Brian MacLean

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.

Hudson Strait ice streams: a review of stratigraphy, chronology and links with North Atlantic Heinrich events

We review the literature on the occupation of Hudson Strait (800 km long by 90 km wide) by late Quaternary ice streams, and the importance of Hudson Strait as the major source for sediments associated with the North Atlantic Heinrich (H-) events. Glacial erosion of the Paleozoic outcrop on the floor of Hudson Strait and Ungava Bay resulted in the export of detrital carbonate-rich sediments to ice-proximal locations on the slope and floor of the NW Labrador Sea, mainly in meltwater and turbidite plumes, and to ice distal sites thousands of kilometres away largely as iceberg-rafted detritus (IRD). Erosion of bedrock from the Precambrian Superior and Churchill provenances of the Canadian Shield is also indicated by the isotopic analyses of sediments. The major late Quaternary H-events (H-4, H-2 and H-1) are represented in southeast Baffin Island slope sediments as detrital carbonate-rich intervals up to 40 cm in thickness and appear to represent flow along the axis of the Strait. However, the late marine isotope stage #3 event, H-3 (∼27 ka), and a younger event (H-0, ∼11 ka), are not as dominant in the sedimentary record and probably represent a different glaciological regime with flow across Hudson Strait from eastern Ungava-Labrador. The freezing-on of sediments by supercooling in the rise from the 900 m deep Eastern Basin to the 400 m sill is proposed as the source of the abundant carbonate-rich glaciomarine sediments some 250 km from the outcrop in Eastern Basin. Sediment transport by meltwater and turbidity currents was the major process during H-events in ice-proximal settings. IRD was not a key diagnostic process at sites fronting Hudson Strait. A key feature in the instability of this ice stream might be the great depth (600 m) at the shelf break, and the deep basin, which lies seaward of the outer Hudson Strait sill.

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.

Marine evidence for the last glacial advance across eastern Hudson Strait, eastern Canadian Arctic

Data from accelerator mass spectrometer radiocarbon dated sediment cores and Huntec high-resolution seismic profiles were used to investigate the age and origin of the sediments in the Eastern Basin of Hudson Strait. The data indicate that the ice-contact and glacial-marine sediments on the basin flanks and much of the upper sequence in the deep floor of the basin were produced during the Noble Inlet advance (8.9 to 8.4 ka), the last northward expansion of the Labrador Dome on to southeastern Baffin Island. On the northern flank of Eastern Basin one sequence of ice-contact sediments and glacial-marine deposits overlies bedrock; the glacial-marine sediments are transitional upslope to ice-contact sediments, and form at least two successive ice-sheet grounding zones. The earliest abundance peaks of benthic Foramininfera in glacial-marine sediments date ca. 8.6 and 8.4 ka, and correlate to sediments near the base of the 58-m-thick glacial-marine section in the deepest part of Eastern Basin. This correlation suggests that Noble Inlet ice was grounded throughout Eastern Basin during the early part of its advance. In later stages the thinning ice produced grounding zones on the basin flanks while glacial-marine sediments were deposited in the deep basin.

The surficial geology of the Canadian eastern Arctic and Polar continental shelves

We divide the Arctic continental shelf of Canada into three regions: (1) the Baffin Shelf, (2) the Arctic Channels and (3) the Polar Shelf. All are deep ice-dominated shelves largely floored by relict sediments. Iceberg scours occur to depths of 315 m on the Baffin Shelf but scours at depths deeper than this, and most in the Arctic Channels, are relict. All areas have been affected by late glacial fluctuations of the Laurentide Ice Sheet and local glaciers. Three principal seismic stratigraphic units are recognized and are interpreted as a glacial, glacial marine and postglacial stratigraphic sequence. Seismic Unit I is a transparent unit (mud) that lies in basins, Unit II is acoustically stratified with a mantling geometry and Unit III is acoustically incoherent with a constructional geometry in places. Units II and III interfinger in some areas. Core samples show that Unit I consists of bioturbated hemipelagic muds with ice-rafted sand and gravel, Unit II varies from a massive to laminated mud deposited from suspension and Unit III, rarely sampled, is a diamicton. In the Arctic Channels Unit II is noticeably thinner than it is on Baffin Shelf. Radiocarbon dates on foraminifera or bivalves indicate that the base of Unit II varies from 30,000 years to circa 8000 years, whereas postglacial Unit I was deposited over the last 5000–7000 years. During much of the Holocene the shelves have been starved of sediments as fiord basins were exposed during ice retreat and served as sediment sinks.

