Deglaciation of Nova Scotia: Stratigraphy and chronology of lake sediment cores and buried organic sections

Abstract

The deglaciation of Nova Scotia is reconstructed using the AMS-dated chronology of lake sediments and buried organic sections exposed in the basins of former glacial lakes. Ice cleared out of the Bay of Fundy around 13.5 ka, punctuated by a brief read- vance ca. 13-12.5 ka (Ice Flow Phase 4). Glacial Lake Shubenacadie (1) formed in central Nova Scotia, impounded by a lobe of ice covering the northern Bay of Fundy outlet. Drainage was re-routed to the Atlantic Ocean until the Fundy outlet became ice free after 12 ka. When this lake drained, bogs and fens formed on the lake plain during climatic warming. Organic sediment (gyttja) began to accumulate in lake basins throughout Nova Scotia. Glacierization during the Younger Dryas period (ca. 10.8 ka) resulted in the inundation of lakes and lake plains with mineral sediment. The nature and intensity of this mineral sediment flux or "oscillation" varies from south to northern regions. Southern lakes simply record changes in total organic content whereas northern lakes, where most buried peat sections are found, feature a thick inorganic sediment layer. Glacial ice or permanent snow cover and seasonal melting are essential in the formation of this mineral sediment layer; both to provide the water source for erosion, and to prevent plant re- colonization and landscape stabilization. Some northern lakes do not appear to record the Younger Dryas event, with organic accumulation starting around 10 ka. During the Younger Dryas, fine and coarse-grained deposits were deposited in Glacial Lake Shubenacadie (2) and other lowland areas at elevations similar to former (12 ka) lake levels, impounded by re-invigorated residual ice caps and permanent snow/aufeis.Il s'agit d'une reconstitution à partir de la chronologie par spectométrie de masse (SMA) de sédiments lacustres et de certaines coupes de matériaux organiques enfouis dans les bassins d'anciens lacs glaciaires. La baie de Fundy, libre de glace vers 13,5 ka, a connu une récurrence vers 13-12,5 ka. Le Lac glaciaire Shubenacadie (1), qui s'est formé au centre de la Nouvelle-Écosse, a été endigué par un lobe glaciaire qui recouvrait la sortie de la baie de Fundy au nord. L'écoulement a alors été détourné vers l'océan Atlantique jusqu'au retrait de la glace vers 12 ka. Une fois le lac asséché, tourbières et marécages se formèrent sur l'ancien fond lacustre au cours du réchauffement climatique. Ensuite, la gyttja s'accumula dans les bassins lacustres à travers la Nouvelle-Écosse. L'englacement au cours du Dryas récent (vers 10,8 ka) a entraîné le comblement des lacs et des plaines lacustres par des sédiments minéraux.Lanatureetl'intensitédecefluxdesédiments ou « oscillation » varient du sud au nord. Dans les lacs du sud, la teneur organique totale a simplement varié, tandis que dans les lacs du nord, une importante couche de sédiment inorganique a été déposée. Certains lacs du nord ne semblent pas avoir enregistré l'épisode du Dryas récent, l'accumulation de matière organique ayant commencé vers 10 ka. Au Dryas récent, des dépôts à...

The Laurentide and Innuitian ice sheets during the Last Glacial Maximum

“…In the current view, ice reached the continental slope off Nova Scotia before 18.3 14 C ka BP (Mosher et al, 1989). Ice was receding on the central shelf by 17,0507155 14 C yr BP (Beta-27229; Piper et al, 1990), the Scotian Shelf End Moraine Complex on the inner shelf was forming B15-16 14 C ka BP (King, 1996;Stea and Mott, 1998;Todd et al, 1999), and some terrestrial sites were ice-free in Nova Scotia by 14,010790 14 C yr BP (TO-2324; Mayle et al, 1993). Laurentide ice still extended to the Laurentian Moraine in the outer Laurentian Channel adjacent to Cape Breton Island until B14.3 14 C ka BP (Josenhans and Lehman, 1999).…”

“…An extensive, but thin, LGM ice load of short duration would probably not conflict with the sea level history because most of that ice load would have been replaced by the current water load. However, current interpretations favour ice loads, including those in offshore areas, thick enough to have survived and readvanced to the continental slope as late as 11.5 14 C ka BP (Bonifay and Piper, 1988) or into Younger Dryas time (e.g., King, 1994;Stea and Mott, 1998;. A sustained ice load would have delayed crustal rebound until after much of the eustatic sea level rise had occurred, hence resulting in raised shorelines of Holocene age through much of the region.…”

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…New 14 C AMS radiocarbon ages from marine sediments on the continental shelf off Nova Scotia and southern Newfoundland also dated sediment above the youngest till to be of post-LGM ages (e.g. Amos and Knoll, 1987;Bonifay and Piper, 1988;Gipp and Piper, 1989;Mosher et al, 1989;Amos and Miller, 1990;Forbes et al, 1991;Gipp, 1994;King, 1996;Stea et al, 1998;Josenhans and Lehman, 1999). To the north, sedimentological studies and high-resolution AMS dating of marine sediment cores from the SE Baffin and Labrador shelves, and adjacent slopes, led to a reconsideration of LLGM ice extent in that region (Dyke et al, 2002).…”

Laser Altimetry: What Can Be Learned About Geology and Surface Processes from Detailed Topography

“…12). Erosion rates are calculated from the stream incision depth curves and sediment flux from the erosion depth map assuming erosion began after deglaciation at 12 ka ± 200 yr (1) (Stea and Mott, 1998) …”