Glacimarine Sediments Research Articles

Palaeoceanographic information derived from acoustic surveys of glaciated continental margins: examples from eastern Canada

Abstract Much palaeoceanographic information can be gleaned from seismic, sidescan and bathymetric data on glaciated continental shelves. High-resolution seismic reflection surveys of regional ice terminus features define palaeo-ice margins, datable using interfingering ice-proximal glacimarine deposits. Isopach maps show differences in regional accumulation rates of sediments during deglaciation phases and help locate positions of former glacifluvial discharge outlets. Maps of ice-distal glacimarine muds suggest that surface currents carrying buoyant plumes of glacial flour may extend >100 km from an ice margin. Transport and melt of icebergs controlled by circulation of deeper outer shelf and slope currents and episodic storms can result in a glacial influence >1000 km from the ice margin, but most iceberg-rafted sedimentation occurs within a few hundred kilometres of calving. The direction of these palaeo-mid-depth currents may be obtained from statistical analysis of relict iceberg scour patterns and from sediment dispersal patterns. The geometry of glacimarine deposits commonly suggests that there was water column stratification with associated weak near-seafloor currents. Comparison of the shape of glacimarine and post-glacial sediment packages shows that in many places the tidal current intensity has increased through the Holocene, reflecting sea-level change on the shelf.

Patterns of glacial erosion and deposition in Prydz Bay and the past behaviour of the Lambert Glacier

Styles of glacial sedimentation and erosion in Prydz Bay respond to glacial and interglacial cycles and fall into three zones; an inner zone of net erosion, a middle zone of subglacially eroded and deformed transitional glacial marine deposits and an outer zone of subglacial till deposition and shelf progradation. The inner zone is the region of maximum basal shear stress and inner-shelf deep formation by enhanced erosion in areas where tributary glaciers converge with the extended Lambert Glacier. The middle zone is underlain by sediments deposited near the ice-grounding zone during retreat, both as blanket like deposits and as grounding-line moraines. This material is then deformed into elongate subglacial bedforms (megaflures or drumlins), a process that probably involves some erosion. Deforming subglacial bed conditions extend to the shelf edge within a valley crossing the shelf on the western side of Prydz Bay. The outer zone is a zone of net deposition of compact subglacial till and prograding continental slope deposits formed during full glacial conditions and glacial marine sediment formed during ice retreat. The inferred build up of ice on the Ingrid Christensen Coast may have been responsible for the development of the western ice stream that flowed in Prydz Channel. The geometry of seismic sequences in Prydz Channel suggests that this ice stream and its associated trough mouth fan developed after a major episode of shelf and slope erosion during the Pliocene.

Post-glacial environments of the southeastern Barents Sea: foraminiferal evidence

Abstract Quaternary sediment records from the southeastern Barents Sea were used to reconstruct palaeoceanographic environments since the last deglaciation based on lithology, foraminiferal assemblages and AMS 14 C dates. After the ice sheet retreat at 13 ka BP two pulses of glacimarine sedimentation occurred, separated by non-deposition between approximately 12 and 10.5 ka BP . Proximal sedimentation from meltwater overflows prevailed during the first pulse, whereas the second pulse reflects distal glacimarine environments with some inflow of Atlantic water. Full marine environments were established by 9.3 ka BP , associated with increased Atlantic water advection, intensified currents and reduced sedimentation rates. The maximum Atlantic influence lasted until approximately 5 ka BP , followed by an advance of Arctic surface water with winter sea ice cover.

Foraminiferal sequence biostratigraphy and seismic stratigraphy of a tectonically active margin; the Yakataga Formation, northeastern Gulf of Alaska

