--> ABSTRACT: Quaternary Evolution of Aitutaki Atoll, Cook Islands, by James R. Hein, Bruce M. Richmond, and Lisa A. Morgenson; #91038 (2010)

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Quaternary Evolution of Aitutaki Atoll, Cook Islands

James R. Hein, Bruce M. Richmond, Lisa A. Morgenson

In May and June 1986, six holes were drilled in the roughly triangular-shaped lagoon of Aitutaki Atoll; the lagoon measures about 12 km in both the maximum north-south and east-west dimensions. Three of the six holes reached volcanic basement at 30 to 35 m depth; the other holes were terminated in recrystallized limestone at 70 m, 52 m, and 30 m; basalt flows were recovered within the sedimentary sections at two of these three holes. The upper part of the basaltic basement was subaerially weathered and several basalt flows were recovered from the basement in each of these holes. The sedimentary section at four sites is predominantly reefal limestone, at one site mostly volcaniclastic muds and silts, and at the final site mostly white carbonate mud and silt and volcaniclas ic sand with tuff interbeds. Cores from each site contain some pyroclastic beds, which are younger than any of the volcanic rocks dated (about 0.8 Ma) from adjacent Aitutaki Island. Limestone samples from the cores are presently being dated by uranium-series and microfossils, but we believe the oldest rocks recovered are less than 200,000 years. Notable diagenesis of the limestone sections begins between 12 and 17 m depth and probably marks the Holocene-Pleistocene boundary. Alternating sections of tightly cemented and porous limestone mark places where seawater and freshwater diagenesis dominated. Layers of sparry calcite with crystals up to 4 cm long occur in several places. Some limestone beds are dominated by calcareous algae, others by silicosponges. The diagenesis of the limestones input of volcaniclastic debris, and ages will be used to determine relative changes in sea level.

AAPG Search and Discovery Article #91038©1987 AAPG Annual Convention, Los Angeles, California, June 7-10, 1987.