Paleoanthropologically significant South African sea caves dated to 1.1-1.0 million years using a combination of U-Pb, TT-OSL and palaeomagnetism
Deposits in sea caves found along the southern coastline of South Africa have produced a rich and detailed archaeological record of early modern humans. There is, however, little evidence for coastal cave deposits and human occupation older than MIS5e (∼120 ka). Based on the correlation of four different chronological methods we present evidence for remnant cave deposits of 1.1–1.0 Ma from the quartzite sea cliff of Pinnacle Point, near Mossel Bay. Initial uranium–thorium ages at isotopic equilibrium indicated an age of >500 ka for two flowstone layers, confirmed by uranium–lead dating of these flowstones from 1.099 ± 0.012 to 1.047 ± 0.011 Ma. TT-OSL (thermally transferred optically stimulated luminescence) provides an age of 1.02 ± 0.088 Ma for the sand grains imbedded in the tufa underlying the flowstone and 0.720 ± 0.066 to 0.665 ± 0.056 for the overlying beach sediments, producing an internally consistent age sequence centring on 1.0–1.1 Ma. The normal palaeomagnetic signal of the younger section of the flowstone is interpreted to represent the Jaramillo between 1.07 and 0.99 Ma. There is a clear hiatus in the middle of this flowstone, leading us to interpret the lower normal signal as the Punaruu event at ∼1.115–1.1051 Ma. Together these four techniques point to an age of 1.1–1.0 Ma for these cave deposits at Pinnacle Point, far older than anticipated. The persistent presence of these 1.1–1.0 Ma deposits means that the enigmatic lack of Earlier Stone Age (Acheulean) artefacts in the sea caves along this coastal region can no longer be explained entirely by the age of the caves or through removal of sediments by previous sea level highstands. We believe that these and other coastal caves from this region, if located high enough above sea level, may contain deposits of great antiquity, which could provide outstanding records of climate, environment, sea level change, and human occupation back into the early to middle Pleistocene.