Upper Miocene through Recent glacial-marine deposits of the Yakataga Formation, which underlie the northern Gulf of Alaska continental shelf, are the focus of an integrated study to understand the depositional and climatic history of the upper Cenozoic Gulf of Alaska. Biostratigraphic, lithologie, and multichannel seismic data were integrated in a sequence stratigraphic analysis of the Yakataga continental margin. A paleontologically based approach to sequence stratigraphy, known as sequence biostratigraphy, was used to define eight seismic stratigraphic sequences on this tectonically active, glaciated continental margin. Foraminifera provide information on the age, paleoenvironments, and paleoclimates of strata within these eight sequences. Lithologic evidence is used to infer the presence and influence of tidewater glaciers.The three oldest sequences, arbitrarily labeled Brown, Red, and Orange (early Pliocene, mid-Pliocene, late Pliocene, respectively), were deposited in mainly outer neritic through upper bathyal environments. Planktic foraminiferal assemblages show that sea surface temperatures during deposition of these sequences were mainly cool temperate in the Gulf of Alaska at this time, yet benthic assemblages indicate cold bottom waters and dropstones indicate glacial-marine sedimentation during the late Pliocene.The five youngest sequences (labeled Yellow, Green, Aqua, Blue, Violet), which are Pleistocene to Recent in age, were deposited in deeper environments on average (upper bathyal to middle bathyal) than the older sequences. Glacial-marine sedimentation was common during deposition of these sequences (abundant dropstones) and foraminiferal assemblages indicate both cold sea surface and bottom water temperatures.

Vendian basin evolution in East Greenland and NE Svalbard

In order to help focus new biostratigraphic and chemostratigraphic work, the sedimentology and stratigraphy of Vendian successions in central East Greenland and NE Svalbard (NE Spitsbergen and Nordaustlandet) are reviewed. These areas originally formed part of a contiguous sedimentary basin as illustrated by comparison of two measured sections, 750 m thick, in which a number of matching divisions occur. At the base, a carbonate platform succession (“bed-group 20” in Greenland, Elborbreen Formation member E1 in Spitsbergen) is followed by two discrete glacial facies associations separated by non-glacial sediments (Ulvesø, Arena and Storeelv Formations of Greenland and members E2, E3–E4 and the Wilsonbreen Formation of Spitsbergen), and a transgressive shale succession (Canyon Formation and Dracoisen Formation, respectively) with basal dolostone. Whereas NE Spitsbergen displays a further 300 m of section within the Dracoisen Formation, mostly of probable playa lake facies, in Greenland a 50-m-scale regressive dolostone unit (upper Canyon Formation) is capped by only 20 m of lacustrine facies (Spiral Creek Formation). In each case, lower Cambrian sandstones rest on the Vendian sections. Later Vendian times (Ediacaran interval) seem to be virtually unrepresented by marine strata. Reconstruction of the stratigraphic architecture along the 180 km N S outcrop belt in NE Svalbard and the 300 km N S belt in East Greenland reveals few lateral changes because of an orientation nearly parallel to the depositional strike. Syn-depositional faulting apparently controlled accelerated subsidence in the East Greenland area, leading to the development of carbonate slope facies (“bed-group 19”), either overlain locally by “bed-group 20”, or conformably overlain by glacimarine deposits. A section towards the southeastern limit of the basin in East Greenland, in Canning Land, shows the glacigenic Storeelv Formation resting on a major erosion surface on platform carbonates. In the far southwest, it rests directly on basement; this represents the main source area of sediments in the basin. The upper Canyon Formation shows evidence of progradation from the south. Chronostratigraphic interpretation of the succession leads us to the belief that the base of each glacial unit represents a sequence boundary, although only limited erosion occurred within the main outcrop belt. A sequence boundary may also be present at the base of the Elbobreen Formation. Submarine erosion must have led to a slight hiatus at the close of the second glaciation, temporally following but spatially coincident with a sequence boundary. The upper Canyon Formation is probably a highstand systems tract and the overlying base of the Spiral Creek Formation is a sequence boundary. The transgressive base of the Cambrian sandstones overprints another sequence boundary, at least in Greenland.

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.

