to evaluate when and where glaciers extended across the outer continental shelf off eastern canada the outer shelf and upper slope are commonly hard bottomed or have a great thickness of post glacial sediment in either case making direct sampling and dating of ice margin sediment impossible the timing and extent of glacier ice is important for understanding continental slope sedimentation and ice sheet dynamics we have therefore determined the lithologic components of the 1 4 mm granule fraction of over 100 well dated samples from 40 cores from the more distal parts of the deep water margin off nova scotia and newfoundland this fraction is demonstrably ice rafted in these cores and geographic variation in component results from input of icebergs at different calving margins the samples show that heinrich layers have a distinctive granule fraction that shows some areal variation as a result of dilution by sources other than hudson strait heinrich event 2 ca 21 ka is widespread as far southwest as the west scotian slope but by the last glacial maximum lgm numerous discrete sources of ice rafted granules are recognised implying that calving ice margins were present in several places off newfoundland and nova scotia including off banquereau a distinctive purplish lgm gravelly mud is recognised on the eastern newfoundland margin derived from a calving margin on the ne newfoundland shelf at the time of heinrich event 1 ca 14 ka there was a calving ice outlet somewhere on the grand banks and another in halibut channel retreat of ice from the gulf of st lawrence can be tracked by changing granule petrology from the lgm to 13 ka these data suggest that final ice retreat from many parts of the outer shelf was later than is shown in many recent ice margin reconstructions

a conceptual model of the deglaciation of atlantic canada abstract we present a conceptual model for the deglaciation of atlantic canada in which a role is played by ice streams the ice margin lay close to the edge of the continental shelf at the last glacial maximum ice streams occupying shelf troughs comprised 1 a major ice stream in the laurentian channel 2 secondary streams in the bay of fundy gulf of maine trinity trough and notre dame channel and 3 lesser ice streams elsewhere early retreat in the northeast notre dame bay and in the southwest bay of fundy gulf of maine was mainly by calving along embayments by 18 ka radiocarbon years a calving embayment had opened on emerald basin scotian shelf retreat along channels marooned ice on intervening banks a major calving episode beginning just before 14 ka removed ice from the gulf of st lawrence triggering re advances down secondary troughs isolation of a newfoundland ice cap produced radial drainage via fiords and more extensive flow into the st george s bay lowlands on the west coast by 13 ka most ice was on land and was ablating by melting rather than calving shelf ice caps persisted until 11 ka

sm nd in marine carbonates and phosphates implications for nd isotopes in seawater and crustal ages this study explores the possibility of establishing nd isotopic variations in seawater over geologic time calcite aragonite and apatite are examined as possible phases recording seawater values of nd modern biogenic and inorganically precipitated calcite and aragonite from marine environments were found to have nd concentrations of from 0 2 to 70 ppb showing that primary marine caco 3 contains little ree and that nd ca is not greatly enhanced relative to seawater during carbonate precipitation very young marine limestone and dolomite containing no continental detritus have 200 ppb nd all the carbonates are lree enriched 0 16 sm nd 0 45 modern and very young atlantic and pacific carbonates have nd in the range of shallow atlantic and pacific seawater respectively implying that they derive their ree from local seawater the nd in well preserved carbonate fossils is 4 10 4 ppb much greater than in their modern counterparts but like the high values found for carbonates in other studies we believe the high ree contents at the 500 ppb level in some detritusfree carbonates are due to ree rich fe hydroxide in on the carbonate in favorable cases such material may record seawater nd values however introduction of extraneous ree may obscure the original isotopic composition of pure caco 3 because of its very low intrinsic primary ree abundance modern biogenic apatite is also shown to have very low ree content 150 ppb nd but appears to quickly scavenge ree from seawater inorganically precipitated apatite from phosphorites has high concentrations of seawater derived ree young phosphorite apatite from the atlantic and pacific oceans has nd in the range of the seawater from these oceans older apatite samples of similar age from different localities bordering common oceans record similar values of nd t sedimentary apatite has sr t values in good agreement with the curves for 87 sr 86 sr of seawater as a function of time individual conodonts from a single formation yield the same sr t and nd t other workers have shown that sedimentary apatite preserves seawater ree patterns these characteristics suggest that sedimentary apatite can be used to determine nd t in ancient seawater the seawater values so inferred range between 1 7 and 8 9 over the last 700 my and lie in the range of modern seawater showing no evidence for drastic changes high values of seawater nd t in the triassic and latest precambrian may correlate with the breakup of large continental landmasses the initial nd t 15 0 of a 2 ae old phosphorite implies the presence of 1 5 ae old continental crust at 2 ae ago the approach outlined here can be used to constrain the age of the exposed crust as a function of time

