magnetic polarity stratigraphy of a plio pleistocene marine sequence of north island new zealand abstract thick sequences of relatively undisturbed plio pleistocene sediments in the wanganui basin north island new zealand consist of well exposed silts clayey silts sandstones rare limestones and several tephras oriented specimens were collected from a section more than 2500 m thick and palaeomagnetic measurements were made using a c demagnetisations in fields up to 35 mt with the aid of tephrochronology the age of the upper sequence is now well established and falls within the matuyama epoch the lower two thirds of the section except for the basal 500 m is predominantly normally magnetised and is interpreted as a very extended sequence of the gauss epoch the lowest 500 m then represents the gilbert epoch the plio pleistocene boundary as defined at vrica italy falls within the upper part of the section studied in the upper nukumaruan stage for the first time a reliable correlation is made with the international boundary using as intermediaries the palaeomagnetic and tephrostratigraphy of deep sea cores from the southwest pacific as a result of the high deposition rate of the order of 1 2 m ky and the apparent lack of unconformities the temporal resolution is high short lived magnetic events are detected especially in the lower matuyama and upper gauss epochs these generally correlate well with events reported from other extended sections

a 1100 year paleoclimatic record from burton bay tarr inlet baffin island pollen studies were carried out in the upper frobisher bay area baffin island as part of joint paleoenvironmental archaeological investigations in the area pollen data from southern baffin island are rare and this paper expands this record a shallow peat section and several recent pollen records are presented they suggest a contrast between an earlier assemblage dated 2000 1650 bp which was characterized by a rich diverse flora especially birch shrubs and a subsequent pollen assemblage dominated by grass pollen and interpreted as representing colder and drier conditions to 900 bp

hudson bay hudson strait jokulhlaups and heinrich events a hypothesis abstract abrupt temperature changes in the northern north atlantic occurred frequently throughout the last glaciation as shown by proxy records from greenland ice cores deepsea cores and norway speleothems many of these variations occurred in irregular sawtooth cooling cycles which sometimes ended with the deposition of thick layers of ice rafted debris ird in the deep ocean that are known as heinrich events the lithologies of most of the ird deposits are consistent with widespread surges of the laurentide ice sheet that may have resulted from the accumulation of deformable sediments in portions of the ice sheet bed an alternative conceptual model proposed here to explain the sawtooth coolings and the surges involves repetitive jokulhlaups from a hudson bay lake dammed by ice at the mouth of hudson strait the slow sawtooth coolings may be explained by storm track diversion due to progressive coverage of the lake by icebergs and the surges by abrupt losses of water pressure and buttressing ice shelves at all ice sheet fronts in the lake when the ice dams failed

holocene and pleistocene dissolution cycles in deep sea cores of baffin bay and davis strait palaeoceano graphic implications abstract calcium carbonate dissolution has been studied in several grab samples and piston cores from baffin bay and davis strait ranging in water depth from 200 to 2300 m the intensity of dissolution was determined from examining 1 the ratio of arenaceous to calcareous benthonic foraminifera 2 the ratio of benthonic to planktonic foraminifera 3 the relationships between the dissolution susceptible and dissolution resistant foraminifera 4 the degree of foraminiferal test fragmentation and 5 the relationships between plankton tows and the fauna in the surface sediments all core tops and grab samples from baffin bay surface sediments below 600 900 m water depth demonstrated intense dissolution of calcium carbonate sediments below 900 m were biogenic carbonate free indicating 100 foraminiferal loss due to dissolution possible causes of substantial undersaturation in calcium carbonate of baffin bay bottom water are very low temperatures and higher concentrations of carbon dioxide all cores also demonstrated intense dissolution during interglacial or interstadial isotope stages 1 3 5 7 and 9 similarities in planktonic foraminiferal assemblages suggested the presence of similar bottom water masses during these periods the preservation state of biogenic carbonate debris in glacial isotope stages 2 4 6 8 and 10 is similar to the assemblage found in the water at present

labrador shelf benthic foraminifera and stable oxygen isotopes of cibicides lobatulus related to the labrador current foraminifera from 38 samples of surface sediments contained 22 calcareous and 17 agglutinated species eight stenotopic species relate to different waters of the labrador current cassidulina reniforme reophax arctica and cribrostomoides crassimargo are associated with the inner shelf estuarine environment islandiella helenae and haynessina orbiculare are associated with the cold and diluted inner shelf waters buccella frigida is related to the slope waters and melonis zaandamae is related to the deep waters of the basins and the outer labrador shelf the distribution of these species down core in core 13 collected from one of the basins on the labrador shelf indicates the presence of inshore waters in the bottom of the basin about 15 000 years bp the ratios of the two stable oxygen isotopes 18o and 16o were determined in the tests of cibicides lobatulus from surface sediment samples collected at 28 localities on the labrador shelf the range of bottom salinities at station locations was 28 6 to 34

latest quaternary and holocene paleoceanography of the eastern baffin island continental shelf canada benthic foraminiferal evidence foraminiferal zones radiocarbon ages on shells and corrected ages on pretreated organic sediment from four cores from the eastern baffin island continental shelf suggest a three stage deglacial to postglacial history late wisconsin to holocene the earliest sediments in the cores contain foraminiferal species elphidium excavatum cassidulina reniforme islandiella helenae indicative of distal glaciomarine environments that lasted at least several thousand years an oceanographic change about 8500 years ago is indicated by a melonis zaandamae zone in northern and central shelf cores collected from 200 800 m water depth the presence of m zaandamae in the north and its absence in the south suggest warmer and more saline postglacial water in northern baffin bay whose influence became diluted with cooler coastal meltwater as the current flowed south along the baffin island shelf sediments after 6000 years ago on the northern and central shelf are dominated by agglutinated foraminifera suggesting dis

deglacial warming of the northeastern atlantic ocean correlation with the paleoclimatic evolution of the european continent abstract isotopic micropaleontologic and pollen analyses of deep sea cores from the bay of biscay and the northeastern atlantic ocean show that the deglacial warming of this oceanic area was closely correlated with the paleoclimatic evolution of the adjacent european continent temperatures were at least as warm as those of today in the bay of biscay between 13 300 and 11 000 b p coinciding with the combined bolling allerod warm continental events a major spread of polar water occurred between 11 000 and 10 000 b p during this event which coincides with the younger dryas continental cold event marine temperatures were almost as low as those of the last glacial maximum the final deglacial warming of the norteastern atlatntic ocean occurred during the following 3000 yr

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

lowstand shorefaces transgressive incised shorefaces and forced regressions examples from the viking formation joarcam area alberta abstract in the joarcam beaverhill lake area of alberta there are three long 40 km narrow 5 km sandbodies in the late albian viking formation they are surrounded by offshore open marine mudstones and have previously been interpreted as offshore bars however the sandbodies are both underlain and overlain by erosion surfaces joarcam is the only field with abundant cores and the sandbody shows a sandier upward and coarsening upward succession all three fields have recently been reinterpreted in the literature as lowstand shoreface deposits but the order in which they formed remains controversial our well log cross sections suggest that the lindbrook shoreface was the first to form at a time of maximum lowstand of sea level it was truncated as sea level began to rise and the lindbr ok transgressive surface of erosion tse has been traced into the erosion surface that underlies joarcam joarcam can therefore be interpreted as a shoreface incised during a pause in an overall transgression both the lindbrook and joarcam shorefaces appear to be truncated by the regressive surface of erosion rse that underlies beaverhill lake this suggests that beaverhill lake is the youngest of the shorefaces and implies a second major fall of relative sea level the lowstand shorefaces tend to be thinner because of reduced accommodation space during sea level fall they tend to prograde farther beaverhill lake about 23 km because of abundant sediment supply at lowstand but consist largely of sandstone directly overlying the rse at beaverhill lake the shoreface sediments prograded at least 10 km before any mud in the offshore to shoreface transition was preserved by contrast the transgressive shorefaces tend to be thicker because of accommodation space created during transgression however they tend not to prograde so far joarcam up to 13 km possibly because of reduced supply of sediment to the shoreface during transgression the two proposed episodes of lowering of relative sea level are tentatively correlated with the two separate valley incisions documented at crystal about 90 km to the southwest these incisions represent type 1 sequence boundaries but the boundaries are not continuous regressive surfaces of erosion from crystal to the joarcam beaverhill lake area in both cases the falling stage rses have been eroded by the subsequent tses these tses are the only surfaces preserved between the incised valleys and the lowstand shorefaces

