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

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 Al) 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 5°C less than the present day. Basal Postglacial conditions were the reverse, with higher rainfall and temperatures averaging up to 2°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.