Constraints on the amplitude of late Pliocene eustatic sea-level fluctuations: New evidence from the New Zealand shallow-marine sediment record

Abstract

Since 2.5 Ma, global eustatic sea-level fluctuations have driven recurrent transgressions and regressions of the shoreline across the world9s continental shelves. The resulting shallow-marine sedimentary record is cyclothemic, each cyclothem corresponding to a single Milankovitch climatic or sea-level cycle. Wanganui Basin, New Zealand, contains one of the most complete late Neogene shallow-marine stratigraphic records in the world in the form of a continuous cyclostratigraphy representing every 41 k.y. and 100 k.y. sea-level cycle since oxygen isotope stage 104 (ca. 2.6 Ma). A eustatic sea-level curve is derived for oxygen isotope stages 100–74, from high-resolution faunal paleobathymetric, subsidence, and stratigraphic analyses of 12 superposed, shallow-marine cyclothems in the Rangitikei River section, Wanganui Basin. Between 2.6 and 2.0 Ma minimum amplitudes of eustatic sea-level fluctuations ranged from 110 ± 20 m (stages 100–99) to 25 ± 10 m (stages 76–75). These independently derived fluctuations are ∼20% larger than previous estimates, and imply greater climatic variability during the onset of major Northern Hemisphere ice ages.