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

initiation of fennoscandian ice sheet retreat during the last deglaciation although the retreat history of the southern margin of the laurentide ice sheet during the last deglaciation has been well known for several decades1 3 and recently supported by evidence from accelerator mass spectrometer ams radiocarbon dating of meltwater in the gulf of mexico4 and the north atlantic subtropical gyre5 the retreat history of the fennoscandian ice sheet before 13kyr ago is still poorly documented from ams 14c dating and isotopic analysis of a rapidly deposited series of supra till sediments in the norwegian channel north sea we find that the southern margin of the fennoscandian ice sheet was in retreat by 15 kyr bp before present approximately 2 000 yr earlier than previously supposed oxygen isotope analyses in the channel sediments confirm earlier evidence from deep norwegian sea sediment cores for low salinity due to ice sheet discharge beginning 15 14 5 kyr bp ref 6 recent recalibration of the 14c timescale indicates that the onset of deglaciation within the norwegian sea occurred during an interval of rapidly increasing summer insolation beginning 18 000 calendar yr bp ref 7 suggesting that ice sheet retreat may have been caused by increasing insolation acting on a particularly climate sensitive ice sheet configuration fresh water and icebergs discharged into the norwegian sea at this time reached the north atlantic and may have contributed to a brief interval of extreme oceanic cooling8 and reduced production of north atlantic deep water9 10 these factors may also have helped to briefly reverse the deglaciation trend erie interstade already underway in north america

cryosphere ocean interactions at the margin of the laurentide ice sheet during the younger dryas chron se baffin shelf northwest territories cores hu82 034 057 and hu84 035 008 resolution basin se baffin shelf contain 200 and 450 cm respectively of sediment that spans the younger dryas chron in both cores the interval is bracketed by 14c dates on foraminifera or molluscs these sites were close to the margin of the late wisconsin foxe ice sheet as it flowed toward the labrador sea prior to 11 ka both cores record moderate to high accumulations of foraminifera relatively high del 18o values in planktonic foraminifera and low values of detrital carbonate the diatom and percent opal records imply occasional seasonally open water conditions during part of the younger dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production suggesting surface water conditions affected by increased sea ice and or reduced nutrients in addition the younger dryas interval is marked by an increase in coarse sand and detrital carbonate a decrease in total organic carbon and foraminifera and high rates of sediment accumulation the inferred environment during the younger dryas is ice proximal in hu82 034 057 the foraminifera and other data suggest a change in conditions during the middle part of the younger dryas chron

a high resolution late glacial and early holocene diatom record from baffin island eastern canadian arctic an interval of late glacial to early holocene sedimentation spanning the period 12 9 8 4 ka bp 14c dated by accelerator mass spectrometry is contained within 15 cm of gyttja in a core from a small lake on southwestern cumberland peninsula baffin island this sediment was subsampled in continuous 2 5 mm increments for diatom analysis extremely low sediment accumulation rates 1 8 cm ka 1 are characteristic of the initial phase of organic sedimentation but they increase rapidly to 14 2 cm ka 1 after 9 ka bp the first 0 5 cm of gyttja contained an acidophilous diatom flora resembling that of underlying mineral sediments thereafter and throughout the late glacial and earliest holocene diatom floras were dominated by alkaliphilous and circumneutral species of fragilaria around 9 ka bp shifts to acidophilous floras dominated by brachysira brebissonii and later eunotia rhomboidea and frustulia rhomboides vars saxonica and crassinervia suggest a period of natural lake acidification high dia

magnetic susceptibility of late quaternary marine sediments frobisher bay n w t an indicator of changes in provenance and processes abstract twelve piston cores from the floor of frobisher bay and adjacent inner portion of the se baffin shelf show holocene variations in volume magnetic susceptibility k over three orders of magnitude 1 1000 10 5 si the variations are a function of changes in provenance in the inputs of detrital carbonates and organic carbon and grain size the chronology of depositional events within this region marginal to the laurentide ice sheet has been clarified by 14c ams dates on marine shells or foraminifera correlations between cores are further refined by the use of core segmentation and sequence slotting algorithms two well defined magnetic susceptibility units are recognized during the last 10 000 years which are further sub divided into smaller events which are coeval with intervals of glacial re advance and retreat mapping magnetic susceptibility in time distance space indicates a double plume of high magnetic susceptibility which occurred in the outer bay between 8 10 ka this plume appears to be associated with a n ne flow of ice across the tip of se baffin island from hudson strait possibly from labrador ungava

sedimentology and high resolution sequence stratigraphy of the late middle to late miocene angostura formation western borbon basin northwestern ecuador an integrated analysis of facies and palaeontological content of the middle to late miocene c 12 4 9 1 ma angostura formation led to the identification of facies associations indicative of shoreface and inner shelf settings the angostura formation comprises eight high frequency sequences that are stacked to form a tectonically driven lowstand sequence set the most complete examples of sequences are bounded by transgressively modified unconformities and exhibit a threefold subdivision 1 a basal suite of deepening upward shoreface sediments transgressive systems tract including a base of cycle shell concentration 2 a mid cycle shell bed consisting of molluscan shells dispersed in a matrix of inner shelf muddy fine grained sandstones 3 a shallowing upward unit of inner shelf to lower shoreface sediments almost barren of mollusc fossils highstand systems tract biostratigraphic constraints allowed a reasonable correlation between sequence bounding unconformities and the late middle to late miocene high frequency glacio eustatic changes derived from recent 18 o studies this correlation has far reaching implications and leads to the following conclusions 1 glacio eustasy in tune with oxygen isotope changes at fourth order frequency 200 ka 1 ma duration may have been the principal factor regulating stratigraphic packaging in the angostura formation 2 these sequences provide an excellent shallow marine outcrop record of late middle to late miocene antarctic glaciations

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

high resolution isotope study of the latest deglaciation based on bermuda rise cores abstract a stable isotope and 14c investigation of carbonates from three late quaternary cores with high rates of sedimentation from the northeastern bermuda rise has produced the highest resolution record of the glacial maximum to holocene stable isotope change yet obtained from an open ocean location the record includes a three step termination and the first direct evidence of an early deglacial meltwater spike in the open sea

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

characteristic strength of soils underlying foundations considering effect of spatial variability in eurocode ec7 a characteristic strength is used as a cautious estimate of the local average strength that governs the bearing capacity of the foundation the objective of this paper is to exam

stable isotope stratigraphy and paleoceanography during the last deglaciation on the continental shelf off troms northern norway a stable oxygen and carbon isotope stratigraphy is established for a late weichselian holocene glaciomarine marine sequence in andfjorden and malangsdjupet on the continental shelf off troms northern norway the stratigraphy demonstrates that the global signals termination i b and possibly also i a upper parts are present and radiocarbon date to 10 3 9 7 kyr b p and 14 13 5 kyr b p respectively a temperature increase of 5 6 c and possibly a small salinity increase occurred during term i a near glacial environment between 13 and 14 kyr b p was characterized by poorly ventilated bottom waters followed by a meltwater pulse at circa 13 kyr b p during the beginning intrusion of atlantic water between 13 and 10 kyr b p the bottom water was characterized by somewhat fluctuating temperatures and salinities temperatures close to those of the present were established around 9 7 kyr b p and seem to have been rather stable since

