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Three-Dimensional Geologic Block Model of a Polar Fan-Delta Complex, Canning River, North Slope, Alaska

By
John F. Lindsay
John F. Lindsay
Bureau of Mineral Resources Canberra, ACT, Australia
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Published:
January 01, 1992

Abstract

The Canning River delta on the Beaufort Sea coast of Alaska has been modeled in three dimensions as a typical example of a polar fan-delta complex. Polar deltas result from severely inhibited sedimentary processes. Free water is abundant only during the short summer when the carrying capacity of the stream is greatly exceeded so that most deposition occurs subaerially in braided-stream channels. Consequently, polar fan-deltas prograde seaward only minimally.

Three-dimensional geologic block modeling with the computer was highly effective in assimilating the large volumes of data available from shallow borings and has provided a new and unexpected insight into the structure and origin of this complex sedimentological body. The model shows that at least five depositional sequences are present beneath the delta surface. Each sequence began with the subaerial deposition of a massive, poorly sorted gravel unit in braided-stream channels. The massive gravels are generally followed by thick units of dark-colored, poorly sorted silt or silty sand. These reflect a fresh or brackish water swamp environment in the lower section and suggest shallow-water nearshore marine deposition in the upper sections. The shallow-water marine sediments show signs of ice scouring and some sequences are not complete because erosion has occurred during extreme sea-level lows. Thus some apparently massive gravel units are complexes representing more than one sea level cycle.

Barrier islands are common along the Beaufort Sea coast and their origin has been frequently discussed in the literature. The Canning River delta model shows the islands to be ephemeral structures built around cores of earlier gravels or marine sediments left behind from the Woronzofian transgression. These islands and their associated lagoons may not be typical of polar fan-deltas but may be a fortuitous occurrence resulting from the fact that the present sea level is slightly lower than during the Woronzofian sea-level maximum. The main effect of the lack of a lagoon would be reduction of the width of the zone of shore-fast sea ice, which would result in more intense scouring of the shallow-water marine sediments by sea ice.

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Figures & Tables

Contents

Computer Applications

Computer Modeling of Geologic Surfaces and Volumes

David E. Hamilton
David E. Hamilton
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Thomas A. Jones
Thomas A. Jones
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American Association of Petroleum Geologists
Volume
1
ISBN electronic:
9781629811055
Publication date:
January 01, 1992

GeoRef

References

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