Tuatara: Volume 16, Issue 1, April 1968
Palaeobotanical Evidence for Changes in the Tertiary Climates of New Zealand
Palaeobotanical Evidence for Changes in the Tertiary Climates of New Zealand
Tertiary Climatic changes are inferred from changes in the plant micro-fossils described by Couper (1960). Critical forms are: the Nothofagus ‘fusca’ group for temperate conditions, the Nothofagus ‘brassi’ group for warm temperate or equivalent subtropical montane conditions, and some other forms of present day subtropical distribution.
The Basis of Palaeoclimatic Interpretation by Plant Fossils
Many Plants are sensitive climatic indicators and their fossils can give a good idea of past climates. There are several types of plant fossils but for only three has there been much published in New Zealand: leaves; spores and pollens; and fruits.
Leaves are variable and have few diagnostic features related to the taxonomy of living plants, so for most of the Tertiary fossil leaves it is impossible to determine them even to a generic level.
Taxonomic determination is more feasible for spores and pollens than for leaves, and the spores and pollens of the New Zealand Tertiary have been described in considerable detail by Couper (1960), whose work forms the basis of the palaeoclimatic interpretations in this paper.
The small size of spores and pollens gives them an additional advantage over leaves. Fossil spores and pollens are mostly whole, whereas fossil leaves, particularly in New Zealand, are rarely found page 50 whole. This lack of entire leaves is largely the result of the strong deformation of most of New Zealand's Tertiary rocks.
Fruits can often be identified with precision, but in New Zealand they are rare, except in Quaternary deposits.
The usefulness of plants as climatic indicators is offset to some degree by transport before fossilization. Leaves that have been washed from mountains, where the climate is appreciably cooler, have been found in the process of being buried in lake beds some 2,000 feet lower. (McQueen, unpubl). Spores and pollens, being much smaller, are transported further and not necessarily downhill (Moar, 1967), as with leaves.
In interpreting past climates, greater weight must be placed on plant assemblages than on individual species. If a particular plant assemblage is restricted to a particular climatic range today, then the same climatic range is inferred for the past, if the same plant assemblage were to be found as fossils.
Of the forest trees of New Zealand, Nothofagus spp. (southern beeches) are one of the most important elements at present and have probably been equally important for most of the Tertiary. It is fortunate that the three groups within Nothofagus, distinguishable by their pollens, are favoured by different climates.
Nothofagus menziesii grows only in the cooler parts of New Zealand: at sea level in Southland and above 2,000 feet in the Wellington district. The ‘jusca' group of three species with indistinguishable pollens, occupies a broader climatic belt than N. menziesii, but does not grow at sea level north of latitude 39°S. Nothofagus, with pollens referable to the N. ‘fusca' and N. “menziesii’ groups, also grows in South America, Australia and Tasmania, in about the same climatic conditions as in New Zealand.
Nothofagus ‘brassi’ is used here for the pollen group representing the large-leaved species of Nothofagus, now extinct in New Zealand. Species of this group still grow in New Caledonia above 2-3,000 feet (Dawson, 1966) and in New Guinea above 8,000 feet (Brass, 1956). Judged by their distribution in New Caledonia and New Guinea, species of the N. “brassi’ group indicate a climate of constant humidity and one warmer than that occupied by the N. “fusca’ group.
Couper (1960) records pollen of the group N. “brassi’ for the whole length of New Zealand from the middle Eocene until the end of the Pliocene. Species of the Proteaceae were much more numerous in the New Zealand Tertiary than they are today and it may be significant that the great majority of proteaceous species are now found in areas of seasonal rainfall (South and West Australia, Cape Province and Central Africa).page 51
Another group of plants found in New Zealand forests today, and well represented in the Tertiary, are the conifers of the family Podocarpaceae. This family has a distribution embracing that of all three Nothofagus groups, and can not be used with confidence in climatic interpretation, unless pollen of present-day species is found.
The present-day distribution of New Zealand plants is partly controlled by temperature differences related to latitude zones, and these zones probably existed during the Tertiary. One such example is Bombacacidites, which was common in New Zealand, north of latitude 40°S in much of the Tertiary, but is not known to the south. Bombacacidites is identified from its pollen (Couper, 1960) and considered to be related to Bombax, the kapok tree of the tropical zones.
It is almost certain that the distribution of several other species could be shown to be related to latitude if the unpublished lists based on pollens and spores were to be analysed with latitudinal zonation in mind.
Evidence for Tertiary climate, indicated by spores and pollens, is outlined below and it should be noted that evidence of latitudinal zonation within the range of 35°-46°S, exists only for those periods where it is mentioned.
Two pollen species from the Dannevirke Series indicate a climate considerably warmer than at present. Cupanieidites is not uncommon throughout and is probably related to the living genus Cupania which lives in the tropical and subtropical zones, and is not known south of latitude 34°S. Anacolosidites, not uncommon in the early Dannevirke, but absent from the late Dannevirke, is probably related to Anacolosa, a tropical genus that now lives in India.
