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) C94007Received 21 February 1994; accepted 26 July 1994 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.

An MIS 5a to MIS 4 (or early MIS 3) environmental and climatic reconstruction from the northwest South Island, New Zealand, using beetle fossils

“…The second site, Sunday Creek (Dickson, 1972;Moar and Suggate, 1996), near Greymouth, indicates that the transition from late MIS 5 to early MIS 4 is a period of rapid change from a Nothofagus fusca type forest to grassland. This is similar to examples of the MIS 5a/MIS 4 transition from elsewhere in the country such as the Canterbury region of central South Island (Moar and Gage, 1973) and southern Wellington (Mildenhall, 1994(Mildenhall, , 1995, Wairarapa (Harper, 1989;McGlone, 1989;Carter andLian, 2000), central Tongariro (McGlone andTopping, 1983) and eastern Hawkes Bay (Okuda et al, 2002) regions of the North Island. In all these cases, environments dominated by Nothofagus fusca type forests underwent a transition to either grassland or grass/ shrubland.…”

“…Sunday Creek does not cover the rest of MIS 4 and early MIS 3 but following the transition to a shrub/grassland environment records from Okarito Bog (Vandergoes et al, 2005) indicate that open vegetation continued for the entire period between 74 and 40 ka. To the north, records from Wellington (Mildenhall, 1994) also indicate the continuance of a shrub/ grassland dominated flora through MIS 4 and MIS 3 but with stands of N. menziesii (silver beech) becoming more significant during the latter part of this period. MIS 3 records from south of Greymouth (e.g.…”

A New Zealand climatic template back to c. 3.9 Ma: ODP Site 1119, Canterbury Bight, south‐west Pacific Ocean, and its relationship to onland successions

“…This is approximately twice the traditionally accepted figure of 5-6°C atmospheric cooling during South Island glaciations, calculated from estimates of snowline depression (Willett 1950;cf. Porter 2001) or pollen analysis (Mildenhall 1995). Furthermore, and though it is a tropical location, Smith et al (2005) have recently estimated a Last Glacial Maximum (LGM) temperature depression of only 2-3°C from studies of moraines in Peru and Bolivia.…”

Quaternary stratigraphy, structure, and deformation of the Upper Hutt Basin, Wellington, New Zealand

“…3) passed through mterbedded silt, silty clay, peat, and gravel of seismic unit A. Drillhole UHS-1 also penetrated the upper 70 m of unit A, and palynostratigraphy of the drillhole sediments (Mildenhall 1994) show that their age is c. 80 ka at 70 m. If this is taken to be representative of the sedimentation rate throughout the sequence, and no unconformities are present, then the age of sediments at the base of unit A (at c. 260 m depth) would be c. 300 ka.…”

“…A brown-stained horizon at 32 m depth in UHS-1 (and also found in other drillholes in the area) is interpreted as the boundary between Holocene and late Last Glacial gravel. Pollen assemblages from 54.0, 60.0 and 68.0 m depth have cold climate affinities (Mildenhall 1994) and are correlated with early Last Glacial zones (50-80 ka) (Palynozone A2 (54, 60 m), and Al (68 m) of Mildenhall 1993). The drillhole therefore provides the thickest early Last Glacial to Recent sequence known in the Wellington region.…”