COLLUVIAL FAN GRAVELS, DEPOSITIONAL ENVIRONMENTS AND LUMINESCENCE DATING: A KAROO CASE STUDY

ABSTRACT

The headwater basin of the Klein Seekoei River to the west of the Great Escarpment displays evidence of multiple episodes of deposition of colluvial and fluvially derived sediments. The earliest depositional phase is represented by deeply weathered, calcretised gravel deposits which were likely emplaced by debris flow and fluvial processes in the form of a fan. These deposits were subsequently buried by finer-grained, largely unconsolidated sediment, with much of this emplacement occurring during the Holocene, and an ongoing phase of sediment transfer from hillslopes into the drainage system. A chronology for the Holocene emplacement has been established, and current sediment dynamics are the subject of ongoing research. The extent, emplacement and chronology of colluvial gravels situated landward of the Great Escarpment is poorly understood. This paper examines the depositional environment of the colluvial gravel fan and reviews the problems associated with applying optically stimulated luminescence techniques within the context of previous attempts to date colluvial sediments in South Africa.