Geology of Wharekuri and the adjoining area, North Otago and South Canterbury
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In North Otago, in the South Island of New Zealand, a complete sequence of Cretaceous-Tertiary sediments representing a marine transgression followed by regression are found in the northwest-southeast trending fault angle depression of the Wharekuri Basin.
Basement southwest of the Wharekuri Fault (the bounding fault on the southwest side of the basin) consists of weakly schistose quartzo-feldspathic greywacke and phyllite of the Haast Schist Group. The basement in the remainder of the study area consists of massive greywacke or flysch sequences of the Torlesse Supergroup.
The stratigraphy and geological map of the study area are shown in figures 1.2 and 1.3 respectively. Age of the sediments is based on observed fossil assemblages or correlation outside the area.
Papakaio Formation, at the base of the transgressive sequence, is interpreted to consist of sediments deposited in a meandering river system; the first marine sediments are the inferred estuarine or tidal flat sands and silts of the Awahokomo Formation. A conglomerate facies within the Awahokomo Formation is presumed to be a channel deposit.
The overlying fossiliferous Pinegrove Conglomerate (which includes some glauconitic quartz sands) is also inferred to be of beach to shallow marine origin.
Members A, B and C of the Wharekuri Greensand are interpreted to have been deposited in shallow marine to lagoonal, barrier island and transitional to offshore environments respectively. The Marshall Paraconformity is found in the Wharekuri Greensand lying between crudely bedded, calcareous, glauconitic siltstone (Globigerina euapertura zone) and the pebbly, concretionary, fine greensand (Globigerina angiporoides zone) represented by a bored fine grained greensand.
Increasing carbonate content in the upper part of the Wharekuri Greensand marks a gradation into the inferred shelf deposits of the Otekaike Limestone which has a massive basal member (A) and bedded upper member (B) which grades into the overlying shallow marine Gee Greensand.
The Southburn Sand has a similar variety of facies to the Awahokomo Formation i.e. barrier island deposits, subtidal zone sediments, tidal channel deposits, tidal flat sediments and mud-flat zone deposits. The Southburn Sand which has a shallower water nature than the immediately underlying units indicates marine regression.
Overlying the Southburn Sand are the complex Waitangi Coal Measures. Inference from stratigraphic relations within the Waitangi Coal Measures and facies analysis have resulted in a picture of deposition in a tectonically subsiding lacustrine environment with two "shallowing" cycles. As well as the lacustrine sediments, the Waitangi Coal Measures include lacustrine delta, meandering river and flood basin deposits.
Further tectonic uplift is marked by the incoming of alluvial fan and braided river deposits of the Kurow Group and Quaternary terrace gravels (on seven recognizable levels).
Field evidence indicates dip -slip movement on faults as follows:
Wharekuri Fault (pre-Tertiary) ...................300 m (NW trending)
Dryburgh Fault (Late Oligocene- Early Miocene)....600 m (NW trending)
Waitangi Fault (Late Miocene- Early Pliocene).....150 m (NW trending)
Deep Creek Fault (Pliocene- Pleistocene)..........120 m (NE trending)
Kurow Fault (Pliocene- Pleistocene)............... (NE trending)
Little Awakino Fault (Pliocene- Pleistocene) ..... (NE trending)
Fern Gully Fault (Pliocene- Pleistocene) ......... (NE trending)
The two sets of faults striking northwest and striking northeast to north are clearly recognized as lineaments on landset photographs.
Provenance studies based on point counts of detrital mineralogy indicate that the Wharekuri Basin first became open to the sea during deposition of the Awahokomo Formation, as marked by an influx of heavy mineral types indicating a plutonic provenance (probably from the Foveaux Strait area).
Volcanic material, probably derived from the nearby Waiareka Volcanics, first appears in the Wharekuri Greensand.
With the deposition of the Southburn Sand, the Wharekuri Basin appears to be closed off again from sediment sources outside the immediate area. The heavy concentrate of this unit and overlying sediments consists overwhelmingly of epidote and pumpellyite, presumably derived from the local metamorphic rocks.
