Daily cycles in coastal dunes

摘要: Abstract Daily cycles of summer sea breezes produce distinctive cyclic foreset deposits in dune sands the Texas and Oregon coasts. In both areas winds are strong enough to transport sand only during part day, reach a peak afternoon, vary little direction period transport. Cyclicity is made evident by variations type sedimentary structure, texture, heavy-mineral content sand. Some up entirely one basic which character structure varies cyclically; for example, angle climb climbing-wind-ripple may cyclically. Other characterized alternations two or more structural types. Variations concentration fine-grained heavy minerals, account most striking cyclicity, arise mainly because segregation on wind-rippled depositional surfaces: where ripples at low angles, coarsegrained light accumulate preferentially ripple crests, tend be excluded from local deposit. thickest best developed small dunes least recognizable near bases large dunes.