A quantitative palynostratigraphy of the Miocene ...

Journal of the Royal Society of New Zealand

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A quantitative palynostratigraphy of the Miocene Manuherikia Group, New Zealand Mike Pole & Barry Douglas To cite this article: Mike Pole & Barry Douglas (1998) A quantitative palynostratigraphy of the Miocene Manuherikia Group, New Zealand, Journal of the Royal Society of New Zealand, 28:3, 405-420, DOI: 10.1080/03014223.1998.9517572 To link to this article: http://dx.doi.org/10.1080/03014223.1998.9517572

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© Journal of The Royal Society of New Zealand, Volume 28, Number 3 September 1998 pp 405-420

A quantitative palynostratigraphy of the Miocene Manuherikia Group, New Zealand

Downloaded by [200.24.241.186] at 10:03 28 January 2016

Mike Pole1 and Barry Douglas2

A quantitative palynostratigraphy is presented for the Manuherikia Group, New Zealand Six stratigraphic sections were studied from the northern Manuherikia basin where the relative proportions of six pollen taxa were compared Nothofagus 'brassu type', Nothofagus 'fusca type', Casuannaceae, Myrtaceae, Arecaceae, Asteraceae, and Chenopodiaceae A consistent order of dominance is apparent and zone boundaries are erected based on dominance of the latter five taxa over that of Nothofagus 'brassu type' Four new zones are proposed the Nothofagus 'brassu type' Zone, the ArecaceaeMyrtaceae Zone, the Casuannaceae Zone, and the Asteraceae-Chenopodiaceae Zone The latter is essentially a redefinition of the Chenopodipolhs chenopodiaceoides Zone of Mildenhall and Pocknall Correlation with the International time scale is attempted the N 'brassu type' Zone is Early Miocene, while the base of the Casuannaceae Zone or the Asteraceae-Chenopodiaceae Zone may correlate with major global cooling recognised at approximately 14 Ma Keywords biostratigraphy, climate change, Manuhenkia Group, Miocene, palynology

INTRODUCTION In the interior of the southern part of New Zealand a once extensive Miocene fluviallacustnne basin is exposed as small fault-bounded slivers This is the Manuhenkia Group which is often rich in plant remains, both leaves and pollen Two major stratigraphies have been developed for the region Douglas (1986) proposed a hthostratigraphy where earlier braided river sedimentation in incised valleys was followed by an extensive meandering stream/floodplain environment, which then culminated in a very large (>5,000 km2) lacustrine environment The basin was terminated by mountain uplift, accepted generally as Pliocene (see Gabites & Adams 1978, Adams 1979, Field & Browne 1986 for dates of Maori Bottom correlatives) The palynostratigraphy of Mildenhall & Pocknall (1989) divided the Manuherikia Group into three zones The earliest two, the Proteacidites isopogiformis Zone and the Spinitncolpites latispinosus Zone, had already been defined during a study of the paleo-coastal Miocene by Pocknall & Mildenhall (1984) The boundary between these zones was defined on first and last appearance cntena but the uppermost boundary was not defined The zones were dated as Early to possibly Middle Miocene Mildenhall (1989) regarded the P isopogiformis Zone as Otaian-Altoman and the S latispinosus Zone as Altonian and "possibly slightly younger", while Pocknall (1989) placed the P isopogiformis Zone entirely within the Otaian and the S latispinosus Zone as Otaian and extending, at least, into the Altonian (both stages of the Early Miocene according to Edwards et al 1988) Mildenhall & Pocknall (1989) introduced a new, youngest zone, the Chenopodipolhs chenopodiaceoides Zone It was qualitatively different, being defined on "overall content" and with undefined upper and lower boundaries It was dated as Late Miocene 1

Department of Botany, University of Queensland, St Lucia, Brisbane, QLD 4072, Australia 14 Jubilee Street, Dunedin, New Zealand

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Journal of The Royal Society of New Zealand, Volume 28, 1998

