The Regressive History of a Transgression: Early Turonian Tuskoola Sandstone (Kaskapau Formation), Western Canada Foreland Basin

Bogdan L. Varban¹ and A. Guy Plint^2
1 University of Western Ontario, Dept. of Earth Sciences, London, ON
² Department of Earth Sciences, University of Western Ontario, London, ON

In northeastern British Columbia, between Tumbler Ridge and Chetwynd, the 155 m thick Tuskoola Sandstone within the Vimy Member of the Kaskapau Formation is exposed on the edge of the Rocky Mountain Foothills as a series of sandstone tongues. Due to rapid facies variations the Tuskoola Sandstone becomes muddier eastward over a distance of 20 km. In subsurface the Tuskoola Sandstone can be correlated over approximately 40,000 km2 as a vertical succession of six sandier-up allomembers bounded by flooding surfaces. The approximate duration of each allomember is 116 ka. In the eastern part of the study area (6th meridian) the six allomembers forming the Tuskoola Sandstone correlate with the upper part of the Second White Speckled Shale.

In outcrop the Tuskoola Sandstone consists of a series of stacked 10 –15 m thick sandier–upward successions. Each succession contains a thin (less than 1 m) transgressive package overlain by a sharp-based shoreface sandstone, commonly rooted at the top. Each succession is interpreted to be the result of a high-frequency (tens of thousands years) relative sea-level change superimposed on a longer (hundred thousand years) cycle.

The early Turonian (Watinoceras time) in the Western Interior Basin corresponds to the transgressive peak of the Greenhorn Cycle. However the Tuskoola Sandstone contains evidence for repeated relative sea-level changes suggesting that 10 to 15 m of accommodation was repeatedly generated and filled on a tens of thousands years timescale.

We interpret the deposition of the Tuskoola Sandstone to record the interplay between eustacy and tectonics.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005