New Zealand Journal of Geology and Geophysics abstracts
Tectonic and paleoclimatic significance of Quaternary river terraces of the
Waipaoa River, east coast, North Island, New Zealand
KELVIN BERRYMAN
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
email: k.berryman@gns.cri.nz
MICHAEL MARDEN
Landcare Research
Private Bag 445
Gisborne, New Zealand
DENNIS EDEN
Landcare Research
Private Bag 11052
Palmerston North, New Zealand
*Present address: Department of Geography, Tokyo Metropolitan University,
Tokyo, Japan.
COLIN MAZENGARB
Institute of Geological & Nuclear Sciences
Lower Hutt
YOKO OTA
Emeritus Professor
Department of Geography
Yokohama National University
Yokohama, Japan
ICHIO MORIYA
Department of Geography
Kanazawa University
Kakumacyo
Kanazawa 920-11, Japan
Abstract Remnants of four aggradational terraces in the lower
45 km of the main branch of the Waipaoa River have been correlated with
cold/cool climate episodes of the Otiran glaciation. The youngest of the
aggradation levels--the Waipaoa-1 terrace--has the c. 14.7 ka
Rerewhakaaitu Tephra as the oldest part of the coverbed sequence, indicating
cessation of aggradation about 16 ka BP. This terrace is broadly
correlated with Ohakean-aged terraces in other parts of the North Island. The
second most recent episode of aggradation--the Waipaoa-2 terrace--is slightly
older than the c. 28 ka Mangaone Tephra, and is broadly correlated
with the Rata terrace. The third most recent aggradation episode--the Waipaoa-3
terrace--is slightly older than the c. 55-57 ka Rotoehu Tephra (age
estimate based on stratigraphic relationships in this study), indicating
cessation of aggradation at c. 65 ka BP, and correlative with the
Porewa terrace. The fourth, and oldest, aggradation episode we identify in the
present landscape--the Waipaoa-4 terrace--has poor age constraints, but is
probably related to the cool period of late oxygen isotope stage 5 at
c. 90 ka BP or the glacial period of oxygen isotope stage 6 at
c. 140 ka BP.
Tectonic deformation in the middle reaches of the Waipaoa catchment is deduced
from the elevation difference of pairs of aggradation terraces, and takes the
form of broad regional uplift in the range of 0.5-1.1 mm/yr. Uplift is
probably driven by subduction processes in the middle part of the catchment and
by a combination of deep-seated subduction processes and local deformation
associated with active faults and folds in the lower valley area. Downcutting
rates of up to 7 mm/yr occur in upper reaches of the river. In the middle
reaches of the valley, where there are both uplift and downcutting data, we
find that downcutting is about four times faster than tectonic uplift. Thus,
climate fluctuations are interpreted to be the primary control on formation of
fluvial terrace landscapes in the region.
Keywords Quaternary; fluvial terraces; aggradation;
downcutting; paleoclimate; uplift; tectonic deformation; tephra; Waipaoa River;
Poverty Bay; Raukumara Peninsula
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
229-245
0028-8306/00/4302-0229 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (3625K); (scanned from paper original: notes about this process)
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