Pre-obduction records of Eocene foreland basins in central New Caledonia: an appraisal from surface geology and Cadart-1 borehole data.

The Bourail Anticline in central New Caledonia has been a target for petroleum exploration since the 1950s. It is a broad structure in which a 4-km-thick pile of Eocene turbidite (Eocene Bourail Flysch) is exposed. The Cadart-1 exploration borehole (1930 m deep) was drilled on the anticlinal axis in 1999, intersecting the Paleogene and underlying Late Cretaceous sedimentary rocks. A sedimentological, stratigraphic and provenance analysis is presented. Volcanic debris appears progressively in the upper part of the flysch, becoming predominant upwards along with the intercalation of upward-thickening and -coarsening debris flow breccia. Clinopyroxene and basalt clasts in the upper part of the flysch were derived from enriched tholeiite (E-MORB) of the Poya Terrane. The Eocene paleogeography can be interpreted as a foreland basin system with a depocentre close to the area of Bourail Anticline, an accretionary complex to the northwest and a forebulge to the southeast. This system migrated southeastward through New Caledonia from the Paleocene to the Late Eocene. [ABSTRACT FROM AUTHOR]