The sedimentary sequences found within estuaries in the north west Nelson region of central New Zealand are investigated in order to quantify the timing of the end of the Post Glacial Marine Transgression. This region has been identified as being relatively stable in terms of vertical tectonic movement during the Holocene, but is yet to yield any reconstructions of eustatic sea level. In this study, we investigate the Holocene infill of a barrier estuary (Parapara Inlet) through sedimentological analysis and radiocarbon dating of 18 vibracores up to 4.2 m in length. It is found that the estuary infilled through a combination of lateral flood tide and fluvial delta progradation as well as vertical central basin infill. The central basin infilled at a consistent rate of 0.4 mm/year in both the mid (7.0–6.0 ka) and late-Holocene (2.5–1.5 ka). By the time of early human (Maori) settlement (c. 1 ka), the estuary surface was at low intertidal elevations with sediment being transported from the fluvial to tidal delta. A discernible change in sedimentation rates could not be associated with Maori settlement; however, infill rates increased to at least 12.5 mm/year in the past 150 years due hydraulic sluicing associated with mining. The sedimentary history of Parapara Inlet is compared to nearby Whanganui Inlet, d’Urville Island and Nelson to establish the character of regional Holocene sea level movement. It is found that relative sea level reached modern elevations between 8 and 7 ka in the region. The similarity between sea level curves for the end of the post glacial marine transgression (PMT) to other tectonically stable sites in northern New Zealand suggests that this curve can now be considered a true eustatic signal for the New Zealand archipelago.

<p>Estuaries are depositional environments formed within drowned river embayments which receive sediment from both marine and terrestrial sources. In many cases a beach-barrier sequence forms subaerially at the mouth of the flooded embayment and the area behind it is termed a barrier estuary. Such estuary types are found around the New Zealand coast especially in areas of relative tectonic stability and their sediments are often used to reconstruct Holocene sea level. Infill of these estuaries is initially dominated by marine flood tide delta sediments, with later infill occurring through fluvial processes. The final stages of infill within these estuaries is poorly understood. Parapara Inlet in Golden Bay, New Zealand, is a Holocene barrier estuary influenced by hydraulic sluice mining within its river catchment. A study of Parapara Inlet was undertaken to discover how human disturbance within a river catchment can affect the evolution of a barrier estuary, by comparing previous models of barrier estuary evolution to the stratigraphy record within Parapara Inlet. 18 vibracores were sampled from Parapara Inlet in November 2009. Radiocarbon dating (AMS) within these cores provided a maximum age of 7090-6910 Cal BP. Deposition within the estuary has occurred in three stages; the first in Pre-Holocene marsh or lake environments; the second after inundation 6500-7500 years Cal BP, as fluvial sediments dominate the centre of the estuary; and thirdly in a series of quartz dominated gravels and sands within 1m of the surface. These units vary from the traditional models of evolution as the topography of the estuary has influenced the extent of deposition within the central mud basin. Mining sediment forced Parapara Inlet into a late stage of evolution, however the amount of sediment provided through sluice mining was not large enough to force the estuary into a supratidal stage.</p>