The Wave-Dominated William River Delta, Lake Athabasca, Canada: Its Morphology, Radar Stratigraphy, and History
Derald G. Smith, Harry M. Jol, Norman D. Smith, Raymond A. Kostaschuk, Cheryl M. Pearce, 2005. "The Wave-Dominated William River Delta, Lake Athabasca, Canada: Its Morphology, Radar Stratigraphy, and History", River Deltas–Concepts, Models, and Examples, Liviu Giosan, Janok P. Bhattacharya
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The wave-dominated Holocene William River delta, located along the south coast of Lake Athabasca, northern Saskatchewan, is a lobate sand body 9 km long by 8 km wide by 15-22 m thick. Mean lake elevation is 209 m and fluctuates ± 1.5 m (1810-2000). Periodic strong winds, waves, and currents generated in deep water (50-100 m)with long fetches (50-110 km) shape the delta morphology and determine its internal sedimentary structure. Its surface is dominated by multiple arcuate sets of eolian-dune-capped beach ridges separated by peatlands. A one-kilometer-wide arcuate, subaqueous shelf is covered by multiple (up to 19) offshore bars and troughs in water depths to 5.5 m. Farther offshore, a 1 to 7° foreset slope plunges to a depth of 15 to 17 m. Lakeward from the toe of the foreset slope, gently sloping (0.0072 or 7.2 m/km) bottomset beds of thin sand lenses interfinger with lacustrine mud. Luminescence and radiocarbon dates suggest that the rate of delta progradation has declined an order of magnitude from an initial 1.4 m yr-1 (9800 to 7000 cal yr BP) to the present 0.16 m yr-1, because of reduced fluvial sediment influx from a nearby depleting eolian dune field and exponentially larger volumes of sand required to maintain constant rates of linear expansion.
Radar stratigraphic profiles to depths of 15-22 m along depositional dip and strike indicate lakeward-inclined erosional surfaces and lensoid sand bodies. Nested within these lenses are “J-shaped” reflections which represent progradational sequences deposited by annual to decadal storms. Several gently basinward-dipping (< 1°) erosional surfaces between 5 and 14 m deep are interpreted to have formed by severe millennial-frequency storms.
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Deltas are amongst the most environmentally and economically important coastal sedimentary environments. Studies of deltas lag behind research in both fluvial and deep-water depositional systems, as well as more geomorphologically oriented land studies. This knowledge lag reflects both a reorientation of the petroleum industry in the last two decades toward deep-water systems, as well as the difficulty of working across the shoreline with the traditional tools used for oceanographic or land-based work. However, deltaic studies are experiencing a renewed focus, because of their global importance in environmental and other societal concerns. This volume stems from a special session: Deltas: Old and New, held at the Annual Geological Society of America conference in October 2002, that was convened to highlight these new directions in deltaic research.