New Zealand Journal of Geology and Geophysics abstracts
Deep-sea record of Pliocene and Pleistocene terrestrial palynomorphs from
offshore eastern New Zealand (ODP Site 1123, Leg 181)
D. C. Mildenhall
Institute of Geological & Nuclear Sciences
P.O. Box 30 368
Lower Hutt, New Zealand
Abstract Terrestrial palynomorph assemblages of Pliocene
and Pleistocene age have been recovered from ODP Site 1123 (Leg 181), 1100
km offshore from eastern New Zealand and from a water depth of 3300 m. Palynomorphs
occur in such significant numbers as to allow for a greatly enhanced correlation
between the orbitally tuned marine record and climatically controlled changes
in terrestrial vegetation, despite a long distance from shore and a great
depth. Gradual changes in the dominant pollen types from more mesothermal
taxa (Nothofagus subgenus Brassospora), in the Pliocene and
early Pleistocene, to less mesothermal (Nothofagus subgenus Fuscospora
and podocarp conifers) taxa in the middle and late Pleistocene reflect what
have been detected in shorter onshore sections. Since assemblages are regional
in origin, this suggests a gradual change from warm, humid, maybe cloudy conditions
to a cooler, drier climate over time superimposed upon more intense glacial/interglacial
cycles. The glacial periods in this marine setting have more Halocarpus,
Phyllocladus, Nothofagus subgenus Fuscospora, and Coprosma
pollen relative to the interglacials.Overall, the palynomorph assemblages
are derived from regional podocarp/hardwood forest vegetation from the southern
part of North Island, New Zealand, with pollen and spores from a range of
terrestrial environments represented in all samples. Recycling has occurred
but is difficult to quantify because of the great variation in the quality
of preservation and the different sources and possible modes of transport
of palynomorphs to the site of deposition.Angiosperm pollen are dominated
by Nothofagus, but angiosperm pollen generally are relatively sparse,
while robust spores such as Cyathea, and bisaccate pollen such as
Podocarpus/Prumnopitys, with the ability to float great distances,
are over-represented. This over-representation is the result of a constant
supply of these taxa to the deposition site despite changes in the strength
and direction of the wind and water currents over the depositional site,
and changes in the vegetation, climate, and rates of erosion in source areas.
A gradual decrease in the rate of extinction through the section occurs up
to and within the Mid-Pleistocene Climate Transition with rare, probably recycled,
extinct taxa appearing later than this. These extinctions provide a biostratigraphic
link to the onshore terrestrial record, and the marine record has the potential
to provide accurate dates for terrestrial extinctions.
Keywords New Zealand; Southwest Pacific Ocean; ODP
Leg 181; Mid-Pleistocene Climate Transition; palynology; biostratigraphy;
climate cycles; vegetation history; Pliocene; Pleistocene; cyclic sedimentation;
extinctions
G02017; Received 20 March 2002; accepted 3 February 2003; online publication
date 10 September 2003
New Zealand Journal of Geology & Geophysics, 2003, Vol. 46: 343-361
0028-8306/03/4603-0343 $7.00/0 © The Royal Society of New Zealand
2003
PDF file of entire paper: Print-quality (2916K) |
screen-quality (2504K)
This year's abstracts |
Journal home page |
All abstracts |
Publishing home page
