Geology of the Haycocks-Snowden Forest region, Western Southland / W.M.A. Harrington.


Harrington, William Michael Allen.


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Geological and geophysical interpretations are presented for a region in Western Southland, in the vicinity of The Haycocks and the southern extent of the Snowdon Forest.
Three Tertiary sedimentary units are described and discussed. The Haycocks Formation of Pareora Series age is a steeply dipping, fault-bounded, mainly sandy, lithic flysch, derived from a low-grade metamorphic source from the north-east. Faunal evidence suggests a depth of deposition of approximately 500 metres, and interpretation of diagenetic reactions involving quartz solution, -carbonate solution and replacement, and clays suggests an overall depth of burial of approximately 3500m.
Unconformably overlying the Haycocks Formation, are shallowing-upward silts, sands and conglomerates of the mainly Southland Series age Woodburn Formation, which is correlated with an equivalent shallowing shelf sequence in the Upukerora-Whitestone region to the north. These sediments appear more quartzofeldspathic than those of the Haycocks Formation, and an incoming of an additional source area from Fiordland is inferred.
A sequence of indurated fluvial gravels and sands, the Prospect Formation, regionally overlies the marine sequence in the Te Anau basin and also the Waiau basin to the south. Clasts are dominantly Caples Terrane derived and paleocurrent interpretation suggests derivation from the north. This formation, along with the others, has been folded into a northward plunging syncline at Dale Creek, which has in turn been compressed and offset by right-lateral fault activity on the Moonlight Fault Zone during Kaikoura Orogeny deformation in the late Tertiary.
An extensive cover of Quaternary glacial and fluvial gravels unconformably overly the earlier deposited units. Slight tilting suggests recent tectonic activity.
A small hill, correlated with Maitai Group sedimentary units to the north is inferred to have undergone as much as two kilometres or more of right lateral offset along the Mararoa Fault, which, along with the Haycocks Fault (Moonlight Fault, sensu stricto?) passes through the area trendng NNE.
Structural features observed and stratigraphic relations suggest a reasonably close accord with plate tectonic predictions for southern New Zealand.
Mapping of structural features was assisted by the use of various geophysical methods -magnetic, gravity and seismic.

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120 leaves : ill., maps ; 30 cm.


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Harrington, William Michael Allen., “Geology of the Haycocks-Snowden Forest region, Western Southland / W.M.A. Harrington.,” Otago Geology Theses, accessed May 22, 2024,

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