Grant: Discovery Grants Program - Individual

The Neoproterozoic Windermere Supergroup (WSG) in the southern Canadian Cordillera is one of a small number of passive margin turbidite systems in the ancient sedimentary record. Work by two groups, principally the Geological Survey of Canada (Calgary) and the Windermere Consortium (University of Ottawa), have studied Windermere stratigraphy for the past many years. Work by GSC geologists, principally Dr. Margot McMechan, have focussed on the regional-scale lithological make-up and areal distribution of WSG strata in the central Rocky Mountains. The Windermere Consortium, working immediately to the south in the southern Rocky Mountains, and especially Cariboo Mountains, have adopted a somewhat more comprehensive approach, including detailed sedimentology, high resolution stratigraphy, detrital geochronology and elemental, isotopic and organic geochemistry. This very detailed analysis has identified some very profound differences in the make-up of the WSG in these two regions. Previous workers have interpreted major structural features along the length of the western Laurentian margin - one that closely coincides with the lithological changes noted between the southern and central Rocky Mountains, and therefore may have partitioned the Windermere deep-water basin into two parts that appear to have experienced little interaction. These preliminary observations indicate the need for a better understanding of the stratigraphic and tectonic framework along at least this part of the western margin of Neoproterozoic Laurentia. The second research objective is to experimentally investigate the origin of one of the most common styles of stratification in the sedimentary record, namely planar stratification in fine-grained strata, and its distinctive rhythmic alternation of texturally differentiated interlayers. Our recent exploratory work has shown that the grain size distribution changes little between adjacent layers, but the clay content does, and that the interlayering occurs on scales that range from several mm to as thin as a single silt grain. Such limited thickness indicates that its origin is controlled by very near-bed processes that result in rhythmic changes in sediment sorting and timing of deposition. To-date, experimental investigations to study these strata by other researchers have been conducted using open-channel flows. However, the strata described here are deposited by sediment-gravity flows, which have different near-bed sediment concentration and sediment distribution characteristics. In the experiments proposed here subaqueous, sediment-propelled silt-clay mixtures of different concentration and grain size distribution will be analyzed using high-speed, very high-resolution photography to capture fluid and sediment motions in the very near-bed region. Also, cores will be taken and prepared into ultra-thin sections for optical and scanning electron microscopy to document and verify the textural characteristics of the deposits.