late pleistocene holocene paleoceanographic changes on the eastern canadian margin stable isotopic evidence abstract earlier studies of this area show profound holocene pleistocene paleoceanographic changes along the eastern continental margin of canada based on benthic foraminiferal assemblages here we demonstrate that stable isotopic measurements from benthonic foraminifera substantiate and place numerical limits on physical parameters from some of the glacial postglacial environments in holocene intervals where modern analogues of present day benthonic foraminiferal faunas can be used to delimit the physical environment the isotopic results closely parallel the faunal results in the glacial marine intervals where we have no modern analogues the isotopic results provide us with the first independent evidence that the salinities were not lower than 30 in the bottom waters along this former ice margin at the time of peak glaciation salinities may actually have been above normal we see no indication of a large meltwater event in the 10 11 k y b p time period that has been suggested to occur with the younger dryas events these results demonstrate that stable isotopes can be useful outside the context of relatively stable deep sea environments

biostratigraphy and late cenozoic paleoceanography of the arctic ocean foraminiferal lithostratigraphic and isotopic evidence detailed studies of benthonic foraminifera stable isotopes and lithofacies in cores from the southeastern alpha ridge central arctic ocean reveal some new aspects of arctic ocean paleoceanography high ratios of benthonic to planktonic foraminifera are found in most of the quaternary sediment units and ratios of 1 1 appear to characterize the arctic deep water sediments benthonic foraminifera in the carbonate mud unit m show a succession of calcareous species reflecting increased influx of norwegian sea bottom water to the arctic ocean during the past 0 4 m y foraminiferal and lithological data indicate less uniform sedimentation during a warmer interval from 0 4 to 0 6 ma when most of the silty lutite unit l was deposited at the cesar site lower pleistocene units j to i contain less limestone and more dolomite and they contain a uniform faunal assemblage with low numbers of calcareous foraminifera upper pliocene units h to ab contain rare limestone and relatively large amounts of do lomite and quartz sand middle to upper pliocene units ab to a3 are marked by abundant sand sized ferromanganese coated particles which in many cases have a silt nucleus hence much of the coarse sand in these units does not indicate increased ice rafting the pliocene sediments mostly contain a low diversity assemblage of agglutinated foraminifera but a mixed calcareous arenaceous fauna occurs in a short interval above the matuyama gauss boundary 2 4 ma stable isotopic curves occur within sequences which broadly correspond to stages 1 9 of the global record below stage 9 the record is discontinuous strong vertical mixing apparently prevailed during most of the pliocene and early pleistocene then decreased during the past 0 4 m y owing to damping by a perennial ice cover isotopic and foraminiferal data however suggest that an interval of perennial sea ice also occurred during the late pliocene at the time of the earliest glacial event recorded in the north atlantic

the stratigraphic architecture of late pliocene 2 8 2 4 ma asymmetrical shelf sequences western wanganui basin new zealand abstract the western wanganui basin in the vicinity of parikino contains a 410 m thick succession of thirteen sequences that accumulated between 2 8 and 2 4 ma traditional facies analysis of the succession indicates accumulation of the sequences in shoreface to mid shelf depositional palaeoenvironments the late pliocene sequences have been correlated with oxygen isotope stages g10 to g92 and each of 41 ka glacial interglacial stage couplets is represented by an individual depositional sequence comprising transgressive tst highstand hst and regressive rst systems tracts most sequence boundaries are unconformable and coincide with transgressive surfaces of erosion tse ravinement surface with ophiomorpha burrows extending down into underlying sandstone one sequence boundary at the base of the wilkies shellbed is a correlative conformity two types of shellbed occur within tsts and are associated with key sequence stratigraphic surfaces onlap and backlap shellbed onlap shellbeds onlap the tse and sequence boundary backlap shellbeds result from stratigraphic condensation at the top of the tst and are overlain by the downlap surface dls in most of the sequences the onlap and backlap shellbeds are superposed forming compound shellbeds rarely a downlap shellbed overlies the dls within the base of hsts hsts are composed typically of massive aggradational mid shelf siltstone that grades up into sandstone which forms thick progradational inner shelf to shoreface lithofacies attributed to regressive systems tracts rst lensoidal toplap shellbeds comprised of reworked nearshore storm emplaced fauna occur within the upper part of rsts all of the parikino sequences have asymmetrical architectures with thin tsts this arises because of the very low rates of non tropical carbonate accumulation during the transgressions that is about half of the 41 ka period of each cycle amounting to a few metres at most of shellbed followed by very high rates of terrigenous sediment accumulation during the latter half of cycles an implication of this work is that marked 40 60 m eustatic sea level changes occurred repeatedly during the interval 2 8 to 2 4 ma this implies substantial and successive continental glaciations from at least 2 8 ma probably in the northern hemisphere

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

basin physiography and tectonic influence on sequence architecture and stacking pattern pleistocene succession of the canoa basin central ecuador facies shell bed features and sequence stratigraphic framework for the shallow marine pleistocene upper canoa and tablazo formations are presented based on outcrop data from the southern coast of cabo san lorenzo ecuador sediments of this succession exhibit a distinct cyclic pattern consisting of a stack of eight depositional sequences cyclothems likely developed under the main control of orbitally induced sea level changes as a rule within the studied interval an idealized cyclothem is composed of a transgressive systems tract tst and a highstand systems tract hst whereas deposits attributable to the lowstand and falling stage systems tracts are not present transgressive lithosomes may be defined by estuarine deposits interposed between the sequence boundary and the ravinement surface back barrier wedge and by upward fining shoreface to inner shelf facies successions above the ravinement backstepping shelf wedge separated by an expanded siliciclastic core hiatal shell concentrations occur at the base onlap shell beds and the top backlap shell beds of the transgressive shelf wedges and some occur at the base of highstand systems tracts downlap shell beds on the basis of sedimentary facies geometry taphonomy and paleoecology of shell beds and the nature of the transition between siliciclastic and mollusk bearing sediments cyclothems were classified into two main types that show dependence upon paleoshoreline morphological configuration sheltered in the upper canoa formation and exposed in the tablazo formation notwithstanding the different synsedimentary tectonic and climatic regimes the ecuadorian cyclothems share basic patterns of condensation and facies assemblages with other roughly coeval cyclothemic successions around the world this suggests that 1 hiatal shell bed development is not just a temperate latitude phenomenon 2 a global process such as glacio eustatic sea level change is the primary mechanism of control for the general architecture of sequences and 3 specific paleogeographic settings play an important role by determining the taphonomic and paleoecologic characteristics of key shell beds the nature of their contacts with the encasing sediments and the type of the component set of facies at a multicycle time scale tectonics influenced the long term trend of the relative sea level changes and consequently the large scale stratigraphic organization owing to the continued tectonic uplift of the area successive high frequency depositional sequences are nested to form a longer order falling stage sequence set

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

late quaternary paleoceanography of the western baffin bay region evidence from fossil diatoms seven marine cores from the east coast of baffin island were examined for variations in diatom content the cores have good age control and were used for holocene paleoceanographic reconstruction

two step deglaciation 14c dated high resolution δ18o records from the tropical atlantic ocean abstract eight box cores from the tropical atlantic were studied in detail with regard to foraminiferal oxygen isotopes radiocarbon and globorotalia menardii abundance a standard atlantic oxygen isotope signal was reconstructed for the last 20 000 yr it is quite similar to the west equatorial pacific signal published previously deglaciation is seen to occur in two steps which are separated by a pause onset of deglaciation is after 15 000 yr b p the pause is centered between 11 000 and 12 000 yr b p but may be correlative with the younger dryas 10 500 yr b p if allowance is made for a scale shift due to mixing processes on the sea floor step 2 is centered near 10 000 yr b p and is followed by a brief excursion toward light oxygen values this excursion the m event may correlate with the gulf of mexico meltwater spike

a new geomagnetic polarity time scale for the late cretaceous and cenozoic we have constructed a magnetic polarity time scale for the late cretaceous and cenozoic based on an analysis of marine magnetic profiles from the world s ocean basins this is the first time since heirtzler et al 1968 published their time scale that the relative widths of the magnetic polarity intervals for the entire late cretaceous and cenozoic have been systematically determined from magnetic profiles a composite geomagnetic polarity sequence was derived based primarily on data from the south atlantic anomaly spacings in the south atlantic were constrained by a combination of finite rotation poles and averages of stacked profiles fine scale information was derived from magnetic profiles on faster spreading ridges in the pacific and indian oceans and inserted into the south ariantic sequence based on the assumption that spreading rates in the south atlantic were smoothly varying but not necessarily constant a time scale was generated by using a spline function to fit a set of nine age calibration points

astronomic timescale for the pliocene atlantic δ18o and dust flux records of ocean drilling program site 659 high resolution benthic oxygen isotope and dust flux records from ocean drilling program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the atlantic from 2 85 ma back to 5 ma spectral analysis of the 18o record indicates that the 41 kyr period of earth s orbital obliquity dominates the pliocene record this is shown to be true regardless of fundamental changes in the earth s climate during the pliocene however the cycles of sahelian aridity fluctuations indicate a shift in spectral character near 3 ma from the early pliocene to 3 ma the periodicities were dominantly precessional 19 and 23 kyr and remained strong until 1 5 ma subsequent to 3 ma the variance at the obliquity period 41 kyr increased the timescale tuned to precession suggests that the pliocene was longer than previously estimated by more than 0 5 m y

