50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
50thKaikoura05 -1- Kaikoura 2005 CHARACTERISATION OF NEW ...
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and that the MTL marks a Late Carboniferous<br />
continental truncation zone. The date of truncation,<br />
c. 305 Ma, matches the date of opening of the<br />
extensional Sydney-Bowen and Cooper Basins<br />
(Harrington, BMR Bull. 231).<br />
The Brook Street–Gympie volcanic arc was out in<br />
the ocean, far out, because it contains no record of<br />
the intense Permian glaciation on the continent. It<br />
is possible to argue that Late Devonian and<br />
Carboniferous arc split in the Early Permian into<br />
active and remnant arcs separated by an interarc<br />
basin in which the non-continental Maitai<br />
sediments were deposited. The two arcs had wide<br />
outer arc-flanks one of which is preserved between<br />
Gympie and the Esk Basin, and another in the<br />
Caples Terrane.<br />
The Carboniferous truncation zone had thin<br />
Permian passive margin sediments on it. It became<br />
an arc-continent suture zone when the oceanic<br />
Brook Street volcanic arc system docked with it in<br />
the Early and Mid Triassic. Sediment sources then<br />
changed dramatically. The key to that is best<br />
preserved in Queensland where a major foreland<br />
volcanic basin, the Esk Basin, 400 km long and<br />
with associated plutons, formed immediately to the<br />
west of the suture. Resedimented ashfalls from the<br />
Esk andesitic and felsic volcanoes, and from<br />
volcanoes in younger basins to the south, formed<br />
the main sediments in the Murihiku-Maryborough<br />
portion of the interarc basin. In New Zealand the<br />
Mid and Late Triassic rocks of the Rakaia Subterrane<br />
were further from the ashfalls and so<br />
received mainly continental material.<br />
POSTER<br />
MICR<strong>OF</strong>OSSIL RECORD <strong>OF</strong> SEVEN LARGE<br />
EARTHQUAKES IN THE PAST 7500 CAL.<br />
YRS IN SOUTHERN HAWKE’S BAY<br />
1 B.W. Hayward, 1 H.R. Grenfell, 1 A.T. Sabaa,<br />
1 R. Carter, 1 M.S. Morley, 2 U. Cochran,<br />
3 J.H. Lipps, 4 P.R. Shane<br />
1 Geomarine Research, 49 Swainston Rd, St Johns,<br />
Auckland.<br />
2 Institute of Geological and Nuclear Sciences, P.O.<br />
Box 30 368, Lower Hutt.<br />
3 Department of Integrative Biology and Museum of<br />
Paleontology, University of California, Berkeley,<br />
California, 94720, United States.<br />
4 Department of Geology, University of Auckland,<br />
Private Bag 92 019, Auckland.<br />
(b.hayward*geomarine.org.nz)<br />
Foraminiferal and diatom assemblages in eleven<br />
cores (3-7.5 m deep) from brackish Ahuriri Inlet in<br />
southern Hawke’s Bay, New Zealand, provide a<br />
record of 8.5 m of subsidence followed by 1.5 m of<br />
uplift in the last 7500 cal years. Modern Analogue<br />
Technique was used to estimate paleotidal elevation<br />
(subtidal to extreme high water spring level) of the<br />
97 richest foraminiferal assemblages. The most<br />
precise estimates are for marginal high tidal salt<br />
marsh assemblages and the least precise are from<br />
low tidal and subtidal assemblages from near the<br />
centre of the inlet. These paleoelevation estimates<br />
combined with sediment thicknesses, age<br />
determinations (from tephrostratigraphy and<br />
radiocarbon dates), the New Zealand Holocene sea<br />
level curve, and estimates of compaction, identify<br />
the Holocene land elevation changes and<br />
earthquake-displacement events in each core.<br />
By combining the records from all cores, we<br />
recognise the following major, earthquake-related<br />
displacements: ~7200 cal yrs BP (>-0.6 m<br />
displacement); ~5800 cal yrs BP; ~4200 cal yrs BP<br />
(~ - 1.5 m); ~3000 cal yrs BP (-1.4 to -1.8 m);<br />
~1600 cal yrs BP (~ -1.7 m); ~600 cal yrs BP (~ -1<br />
m); 1931AD Napier Earthquake (+1.5 m). The six,<br />
large (possibly subduction interface) subsidence<br />
events in the last 7200 years have had a return time<br />
of 1000-1400 years. Identified displacement events<br />
have a range of sedimentary expressions, from an<br />
eroded and burrowed hiatus surface, to an abrupt<br />
lithologic switch from mud to sand, or peat to<br />
shelly mud, or in some places no change in<br />
sediment character whatsoever.<br />
ORAL<br />
CRETACEOUS OCEANIC RED BEDS<br />
(CORB’S) IN <strong>NEW</strong> ZEALAND: EVIDENCE<br />
FOR A GLOBAL PHENOMENON?<br />
D.C.H. Hikuroa 1 &J.S.Crampton 2<br />
1 Department of Geology, University of Auckland,<br />
New Zealand<br />
2 Institute of Geological & Nuclear Sciences, Lower<br />
Hutt, New Zealand<br />
(d.hikuroa*auckland.ac.nz)<br />
During the Cretaceous, New Zealand occupied a<br />
position on the Pacific margin of Gondwana. In the<br />
Aptian it was located at a latitude of 75°S – 85°S<br />
and, by the end of the Maastrichtian, was at a<br />
latitude of 55°S – 65°S. The Cretaceous System<br />
spans a major transition in the geological history of<br />
New Zealand, marking the end of prolonged<br />
subduction on the Pacific margin of Gondwanaland,<br />
and by the end of the Cretaceous, complete<br />
separation of New Zealand from all other<br />
Gondwanan fragments.<br />
Early Cretaceous strata occur as structurally<br />
complex, uppermost sections of a thick, Mesozoic<br />
‘basement’ sequence. Unconformably overlying<br />
the ‘basement’ rocks are structurally relatively<br />
uncomplicated late Early to Late Cretaceous<br />
‘cover’ formations, comprising three characteristic<br />
successions. (1) Thick (up to 4000 m) non-marine<br />
sequences; (2) thick (up to 3000 m) relatively<br />
50 th <strong>Kaikoura</strong>05 -35- <strong>Kaikoura</strong> <strong>2005</strong>