The present palynological zones include samples with marked quantitative variation in the dominant pollen taxa as well as a significant variation in the macroflora (Pole 1993). The macroflora changes apparent in the Manuherikia Group seem not to be reflected by sufficient extinction or appearance events in the pollen fossil record to practically further subdivide the zones. Presumably they are reflected in the subtle changes in frequency of the less common pollen types. In addition the key taxa in the P. isopogiformis and S. latispinosus zones tend to be uncommon. This prompts a different approach, and the most useful, once a reasonable lithostratigraphic framework has been established, is that used by Quaternary palynologists (dealing with a similar situation regarding extinction or appearance of key taxa) - utilising the changes in pollen abundance. The use of quantitative palynological zones has been well established in New Zealand with at least half of all those published for the CretaceousTertiary (Couper 1960; Raine 1984; Pocknall & Mildenhall 1984; Nelson et al. 1988; Mildenhall & Pocknall 1989; Pocknall 1991) based on such criteria. In Australia we note the excellent work of H. A. Martin, who, working in a region where outcrop, long fossiliferous successions, and changes in potential key taxa are few (the Neogene of the Murray River Basin) has succeeded in developing a workable palynostratigraphy utilising quantitative criteria (e.g. Martin 1973, 1984a, b, 1987). For a period of several millions of years, from near the start of the Oligocene to within the Early Miocene, the pollen rain in New Zealand was almost always dominated by the Nothofagus 'brassii type' (Pocknall 1989). This pollen type was ubiquitously dominant in all facies; freshwater, offshore, swamp and fluvial (Pocknall 1981a, 1982a, b, 1989; Pocknall & Mildenhall 1984). While a variety of community types no doubt existed on different substrates, the palynological signal of the regional vegetation was stronger. Furthermore, while climatic change undoubtedly occurred over this period, it was not sufficient to change the regional vegetation to such a degree that the proportion of another pollen type surpassed that of Nothofagus 'brassii type'. All of this changed in the Early Miocene, where samples can be dominated by any of a number of pollen types. This cannot be attributed to simple facies changes so is likely to represent climatic effects. Given its strong temporal and facies persistence, Nothofagus 'brassii type' pollen seems like a practical 'benchmark' with which to compare the proportions of other taxa, and to form the basis of a zonation. By just comparing relative frequencies of key taxa against Nothofagus 'brassii type', the effects of local over-representation and broad facies changes are minimised. For example the upper portions of most of our sections fall within the lacustrine Bannockburn Formation, and are sometimes overwhelmingly dominated by aquatic or semi-aquatic plant pollen such as Cyperaceae. The seven taxa we choose to study are discussed below. 1 and 2. Nothofagus 'brassii type' and Nothofagus 'fusca type' (sensu Cookson & Pike 1955). The relative proportions of the pollen of these two groups have often been used to infer climate, with the Nothofagus 'brassii type' type reflecting mild, equable conditions, and Nothofagus 'fusca type' dominating when aspects of climate deteriorated to include extremes of cold or drought (e.g. Mildenhall & Pocknall 1989; Pocknall 1989; McGlone et al. 1996). We use the older 'brassii-fusca' terminology rather than applying the infrageneric classification of Nothofagus by Hill & Read (1991). Dettmann et al. (1990) divided Nothofagus 'fusca type' pollen grains into two subgroups, 'type a' and 'type b' based on the form of the colpal margins. Hill & Read (1991) noted that these subgroups compared with their subgenera Fuscospora and Nothofagus respectively. Dettmann et al. (1990) placed one of the New Zealand fossil representatives of the Nothofagus 'fusca type' (Nothofagidites brachyspinulosus (Cookson) Harris) into their 'type a' and the remaining three (Nothofagidites flemingii (Couper) Potonie, N. lachlaniae (Couper) Pocknall & Mildenhall, and TV. waipawaensis (Couper) Fasola) into their 'type b'. Pocknall & Mildenhall (1984) had previously synonymised N. brachyspinulosus with N. lachlanae, and noted this was the species which is effectively produced by the extant