imaging the subsurface stratigraphy in the ubehebe hydrovolcanic field death valley california using ground penetrating radar abstract ground penetrating radar gpr surveys were carried out to collect subsurface images of the basaltic base surge deposits in the ubehebe hydrovolcanic field death valley national park california antennae with frequencies of 50 100 and 200 mhz were used this technique allowed the collection of useful geologic data for example the lower stratigraphic boundary of the pyroclastic deposits can be imaged and their thickness can be estimated different radar responses were also obtained from base surge deposits and underlying sedimentary rocks which enable their recognition where no outcrops are available furthermore gpr data confirmed the presence of small eroded craters which are partially filled by alluvium in this case an unconformity between the overlying horizontally bedded alluvium and the underlying bowl shaped base surge deposits can be recognized within the crater and the thickness of the alluvium estimated common mid point cmp surveys suggested subsurface velocities of the electromagnetic waves in the upper part of these deposits between 0 095 0 1 m ns

geochronology and mass transfer in gulf coast mudrocks south central texas u s a rbsr smnd and ree systematics whole rock shale and 0 5 m sized clay separates from a well spanning 3500 m of burial in south central texas have been analyzed for there ree sm nd and rb sr contents clay rb sr and sm nd hcl leachate residue pairs yield ages which decrease with depth implying that these samples have not experienced a punctuated diagenetic event rb sr ages from the most deeply buried clay samples are younger than their depositional ages but sm nd leachate residue ages are always equal to or greater than depositional age leachate sr appears to be in isotopic equilibrium with present day sandstone formation waters implying that pore fluids readily pass between the two lithologies during and after diagenesis the ree are redistributed and fractionated on a local mineral grain scale during burial diagenesis the hcl soluble ree reservoirs decrease from 20 to 8 in whole rock and from 35 to 7 in 0 5 m clay and become progressively enriched in the middle ree relative to the light and heavy ree conversely the hcl insoluble silicate reservoirs become progressively enriched in the light and heavy ree relative to the middle ree this fractionation which is more pronounced in the clay than in the whole rock appears to be a result of authigenic illite and phosphate formation during burial diagenesis although the ree are redistributed on a local scale there is little evidence that the ree are gained or lost by the mudrocks during diagenetic redistribution combined nd and sr isotopic data show that the whole rock shale system may be modelled as a three component system composed of young volcanic derived and old craton derived detritus and a seawater derived component these three components are partially homogenized during diagenesis and as a result the sr nd provenance information originally held in the silicate fraction of whole rock shale becomes obscured

upb pbpb and smnd dating of authigenic monazite implications for the diagenetic evolution of the welsh basin abstract authigenic monazite nodules from silurian turbiditic rocks in the central welsh basin are zoned with respect to nd isotope composition the cores are relatively radiogenic and the rim to core trend projects toward the composition of associated very early authigenic apatite concretions these authigenic phases therefore equilibrated with changing fluid composition as they formed the apatites and the monazite nodule cores may have included significant nd from organic matter or seawater whereas the rees in the outer parts of the monazite nodules were derived from clastic detritus the apparent sm nd age obtained from these phosphates is a mixing line which gives an ordovician age for these silurian rocks the u pb isotope system does not show similar trends and shows promise as an alternative method for dating such phosphates a date of 417 11 ma 2 mswd 107 agrees well with recent estimates of the time of the diagenetic smectite illite transition in the rocks of this study a pb pb isochron gave an age of 422 24 ma 2 mswd 0 9 this shows that the pb is in isotopic equilibrium and is undisturbed and that the elevated mswd of the u pb regression is caused by slight subsequent mobility in the u pb system the event dated by the monazite is probably compactional dewatering during accelerated mid silurian sediment loading in the central welsh basin

