Abstract154 gravity stations were sited in the lower Taylor Valley, along 4 survey lines between Suess Glacier and New Harbour, Antarctica. Basement profiles across and along the valley show that, below the glacial and sedimentary overburden, Paleozoic basement rock forms a symmetrical valley, deepening to about 600 m below sealevel at New Harbour. Basement topography generally is smooth, except for a series of ridges between Lakes Hoare and Fryxell.

Two-dimensional and three-dimensional gravity models of the Mesozoic basement topography in the Wairarapa show that the major feature is the Wairarapa Trough, aligned SSW-NNE through the area. The Trough has two arms, one north of Eketahuna and the other south of Carterton. All three features are fault-angle depressions, bounded to the west by the West Wairarapa, Wellington, and Dry River Faults, respectively, and reaching their greatest depths at these faults. A structural contour map of the Mesozoic surface in the Wairarapa shows that the basement is covered by more than 3000 m of Cenozoic material. The West Wairarapa Fault is shown to be reverse in the south, with a dip as low as 15°. The other faults are apparently near-vertical.

A marine seismic reflection survey was conducted in the upper Waitemata Harbour, using a high-resolution acoustic prafiling system. The depths to the identified seismic reflectors agree dosely with the measured strata depths from borehole data, the differences between the two sets having a standard deviation of ± O-9 m. This is despite the paar signal-to-noise ratio resulting hecause the water depth was at tirnes less than 2 m.The structure of the area is complex, but three principal stratifications have been identified. Waitemata Formation sandstones of the Miocene Period are overlain byPleistocene materials (days and silts, with mucl-fine sand), which vary in thickness fram 0 to more than 30 m. Most of the area is covered with up to 18 rn of Recent marine deposits, typically a very soft, silty day. Each zone, especially the Pleistocene, exhibits internal structure. The two rnajor boundaries have been contoured. Two anomalous features were recorded in the Recent marine sedirnents : astrang reflector which has not been related to any change in physical praperties of the sediments, and localised acoustically opaque zones which are probably a result of gas bubbles occurring within the sediments.

No abstract

No abstract