Pole & Douglas—Palynostratigraphy of the Miocene Manuhenkia Group

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Nothofagus s g Fuscospora in New Zealand today {Nothofagus fusca (Hook fil ) Oerst, N solandn (Hook fil ) Oerst, and N truncata (Colenso) Cockayne) This move was rejected by Dettmann et al who maintained that (p 37) they "have similar apertural morphology but can be differentiated on the basis of size, shape and distribution of sculptural elements" If it is the case that these forms have similar apertural morphology it is difficult to see how they can be placed in separate groups ('type a' and' type b') which are distinguished on apertural differences As recognition of the two groups is based on subtle characters and involves some controversy, for the purposes of a workable stratigraphy we feel it safer not to attempt the distinction 3 Casuannaceae (the pollen type Haloragaadites harnsn (Couper) Hams) Pocknall ( 1991 ) used the dominance of this taxon as the basis for his Late Eocene Haloragacidites harnsu Zone in the Te Kuiti Group This taxon dominates some of our samples, the first time it does so consistently since the Late Eocene, and we simply apply PocknalPs criteria of dominance to the Manuhenkia Group 4 Myrtaceae (the pollen type Myrtaceidites spp ) The relative importance of Myrtaceae pollen has been used by Martin (1973 1987) for quantitative pollen stratigraphy in Australia 5 Arecaceae (mostly the pollen type Arecipites otagoensis (Couper) Mildenhall & Pocknall) Although domination by this type may be strongly controlled by edaphic conditions (I e 'peat swamps'), Arecaceae pollen is absent to rare in the older Manuhenkia Group lignites, but is super abundant m later lignites Its domination is of at least local stratigraphic importance and may be reflecting a general climate change Although Arecaceae pollen is often present m the Australian Tertiary it almost never dominates That it consistently does so in the Manuhenkia Group is further evidence that it has some stratigraphic value rather than simply reflecting edaphic conditions 6 Chenopodiaceae (the pollen type Chenopodipolhs chenopodiaceoides (Martin) Truswell, and 7 Asteraceae (Tubuliflorae) (the pollen type Tubuliflondites Cookson, ex Potonie) As stated by Mildenhall & Pocknall (1989), these taxa are characteristic of the younger Manuhenkia Group sediments We include them to further develop the concept of their Chenopodipolhs chenopodiaceoides Zone Our research has concentrated on the northern part of the Manuhenkia Basin The sediments there range up from the oldest, the St Bathans Member, through the Fiddlers Member, and in to the Bannockburn Formation They are well-exposed, contain no major unconformities, and distinct hthostratigraphic horizons can be traced over several kilometres This region also includes a previously unreported conformable transition upwards of Bannockburn Formation lacustrine into the gravels of the Pliocene Maori Bottom Group, representing mountain uplift The aim of this paper is to document the relative abundance of some of the major pollen types of the Manuhenkia Group and to use them to extend the quantitative biostratigraphy initiated by Mildenhall & Pocknall with the C chenopodiaceoides Zone Given that this zone was charactensed by dominance of a family widely known to be strongly edaphically controlled, at least this zone is not likely to be of New Zealand-wide use Our stratigraphy is designed for local use, although we suspect our zone boundaries may be expressed elsewhere, even though other taxa are involved We aim to produce a stratigraphy which is simple to apply, m the sense that it utilises common and easily recognisable taxa, and taxa which may be relatively simple to interpret in terms of climate change METHODS We have examined six stratigraphic sections (surface exposures) in the northern Manuhenkia basin 'Vinegar Hill', 'Blue Lake', 'Grey Lake', 'Upper Mata Creek', 'Lower Mata Creek', and 'Manuhenkia River' (Fig 1), as well as taking 'spot samples' from the Ida Valley and Cambrians coal seams All sections are stratigraphically comparable, extending from either

408


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Fig. 1 Locality map. The locality of the six sections detailed in this paper are shown in the upper map. The regional setting, including positions of sections published by Mildenhall and Pocknall (1989) are shown in the lower map.

Pole & Douglas—Palynostratigraphy of the Miocene Manuherikia Group

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the St Bathans Member, or the Fiddlers Member up into the Bannockburn Formation. Samples were taken from carbonaceous horizons in each section and were often separated stratigraphically by non-carbonaceous gravel, sand, or green clay. Details of section location are given as Appendix 1. After standard palynological preparation each pollen count was continued until a minimum of 100 specimens of the key taxa was achieved (except for two preparations which yielded sparse pollen). This number was found to be robust and consistently place samples into the zones we devised. Pollen preparations are stored in the Department of Botany, University of Queensland. RESULTS The pattern of key taxa The results are shown in Figs 2-6. These show the relative proportions of the seven key taxa. The generally consistent pattern of dominance relative to Nothofagus 'brassii type' allows an operationally-simple zonation and correlation of the northern part of the Manuherikia Group. We propose four zones based on taxa, or pairs of taxa which clearly and consistently dominate over Nothofagus 'brassii type'. "Clearly" because on either side of the zone of clear dominance may be a 'tail' where taxon proportions are almost equal, and "consistently" because there are odd samples which do not fit the overall pattern. As a model for our zone boundary definitions we follow Pocknall (1991). 1. Biozones Nothofagus 'brassii type' Zone (see Figs 2,3, 5, 7) The proportion of Nothofagus 'brassii type' is clearly and consistently greater than any of the other six key taxa. The stratigraphically lowest units of the northern Manuherikia Group are all dominated by N. 'brassii type' both in the restricted sense of the selected group of key taxa, as well as the total pollen count. This includes mudstone from the St Bathans paleochannels, and lignite from the Cambrians and Ida Valley seams. Arecaceae-Myrtaceae Zone (see Figs 2, 5, 7) The proportion of Arecaceae plus Myrtaceae pollen is clearly and consistently greater than that of Nothofagus 'brassii type' . This zone is associated with lignites and therefore the dominance of these two taxa is likely to be reflecting the swamp vegetation. However, as older lignites are poor in Arecaceae and Myrtaceae, they appear stratigraphically useful. At the base of the Manuherikia River section Casuarinaceae clearly dominates while Arecaceae + Myrtaceae barely dominate over Nothofagus 'brassii type'. While we place this region into our Casuarinaceae Zone, it may also be interpreted as a range of zone overlap with the Arecaceae+Myrtaceae. Arecaceae+Myrtaceae do not dominate in any of the Vinegar Hill samples. Carbonaceous deposits are sporadic in the channel-gravel lithology where we predict it should be and we may not have sampled the zone, or it may have been removed by local channel erosion. Sporadic peaks of Myrtaceae over Nothofagus 'brassii type', such as near the top of the Upper Mata Creek Section and in the lower part of the Blue Lake Section are disregarded as inconsistent within the overall trend. Casuarinaceae Zone (see Figs 3, 4, 5, 6, 7) The proportion of Haloragacidites harrisii is clearly and consistently greater than that of Nothofagus 'brassii type'. A possibly equivalent Nothofagus 'spike' is present within this zone in the Upper and Lower Mata Creek Sections (see Figs 4 and 5). The proportion of Nothofagus 'fusca type' rises from being much less than N. 'brassii type' to parity, or sometimes dominance within this zone. This dominance continues up through the next zone and is present in the highest sample we investigated, 100 m below the incoming of the Maori Bottom gravel.