Nothofagus menziesii appeared in the Mata Series at the end of the Cretaceous and continued in small numbers until the end of the Tertiary and then in much larger numbers in the Pleistocene and Recent.
One species of the Nothofagus “brassi’ group was abundant at the end of the Cretaceous but the group is not known from the Dannevirke, although it reappeared immediately after in Arnold times. The place of the Nothofagus “brassi’ group appears to be taken by podocarps which could indicate humid, subtropical conditions.
Fig. 1: Fluctuations in plant fossil content and inferred climates from rocks of Tertiary and early Pleistocene age in New Zealand. All records, except for the leaves in the Hautawan, are of pollen grains from Couper (1960). Climatic zones below are based on Zotov (1938).
(Black triangle represents pollen of Nothofagus “fusca’ group and N. menziesii with leaves of N. menziesii and N. solandri var. cliffortioides.).
The Arnold Series flora is well-known from both marine and non-marine sequences. In Bortonian and Kaiatan times Nothofagus “fusca’ group pollen is abundant in Southland. In the Waikato Nothofagus is absent, and podocarps are abundant, along with Cupanieidites and Dysoxylum. Thus Bortonian and Kaiatan climates appear virtually identical to those today in these two parts of New Zealand.
In the Runangan, the youngest stage of the Arnold Series, there is an abrupt change in Nothofagus from the “fusca’ group, which had been dominant in the lower Arnold, to the “brassi’ group. page 53 It is inferred that there was a relatively sudden change to a climate much warmer than that of the present day. The presence of palm pollen (Rhopalostylis) is supporting evidence for warmth.
A climate warmer than that of the present day persisted throughout the Landon Series and into the Otaian, the oldest stage of the Pareora Series. The flora included Nothofagus “brassi’ group, Cupanieidites, Proteaceae, rare Nothofagus “fusca’ group and rare podocarps, and, in the north, Bombacacidites.
According to Fig. 3 in Couper (1960) the Nothofagus “brassi’ group was dominant over the N. “fusca’ group from the Waitakian to Lillburnian Stages, but in the Hutchinsonian to Awamoan Stages this dominance was less pronounced than before or after, and the climatic interpretation becomes more complex. In the Awamoan, for instance, there is a rather bewildering floral combination present: an abundance of podocarps, warm climate indicators (Bombacacidites, Cupanieidites, and Nothofagus “brassi’ group), and cool climate indicators (Nothofagus “fusca’ group). It is thought that there was a subtropical flora at sea level at 45°S., and forests of Nothofagus “fusca’ group on inland hills. The presence of proteaceous pollen in most samples suggests seasonal rainfall.
All Southland pollen and spore samples indicate warm temperate to subtropical conditions. The Nothofagus “brassi’ group and proteaceous pollens are consistently present and small fossil coconuts have been found in North Auckland.
The flora includes both warm and cool climate indicators, and is, as for the Pareora Series, best explained by considering that the climate at sea level was warm temperate to subtropical and that there were hills or mountains inland. The Putangirua Conglomerate on the Wairarapa coast is extremely coarse and very local in its distribution and a good geological indicator of considerable relief at that time. It contains a typical Taranakian flora.
Older Part of Wanganui Series:
The flora of the two lower Wanganui stages, Opoitian and Waipipian, is a mixed cool and warm one similar to that of the Taranakian and is interpreted in the same way. Relief of at least 1,500 feet is shown in the Upper Rangitikei area by the top of the greywacke, beneath the Opotian—Waipipian beds, page 54 containing a mixed Nothofagus “fusca’ group and N. “brassi’ group flora.
Younger Part of Wanganui Series:
According to Couper and Harris (1960) and Couper and McQueen (1954) there is clear evidence of a marked change from a warm climate in the Waitotaran Stage to a cold climate in the lower Nukumaruan Stage. Waitotaran floras of the North Island of New Zealand are dominated by Nothofagus “brassi’ group with Cupanieidites and Nukumaruan floras by Nothofagus “fusca’ group pollens, with leaves of N. solandri var. cliffortioides and N. menziesii, and pollen of Gramineae and Compositae abundant at localities in the South Island.
The Pleistocene cooling, well shown by fossil leaves from the Hautawan, removed the larged leaved Nothofagus of the N. “brassi’ group from the New Zealand flora. Dumbleton (1967) infers this removal was due to aridity of the climate at the end of the Pliocene, but there is nothing in the floras at the end of the Pleistocene which would suggest aridity. N. “brassi’ could probably live in North Auckland today (Fleming, 1963), but has been unable to migrate back to New Zealand.
