Geoarchaeology of Tonga: Geotectonic and geomorphic controls

Ancient settlement patterns in central Tonga, at the southeastern limit of Lapita expansion into Remote Oceania similar to 3 ka, were conditioned by island geomorphology as controlled by spatial geotectonic features and temporal changes in relative sea level on island coasts. Volcanic islands provided lithic resources, but human populations were concentrated on nonvolcanic forearc islands underlain by limestone covered by airfall tephra blankets that weathered to form rich agricultural soils and eroded to provide terrigenous sand for ceramic temper. The forearc islands lie along the Tonga platform, a linear tract of shoals uplifted diachronously by subduction of the buoyant Louisville Ridge at the Tonga Trench. Multiple transverse structural discontinuities break the forearc into discrete structural blocks, some tectonically stable during late Holocene time but others undergoing postuplift subsidence. Understanding the paleoenvironmental settings of Tongan archaeological sites requires reconstructing the contrasting geologic histories of different forearc island clusters. (c) 2007 Wiley Periodicals, Inc.