Geophysical signatures and sand thickness at Bestwood Farm, South Africa

English Abstract:

The Bestwood Valley, an archaeological complex located near the town of Kathu, South Africa, covers an area of about 700 by 1200 m and is dated to the Early Stone Age based on the type varieties of local handaxes, blades, and other lithic tools. The valley consists of ironstone hills of cobble sized clasts (many of which are the archaeological artefacts) grading into a flatter area of red siliceous sands blown in from the Kalahari desert. Our study attempts to compare different geophysical data sets, and depth from two ground-truthing excavations, collected in summer 2014. Analysis of a dozen 500 m long GPR lines across the valley give a good sense of sand thickness in the northern part of the valley; the sand becomes too thick in the southern part to produce radar reflections. Seismic refraction data were collected using 4.5 Hz vertical geophones on two crossing 100 m lines and show clear first arrivals. A magnetic walking survey shows very large (>1000 nT) variations in total field amplitude over short (10s of meters) distances near the edges of the sand fill, these variations become less pronounced towards the center of the valley. We are currently working on determining how signatures of the three different methods may relate to the sand thickness, and how the magnetic amplitude and wavelength may be used in areas where GPR becomes ineffective.