Reef and island formation and late Holocene sea-level changes in the Chagos Islands

Some of the most interesting geological features of the Chagos and other Indian Ocean atolls are the _reef flats?, which are emerged conglomerate platforms extending up to 100 m or more to seawards. To determine their ages and rate of horizontal growth we dated fossil corals from various islands using U/Th mass-spectrometry. Seven out of eleven coral ages cluster closely between 2.8 to 3.8 ka B.P. This is similar to other Indian Ocean islands. A qualitative model discusses how these platforms were formed in the light of the generally decreasing Indian Ocean sea level over the last 6.5 ka. The cluster of coral ages found here is interpreted to reflect intense coral growth and horizontal reef progradation during relatively stable sea level above its present position, in a time of generally warmer climate from about 2.8 to 4.3 ka B.P. Only a few scattered coral ages are older (6.5 to 4.3 ka B.P.) or younger (2.8 ka B.P. to present) than the main group. The scattered coral ages may reflect periods of rapid sea level oscillations, or may be from fossil corals displaced from their original position. The general geological framework for the Chagos Archipelago is first explained.
Eisenhauer A , Heiss G , Sheppard Charles , Dullo W .
geology, reef flats, mass-spectrometry, fossil corals, geological framework, reef age