Continental shelf sedimentation east of Karitane Point, East Otago, New Zealand.
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The nature and distribution of continental shelf sediments in and to the north of Blueskin Bay are controlled by several factors:
1) river discharge and sediment input of the Clutha River 96km. south of the area studied,
2) the Southland Current which eddies into Blueskin Bay,
3) the wave height of the southerly swell almost always present, and
4) reworking by benthic organisms.
By tracing the five prominent detrital sediment modes calculated by Andrews (1973) it is possible to determine the late Quaternary depositional history in the area. At lower sea levels Modes I, II, III, IV and V, derived mainly from the Clutha River, were moved northward by a sediment transport system - probably a combination of the Southland Current and a longshore drift mechanism. After attainment of the approximate present sea level (c.6>000 years B.P.) hydrological conditions on the shelf have only been capable of shifting mode IV and V sediment (finer than 3)although considerable northward movement of coarser sand probably occurs in the littoral zone during severe southerly storms.
Tracing the distribution of fine sand size mica has proved useful in indicating hydrological conditions and depositional regimes on the East Otago continental shelf.
The outer shelf (depths greater than 40m.) is covered by gravelly sands ( > 40% carbonate gravel material) and is regarded as a residual relict deposit. The inner shelf (depths less than 40m.) is covered by fine and silty very fine sand regarded as an example of a "palimpsest" deposit. The palimpsest sands consist of a mixture of relict and recent sediment. Relict sediment was derived from the outer shelf gravelly sands by winnowing currents during the Holocene transgression and the recent sediment is being derived from the Clutha River at present.
1) river discharge and sediment input of the Clutha River 96km. south of the area studied,
2) the Southland Current which eddies into Blueskin Bay,
3) the wave height of the southerly swell almost always present, and
4) reworking by benthic organisms.
By tracing the five prominent detrital sediment modes calculated by Andrews (1973) it is possible to determine the late Quaternary depositional history in the area. At lower sea levels Modes I, II, III, IV and V, derived mainly from the Clutha River, were moved northward by a sediment transport system - probably a combination of the Southland Current and a longshore drift mechanism. After attainment of the approximate present sea level (c.6>000 years B.P.) hydrological conditions on the shelf have only been capable of shifting mode IV and V sediment (finer than 3)although considerable northward movement of coarser sand probably occurs in the littoral zone during severe southerly storms.
Tracing the distribution of fine sand size mica has proved useful in indicating hydrological conditions and depositional regimes on the East Otago continental shelf.
The outer shelf (depths greater than 40m.) is covered by gravelly sands ( > 40% carbonate gravel material) and is regarded as a residual relict deposit. The inner shelf (depths less than 40m.) is covered by fine and silty very fine sand regarded as an example of a "palimpsest" deposit. The palimpsest sands consist of a mixture of relict and recent sediment. Relict sediment was derived from the outer shelf gravelly sands by winnowing currents during the Holocene transgression and the recent sediment is being derived from the Clutha River at present.
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92 p. : illus., chart in pocket ; 30 cm.
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1975Loutit
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Loutit, Tom Stuart., “Continental shelf sedimentation east of Karitane Point, East Otago, New Zealand.,” Otago Geology Theses, accessed April 22, 2025, https://theses.otagogeology.org.nz/items/show/87.