New Zealand Journal of Geology and Geophysics abstracts

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Palynostratigraphy and paleoenvironments of Wellington, New Zealand, during the last 80 ka, based on palynology of drillholes

D. C. MILDENHALL

Institute of Geological & Nuclear Sciences Ltd
P.O. Box 30 368
Lower Hutt, New Zealand

Abstract  About 20 pollen profiles from the Wellington area are correlated and zoned according to their pollen characteristics. Sequences from many of the larger sedimentary deposits are shown to contain little or no sediment of late Last Glacial and early Postglacial age, while late Postglacial sedimentation is restricted to a few localities. Sediments of middle and early Last Glacial age are well represented and widespread over the Wellington area. Pollen diagrams from Last Glacial and Postglacial sediments are zoned as follows: Zone A, 80 000-60 000 yr B.P. (lower end of range more likely) and provisionally correlated with oxygen isotope stages 5a and basal 4; Zone B, 70 000-50 000 yr B.P. (lower end of range more likely), provisionally correlated with upper oxygen isotope stages 4 and basal stage 3; Zone C, a short zone just beyond the range of radiocarbon dating at the top of Zone B of 60 000-50 000 yr B.P., correlated with the middle of oxygen isotope stage 3; Zone D, 50 000-10 000 yr B.P., with a major period of nondeposition or erosion between c. 18 000 and 10 000 yr B.P., correlated with the upper part of oxygen isotope stages 3 and all of 2; Zone E, 10 000-1000 yr B.P. (Postglacial); Zone F, last 1000 years (human occupation zone). During this time the vegetation changed from a beech forest (Zone A1) to a shrub/grassland, with pollen from the dominant tree taxa being Nothofagus fusca type (Zone A2), N. menziesii with Phyllocladus (Zones B, C), Phyllocladus with N. menziesii (Zone D), Dacrydium cupressinum (Zone E), and Nothofagus fusca with D. cupressinum (Zone F).

Climatic conditions during the Last Glaciation were generally colder, drier, and stormier relative to the present day. The virtual absence of sediment of this age suggests widespread nondeposition or erosion under unstable conditions. Zones B-D represent the harshest conditions, with temperatures averaging up to 5deg.C less than the present day. Basal Postglacial conditions were the reverse, with higher rainfall and temperatures averaging up to 2deg.C higher than the present day. From sometime before 5000 yr ago, conditions deteriorated towards the present day with increased frostiness and droughts.

Tephras were deposited in the Wellington area during previous glacial episodes. The Rangitawa Tephra was deposited during the mid middle Pleistocene (early Haweran) at a time when the region was covered in a low subalpine scrubland and climatic conditions were similar to that of the Last Glaciation. During the early middle Pleistocene (Okehuan) an unnamed tephra was deposited during a period of similarly cold, dry conditions and onto a similar vegetation.

Keywords  palynology; pollen analysis; oxygen isotope stages; pollen zones; Wellington; Hutt Valley; Last Glacial; Postglacial; Aranuian; Otiran; early Haweran; Okehuan; paleoenvironments; paleoclimate; fire; vegetation history; stratigraphy

New Zealand Journal of Geology and Geophysics, 1994, Vol. 37: 421-436

0028-8306/94/3704-0421 $2.50/0 (c) The Royal Society of New Zealand 1994

PDF file of entire paper: medium quality (1923K); (scanned from paper original: notes about this process)

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