Southwest Dunedin urban area. Scale 1:25,000

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McKellar, I.C. 1990 Southwest Dunedin urban area. Scale 1:25,000. Lower Hutt: New Zealand Geological Survey. Miscellaneous series map / New Zealand Geological Survey 22 1 fold. map + 1 booklet

Abstract: The Southwest Dunedin Urban map area includes the west edge of Dunedin City and extends 10 km west and 15 km southwest to cover several smaller urban areas, and intervening rural land which will be in demand in future for urban and industrial expansion. From the western and southwestern margins of the central part of the Dunedin volcanic centre, outliers of volcanic rocks are underlain by eastward-dipping Tertiary marine sediments resting on a thin sequence of Upper Cretaceous quartz gravel, sand, and clay with some coal seams. These in turn rest on a basement of Mesozoic Haast Schist. Quaternary alluvial gravel and sand formations occupy the Taieri and Kaikorai valleys. Most of the map area is mantled by colluvium and loess regolith. Various geological hazards place constraints on urban development. The most important of these being landsliding which originates mostly in the clay-rich marine sediments of the Saddle Hill Siltstone and Abbotsford Formation, but also occurs in the regolith. The latter is derived partly from these sediments, and from loess and colluvium which mantle the hill slopes. The landslide hazard which exists in some places was highlighted in 1979 by the east Abbotsford landslide. No active faults are known in the mapped area, although significant earthquake (up to magnitude 8.0) risk exists. Underground mining in the Green Island coalfield started in the 1860s and continued into the early part of this century. Old underground workings constitute a hazard under areas potentially useful for housing and industry. Gold and scheelite occur in quartz reefs in the Haast Schist at the south end of the Chain Hills. Rock for building, roading, and ballast comes from the harder rocks of the Dunedin Volcanic Group. Quartz gravel and sand are procured from the Fairfield sand pit and the Walton Park quarry. The Green Island Sand Formation provided moulding sand and fill. Field tiles and other clay products are produced from clay-rich loess and colluvium. Burnside Mudstone formally produced marl for cement manufacture. (auth)

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