Edwards, Eriksson, K.A. and Kier, R.S. 1984: Paleochannel geometry and flow patterns determined from exhumed Permian point bars in North-Central Texas. J. Sedim. Petrol. 53, 1261-1270.
ABSTRACT
Point-bar deposits in the Clear Fork Group (Lower
Permian) of north-central Texas are exposed both in cross section and
in plan as exhumed arcuate accretionary ridges. A thin basal lag of
locally derived caliche and mudstone fragments is overlain by a 2 to
3 m thick epsilon cross-stratified unit which fines upward from very
fine sandstone at the base to mudstone at the top. Sandstone beds in
the epsilon units are almost entirely cross-laminated and were deposited
by straight-crested ripples, most of which are oriented at 40° to 65° to
the main channel direction.
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The Clear Fork point bars were deposited
by small, variable-discharge, perennial streams with high
sinuosity. The straight-crested ripples migrating on the
point bar surfaces are oblique rather than perpendicular
to the near-bed flow direction. The cause of such considerable
obliquity was primarily a large transverse gradient in
local downstream sediment transport rate and, to a lesser
degree, components of transverse near-bed fluid velocity
due to helicoidal flow.
©by Marc B. Edwards
Consulting Geologists, Inc