Neogene Lithofacies Evolution on a Small Carbonate Platform in the Loyalty Basin, Mare, New Caledonia
Donald F. McNeill, Andrzej Pisera, 2010. "Neogene Lithofacies Evolution on a Small Carbonate Platform in the Loyalty Basin, Mare, New Caledonia", Cenozoic Carbonate Systems of Australasia, William A. Morgan, Annette D. George, Paul M. (Mitch) Harris, Julie A. Kupecz, J. F. (Rick) Sarg
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The succession of biofacies recorded in a small carbonate platform (Maré, ∼ 40 km diameter) in the Loyalty Islands, New Caledonia, is used to evaluate the geological and paleoenvironmental evolution of the platform. The depositional succession shows a distinct change in biotic assemblages across a subaerial discontinuity at the Miocene-Pliocene boundary. This change from an underlying late Miocene fringing reef and rhodolith shelf built around the volcanic core, to a thin bed (∼ 2 m) of early Pliocene foraminifera-algal (foralgalith) macroids that forms the base of a massive coral-dominated atoll. The rhodolith facies is dominated by coralline red algae, whereas the foralgaliths contain abundant sessile acervulinid foraminifera, some crusts of coral, and minor coralline red algae. This foralgalith macroid composition indicates initial deepening before a switch to coral-dominated biota that formed the steep-sided atoll rim. These new data and existing petrographic evidence suggests a sequence of marine cementation of the rhodoliths followed by subaerial exposure and shoreline erosion around the platform rim. Subsequently the platform was reflooded in the early Pliocene, partially drowned, and recovered with the deeper-water foralgalith facies followed by the establishment of a massive coral atoll. This platform-atoll evolution closely reflects eustatic sea-level changes and local tectonic uplift related to lithospheric flexure. A switch to a coral-dominated atoll in the Pliocene likely reflects a (global?) trend of decreased coralline red algae species richness, improved water quality, and the reestablishment of photic-zone conditions more favorable to warm-water carbonates. The combination of refined age control integrated with biotic changes provides sufficient sensitivity of the carbonate facies to record local tectonic changes, ecologic changes, and eustatic events. These results provide calibration of the lithofacies successions that may occur on small, tectonically active tropical Pacific platforms.
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Cenozoic Carbonate Systems of Australasia
The Cenozoic carbonate systems of Australasia are the product of a diverse assortment of depositional and post-depositional processes, reflecting the interplay of eustasy, tectonics (both plate and local scale), climate, and evolutionary trends that influenced their initiation and development. These systems, which comprise both land-attached and isolated platforms, were initiated in a wide variety of tectonic settings (including rift, pas-sive margin, and arc-related) and under warm and cool-water conditions where, locally, siliciclastic input af-fected their development. The lithofacies, biofacies, growth morphology, diagenesis, and hydrocarbon reser-voir potential of these systems are products of these varying influences. The studies reported in this volume range from syntheses of tectonic and depositional factors influencing carbonate deposition and controls on reservoir formation and petroleum system development, to local studies from the South China Sea, Indonesia, Kalimantan, Malaysia, the Marion Plateau, the Philippines, Western Australia, and New Caledonia that incor-porate outcrop and subsurface data, including 3-D seismic imaging of carbonate platforms and facies, to un-derstand the interplay of factors affecting the development of these systems under widely differing circum-stances. This volume will be of importance to geoscientists interested in the variability of Cenozoic carbonate systems and the factors that controlled their formation, and to those wanting to understand the range of po-tential hydrocarbon reservoirs discovered in these carbonates and the events that led to favorable reservoir and trap development.