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Fig. 2 Summary charts for the Blue Lake Section and the Grey Lake Section. The majority of these sediments accumulated as fluvial gravels in an incised river valley. Column shading: grey - St Bathans Member of Dunstan Formation, black - Dunstan Formation other than St Bathans Member. N=number of observations in count.


411

Vinegar Hill Section 80 m VH1(N=100)

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Nothofagus brasai-type' Zone

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Fig. 3 Vinegar Hill Section. The lower part of this section is river gravel. A single sample from the Cambrians coal seam is shown, which is stratigraphically equivalent to the base of this section. Column shading: grey - St Bathans Member of Dunstan Formation, black - Dunstan Formation other than St Bathans Member, white- Bannockburn Formation. N=number of observations in count.

Uppei Miatai Creek Section Top (N-194) M1 (N=187) M2(N=201)

AsteraceaeChenopodiaceae Zone

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251/6 {N=1S8)

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WlÊÉ 25CV6 (N-204) P9(N=112>

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Casuannaceae Zone Nothofagus spike

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Fig. 4 Upper Mata Creek Section. Column shading: black - Dunstan Formation other than St Bathans Member, white - Bannockburn Formation. N=number of observations in count.

Asteraceae-Chenopodiaceae Zone (see Figs 4, 5, 6, 7) Currently the key phrase of the definition of the C. chenopodiaceoides Zone (Mildenhall & Pocknall 1989, p. 22) is: "[The] frequency and abundance [of C. chenopodiaceoides] are much greater in this zone, and along with Compositae (Tubuliflorae) pollen it forms a conspicuous component of the spore-pollen assemblages". There is an opportunity now to more precisely define this zone. In our sections both Asteraceae and Chenopodiaceae pollen appear and then tend to increase at an approximately similar stratigraphic level. We note however that the proportions of Chenopodiaceae pollen fluctuate widely and are even absent in some samples clearly within the C. chenopodiaceoides Zone, sensu Mildenhall & Pocknall. As the presence of Asteraceae (Tubuliflorae) is more

Lower Mata Creek Section Downloaded by [200.24.241.186] at 10:03 28 January 2016

70 m

I

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60 m

AFW33(N=121)

50 m

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40 m

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AFW27(N=113) AFW25(N=106)

30m

Casuarinaceae Zone Nothofagus spike

AFW24(N=111) AFW22(N=116)

20m

AFW21(N=12S) I AFW19(N=115)

10 m

MyrtaceaeArecaceae Zone

AFW8(N=117) AFW11 ( N = -

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Area

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Fig. 5 Lower Mata Creek Section. Column shading: black - Dunstan Formation other than St Bathans Member, white - Bannockbum Formation. N=number of observations in count.

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413

Manuherikia River Section Approx. 100 m to incoming of Maori Bottom Gravels MR019IN.1H)

