Geology of Elmwood Station, Western Southland, with emphasis on Stratigraphy and Provenance of Cenozoic Sediments.

Author:

Hall, Charlotte Elizabeth, 1964-

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Abstract:

An area approximately 36 km2, located 26 km southeast of Te Anau, Western Southland was mapped in detail. In the south, Permian rocks of the Takitimu Group (northern Takitimu Mountains), comprise a variety of volcanoclastic sediments including tuffs, volcanic breccias, sandstones and andesites. In faulted contact with the Takitimu basement, to the north, are Cenozoic sediments of the Te Anau basin. In stratigraphic order, these sediments begin with the non-marine Beaumont Formation of Eocene age ( 430 metres thick) passing up into marine sediments of the Oligocene Spear Peak Formation (1080 metres), Elm Tree Limestone (55 metres) and the Waicoe (Mudstone) Formation (1600 metres) both early Miocene. Unconformably overlying the Waicoe Formation are late Miocene fluvial deposits of the Prospect Formation. Quaternary deposits record three periods of glacial advance, from oldest to youngest these are, Whitestone Stratified Drift, Elmwood Formation and the Mavora Outwash Member.
Petrographic, QFL data and major element analysis of biotite rich quartzofeldspathic sandstones from the Beaumont Formation indicate derivation from a plutonic source , that was part of a rapidly eroding Eocene tectonically active margin in what is now Eastern Fiordland.
Lithological and stratigraphic differences have permitted subdivision of the Spear Peak Formation into two members; Elmwood-Waituna member ( 500 metres) and the Wood Hill member (1080 metres). The Spear Peak Formation indicates the onset of marine conditions in the late Eocene and early Oligocene and the establishment of rapidly subsiding basins associated with movement on the Moonlight Fault System. Olistoliths of Takitimu Group rocks are found within both members, but Fiordland derived material sediment remains present as well. A limestone breccia in the Wood Hill member contains limestone clasts showing mylonitic deformation features. Recrystallised Atomodesma prisms within the clasts closely resemble similar prisms in the Melita limestone in the upper Eglinton Valley.
The Waicoe Formation, a deep marine mudstone of widely varying age found throughout the Te Anau and Waiau basins, is shown to be Altonian age in Elm Tree Creek (benthic and planktic foraminifera). Mass flow deposits within the mudstone indicate reworking of shallow marine shelly sediment into deeper waters.
Prominent northeast-southwest trending faults passing through the area mapped, such as the Takitimo Fault and older, less continuous, northwest- southeast trending faults are a continuation of the Moonlight Fault System. Recent Fault tracing indicates that deformation remains active into the Holocene.

Thesis description:

iv. 89 p. ill. Photos. (Map folded in pocket); 30 cm.

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OU geology Identifier:

1989Hall

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Location (WKT, WGS84):

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Files

http://download.otagogeology.org.nz/temp/Abstracts/1989Hall.pdf

Collection

Citation

Hall, Charlotte Elizabeth, 1964-, “Geology of Elmwood Station, Western Southland, with emphasis on Stratigraphy and Provenance of Cenozoic Sediments.,” Otago Geology Theses, accessed March 9, 2021, http://theses.otagogeology.org.nz/items/show/230.

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