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Tuatara: Volume 16, Issue 1, April 1968
The Calcareous Nannoplankton Evidence for New Zealand Tertiary Marine Climate
The Calcareous Nannoplankton Evidence for New Zealand Tertiary Marine Climate
Introduction
New Zealand marine Cenozoic rocks commonly contain large numbers of minute, often complexly sculptured calcareous plates known to paleontologists as the calcareous nannoplankton or “coccoliths’ which once formed the external cover of the coccolithophorids, braarudosphaerids, discoasters and related planktonic organisms. Although almost all of the Tertiary species are now extinct many belonged to groups which have living representatives and it is on the temperature tolerances and preferences of the living taxa that the assessments of past marine climates given in this paper are based.
Reliability of Indicators Selected
Modern marine calcareous nannoplankton can, as a group, tolerate temperatures ranging from minus 2°C to in excess of 34°C but most species prefer temperatures above 9-13°C. However, regional or local variations in other environmental factors such as nutrient supply, salinity and turbidity are probably more important than temperatures alone in determining the actual composition of living assemblages. Since the relative importance of each of these factors can not be determined for fossil assemblages the interpretation of these in terms of past climate is fraught with difficulties.
The temperature and other ecological characteristics attributed to living species below are based on the investigations summarised in Bernard (1942), Hasle (1959, 1960), Martini (1961) and Norris (1961). Preliminary investigations by the writer of SW Pacific bottom sediments have confirmed that the distributional patterns given by these authors are generally valid in the New Zealand area. The occurrence of the fossil taxa was determined by the examination of 300 samples from selected sections.
Braarudosphaera bigelowi, a living species which prefers coastal waters having temperatures between 14 and 19°C but can tolerate temperatures as low as 8°C, and the other, now extinct, braarudosphaerids found in the New Zealand Tertiary have almost page 27 identical stratigraphic distributions and are therefore concluded to have had similar ecological requirements to that of the only living member of this group.
The genus Cyclococcolithus is fairly consistently present in New Zealand Cenozoic strata but never approaches the frequency attained by its modern representatives which are rarely found south of the subtropical convergence according to the observations of Hasle (1960) and the writer. For the purpose of this paper its presence in fossil assemblages is considered to indicate the absence of very cold temperatures.
Although the ecological requirements of living Discolithina are not known the writer's observations suggest that it prefers temperate to tropical coastal waters. Support for this conclusion is given by the investigations of sub-fossil and fossil material by Cohen (1964), Martini (1965, p. 400) and McIntyre and Bè (1966).
Ericsonia ovalis sensu lato, the dominant form through most of the New Zealand Tertiary, appears to have had ecological requirements similar to that of the related late Cenozoic species Coccolithus pelagicus which today dominates the cold to cool temperate assemblages around southern New Zealand. According to Bernard (1942) C. pelagicus prefers the upper 100 meters of agitated waters having temperatures between 4 and 15°C but can tolerate temperatures as low as minus 1.5°C and as high as 26°C. However, as Hasle (1960), p. 82) has pointed out this species is unaccountably absent from Pacific and Atlantic subantarctic waters.
The ecological requirements of Helicosphaera are not well known but the published records supplemented by the writer's observations suggest that the only living species prefers warm temperate to tropical near surface oceanic waters but can occur in cool temperate and/or coastal areas. The fossil species are presumed to have had similar requirements.
The fossil rhabdoliths, which in part belong to the probably extinct genus Blackites, have specially shaped coccoliths which, like those of the related modern genus Rhabdosphaera, added greatly to the bouyancy of the cells they cover. Since Rhabdosphaera prefers the upper 200 metres of calm off-shore waters having temperatures higher than 10°C it seems reasonable to attribute similar ecological preferences to the fossil representatives of this group.
Scyphosphaera, a rather rare living genus having distinctive “float’ coccoliths (lopodoliths), prefers warm temperate or subtropical near-shore surface waters although it is present in SW Pacific oceanic waters (Norris, 1961 and the writer's observations) and can tolerate temperatures as low as 9 to 12°C. The fossil representatives are considered to have inhabited similar environments.
The stratigraphic occurrence and relative abundance, in terms of the New Zealand Series and Stages, of the above taxa are given in Table 1.
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Table 1: Occurrence of temperature indicative calcareous nannoplankton in Dannevirke to Southland Series strata.
Marine Climate
The estimated marine climate of the surface waters (0-200 metres) in the vicinity of Wellington (latitude 41°S) during Danian to Mid Miocene time is given in Fig. 1. With the exception of the Southland Series (see below) the wide geographic distribution of the sections studied made unnecessary any weighting of the averaged results for latitude.
