Quaternary geology, biota and climate at Mason Bay, Stewart Island, New Zealand.

Wood, Jamie (Jamie Russell)

This dissertation examines late Quaternary sedimentary deposits and their associated biota at Mason Bay, Stewart Island. The basement geology at Mason Bay consists of amphibolite xenolith-bearing Mason Bay Pluton granites, and Walker's Pluton diorites, which outcrop on the tops of hills around Mason Bay. The Hellftre Formation (new), of late Quaternary age, is described here. The formation rests unconformably on the Mesozoic basement, and consists of two distinct cyclothems, each of which represents an interglaciala glacial cycle. The lower cyclothem is comp;fsed of the Duck Sand (new) (Karoro) and Martin's Breccia (new) (Waimean) while the upper cyclothem is compfsed of the Wreck Sand (new) (Kaihinu) and Cavalier Breccia (new) (Otiran). Sands are laminated tidal rhythmites w"'-e"tC--<. deposited at interglacial high sea level stands, white breccias represent felsenmeer (block ftelds) formed by periglacial processes. Late Pleistocene - Early Holocene dunes, common on the Island Hill Flats east of Mason Bay are uncommon in outcrop at the bay, but provided the substrates for the forests forming the peat horizons at Mason Bay. Three distinct peats occur at Mason Bay, Mason Peat (new) (latest Pleistocene-earliest Holocene), Leask Peat (new) (~7k.a.) and Kilbride Peat (new). A diverse assemblage of subfossil invertebrates was found in the Leask Peat, including beetles from the families Carabidae, Curculionidae, Hydrophilidae, Chrysomelidae, Scirtidae, and Scarabidae, and possible fragments of Peripatus, which if verified, would be the ftrst record of this taxon from Stewart Island. The active Holocene dunes at Mason Bay form one of the most extensive dune systems in New Zealand. During fteldwork, 2632 disarticulated bird bones were collected from the active dunes. The majority are from South Georgian diving petrels (Pe!ecanoides georgicus), which formerly bred at Mason Bay. 27 other bird species were represented in the dune assemblage, including the ftrst subfossil records of yellow-eyed penguin, New Zealand falcon, pied oystercatcher, New Zealand pigeon and nfi at Mason Bay, as well as the second record of piopio from Stewart Island. Dunes ftxed by forest near the southern end of Mason Bay do not contain bone or shell, possibly due to the presence of humic acid. The influence of pH and sand abrasion on bird bone preservation was examined experimentally, and found to signiftcantly affect the condition of bone. The dissolution of bone by groundwater with 13 low pH (resulting from humic acids) may explain the lack of (bird) bones in the New Zealand terrestrial fossil record.

89 leaves : ill. (some col., some folded), maps (some col., some folded) ; 30 cm.

2003Wood

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