The Timing and Environmental Significance of Late Quaternary Linear Dune Development in Western Zambia

Abstract

Optical luminescence dates for 19 samples from the degraded linear dune field of western Zambia indicate multiple periods of regional dune building for the late Quaternary, 32,000–27,000, 16,000–13,000, 10,000–8000, and 5000–4000 yr ago. These dates show that the last glacial maximum was not the only time when dune construction, commonly linked to marked aridity, occurred in central-southern Africa during the late Quaternary. Whereas rainfall significantly less than today's ca. 1400 mm yr −1 is a prerequisite for dune construction in the area, adequate sediment supply also determines dune construction and preservation, so that dune building cannot be simply and singularly linked to marked aridity. The Zambezi River system is proposed as an important source of dune sediments, with the nature of linear dune activity explaining why stacked sediments preserve several phases of dune formation. Chronologies of dune construction in western Zimbabwe and the southwest Kalahari are in broad agreement with our Zambian chronology and support a model of rainfall shifts along a SW–NE gradient, with some notable disparities. These are probably a function of interregional sediment supply differences, the number of samples used to delimit constructional periods, and the multicausal nature of forcing mechanisms.