Quaternary sediments and plant microfossils from Enderby Island, Auckland Islands

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Abstract
At Enderby Island, a deposit of till, here named the Enderby Formation, locally separated into upper and lower members by lenses of laminated lake siltstone, overlies a sequence of flat-lying basalt flows, perhaps benched by ,the sea during an interglacial period of high sea level. Except on the coast these deposits are blanketed by zonal peat, 3 m thick, which contains the record of post-glacial vegetation. The Lower Till waS deposited by the extended glacier that spread out from Laurie Harbour, at the head of Port Ross, flowing from the higher parts of the Ross Volcano when sea level was low, presumably during an early stadal of the last (or Otiran) glacial stage. The Laminated Siltstone (5 m), deposited in a pro-glacial meltwater lake dammed by moraine during a lateral swing or temporary retreat of the glacier, is injected by curious carrot-shaped structures of till, each apparently emplaced by the rapid sinking of a mass of rock-laden iceberg which penetrated the unconsolidated silts to depths of almost two metres. The emplacement of such “till carrots” was contemporary with deposition of the silt. The ice re-advanced to deposit an Upper Till Member over the underlying members, locally deforming ,them and picking up siltstone clasts. The Laminated Siltstone and a clast of siltstone from the Upper Till contain pollen and spores indicating a cold-climate vegetation of dominant Compositae whh associated herbs, grass, sedge and scrub (Coprosma, Dracophyllum, and Myrsine) but lacking Metrosideros and other trees of the present Auckland Island vegetation. The till members may represent two stadials of the last glaciation and the siltstone an interstadial between ,them, or they may merely represent fluctuations of minor significance. The blanket peat overlying the till sequence has three members, a lower peat with tree stumps, a middle sandy peat containing angular sand and subangular basalt clasts (up to 45 cm through), and an upper peat with scattered well-rounded basalt pebbles, identified as seal gastroliths. The sandy peat is tenta,tively attributed to the influence of blown sand advancing inland when the post-glacial sea (also represented by an elevated beach) first approached its maximum level. Four zones in the peat can be defined from pollen analysis. In Zone 1, woody elements (e.g. Myrsine, Coprosma) and Compositae are abundant, with sedge and grass, and at the top of the zone rooted stumps of Dracophyllum (under-represented by pollen) gave a 14C age of 8630 ± 80 yr BP. In Zone 2, Anisotome pollen increases, Myrsine, Coprosma and Olearia-type pollen grains decrease, Dracophyllum enters with various herbs, and persistent grass is dominant over sedge. In Zone 3, Metrosideros pollen is relatively common. Tillaea and sedges rise steeply as grass declines but Myrsine, Coprosma and Dracophyllum decrease. In Zone 4, grass increases once more (with Myosotis and Myrsine) while Bulbinella, Anisotome and woody shrubs decrease. The Metrosideros phase in Zone 3 (reflecting a warm interval from ca. 6000 to 3000 yr BP) and available 14C dates allow other Auckland Island pollen spectra to be correlated and dated, and the sequence of wind-transported exotic pollen confirms correlation with South Island post-glacial vegetation sequences.

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