Primary structures of a seif dune and associated deposits in Libya

The seif dune near Sebhah oasis is largely composed of round, well-sorted, fine to coarse sand forming large-scale cross strata dipping at high angles in opposite directions. The interdune sand is consistently less well sorted with horizontal laminae or low-dipping strata. In the adjoining area clay, silt, and lag gravels, as well as sand, poorly sorted, form low-angle to horizontal strata. Differentiation of fossil seif (longitudinal) from fossil barkhan dunes should be possible by an analysis of dip directions.