50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
You also want an ePaper? Increase the reach of your titles
YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.
2 National Institute of Water and Atmosphere Ltd,<br />
PO Box 8602, Christchurch, New Zealand.<br />
(a.wells*gns.cri.nz)<br />
A study of five shore-parallel dune ridge sequences<br />
in southwest New Zealand shows that tectonic<br />
activity has been the primary controlling influence<br />
in their formation since at least AD 1450. The<br />
timing of dune building episodes at the mouths of<br />
the Haast, Okuru, Waiatoto, Arawhata and Awarua<br />
Rivers was determined using the ages of colonizing<br />
trees. Episodic dune formation was indicated by<br />
clear discontinuities in tree ages, with distinct<br />
cohorts having colonized successive, newlyformed,<br />
dune ridge-swale units. At Haast and<br />
Okuru, four dune ridge-swale units have formed<br />
since AD 1460, with each unit closely post-dating<br />
an Alpine fault rupture (c. AD 1490, c. AD 1615,<br />
AD 1717, AD 1826). At Waiatoto, Arawhata and<br />
Awarua, three dune-swale units have formed since<br />
AD 1490 and each of these also closely post-dates<br />
an Alpine fault rupture (c. AD 1490, AD 1717, AD<br />
1826). Colonizing cohorts of trees started growing<br />
within 17-47 years after an earthquake, and at all<br />
five sites all known major regional earthquakes that<br />
affected each site since AD 1460 had resulted in a<br />
dune building episode at that site. No other dunes<br />
are present at any site.<br />
Progradational coastal dune systems have potential<br />
as a tool for paleoseismic studies. In regions with<br />
high background levels of sediment delivery to<br />
limit erosion/burial of dunes and with little<br />
coseismic subsidence, dune systems may offer a<br />
near-complete, spatially discrete record of<br />
earthquake-induced sedimentation events over the<br />
last 6500 years or so. Earthquakes are a key driver<br />
of paleoenvironmental change and coastal plain<br />
development in this tectonically active region.<br />
ORAL<br />
MECHANISMS <strong>OF</strong> LATE QUATERNARY<br />
FOREARC UPLIFT: A CASE STUDY <strong>OF</strong> THE<br />
NORTHEASTERN RAUKUMARA<br />
PENINSULA, <strong>NEW</strong> ZEALAND<br />
Kate Wilson 1 , Kelvin Berryman 2 , Tim Little 1 ,<br />
Nicola Litchfield 2 & Ursula Cochran 2 .<br />
1 Victoria University of Wellington, PO Box 600,<br />
Wellington.<br />
2 Institute of Geological and Nuclear Sciences, PO<br />
Box 30368, Lower Hutt.<br />
(K.Wilson*gns.cri.nz)<br />
On the northeastern Raukumara Peninsula at Hicks<br />
Bay and Te Araroa, we have investigated Holocene<br />
landforms and coastal stratigraphy with the aim of<br />
documenting coastal uplift mechanisms. Drill cores<br />
of incised-valley infill sediments at Hicks Bay<br />
show apparently continuous estuarine<br />
sedimentation at intertidal elevations throughout the<br />
early Holocene. Radiocarbon ages allow<br />
comparisons between the thickness of sediment<br />
preserved and the amount of accommodation space<br />
expected to have been created within the estuary<br />
due to eustatic sea level rise. Accommodation space<br />
deficits indicate tectonic uplift did take place during<br />
deposition of the sequence, yet the continuity of<br />
estuarine sedimentation implies this tectonic uplift<br />
was relatively gradual and continuous as opposed to<br />
the sudden and infrequent uplift characteristic of<br />
earthquakes.<br />
Raised beach ridges at Te Araroa, ~ 8 km southeast<br />
of Hicks Bay, display a seaward-sloping, stepped<br />
morphology. The seaward slope indicates that<br />
gradual tectonic uplift continued through the midlate<br />
Holocene. The beach ridge steps have an<br />
amplitude of