Bovie Structure: Its Evolution and Regional Context

Bovie Structure, which marks the eastern limit of Upper Cretaceous strata in the Liard Basin, is interpreted from seismic and well data to be a product of two major stages of development: the first, crustal uplift and compression during the late-Carboniferous to early Permian; the second, horizontal convergence during the Laramide Orogeny. North of Trout Lake Fault zone the second phase involved a shallow decollement fault whereas south of Trout Lake Fault zone, Laramide stresses may have caused transpressional movement on the crustal scale fault and development of a ‘flower’ structure. Bovie Fault, which has long been considered to be extensional, is here interpreted to be convergent and a product of the earlier uplift. The structure is here divided into three zones—northern and central zones, which lie north of Trout Lake Fault zone, and a southern zone. The central zone, where Bovie Structure is most fully developed, contains Bovie anticline, which is seen at surface as a chain of three N–S striking ridges. This anticline is interpreted to consist of blocks of Carboniferous strata that first have been uplifted on a west-directed, steeply-dipping, crustal-scale thrust fault. Then, during the Laramide Orogeny, blocks of these Carboniferous strata were severed and carried eastward on the shallow detachment of the Bovie Lake Thrust. Bovie Fault rapidly diminishes northward across the northern zone until the remaining basement strain is transferred eastward to a second, smaller en echelon fault. In this zone, strata are interpreted to have responded to uplift of the eastern block with a combination of faulting and monoclinal folding. There is no evidence of a shallow Bovie Lake Thrust detachment in the northern zone. Southward, Bovie Structure turns abruptly southwest across the Trout Lake Fault zone, and the west-directed deep fault steps eastward in an en echelon manner. In the southern zone, there is little evidence for a shallow-detachment fault, and the second phase of development is interpreted to be one of transpressional reactivation of the west-directed, crustal-scale fault producing ‘flower’ structures. Uplift on Bovie Fault may have coincided with uplift of Celibeta High, which developed immediately east of Bovie Structure. Adoption of a two-stage contractional model has led to the identification of new conceptual plays on Bovie Structure.

Iceberg Turbate on Southeastern Baffin Island Shelf, Canada

Huntec DTSTM high resolution seismic reflection profiles and core data indicate that glaciomarine sediments on parts of the Southeastern Baffm Island continental shelf have been extensively reworked by the keels of grounding icebergs [Praeg et al., 1986] into an iceberg turbate. This term was first applied by Vorren et al., (1983) to the deformed and reworked sediments resulting from the iceberg ploughing process.

Thick Multiple Ice-contact Deposits Adjoining the Sill at the Entrance to Hudson Strait, Canada

Hudson Strait has been a major route for drawdown and discharge of Laurentide ice from Hudson Bay and adjoining Ungava and Baffin land masses onto the continental shelf and into the North Atlantic during the Quaternary [see e.g. Dyke and Prest, 1987; Hughes, 1987].

Submarine Lateral Moraine in the South Central Region of Hudson Strait, Canada

Huntec DTSTM high resolution and single channel (655 cm3 air gun) seismic reflection profiles show the occurrence in south central Hudson Strait of a late glacial moraine up to 70 m in thickness. This is a constructional feature composed of acoustically unstratified, and relatively consolidated material considered to be ice-contact sediments deposited subglacially and adjacent to the margin of a glacial ice sheet. A small till tongue or local debris flow deposit occurs at the foot of the moraine.