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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 50 (1966)

Issue: 9. (September)

First Page: 1899

Last Page: 1917

Title: Deep Channels in Turbidite-Bearing Formations

Author(s): Roger G. Walker (2)

Abstract:

Channels from 3-20 m. deep occur in three turbidite-bearing formations in England, the Shale Grit and Grindslow Shales (Upper Carboniferous, North Derbyshire) and the Westward Ho! Formation (Upper Carboniferous, North Devon). Although most channels in the Shale Grit and Grindslow Shales are single cuts, some show several related phases of cutting and filling. The walls generally have gentle slopes, but in one channel they slope 70°. The channel-fill sediments consist of thick sandstone beds interpreted to be proximal turbidites. The Westward Ho! Formation has two wide, shallow-walled, turbidite-filled channels, and three mudstone-filled channels in which both the pre-channel sediments and the fill are of the same facies.

Based on studies of the processes of channel erosion by permanent ocean currents, tidal currents, turbidity currents, catastrophic currents, rivers of sand, and sand creep, it is concluded that the most likely process for the erosion of the deep channels in the Shale Grit and Grindslow Shales was by fast underladen turbidity currents. In the Westward Ho! Formation some channels could have been cut either by underladen turbidity currents or by permanent ocean currents, but there is insufficient evidence to permit a more definite interpretation. The other Westward Ho! Formation "channels" are believed to be slump scars. Processes of channel fill are: deposition from traction currents, sand creep, and turbidity currents; the last is considered to be the most likely process in all three f rmations. Erosion by underladen turbidity currents usually takes place only at the up-current edge of the apron of turbidites in a basin. The presence of deep channels in turbidite-bearing formations therefore has paleogeographic significance.

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