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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VEGETATION AND CLIMATE CHANGE AT<br />
THE PALEOCENE-EOCENE TRANSITION<br />
E.M. Crouch, J.I. Raine & E.M. Kennedy<br />
GNS Science, PO Box 30368 Lower Hutt.<br />
(e.crouch*gns.cri.nz)<br />
Plant microfossil (spore/pollen) assemblages from<br />
New Zealand Paleocene–Eocene (P–E) sedimentary<br />
sections show a general change from predominantly<br />
gymnosperm-rich Paleocene floras (zone PM3) to<br />
Casuarina-dominated angiosperm-rich floras in the<br />
Early Eocene (zone MH1). Modern relatives of the<br />
fossil plant taxa and vegetation analogues indicate<br />
this change is related to significant climatic<br />
warming, although the precise timing and extent of<br />
more subtle vegetation change during the P–E<br />
transition remains poorly documented. Previous<br />
studies (e.g., Tawanui section, Hawkes Bay, and<br />
Moeraki-Hampden section, Otago) suggest that the<br />
main vegetation change in the Paleocene–Eocene<br />
occurred in the upper Waipawan Stage (earliest<br />
Eocene) and post-dated the significant climatic and<br />
carbon cycle perturbation at the P–E boundary (~55<br />
Ma). Plant microfossil records are currently being<br />
studied from a silica-sand quarry at Mt Somers,<br />
South Canterbury, and in the Kumara-2 core,<br />
central Westland, to elucidate the timing and scale<br />
of vegetation change during the P–E transition.<br />
Gymnosperm pollen and Proteaceae and small<br />
triporate angiosperm pollen are abundant in the<br />
lower part of the Kumara-2 core (1739-50 m), and a<br />
Late Paleocene age is suggested. Coastal marine<br />
sediments are present from ~1733-38 m, with<br />
abundant cysts of the marine dinoflagellate genus<br />
Apectodinium recorded in the middle of this unit.<br />
Coincident with the base of the marine horizon,<br />
pollen indicative of warm climates (e.g.,<br />
Cupanieidites orthoteichus, Spinizonocolpites<br />
prominatus) are first recognised and become a<br />
recognisable component of the spore/pollen<br />
assemblage. Spores/pollen are absent from a<br />
channel fill sand at 1722-33 m, but above this unit<br />
the assemblage is diverse, angiosperm pollen are<br />
abundant and Casuarina pollen (zone MH1)<br />
markedly increase in the upper part of the studied<br />
core. Abundant Apectodinium dinocysts in the<br />
coastal marine unit suggests this interval lies very<br />
close to the P–E boundary, and it appears this<br />
marine incursion may be related to a thermal<br />
expansion of ocean waters and slight sea-level rise<br />
at the time of extreme warming at the P–E<br />
boundary. Compound-specific organic carbon<br />
isotope analyses are currently being completed to<br />
confirm the presence and position of the P–E<br />
boundary.<br />
Within the sand dominated Broken River<br />
Formation-Homebush Sandstone section at Mt<br />
Somers, fine-grained mudstone layers were<br />
sampled where possible and palynomorph<br />
assemblages examined. A Late Paleocene sample<br />
contains common gymnosperms and appears to be<br />
terrestrial, although marine dinocysts have<br />
previously been recorded from a similar horizon.<br />
Above this, a prominent ~3 m grey mudstone<br />
contains abundant cysts of the marine dinoflagellate<br />
genus Apectodinium, indicating an early Waipawan<br />
age. Marine conditions persist in the overlying<br />
mudstone layers examined, with an uppermost<br />
glauconitic sandstone unit containing dinocysts<br />
indicative of the Mangaorapan Stage. Pollen<br />
indicative of warm climates are present by the early<br />
Waipawan (prominent mudstone unit), and<br />
Casuarina pollen (zone MH1) is abundant in the<br />
upper glauconitic sandstone unit.<br />
POSTER<br />
“100 KM PER MILLION YEARS” A<br />
HIGHLY-DYNAMIC DEPOSITIONAL<br />
MODEL FOR LATE MIOCENE ROCKS IN<br />
TARANAKI BASIN<br />
Martin Crundwell &MalcolmArnot<br />
Geological and Nuclear Science Limited, PO Box<br />
30-368, Lower Hutt, NZ<br />
(m.crundwell*gns.cri.nz)<br />
New biostratigraphic dating techniques challenge<br />
traditional exploration paradigms and suggest a<br />
highly dynamic depositional model is more<br />
appropriate for late Miocene rocks in Taranaki<br />
Basin, with multiple deep-water sedimentary<br />
systems of considerable thickness, developed on<br />
local geographic scales, over timescales of orbital<br />
proportions (40-100 kyr). Although the general<br />
pattern and tempo of late Miocene sedimentation<br />
are clearly dictated by climate forcing, suborbitalscale<br />
variations in sedimentary patterns and rates of<br />
deposition reflect a complex history of shelf<br />
progradation, tempered by sediment supply and<br />
accommodation, and tectonic controls within and<br />
adjacent to the basin. The observed dynamism in<br />
sedimentation is consistent with the tectonic<br />
development of the eastern Taranaki Basin margin<br />
(e.g. King and Thrasher, 1996), and with detailed<br />
outcrop based stratigraphic studies undertaken by<br />
GNS (e.g. King et al., 1993; Browne and Slatt,<br />
2002), and also with many of the problems<br />
associated with hydrocarbon reservoir sequences<br />
(e.g. poor correlation and dating, rapid facies<br />
variations, and variable reservoir characteristics).<br />
In this presentation, we outline some of the new<br />
biostratigraphic tools that have been developed<br />
specifically to address correlation problems<br />
associated with late Miocene rocks in Taranaki<br />
Basin. Examples from Pukearuhe-1 and outcrop<br />
studies are given, of extremely high estimated rates<br />
of sedimentation, based on weight standardized<br />
counts of planktic and benthic foraminifers,<br />
50 th <strong>Kaikoura</strong>05 -23- <strong>Kaikoura</strong> <strong>2005</strong>