New Zealand Journal of Geology and Geophysics abstracts

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Pre-Miocene and post-Miocene deformation in the Bannockburn basin, Central Otago, New Zealand

I. M. TURNBULL

Institute of Geological & Nuclear Sciences Ltd
Private Bag 1930
Dunedin, New Zealand

D. CRAW R.
R. J. NORRIS

Geology Department
University of Otago
P. O. Box 56
Dunedin, New Zealand

Abstract The Bannockburn basin is the southern extension of the Upper Clutha basin, one of a series of prominent northeast-trending structural and topographic basins in Central Otago. Post-Miocene structure within the Bannockburn basin is shown up by deformation of an unconformity cut into schist basement beneath Miocene terrestrial sediments. The post-Miocene deformation has been accommodated largely by flexure, and the structure consists of broad north-trending synforms and antiforms in schistosity, mimicked by folds in the overlying sediments. The northwestern margin of the basin trends northeast, and the unconformity is steeply dipping or locally overturned, but there is no major fault separating the basin from the range immediately to the west. Minor faults in this area have normal, reverse, or strike-slip senses of movement. The southwestern margin of the basin trends northwest and is marked by distinct faults which offset the unconformity. The present-day Bannockburn basin coincides with a complex pre-Miocene graben structure, within which a complex set of northeast- and northwest-striking faults has juxtaposed differing textural zones within the schist, with the Bannockburn basin lying on the downthrown blocks. This pre-Miocene structure probably controlled the location of the present basin, and similar structures may have influenced the formation of other Central Otago basins. The characteristic Central Otago, post-Miocene range and basin structure may thus be inherited from pre-Miocene extension.

Keywords Central Otago; structure; faults; folds; basin inversion

Received 2 June 1992; published 13 April 1993
New Zealand Journal of Geology & Geophysics, 1991, Vol. 36: 107—115
0028Ð8306/06/3601—0107 ©The Royal Society of New Zealand 1991

PDF file of entire paper: medium quality (849K); (scanned from paper original: notes about this process). Digitisation of this article from the printed journal was kindly facilitated by the Geological Society of New Zealand

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