PALEO SUPER WINDSTORMS (> 2000 YR EVENTS) INTERPRETED FROM HOLOCENE DELTAIC STRATIGRAPHY

Paleo super windstorms have been interpreted from ground penetrating radar (GPR) reflections from stratigraphy in the Holocene prograding wave-dominated William River delta. Located on the south coast of Lake Athabasca (250km by 40km) in northwestern Saskatchewan, western Canada, the sandy lobate-shaped delta measures 9km by 8km. GPR stratigraphy shows three prominent reflections as erosional surfaces in sediments deposited during the past 4000 years (OSL ages). We interpret these erosional surfaces as having been eroded by paleo super windstorms then subsequently buried by normal deltaic progradational processes. The erosional surfaces are sloping lakeward at 1°, sandwiched by higher angle foreset beds dipping up to 7°. Orientations of eolian beach ridge blowouts, GPR stratigraphy, and numerical modeling suggest that severe winds from the northwest attained velocities greater than 120 km/hr for at least 3 days to form the most prominent of the three erosional surface. The largest of the three paleo storms eroded and transported 12.5x106 m3 of sand from the subaqueous shelf, depositing it farther offshore and down drift into deeper water; the resulting morphology was an erosional surface that is mappable with GPR. If such a storm were to occur today at the nearby (200km) Alberta Oil Sands synthetic crude oil extraction facilities, the damage could be in the hundreds of millions of dollars and the temporary loss of 800,000 barrels (130,000 m3) of oil production per day.