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

wisconsinan refugia and the glacial history of eastern baffin island arctic canada coupled evidence from cosmogenic isotopes and lake sediments new data constrain the timing and character of glaciation of eastern baffin island arctic canada lake sediments radiocarbon dated to between 14 and 52 ka coupled to 10 be and 26 al exposure ages 35 ka from adjacent moraines and bedrock demonstrate that some coastal uplands remained above the limits of continental glaciation throughout oxygen isotope stage 2 at lower elevations exposure ages from a flight of distinct lateral moraines range from 10 to 35 ka and imply that low gradient outlet glaciers reached the outer coast during the late wisconsinan collectively these results reconcile terrestrial evidence for the presence of ice free refugia through the late wisconsinan with marine evidence for extensive outlet glaciers in the major fiords and bays of eastern baffin island

structure and timing of the last deglaciation oxygen isotope evidence foraminiferal oxygen isotope data from 24 tropical atlantic sediment cores constrained by 77 14c dates are stacked to form a composite record of isotopic termination 1 this record indicates that most of the isotopic transition at the end of the last ice age occurred between 14 ka bp and 6 ka bp minor isotopic expression of deglaciation is permitted as early as 16 ka bp but the most rapid rate of change occurred between 14 ka bp and 12 ka bp three steps of maximum change are present although they are close to the statistical limits of detection in the composite record the clear presence of the steps in individual records suggests that they are real we estimate their timing at 14 12 ka bp termination 1 a 10 9 ka bp termination 1 b and 8 6 ka bp termination 1 c centering of the termination near 11 ka bp is consistent with the milankovitch hypothesis that high summer insolation caused deglaciation in detail however maximum rates of change prior to the 11 ka bp insolation extreme and the inferred steps require additional mechanisms controlling the tempo of glacial interglacial climate change steps equivalent to those in 18o have not been detected in ice margin retreat data steps in the isotopic transition if real may record thinning of the ice sheets not accompanied by loss of area alternation between near equilibrium and near stagnant ice sheet profiles during deglaciation is hypothesized perhaps due to calving and unstable down draw of the ice sheets followed by partial re equilibration significant problems remain the effects of temperature on the isotope record are only partially constrained presently available data allow only semi quantitative intercalibration of ice volume sea level and isotopic estimates of glaciation

evidence for high frequency late glacial to mid holocene 16 800 to 5500 cal yr b p climate variability from oxygen isotope values of lough inchiquin ireland a 7 6 m core recovered from lough inchiquin western ireland provides evidence for rapid and long term climate change from the late glacial period to the mid holocene we determined percentage of carbonate total organic matter mineralogy and d 18 ocalcite values to provide the first high resolution record of climate variability for this period in ireland following deglaciation rapid climate amelioration preceded large increases in gisp2 d 18 oice values by 2300 yr the oldest dryas 15 100 to 14 500 cal yr b p late glacial event is documented in this record as a decrease in d 18 ocalcite values brief warming at 12 700 cal yr b p was followed by characteristic younger dryas cold and dry climate conditions a rapid increase in d 18 ocalcite values at 10 500 cal yr b p marked the onset of boreal warming in western ireland the 8200 cal yr b p event is represented by a brief cooling in our record prior to general warming a larger and previously undescribed climate anomaly between 7300 and 6700 cal yr b p is characterized by low d 18 ocalcite values with high frequency variability

wisconsinan late glacial environmental change on the southeast baffin shelf southeast baffin island and northern labrador the importance of the baffin labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the laurentide ice sheet and the probable effects of this on the thermohaline circulation of the north atlantic the chronology of glaciation and deglaciation in the region is summarised reference is made to recent marine records from the baffin shelf isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the baffin shelf labrador sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14 0 11 0 ka bp

reconstructed ice flow patterns and ice limits using drift pebble lithology outer nachvak fiord northern labrador discussion on the basis of their analysis of pebble lithologies and age estimates of marine shells the authors presented an interpretation for late quaternary events in outer nachvak fiord that they sav is incom atible with the late wisconsinan ice model of f k k and osh josenhans et al 1986 clark 1988 we believe that much of their data when reinterpreted do not conflict with our reconstruction and in fact can be accommodated by our reconstruction in contrast our data from nachvak fiord and the adjacent continental shelf are not compatible with their hypotheses nor have they directly addressed these data in their hypotheses in this discussion we will evaluate the clast morphologic and chronologic data used by the authors to develop their hypotheses we also summarize our work related to the glacial history of nachvak fiord and the adjacent shelf for the purpose of discussion and comparison with their hypotheses

late quaternary stratigraphy and paleoecology of northwest labrador sea abstract sedimentological study of 20 piston cores from the northwestern labrador sea shows that thin bedded distal turbidites are important constituents of the quaternary strata on the continental slope and rise sedimentation on the outer shelf ca 500 900 m is dominated by ice rafting and hemipelagic deposition detailed study of two outer shelf cores reveals a stratigraphic record extending to oxygen isotopic stage 9 studies of foraminifera and dinoflagellates show that subarctic surface waters penetrated into the northern labrador sea during the early middle glacial stages and pollen data indicate that northward advection of warm air masses occurred at the same time microfossil data indicate that late glacial stages were characterized by year around sea ice cover and arctic surface water and by the dominance of cold dry arctic air masses transitions from glacial to interglacial stages are marked by the presence of low salinity melt water these data support models which postulate that open water in the labrador sea played an important role in supplying moisture to laurentide and greenland ice sheets

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

a review of wanganui basin new zealand global reference section for shallow marine plio pleistocene 2 5 0 ma cyclostratigraphy abstract wanganui basin new zealand contains one of the most complete late neogene marine stratigraphic records in the world the ca 2 km thick basin fill for the last ca 2 5 ma comprises 47 superposed cyclothems which correspond to successive 5th 100 ka and 6th 41 ka order glacio eustatic sea level fluctuations on the palaeo new zealand shelf since oxygen isotope stage 100 stages 100 to 5 are represented by marine cyclothems whereas stages 17 to 3 are represented by a suite of coeval and younger uplifted marine terrace sequences additionally a predominantly glacial loess stratigraphy exists for isotope stages 12 2 the presence of interbedded tephras and an established paleomagnetic stratigraphy allows the development of an integrated cyclostratigraphy for wanganui basin which correlates closely with the global oxygen isotope scale in all except two cases cycles 12 and 36 individual unconformity bound cyclothems sequences represent a single glacial interglacial couplet of milankovitch frequency lithologic and faunal variation within the cyclothems corresponds closely to that predicted by the sequence stratigraphic model each cyclothem generally contains a transgressive systems tract a mid cycle condensed shellbed a highstand systems tract and often a regressive systems tract six common cyclothem motifs are inferred to represent deposition in shelf locations between the highstand and lowstand shorelines viz the hawera maxwell turakina seafield castlecliff and rangitikei motifs a seventh type the nukumaru motif includes coquina limestone and represents deposition in shoreface and very shallow water marine environments