Carbonate Accumulation on the Inner Continental Shelf of Maine: A Modern Consequence of Late Quaternary Glaciation and Sea-level Change

ABSTRACT Accumulations of skeletal carbonates are associated with late Quaternary glacigenic sediments on the inner continental shelf of Maine despite cold waters that are generally considered corrosive to calcium carbonate. These shelly lithosomes (up to 100% CaCO3) are confined to a small area in the vicinity of Mt. Desert Island, a granitic massif on the deeply embayed coast. Exposure to waves is a strong control on sediment accumulation and varies due to orientation of the coast, presence of numerous islands, and extremely irregular bathymetry. Postglacial regression and subsequent transgression have greatly influenced the nature and distribution of surficial sediments on shallow parts of the shelf (less than approximately 60 in depth). On the basis of bathymetry, bottom sedimen properties, and geophysical characteristics, five major physiographic zones are recognized: nearshore basins, shelf valleys, outer basins, rocky zones, and nearshore ramps. Thick deposits of marine mud, often charged with natural gas and pockmarked in places, exist inside sheltered embayments (nearshore basins) and offshore below the influence of sea-level changes (outer basins). Shallower areas are dominated by rock outcrops (rocky zones) that support a prolific fauna of calcareous organisms such as barnacles, echinoderms, mussels, and assorted bivalves and gastropods. There are no significant sources of terrigenous sediments nearby. In their absence, abundant sand- and gravel-size shell fragments accumulate in rocky zones and adjacent nearshore ramps, form a thin layer capping glacial marine sediments and till, and supply sediment for two carbonate sand beaches. These deposits provide a useful analog for deciphering the origins of some ancient limestone-diamictite successions.

Layer charge of expandable 2:1 phyllosilicates in selected parent materials of some Canadian soils

We investigated the nature of the layer charge of the different expandable 2:1 phyllosilicates present in glacial till, marine sediment, beach sand, loess, weathered sandstone and acid shale parent materials of selected soils from the arctic, alpine and interior plateau regions of Canada. Detailed characterization of 2:1 clay minerals, using the layer charge, was done by intercalation of the clay fractions with different chains (nc = 6 to 18) of n-alkylammonium cations (AC).Results indicated that AC were able to detect a mixture of smectite and vermiculite that was not detected by previous studies, using the glycerol (GLY) and ethylene glycol (EG) solvation techniques. The mean unit cell layer charge [in mol(+)/Si,Al)4O10)] varies from 0.30 to 0.39 for the smectite and from 0.71 to 0.74 for vermiculite. Vermiculite from the beach sand is trioctahedral in which most of the charge is located in the tetrahedral sheet, while vermiculite in the weathered sandstone is dioctahedral in which part of the charge originates from the octahedral layers. The presence of smectite, associated with the weathering of chlorite and an expanding component associated with the degradation of biotite, was also observed. Key words:n-alkylammonium cations, mean layer charge, 2:1 phyllosilicates

Sediment Thicknesses and Holocene Glacial Marine Sedimentation Rates in Three East Greenland Fjords (ca. 68°N)

We compared measured and estimated sediment budgets in heavily glaciated fjords in East Greenland. Mass balance calculations and regional glacio-climatic conditions suggest that the sediment flux to the seafloor in Kangerdlugssuaq and Nansen fjords should be dominated by iceberg rafting and not by the rain-out of suspended particulates in meltwater, as the glacier calving flux is estimated at 15 and , compared to meltwater volumes of 4.4 and , respectively. Gravity cores in the three fjords indicate that the uppermost 1-2.5 m of sediment consists of diamictons or fine-grained laminated muds. AMS radiocarbon dates on calcareous foramininfera or shells (16 total) indicate sedimentation rates of 110 to 340 cm/ka within the fjords over the last 1 ka, and 10-20 cm/ka during the Holecene on the inner and middle shelf. Annual sediment discharge is around tonnes/yr within the Kangerdlugssuaq Fjord and Trough system, which translates into an average basin-wide rate of denudation of 0.01 mm/yr (0.01 m/ka). Air gun and deep-towed (Huntec) seismic profiling was carried out in Kangerdlugssuaq and Nansen fjords, East Greenland, and showed that sediment fills averaged 500 and 350 m respectively; they consist primarily of acoustically stratified sediments. If the sediment fills are entirely Holocene in age then the required average sediment accumulation rates of 35-50 m/ka are an order of magnitude larger than the controlled rates of the last 1-2 ka. This raises the possibility that fjord sediments may be by-passed and not always recycled during glacial advances; this will affect sedimentation rates on adjacent shelves and deep-sea areas during successive glaciations.

