L. G. Kessler¹, Jeffrey D. Parsons², Wayne W. McCool²

(1) Marathon Oil Company, Houston, TX
(2) Dept of Oceanography, University of Washington, Seattle, WA

ABSTRACT: The Mechanics and Runout Potential of Large Submarine Debris Avalanches or Sturzstroms

Examination of an Ordovician submarine debris avalanche deposit (Lower Head Flow: volume~108 m3, thickness=109 m) at the top of the Cow Head Group of western Newfoundland reveals striking similarities to large subaerial landslides often referred to as sturzstroms. Sturzstroms are distinguished from other slope collapses by their large volume (>106 m3), rapid runout, and long transport distance. The runout of such flows is inversely proportional to the size (volume)of the event. Sturzstrom deposits, unlike the deposits of debris flows, preserve pre-failure stratigraphy, contain large (10-100's m) shattered clasts with nearby pieces, and have significant interaction with the underlying bed. Sturzstrom movement results from early rapid clast fragmentation and maintenance of constant shear strength. The viscosity associated with an acoustically fluidized medium is very high (~105 poise). Because of this, high velocity (10+ m/s) slides are still laminar (Re<100). These apparently contrasting physics make for unique deposits that exhibit high basal shear rates (>106 Pa), but poor mixing. The Lower Head deposit exhibits this odd combination of features. At the top of the flow several large angular to sub-rounded clasts of biohermal limestone (e.g., 180x116 and 90x17 m) separated by mud matrix containing rip-up clasts which exhibit subtle deformation and original stratigraphy. Significant erosion of underlying beds is observed. Other apparent submarine sturzstroms of similar scale are observed from well and seismic data from the Permian of west Texas and Plio-Pleistocene of the Atlantic Margin.

AAPG Search and Discovery Article #90906©2001 AAPG Annual Convention, Denver, Colorado