Geology of an area west of Lake Fergus, Upper Eglinton Valley.
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Abstract:
A Lower Permian geosynclinal sequence, previously mapped as Eglinton Volcanics, is found to be predominantly volcanogenic feldspathic sandstone and siltstone with minor tuffs, tuffaceous sandstones, Atomodesma bearing limestone and keratophyres. The sequence is divided into the Falls Creek Formation, (which includes the Melita Limestone Member), Kaka Creek Siltstone, Consolation Formation, Divide Creek Formation and Fergus Formation - all newly defined. Correlation with other areas is discussed. The rocks have been metamorphosed to prehnite-pumpellyite and pumpellyite-actinolite-schist facies. Justification for the use of the name Alabaster Group, rather than Eglinton Volcanics, is given.
Basic and ultrabasic dykes, intruding the above sequence, are described in some detail.
A quartz-dolerite intrusive body, here named the Gunn Intrusives, is tentatively correlated with the Mackay Intrusives. To the west, in fault contact (Skelmorlie Fault) with the Alabaster Group, is the so-called Darran Diorite. In this urea it is actually oligoclase-granite and hence it is proposed that the name Darran Complex be used. Rafts in the Darran Complex are metamorphosed to hornblende-hornfels facies.
Graben fault blocks of Otamitan and Tertiary marine sediments are infaulted along the Hollyford Fault, which bounds the eastern edge of the Alabaster Group. The sparsely fossiliferous Otamitan (Windy Point Formation) is comprised of sandstones, siltstones, tuffs and conglomerates and is correlated with the Murihiku Super-group. Analcime from one tuff-bed has a composition identical to that of analcim from burial metamorphic rocks of the Taringaturas, Southland. Metamorphism is to zeolite facies.
The sparsely fossiliferous Lake Lochie Beds (L-P age) consist primarily of arkosic sandstones (derived from Fiordland Complex) with rare volcanic conglomerates (derived from the Eglinton Volcanics.
Basic and ultrabasic dykes, intruding the above sequence, are described in some detail.
A quartz-dolerite intrusive body, here named the Gunn Intrusives, is tentatively correlated with the Mackay Intrusives. To the west, in fault contact (Skelmorlie Fault) with the Alabaster Group, is the so-called Darran Diorite. In this urea it is actually oligoclase-granite and hence it is proposed that the name Darran Complex be used. Rafts in the Darran Complex are metamorphosed to hornblende-hornfels facies.
Graben fault blocks of Otamitan and Tertiary marine sediments are infaulted along the Hollyford Fault, which bounds the eastern edge of the Alabaster Group. The sparsely fossiliferous Otamitan (Windy Point Formation) is comprised of sandstones, siltstones, tuffs and conglomerates and is correlated with the Murihiku Super-group. Analcime from one tuff-bed has a composition identical to that of analcim from burial metamorphic rocks of the Taringaturas, Southland. Metamorphism is to zeolite facies.
The sparsely fossiliferous Lake Lochie Beds (L-P age) consist primarily of arkosic sandstones (derived from Fiordland Complex) with rare volcanic conglomerates (derived from the Eglinton Volcanics.
Thesis description:
ii. 52 p. ill. Map (folded in pocket). 27 cm.
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1969Corner
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Citation
Corner, NG, “Geology of an area west of Lake Fergus, Upper Eglinton Valley.,” Otago Geology Theses, accessed April 23, 2025, https://theses.otagogeology.org.nz/items/show/33.