29 Large Scale Glacial Geomorphology—What Can It Tell Us?

REINTERPRETATION OF THE BELAIR MORAINE, SOUTHEASTERN MANITOBA, CANADA, BASED ON A REGIONAL DIGITAL ELEVATION MODEL AND NEW GEOLOGICAL DATA

Paper number: 29-10
Program: SYMPOSIA SESSIONS
Time: 2:40 AM – 3:00 AM

Authors

Abstract

During the last glaciation, southeastern Manitoba was in a zone of confluence between ice flowing from the low-relief Paleozoic terrane to the northwest and ice flowing from the rugged Precambrian shield to the northeast. Several large glaciofluvial deposits were formed in this area, including the Belair Moraine. The moraine, which extends 100 km from the Red River lowland to the eastern shore of Lake Winnipeg, is composed of a generally north-south trending belt of sandy and gravelly uplands rising 30 to 50m above the surrounding gently rolling till and glacial Lake Agassiz clay plains. It was previously unclear whether the Belair Moraine was formed in an interlobate setting, at the margin of northwest ice, or at the margin of northeast ice.

A new detailed digital elevation model (DEM) for southern Manitoba has clarified, however, that the Belair Moraine is part of a series of deposits that are in arcuate alignment with Birds Hill, located near the City of Winnipeg. Furthermore, portions of the moraine show a gentle slope to the northwest and a steep slope to the southeast. Together, these observations strongly imply formation at the margin of northwest ice. Further evidence has been obtained from new surficial geological and 3D mapping that is supported by extensive digital databases of descriptive, analytical, drillhole, and geophysical information.

Exposures in the moraine reveal unsorted and sorted glacial sediments that generally fine upwards and to the southeast. Many of the heterogeneous, imbricate and cross-bedded bouldery and cobbley sediments as well as cross-bedded and ripple laminated sands and silts reveal southward to eastward paleocurrents. These textural and paleocurrent trends support the interpretation that the moraine was deposited at the margin of ice flowing from the northwest, while the facies architecture indicates that the Belair Moraine was formed in a subaqueous outwash, grounding-line environment.