Abstract: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 fo… Show more
“…11). It is acoustically similar to the ice proximal glaciomarine sediments described by Josenhans et al (1986), Josenhans et al (1988), and King ef al. (1991).…”
Section: Profil Sismique C-c (Fig 1) Illustrant La Topographie En Fosupporting
confidence: 83%
“…These four units were interpreted on the basis of their similarity to units established in other similar areas; i.e. Hudson Bay (Josenhans et al, 1988;Josenhans and Zevenhuizen, 1990), Labrador Shelf (Josenhans et al, 1986). Scotian and mid-Norwegian Shelves (King et al, 1991), and Gulf of St. Lawrence (Syvitski and Praeg, 1989).They are designated as: ice contact sediments (unit 2), rythmically bedded clays and silts (unit 3), postglacial marine muds (unit 4) and, distal fluvio-deltaic sediments (unit 5).…”
Section: Acoustic and Lithostratigraphic Characteristics Of The Unitsmentioning
The regional distribution of Holocene sediments of eastern Hudson Bay off the Grande Rivière de la Baleine mouth was mapped using a grid of reflection seismic lines (approximately 300 km long and covering an area of approximately 800 km2) and data from 7 piston cores. Based on the seismic records and piston cores, 4 stratigraphic units overlying the Proterozoic bedrock (unit 1) were defined and interpreted: (unit 2) glacial till deposited by a westward flowing ice sheet, (unit 3) rhythmically bedded clays and silts presumably deposited in glacial Lake Ojibway, (unit 4) postglacial marine muds deposited in the Tyrrell Sea overlain by undifferentiated modern marine muds, and (unit 5) distal fluviodeltaic sediments from Grande Rivière de la Baleine. Similar stratigraphie units have been described onshore. Textural and geochemical analyses suggest that unit 3 rhythmites are true varves; dark "summer" laminae were deposited mainly by underflows during the open water season, and light "winter" laminae were deposited by overflows-interflows along thermal stratifications under a seasonal ice cover. Unit 5 covers approximately 400 km2 and occurs as a deltaic constructional wedge protruding as far as 11 km offshore of the Grande Rivière de la Baleine entrance with thicknesses reaching 30 m along the coast. It was deposited between 3500 BP and the present from remobilization of glacial sediments farther upstream due to river downcutting during emergence.La répartition régionale des sédiments holocènes de l'est de la baie d'Hudson, face à l'embouchure de la Grande rivière de la Baleine, a été cartographiée à l'aide d'un grille de profils de sismique réflexion (d'environ 300 km de long et d'une superficie de 800 km2) et de données provenant de sept forages par carottier à piston. Quatre unités stratigraphiques reposant sur le socle protérozoïque (unité 1) ont été définies et interprétées : un till (unité 2) déposé par un glacier progressant vers l'ouest, des argiles et silts stratifiés (unité 3) probablement déposés dans le Lac glaciaire Ojibway, des boues marines postglaciaires (unité 4) déposés dans la Mer de Tyrrell auxquelles se superposent des boues marines récentes indifférenciées et des sédiments fluvio-deltaiques distaux (unité 5) provenant de la Grande rivière de la Baleine. Les mêmes unités stratigraphiques ont été décrites sur la côte. Les analyses granulométriques et géochimiques laissent croire que les rythmites de l'unité 3 sont des varves; les couches foncées d'été ont surtout été déposées par des courants de densité s'écoulant sur le fond pendant la période libre de glace et les couches pâles d'hiver ont été transportés en suspension le long de stratifications thermiques sous un couvert de glace saisonnier. L'unité 5 couvre environ 400 km2 et forme un prisme s'étendant jusqu'à 11 km de l'embouchure de la Grande rivière de la Baleine avec des épaisseurs atteignant 30 m le long de la côte. La mise en place de l'unité 5 s'est faite entre 3500 BP et aujourd'hui et résulte de l'érosion et de l'apport de sédiments d...