late quaternary sea surface conditions in the laurentian fan evidence from coccolith and dinocyst assemblages abstract the analyses of coccoliths and dinocysts from the images core md95 2033 collected on the laurentian fan 44 39 87n 55 37 21w water depth 1412 m in the northwest north atlantic provide a new dataset to assess the magnitude of climatic changes during the holocene with a millennial time resolution coccolith and dinocyst data were combined to reconstruct changes in past sea surface conditions in addition the dinocyst assemblages were used to reconstruct the sea surface temperature sst and salinity sss based on the modern analog technique the distribution of the coccolith and dinocyst assemblages suggests a succession of climatic events during the late quaternary and early holocene linked to change in the influence of the labrador current and or the st lawrence river discharge the dinocyst assemblages recorded a thermal optimum during the mid holocene in the late holocene coccolith concentrations show two peaks at 2 3 and 1 1 ky which coincide with the presence of species with different ecological properties likely due to the localized influence of the slope water jet swj current the presence of this current has played a role in the development of the coccolith and dinocyst assemblages and sst fluctuations especially in the last 2 ky overall the interaction between the st lawrence river the swj the lc and the nac has all controlled the sss ssts and the development of the coccolith and dinocyst assemblages confirming a significant regionalism of the entire area

genesis of gray monazites evidence from the paleozoic of belgium systematic mineralogical investigations carried out on panned stream concentrates from the northwestern part of the cambro ordovician stavelot massif belgium led to the discovery of nodular gray monazites these were later identified in situ in black slates associated with conglomeratic levels containing phosphatic material microscopic investigation shows that gray monazites are authigenic and predate cleavage to test the hypothesis of a sedimentary origin for rare earth elements samples of shales phosphatic conglomerates and monazite concentrates were submitted to sequential inductively coupled plasma analysis results show that the rare earth element pattern in gray monazites is a reflection of the abundance of these elements in the host rock this suggests a model invoking desorption of the rare earth elements from their clayey support and differential precipitation of rare earth phosphates in the sediment initiated by p mobility during diagenesis the genetic model for gray monazite mineralization assumes three essential and complementary phenomena 1 sedimentation of clays in a reducing marine environment 2 a phosphate anomaly in the same lithological sequence and 3 evolution to low grade epizonal metamorphic conditions these nonrestrictive genetic conditions clearly suggest that gray monazites have been generally overlooked and must be much more widespread than believed the economic interest of gray monazite lies in potential stream or beach placers their low th content and comparatively high eu content are interesting features in the scope of ore beneficiation

the 8200 year b p event in the slope water system western subpolar north atlantic 1 stable isotope trace metal alkenone paleothermometry and radiocarbon methods have been applied to sediment cores in the western subpolar north atlantic between hudson strait and cape hatteras to reveal the history of climate in that region over the past 11 kyr we focus on cores from the laurentian fan which is known to have rapid and continuous accumulation of hemipelagic sediment although results among our various proxy data are not always in agreement the weight of the evidence alkenone sea surface temperature sst 18o and abundance of globigerinoides ruber indicates a continual cooling of surface waters over laurentian fan from about 18 c in the early holocene to about 8 c today alternatively mg ca data on planktonic foraminifera indicate no systematic change in holocene sst the inferred long term decrease in sst was probably driven by decreasing seasonality of northern hemisphere insolation two series of proxy data show the gradual cooling was interrupted by a two step cold pulse that began 8500 years ago and lasted about 700 years although this event is associated with the final deglaciation of hudson bay there is no 18o minimum anywhere in the labrador sea yet there is some evidence for it as far south as cape hatteras finally although the 8200 year b p event has been implicated in decreasing north atlantic ventilation and hence widespread temperature depression on land and at sea we find inconsistent evidence for a change at that time in deep ocean nutrient content at 4 km water depth