Chapter 7 Post-obduction evolution of New Caledonia

Abstract

The post-obduction formations of Grande Terre, New Caledonia, comprise igneous intrusions, regolith cover, and marine and terrestrial sedimentary rocks. Two restricted Late Oligocene granitoid bodies are intruded into the Peridotite Nappe and its substrate in the south of the island. Thick regolith cover developed over the Peridotite Nappe from the Late Oligocene or earlier. The Népoui Group comprises Late Oligocene–Early Miocene mixed marine carbonate and siliciclastic deposits. It mainly reworks the Peridotite Nappe and its regolith cover. Its development pattern is mainly controlled by tectonic uplift and subsidence. The Gwa N'Doro Formation on the eastern coast and the Fluvio-lacustrine Formation in the south are remnants of the Miocene–Present river network. Offshore, thick Oligocene to Neogene sedimentary successions are imaged by seismic surveys on the margins of Grande Terre, although these successions have not been drilled and remain undated. Several dredges have recovered shallow Miocene sedimentary rocks, indicating substantial Neogene subsidence. Quaternary formations are represented inland by aeolianite, vertisols and calcrete and offshore by the large barrier reef–lagoon complex, the onset of which is dated at c. 400 ka. This chapter discusses the different models proposed for the post-obduction evolution of Grand Terre.

Chapter 1 Introduction to New Caledonia: geology, geodynamic evolution and mineral resources

“…Chapter 7 considers the post-obduction evolution of New Caledonia (Sevin et al 2020). The post-obduction formations in New Caledonia comprise a variety of disparate and areally restricted Neogene geological units.…”

Origin and Composition of Ferromanganese Deposits of New Caledonia Exclusive Economic Zone

“…The Middle Miocene is also the time when the North-East dipping Vanuatu subduction zone initiated along the Vitiaz Lineament and rolled back to its present-day position [36,57]. The subduction of the Australian plate under the Vanuatu Arch induces a flexure of the downgoing lithosphere and hence uplift and extensional tectonics as far as southern Grande Terre [58,59].…”

Leaves in Iron Oxide: Remarkable Preservation of a Neogene Flora From New Caledonia

“…Within the fluvio-lacustrine sediments, and later within the soils, concretionary ironstone horizons (duricrusts) formed in situ with the precipitation of hematite and goethite cements around existing grains, filling voids and greatly reducing the porosity and permeability of the horizon (Sevin et al 2011;Folcher et al 2015). Duricrusts commonly contain root casts and trunks preserved in growth position (Folcher et al 2015;Sevin et al 2020).…”

“…Many of these deposits are concealed beneath the recent regolith, but several have been eroded and provide good exposure (Folcher et al 2015). The timing of their deposition is unknown, as the iron-oxide dominated sediments are not suitable for radiogenic dating, lack index fossils, and paleomagnetic dating techniques reveal ages ranging from latest Oligocene to Holocene Folcher et al 2015;Maurizot et al 2020;Sevin et al 2020).…”