Pliocene glacial-interglacial sea-level change

• Main Author: Grant, Georgia
• Format: Thesis
• Language: unknown
• Published: 2019
• Subjects: Marine geoscience; Sedimentology; Stratigraphy (incl. biostratigraphy; sequence stratigraphy and basin analysis); Pliocene; Climate; Sea-level change; Sea-level; School: School of Geography; Environment and Earth Sciences; Unit: Antarctic Research Centre; 040310 Sedimentology; 040305 Marine Geoscience; 040311 Stratigraphy (incl. Biostratigraphy and Sequence Stratigraphy); 960310 Global Effects of Climate Change and Variability (excl. Australia; New Zealand; Antarctica and the South Pacific) (excl. Social Impacts); Degree Discipline: Geology; Degree Level: Doctoral; Degree Name: Doctor of Philosophy; Stratigraphy (incl. Biostratigraphy and Sequence Stratigraphy); Antarctic; Pacific; Antarc*; Antarctica
• Online Access: https://doi.org/10.26686/wgtn.17135030; https://figshare.com/articles/thesis/Pliocene_glacial-interglacial_sea-level_change/17135030

The mid- to late Pliocene (3.3-2.6 Ma) spans one of the most significant climatic transitions of the Cenozoic. It is characterised by global cooling from a climate with an atmospheric CO2 concentration of ~400 ppm and temperatures of 2-3°C warmer-than-present, to one marked by the progressive expansion of ice sheets on northern hemisphere. Consequently, the mid-Pliocene warm period (MPWP; 3.3-3.0 Ma) provides the most accessible and recent geological analogue for global sea-level variability relevant to future warming. Global mean sea level has been estimated at 22 ± 10 m above present-day for MPWP. However, recent re-evaluations of this estimate suggest that spatially-varying visco-elastic responses of the crust, local gravitational changes and dynamic topography from mantle processes may preclude ever being able to reconstruct peak Pliocene mean sea level. The Whanganui Basin, New Zealand, contains a ~5 km thick stratigraphic succession of Pliocene-Pleistocene (last 5 Ma), shallow-marine, cyclical sedimentary sequences demonstrated to record orbitally-paced, glacial-interglacial global sea-level fluctuations. A limitation of the Whanganui sea level record, to date, has been an inability to resolve the full amplitude of glacial-interglacial water depth change due to the occurrence of cycle bounding unconformities representing sub-aerial erosion during glacial lowstands. This thesis analyses a new ~900 m-thick, mid- (3.3-3.0 Ma) to late Pliocene (3.0-2.6 Ma), shallow-marine, cyclical sedimentary succession from a remote and relatively understudied part of Whanganui Basin. Unlike previous studies, these shelf sediments were continuously deposited, and were not eroded during sea-level lowstands, and thus provide the potential to reconstruct the full amplitude of glacial-interglacial sea-level change. On orbital timescales the influence of mantle dynamic processes is minimal. The approach taken applies lithofacies, sequence stratigraphy, and benthic foraminiferal analyses and a novel depth-dependent sediment grain ...