Notes on the Late Cenozoic history of the Kai Islands, Eastern Indonesia

Abstract

Field and laboratory data on Cenozoic deposits of the islands of Kai Kecil and Kai Besar provide broad age-depth constraints, but are insufficient for a detailed geohistory analysis to determine the timing, rate and magnitude of vertical movements in the eastern segment of the outer Banda Arc. Yet, a tentative reconstruction of the vertical movements of the islands could be made. On Kai Besar, lower bathyal-upper abyssal Middle-Late Eocene calcilutites and marls, in combination with Upper Oligocene and Lower-Middle Miocene middle bathyal deposits record an Eocene-Miocene passive margin fill. Kai Besar must have emerged sometime during the Late Miocene to Pliocene-Pleistocene, associated with the development of the Banda Arc thrust belt. The absence of elevated coral reefs, which are present on surrounding islands, suggests that the island is presently subsiding. On Kai Kecil, Late Pleistocene middle bathyal bioclastic turbidites and marls are nowadays situated just above sea level documenting uplift rates up to 500 cm/ka. In contrast to Kai Besar, Kai Kecil has 4-5 elevated reefs, unconformably overlying the Pleistocene core, showing that the island continues to rise.