First evidence of walrus (Odobenus rosmarus L.) in Late Pleistocene Champlain Sea sediments, Quebec

The almost complete skull of a walrus has been discovered in Champlain Sea sediments at Sainte-Julienne-de-Montcalm, 60 km north of Montréal. It is the first report of that species in glacial marine deposits west of Québec City. The skull has been dated by accelerator mass spectrometry at 10 090 ± 60 BP (TO-2224) and the shells in the sediment adhering to it at 10 880 ± 60 BP (TO-2225). The discrepancy between the two age determinations is attributed to diachronism between the skull and the shells, the latter having been redeposited. The radiometric age implies that walruses were part of a Champlain Sea marine vertebrate fauna consisting of three species of seals and five whale species. As the sea drained, walruses withdrew toward the Gulf of St. Lawrence, where they have been hunted to extinction in historic times.

Skeletal and Isotopic Composition and Paleoclimatic Significance of Late Pleistocene Carbonates, Ross Sea, Antarctica

ABSTRACT Carbonates cover an extensive area of the northwestern Ross Sea continental shelf. Radiocarbon dates yield late Pleistocene (Stage 3) ages for these deposits, hence the carbonates appear to be correlative with widespread tills and glacial marine deposits in the region. Four carbonate facies are recognized on the basis of skeletal composition: a barnacle/foraminifer facies, a muddy bryozoan facies, a bryozoan/barnacle/pelecypod/foraminifer facies, and a planktonic foraminiferal facies. These deposits occur on the shelf and upper slope, while carbonate turbidites derived from them occur on the adjacent continental slope and rise. Compositional analyses of Ross Sea carbonates lend support to previously recognized criteria for identifying cold water carbonates. These include: 1) the presence of an associated ice-rafted component (including dropstones); 2) a dominance of calcite relative to other carbonate minerals (the remaining fraction consists solely of aragonite); 3) allochems that are entirely skeletal; and 4) heavy oxygen isotopic compositions (in the range of + 3.0 to +5.1% PDB).

Preliminary observations of Neogene–Quaternary depositional processes in the Faeroe–Shetland Channel revealed by high-resolution seismic facies analysis

The Neogene and Quaternary sediments of the Faeroe–Shetland Channel and West Shetland slope have been deposited and modified through the interaction of a variety of downslope and parallel-to-slope depositional processes. The upper slope is dominated by mass-transport deposits (debris flows) which progressively diminish downslope. These were apparently deposited during glacial cycles when ice sheets reached the shelf edge and supplied large amounts of terrigenous sediment to the slope. Thin, prograding clinoforms separate packages of debris flows and may represent glacial marine sedimentation during periods of ice retreat from the shelf edge (e.g. interstades). A few submarine canyons occur on the slope and probably provide conduits to the basin for turbidity currents and related mass flows. The middle to lower slope appears to be dominated by glacial marine, hemipelagic and possibly turbidity-current deposits, which have been subjected to reworking by contour currents at many locations. A thick deposit that has the appearance of a deep-sea fan occurs on the middle slope in the northeast part of the area. Although many individual seismic packages within this feature have the appearance of aggradational channel–levee systems, these packages may actually represent contourite deposits. Large migrating sediment waves occur just downslope from this feature and suggest that strong contour currents have interacted with the downslope processes to redistribute sediments on the lower slope. The basin floor has thin conformable sediments that appear to be predominantly glacial marine and hemipelagic with occasional turbidites and debris flows. Thick, extensive debris-flow deposits also occur beneath the basin floor in the northeastern part of the area. The Neogene–Quaternary sediments are separated from the Paleogene section by a major regional unconformity of latest Oligocene or early to middle Miocene age, which forms a major sequence boundary throughout the region.

