Quaternary Reef Record of Differential Uplift at Luwuk, Sulawesi East Arm, Indonesia.

The coastal morphology of Luwuk (Sulawesi) is dominated by raised coral reef terraces, reaching elevations of over 400 m. A lower group of 6 to 10 terraces reach maximum heights varying between 30 and 100 m. A middle group, elevated up to 250 m, forms an 18° to 22° seaward sloping surface that is bordered by coast-parallel faults. The upper group of terraces is more than 400 m above sea level. Four reef terraces at 410, 62, 19 and 6.6 m above high tide have U/Th ages ranging from 350 ka to 67 ka and, except for the oldest terrace, can be correlated with several stages of interglacial reef growth at Huon Peninsula, New Guinea. Using the sea level curve established for the Huon reefs, uplift rates for the Luwuk area can be calculated. The highest terrace has risen at an average rate of 184 cm·ka-1. The 3 dated terraces of the lower group also indicate net uplift, but at a much lower rate, which is partially due to subsidence at 53 cm·ka-1 between 101 ka and 67 ka. Intermittent subsidence could be due to isostatic compensation and/or drag by the downthrown parts during periods of crustal relaxation in the fault zone.