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(Early Pliocene). Compositae (Liguliflorae) was regarded as first appearing in the fossil record in Late Miocene time in New Zealand by Mildenhall (1980). The establishment of the C. chenopodiaceoides Zone involves a problem, however. In one of the three sections in which it was first detailed, the Haughton's Hill drillcore, it does not succeed the S. latispinosus Zone, but the older P. isopogiformis Zone. A major unconformity, equivalent to approximately 200 m of sediment and involving most of the Middle Miocene, was proposed to account for the missing strata. A similar unconformity was also suggested in the nearby Ranfurly drillhole. Here, the C. chenopodiaceoides Zone sediments do overlie the S. latispinosus Zone, although Chenopodiaceae pollen was not explicitly stated to be present. We have examined the Haughton's Hill drillcore. Its pollen sequence (Pocknall 1981b; pers. obs.) is like the other sections we have studied which include the transition from the Fiddlers into Bannockburn Formation: Casuarinaceae dominates at the base, Asteraceae and Chenopodiaceae appear, then rise in frequency up through the sequence. In addition N. "brassii type' dominates over N. 'fusca type' at the base, then this situation reverses for the rest of the sequence. We would see this as passing from our Casuarinaceae Zone into the Asteraceae-Chenopodiaceae Zone. Like the other sections, we do not see any sign of a break in sedimentation, major erosion, or signs of uplift at its base. We reject the hypothesis of a major unconformity and believe sedimentation was essentially continuous. If it is not a problem of contamination, then the definition of the P. isopogiformis Zone needs to be reviewed. The magnitude of the problem is lessened if the base of the C. chenopodiaceoides Zone is not as young as Late Miocene, and there are several reasons to believe this is the case. Firstly, assuming the lower units are well dated as Early Miocene, the absence of any significant hiatuse suggests the succeeding strata are most likely Middle Miocene. Secondly, Asteraceae (Liguliflorae) was regarded by Mildenhall (1980) as first occurring in New Zealand at the same level as elsewhere in the world (latest Miocene). It has since (Muller 1981) been reported from the Early Miocene in South America. Furthermore, we noted Asteraceae (Liguliflorae) in the upper part of the Vinegar Hill section, placed by Mildenhall and Pocknall into the S. latispinosus Zone. Thirdly, the comparison of the C. chenopodiaceoides Zone with Blind River and Paliser Bay was based on the dominance of Nothofagus 'fusca type' and podocarps. N. 'fusca type' is already dominant at the unconformable base of the Blind River section. Therefore its rise to dominance may be older than Middle Tongaporutuan, and could conceivably extend back into the Middle Miocene. The dominance of N. 'fusca type' was suggested by Mildenhall & Pocknall (1984) to be a result of the Kaikoura Orogeny when uplift produced a rainshadow effect. This was clearly not the case in Central Otago, where there is absolutely no sedimentological evidence of major uplift at this level, or for some considerable time afterwards (approximately 300 m of overlying fine-grained sediments). The C. chenopodiaceoides Zone sediments in Central Otago are therefore likely to be older than those at Blind River. Closer to the Manuherikia Group (perhaps representing its coastal margin) is the upper portion of the White Rock River section, Canterbury (Gair 1959). Here the White Rock Coal Measures have a pollen spectrum (Pocknall 1982b) where both Nothofagus 'fusca type' and Casuarinaceae dominate over N. 'brassii type'. Asteraceae (Tubuliflorae) were prominent, but less than N. 'brassii type' (Chenopodiaceae were not recorded and this absence may reflect the difference between an inland and a coastal situation). The Coal Measures overlie marine sediments of the Southburn Sand, which forms the type section of the Early Miocene Altonian local stage and where Nothofagus 'brassii type' pollen dominates. Pocknall (1982) regarded the Coal Measures as Late Miocene, based on similarity with C. chenopodiaceoides Zone samples of the Manuherikia Group. However, according to Gair (1959, p. 275) the Southburn Sand "grades upwards" into the White Rock Coal Measures. This suggests the



417

base of the Coal Measures are more likely to be basal Middle Miocene, providing a more precise datum for a change to Nothofagus 'fusca type' dominance. Finally, Heuser (1986) dated a major transition between Early Miocene and Middle Miocene palynofloras in DSDP Holes 594 and 594 on the Chatham Rise (these sediments accumulated offshore, to the east of the Manuherikia Group). She noted the Early Miocene samples were dominated by Nothofagus 'brassii type' with herbaceous and shrub pollen essentially absent. Mid Miocene samples were dominated by Nothofagus 'fusca type', while Gramineae, Asteraceae, Chenopodiaceae were present, along with a few Sphagnum-like grains. N. 'fusca type' continued to dominate over N. 'brassii type' until the later became extinct in the Pliocene-Quaternary. Based on this, the Casuarinaceae Zone could be at least mostly Middle Miocene, and the base of both the C. chenopodiaceoides Zone and our Asteraceae-Chenopodiaceae Zone could be Middle, rather than Late Miocene. The change in pollen composition reflects dramatic changes in the vegetation, resulting in part from major climate shifts. We emphasise the important distinction between what dominates a pollen rain and what actually dominates the biomass of the vegetation, and, once again, that the changes in pollen dominance documented here are not related to simple, local facies changes. They are regional in the sense of the Manuherikia Basin. Although a detailed examination of the climatic implications is beyond the scope of this paper, the major changes are clear. The shift from N. 'brassii type' to Nothofagus fusca type' dominance reflects a change from a climate where cold extremes of temperature or drought were minimal, to a more seasonal one where they were important (e.g. Mildenhall 1989). The rise of Asteraceae and Chenopodiaceae will also reflect this increase in seasonality. Dominance of Casuarinaceae pollen, judged by its prominence in the Quaternary record of Australia (e.g. Kershaw 1988, 1989; Kershaw et al. 1994; Harle 1997), possibly reflects a peak of effective dryness. We see Miocene periods of regional Casuarinaceae pollen dominance as possibly simply earlier expressions of what Kershaw and others have documented for later periods. Flower & Kennett (1994) summarised data for a major global "threshold event" in Cenozoic cooling from ~14.8 Ma to 14.1Ma, just after the Early/Middle Miocene boundary. Inferred changes in deep ocean circulation increased the meridional surface temperature gradient and intensified boundaries between climatic zones. A major shift in global vegetation resulted, with for instance, forests in some areas being replaced by grasslands. In the Australasian region the first appearance of opal phytoliths on Lord Howe Rise is dated to 14.5 Ma (Locker & Martini 1986) and records the initial expansion of open grasslands in Australia; and a marked increase in illite at DSDP site 588 in the early Middle Miocene is considered by Stein & Robert (1986) to record an increase in aridity of northern and central Australia. This event may correlate with the major floral change at the base of the Casuarinaceae or Asteraceae-Chenopodiaceae Zone as implied by Axelrod (1992). A similar sequence to ours may be recorded in south eastern Australia. The highest major seam of coal in the Latrobe Valley, Victoria is the Yallourn Seam, dated to between 15.3 and 16 Ma (Holdgate et al. 1995; Sluiter et al. 1995), i.e. earliest Middle Miocene. This period covers the global Miocene climatic optimum according to McGowran & Li (1994), after which there was "pronounced global cooling". This cooling, and associated drying, probably caused the cessation of peat growth in the Latrobe valley. Extensive lignite accumulation may have ceased in both New Zealand and south eastern Australia at approximately the same time, in response to the same event. SUMMARY The Manuherikia Group shows a consistent pattern of change in six key pollen taxa with time. This can be generalised as a series of stratigraphically overlapping waves of dominance. Nothofagus 'brassii type' is always prominent in the oldest samples and is typically several times the amount of N. 'fusca type'. Arecaceae pollen is absent or rare. Asteraceae


