Print this pageBasin Floor Fan and Channel-Levee Complexes, Permian Bell Canyon Formation
BARTON, MARK D.
The middle Permian Bell Canyon Formation is composed of cyclically interbedded sandstones, siltstones, and organic-rich siltstones. Although it has long been recognized that laterally extensive, organic-rich siltstones, interpreted as marine-condensed sections, subdivide the Bell Canyon Formation into a number of genetic stratigraphic units, processes of deposition remain controversial. Stratal relationships within a single genetic unit exposed in Culberson County, Texas, suggest that sandstones were deposited by turbidity currents during the progradation, aggradation, and retrogradation of a submarine fan and channel-levee system.
A basal organic-rich siltstone is conformably overlain by thin beds of laminated siltstones and massive to normally graded, fine sandstones that coarsen and thicken upward. The succession, as much as 10 m thick, has a broad sheetlike geometry that extends beyond the limits of the outcrop. This basal succession is locally eroded by a series of vertically and laterally stacked, lens-shaped sandstone bodies that are up to 20 m thick and 200 to 300 m wide. These sandstones have decimeter-thick sets of low-angle cross-strata that climb vertically or migrate basinward. The lens-shaped bodies can be traced to the south for 5 km and are flanked by 1- to 6-m-thick, upward-fining successions of thinly bedded, ripple-laminated siltstones and sandstones. The flanking successions thin and fine away from the lens-shaped sandstones over a distance of a few hundred meters and are conformably overlain by another organic-rich siltstone. Basal sandstones are interpreted to be deposited by unconfined flows to build the floor on the lower to middle portion of a submarine fan. The overlying lens-shaped sandstone bodies and laterally adjacent ripple-laminated siltstones are interpreted to be deposited by a system of channels and levees on the middle to upper portion of this fan.