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Abstract

The Rader Member contains coarse, allochthonous carbonate debris deposited on low-angle slopes (<10°) basinward of a ~500 m, higher-angle (30°) foreslope (Rigby, 1953; King, 1948). Subaqueous gravity flows fill channels which have up to 40 m of relief. Bed thickness for a single flow ranges from <1 m to as much as 15 m. Some mass flows are traceable >6.5 km parallel to depositional strike and extend >17 km southeast from the toe-of-slope into the Delaware Basin. A previously undocumented, prominent basin-sloping erosion surface occurs at the base of the mass flows and truncates 55 m of section in the toe-of-slope (Fig. 1). The angle of truncation is as high as 7° in the toe-of-slope and diminishes to <1° along the basin slope.

Subaqueous gravity flows in the Rader section exhibit features which suggest deposition from debris flows, turbidity flows, and possibly from density-modified grain flows (or grain flow-debris flow (Hampton, 1979)). Features which imply a debris-flow origin include poorly sorted and graded debris, a wide range of clast sizes, chaotic orientation of clasts, matrix support, and some large rafted clasts near the top of the bed. Atypical features observed are a fine, quartz-rich sand matrix with a small amount of mud (<1%) and appreciable rounding of the clasts. Rader debris flows were competent to carry limestone boulders up to 10 m across in their longest exposed dimension.

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