This road cutting, on State Highway 6, south of Charleston, reveals an unconformity (time break) between the dark-coloured Brunner Coal Measures and the underlying weathered granitic rocks. In some places the rocks have been so deeply weathered that they now consist of little more than kaolin clay and quartz. Locally the clay has been quarried and processed for use in the production of pottery and ceramic ware.
The unconformity represents the widespread Waipounamu erosion surface, found over many parts of New Zealand about 65–50 million years ago, when the land was reduced to a peneplain. When tectonic activity was renewed in the late Eocene period (40 million years ago), coal measures and other sediments were deposited on top of the peneplain.
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Photograph by Simon Nathan
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