Post-obduction dismantling of the early regolith and related conglomerates in the Kopeto-Boulinda-Nepoui area (New Caledonia): a possible Lower Miocene uplift and paleolandscape - Archive ouverte HAL Accéder directement au contenu
Communication Dans Un Congrès Année : 2012

Post-obduction dismantling of the early regolith and related conglomerates in the Kopeto-Boulinda-Nepoui area (New Caledonia): a possible Lower Miocene uplift and paleolandscape

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Résumé

In New Caledonia post obduction uplift caused the erosion of the early regolith, but their timing is poorly constrained. The Nepoui Formation, on the west coast, is a witness of post-obduction deposits. This area presents stepped ferruginized surfaces from the Kopeto-Boulinda Massif to the Nepoui Peninsula, indicating a large single paleosurface slightly tilted and incised by the river system or successive planation surfaces. Palaeomagnetic analysis and petrographic study of the ferricretes capping those stepped surfaces have been performed. Samples from the Kopeto-Boulinda Massif and lower Nepoui surfaces could not be dated by paleomagnetism, except the silico-ferruginous matrix of the Nepoui conglomerate close to 10-25 Ma. This age is rather imprecise but 1) the weathering of the fluvial conglomerates fossilized by the silicification followed their deposition and 2) conglomerates are locally interstratified in Lower Miocene marine limestones. In addition the detailed petrographic study of the ferricretes confirms rearrangements of nodules and pisolites, more important in the upper parts of the toposequence, where they follow smooth upper slopes of the topography. Therefore the term of lateritic ferricretes cannot be used, as they result from the dismantling of lateritic materials capping a former landscape. The late siliceous phase has been observed locally upstream, but it is more abundant downstream. All the data can be interpreted in reconstructing a fossil paleolandscape in that part of New Caledonia triggered by a Lower Miocene uplift, responsible for the drastic erosion of oldest profiles, creation of highly incised river systems and deposition of fluvial conglomerate.
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Dates et versions

hal-00740887 , version 1 (11-10-2012)

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  • HAL Id : hal-00740887 , version 1

Citer

Brice Sevin, Caroline Ricordel-Prognon, Florence Quesnel, Dominique Cluzel, Pierre Maurizot. Post-obduction dismantling of the early regolith and related conglomerates in the Kopeto-Boulinda-Nepoui area (New Caledonia): a possible Lower Miocene uplift and paleolandscape. 34th International Geological Congress, Aug 2012, Brisbane, Australia. p. 1000. ⟨hal-00740887⟩

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