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(Tubuliflorae) and/or Chenopodiceae are always absent. Nothofagus dominance gives way to Myrtaceae and Arecaceae dominance. Arecaceae then disappears and then there is a prominent zone of Casuarinaceae dominance. Nothofagus 'fusca type' pollen dominates over, or reaches equal proportions with Nothofagus 'brassii type' but sporadic samples may be dominated by Nothofagus 'brassii type'. In stratigraphically higher samples Asteraceae pollen appears and is consistently present in younger samples. Chenopodiaceae pollen appears at approximately the same time, but is inconsistently present. Based on this sequence four palynological zones have been defined. Our AsteraceaeChenopodiaceae Zone is effectively similar to Mildenhall & Pocknall's (1989) C. chenopodiaceoides Zone. Most of their S. latispinosus Zone correlates to our three new zones, the Casuarinaceae Zone, the Arecaceae-Myrtaceae Zone, and the Nothofagus 'brassii type' Zone. The small amount of the Proteacidites isopogiformis Zone, the oldest recognised by these authors in this region, we would place in the mid to younger part of the sequence. We do not accept the existence of a major break in sedimentation within the Manuherikia Group, only those small breaks expected in a fluvial environment. Most of the Miocene may be represented in the Manuherikia Group. The existence of a long Miocene record in a land mass essentially unaffected by gross topographic or continental complications (i.e. there were no major orographic effects on rainfall or 'continentality' effects leading to freezing) is of great importance for paleoclimate studies. The over-all change from wetter Nothofagusdominance, to drier and/or cooler Casuarinaceae+Asteraceae prominent vegetation makes the Manuherikia Group an interesting earlier extension of the long Pleistocene records of Australia. ACKNOWLEDGEMENTS We are particularly grateful to the land owners of the St Bathans region for access to their properties and to Kate Harle and the Centre for Palynology at Monash University for assistance with palynological technique. We thank W. Harris for his comments on the manuscript and the reports of D. C. Mildenhall and a further, anonymous, referee. This work was completed at the Department of Botany, University of Queensland where Mike Pole was funded via an ARC grant to M. Dettmann and G. Stewart.

