Abstract:

An exceptional sequence of raised coral reef terraces is visible at Cape Laundi, on the north coast of the island of Sumba, in the Savu Sea, in which at least eleven terraces wider than 100 m, six of them even being over half a kilometer wide, are geomorphologically distinguishable between an ancient patch reef now at +475 m and the present sea level. ESR date estimations of almost unrecrystallized corals, most of them in situ, make possible a tentative identification of the terraces corresponding to isotope Stages 15 (ca. 600 ka ago) and 9 (ca. 330 ka ago). When the uplift trend deduced from the present altitude of dated terraces (0.49 ± 0.01 mm/yr) is extrapolated to the whole raised section, most geomorphological features appear to correspond to interglacial stages of the astronomically calibrated oxygen-isotope record, up to stage 27 (ca. 0.99 Ma), beyond the Matuyama/Jaramillo geomagnetic boundary. The upper terraces would in this case be twice as old as previously estimated (ca. 0.5 Ma). Main terraces seem to correspond to high sea levels at certain interglacial stages and substages, but in some cases the action of low sea levels at glacial stages cannot be ruled out. For terraces between 30 and 70 m in altitude, Th/U and ESR dates reveal that aragonitic corals at similar elevations may differ in age as much as 100 ka; this can be explained by taking into account a polycyclic origin for several terraces, reconstructions available of changes in the eustatic sea level during the last 250 kyr, and the fact that coral reef development may have been scattered at some periods only, without totally covering subjacent, older formations. The Sumba sequence of marine terraces at Cape Laundi is among the longest and most complete for the past million years reported in the literature. Its relatively good state of preservation will probably give impetus to a number of new studies on the chemical, physical, isotopic, morphological, palaeoclimatic, pedological, ecological and diagenetic changes which have occurred during the past one million years.