Wave-Enhanced Fluid Mud-Flows in the Fine-Grained Sedimentary Record. the Main Mechanism of down-Dip Sediment Dispersal from Continental Shelves
Using fine-grained sediment distributions on Recent continental shelves as an analog, geologists typically assume that ancient, marine fine-grained siliciclastic sedimentary rocks (e.g. shales, mudrocks, mudstones) were deposited in distal low energy settings, by suspension settling from sediment being dispersed around sedimentary basins by currents. Lack of any obvious preserved sedimentary structures and predominance of fissility / lamination in hand specimen reinforces this view.
Recent, high-resolution studies utilising optical and electron optical techniques to investigate unusually thin polished thin sections reveals, contrary to expectations, that these rocks contain a great deal of evidence (e.g. starved ripple lamination) of advective sediment transport operating at the time of deposition to facilitate sediment dispersal. These analyses also reveal that enigmatic erosion-based, upward-fining beds, that contain homogenous lower lamina, overlain by continuous intercalated silt and clay-rich lamina in their middle portions, and bioturbated, clay-rich lamina at their tops are present.
We propose that these structures were produced by wave-enhanced fluid mud flows and were the main mechanism of sediment dispersal in many mud-dominated ancient continental shelf successions. The origin and significance of these deposits for hydrocarbon exploration strategies (distribution source rocks and potential shale gas reservoirs) is explored here.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009