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.

Seismic refraction and variable angle reflection measurements made using sonobuoys at 48 sites in the Ross Sea have been interpreted to define seismic velocity-depth structure of the deep sedimerttary basins underlying the Ross Sea. Three major basins exist in the region and the data show distinctly different seismic velocity-depth functions for each. In the east the continental shelf is underlain by a basin containing up to 4 km of sediments which show a simple linear increase in velocity with depth. This basin is considered to have formed partially in response to loading by glacial sediments since the Oligocene. A major trough of sediments, also up to 4 km deep, underlies the western part of central Ross Sea. The velocity-depth functions consist of several (usually 3) segments with linear velocity increase with depth, with the gradient of the segments increasing with depth. The trough is aligned approximately north-south and is considered to have been: formed by a failed crustal rift in the Late Cretaceous or early Tertiary. The third sediment basin is a trough running along the eastern side of the Transantarctic Mountains from McMurdo Sound to Coulman Island. About 3 km of sediments occur in this trough and show a distinct layered velocity structure. The trough has formed in association with the uplift of the Transantarctic Mountains, possibly as a result of compressive lithospheric -motion.

Seismic profiles obtained from the eastern side of New Zealand, in transit to and from Site 594, illustrate the evolution of the western end of the Chatham Rise and the southern extremity of the Hikurangi Trough. They show several unconformities and several major changes in tectonic and depositional regime. The unconformities represent major changes in oceanic circulation, possibly triggered by large lowerings of sea level in the late Oligocene and late Miocene. Tectonism is exemplified by a Late Cretaceous phase of block faulting, heralding the rift from Gondwanaland, and by Plio-Pleistocene normal faulting on the northern flank of the rise antithetic to the oblique-collision plate boundary in the southern Hikurangi Trough. This active normal faulting may indicate that the northwestern corner of Chatham Rise continental crust is being dragged down with the subducting slab to the north. The depositional regime has changed from Late Cretaceous infilling of fault-angle depressions, through an early Tertiary transgression and mid-Tertiary carbonate drape, to a late Miocene-Recent sequence recording repeated glacial-interglacial events. This upper stratified unit onlaps a late Miocene erosion/phosphatization unconformity toward the crest of the rise. It is locally truncated by a slope-parallel erosion surface, with downslope buildup, which may indicate either current scour and deposition or mass movement. INTRODUCTION BackgroundIn transit between Cook Strait and Site 594, the Glomar Challenger obtained seismic profiles along approximately 900 km of ship's track. Because they are tied to borehole data and because they cross areas where tracks are sparse, the Glomar Challenger profiles provide a significant increase in our understanding of the stratigraphy of eastern New Zealand and of tectonism in continental crust adjacent to an oblique-collision plate boundary.In this paper we integrate the Glomar Challenger profiles with published syntheses, with seismic data obtained by D.S.I.R. divisions, and with compilations of oil company data on open file at the New Zealand Geological Survey. Oil company data used in this study include profiles collected by Mobil Oil Corporation, Magellan Petroleum (New Zealand) Ltd., Australian Gulf Oil company, and B.P. Shell Todd (Chatham Rise) Ltd. Geomorphological SettingThe Glomar Challenger profiles traverse the Mernoo Saddle, a depression between the continental shelf of eastern New Zealand and the east-west-trending Chatham Rise ( Fig. 1; Fig. 3, later). The saddle's sill depth is over 500 m deep, contrasting with shelf depths to east Kennett, J. P., von der Borch, C. C, et al., Init. Repts. DSDP, 90: Washington (U.S. Govt. Printing Office).

Geochemical studies, reinterpretation of early seismic data and information from new seismic surveys are extending the concept of economic basement for hydrocarbons in several New Zealand basins. Older Cretaceous and even Jurassic and Triassic rocks, previously considered to be 'basement' by petroleum explorationists, may have significance as petroleum prospects.Triassic–Jurassic Murihiku Supergroup sedimentary sequences are up to 15 km thick, and the upper parts are still of low metamorphic rank. Vitrinite reflectances and Hydrogen Indexes from Murihiku Supergroup coals sampled from outcrop and drillholes indicate good oil potential, and, together with rock porosity of up to 18%, suggest that the Murihiku Supergroup may be prospective.In the offshore Canterbury Basin, reinterpretation of seismic data has shown there is probably a thick sedimentary section below what was previously mapped as the regional basement horizon. This seismic interval can be related to a similar section developed in the adjacent Great South Basin where a mid-Cretaceous, rift- fill section of hydrocarbon-bearing rocks, drilled in the Kawau–1 well had good source and reservoir potential.In the onshore Canterbury Basin, a recent vibroseis survey has revealed apparent sedimentary section extending down to more than 4,000 m which might also be the expression of a mid-Cretaceous rift-fill section, similar to that in the nearby Great South Basin and in the formerly adjacent Taranaki Basin, or possibly the older Murihiku Supergroup. This potential for a mature oil and gas source section provides the basis for further exploration of the area.There are similar prospective sequences in several other New Zealand basins.

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