Sedimentology in the Southwestern Lagoon of New Caledonia, SW Pacific

Abstract

The southwestern lagoon of New Caledonia belongs to a large reef complex. It can be divided into coastal bays and a true coral reef lagoon which includes from the shore to the open sea: a coastal channel, a submerged coral plateau with cay reef flats, and a back reef area limited by a barrier reef line. During each tide the flood enters by the southeast part of the lagoon through the passes, and above the barrier reefs. The passes play a prominent role during the ebb tide. Resulting tidal currents added to the influence of the trade winds are one of the main factors playing on sediment distribution. The color of sediments, their chemical composition and size distribution and the constitution of bioclasts show that three sedimentary stocks are present in the lagoon. The first one of medium size (M_d = 0.5 mm) exists in almost every part of the lagoon. It is replaced by a second one, finer (M_d = 0.063 mm) and mostly of continental origin within the coastal bays. This stock is spread out in the coastal channel and the submarine valleys. The last one (M_d = 0.125 mm), which can be found near the barrier reef area is poor in large living Formanifera, The erosion of the barrier reef during the last 3,000 years might have produced this latter stock.