Geological map of New Zealand 1:63,360 Sheet S133 Cromwell

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Turnbull, I.M. 1988 Geological map of New Zealand 1:63,360 Sheet S133 Cromwell. Wellington: Department of Scientific and Industrial Research. Geological map of New Zealand 1:63,360 S133. 1 fold. map + 1 booklet

Abstract: Some 435 square miles (1150 sq km) of Central Otago were mapped for Sheet 133 Cromwell. Physiography is dominated by tor-studded block faulted mountains, and intermontane basins. A formerly extensive cover of middle Tertiary sediments which overlay a peneplain eroded across basement rocks during the early Tertiary is now only preserved in fault-bounded depressions. Extensive glacial outwash gravels and moraines associated with Pleistocene glaciations in the Clutha and Kawarau catchments infill the main valleys. Steeper slopes are mantled by widespread mass movement deposits. Structurally complex and lithologically variable metamorphic rocks of the Haast Schist Zone form basement to the area. Remnants of fluvial and lacustrine sediments of the Manuherikia Group unconformably overlie weathered schist basement. These are in turn conformably overlain by fluvial-deltaic gravel and sand. Quaternary deposits consist of several flights of terraces formed of fluvioglacial sediments related to morainic deposits of the Wakatipu and Hawea- Wanaka glaciers. Recent deposits include cirque moraines, streambed alluvium, travertine, and solifluxion, slopewash, and landslide deposits. The structure of the area reflects two major deformational events. The syn- metamorphic to immediately post-metamorphic Rangitata Orogeny resulted in at least three phases of folding of the schists, as well as faulting. The younger Kaikoura Orogeny deformed both schists and Cenozoic sediments by folding and faulting. No earthquakes greater than magnitude 5 have been recorded, although several active fault scarps have been identified. The Dunstan, Carrick and other goldfields in the district have been important producers of gold from Quaternary sediments, and lodes in basement schists. Other economic minerals include silver, stibnite, scheelite, sulphides, lignite, montan wax, quartz sand and gravel, clay, serpentine, asbestos, graphite, building stone, gravel, and sand. Most Quaternary terrace gravels are potential groundwater aquifers. Properties of the rock units are described in terms of engineering geology and geological hazard factors.


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