holocene sea surface conditions in the north atlantic contrasted trends and regimes in the western and eastern sectors labrador sea vs iceland basin abstract two sediment cores from the labrador sea and one from the iceland basin were analysed in order to compare holocene sea surface conditions across the northern north atlantic 18o measurements on meso and epi planktonic foraminifera neogloboquadrina pachyderma left coiling and globigerina bulloides along with sea surface condition reconstructions using transfer functions based on dinoflagellate cyst assemblages were used to document thermohaline properties of the upper water column at the labrador sea sites a decreasing trend in sea surface temperature following an early holocene maximum is observed at the iceland basin site a hiatus between 13 and 8 ka bp prevents us from documenting the entire holocene but a stable to slightly decreasing trend is observed from 8 ka bp onwards sea surface salinity and potential density show little variation at the orphan knoll site in the labrador sea since 7 ka bp whereas they depict a decreasing trend at the two other sites since ca 8 ka bp this shift in values suggests a progressive enhancement of labrador sea water formation and a relative decrease in the nordic seas components of the north atlantic deep water i e denmark strait overflow water and norwegian sea overflow water discrepancies are also observed with regard to millennial frequency oscillations in sea surface conditions at the easternmost site they likely match previously documented cold water pulses in the north eastern atlantic whereas they do not show any clear pattern at the westernmost sites hence the western and eastern areas show different behaviours with respect to both long term and high frequency fluctuations

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

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

sedimentation rates in baffin island fiord cores from comparative radiocarbon dates five accelerator tams system university of arizona radiocarbon dates on small 30 50 mg paired bivalves or shell fragments have been obtained on two piston cores these dates are compared with conventional and accelerator 14c dates on the total organic fraction 2 m size fraction from similar levels in the two cores the shell dates are always younger by several thousands of years we argue that the shell dates are the more reliable for example we demonstrate that pre quaternary pollen is abundant in the lowermost 6 m in core hu77 159 from frobisher bay since the occurrence of shells is rare in piston cores we have developed an empirical relation that enables us to change dates on organic matter to a more probable true age if this correction is applied to dates on the total organic fraction that we obtained on an additional five cores from fiord and shelf sites a consistent pattern of sedimentation rate variations is shown this indicates that sedimentation rates were highest between ca 9

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

forward modelling of the sequence stratigraphic architecture of shelf cyclothems application to late pliocene sequences wanganui basin new zealand we demonstrate a procedure for forward modelling of the sequence stratigraphic architecture i e positions of systems tract boundaries of shelf cyclothems as observed at outcrop sites or in well logs the 1 d model is based on the fact that the deposition of facies within shelf sequences and those defining the key stratigraphic surfaces between systems tracts respond directly to changes in depth between the sea surface and seafloor this accommodation bathymetry model incorporates three reference surfaces sea surface seafloor and lower sequence boundary each of which varies independently as a result of changes in the rates of eustatic sea level sedimentation and subsidence the model input and boundary conditions are an eustatic sea level curve i e late cenozoic deep sea 18o record an independent chronology for the outcrop or well section and a subsidence curve the model outputs are changes in accommodation and palaeobathymetry throughout the sequence and the time missing at erosional sequence boundaries the main variable in the model i e sedimentation rate is established by comparison of a model output bathymetry with the model target palaeobathymetry established from the faunal and facies content of the sequence being modelled when the model output and target are compatible the model sedimentation rate curve is adopted and the theoretical positions of the systems tract boundaries can be read off the model in relation to the lower sequence boundary and compared with independent field based interpretations of their stratigraphic position the model is designed to predict the architecture of sequences as they appear at particular outcrop sites or in well sections its usefulness lies in establishing the timing of accumulation of systems tracts in relation to stages in a eustatic sea level cycle in particular distinguishing between units deposited during highstand versus regressive systems tracts the model is applied to 6th order 41 ka plio pleistocene cyclothems in wanganui basin new zealand where it distinguishes the boundary between highstand systems tracts hst and regressive systems tracts rst the modelling has implications for the definition of systems tracts especially in late cenozoic successions for which the record of eustatic sea level changes is known independently

varve studies at hector lake alberta canada and the relationship between glacial activity and sedimentation glacial lake sedimentary records from hector lake in banff national park alberta are examined with the aim of clarifying the relationship between glacial activity and outwash sedimentation rhythmic couplets in lake bottom sediments provide a method for accurate documentation and dating of recent sedimentation chronology as analysis of 137cs content indicates that the couplets are of annual periodicity i e varves a comparison of sedimentation rate records with recent regional glacial history indicates that high sedimentation rates of one to a few decades duration occur either during and immediately following periods of moraine deposition ie maximum ice stands or during periods of rapid ice recession comparison of sedimentary records with somewhat longer term glacial and vegetation records indicates that sedimentation rate variations of several centuries duration closely parallel changes in upvalley ice extent over this time scale high sedimentation rates occur during periods of relatively increased ice extent low rates during periods of reduced ice extent within this general pattern however sedimentation rates may remain very high for nearly a century following maximum ice stands due to the exposure of unstable glaciogenic deposits to fluvial reworking during ice recession

vegetation pattern and sedimentation changes in the context of the lateglacial climatic events case study of staroje lake eastern belarus abstract a lake sediment core collected from the staroje lake southeastern belarus reveals significant changes of the terrestrial and limnic environmental during the lateglacial and early holocene in the periglacial zone of the late weichselian glaciation the combination of lithological loss on ignition palaeobotanical pollen non pollen palynomorphs diatoms and isotopic 18o 13c 14c proxy parameters was applied for the reconstruction of the vegetation pattern and sedimentation regime the lateglacial pre interstadial gs 2 vegetation was dominated by mineral soil pioneers with scattered occurrence of pinus and betula an interstadial gi 1 dominated by pinus forest with increasing representation of open ground species since approximately 13 500 cal bp and lateglacial stadial gs 1 with recurring opening of the vegetation pattern with scattered tree patches including those of picea presence of pinus stomata confirms the local origin of this plant since the pre interstadial starting from the holocene birch later accompanied by other deciduous species ulmus alnus quercus corylus took over in the local vegetation structure isotopic records 18o 13c obtained on bulk carbonates as well as diatom data exhibit several shifts reflecting variations both in terrestrial and limnic environment distinct negative excursion of 18o curve recorded during the first half of the gi 1 event suggests intensive groundwater discharge accompanied by active transportation of detrital carbon in to the basin limited basin productivity is also indicated by lithological and diatom records since approximately 13 700 cal bp sedimentation regime in the lake stabilised and productivity of the basin started to increase in positive correlation with loi data a considerable decrease in 18o values punctuated by a rapid jump in the middle of the interval was recorded during the gs 1 stadial and could be associated with the deterioration of the environmental regime and degradation of the soil layer increasing erosion activity alongside the rising input of detrital carbonates into the basin the water table was low as indicated by diatom data recovery of the environmental regime preceded the gs 1 holocene boundary as is seen in lithostratigraphical and isotopic data during the early holocene stable isotopes show several episodes with altered levels suggesting instability of the environmental regime most probably related with the global climatic alterations

