New Zealand Journal of Geology and Geophysics abstracts
Mineralogy, stratigraphy, and provenance of soil coverbeds in the Kumara
district, Westland
V. E. NEALL
R. B. STEWART
R. C. WALLACE
M. C. WILLIAMS
Soil and Earth Sciences
Institute of Natural Resources
Massey University
Private Bag 11 222
Palmerston North, New Zealand
G. MEW
2/77 Kairimu Street
Stokes Valley
Lower Hutt, New Zealand
Abstract The sand and silt mineralogy of four soils preserved
on fluvioglacial outwash terraces at Kumara indicates that the main soil body
is developed in up to 1 m of loessial coverbeds that accumulated subsequent to
cessation of gravel terrace formation. Oxygen isotope abundances of the
dominant mineral quartz in these soils show a higher temperature origin for the
>250 μm fraction, consistent with derivation from local granodiorites.
Finer quartz is of a mixed provenance origin consistent with the variety of
rock types in the region. The finest quartz, <5 μm, of aerosolic origin,
can be used as a proxy time record for the coverbed accumulations.
The widespread 22 590 yr BP Aokautere Ash chronohorizon is preserved in
three of the profiles, whilst wind redeposition of the glass shards is
responsible for traces of rhyolitic glass in all subsequent horizons.
Widespread landscape erosion is postulated either immediately before or during
deposition of the K-1 terrace, so that similar subsequent coverbed sequences
are preserved on the K-1 and all older terraces in this district. Magnetic
mineral assemblages in the profiles indicate a slightly different loessial
provenance for the Cockeye, K-1, and K-2.1 profiles, but the K-2.2 is
significantly different from the rest. This is probably a function of aeolian
winnowing and variability of source materials. In the past, different mountain
catchments have connected with different lower river reaches, due to
transcurrent movement on the Alpine Fault. This is interpreted as having led to
changing provenance of river sediment supplying loess to local soils.
Keywords Kumara; Westland; Quaternary; mineralogy; glacial
outwash surfaces; soils; aerosolic dust; oxygen isotopes; Aokautere Ash;
chronostratigraphy; loess; Alpine Fault
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
205-218
0028-8306/01/4402-0205 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (1665K); (scanned from paper original: notes about this process)
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