Wisconsinan glaciation of the Atlantic continental shelf of southeast Canada

Abstract

On the Scotian Shelf, eastern Gulf of Maine, and the Grand Banks of Newfoundland, the surficial succession occurs as a thin blanket (approximately 50m thick) across the submerged coastal plain surface, and is composed of five formations: Scotian Shelf Drift (glacial till), Emerald Silt ( glaciomarine), Sam bro Sand, LaHave Clay, and Sable Island Sand and Gravel. The Scotian Shelf Drift was derived from sub glacial meltoul debris from a neutral to negatively buoyant active ice shelf in direct contact with the seabed. Emerald Silt formed from subglacial meltout debris from a pinned but floating ice shelf. The debris is thought to have settled through a water column of variable thickness to form the conformable, rhythmically banded deposits which mimic a highly irregular substrate which is recognized over very broad areas. Horizontal migration of the ice-seabed contact (buoyancy line), induced by changes in ice thickness and changes in relative sea level, leads to the development of thick regional moraines (regional subglacial ice shelf moraines) interbedded with the glaciomarine deposits. Wedge-shaped till deposits (till tongues) are often formed at the distal side of the moraines through advance and subsequent retreat of the buoyancy line. The configuration of the seabed beneath an ice shelf is another important factor in the stratigraphic development of these marine deposits. We have used the Carey and Ahmad ice model as an aid in interpreting the seismostratigraphy of the surficial sediments on the continental shelf and integrated these studies with sample data to postulate the glacial history. This stratigraphy is correlated with the adjacent land area. In late Early Wisconsinan time the entire shelf was occupied by an ice sheet (the Scotian Shelf-Grand Banks advance). This wasted to an ice shelf which became buoyant in the deeper basins at about 46 OOO BP. At this time a till blanket with numerous discrete ridges (lift-off moraines) on its surface and associated glaciomarine sediment was deposited. During the period 46 OOO to 32 OOO BP the buoyancy line oscillated intermittently, resulting in the development of till tongues at the periphery of the banks and outer edge of the inner shelf which were intercalated with glaciomarine sediments in the basins. At the western end of the Scotian Shelf the ice may ha1·e receded along the Bay of Fundy re-entrant to deposit the Salmon River beds (38 OOO BP) north of Yarmouth. During the latter part of the Middle Wisconsinan and Late Wisconsinan (32 OOO to 16 OOO BP) the buoyancy line receded to the coastal areas except in the eastern Gulf of Maine where the ice shelf again grounded to deposit till in the areas peripheral to Georges Basin, the southern flank of Browns Bank, and the Fundian Moraine of Sewell Ridge. The youngest moraine (= 17 OOO BP) occurs on Trnxton Swell. Subsequently the buoyancy line receded to the coastal areas of Maine and New Brunswick, and the resulting glaciomarine deposits emerged through glacioisostatic rebound. Evidence for the Late Wisconsinan sea level, which we date within the range of 15 OOO to 14 500 BP, and for 1he Late Wisconsinan-Holocene transgression is well expressed along the entire shelf.

Évolution des structures deltaïques du delta de la rivière Natashquan, Québec

“…Ils sont comparables aux dépôts du plateau de la Nouvelle-Ecosse (King et Fader, 1986), quant à leur nature.…”

Geomorphic Evidence of Postglacial Terrestrial Environments on Atlantic Canadian Continental Shelves

“…Although fluvial landscapes probably existed in formerly emergent areas, most of the geomorphic evidence on the offshore banks has been destroyed by high wave energy during the postglacial transgression (Fader, 1989;King and Fader, 1986). Although only small parts of the offshore banks have been mapped with multibeam systems, evidence of fluvial activity is identifiable.…”

Timing and position of Late Wisconsinan ice-margins on the upper slope seaward of Laurentian Channel

“…This unit has the acoustic character of tills that have been sampled on the continental shelf (cf. King and Fader, 1986). The distribution of this unit is patchy, but it is generally about 5 ms (~4 m) thick.…”

“…is underlain by material with incoherent seismic reflections identified as till (King and Fader, 1986). This inferred till, corresponding to the Lower Till of Josenhans and Lehman (1999), occurs as a morainal ridge with several tens of metres of seabed relief at the outermost edge of Laurentian Channel (Fig.…”