Pliocene glacial-interglacial sea-level change
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 expans...
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| Format: | Thesis |
| Language: | unknown |
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2019
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| Online Access: | https://doi.org/10.26686/wgtn.17135030 https://figshare.com/articles/thesis/Pliocene_glacial-interglacial_sea-level_change/17135030 |
| Summary: | 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 ... |
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