Geology of the Tewatapoki-Waikaura Creek area

Author:

Giessmann, Wilko, 1969-

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Abstract:

The geology of th~ Tewtapoki-Waikaura Creek area comprises deformed greywackes and argillites with sub-vertical foliation which were metamorphosed during the Early Jurassk to Textural Zone 2B of the Otago Schist. Pumpellyite is present but prehnite is not seen in any thin section suggesting pumpellyiteactinolite fades. The metamorphic grade does not change for at least 6 km across the northwest striking schistosity. The schist is deeply weathered . The schist basement has undergone a series of deformation events. Pre-, syn-, and post-metamorphic deformation are recognised. Compression related to a collision led to folding; tilting, and transposition of the original_ layers, Iinalfy causing the foliation and lineation. Post-metamorphic brittle deformation caused major faults in the area. The Tewatapoki Fault runs across the area and is northeast-southwest striking. For this fault, the stress field of normal faulting has been identified. The Waikaura photolineament is sub-parallel and seems to be related to the Tewatapoki Fault. Northwest trending photolineaments are sub-parallel to the Dryburgh Fault and may represent thrust faults. Joints seem to be partly systematic and strongly associated to northwest trending normal faults or due to ·stress relaxation subparallel to the foliation. The fabric of the schist ranges from massive, with nearly undeformed detrital grains to flattened with rotated grains of quartz and albite within highly deformed schist. The schist basement is overlain by a cover sequence comprising shallow marine and fluvial deposits of Taratu Formation. A Late Cretaceous transgression event has been established by in situ glauconite and occurrence of detrital potassium feldspars. Potassium feldspars are assumed to be derived from the Western Province of Stewart Island or Fiordland. Upper sequences of Taratu are fluvial in origin and form together with the marine sequence approximately 45 m of sediment. Coarse cobble gravel in the upper layers of the Late· Cretaceous Taratu Formation may indicate the the existence of the Waitaki Valley. Mid Tertiary shallow marine sediments unconformably overlay the Taratu Formation. Tapui, Earthquake Marl, and Kokoamu Greensand formation are inferred to underlie parts of the area but have not been seen due to poor outcrop exposure. 4 I I I I I I •• • 11 11 11 11'' 11' 11 11. 11 11 11 I: Otekaike Limestone, as the youngest mid Tertiary deposit, is highly fossiliferous and contains foraminifera of Duntroonian to Waitakian (both Late Oligocene) age. Two different Quaternary fluvial conglomerates can be distinguished, the Older and the Recent Gravels. They vary in thickness across the mapping area and become .thicker going to the northeast. Older Gravels are very coarse cobble gravel containing mainly graywacke clasts. Loess is interbedded with the more recent fluvial sediments and can be up to 4.50 m thick.

Thesis description:

80 leaves : ill. (some col.), col. maps ; 30 cm.

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OU geology Identifier:

1996Giessmann

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Location (WKT, WGS84):

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Files

http://download.otagogeology.org.nz/temp/Abstracts/1996Giessmann.pdf

Collection

Citation

Giessmann, Wilko, 1969-, “Geology of the Tewatapoki-Waikaura Creek area,” Otago Geology Theses, accessed February 8, 2025, https://theses.otagogeology.org.nz/items/show/321.

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