REFERENCES Adams, C. J. D. 1979: Age and origin of the Southern Alps. In: Walcott, R. I. & Cresswell, M. M. (eds) The Origin of the Southern Alps, pp 73-78. The Royal Society of New Zealand, Wellington. Axelrod, D. I. 1992: 'Climatic pulses, a major factor in legume evolution.' In: Herendeen, P. S. & Dilcher, D. L. (eds) Advances in Legume Systematics: Part 4. The Fossil Record, pp 259-279. The Royal Botanic Gardens, Kew. Cookson, I. C.; Pike, K. M. 1955: The pollen morphology of Nothofagus Bl. subsection Bipartitae Steen. Australian journal of botany 3: 197-206. Couper, R. A. 1960: New Zealand Mesozoic and Cainozoic plant microfossils. New Zealand Geological Survey palaeontological bulletin 32: 1-87. Dettmann, M. E.; Pocknall, D. T.; Romero, E. J.; Zamaloa, M. D. C., 1990: Nothofagidites Erdtman ex Potonie. 1960; a catalogue of species with notes on the paleogeographic distribution of Nothofagus Bl. (southern beech). New Zealand Geological Survey paleontological bulletin 60: 1-79. Douglas, B. J., 1986: Lignite resources of Central Otago. New Zealand Energy Research and Development Committee. Publication P 104. Edwards, A. R.; Homibrook, N. de B.; Raine, J. I.; Scott, G. H.; Stevens, G. R.; Strong, C. P.; Wilson, G. J., 1988: A New Zealand Cretaceous-Cenozoic geological time scale. New Zealand Geological Survey record 35: 135-149. Field, B. D.; Browne, G. H. 1986: Lithostratigraphy of Cretaceous and Tertiary rocks, southern Canterbury, New Zealand. New Zealand Geological Survey record 14: 1-55. Flower, B. P.; Kennett, J. P. 1994: The middle Miocene climatic transition: East Antarctic ice sheet development, deep ocean circulation and global carbon cycling. Palaeogeography, palaeoclimatology, palaeoecology 108: 537-555.


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Gabites, J E , Adams, C J 1978 Excess radiogenic argon and age of metamorphism in the Haast Schists, Hast Pass, Lakes Wanaka and Hawea, South Island, New Zealand In Proceedings of the Fourth International Conference on Geochronology, Cosmochronology and Isotope Geochemistry' (not paged) U S Geological Survey Special Publication, Snowmass-at-Aspen, Colorado Gair, H S 1959 The Tertiary geology of the Pareora district, south Canterbury New Zealand journal of geology and geophysics 2 265-296 Harle, KJ 1997 Late Quaternary vegetation and climate change in southeastern Australia palynological evidence from marine core E55-6 Palaeogeography palaeochmatology palaeoecology 131 465483 Heuser, L E 1986 Palynology of selected Neogene samples from Holes 594 and 594A, Chatham Rise In Blakeslee, J H (ed ) Initial Reports of the Deep Sea Drilling Project 90 part 2 ,pp, 1085-1092 U S Govt Printing Office, Washington Hill, R S , Read, J 1991 A revised infragenenc classification of Nothofagus (Fagaceae) Botanical journal of the Linnean Society 105 37-72 Holdgate, G R , Kershaw, A P , Sluiter, I R K 1995 Sequence stratigraphic analysis and the origins of Tertiary brown coal lithotypes, Latrobe Valley, Gippsland Basin, Australia International journal of coal geology 28 249-275 Kennett, J P 1966 Faunal succession in two Upper Miocene-Lower Pliocene sections, Marlborough, New Zealand Transactions of the Royal Society of New Zealand Geology 3 197-213 Kershaw, A P 1988 Australasia In Huntley, B , & Webb, T I (eds) Vegetation History, pp 237-306 Kluwer, New York Kershaw, A P 1989 Was there a 'Great Australian And Period'? Search 20 89-92 Kershaw, A P , Bulinan, D , Busby, J R 1994 An examination of modern and pre-European settlement pollen samples from southeastern Australia - assessment of their application to quantitative reconstruction of past vegetation and climate Review of palaeobotany and palynology 82 83-96 Locker, S , Martini, E 1986 Phytohths from the southwest Pacific, Site 591 In Blakeslee, J H (ed ) Initial Reports of the Deep Sea Drilling Project 90 part 2 , pp 1079-1084 U S Govt Printing Office, Washington Martin, H A 1973 Upper Tertiary palynology in southern New South Wales Special Publications Geological Society of Australia 4 35-54 Martin, H A 1984a The use of quantitative relationships and palaeoecology in stratigraphic palynology of the Murray Basin in New South Wales Alcheringa 8 253-272 Martin, H A 1984b The Tertiary stratigraphic palynology of the Murray Basin in New South Wales II The Murrumbidgee Area Journal and Proceedings Royal Society of New South Wales 117 3 5 44 Martin, H A 1987 Cainozoic history of the vegetation and climate of the Lachlan River region, New South Wales Proceedings of the Linnean Society of New South Wales 109 213-251 McGlone, M S , Mildenhall, D C , Pole, M S 1996 The History and Paleoecology of New Zealand Nothofagus forests In Veblen, T T , Hill, R S , & Read, J (eds) Nothofagus Ecology and Evolution, pp 83-130 Yale University Press, Yale McGowran, B , Li, Qianyu, 1994 The Miocene oscillation in southern Australia Records of the South Australian Museum 27 197-212 Mildenhall, D C 1980 New Zealand late Cretaceous and Cainozoic plant biogeography a contribution Palaeogeography palaeochmatology palaeoecology 31 197-233 Mildenhall, D C 1989 Summary of the age and paleoecology of the Miocene Manuhenkia Group, Central Otago, New Zealand Journal of the Royal Society of New Zealand 19 19-29 Mildenhall, D C , Pocknall, D T 1984 'Palaeobotamcal evidence for changes in Miocene and Pliocene climates in New Zealand' In Vogel, J C (ed ) Late Cainozoic palaeochmates of the Southern Hemisphere, pp 159-171 South African Society for Quaternary Research International Symposium, Swaziland 1983 A A Balkema, Rotterdam Mildenhall, D C , Pocknall, D T 1989 Miocene-Pleistocene spores and pollen from Central Otago, South Island, New Zealand New Zealand Geological Survey palaeontological bulletin 59 1-128 Muller, J 1981 Fossil pollen records of extant angiosperms Botanical review 4 7 1-142 Nelson, C S , Mildenhall, D C , Todd, A J , Pocknall, D T 1988 Subsurface stratigraphy, paleoenvironments, palynology, and depositional history of the late Neogene Tauranga Group at Ohinewai, Lower Waikato lowland, South Auckland, New Zealand New Zealand journal of geology and geophysics 31 21-40