Glacial Marine Sedimentation: Paleoclimatic Significance

This publication resulted from a symposium held during the 1988 Annual Meeting of the Geological Society of America. Many, but not all, contributors to the symposium have papers in this volume. This Special Paper consists of 14 chapters and a Subject/Geographic index. Each chapter has is own list of references. The papers cover a wide range of modem climate/ ocean environments, including papers on glacial marine sediments from Antarctica, the fiords of Alaska, and sediments from the Canadian High Arctic. In addition, three papers discuss [open quote]old[close quotes] glacial marine records (i.e., pre-Tertiary), and one paper discusses the Yakataga Formation of the Gulf of Alaska which is a Miocene-to-late-Pleistocene sequence. The last chapter in the book includes a survey and summary of the evidence for the paleoclimatic significance of glacial marine sediments by the two editors, John Anderson and Gail Ashley. It is worth noting that Anderson and Domack state in the Foreword that there is a considerable variation in terminology; hence they employ a series of definitions which they urge the other authors to employ. They define and explain what they mean by [open quotes]polar ice cap,[close quotes] [open quote]polar tundra (subpolar),[close quotes] and [open quotes]temperate oceanic and boreal[closemore » quotes] in terms of the dominant glacial and glacial marine processes. Although one might quarrel with the terminology, the broad differences between these three glaciological regimes are indeed fundamental and need to be sought in the geological record. The flavor of the volume can be judged by some of the chapter titles. Contributions on Antarctica include a paper by Anderson and other entitled [open quote]Sedimentary facies associated with Antarctica's floating ice masses[close quotes] and a companion paper by Anderson and Domack which deals with the extremely complex glacial marine facies (13 facies are delimited) in McMurdo Sound, Antarctica.« less

Carboniferous glaciation in Gondwana. Evidence for grounded marine ice and continental glaciation in southwestern Argentina

Upper Paleozoic sedimentary rocks in western Argentina accumulated in retro-arc foreland basins in the Gondwana continental margin. A glacial component in these rocks was recognized early in this century but reconstructions of the nature of the glaciation differ markedly. The dominant proposal sustains that glaciation in this region was of alpine-type, with glaciers descending from mountain ranges both inland and along the edge of the continent, and that the numerous intercalated diamictites were mostly deposited as subaquatic debris flows only indirectly connected with the presence of glacier ice. A stratigraphic and sedimentologic study of Middle Carboniferous glacigenic deposits of the Tepuel Group in central western Patagonia, southwestern Argentina, shows that two major diamictite facies are present: (a) massive diamictite, the more abundant, forms regionally extensive and thick (<60 m) pebbly bodies with boundaries transitional to non-glacial open shelf deposits; these are interpreted as rain-out till; and (b) chaotic diamictite, yielding thin (< 10 m) laterally discontinuous bouldery bodies showing erosive bases, strong substratal deformation, and upward transition to massive diamictite; these are interpreted as subglacial till. A third type of glacial deposit consists of interbedded current-deposited and wave-worked conglomerates and sandstones, in strata that downlap onto non-glacial shelf mudstones; these are interpreted as submarine outwash fan deposits. The position of subglacial till and outwash fans relative to the paleoshoreline indicate deep regional incursions of grounded ice onto the shelf. In addition, deepening of the shelf coincident with initial glacial marine sedimentation in the early Middle Carboniferous, at a time of global lowstand, argues for glacio-isostatic depression of the shelf and suggests a considerable ice thickness. Paleotopographic considerations indicate that the centres of ice dispersal were located on moderately high intracratonic highlands. A regional erosion surface across these highlands is attributed to subglacial scour under a Patagonian ice cap that expanded onto the adjacent shelf during glacial maxima. Published information concerning ice distribution in Middle Carboniferous Gondwana supports the existence of an ice cover similar in lateral extent to that in modern Antarctica. The Patagonian ice cap would have been peripheral to this continental-sized ice mass.

Limitations of thermoluminescence to date waterlain sediments from glaciated fiord environments of western spitsbergen, svalbard

