The highest of these surfaces (A0) occupies the northwestern corner of the study
area at 13.9 ± 1.6m, and has beach ridges and frequent longitudinal dunes (Suppl. Fig. 1a) formed on it. Based on SRTM elevation data, two successively lower surfaces (A1 and A2; Suppl. Fig. 1a, b) occupy elevations around 9.0 ± 1.6 m and 7.3 ± 1.5 m, respectively,and locally exhibit remnants of paleochannel morphology(Suppl. Fig. 1c). A0eA2 have strong reddish-brown surface colour pointing to significant weathering and the existence of welldeveloped surface soils.