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

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

glacial geomorphology and chronology in the selamiut range nachvak fiord area torngat mountains labrador the summits of the selamiut range are the highest in the torngat mountains of northern labrador and contain some of the only permanent ice bodies of the eastern canadian mainland as they may have constituted a physical barrier to ice moving eastward from the ungava ice dispersal centre their glacial history is elaborate in a regional context consequently a complex interaction of local and regional ice masses is manifest in the morphochronological record dating from the late quaternary through the holocene physiographically the selamiut range is a plateau dominated by deep cirques and cirque outlet valleys with precipitous bounding rock walls colluvial processes are extremely active and consequently many surficial units have been extensively remodelled in dynamic landscape systems the northern half of the field area contains a wealth of glacial and periglacial landform assemblages and former local and regional ice activity has been determined from the cross cutting relationships of certain morainic features within the mccornick river valley a sequence of shorelines documents the depths and extent of ice dammed lakes during glaciation a further 33 metre marine limit demarcates former sea level during the final glaciation of the area three glaciations or stillstands are suggested for the field area after consideration of the landform evidence and are named the ivitak nachvak and superguksoak glaciations the adoption of a 1 5 cm ka soil development rate dates the three glaciations or stillstands for the selamiut nachvak area the ivitak glaciation at 40 ka the nachvak glaciation at c 23 ka and the superguksoak i glaciation at 10 12 ka b p two further neoglacial events were restricted to the cirque basins and are correlated locally by a combination of pedology lichenometry and morphologic superimposition a number of chronocorrelative inferences are made for northern labrador based upon the existing empirical data glacial styles appear to differ quite considerably from fiord to fiord along the coastal section of the torngat mountains the solution of discrepancies within the general northern labrador chronology resides in the successful construction of an absolute dating framework for the marine limits of the region relative chronologies may then attain a significant applicability

high resolution magnetostratigraphy of mid pliocene 3 3 3 0 ma shallow marine sediments whanganui basin new zealand

glacial geology of the torngat mountains labrador two late quaternary alloformations are identifed throughout the torngat mountains by degree of soil profile development in till with a granitic composition morphologic expression of deposits and their relative areal distribution the two alloformations are interpreted to represent two successively limited glaciations of the torngat mountains by the laurentide ice sheet deposits of the shoal cove alloformation mantle hillslopes distal to deposits of the younger saglek alloformation deposits are primarily soliflucted till found around coastal regions soils developed in till of the shoal cove alloformation are characterized by well expressed bw horizons 19 cm thick deposits of the younger saglek alloformation are characterized by prominent well preserved moraines outwash fan surfaces and ice marginal channels soils described in till are poorly developed with a horizons directly overlying cox horizons or separated from cox horizons by thin transitional ac ca horizons or poorly expressed bw

mid to late pliocene 3 3 2 6 ma global sea level fluctuations recorded on a continental shelf transect whanganui basin new zealand abstract we present a 900 m thick mid 3 3 3 0 ma to late pliocene 3 0 2 6 ma shallow marine cyclical sedimentary succession from whanganui basin new zealand that identifies paleobathymetric changes during a warmer than present interval of earth history relevant to future climate change our approach applies lithofacies sequence stratigraphy and benthic foraminiferal analyses to two continuously cored drillholes integrated with new and existing outcrop studies we construct a depositional model of orbitally paced global sea level changes on a wave graded continental shelf unlike many previous studies these shelf sediments were not eroded during sea level lowstands and thus provide the potential to reconstruct the full amplitude of glacial interglacial sea level change paleobathymetric interpretations are underpinned by analysis of extant benthic foraminiferal census data and a statistical correlation with the distribution of modern taxa in general water depths derived from foraminiferal modern analogue technique mat are consistent with variability recorded by lithofacies the inferred sea level cycles co vary with a qualitative climate record reconstructed from a census of extant pollen and spores and a modern temperature relationship a high resolution age model is established using magnetostratigraphy constrained by biostratigraphy and the dating and correlation of tephra this integrated chronostratigraphy allows the recognition of 23 individual sedimentary cycles that are correlated across the paleo shelf and a possible one to one relationship is made to deep ocean benthic oxygen isotope 18o records in general water depth changes were paced by 20 kyr duration between 3 3 and 3 0 ma after which cycle duration is 40 kyr during the late pliocene 3 0 2 6 ma this record provides a future opportunity to evaluate the amplitude and frequency of global pliocene glacio eustatic sea level change independent of the global benthic 18o record

sequence stratigraphy of sixth order 41 k y pliocene pleistocene cyclothems wanganui basin new zealand a case for the regressive systems tract this study is based on a late pliocene and early pleistocene approximately 2 6 1 7 ma succession about 1 km thick of 20 sixth order 41 k y duration cyclothems of shelf origin exposed in the rangitikei river valley in the eastern part of wanganui basin the cyclothems correlate with 18 o isotope stages 100 58 and each 41 k y glacialinterglacial stage couplet is represented by an individual depositional sequence comprising transgressive highstand and regressive systems tracts unlike most examples inferred from the stratigraphic record these systems tracts were deposited during phases of known sea level cycles indicated by the contemporary oxygen isotope ice volume curve because of the high rate of subsidence of wanganui basin glacioeustatic sea level falls during most cycles were not of sufficient magnitude to expose the outer shelf thus the rangitikei section provides an exceptional example of regressive strata deposited landward of the contemporary shelf break simple one dimensional modeling shows that moderate to high rates of basin subsidence 1 2 mm yr and low rates of sedimentation 0 2 mm yr during transgressions combined to produce an accommodation surplus at the relative highstand this surplus accommodation was infilled during the late highstand and ensuing fall partly by aggradational highstand systems tract shelf siltstone and chiefly by strongly progradational shoreface sediments of the regressive systems tract rangitikei regressive systems tracts are distinguished from forced regressive systems tracts sensu hunt and tucker 1992 by their different stratal geometry by definition forced regressive systems tracts display an erosional contact with the underlying highstand systems tracts and typically occur as a series of downstepped disjunct shoreline wedges stranded on the shelf and or slope in contrast regressive systems tracts exhibit a gradational lower contact above which parasequences are stacked in a strongly progradational pattern terminated by the superjacent sequence boundary cyclothems display two types of motif termed rangitikei dt depositional transgression and rangitikei nt nondepositional transgression which include the following architectural elements in ascending stratigraphic order 1 a basal sequence boundary that is coincident with either the transgressive surface of erosion which displays small scale up to 50 cm erosional relief and may be penetrated by the ichnofossil ophiomorpha or its deeper water correlative conformity 2 either a thick 5 30 m transgressive systems tract comprising a deepening upward nearshore to inner shelf mixed carbonate siliciclastic lithofacies succession depositional transgression or a thin 2 m transgressive systems tract comprising condensed fossiliferous facies deposited on the sediment starved offshore shelf nondepositional transgression 3 a sharp downlap surface separating condensed fossiliferous facies of the transgressive systems tract from terrigenous siltstone of the superjacent highstand systems tract 4 a highstand systems tract comprising a 10 20 m thick interval of aggradational shelf siltstone and 5 a thick up to 45 m progradational inner shelf to shoreface lithofacies assemblage ascribed to the regressive systems tract condensed shell beds are associated with intrasequence and sequence bounding discontinuities and together with the sedimentological and stratal characteristics of the sequences are important indicators of stratigraphic architecture four types of shell bed are associated with surfaces formed by four different types of stratal termination onlap backlap downlap and flooding surface shell beds cf kidwell 1991 are associated respectively with the transgressive surface of erosion apparent truncation at the top of the transgressive systems tract the downlap surface and local marine flooding surfaces a fifth shell bed type termed a compound shell bed forms in offshore environments where the downlap surface converges with the sequence boundary and elements of both the downlap and the backlap shell beds become mixed or superposed the shell beds mark zones of stratal attenuation and can be used as surrogates for seismic discontinuities when applying sequence stratigraphic concepts at outcrop scale

defining the quaternary abstract the quaternary system is under threat of extinction as a chronostratigraphic unit in the international geological time scale in its place the neogene system previously comprising miocene and pliocene series is to be extended to include the pleistocene and holocene series it may be possible to save the quaternary by defining it as a subsystem of the neogene in doing so it would be an opportune time to extend the base of the quaternary to 2 6 ma to encompass the time during which 1 earth s climate has been strongly influenced by bi polar glaciation and 2 the genus homo first appeared and evolved