“…11). It is acoustically similar to the ice proximal glaciomarine sediments described by Josenhans et al (1986), Josenhans et al (1988), and King ef al. (1991).…”
Section: Profil Sismique C-c (Fig 1) Illustrant La Topographie En Fosupporting
confidence: 83%
“…These four units were interpreted on the basis of their similarity to units established in other similar areas; i.e. Hudson Bay (Josenhans et al, 1988;Josenhans and Zevenhuizen, 1990), Labrador Shelf (Josenhans et al, 1986). Scotian and mid-Norwegian Shelves (King et al, 1991), and Gulf of St. Lawrence (Syvitski and Praeg, 1989).They are designated as: ice contact sediments (unit 2), rythmically bedded clays and silts (unit 3), postglacial marine muds (unit 4) and, distal fluvio-deltaic sediments (unit 5).…”
Section: Acoustic and Lithostratigraphic Characteristics Of The Unitsmentioning
The regional distribution of Holocene sediments of eastern Hudson Bay off the Grande Rivière de la Baleine mouth was mapped using a grid of reflection seismic lines (approximately 300 km long and covering an area of approximately 800 km2) and data from 7 piston cores. Based on the seismic records and piston cores, 4 stratigraphic units overlying the Proterozoic bedrock (unit 1) were defined and interpreted: (unit 2) glacial till deposited by a westward flowing ice sheet, (unit 3) rhythmically bedded clays and silts presumably deposited in glacial Lake Ojibway, (unit 4) postglacial marine muds deposited in the Tyrrell Sea overlain by undifferentiated modern marine muds, and (unit 5) distal fluviodeltaic sediments from Grande Rivière de la Baleine. Similar stratigraphie units have been described onshore. Textural and geochemical analyses suggest that unit 3 rhythmites are true varves; dark "summer" laminae were deposited mainly by underflows during the open water season, and light "winter" laminae were deposited by overflows-interflows along thermal stratifications under a seasonal ice cover. Unit 5 covers approximately 400 km2 and occurs as a deltaic constructional wedge protruding as far as 11 km offshore of the Grande Rivière de la Baleine entrance with thicknesses reaching 30 m along the coast. It was deposited between 3500 BP and the present from remobilization of glacial sediments farther upstream due to river downcutting during emergence.La répartition régionale des sédiments holocènes de l'est de la baie d'Hudson, face à l'embouchure de la Grande rivière de la Baleine, a été cartographiée à l'aide d'un grille de profils de sismique réflexion (d'environ 300 km de long et d'une superficie de 800 km2) et de données provenant de sept forages par carottier à piston. Quatre unités stratigraphiques reposant sur le socle protérozoïque (unité 1) ont été définies et interprétées : un till (unité 2) déposé par un glacier progressant vers l'ouest, des argiles et silts stratifiés (unité 3) probablement déposés dans le Lac glaciaire Ojibway, des boues marines postglaciaires (unité 4) déposés dans la Mer de Tyrrell auxquelles se superposent des boues marines récentes indifférenciées et des sédiments fluvio-deltaiques distaux (unité 5) provenant de la Grande rivière de la Baleine. Les mêmes unités stratigraphiques ont été décrites sur la côte. Les analyses granulométriques et géochimiques laissent croire que les rythmites de l'unité 3 sont des varves; les couches foncées d'été ont surtout été déposées par des courants de densité s'écoulant sur le fond pendant la période libre de glace et les couches pâles d'hiver ont été transportés en suspension le long de stratifications thermiques sous un couvert de glace saisonnier. L'unité 5 couvre environ 400 km2 et forme un prisme s'étendant jusqu'à 11 km de l'embouchure de la Grande rivière de la Baleine avec des épaisseurs atteignant 30 m le long de la côte. La mise en place de l'unité 5 s'est faite entre 3500 BP et aujourd'hui et résulte de l'érosion et de l'apport de sédiments d...
