DEVELOPMENT OF AN EOCENE SHALLOW CARBONATE PLATFORM IN A TECTONICALLY ACTIVE REGION: THE UITOE LIMESTONE OF NEW CALEDONIA

The Uitoe Limestone of western New Caledonia is a 26.6 m thick succession of shallow water Eocene limestones associated with a succession of Paleocene and Eocene age deep water limestones (the Globigerina Limestones of earlier workers). The Uitoe Limestone sits unconformably upon deformed Triassic volcaniclastic sandstones (greywackes) and is overlain by an olistostromal chert breccia of late Eocene(?) age. The Uitoe Limestone is geographically restricted cropping out in and around Baie de Saint-Vincent near the town of Boulouparis. The Uitoe is considered to be late middle Eocene (Bartonian) in age based on the macroforaminiferal fauna.

The succession in the Uitoe Limestone consists of a coarse conglomerate bed above the transgressive surface followed by a series of cross-bedded bioclastic mudstone and grainstones from the basal conglomerate to 7.2 m. This unit is overlain by a foraminiferal-algal wackestone. These wackestones contain a high diversity macroforaminiferal fauna including Discocyclina, Heterostegina, and Nummulites among others. The wackestones are overlain by a series of grainstones and rhodolith floatstones interbedded with a polymict breccia. The wackestone, grainstones, rhodolith floatstones and breccias are found to a thickness of 22.6 m. The Uitoe Limestone sequence is capped by poritid coral bafflestones. The various taxa of macroforaminifera are present within the entirety of the 26.6 m section. Glauconite increases in abundance through the lower part of the section comprising 20% of the rock at 3.5 m above the base of the Uitoe. Over the next 3 m, the glauconite percentage decreases to trace amounts. There are only trace amounts of glauconite present in the remaining 20.1 m of the section.

The record of the Uitoe Limestone represents a transgressive sequence on a carbonate platform followed by sediment progradation. Further work on the biostratigraphy of the macroforaminifera in the Uitoe will enable correlation to the global geochronologic scale. This should permit the development of a more complete picture of sedimentologic and paleocologic events during the middle Eocene of New Caledonia and their relationship to tectonics of the region.