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Bedforms From Abandoned Fluvial Channels, Carboniferous, Maritime Provinces: Abstract
Fining-upward fluvial sequences in the upper Shepody and Boss Point Formations (mid-Carboniferous in the Chignecto Bay area of New Brunswick and Nova Scotia) are in the order of 25 m thick. Several sequences are incomplete with the fining-upward sequence truncated by a mudrock bed. The truncation of these sequences was probably produced by abandonment of the channel by meander neck cutoff or avulsion. In a few places the mudrock drape has been removed leaving surfaces, up to 300 m2 in area, covered with bedforms present in the river when it was abandoned. Preservation of the bedforms is excellent and even individual avalanche lobes can be seen.
Ripples, sandwaves, dunes and longitudinal bars have been recognized. The larger bedforms show evidence of falling stage modification: small dunes are washed out: ripples in the troughs of larger bedforms indicate a low stage runoff: and the crestlines of some sandwaves and longitudinal bars have been rounded or modified by minor lobes. The preservation of the bedforms allows a far better understanding of the stratification within the fining upward sequences than would otherwise be possible.
Acknowledgments and Associated Footnotes
1 Department of Geology, University of Nebraska, Lincoln, Nebraska 68588
Copyright © 2009 by the Canadian Society of Petroleum Geologists