Jay A. Stravers

Abrupt early Holocene (9.9-9.6 ka) ice-stream advance at the mouth of Hudson Strait, Arctic Canada

Radiocarbon-dated glacial-geologic evidence documents an abrupt advance of the northern margin of the Labrador sector of the Laurentide Ice Sheet during the last deglaciation. Ice-flow directional indicators, together with ice-marginal features found onshore and offshore, delimit an ice stream that advanced north-northeast >300 km, crossed the mouth of Hudson Strait and outer Frobisher Bay, and overran summits ∼400 m above sea level on outer Hall Peninsula, southeast Baffin Island. Fifty-eight 14 C ages, including 27 accelerator mass spectrometry ages on single shells, indicate that the advance was extremely rapid. The entire advance-retreat cycle took place in an ∼300 yr ( 14 C) interval, 9.9-9.6 ka. At its maximum extent, the ice stream supported a calving margin >200 km long terminating in open water ∼500 m deep, implying a massive iceberg release. Marine evidence for the outflow is preserved along the Labrador Sea shelf as thick carbonate-rich glacial-marine drift but has not been recognized farther east in the North Atlantic. Either the discharge of icebergs was insufficient to produce a trans-North Atlantic, carbonate-rich (Heinrich) layer, or the icebergs tracked southward where they encountered warming sea-surface temperatures. Although the advance seems to have been coincident with a brief interval of minor regional cooling, it failed to trigger a significant climate perturbation, suggesting that the ocean-atmosphere system had attained its stable interglacial condition by that time.

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.

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

Abstract 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.

Seismic facies changes along a nearly continuous 24° latitudinal transect: the fjords of Chile and the northern Antarctic Peninsula

Abstract High-resolution seismic reflection profiles and piston cores from bays, fjords, and straits of the inland passage of Chile and the northern Antarctic Peninsula region were used to examine changes in seismic facies along a nearly continuous 24 ° latitudinal transect that encompasses temperate, subpolar, and polar climatic regimes. These climatic regimes are characterized by differences in seismic facies. Eight seismic facies are recognized on the basis of reflection character, intensity of acoustic contrast at bounding surfaces, and external shape of the unit. The northern and central Chilean fjord region is a temperate maritime setting characterized by thick ice-proximal and ice-distal glacial-marine strata and a variety of morainal features. The southern inland passage and the South Shetland Islands of Antarctica represent transitional (sub-polar) glacial-marine settings. These areas are characterized by relict ice-proximal glacialmarine facies and relatively thin ice-distal glacial-marine facies. Morainal ridges occur in bays and fjords of Chile. The northern Antarctic Peninsula is a polar climatic setting. The straits, bays, and fjords of the region have been virtually scraped clean of sediments. A thin, draping glacial-marine unit occurs locally in these areas.

GLACIAL DEBRIS FLOW DEPOSITS ON THE BAFFIN ISLAND SHELF : SEISMIC FACIES ARCHITECTURE OF TILL-TONGUE-LIKE DEPOSITS

Abstract 3-D seismic facies modeling of late Foxe/Wisconsin glacial deposits in the Savage Basin provides important new data concerning the morphology and origin of acoustically unstratified seismic units on high-latitude continental shelves. Savage basin contains a thick sequence (up to 110 m) of morainal bank deposits (Unit II) similar to ‘till tongue root’ deposits described from the Scotian and Norwegian shelves. In 2-D longitudinal cross-section, Unit II thins and differentiates northward into two acoustically unstratified wedges or ‘till tongue’-like deposits (Units IIAw and IIBw) which are observed to interbed with stratified glacimarine sediments (Unit I). Sediment transport was northeastward, away from a late glacial ice margin in outer Frobisher Bay. Both unstratified wedges are lobate in plan view with the thickest portion (5 m to 50 m) lying along the lobe axis. Upper surface contours are convex to the north and concentric to the lobate margin. Southward, at the transition to the morainal bank, the contours become concave to the north. This morphology is consistent with that of lobate debris flow deposits with the concave contours defining a zone of sediment failure. The data indicate sediment failure within morainal bank deposits which accumulated near the terminus of a temperate tide water ice sheet. Truncations of Unit I reflectors against the lower surface of the debris flows indicate that the flows were deposited episodically and that they remobilized or eroded some of the Unit I sediments. This unconformable relationship gives the same stratigraphic sequence that King et al. (1991) proposed to explain ‘till tongue’ formation from subglacial meltout beneath buoyant glacier ice in contact with the seabed. Coalescing debris flow lobes are observed along the entire distal slope of the morainal bank. These give the appearance of a continuous till tongue wedge in seismic cross-sections taken parallel and distal to the paleoice margin. Without 3-D geometry reconstructed at contour intervals ≤ 10 m, the complex lobate morphology could not be resolved.

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?).

A Late Glacial Readvance Moraine in the Central Chilean Fjords

During the 1993 cruise of R/V Polar Duke, seismic data were collected from Seno De Las Montanas (Fig. 1), a fjord that is isolated from outflow of the South Patagonia Ice Cap by a prominent bedrock ridge and contains significant deposits from late glacial readvances which flowed into the fjord from the south.