Neogene terrestrial sediments: a record of the post-obduction history of New Caledonia
Résumé
The poorly studied iron-rich terrestrial sediments, referred to as the Fluvio-lacustrine Formation, that crop
out in the southern part of the Grande Terre of New Caledonia document the last 25 Ma of the
geological history of the island. The age of this formation, which is mainly derived from the erosion of an
ultramafic regolith, is not tightly constrained yet; however, it has recorded several episodes of postobduction
erosion and sedimentary infill preceded and followed by weathering and reactivated
erosion. A correlation with early Miocene slab break-off, which may have triggered a first stage of
erosion marked by coarse conglomerate, is suggested. Thereafter, sediments filled topographic lows
and were in turn weathered during an interval of tectonic quiescence. Finally, Holocene sea-level drop
and southward tilt of southern New Caledonia, owing to the involvement of eastern Australian Plate in
the New Hebrides (Vanuatu) subduction zone, locally changed the drainage pattern and deeply
eroded the sediments.