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Thuy A. Trinh1, Frank G. Ethridge2
(1) Chevron, River Ridge, LA
(2) Colorado State University, Fort Collins, CO

Abstract: Effects of base-level fluctuations on passive margins: An experimental flume study

A series of experiments designed to study the effects of base-level fluctuations and initial drainage basin slopes (8%, 5% and 2% gradients) on the erosion and deposition of sediment in a passive margin setting, were completed in a 2.2 m X 1.0 m X 0.6 m, wooden flume. Erosion was dominant in the drainage basin during all base-level stages. Higher drainage basin gradients caused erosion to be concentrated in tributary channels, while lower drainage basin gradients resulted in more widespread erosion patterns.

Net sediment deposition occurred on the continental shelf during base-level rise and highstand, while net erosion occurred during base-level fall and lowstands. During highstands a shelf-phase delta developed. During base-level fall and lowstand, a valley incised the former shelf-phase delta and a shelf-margin delta developed. During lowstand, the incised valley partially filled with sediments while deltaic lobes prograded basinward. Backstepping bay-head deltas filled the valleys during base-level rise.

Sediment bypassed the continental shelf and was deposited on the continental slope during falling and lowstand stages, building a subaqueous platform and delta that extended seaward from the shelf edge. Deposition on the continental slope started and was the greatest when the shoreline fell below the continental shelf break. Higher drainage basin slopes resulted in a shelf-edge delta that extended basinward onto the upper reaches of the continental rise. Lower drainage basin slopes created wider but narrower deltas that did not extend onto the continental rise. The ocean basin floor was unaffected during any base level stage.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana