--> ABSTRACT: Temporal Evolution of Continental Slope Channels—A Matter of Sediment Volume and Grain Size Distribution, by Arnott, Bill Arnott; Navarro, Lilian ; Khan, Zishann ; #90142 (2012)

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Temporal Evolution of Continental Slope Channels—A Matter of Sediment Volume and Grain Size Distribution

Arnott, Bill Arnott *1; Navarro, Lilian 2; Khan, Zishann 3
(1) Earth Sciences, University of Ottawa, Ottawa, ON, Canada.
(2) Earth Sciences, University of Ottawa, Ottawa, ON, Canada.
(3) Earth Sciences, University of Ottawa, Ottawa, ON, Canada.

Slope channel deposits of the Isaac Formation (Neoproterozoic Windermere Supergroup, western Canada) commonly show a vertical change from broad (100s to >1000 m wide), sandstone rich channel deposits, herein termed large channels, overlain, in most cases abruptly, by much smaller scale channels bounded by mudstones (i.e. thin bedded turbidites). These latter channels are termed small channels. Large channels range from a few meters to 15 m thick and are filled mostly with coarse sandstone to granule conglomerate in beds that range from a few decimeters to a few meters thick. Low in the stratigraphy, channel fills show little change in grain size upward or laterally, whereas upward there is a consistent lateral axis-to-margin fining and thinning. Small channels, by contrast, consist of single, flat-based channel fills with well-developed lateral accretion deposits. Channel fills range from 10-15 m thick and consist of amalgamated, decimeter-thick, very coarse sandstone/granule conglomerate that grade upward to medium sandstone. These sand-rich strata consist of well-developed lateral accretion deposits that show negligible lateral or upward fining, but are overlain sharply by thin-bedded turbidites (inner bend levee deposits). Moreover, small channels commonly show significant aggradation.

The broad, sand-rich fill of large channels is the result of significant cannibalization and juxtaposition of its smaller constituent channels that fill the larger channel “container”. In small channels, on the other hand, fine-grained off-channel deposits are well developed and also preserved, which commonly causes the channels to aggrade steeply. Collectively, these differences are interpreted to relate to systematic changes in the volume and distribution of grain sizes in the sediment supply. Large channels are filled by large volume flows containing a range of grain sizes whereas small channels experienced smaller volume flows comparatively impoverished in the intermediate sediment fraction, specifically sand. Changes in the volume and granular make up of the input flows is interpreted to be caused by systematic changes in sediment supplied to the sediment staging area, specifically hinterland or relict/palimpsest derived sediment, which ultimately was controlled by the position of relative sea level.

 

AAPG Search and Discovery Article #90142 © 2012 AAPG Annual Convention and Exhibition, April 22-25, 2012, Long Beach, California