“…Hence we place the ice limit off the south and central Labrador coast but behind the rim of the Torngat Mountains in the north where weathering zones and soil development on moraines argue for existence of Late Wisconsinan nunataks above and beyond the Saglek Moraines (CLARK and JOSENHANS, 1986). JOSENHANS et al (1986) conclude that Late Wisconsinan Labrador Ice advanced well out on the Continental Shelf and deposited a till. The till is only slightly consolidated and is thought to have been deposited during retreat as the ice became buoyant sometime after about 20 ka.…”
AbstractEleven paleogeographic maps and a summary ice retreat map outline the history of advance, retreat, and readvances of the Laurentide Ice Sheet along with associated changes in proglacial drainage and relative sea level oscillations for Late Wisconsinan and Holocene times. The text outlines pertinent chronological control and discusses the paleoglaciology of the ice sheet, with attention to location and migration of ice divides, their attendant domes and saddles, and to ice streams, ice shelves, and mechanisms of déglaciation. At 18 ka the ice sheet consisted of 3 sectors with an interlocked system of ice divides joined at intersector saddles. A throughgoing superdivide is recognized and named the Trans Laurentide Ice Divide. The ice sheet retreated slowly from 18 to 13 ka, mainly along the west and south margins, but still held a near maximum configuration at 13 ka. A regional change in flow pattern over the Prairies just before 14 ka is thought to represent a large reduction in ice volume, but not in extent, and likely was triggered by a switch from nondeforming to deforming bed conditions. Retreat between 13 and 8 ka was vastly more rapid in the west than in the east, which resulted in eastward migration of the divide system of Keewatin Ice but relatively static divides of Labrador and Foxe Ice. By 10 ka the Trans Laurentide Ice Divide had been fragmented as Hudson Ice became increasingly autonomous. By 8 ka Hudson Ice had disappeared, little ice was left in Keewatin, but Foxe Ice still held its near maximum configuration and Labrador Ice was still larger than Foxe Ice. Repeated surging along aquatic margins and calving back of margins thinned by surging probably was the most important mechanism of deglaciation of Keewatin and Hudson Ice. The core of Foxe Ice disintegrated at 7 ka but retreat and readvance of Foxe Ice remnants continued throughout the Holocene.
“…These ice sheets played an important role in transporting sediments to the shelf break through glacial erosion, sediment mass wasting (Dowdeswell et al, , 2002 and calving of icebergs (e.g. Josenhans et al, 1986;Shipp et al, 2002). A fraction of the sediments is further transported from the shelf break of the Barents and Kara seas far to the east via the Atlantic Layer (Knies et al, 2001).…”
Section: Present and Past Oceanographic Settingmentioning
Abstract. Knowledge on past variability of sedimentary organic carbon in the Arctic Ocean is important to assess natural carbon cycling and transport processes related to global climate changes. However, the late Pleistocene oceanographic history of the Arctic is still poorly understood. In the present study we show sedimentary records of total organic carbon (TOC), CaCO 3 , benthic foraminiferal δ 18 O and the coarse grain size fraction from a piston core recovered from the northern Northwind Ridge in the far western Arctic Ocean, a region potentially sensitively responding to past variability in surface current regimes and sedimentary processes such as coastal erosion. An age model based on oxygen stratigraphy, radiocarbon dating and lithological constraints suggests that the piston core records paleoenvironmental changes of the last 155 kyr. TOC shows orbital-scale increases and decreases that can be respectively correlated to the waxing and waning of large ice sheets dominating the Eurasian Arctic, suggesting advection of fine suspended matter derived from glacial erosion to the Northwind Ridge by eastward flowing intermediate water and/or surface water and sea ice during cold episodes of the last two glacialinterglacial cycles. At millennial scales, increases in TOC might correlate to a suite of Dansgaard-Oeschger Stadials between 120 and 45 ka before present (BP) indicating a possible response to abrupt northern hemispheric temperature changes. Between 70 and 45 ka BP, closures and openings of the Bering Strait could have additionally influenced TOC variability. CaCO 3 content tends to anti-correlate with TOC on both orbital and millennial time scales, which we interpret in terms of enhanced sediment advection from the carbonaterich Canadian Arctic via an extended Beaufort Gyre during warm periods of the last two glacial-interglacial cycles and increased organic carbon advection from the Siberian Arctic Correspondence to: M. Uchida (uchidama@nies.go.jp) during cold periods when the Beaufort Gyre contracted. We propose that this pattern may be related to orbital-and millennial-scale variations of dominant atmospheric surface pressure systems expressed in mode shifts of the Arctic Oscillation.
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