| Popis: |
Full understanding of sea level, ice sheet and earth interactions during the Holocene, and the impact of current and future global sea-level rise requires observations of Holocene relative sea-level change from both near- and far-field locations. North Queensland is an ideal far-field location for testing models of mid/late Holocene global meltwater discharge and the viscosity structure of the solid earth, despite problems with indicators and gaps in its Holocene sea-level record. This thesis addresses inadequacies in the record of Holocene sea-level changes in North Queensland using for the first time a foraminifera-based transfer function, which employs vertically zoned modern intertidal and shallow subtidal calcareous foraminifera to reconstruct past water-level changes from fossil foraminiferal assemblages. This technique provides reconstructions which are of equal or greater vertical precision than reconstructions using mangrove mud or coral indicators on this coastline. AMS 14C dated calcareous foraminifera provide intra-site correlation of environmental and sealevel changes over the past 6000 calibrated years. This thesis also highlights problems which limit the applicability of the transfer function technique in this environment, including poor preservation of agglutinated foraminifera in fossil sediments and reworking of Holocene intertidal and shallow subtidal sediments which is not obvious from visual, bio- or litho-stratigraphical analysis. By creating new sea-level index points and re-calibrating existing ones from other indicators I infer the general form of the mid/late Holocene sea-level record in central North Queensland as sea level rising above its present value prior to 6700 cal years BP, with relatively stable sea level 1-2.3 m above present between 6700-5000 cal years BP, and between 1-2.8 m above present between 5000-3000 cal years BP. This is followed by sea-level fall to between 0.4-0.8 m above present until 1200 cal years BP and subsequent slow fall to present. This sea-level data supports theories suggested by geophysical models of a gradual end to global ice sheet melt, with melting ending after 5000 cal years BP. |
