New Zealand Journal of Geology and Geophysics abstracts
Holocene motion on the Akatore Fault, south Otago coast, New Zealand
NICOLA J. LITCHFIELD
RICHARD J. NORRIS
Department of Geology
University of Otago
P.O. Box 56
Dunedin, New Zealand
Abstract The Akatore Fault comprises the onshore
leading edge of the Otago reverse fault-fold belt, part of the outboard zone of
Australia-Pacific plate continental collision in the South Island. We examine
stratigraphic and sedimentologic evidence of late Holocene reverse faulting
along the Akatore Fault, and use radiocarbon dating to constrain fault rupture
events and associated uplift of the Akatore fault block. Two fault rupture
events are recorded in swamps on the downthrown, upstream side of the fault, as
forest and/or peat horizons buried by silt, dated at post-3800 yr BP and
1150-1000 yr BP. The latest event coincides with the timing of uplift of a
3 m marine terrace on the coast, and the uplift of a second (6 m) is
tentatively correlated to the penultimate event. The terrace height data,
together with the amount of offset of alluvial gravels resting on the fluvial
strath surface at the blocked swamp sites, suggests an average of 3 m of
throw per uplift event. Distribution of throw along the fault suggests that the
last event was not symmetrical about the centre of the scarp in the manner of
the long-term throw. Offset of the third highest marine terrace, dated at
80 ka, can be wholly accounted for by the Holocene events, suggesting a
period of quiescence between 80 000 and 3800 yr BP.
Keywords Holocene; paleoseismology; reverse fault; marine
terrace; antecedent drainage; Otago; New Zealand
New Zealand Journal of Geology & Geophysics, 2000, Vol. 43:
405-418
0028-8306/00/4303-0405 $7.00/0 (c) The Royal Society of New Zealand
2000
PDF file of entire paper: medium quality (2355K); (scanned from paper original: notes about this process)
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