Dannevirke Series (Danian to Middle Eocene):
Due to the almost total extinction of the calcareous nannoplankton at the base of the Teurian Stage, only the probable absence of extreme temperatures can be determined from the earliest Dannevirke assemblages. During the remainder of the Dannevirke Series the consistent occurrence of Cyclococcolithus, Discolithina and common Ericsonia ovalis sensu lato clearly indicate the general prevalence of cool temperate conditions although the distribution of the rhabdoliths suggests that a minor warming may have occurred during late Waipawan time. The total absence of the braaradosphaerids from pre-Arnold Series strata is attributed to the inability of this typically northern hemisphere group to reach the SW Pacific rather than to the absence of suitable environments in the New Zealand region.
Arnold Series (Middle and Upper Eocene):
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Fig. 1: Estimated marine climate at latitude 41°S during Dannevirke to Southland Series time.
Landon Series (Oligocene and Earliest Miocene):
The early Landon distribution of the selected taxa clearly continue the trends established in the late Arnold Series and appear to give good evidence for the occurrence of a climatic deterioration across the Eocene-Oligocene boundary (see also Edwards, this issue). The estimation of mid and late Landon Series climates is complicated by the sudden fluctuations in the abundance of Ericsonian ovalis sensu lato which are complementary to those of the extinct species Reticulofenestra placomorpha and by uncertainties regarding the effects of the maximum submergence of the New Zealand area during mid Tertiary time when deposition of calcareous sediments reached its culmination. However the absence of rhabdoliths and braarudosphaerids clearly implies either the absence of coastal environments or the presence of cool temperate conditions through much of the Landon Series. The upward increase in the frequency of Helicosphaera can be interpretated as indicating a slight warming in late Landon time.
Pareora Series (Early Miocene):
The occurrence of the selected taxa in early and mid Pareora time is almost identical to that of the late Landon Series and both are here considered as suggesting the prevalence of almost warm temperate conditions. The late Pareora differs only in the presence of rhabdoliths which may suggest the presence of a more truly page 30 warm temperate climate in latest Pareora time. The reasons for the absence of Cyclococcolithus is not known.
Southland Series (Early to Mid-Miocene):
The distribution patterns of the braarudosphaerids, of Ericsonia ovalis sensu lato and to a lesser extent of the rhabdoliths in the Clifden section suggests that the warm temperate conditions which then prevailed in Southland may have reached their peak in the Clifdenian Stage. The presence of a warm temperate climate so far south implies that at least marginally subtropical conditions probably occurred in the vicinity of Wellington and the curve in Fig. 1 is accordingly adjusted.
Taranaki and Early Wanganui Series (Late Miocene and Pliocene):
At present insufficient is known of New Zealand late Tertiary calcareous nannoplankton assemblages to deduce their climatic implications apart from the probable absence of very cold conditions and a possible decline in temperature through the early Wanganui Series.
Discussion
Dr C. A. Fleming. Has the study of the nannoplankton occurrences been used before as a method of determining Tertiary paleoclimates? Mr. A. R. Edwards. As far as I know it has not. It has been used in the study of the Pleistocene in various ways including the examination of deep-sea cores from the Caribbean where the results were related to oxygen isotope measurements.
Mr. I. Devereux. Could you explain the double line you have in the Mid-Tertiary? Which line would you favour?
Mr. A. R. Edwards. The interpretation of the climate at that time is problematical because we don't know what effect the widespread submergence at that time had. The lower line is based on the absences I mentioned but if these absences were caused by the lack of coastal waters due to submergence rather than to the presence of cool waters, then the upper line would be closer to the actual climate. I wouldn't say which one I preferred.
Dr. C. A. Fleming. I would just emphasise the point that this study by Mr Edwards is a new approach to this problem of Tertiary temperatures.
References
Bernard, F., 1942. Essai sur les facteurs de repartition des Flagelles calcaires. Ann. Inst. Oceanogr. (Monaco), ser. 2, 21: 29-112.
Cohen, C. L. D., 1964. Coccolithophorids from two Caribbean deep-sea cores. Micropaleont. 10: 231-250.
Edwards, A. R., 1967. Marine Climates in the Oamaru District during late Kaiatan to early Whaingaroan time. Tuatara (this issue).
Hasle, G. R., 1959. A quantitative study of phytoplankton from the equatorial Pacific Deep-Sea Res. 6: 38-59.
—— 1960. Plankton Coccolithophorids from the subantarctic and equatorial Pacific. Nytt Mag. Bot. 8: 77-88.
Martini, E., 1961. Ein Kalkflagellat in den Meeren der Gegenwart und Vorzeit. Natur u. Volk 91 (9): 335-9.
—— 1965. Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. In W. F. Whittard and A. B. Bradshaw (ed.), Submarine geology and geophysics. (Proc. 17th Symp. Colston Res. Soc.), London: Butterworths, pp. 393-411.
McIntyre, A.; Be, A. W. H.; 1966. Coccolithophorids as ecologic indicators in oceanic sediments. Bull. Amer. Ass. Petrol. Geol. 50, 3 (1): 624-5.
Norris, R. E., 1961. Observations on phytoplankton organisms collected on the N.Z.O.I. Pacific Cruise, September 1958. N.Z. J. Sci. 4: 162-188.