THE SPECTACULAR AND ENIGMATIC LARGE-SCALE DEFORMATION STRUCTURES OF THE UPPER GLACIAL LAKE PEACE SEDIMENTS, NORTHERN ALBERTA, CANADA

The Peace River valley, in northern Alberta is renowned for its thick exposures of bedrock and Quaternary sediments and its long history of landslides. The Quaternary valley fill mainly comprises, from oldest to youngest, preglacial sands and gravels, Late Wisconsin glacial sediments and thick glaciolacustrine silts and clays.

At the top of the uppermost glaciolacustrine sequence, an exposure south of the town of Peace River has impressive mega-scale soft sediment deformation structures. These chaotic structures often extend over many metres in both the horizontal the vertical dimensions. Several massive blocks of sediment within the deformation zone exhibit relict sedimentological forms such as, ripples, graded beds, crossbeds and other glaciolacustrine phenomenon such as dropstones. The deformation zone occurs at the top of the glaciolacustrine sequence and above many of the landslides that plagues the Peace River valley. A small bed of loess caps the sequence.

Such large soft-sediment deformation features have never been documented in Glacial Lake Peace sediments. Their impressive size and chaotic nature of the sediments along with their stratigraphic setting provides a unique geological enigma.