ABSTRACT: Effects of Base-Level Change on Coastal Plain-Shelf-Slope Systems: An Experimental Approach

Lesli J. Wood, Frank G. Ethridge, Stanley A. Schumm

Research in sequence stratigraphy has resulted in a number of assumptions about the manner in which coastal plain-shelf-slope systems along passive margins react to base-level changes. A series of experiments were performed in a 5 by 9 m flume to test these assumptions by examining the effects of rate of base-level fluctuation on a coastal plain-shelf-slope system.

Results indicate that the rate of base-level change has a strong influence on the types of fluvial valley systems that develop, on the thickness, character, and geometry of the valley fill, and on the preservation potential of fluvial, deltaic, and slope deposits. Initially a fast base-level fall causes high sediment production that produces a broad fluvial braidplain on the shelf. As valleys cut into the shelf edge they produce fine-grained, small, time-synchronous, slope deltas perched at the valley mouth. One valley eventually captures all of the flow. During subsequent base-level rise, this valley is filled with coarse-grained sediments from the fluvial system while others are filled with fine-grained sediments.

In contrast, a slow base-level fall produces less sediment, a more confined fluvial system, and a single large valley incised at the shelf-slope break. A series of coarse-grained, large, time-transgressive, perched slope deltas form along the valley walls. During subsequent base-level rise this single valley is filled with coarse-grained sediments.

AAPG Search and Discovery Article #91002©1990 AAPG Rocky Mountain Section Meeting, Denver, Colorado, September 16-19, 1990