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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 65 (1981)

Issue: 5. (May)

First Page: 968

Last Page: 968

Title: Submarine-Fan Facies of Late Cretaceous Nanaimo Group in Restricted Nanaimo Basin, Washington and British Columbia: ABSTRACT

Author(s): Jory A. Pacht

Article Type: Meeting abstract


Geometry of submarine fan facies in the Nanaimo basin contrasts greatly with fans developed along unrestricted continental margins. The latter fans are characterized by sediment deposited in distributary channels extending radially outward from a single-point source, forming fining-upward sequences. At the termini of these channels, nonchannelized sandy lobes are developed, forming coarsening-upward sequences. The surrounding basin-plain is characterized by noncyclic shale-rich sequences.

A large part of the Nanaimo Group was deposited as coalescing submarine fans, from several areas, in the restricted Nanaimo basin. These strata are dominated by fining-upward sequences, which indicate most sediment was transported by channelized flow. However, channels trend parallel with basin margins, not radially from them. Sediment transport was largely controlled by regional slope of the basin floor and not by the slope of the basin margins. Coarsening-upward sequences in the Nanaimo Group are not always located at the termini of channels. Some coarsening-upward sequences in the Nanaimo Group are developed in proximal regions of particular fans, alongside time-equivalent, conglomerate-rich, fining-upward sequences. These coarsening-upward sequences may be crevasse splays. Noncycl c, shale-rich sequences are present throughout the Nanaimo basin. Some of these sequences are deposited by overflow from nearby conglomerate-and sandstone-filled channels in large interchannel areas. Others are distal fan deposits.

Much of the hydrocarbon found in submarine fan facies occurs in restricted basins. The Nanaimo basin may serve as an important analog to predict reservoir location and trapping mechanisms.

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Copyright 1997 American Association of Petroleum Geologists