Basement southwest of the Wharekuri Fault (the bounding fault on the southwest side of the basin) consists of weakly schistose quartzo-feldspathic greywacke and phyllite of the Haast Schist Group. The basement in the remainder of the study area consists of massive greywacke or flysch sequences of the Torlesse Supergroup.
The stratigraphy and geological map of the study area are shown in figures 1.2 and 1.3 respectively. Age of the sediments is based on observed fossil assemblages or correlation outside the area.
Papakaio Formation, at the base of the transgressive sequence, is interpreted to consist of sediments deposited in a meandering river system; the first marine sediments are the inferred estuarine or tidal flat sands and silts of the Awahokomo Formation. A conglomerate facies within the Awahokomo Formation is presumed to be a channel deposit.
The overlying fossiliferous Pinegrove Conglomerate (which includes some glauconitic quartz sands) is also inferred to be of beach to shallow marine origin.
Members A, B and C of the Wharekuri Greensand are interpreted to have been deposited in shallow marine to lagoonal, barrier island and transitional to offshore environments respectively. The Marshall Paraconformity is found in the Wharekuri Greensand lying between crudely bedded, calcareous, glauconitic siltstone (Globigerina euapertura zone) and the pebbly, concretionary, fine greensand (Globigerina angiporoides zone) represented by a bored fine grained greensand.
Increasing carbonate content in the upper part of the Wharekuri Greensand marks a gradation into the inferred shelf deposits of the Otekaike Limestone which has a massive basal member (A) and bedded upper member (B) which grades into the overlying shallow marine Gee Greensand.
The Southburn Sand has a similar variety of facies to the Awahokomo Formation i.e. barrier island deposits, subtidal zone sediments, tidal channel deposits, tidal flat sediments and mud-flat zone deposits. The Southburn Sand which has a shallower water nature than the immediately underlying units indicates marine regression.
Overlying the Southburn Sand are the complex Waitangi Coal Measures. Inference from stratigraphic relations within the Waitangi Coal Measures and facies analysis have resulted in a picture of deposition in a tectonically subsiding lacustrine environment with two "shallowing" cycles. As well as the lacustrine sediments, the Waitangi Coal Measures include lacustrine delta, meandering river and flood basin deposits.
Further tectonic uplift is marked by the incoming of alluvial fan and braided river deposits of the Kurow Group and Quaternary terrace gravels (on seven recognizable levels).
Field evidence indicates dip -slip movement on faults as follows:
Wharekuri Fault (pre-Tertiary) ...................300 m (NW trending)
Dryburgh Fault (Late Oligocene- Early Miocene)....600 m (NW trending)
Waitangi Fault (Late Miocene- Early Pliocene).....150 m (NW trending)
Deep Creek Fault (Pliocene- Pleistocene)..........120 m (NE trending)
Kurow Fault (Pliocene- Pleistocene)............... (NE trending)
Little Awakino Fault (Pliocene- Pleistocene) ..... (NE trending)
Fern Gully Fault (Pliocene- Pleistocene) ......... (NE trending)
The two sets of faults striking northwest and striking northeast to north are clearly recognized as lineaments on landset photographs.
Provenance studies based on point counts of detrital mineralogy indicate that the Wharekuri Basin first became open to the sea during deposition of the Awahokomo Formation, as marked by an influx of heavy mineral types indicating a plutonic provenance (probably from the Foveaux Strait area).
Volcanic material, probably derived from the nearby Waiareka Volcanics, first appears in the Wharekuri Greensand.
With the deposition of the Southburn Sand, the Wharekuri Basin appears to be closed off again from sediment sources outside the immediate area. The heavy concentrate of this unit and overlying sediments consists overwhelmingly of epidote and pumpellyite, presumably derived from the local metamorphic rocks.
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Thesis description:
vii, 336 p., ill., diagr., map (in pocket); 30 cm.
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OU geology Identifier:
1986Turkandi
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Abstract Only
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Citation
Turkandi, Tisna, “Geology of Wharekuri and the adjoining area, North Otago and South Canterbury,” Otago Geology Theses, accessed October 9, 2024, https://theses.otagogeology.org.nz/items/show/206.