Fabien Paquet

Controls on active forearc basin stratigraphy and sediment fluxes: The Pleistocene of Hawke Bay, New Zealand

Detailed, high-resolution documentation of forearc basin fi ll is scarce in the literature. In this geological and geophysical study, we investigated the Pleistocene sedimentary record of the tectonically active Hawke Bay forearc domain of the Hikurangi subduction margin of New Zealand. Interpretation of an extensive seismic-refl ection data set that is correlated with marine cores and onshore geological maps identifi es the detailed stratigraphic architecture of the last ~1.1 m.y. This analysis reveals the infl uences and interactions of tectonic deformation, climate, eustasy, and isostasy on forearc basin sedimentation. Eleven ~100 k.y. depositional sequences are recognized in the basin fi ll, thus highlighting the dominance of Pleistocene climate-eustasy on sequence development. The stacking pattern and isopach maps of sequences exhibit an overall retrogradational trend and an arcward migration of depocenters. These trends progressively develop a basinwide diachronous and composite erosion unconformity formed by the lateral succession and landward encroachment of the 12 sequence-bounding unconformities (S12 to S1). Among these, the S5 surface (ca. 430 ka) is an angular unconformity that separates major megasequences of the sedimentary record. The forearc domain evolved from a series of ridge-parallel basins to a succession of connected basins that have progressively developed around major, growing thrust-faulted ridges since ca. 430 ka. This change in basin confi guration and associated signifi cant increase of the preserved sediment fluxes occurred synchronous with the reactivation of major out-of-sequence thrusts and the completion of the mid-Pleistocene transition.