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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truncating three plutonic suites of the Cambrian<br />
Granite Harbour Intrusives (Dry Valley 1a & 1b,<br />
and DV 2) and their metamorphic country rocks.<br />
Provenance analysis was carried out on both<br />
sandstones and conglomerates using clast counts,<br />
petrographic analysis and U–Pb detrital zircon<br />
analysis. Conglomerates are dominated by silicic<br />
igneous clasts, mainly rhyolites, and fine-grained<br />
quartzites, both of which are unknown in outcrop in<br />
southern Victoria Land. Previously recorded<br />
granitoid clasts could not be found.<br />
Rhyolite clasts have a geochemistry typical of<br />
highly evolved subduction-related rocks. Previous<br />
workers have dated rhyolite and tuff clasts at<br />
between 497±17 Ma and 492±8 Ma, ages that are<br />
within error of the Granite Harbour magmatic<br />
suites. This suggests that the volcanic clasts came<br />
from a co-magmatic volcanic arc rather than a<br />
northern Victoria Land source as tentatively<br />
proposed by earlier workers. Detrital zircon U–Pb<br />
ages for the quartzite clasts suggest derivation from<br />
the East Antarctic craton and that the sandstones<br />
had been deposited before the Ross/Delamarian<br />
Orogeny.<br />
Sandstones in the Sperm Bluff Formation are<br />
arkosic to quartzose in composition but<br />
conspicuously lack plagioclase, indicating<br />
significant weathering of a continental source.<br />
Detrital zircon analysis gives a strong 500 Ma peak<br />
characteristic of Ross/Delamarian orogen magmatic<br />
rocks, and consistent with a local source.<br />
Basin analysis of the six lithofacies comprising the<br />
Sperm Bluff Formation suggest foreshore–<br />
shoreface, shallow marine, estuarine and wavedominated<br />
deltaic environments. A large delta, or<br />
fan-delta, composed partially of easterly-derived<br />
conglomerates, as indicated by palaeocurrent<br />
directions and channel orientation where the<br />
conglomerates are thickest, became buried by<br />
marine sandstones during a relative rise in sea level.<br />
The presence of pre-Ross quartzite clasts suggests<br />
that older continental rocks existed to the east.<br />
Westward subduction during the Late Cambrian led<br />
to the emplacement of the Granite Harbour<br />
Intrusives and their superstructure of rhyolitic<br />
volcanoes (DV 1). Dry Valley Suite 2 intrusive<br />
rocks and associated volcanic rocks were probably<br />
emplaced slightly later in a downfaulted<br />
extensional intra-arc basin. This had the effect of<br />
preserving the volcanic superstructure in the<br />
downfaulted block while the volcanic rocks were<br />
being eroded from the upfaulted block to expose<br />
the much deeper Granite Harbour Intrusives. Basin<br />
inversion during the Devonian caused uplift of the<br />
preserved volcanic rocks, supplying rhyolitic and<br />
older quartzite clasts to the lower part of the new<br />
Beacon Supergroup basin. The basin inversion may<br />
have been a far-field effect of tectonic changes<br />
indicated by widespread mid-Devonian<br />
deformation (Tabberabberan Orogeny) and<br />
subsequent granite magmatism in Australia, New<br />
Zealand,<br />
Antarctica.<br />
northern Victoria Land and West<br />
POSTER<br />
LATE CRETACEOUS EUSTASY AND THE<br />
EAST COAST BASIN - THE BAD <strong>NEW</strong>S!<br />
Poul Schiøler 1 , James S. Crampton 2<br />
&MalcolmG.Laird 3<br />
1 Geol. Surv. of Denmark and Greenland, Ø.<br />
Voldgade 10, 1350 Copenhagen, Denmark.<br />
2 Inst. of Geol. & Nucl. Sci., PO Box 30 368, Lower<br />
Hutt<br />
3 Dept. of Geol. Sci., Univ. of Canterbury, Private<br />
Bag 4800, Christchurch.<br />
(pos*geus.dk)<br />
A palynofacies analysis of four sections through the<br />
Paton and Herring Formations of the East Coast<br />
Basin in southern Marlborough shows that the two<br />
formations were deposited in a marine environment<br />
with conspicuous input of plant material from<br />
adjacent land area. The Paton Formation was<br />
deposited on the inner to mid-shelf under oxic<br />
conditions and in proximity to a river delta. The<br />
deposition of the Herring Formation took place<br />
farther offshore, on the mid-shelf, in a muddominated<br />
environment under poorly oxygenated<br />
conditions at the sediment/water interface,<br />
following a landward shift of shoreline. A<br />
stratigraphic analysis of changes in palynofacies<br />
and lithology through the four sections allows a<br />
breakdown of the succession into seven<br />
depositional sequences, separated by<br />
unconformities or their correlative conformities. A<br />
regional sea-level curve for the Middle Coniacian–<br />
Upper Campanian in the East Coast Basin is<br />
proposed on the basis of the inferred sequences and<br />
chronostratigraphic control from dinoflagellate<br />
biostratigraphy. The sea-level cycles thus inferred<br />
for the East Coast Basin show a poor correlation<br />
with the re-scaled Haq cycle chart, suggesting that<br />
regional tectonics rather than eustasy controlled the<br />
East Coast Basin sequences.<br />
Dinoflagellates<br />
(Schiøler & Wilson, 1998;<br />
Roncaglia et al., 1999;<br />
with modifications from<br />
Crampton et al., 2000;<br />
and herein)<br />
Trithyrodinium<br />
suspectum ISZ<br />
Nelsoniella aceras IZ<br />
Isabelidinium cretaceum IZ<br />
Piripauan<br />
Odontochitina porifera IZ<br />
Conosphaeridium abbreviatum IZ<br />
Cymososphaeridium<br />
benmorense IZ<br />
50 th <strong>Kaikoura</strong>05 -77- <strong>Kaikoura</strong> <strong>2005</strong><br />
NZ stages<br />
Upper<br />
Haumurian<br />
(pars)<br />
Lower Haumurian<br />
Teratan<br />
(pars)<br />
Satyrodinium<br />
haumuriense IZ<br />
Isabelidinium<br />
pellucidum IZ<br />
Isabelidinium<br />
korojonense IZ<br />
Vozzhennikovia<br />
spinulosa ISZ<br />
Chlamydophorella ambigua IZ<br />
NS<br />
H<br />
P<br />
Study sections<br />
W E<br />
KR<br />
H<br />
P<br />
UBM<br />
H<br />
P<br />
BMS<br />
H<br />
P<br />
Regional<br />
Sea-level curve,<br />
East Coast Basin<br />
?sb 6<br />
HST<br />
?mf 5<br />
LST-TST<br />
sb 5<br />
HST<br />
mf 4<br />
LST-TST<br />
sb 44<br />
HST<br />
?mf 3<br />
LST-TST<br />
sb 3<br />
HST<br />
mf 2<br />
LST-TST sb 2<br />
LST-HST sb 1<br />
HST<br />
?mf 0<br />
High Low<br />
Sea-level curve<br />
(Haq et al., 1987<br />
as re-scaled by<br />
Hardenbol et al., 1998)<br />
Chronostratigraphy<br />
(time-scale after<br />
Hardenbol et al., 1998)<br />
71.3<br />
Campanian<br />
83.5<br />
Santonian<br />
85.8<br />
Coniacian<br />
89.0<br />
Turonian (part)<br />
Ma