Reef-island accretion and soil development on Makin, Kiribati, central Pacific

The late Holocene accretionary history of reef islands on Makin, the northe rnmost table reef of the Gilbert atoll chain, western Kiribati, has been re constructed based on conventional radiocarbon dating of coral shingle and b ulk sand samples, and AMS radiocarbon dating of individual grains. Makin is geomorphologically and sedimentologically simple, comprising one main isla nd with only a minor residual lagoon, and composed of sand dominated by the reef-flat foraminifera Calcarina spengleri, Amphistegina lobifera and Bacu logypsina sphaerulata. Deposition commenced in mid platform around 2500 yea rs ago; in situ fossil coral (Heliopora) dated at 2400 +/- 80 years BP indi cates that sea level was 0.4-0.5 m above present at that time. Progradation occurred progressively to westward at a relatively constant rate of 200-30 0 m ka(-1). However, progradation was interrupted on the eastern side by la goon encapsulation around 1400 years ago. The soil and vegetation character istics are uniform over most of the reef islands as a result of clearance a nd the planting and maintenance of coconuts, and do not reflect reef-island depositional history. Remnant stands: of Pisonia forest, with an associate d phosphatic soil, are not related to any particular geomorphological featu re, or period of deposition. The reef islands are continuing to accrete as a result of production of foraminifera on the reef flat. (C) 2001 Elsevier Science B,V. All rights reserved.