New Zealand Journal of Geology and Geophysics abstracts
The impact of episodic fault-related folding on late Holocene degradation
terraces along Waipara River, New Zealand
ANDREW NICOL
Institute of Geological & Nuclear Sciences Ltd
P.O. Box 30 368
Lower Hutt, New Zealand
JOCELYN K. CAMPBELL
Department of Geological Sciences
University of Canterbury
Private Bag 4800
Christchurch, New Zealand
Abstract The Waipara River flows eastwards through growing
folds in the tectonically active foothills of New Zealand's Southern Alps. In
the middle Waipara region, flights of degradation terraces are widespread and
rise to 55 m above river channels. Ages of terrace surfaces and
paleoearthquakes on four faults are constrained by radiocarbon samples and
weathering-rind dates from surface cobbles of Torlesse Group sandstone. Terrace
ages indicate rapid incision (c. 30-100 mm/yr) of Waipara River and three
tributaries during the late Holocene. Cumulative-incision curves suggest a
15-25 m lowering of regional base level over the last thousand years and an
additional 20-25 m of local incision 200-600 yr BP along Waipara River where it
crosses Doctors Anticline. Rapid river incision was strongly influenced by rock
uplift on the anticline associated with fault rupture during an earthquake
300-400 yr BP. From incision data we infer that the earthquake was preceded and
followed by aseismic fold growth. Tectonic uplift during folding was probably,
at most, one-third of local river incision; this discrepancy may relate to the
short sample period and to locally elevated stream erosive power due in part to
a reduction in floodplain width.
Keywords active folds; uplift; downcutting; fluvial
processes; paleoseismology; aseismic; weathering rind; radiocarbon; Waipara
River; Canterbury; New Zealand
New Zealand Journal of Geology & Geophysics, 2001, Vol. 44:
145-156
0028-8306/01/4401-0145 $7.00/0 (c) The Royal Society of New Zealand
2001
PDF file of entire paper: medium quality (2236K); (scanned from paper original: notes about this process)
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