SPECTACULAR, LARGE-SCALE DEFORMATION STRUCTURES IN GLACIOLACUSTRINE SEDIMENTS, PEACE RIVER, ALBERTA, CANADA

Recent road construction has uncovered a spectacular exposure of large-scale soft sediment deformation structures at Sagitawa Lookout, south of the town of Peace River, Alberta. The Peace River Valley, is known for its thick exposures of Quaternary sediments and its long history of landslides. The Quaternary valley fill comprises, from oldest to youngest, preglacial sand and gravel, Late Wisconsin glacial sediments, thick silt and clay of glacial Lake Peace and loess in local areas.

The Sagitawa Lookout section shows a wide variety of chaotic structures extending laterally over several hundred metres. This deformation zone occurs at the very top of the glaciolacustrine sequence and above many of the landslides in the Peace River Valley. Individual 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. Such large soft-sediment deformation features have never before been documented in Glacial Lake Peace sediments. The impressive size and the chaotic nature of the sediments along with their stratigraphic setting provide a unique geological enigma.