REGIONAL NEOGENE-QUATERNARY STRATIGRAPHY OF THE PEACE RIVER LOWLAND, NORTHWESTERN ALBERTA

Buried gravel deposits adjacent to the Peace River valley host regionally important sources of potable water and aggregate resources. However, the detailed sedimentology, stratigraphic architecture, and depositional history of the gravel units are not well-understood. Analysis and stratigraphic picking of subsurface data resulted in the identification of three regionally-distributed gravel units. These units are interpreted as (glacio)fluvial deposits of the paleo-Peace River and each unit is graded to a different base level, suggesting repeated events of fluvial incision and aggradation.

In order to understand the correlation and step-wise incision of gravel units on a regional scale, the thalweg of the Peace River was used as a relative elevation datum. Logs were plotted on a distance-elevation profile and gravel picks were correlated using a line of best fit. Dataset populations identified in the distance-elevation profile suggest that three gravel units in north-central Alberta correlate with previously identified paleo-Peace River deposits to the west of the study area in British Columbia. There, overlying glaciolacustrine deposits have been interpreted to record damming of the lower two paleo-rivers by Laurentide ice. In Alberta, a novel deltaic interpretation of the Grimshaw gravel deposit, which correlates with the highest deposit in B.C., is also interpreted to record damming by Laurentide ice. The successively more westward distribution of erratics derived from the Canadian Shield within each gravel unit places a maximum limit on the extent of the preceding Laurentide glacial advance.

Analysis of the geomorphic maturity of each paleo-valley (including widths that are greater than two times that of the modern valley, and depths of incision between paleo-valleys of greater than 100 m, suggests that each paleo-valley developed over a period of time equivalent to at least an interglacial. Therefore, the gravel deposits may provide indirect evidence of at least four glacial advances of the Laurentide Ice Sheet into the Peace River Lowland.