Geophysical surveys in support of coal prospecting in eastern Southland 1977-8

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Broadbent, M.; Carman, A.F.; Carrington, L.W.; Hicks, S.R. 1980 Geophysical surveys in support of coal prospecting in eastern Southland 1977-8. Wellington: DSIR, Geophysics Division. Report / Geophysics Division 144 46 p.

Abstract: Seismic and gravity measurements have been made along a 13 km line across the Mataura-Hedgehope depression, west and south-west of Mataura. The eastern part of the depression is unaffected by major Cenozoic vertical faulting, but it probably contains a syncline in the Cenozoic sediments. The west flank of the depression appears to be formed by several steep Cenozoic faults with total downthrow to the east exceeding 350 m. Some fault scarps are probably notched. Major Cenozoic vertical faulting with downthrow to the east appears to underlie the central Hedgehope Stream valley, where the thickness of the Cenozoic sediments becomes more than 300 m. A Mesozoic hill overlain by about 100 m. of Cenozoic sediments occurs between the Hedgehope and Te Tipua Streams. No faulting is evident near the Te Tipua Stream, which is underlain by about 250 m. of Cenozoic sediments. The use of gravity measurements to derive Cenozoic sediment thicknesses where significant density variations are absent from pre-Cenozoic rocks is appreciably quicker and cheaper than the use of seismic methods. (auth)