Abstract
Kita-daito-jima is a carbonate island lying on a lithospheric bulge of the Philippine Sea Plate. We provide a formal stratigraphic description of the coral reef deposits on this island. The deposits comprise the Daito Formation (>2.0 Ma) overlain by the Kaigunbo Formation (∼12.3 ka) . The Daito Formation is divisible into three units. Unit 1 is dominated by coral framestone rich in massive corals and crops out in the interior basin. Unit 2, resting unconformably on Unit 1, is subdivided into two subunits; lower Subunit 2a and upper Subunit 2b. The lower subunit comprises reef-core facies that constitutes the main body of peripheral rim and backreef facies exposed at the cliffs lining the interior basin. The reef-core facies is represented by coral framestone associated with coral bafflestone. The lower backreef facies consists mainly of rudstone and the upper backreef facies is composed chiefly of coral framestone/bafflestone frequently containing Halimeda segments. Subunit 2b, cropping out around the peak of this island, is constructed by coral framestone and bioclastic packstone. Unit 3 is exposed sporadically on the east coast and unconformably overlies the reef-core facies of Subunit 2a. This unit consists of cross-bedded bioclastic packstone associated with coral framestone. Stratigraphic succession, configuration of lithofacies, and coral assemblages indicate that Unit 1 formed in a table reef without lagoonal environment and that thick atoll deposits accumulated on karstified limestone during the deposition of Subunit 2a. Then, the atoll may have been progressively degraded and no distinct reefs formed at the deposition of Subunit 2b. Shoal and coral patches were scattered on eastern part of the island during the deposition of Unit 3. The Kaigunbo Formation occurs abutting on the coastal cliff at elevations less than llm and consists of framestone, which indicates limited fringing reef formation at the last interglacial stages.
