Reply to discussion by D. I. Cole

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South African Journal of Geology

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Geological Society of South Africa


University of Cape Town

We strongly disagree with D.I. Cole’s contention that our use of strontium isotopes has not lead to any meaningful improvement in the chronostratigraphy of the Prospect Hill Formation exposed in the Tabakbaai Quarry (Franceschini and Compton, 2004). Interpretation of the complex stratigraphy of the West Coast has suffered from a lack of chronostratigraphy. The integration of radiocarbon, uranium disequilibrium and luminescent dating has greatly improved our understanding of upper Pleistocene and Holocene deposits of the West Coast (Roberts and Berger, 1997; Felix-Henningsen et al., 2003; Compton and Franceschini, 2005). The challenge of the beach and aeolian deposits of the Prospect Hill Formation at Tabakbaai Quarry is that they are too old to date using these methods and so we applied the Sr isotope dating method because it has proved to be extremely useful in sorting out the complex late Cenozoic depositional history of the outer shelf offshore of Cape Columbine (Compton et al., 2004; Wigley, 2005). Unfortunately the resolution of the Sr-derived ages we obtained is relatively poor mostly because the marine Sr isotope curve flattens out in the late Miocene (Farrell et al., 1995)