cyclostratigraphy of middle pliocene mid shelf to upper slope strata eastern wanganui basin new zealand correlations to the deep sea isotope record abstract rangitikei valley in eastern wanganui basin contains a well exposed 750 m thick middle pliocene succession that accumulated during the gauss chron traditional facies analysis involving laboratory grain size determinations and benthic foraminiferal census on a suite of closely spaced 5 m samples show that the utiku group lower 350 m accumulated predominantly in a mid shelf environment the overlying mangaweka mudstone 400 m thick accumulated in an outer shelf to upper slope environment combined with the identification of sequence stratigraphic surfaces sequence boundary transgressive surface of erosion and downlap surface four sequences have been identified in the utiku group in the outwardly massive mangaweka mudstone there is no outcrop evidence for sequences seven sedimentary cycles are nevertheless defined by changes in grain size and by variations in foraminiferal paleobathymetry the utiku group sequences show mostly asymmetric sequence architecture with comparatively thin tsts rapid deepening across the utiku group mangaweka mudstone boundary at 3 0 ma involving an increase in water depth of at least 100 m that persisted until 2 55 ma orignated tectonically probably as a result of plate boundary interactions this is the second of two known rapid deepening tectono sedimentary events each separated by about 1 5 my higher order sea level cyclicity involving 11 sedimentary cycles as presently defined are superimposed upon this second tectono sedimentary cycle independent magnetostratigraphies allow the sedimentary cycles to be correlated to the astronomically tuned oxygen isotope stratigraphy for odp site 846 for the interval 3 55 3 0 ma the sedimentary cyclicity reflects the periodicities of the more major enriched 18 o peaks which range from 41 ka mg2 to m2 to 210 ka mg6 to mg2 thus the duration of cyclicty in the utiku group closely corresponds to the duration between significant sea level lowering events which are marked by glacial 18 o shifts of 0 4 on the odp site 846 benthic 18 o curve

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

glacial geology of western hudson strait canada with reference to laurentide ice sheet dynamics hudson strait is a large marine trough that connected the marine based interior of the laurentide ice sheet with the ocean field investigations of the glacial geology of western hudson strait have helped to define the role of the strait in laurentide ice sheet dynamics in general ice converged on western hudson strait from the north west and south upon reaching the strait ice flowing from foxe and ungava peninsulas turned eastward within less than 10 km of the coast to parallel eastwardly flowing ice in the strait glacial erosion of western hudson strait is identified as slight the texture carbonate content ph and the presence of several types of erratics distinguish till on nottingham salisbury and mill islands in western hudson strait from till on southern foxe peninsula and northern ungava peninsula till on the islands is characterized by higher ph and higher proportions of silt clay and carbonate than till on either adjacent peninsula in addition the presence of red sandstones porphyritic intrusives stromatolites omarolluks and iron formation are restricted to the islands with few exceptions that can be explained by ice rafting carbonate is present in the pebble and boulder fractions of till on foxe peninsula and in all fractions of till on the islands but is absent from till on ungava peninsula these data suggest that ice from distant and widely distributed source regions affected western hudson strait and along with evidence for a rapid change in ice flow direction along the margins of hudson strait suggest that the strait was occupied by a relatively fast moving ice stream that had a substantial impact on the interior of the ice sheet through downdraw

constraints on the amplitude of mid pliocene 3 6 2 4 ma eustatic sea level fluctuations from the new zealand shallow marine sediment record ice volume calibrations of the deep ocean foraminiferal delta18o record imply orbitally influenced sea level fluctuations of up to 30m amplitude during the mid pliocene and up to 30 per cent loss of the present day mass of the east antarctic ice sheet eais assuming complete deglaciation of the west antarctic ice sheet wais and greenland these sea level oscillations have driven recurrent transgressions and regressions across the world s continental shelves wanganui basin new zealand contains the most complete shallow marine late neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100ka sea level cycle since ca 3 6ma this paper presents a synthesis of faunally derived palaeobathymetric data for shallow marine sedimentary cycles corresponding to marine isotope stages m2 100 ca 3 4 2 4ma our approach estimates the eustatic sea level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation the sea level estimates are consistent with those from delta18o curves and numerical ice sheet models and imply a significant sensitivity of the wais and the coastal margins of the eais to orbital oscillations in insolation during the mid pliocene period of relative global warmth sea level oscillations of 10 30m were paced by obliquity

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

latest pleistocene holocene paleoceanographic trends on the continental margin of eastern canada foraminiferal dinoflagellate and pollen evidence micropaleontological studies were made of cores from four shelf basins on the eastern canadian margin emerald and canso basins on the scotian shelf 44 46 n notre dame channel newfoundland shelf 50 n and cartwright saddle labrador shelf 55 events were correlated using a combination of14c dates and pollen stratigraphies surface and bottom water changes were compared on the basis of dinoflagellates and benthic foraminifera respectively the results indicate significant paleoceanographic shifts along a north south gradient both prior to and during the holocene distinct late pleistocene holocene paleoceanographic events were distinguished in the emerald canso and notre dame basins these events are less obvious in cartwright saddle which is in deeper water and further off shore pleistocene glaciomarine sediments in all basins contain a fauna dominated byelphidium excavatum f clavata dinoflagellates and pollen are rare or absent the widespreadelphidium fauna probably reflects turbid glacial meltwater and or a permanent ice shelf cover from 20 000 10 000 yrs bp the notre dame core also penetrates older sediment with an outer labrador current fauna which may represent a late wisconsinian interstade at about 23 000 yrs bp from 7 000 10 000 yrs bp a cold water fauna occurred which is similar to modern outer labrador current faunas from about 5000 7000 yrs bp a warm interval is indicated by a relatively warm water calcareous benthonic foraminiferal fauna and increased representation of typical gulf stream dinoflagellates the most recent change occurred in the last 2000 years with an abrupt cooling associated with stronger flow of the arctic inner labrador current this cooling event is marked by an increase in arctic dinoflagellates and by an exclusively agglutinated benthonic foraminiferal fauna at two sites canso and notre dame these holocene paleoceanographic changes are not clearly seen in the benthic fauna of the deep northern basin cartwright saddle although dinoflagellate data at this site indicate that surface water changes have occurred that are similar to those found in shallower basins shifts in the zonal position of the gulf stream and changes in the relative mass transports of the west greenland and labrador currents are mechanisms which may account for the paleoceanographic events the glacial interstadial glacial sequence recorded in the notre dame channel in conjunction with other theories on glacial triggering mechanisms provides biostratigraphic evidence which suggests the onset of a glacial stage in the near future

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

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

stable isotope stratigraphy sedimentation rates and salinity changes in the latest pleistocene to holocene eastern central arctic ocean a high resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents has been performed on undisturbed near surface 0 40 cm sediment sequences taken in the eastern arctic ocean during the international arctic 91 expedition based on the oxygen stable isotope records measured on neogloboquadrina pachyderma sin and ams 14c dating the upper 10 to 20 cm of the sediment sequences represent isotope stage 1 and the base of termination i 15 7 ka can be identified very well stage 1 sedimentation rates vary between 0 4 and 2 0 cm kyr in general glacial stage 2 sedimentation rates are probably lower and vary between 0 4 and 0 7 cm kyr the glacial interglacial shifts in 18o values of n pachyderma sin may reach values of 1 3 to 2 5 indicating 1 that in addition to the glacial interglacial global ice volume signal changes in surface water salinity have effected the isotope records and 2 that these salinity changes have varied laterally glacial interglacial differences in salinity were small in the lomonosov ridge area 0 0 4 and relatively high in the morris jesup rise area up to 1 4 this implies that the supply of low saline waters onto the eurasian shelves and its further transport into the central arctic ocean via the transpolar drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central arctic on the morris jesup rise on the other hand the glacial low saline water signal at that time was strongly reduced in comparison to the modern situation at the glacial interglacial stage 12 boundary a strong meltwater signal is recorded in a sharp depletion in 18o as well as 13c this central arctic ocean meltwater event can be correlated from the makarov basin through the lomonosov ridge and amundsen basin to the eastern gakkel ridge the beginning of this event is ams 14c dated at 15 7 ka i e significantly older than the major decrease in the global ice volume signal which occurs between 9 and 13 5 ka large amounts of freshwater meltwater were probably supplied from the eurasian continent due to the decay of the barents sea ice sheet causing this distinct early meltwater anomaly in the central arctic ocean the extension of a well oxygenated surface near water mass in the arctic ocean and at least seasonal open ice conditions and some increased bioproductivity were probably established at the end of termination i as indicated by the increase in 13c to modern values as well as increased carbonate i e foraminifers coccoliths ostracodes and total organic carbon contents

