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Proxy evidence of relative sea level change indicators and implications Raglan (Whaingaroa) harbour New Zealand
Abstract
Geological observations and macrofossil dating of 4 raised marine terraces reveal active tectonic displacement in the Raglan Harbour, New Zealand (NZ). The 120 km-long harbour shoreline displays multiple examples of block-faulting, stratigraphic displacement, and fresh stress release fracture zones within rock sea-cliffs. Tide-zone rock platforms are indicative of a long-term uplift trend within a major portion of the harbour. Vertical land movement (VLM) rates are found to vary at different locations, signifying active fault displacement. Six proxies establish VLM magnitude and timing constraints applicable to the last 7 decades. One further proxy establishes maximum relative sea level (RSL) throughout the last 23.5 Ka at a specific location in the harbour.
Seventeen 14C dated macrofossils from 4 raised marine terraces identified 2 groups of ages: pMC ~ 1 to 6.5 Ca yr BP and ̴ 6.5 Ka yr BP respectively. Tide dissolution notches in rocks identifiable in historical photographs are compared with modern equivalents at 2 locations. These depict no apparent change in the upper dissolution notch boundary elevations since 1910. Characterisation and U-Th dating of a speleothem located ̴ 0.4 m above the modern high tide level signifies that RSL is near its ̴ 23.5 Ka maximum at this location. Historic aerial imagery identifies a marine terrace that uplifted by < 0.4 m within the period 1979 to 1997. A fault demarcates this feature from a second terrace with stratigraphic evidence of a markedly different VLM history, indicating that the fault is active. Raised trace fossil castings exposed in the foreshore’s mid-tide zone further substantiates evidence of relatively recent uplift at this location.
Type
Thesis
Type of thesis
Series
Citation
Date
2024
Publisher
The University of Waikato
Supervisors
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