Early Onset of Holocene Reef-Island Evolution at Tarawa Atoll, Gilbert Islands, Kiribati

Abstract

The geomorphic development of reef islands in the Pacific coral atolls may have important implications for human migration and settlement in remote Oceania. We examined the geomorphic development of an atoll reef island at the Tarawa Atoll, Gilbert Islands, Kiribati. The island is composed mainly of unconsolidated carbonate sand, and the emergence of the island occurred at ca. 4600 cal yr BP at the oceanward side, under rising sea levels that reached ~0.9 m higher than that at the present. The main body of the island formed rapidly between ca. 4600–4200 cal yr BP under higher and slightly rising sea levels. This early development could have resulted from the low-energy setting of the Tarawa Atoll, which could have allowed the accumulation of sand-sized sediments. Our study is a valuable case study of atoll reef island development in a low-energy setting, and constrains the basis for human settlement in the Gilbert Islands of Kiribati.