A fundamental problem in the TL dating of waterlain sediments, particularly in the Arctic, is the accurate determination of the level of solar resetting prior to deposition. This study determined the effect of wavelength on the solar resetting of the TL signal and concomitant effects on the accuracy of TL age estimates for late glacial and modern glacial and nearshore marine sediments from fiords on Spitsbergen. The reduction in TL level decreases with filtering of wavelengths above 400 nm. Modern and Late Weichselian tills have TL levels at saturation, probably received no light exposure prior to deposition and thus cannot be dated by TL. Glacial-marine sediments deposited within 0.5 km of a glacier terminus yielded TL age estimates 10 times the known age presumably because these sediments received limited light exposure prior to deposition. Modern sublittoral sediments and fiord muds yielded TL apparent ages between < 1–7 ka, in general agreement with a previous TL age estimate and the known age for these samples. However, sublittoral sediments deposited ca. 10 ka BP yielded overestimates in TL ages by 17 to 32 ka, considerably older than a previous TL age estimate of 9.9 ± 1.1 ka. We believe the difference in accuracy of TL age determinations for the modern and late glacial sediments is primarily a function of depositional environment. The TL properties of modern fiord sediments are not an appropriate analog for sediments deposited during the late glacial when relative sea-level and glacial coverage were changing rapidly.

Thermoluminescence properties of a deglacial marine sequence from Cumberland Sound, Arctic Canada: sedimentologic and geochronologic implications

Thermoluminescence (TL) analysis of glacial-marine and postglacial sediments in core 85027-029 from Cumberland Sound, Baffin Island shows that the TL signal can be used to differentiate glacial-marine sediments deposited extremely close (< 0.5 km) to an ice margin from other glacial-marine facies. Sediments deposited in very close proximity to an ice margin are not exposed to light during deposition and retain a high TL level inherited from bedrock. Overlying ice-proximal, ice-distal and postglacial sediments are exposed to sufficient light during transport to undergo a substantial reduction in TL level prior to deposition, these sediment types may be amenable for TL dating but only on time scales of 10 4 to 10 5 yrs.

Developing sediment geochronologies for high-latitude continental shelf deposits: a radiochemical approach

During January and February of 1986, 47 box cores and 55 piston cores were collected from the Bransfield Strait, Gerlache Strait and Marguerite Bay, Antarctica. Apparent sediment accumulation rates established for 100-yr time scales with excess 210Pb chronologies range from 0.08 to 0.34 cm/yr in the Bransfield Strait, 0.15 to 0.51 cm/yr in Gerlache Strait and from 0.10 to 0.27 cm/yr in Marguerite Bay. For the Antarctic Peninsula continental shelf, 137Cs appears to have a limited usefulness in assessing the effects of deep sediment mixing by benthic fauna on seabed excess 210Pb profiles because the observed activities for the regions examined are close to counter detection limits. Conventional 14C ages of surface sediments from the peninsula region range from 1370 to 2820 yr. The spatial variations in the conventional 14C surface ages are thought to be influenced predominantly by inputs of older eroded sediment from lateral transport, current winnowing, mass wasting and/or a variable carbon source. On a 1000-yr time scale, 14C measurements of five piston cores from the Bransfield Strait yielded sediment accumulation rates ranging from 0.06 to 0.49 cm/yr. These data support the assertion by Nelson (1988) that the excess 210Pb sediment accumulation rates (range of 0.08 to 0.34 cm/yr) for this region represent true rates. The two sediment accumulation rates of 0.01 and 0.08 cm/yr for the Gerlache Strait are significantly lower than the observed apparent 210Pb accumulation rates (mean = 0.27 ± 0.12 cm/yr) for this region. Likewise, two piston cores from Marguerite Bay yielded 14C sediment accumulation rates of 0.02 and 0.05 cm/yr, which also are considerably lower than the excess 210Pb apparent accumulation rates (mean = 0.17 ± 0.06 cm/yr) for this area. The one-dimensional advection-diffusion equation of Goldberg and Koide (Geochim. Cosmochim. Acta, Vol. 51, 1962) was solved simulatneously with 210Pb and 14C data for BC18 and BC113 to resolved the effects of sediment mixing and accumulation in Bransfield Strait and Marguerite Bay box core samples, respectively. This model indicates that 210Pb and 14C sediment accumulation rates agree within a factor of 2 in the Bransfield Strait, whereas in Marguerite Bay the apparent 210Pb accumulation rates may be as much as an order of magnitude too high. In the southern high-latitude environments of the Antarctic Peninsula, radiocarbon measurements in the seabed are a better approach than 210Pb for establishing accurate rates of sediment accumulation. The 14C chronologies, when coupled with 210Pb data, provide more reliable assessments of biological deep mixing and sediment accumulation rates than do excess 210Pb data coupled with measurements of bomb-produced 137Cs. The sediment accumulation rates for both 100-yr and 1000-yr time scales tend to decrease southward from the Bransfield Strait to Marguerite Bay, which is consistent with glacial-marine sedimentation processes (as modulated by climate) for the western Antarctic Peninsula. Seabed measurements of 210Pb, 137Cs and 14C also provides valuable insights on water circulation and upwelling, atmospheric inputs and sediment depositional processes for the Antarctic Peninsula region.

