Cenozoic geology of the Lower Nevis Basin with special reference to oil shale deposits

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Williams, G.J. 1974 Cenozoic geology of the Lower Nevis Basin with special reference to oil shale deposits. Wellington: Department of Scientific and Industrial Research. DSIR Bulletin 212 36 p. + 1 folded map

Abstract: The oil shales in the Nevis Valley in Central Otago have been recognised as such for over 40 years. The results of a very detailed geological, drilling, and sampling programme are here presented. Over a schist basement, a Tertiary sequence includes 350 ft of weakly indurated freshwater beds with two lignite horizons, the upper of which is immediately overlain by about 500 ft of fine sedimentary rocks and oil shale; this is succeeded coonformably by previously unrecorded sandy beds containing freshwater molluscs and leaf impressions. Unconformably on these is a thick heterogenous sequence of coarse schist-derived fanglomerates and finer water-sorted material which is regarded as the product of the Late Miocene to Pleistocene Kaikoura Orogeny. The valley has been structurally shaped by strong north-trending faulting and folding. Drill-core sampling showed that the greater part of the oil shale is of no economic value whatever, and even the basal part, ranging in thickness from 42 to 136 ft has a weighted value of only 8.4 gal/ton. ''Probable'' quantities of this material in situations where it could be opencast amount to about 8 million tons - a figure that might be doubled by further drilling for which there is no economic incentive at present. (auth)

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