Glacial advance, occupation and retreat sediments associated with multi‐stage ice‐dammed lakes: north‐central Alberta, Canada

Abstract

Ice sheets that advance upvalley, against the regional gradient, commonly block drainage and result in ice-dammed proglacial lakes along their margins during advance and retreat phases. Ice-dammed glacial lakes described in regional depositional models, in which ice blocks a major lake outlet, are often confined to basins in which the glacial lake palaeogeographical position generally remains semi-stable (e.g. Great Lakes basins). However, in places where ice retreats downvalley, blocking regional drainage, the palaeogeographical position and lake level of glacial lakes evolve temporally in response to the position of the ice margin (referred to here as 'multi-stage' lakes). In order to understand the sedimentary record of multi-stage lakes, sediments were examined in 14 cored boreholes in the Peace and Wabasca valleys in north-central Alberta, Canada. Three facies associations (FAI-III) were identified from core, and record Middle Wisconsinan ice-distal to ice-proximal glaciolacustrine (FAI) sediments deposited during ice advance, Late Wisconsinan subglacial and ice-marginal sediments (FAII) deposited during ice-occupation, and glaciolacustrine sediments (FAIII) that record ice retreat from the study area. Modelling of the lateral extent of FAs using water wells and gamma-ray logs, combined with interpreted outlets and mapped moraines based on LiDAR imagery, facilitated palaeogeographical reconstruction of lakes and the identification of four major retreat-phase lake stages. These lake reconstructions, together with the vertical succession of FAs, are used to develop a depositional model for ice-dammed lakes during a cycle of glacial advance and retreat. This depositional model may be applied in other areas where meltwater was impounded by glacial ice advancing up the regional gradient, in order to understand the complex interaction between depositional processes, ice-marginal position, and supply of meltwater and sediment in the lake basin. In particular, this model could be applied to decipher the genetic origin of diamicts previously interpreted to record strictly subglacial deposition or multiple re-advances.

Sedimentary architecture of a glaciolacustrine braidplain delta: proxy evidence of a pre‐Middle Wisconsinan glaciation (Grimshaw gravels, Interior Plains, Canada)

“…The geographical position of the foreset beds of FA4 is significant because it is situated directly adjacent to the part of the Peace River lowlands in which a lake would have most likely been impounded by the LIS (cf. Slomka & Utting ); hence, foreset beds of FA4 are located in the most basinward position of the Grimshaw gravels deposit, which is consistent with a delta slope environment. Based on the minimum height of the foreset beds recorded in FA4 (Fig.…”

“…) and glaciers (e.g. Mathews ; Slomka & Utting ), both of which have previously resulted in impoundment of lakes within the Peace River lowland in recent geological time. Modern landslide dams in the Peace River lowland are infrequent and relatively short lived (a few days to 1 year; e.g.…”

“…Alternatively, an ice dam is a more effective mechanism for lake impoundment in the Peace River lowland based on previous interpretations of lake impoundment in the Peace River lowlands by the LIS in the Middle and Late Wisconsinan (cf. Mathews ; Slomka & Utting ). Glaciolacustrine sediments overlying Old Fort gravel (Slomka et al .…”

“…The Shaftesbury bedrock valley fill is composed of a basal unit of Middle Wisconsinan fluvial and glacifluvial sediments overlain by Middle to Late Wisconsinan glaciolacustrine and subglacial sediments (based on radiocarbon dates from bone, antler and wood fragments; Tokarsky ; Balzer ; Leslie & Fenton ; Botterill ; Hartman & Clague ; Morgan et al . ; Slomka & Utting ; Fig. ).…”

“…). The till is overlain by glaciolacustrine sediments deposited in Glacial Lake Peace in the late part of the Late Wisconsinan, during which the LIS retreated northward (down the regional topographic gradient), resulting in the impoundment of ice‐contact ice‐dammed lakes in former river valleys (Mathews ; Slomka & Utting ).…”