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Pocknall, D T 1981a Pollen and spores from the Rifle Butts Formation (Altoman, Lower Miocene) Otago, New Zealand New Zealand Geological Survey report PAL 40 1-15 Pocknall, D T 1981b Results of palynological analysis of samples from a drillhole at Gimmerburn near Haughtons Hill, Central Otago, New Zealand (Metric Sheet H42) Unpublished Report DTP 15/81, Palynology Section, New Zealand Geological Survey Not paged Pocknall, D T 1982a Pollen and spores from Blue Lake, St Bathans(H41) and Harhwicks Lignite Pit, Roxburgh (G43), Central Otago, New Zealand Unpublished report DTP 19/82, Palynology Section, New Zealand Geological Survey Pocknall, D T 1982b Palynology of the Bluechffs Siltstone (Early Miocene), Otaio River, South Canterbury, New Zealand New Zealand Geological Survey Report PAL 55 1-26 Pocknall, D T 1989 Late Eocene to Early Miocene vegetation and climatic history of New Zealand Journal of the Royal Society of New Zealand 19 1-18 Pocknall, D T 1991 Palynostratigraphy of the Te Kuiti Group (late Eocene-Oligocene), Waikato Basin, New Zealand New Zealand journal of geology and geophysics 34 407-417 Pocknall, D T , Mildenhall, D C 1984 Late Ohgocene -Early Miocene spores and pollen from Southland, New Zealand New Zealand Geological Survey paleontologwal bulletin 51 1-66 Pole, M S 1993 Early Miocene flora of the Manuhenkia Group, New Zealand 10 Paleoecology and stratigraphy Journal of the Royal Society of New Zealand 23 393-426 Raine, J 1 1984 Outline of a palynological zonation of Cretaceous to Paleogene terrestrial sediments in West Coast region, South Island, New Zealand New Zealand Geological Survey Report 109 1— 82 Sluiter, I R K , Kershaw, A P , Holdgate, G R, Bulman, D 1995 Biogeographic, ecological and stratigraphic relationships of the Miocene brown coal floras, Latrobe Valley, Victoria, Australia International journal of coal geology 28 277-302 Stein, R , Robert, C 1986 Siliciclastic sediments at sites 588, 590, and 591 Neogene and Paleogene evolution in the southwest Pacific and Australian climate In Blakeslee, J H (ed ) Initial Reports of the Deep Sea Drilling Project 40 part 2 ,pp 1437-1454 U S Govt Printing Office, Washington Suggate, R R 1978 (Ed ) The Geology of New Zealand Volume II E C Keating, Government Printer, Wellington

APPENDIX 1. SAMPLE LOCALITIES Blue Lake Section The eastern edge of Blue Lake marks the approximate top of the basement The lower samples (BL5, BL6) are near H41/580883 at the south-east corner of Blue Lake in vicinity of the car park The remaining samples are at the other end of the lake near H41/576887 Grey Lake Section All samples come from a gully exposed by mining 200 m to the north east of Grey Lake centered on H41/593898 The western margin of Grey Lake marks the top of the basement Vinegar Hill Section Located between H41/531875 and H41/535868 A detailed hthostratigraphic section is given in Douglas (1986) Upper Mata Creek Section This section is centered on the prominent loop of Mata Creek at H41/603862, 150 m west of Hawkdun Runs road The base of the section is the prominent lignite horizon near the base of the loop (to the west) and the top is in the steep bank above the apex of the loop (to the east) Lower Mata Creek Section This section is exposed in the bed of Mata Creek, starting about 450 m downstream from the Loop Road at H41/599855 to approximately H41/601850 Manuhenkia River Section The main section is centered on approximately H4161842 on the left bank of the Manuhenkia River, 200 m upstream of the bndge The basal lignite horizon is prominent The upper outlier is situated on the nght bank of the Manuhenkia River at approximately H41/604803

Received 3 October 1997, accepted 12 January 1998