Late Holocene radiocarbon ages from Blueskin Bay estuary : relevance to local eustatic sea-level during the last 7000 years

Eight unpublished and ten published radiocarbon dates from Blueskin Bay estuary, East Otago reflect local eustatic sea levels trends during the last 7000 yrs. The elevation data are corrected to a common datum (MSL) and the sources of error assessed. Using modern lithological and biological relationships relative to present sea-level, radiocarbon dates can be converted into paleosea-level indicators. The upper and lower limit of the paleosea-level dataset provide an envelope representing local relative sea-level changes. The envelope is consistent with a culmination of the post-glacial transgression after 6.5 kyr, followed by a minor regression of -2 m at 5.5-5 kyr, followed by a minor transgression of 1.9 m between 5-3.2 kyr. Both the timing and magnitude of the minor regression and transgression at Blueskin Bay estuary differs somewhat from Gibb (1986), who proposed a minor regression of approximately -0.4 m from 5-4.5 kyr, followed by a minor transgression of 0.6-0.9 m at 4.5-3.5 kyr. The estuaries of Weiti River and Blueskin Bay were both proposed as reference localities for recording New Zealand regional Holocene eustatic sea-levels. Twenty four pulished radiocarbon dates, corrected to a common datum (MSL) are used to constrain relative local sea levels for the Weiti River estuary. The limits of this paleosea-level dataset are consistent with a culmination of the post-glacial transgression at 6.5 kyr, followed by stable eustatic sea-level during the last 6 kyr. Prior to 6.5 kyr a regression of -5.2 m is apparent from 8-7.7 kyr, followed by a transgression of 6.6 m between 7.6-6.2 kyr. The comparison of local relative sea-levels between the two reference localities suggests local variations in eustatic sea-levels maybe significant. Variations in eustatic sea-level will be discussed in the context of the Great Barrier Reef sea-level curve of Larcombe et al. (1995). (auth.)