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

ice sheet dynamics and glacial history of southeasternmost baffin island and outermost hudson strait southeasternmost baffin island is mantled by hudson strait drift it contains abundant limestone erratics and 20 to 50 carbonate in the matrix to the northwest it is replaced by drift dominated by locally derived rock of the canadian shield the sense and orientation of ice erosional features demonstrate that hudson strait drift is associated with northeasterly ice flow that crossed the tip of meta incognita peninsula local drift associated with ice flow s10 w along the hudson strait coast was derived from a dispersal center on the peninsula erratic lithologies contained in the hudson strait drift indicate a labradorean provenance large scale bedrock molding and the distribution of cirques indicate ne flowing ice has been dominant throughout the middle and late quaternary radiocarbon dates of in situ shells confirm that deglaciation began more than 11 000 yr ago with the frobisher bay coast becoming ice free by 9300 yr ago five dates from hudson strait suggest that the strait was deglaciated before 9000 yr bp however ice from the labradorean sector recrossed hudson strait during the cockburn substage about 8500 yr ago damming drainage from the west final retreat of labradorean ice from baffin island was complete by 8000 yr ago at which time the sea was able to penetrate hudson bay

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

late quaternary chronology and environments of square lake torngat mountains labrador sediment pollen and diatom records from square lake a small lake dammed by a segment of saglek moraine cover the period of deposition of and deglaciation from the saglek moraine the basal radiocarbon date 18 210 1900 years bp is on sediment contaminated by reworked pollen and is thus a maximum age however the date was measured on organic carbon recovered from glaciolacustrine couplets associated with deposition of the saglek moraine and thus establishes a late wisconsinan age for the saglek moraine vegetation on the ice free upland surrounding square lake at this time was a sparse tundra vegetation dominated by grasses and herbs the absence of diatoms indicates perennial lake ice cover a major transition is recorded by pollen and diatoms at 8 5 ka vegetation probably remained sparse tundra but birch and willow may have arrived in the area by 8 ka diatoms are first dominated by alkaliphil species reflecting continued influence of glaciolacustrine sedimentation an abrupt change in depos

effect of spatial variation of strength and modulus on the lateral compression response of cement admixed clay slab in deep excavation construction improved soil layers consisting of overlapping cement admixed columns formed by deep mixing method or jet grouting are often used to stabilise an excavation in soft soils the purpose of such soil layers is to resist lateral compression generated by movement of the retaining wall cement admixed soils are well known to have high heterogeneity in strength in this paper the heterogeneity in strength and young s modulus are studied using random finite element analyses considering three sources of variation namely a deterministic radial trend in strength and young s modulus a stochastic fluctuation component due to non uniform mixing and positioning errors arising from off verticality of the mixing shafts the results show that positioning errors have the largest effect on the strength of the slab as a whole whereas the radial trend has the smallest effect when normalised by the volume average strength based on the results obtained methods are proposed which allow e

modern and late quaternary pollen spectra of fiord sediments eastern baffin island arctic canada abstract pollen spectra of thirty surface samples from baffin island fiords are dominated by abetula filicales cyperaceae gramineae association that is somewhat representative of local or regional vegetation however betula and filicales are over represented andsalix cyperaceae and ericales are under represented compared to their importance in the present vegetation two possible causes for this disparity related to the fluvial processes that furnish most pollen to fiords are 1 fluvial reworking of older sediment that contains abundantbetula and filicales and 2 greater resistance of these taxa to corrosion and degradation during fluvial transport the pollen stratigraphy of five piston cores from fiords contains two types of pollen assemblages in the lower portions of the cores exotic pollen types and pre quaternary palynomorphs are abundant the upper portions of the cores contain an assemblage roughly representative of the present vegetation in which cyperaceae and gramineae are abundant and exotic and pre quaternary types are reduced or absent the lower assemblage was deposited during the late glacial deglacial transition and deglaciation ca 12 000 to 6000 b p when eastern baffin island had little vegetation cover and long distance transport and reworking were virtually the only pollen sources a feature of several cores is a major peak in dinoflagellates about 5000 b p this event may be related to the postglacial marine climatic optimum in the eastern canadian arctic between 5000 and 3000 b p

analysis of cement treated soil slab for deep excavation support a rational approach in this study an effective stress model for cement treated soil is employed to carry out a systematic study on cement treated soil slab used to control the wall displacement in excavations with thi

stable isotopes in planktonic and benthic foraminifera from arctic ocean surface sediments oxygen and carbon isotopic analyses have been performed on the tests of planulina wuellerstorfi and three size fractions of sinistral neogloboquadrina pachyderma recovered from 33 arctic ocean surface sediment samples stable isotopic compositions of n pachyderma are found to be dependent on the test size larger specimens show considerable enrichment in both 18o and 18c the difference between the isotopic compositions of the 63 125 and 125 250 m size fractions in n pachyderma can be explained by biogenic fractionation effects during foraminiferal test growth larger 250 500 m n pachyderma displayed accretions of secondary calcite i e the outermost shell contained significant amounts of inorganically precipitated magnesium calcite thus larger foraminifera may not be suited for down core stable isotopic studies there is a difference of 2 between 18o values of surface samples from the eastern and western arctic ocean reflecting large differences between surface water salinity in these re

meltwater and deglaciation se baffin shelf ne margin laurentide ice sheet between 13 5 and 7 ka from o and c stable isotopic data stable isotopic values on planktonic foraminifera in a suite of cores from basins across the se baffin shelf are used to extract a record of meltwater events during termination i deglaciation resolution and hatton basins lie on the se baffin shelf at water depths 500 m seaward of major conduits for ice drainage from the eastern sector of the laurentide ice sheet lis accelerator mass spectrometry 14c dates are used to constrain our chronology of events in ten cores in resolution basin three cores have 14c ams dates on foraminifera of 20 ka at their bases whereas hatton basin cores terminate in sediments 13 kyr sedimentation rates varied between 0 1 to 4 5 m ka stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera neogloboquadrina pachyderma ehrenberg sinistral from seven of the ten cores no evidence was found to indicate that test morphology or size affected 18o between 7 and 13 5 ka the surface water on the shelf was on average 1 lower than the open ocean signal significant temporal variations were found in both 18o and 13c evidence for significant low 18o events occurred between 13 and 8 ka the 13c record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka with positive values between 10 8 and 13 0 ka negative values between 9 and 10 8 ka and positive values from 7 to 9 ka the 18o data suggest the presence of meltwater on the shelf some 3 000 years prior to the first late glacial dates on terrestrial deglaciation at circa 10 4 ka hudson strait must be the real key to the importance of the calving process during deglaciation because it is potentially the largest marine outlet for the laurentide ice sheet and because it leads into the very center of the ice sheet the rates of calving through hudson strait during the period of initial 18o rise unfortunately are unknown w f ruddiman 1987 p 151

dynamics of meltwater discharge from northern hemisphere ice sheets during the last deglaciation during the last ice age ice sheets covered large portions of north america europe asia and the arctic ocean the ice sheets were composed of meteoric water enriched in the light isotope of oxygen 16o leaving oceanic seawater correspondingly enriched1 2 in 18o the volume of past continental ice sheets during the last glacial maximum 18 000 yr ago has been estimated from terrestrial evidence of ice limits3 glaciological modelling4 the 18o of foraminifera from deep sea cores5 6 and sea level evidence from raised coral terraces7 8 oxygen isotope studies of planktonic foraminifera reveal that 18o shifts during deglaciations in areas near sources of ice meltwater like the gulf of mexico and labrador sea baffin bay are often larger than the corresponding average global oceanic shift9 11 and that these variations reflect the timing of ice decay without the ocean mixing lag contained in both distal and benthic 10o variations12 we show here that geographically distinct planktonic 18o gradients can be related to the volume of meltwater discharged through specific meltwater outlets and thus to the initial volume of the ice sheets at the commencement of deglaciation and to the subsequent dynamics of ice sheet decay

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects