WISCONSINAN GLACIAL AND SEA-LEVEL HISTORY OF MARITIME CANADA AND THE ADJACENT CONTINENTAL-SHELF - A CORRELATION OF LAND AND SEA EVENTS

Citation
Rr. Stea et al., WISCONSINAN GLACIAL AND SEA-LEVEL HISTORY OF MARITIME CANADA AND THE ADJACENT CONTINENTAL-SHELF - A CORRELATION OF LAND AND SEA EVENTS, Geological Society of America bulletin, 110(7), 1998, pp. 821-845
Citations number
144
Language
INGLESE
art.tipo
Review
Categorie Soggetti
Geosciences, Interdisciplinary
ISSN journal
0016-7606
Volume
110
Issue
7
Year of publication
1998
Pages
821 - 845
Database
ISI
SICI code
0016-7606(1998)110:7<821:WGASHO>2.0.ZU;2-C
Abstract
The Wisconsinan glacial history of Maritime Canada records the interac tion of landbased glaciers with the sea, which dissects the region alo ng the deep embayments of the Bay of Fundy and the Laurentian Channel. Ice centers, collectively termed the Appalachian ice complex, shifted in a clockwise manner across the varied bedrock terranes of the regio n, producing cross-striated bedrock outcrops and compositionally disti nct till sheets on land. Offshore glacial sediments can be correlated to their terrestrial counterparts on the basis of provenance, thus est ablishing crucial land-sea links in the glacial record. Five glacier f low events have been recognized. During the Caledonia phase in early t o middle Wisconsinan time, ice from eastern Appalachian upland sources crossed Nova Scotia and extended to the continental shelf edge, where a calving margin was established. Slumping at this margin produced pr oximal wedge-shaped bodies of diamicton that interfinger with glacioma rine sediments. The Caledonia phase glacier retreated during middle Wi sconsinan time to the inner Scotian Shelf. During the Escuminac phase in late Wisconsinan time (22-19 ka), an ice center formed over the Mag dalen Shelf (Escuminac ice center) and transported large quantities of local red-bed material southward to the outer shelf-slope margin. Thi s glacier retreated about 18 ka to a tidewater margin at Sable Island Bank and Banquereau. Sea level during this time was falling as a resul t of isostatic recovery from earlier Escuminac phase maximum ice Loads . Just after 18 ka, ice wasted back across the midshelf basins to the tidewater margin of the Scotian Shelf end moraine complex and was stab ilized by falling sea levels. Escuminac ice was reorganized into the S cotian ice divide (Scotian phase) over mainland Nova Scotia and the co ntinental shelf south of Cape Breton Island, Between 15 and 13 ka anot her period of glacier retreat ensued, and the margin settled close to the present-day land areas, Between 13 and 12.5 ka an ice margin was e stablished from local terrestrial ice centers in northern Nova Scotia (Chignecto phase) into the Bay of Fundy and just beyond the present-da y Atlantic coast. Responding to increasing climatic warming, these sma ller glaciers dissipated and their margins retreated landward. A sea-l evel lowstand of -65 m on the inner shelf occurred ca. 11.7 ka. Isolat ed terrestrial remnants of Chignecto phase glaciers were reactivated a s a result of cooling during the Collins Pond phase (Younger Dryas) ca . 10.8 ka. Enhanced ice rafting, evident in the North Atlantic deep oc eanic record, appears to correlate with periods of glacier retreat in the Appalachian ice complex. During melting and sea-level rise, both t he quantity and thickness of icebergs increased due to grounding-line retreat within the Magdalen Shelf thereby increasing the net flux of h ematite-stained quartz to the North Atlantic.