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Experimental Studies of Gas-Escape and Water-Escape Structures: Mechanisms and Morphologies

¹ Department of Earth Sciences, 8888 University Drive, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada
² Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Bldg, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
³ Department of Earth Sciences, 8888 University Drive, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada

Water-escape and gas-escape structures were generated in the laboratory to assess variations in deformational structures generated during these events. Particulate fluidization was observed to be the method by which grains were redistributed during water escape. Resulting structures of particulate fluidization comprised disrupted and downward-deflected primary laminations, and a massive-appearing column of sand above the point source. Gas experiments, with a low flow rate (6.167 x 10^–6 m³/s) allowed gas to disperse through fractures, and only subtle deformation was achieved. Aggregative fluidization (i.e., fluid movement through sediment as bubbles) was the mechanism for grain displacement during gas escape. With increased flow rate (7.67 x 10^–5 m³/s) aggregative fluidization occurred and particles were carried upward in the wake of the passing gas bubble. Aggregative fluidization resulted in broken, upwards-warping laminations and convoluted bedding. Experiments illustrate a significant morphological difference between water escape and gas escape. Water-escape structures were bounded by downwards-warping laminations, consistent with water-escape structures encountered in the rock record. Gas-escape structures displayed upwards-warping laminations, and could represent a formation mechanism for convolute bedding.