Pollens of extinct species and particularly of groups of species indicate both the terrestrial climatic fluctuations in the New Zealand Tertiary and the relief of the land masses of those times. The present interpretation is based only on those pollen forms that have been assigned to taxa known in New Zealand and elsewhere. There remains a large proportion of pollen forms not as yet assigned at the generic, or even family level. It is to be hoped that increasing knowledge of the morphology of plants of the Pacific region will, in the future, enable even more similarities to be discovered between floras of the New Zealand Tertiary and those still surviving to the north of New Zealand.
The authors wish to thank Drs. W. F. Harris and J. W. Dawson for their help in assembling the material for this publication and Professor H. W. Wellman for his invaluable criticism in editing this manuscript.
Mr. I. Devereux. Your pattern of absences in the Dannevirke seems rather similar to that of Dr. Jenkins. He has postulated some page 55 calamitous event to wipe out the foraminifera and then some delay before they repopulated. Could the same sort of explanation be held for your case?
Dr. D. R. McQueen. Possibly, but it does seem a long time delay.
Dr. C. A. Fleming. It there a complete absence of the “brassi’ group or just a lessening of its occurrence?
Dr. D. R. McQueen. From the published results we have examined there is a complete lack of the group.
Professor H. GORDON. Dr. McQueen quite rightly stressed the need to study plants as groups. There are some species that live here today that are outliers of tropical and sub-tropical families and so you would find today quite appreciable pollen from a group that is considered tropical. He also mentioned that the Proteaceae are indicative of a dry climate but there are species living in rather wet climates in Tasmania.
Dr. N. deB. Hornibrook. In the Dannevirke Series there are some very fine sediments so there was presumably very low relief. It is possible that these alpine species retreated to very small pockets until another period of mountain building began? Dr. D. R. McQueen. The question of relief is very important. When the two groups are “mirror images’ of each other everything seems normal but when not a change of relief is suspected.
Brass, L. J., 1956. Results of the Archbold Expedition to New Guinea. Bull. Amer. Mus. Nat. Hist. III, 2.
Couper, R. A., 1952. The Spore and Pollen Flora of the Cocos-bearing beds, Mangonui, North Auckland. Trans Roy. Soc. N.Z. Geol. 97, 3 and 4: 340-8.
—— 1953. Distribution of Proteaceae, Fagaceae and Podocarpaceae in Some Southern Hemisphere Cretaceous and Tertiary Beds. N.Z. Jl. Sci. Tech., 35 (B): 247-50.
—— 1953. Upper Mesozoic and Cainozoic Spores and Pollen Grains from New Zealand. N.Z. Geol. Surv. palaeont. Bull. 22: 77 pp.
—— 1960. New Zealand Mesozoic and Cainozoic Plant Microfossils N.Z. geol. Surv. palaeont. Bull. 32: 87 pp.
—— 1964. In Bowen, F. E. Geology of Ohai Coalfield. N.Z. Geol. Surv. Bull. n.s. 51. 203 pp.
—— and Harris W. F., 1960. Pliocene and Pleistocene Plant Microfossils from Drillholes near Frankton, New Zealand. N.Z. Jl. Geol. Geophys. 3: 15-22.
—— and McQueen, D. R., 1954. Pliocene and Pleistocene Plant Fossils of New Zealand and Their Climatic Interpretation. N.Z. Jl. Sci. Tech. B35: 398-420.
Dawson, J. W., 1966. Observations on Nothofagus in New Caledonia. Tuatara 14, 1: 1-7.
Dumbleton, L. J., 1967. Winter Dormancy in New Zealand Biota and its Palaeoclimatic Implications. N.Z. Jl. Bot. 5, 2: 211-22.page 56
Fleming, C. A., 1963. Age of the Alpine Biota. Proc. N.Z. Ecol. Soc., 10: 15-8.
Harris W. F., 1950. Climatic Relations of Fossil and Recent Floras. Tuatara, 3: 53-66.
—— 1963. Palaeoecological evidence from spores and pollens. Proc. N.Z. Ecol. Soc. 10: 38-44.
McQueen, D. R., 1954. Fossil Leaves, Fruits and Seeds from the Wanganui Series (Plio-Pleistocene) of New Zealand. Trans. Roy Soc. N.Z. Geol. 82: 667-76.
Moar, N. J., 1967. Contributions to the Quaternary history of the N.Z. flora. 5. Pollen diagrams from No Man's Land Bog, Northern Ruahine Range, N.Z. Jl. Bot. 5, 3: 394-9.
Oliver, W. R. B., 1928. The Flora of the Waipaoa Series (Later Pliocene) of New Zealand. Trans N.Z. Inst. 59, 2: 287-303.
—— 1936. The Tertiary Flora of the Kaikourai Valley, Otago, New Zealand. Trans. Roy Soc. N.Z. Geol. 66, 3: 284-304.
Zotov, V. D., 1938. Some Correlations between Vegetation and Climate. N.Z. Jl. Sci. Tech. 19, 8: 474-87.
1 Botany Department, Victoria University of Wellington.
2 Geology Department, Victoria University of Wellington.