A geological and geophysical survey of the Omaramara Basin.

Author:

Udy, AJ

Year:

Project type:

Abstract:

A geological study of the Omarama Basin (inland North Otago) involving field mapping, scanning electron microscopy, and previous palynological data indicates that the late Tertiary-early Quaternary (new) Mackenzie Group gravels and silts of the Mackenzie Basin represent deposition in a glaciofluvial and glaciolacustrine environment. These sediments are the oldest (Mangapanian -Hautawan, Mildenhall,1980) records of a glaciation within the Mackenzie Basin. Several generations of late Quaternary sediments have also been mapped, including the Aviemore Formation glaciofluvial gravels which represent the most recent advance of the last major Pleistocene (Otira) glaciation.
A gravity survey of the area indicates:
i) the depth of sediment within the Omarama Basin may exceed 500m in the centre of the basin, and in the Omarama Stream valley it increases northward from ~20m at the head of the valley to over 200m near Twin Peaks Station,
ii) the Ewe Range is extensively sheared as a result of movement within the Hawkdun Fault Zone. This shearing has produced extensive zones of low density crushed rock which are readily apparent on the survey traverses as gravity lows. The two dimensional models produced for these profiles suggest that the Hawkdun Fault is a high angle reverse fault, and geological evidence indicates compression in a NE-SW direction across the zone. In the light of the present tectonic regime in the South Island, it seems very likely that there is a considerable component of strike slip movement along this fault,
iii) the Ostler Fault Zone in this area is more complex than previously thought and consists of at least three low angle, imbricate reverse faults. This zone may be the toe region of a large scale fold and thrust belt which has been thrust from the northwest due to the compressional tectonic regime present in the South Island since the Miocene.
Several minor faults are associated with the two major fault zones in the area. These have been inferred on the basis of Landsat photograph lineaments, lineament patterns on aerial photographs, the presence of extensive piedmont gravel fans and topography. A presence of a combination of these features may prove useful in mapping the areal extent of faulting elsewhere in Otago.
On the basis of field observations it is suggested that the wetland areas that have developed at the Aviemore Formation-Alluvial Fan Gravel contacts may be a potential source of irrigation water during the dry summer months. Likewise, the extensive crush zones on the flanks of the Ewe Range may also have the potential to produce significant quantities of water. Further investigation of these possible resources, and of the ground water resource in the Red Flat area is warranted.

Named Localities:

Thesis description:

iii. 96 p. diagms, photos, map,(folded in pocket); 30 cm.

Department:

OU geology Identifier:

1987Udy

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Location (WKT, WGS84):

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Files

http://download.otagogeology.org.nz/temp/Abstracts/1987Udy.pdf

Collection

Citation

Udy, AJ, “A geological and geophysical survey of the Omaramara Basin.,” Otago Geology Theses, accessed March 9, 2021, http://theses.otagogeology.org.nz/items/show/217.

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