Constraints on the amplitude of Mid-Pliocene (3.6–2.4 Ma) eustatic sea-level fluctuations from the New Zealand shallow-marine sediment record

Abstract

Ice-volume calibrations of the deep-ocean foraminiferal δ 18 O record imply orbitally influenced sea-level fluctuations of up to 30 m amplitude during the Mid-Pliocene, and up to 30 per cent loss of the present-day mass of the East Antarctic Ice Sheet (EAIS) assuming complete deglaciation of the West Antarctic Ice Sheet (WAIS) and Greenland. These sea-level oscillations have driven recurrent transgressions and regressions across the world's continental shelves. Wanganui Basin, New Zealand, contains the most complete shallow-marine Late Neogene stratigraphic record in the form of a continuous cyclostratigraphy representing every 41 and 100 ka sea-level cycle since ca 3.6 Ma. This paper presents a synthesis of faunally derived palaeobathymetric data for shallow-marine sedimentary cycles corresponding to marine isotope stages M2–100 ( ca 3.4–2.4 Ma). Our approach estimates the eustatic sea-level contribution to the palaeobathymetry curve by placing constraints on total subsidence and decompacted sediment accumulation. The sea-level estimates are consistent with those from δ 18 O curves and numerical ice sheet models, and imply a significant sensitivity of the WAIS and the coastal margins of the EAIS to orbital oscillations in insolation during the Mid-Pliocene period of relative global warmth. Sea-level oscillations of 10–30 m were paced by obliquity.