New Zealand Journal of Geology and Geophysics abstracts

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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

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