Slope Instability in a Tectonically Active Jurassic Sedimentary Basin, Northwest British Columbia, Canada

Jean-Francois Gagnon and John W. F. Waldron
Earth and Atmospheric Sciences, University of Alberta, Edmonton, AB, Canada

Sedimentary rocks of the Upper Hazelton Group exposed near Stewart in British Columbia constitute an excellent modern analog of slope processes in siliciclastic-dominated depositional systems. These sediments were deposited over volcanic arc rocks in an evolving extensional basin during the Middle Jurassic. Frequent tectonic activity along basin-bounding faults created significant instability on the slope that resulted in migration of submarine channels along with deposition of debris flows and slumps.

Detailed geological mapping during the summer of 2007 has allowed the identification of multiple amalgamated channel complexes interbedded with finer-grained turbidites. The sand-rich channels can reach thicknesses up to 35m and be laterally continuous for 200m. Mudstone rip-up clasts up to 30 cm in diameter are common at the bases of the channels and attest to a high energy environment with great erosion potential. The channels are incised into fine-grained well bedded turbidite successions that display partial to complete Bouma sequences. A broad variety of soft-sediment deformation features, including slump folds, sedimentary dikes and décollements, were also identified within the turbidites. Most of these features are attributed to slope failure during reactivation of normal faults.

Understanding slope dynamics in a tectonically active setting is critical to evaluating the distribution of units with potential reservoir characteristics. A sudden increase in the slope angle is likely to trigger rapid incision by submarine channels, which will tend to be vertically stacked rather than laterally extensive.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas