50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...

and that the MTL marks a Late Carboniferous
continental truncation zone. The date of truncation,
c. 305 Ma, matches the date of opening of the
extensional Sydney-Bowen and Cooper Basins
(Harrington, BMR Bull. 231).
The Brook Street–Gympie volcanic arc was out in
the ocean, far out, because it contains no record of
the intense Permian glaciation on the continent. It
is possible to argue that Late Devonian and
Carboniferous arc split in the Early Permian into
active and remnant arcs separated by an interarc
basin in which the non-continental Maitai
sediments were deposited. The two arcs had wide
outer arc-flanks one of which is preserved between
Gympie and the Esk Basin, and another in the
Caples Terrane.
The Carboniferous truncation zone had thin
Permian passive margin sediments on it. It became
an arc-continent suture zone when the oceanic
Brook Street volcanic arc system docked with it in
the Early and Mid Triassic. Sediment sources then
changed dramatically. The key to that is best
preserved in Queensland where a major foreland
volcanic basin, the Esk Basin, 400 km long and
with associated plutons, formed immediately to the
west of the suture. Resedimented ashfalls from the
Esk andesitic and felsic volcanoes, and from
volcanoes in younger basins to the south, formed
the main sediments in the Murihiku-Maryborough
portion of the interarc basin. In New Zealand the
Mid and Late Triassic rocks of the Rakaia Subterrane
were further from the ashfalls and so
received mainly continental material.
POSTER
MICROFOSSIL RECORD OF SEVEN LARGE
EARTHQUAKES IN THE PAST 7500 CAL.
YRS IN SOUTHERN HAWKE’S BAY
1 B.W. Hayward, 1 H.R. Grenfell, 1 A.T. Sabaa,
1 R. Carter, 1 M.S. Morley, 2 U. Cochran,
3 J.H. Lipps, 4 P.R. Shane
1 Geomarine Research, 49 Swainston Rd, St Johns,
Auckland.
2 Institute of Geological and Nuclear Sciences, P.O.
Box 30 368, Lower Hutt.
3 Department of Integrative Biology and Museum of
Paleontology, University of California, Berkeley,
California, 94720, United States.
4 Department of Geology, University of Auckland,
Private Bag 92 019, Auckland.
(b.hayward*geomarine.org.nz)
Foraminiferal and diatom assemblages in eleven
cores (3-7.5 m deep) from brackish Ahuriri Inlet in
southern Hawke’s Bay, New Zealand, provide a
record of 8.5 m of subsidence followed by 1.5 m of
uplift in the last 7500 cal years. Modern Analogue
Technique was used to estimate paleotidal elevation
(subtidal to extreme high water spring level) of the
97 richest foraminiferal assemblages. The most
precise estimates are for marginal high tidal salt
marsh assemblages and the least precise are from
low tidal and subtidal assemblages from near the
centre of the inlet. These paleoelevation estimates
combined with sediment thicknesses, age
determinations (from tephrostratigraphy and
radiocarbon dates), the New Zealand Holocene sea
level curve, and estimates of compaction, identify
the Holocene land elevation changes and
earthquake-displacement events in each core.
By combining the records from all cores, we
recognise the following major, earthquake-related
displacements: ~7200 cal yrs BP (>-0.6 m
displacement); ~5800 cal yrs BP; ~4200 cal yrs BP
(~ - 1.5 m); ~3000 cal yrs BP (-1.4 to -1.8 m);
~1600 cal yrs BP (~ -1.7 m); ~600 cal yrs BP (~ -1
m); 1931AD Napier Earthquake (+1.5 m). The six,
large (possibly subduction interface) subsidence
events in the last 7200 years have had a return time
of 1000-1400 years. Identified displacement events
have a range of sedimentary expressions, from an
eroded and burrowed hiatus surface, to an abrupt
lithologic switch from mud to sand, or peat to
shelly mud, or in some places no change in
sediment character whatsoever.
ORAL
CRETACEOUS OCEANIC RED BEDS
(CORB’S) IN NEW ZEALAND: EVIDENCE
FOR A GLOBAL PHENOMENON?
D.C.H. Hikuroa 1 &J.S.Crampton 2
1 Department of Geology, University of Auckland,
New Zealand
2 Institute of Geological & Nuclear Sciences, Lower
Hutt, New Zealand
(d.hikuroa*auckland.ac.nz)
During the Cretaceous, New Zealand occupied a
position on the Pacific margin of Gondwana. In the
Aptian it was located at a latitude of 75°S – 85°S
and, by the end of the Maastrichtian, was at a
latitude of 55°S – 65°S. The Cretaceous System
spans a major transition in the geological history of
New Zealand, marking the end of prolonged
subduction on the Pacific margin of Gondwanaland,
and by the end of the Cretaceous, complete
separation of New Zealand from all other
Gondwanan fragments.
Early Cretaceous strata occur as structurally
complex, uppermost sections of a thick, Mesozoic
‘basement’ sequence. Unconformably overlying
the ‘basement’ rocks are structurally relatively
uncomplicated late Early to Late Cretaceous
‘cover’ formations, comprising three characteristic
successions. (1) Thick (up to 4000 m) non-marine
sequences; (2) thick (up to 3000 m) relatively
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