The luminescence chronology of dune development on the Maputaland coastal plain, southeast Africa

Abstract

Geomorphological and lithostratigraphic mapping of dune systems on the Maputaland coastal plain of northeastern KwaZulu-Natal Province, South Africa has defined the relative-age relationships between the complex pattern of Quaternary parabolic and hummocky dunes, sand megaridges and the composite coastal barrier dune cordon. Here infra-red-stimulated luminescence (IRSL) ages are presented in the context of regional stratigraphic relationships and serve to bracket the period of accumulation of the main dune systems. The luminescence ages challenge the widely held belief that the north–south aligned dune pattern reflects a coastward-younging sequence. The framework of ages highlights the spatial variations in dune mobilization and long accretion history on some dune forms. Weathered dune and interdune wetland sediments spanning from prior to marine isotope stages (MIS) 11 and up to MIS 7 underlie the coastal plain. At least two generations of decalcified aeolianite of MIS 5 and 4 form the core of the complex coastal barrier dune. On the coastal plain, frequent sand mobilization events during MIS 3–2 resulted in the development of discrete complexes of highly extended, northward directed parabolic dune systems and reworking of the crest of the central sand megaridge. The luminescence-dated dune mobilization history brackets the period of formation of interdune and lacustrine peat and diatomite deposits. During the Holocene marine transgression at least four laterally extensive, complex transverse ridges of coalesced ascending parabolic dunes accreted against the aeolianite core of the coastal barrier. Polyphase dune formation and remobilization is discussed in the context of the regional groundwater and vegetation responses to global climatic changes, wind regimes and glacio-eustatic sea-level fluctuations.