Magneto-biostratigraphic constraints of the Eocene micrite-calciturbidite transition in New Caledonia: tectonic implications

We conducted an integrated magneto-biostratigraphic study of a 37m-thick composite section exposed at two sites near Noumea (New Caledonia). The section contains a transition from pelagic micrite to terrigenous-rich calciturbidites. This transition, observed regionally in coeval records of New Caledonia, marks a shift from pelagic sedimentation on a stable continental submarine plateau to turbidite deposition indicating development of a slope in a convergent tectonic regime. The studied section spans magnetic polarity Chrons C22r to C20r, calcareous nannofossil zones CNE5 to CNE10, and radiolarian zones RP9 to RP11 (49.5 to c.44 Ma), and the micrite-turbidite transition occurred around 45.3 Ma (early middle Eocene). This transition could be the onshore correlative of a regional switch from tectonic extension to compression, which has been inferred from analysis of new seismic profiles acquired for the Tasman-northern Zealandia area, and that has been interpreted as precursor of the Tonga-Kermadec subduction initiation.