--> Abstract: Slope Channels and Fan Channels from Eocene Tyee Formation, Oregon, by Manasij Santra, Ronald J. Steel, and Mike Sweet; #90078 (2008)

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Slope Channels and Fan Channels from Eocene Tyee Formation, Oregon

Manasij Santra1, Ronald J. Steel1, and Mike Sweet2
1Jackson School of Geosciences, University of Texas at Austin, Austin, TX
2Exxonmobil Upstream Research Company, Houston, TX

Eocene Tyee Formation in Southern Oregon shows a range of depositional environments including shelf deltas, deepwater slopes and basin-floor fan complexes. Previous workers have recognized three vertically juxtaposed members within Tyee; from bottom these are Tyee Mountain Member - predominantly fan complexes, Hubbard Creek Member - predominantly slope deposits and Boughman Member - shelf deltaic deposits. There is still some debate about the time-space relationship between basin-floor fans, slope channels and shelf deltas of the Tyee Formation. Sand-filled channels have been observed within both slope and basin-floor fan deposits of the Tyee Formation. The Slope channel-fills contain large volume of fine-grained sediments. Individual channel-fill sandbodies have a blocky to minor fining-upward trend. The slope channel-fill sands are typically encased within siltstone-mudstone heterolithic units. Slope channel-fills show rapid lateral facies changes and often, significant basal erosion, possibly indicating a more confined nature. Slope channel-fills commonly show silt-shale drape above major erosion surfaces - an indication of bypass. The fan channel-fills are characterized by thick (5-15m) structureless, blocky sands with erosive bases. The fan channel-fills appear to be more amalgamated and contain small proportions of fine grained sediments. Minor heterolithic units associated with fan-channel-fills have cm to 10s of cm thick fine sandstone units inter-layered with silt and clay. The channels within fan complexes can be recognized by the presence of erosion surfaces and variations in bedding plane dip. The latter variations in bedding plane dip are small in magnitude but very distinct. As a whole, the slope channels are distinguishable from the fan channels by their more confined nature, lesser degree of amalgamation and more indications of sediment bypass.

 

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas