Lagoonal to reefal ostracod assemblages from Holocene and Recent deposits, Chesterfield Islands and northern New Caledonia (southwestern Pacific)

摘要

As part of a preliminary study on growth and evolution of Holocene reefs from northern New Caledonia and Chesterfield Islands (S.W. Pacific), micropalaeontological investigations on ostracod contents were carried out. The cored material from reef-flat and back-reef zones is composed of skeletal deposits. Bioclastic sands sediments from various reef environments contain ostracod-rich assemblages. Modern associations from the back- reef and lagoonal areas were also analyzed, to serve as ecological analogues. Fifty-three species have been recognized, most of them already known from other areas of the Pacific and Indian Oceans. Using statistical methods, two (paleo)environmental zones can be distinguished: a)lagoonal to back-reef slope, b)inner to outer reef flat zone. In every respect, each zone is characterized by distinctive ostracod assemblages. Autecological data available on Recent living taxa suggest some paleoecological preferences of Holocene assemblages in similar areas. Ostracod assemblages are highly diverse in modern lagoons, the main taxa belonging to Cytheracea (dominant) and Bairdiacea with a few Cypridacea; they are quite diverse in the Recent and Holocene inner reef slopes and poorly represented within the reef flat zone, probably in response to variations in physico-chemical conditions, especially wave-energy. Considerations about relationships between composition of ostracod assemblages through time and previous data on sea-level changes are discussed.