Towards an understanding of sediment deposition on glaciated continental shelves

A simple vertical stratigraphic sequence of Quaternary deposits is recognized on 20 glaciated shelves from around the world reflecting the transition from the most recent glacial to interglacial period. This sequence includes some or all of the following: (1) ice-contact (ice-deposited and/or ice-loaded) sediments; (2) ice-proximal sediments; (3) ice-distal sediments; (4) paraglacial coastal sediments; and (5) post-glacial sediments. Typically, the sequence unconformably overlies sedimentary rocks on the outer shelf and a mixed bedrock basement on the inner shelf. The relative volume of these deglacial units provide important clues for the reconstruction of ice sheet dynamics. Deposition of unit (1) occurred initially during the period of globally (eustatic) lowered sea-level, and later with units (2) and (3) during a period of high sea levels related to isostatic loading. Deposition of unit (4) occurred during the initial fall in sea level (isostatic recovery) when ice had retreated and was rapidly ablating. Deposition of unit (5) occurred during more complex and local sea level fluctuations, that include such effects as collapse of the crustal forebulge. Minor variations to this association of sea level and sedimentation pattern occur, particularly if the glacial cycle is out of phase with the global eustatic cycle. Outstanding seismostratigraphic problems include: distinguishing ice-loaded glacial-marine sediments from subglacially deposited till; distinguishing till from other ice-contact deposits such as grounding-line fans; and distinguishing till from non-glacial debris flow deposits. The incorrect identification of till provides poor data control on ice sheet reconstruction, ice sheet properties and dynamics, especially as related to sediment transport.

Land-sea correlations and evolution of the Cambridge Fiord marine basin during the last deglaciation of Northern Baffin island

Cambridge Fiord functions as a major outlet trough whenever Laurentide ice approaches the eastern coast of Baffin Island. During the last glacial maximum (late Foxe glaciation), an outlet glacier occupied most of the fiord, possibly terminating as far seaward as Buchan Gulf. Glacier retreat began prior to 8800 yr B.P. and was punctuated by the formation of two onshore moraines with upper age limits of 7900 and 7200 yr B.P. Correlative offshore moraines (recognized on seismic reflection profiles) formed prominent submarine sills which partitioned the fiord into three basins. These formed effective sediment traps that restricted the seaward migration of debris flows and turbidites, thus facilitating the accumulation of thick (> 100 m) stratified glacialmarine sediments in the inner fiord. Correlations of onshore and offshore moraines allow time lines to be placed within an offshore seismic stratigraphic section that is inaccessible to piston coring. Resultant estimates of sediment accumulation rates give a mean value of 2.34 × 10 6 m 3/yer for deposits trapped in the inner fiord basins. These thick sequences of sediments do not represent extended Foxe/Wisconsin time periods, but, rather, were rapidly deposited in the inner fiord during the last deglaciation.

An evaluation of seismic and borehole data available from onshore and offshore site investigations of relict glaciated areas

Abstract Using late Quaternary ice marginal sites from the North Sea and Iceland a comparison of the sedimentary information available from subaerial and submarine site investigations was made. This was with regard to palaeo-environmental reconstructions of ice marginal Sedimentation processes. A detailed high resolution seismic survey in-the North Sea was compared to a similar subaerial site in Iceland. Submarine cores were compared with logged sections available from cliffs. These comparisons highlighted the differences in resolution of the structural information available and also the problems of applying existing modeis of glacimarine Sedimentation to offshore sites. This has raised questions concerning the accuracy of reconstructing palaeo-environments and processes in offshore sites presently under investigation. The implications of this for engineering projects in offshore areas requiring very precise site information about relict glaciated areas are significant.