Tuatara: Volume 16, Issue 1, April 1968
Distribution of some Warm Water Benthic Foraminifera in the N.Z. Tertiary
Distribution of some Warm Water Benthic Foraminifera in the N.Z. Tertiary
Attempts to Estimate past sea temperatures from paleontological evidence necessarily involve comparisons of the past distributions of organisms with the present distribution of their nearest living relatives. Some organisms such as certain types of reef building corals are known to be stenothermous within a particular range of temperature, but little information is available about the range of temperature tolerance of Pacific larger Foraminifera upon which most of the deductions from benthic Foraminifera about the New Zealand Tertiary climate have to be made.
However, the differences between the shallow water Foraminifera of the Central Pacific equatorial region and that of New Zealand at the present day are striking since none of the genera (Peneroplis, Operculina, Maginopora, Sphaerogypsina, “Calcarina’, Baculogypsina, Amphistegina) characteristic of the coral reef environment of the Great Barrier Reef and Mid Pacific islands now occur in New Zealand. During the Tertiary, however, many of the Foraminifera now confined to the subtropical and tropical zones were well established in New Zealand and there is no doubt that the climate was considerably warmer than at present. But to translate these faunal differences into actual degrees of temperature is a hazardous business.
The Evidence of Amphistegina
Amphistegina does seem, however, to provide a rough basis for estimating minimum surface temperatures, judging by its present distribution.
This genus, which occurs in great abundance (up to 85% of the sediment) in tropical seas from the littoral down to about 175 metres, is abundant on the Great Barrier Reef, and occurs as far south as Sydney Harbour where the mean annual temperature is about 20°C (Wisely, 1959). It has been recorded from Lord Howe Island by Heron-Allen and Earland (1924), and the writer has found it abundantly in a dredging from Norfolk Island.page 12
It is not now present in New Zealand waters, although it was generally abundant throughout the area from Upper Eocene to Upper Miocene.
The southern limit of the occurrence of Amphistegina appears significant in relation to the seasonal isotherms in the Tasman if we accept temperatures as the main control factor. According to the data provided by Garner, 1954, and Garner and Ridgway, 1965, the mean annual temperature of the surface waters immediately north of New Zealand is subject to wide fluctuations. The temperatures may drop as low as 15°C in winter and reach 22°C in summer. It may therefore be an over-simplification to accept the 20°C mean over several years, about half way between Norfolk Island and North Cape, as meaningful. For all we know it may be the lowest or highest seasonal temperatures that are really significant. It is a fact, however, that 20°C mean annual isotherm roughly corresponds to the southern limit of the distribution of Amphistegina in the Pacific.
If we are justified in drawing an analogy with the distribution of Amphistegina during the Tertiary we can conclude that the 20°C mean surface isotherm lay south of New Zealand from Upper Eocene time to Mid-Miocene as Amphistegina was present more or less continuously in the southern half of the South Island throughout that time. Allowing for a difference of 5°C between the northern and southern extremes of New Zealand the marine surface climate in the latitude of Wellington was therefore within the subtropical zone or was marginally tropical.
In Upper Miocene time, during the Tongaporutuan, Amphistegina was present along the east coast of the North Island from Wairarapa northwards, but there seems to be only one record from the Kapitean, in the East Cape area together with the warm water echinoid, Phyllocanthus. Lack of suitable facies in the South Island may give a misleading picture but its known distribution is suggestive of a northward withdrawal during the Upper Miocene when the 20°C mean annual surface isotherm may have lain across the South Island in Tongaporutuan time and across the lower part of the North Island during part of Kapitean time.
Amphistegina is generally absent throughout the Pliocene and Pleistocene in spite of apparently suitable facies, suggesting that the 20 °C mean annual isotherm moved northwards and a recent discovery of Amphistegina in a submerged limestone of about middle Wanganui Series age, from off North Cape, provides evidence of a late stage in its northward withdrawal.
Fig. 1: Estimates of New Zealand Tertiary temperatures in the latitude of Wellington based on the distribution of Amphistegina and other larger Foraminifera. From Arnold to Southland Series the estimated minimum temperature is based on the more or less continuous presence of Amphisfegina in Southland, allowing for a 2½°C difference for the latitude of Wellington. The estimated maximum temperature is based on the frequency and distribution of larger Foraminifera.
Tertiary Warm Water Foraminiferal Assemblages
Tertiary assemblages of warm water Foraminifera which are now abundant in the shallow waters of the Great Barrier Reef and the mid Pacific Islands provide a rough guide to marine climates. Two extinct groups in particular, the Discocyclinidae in the Eocene, and the Lepidocyclinidae in the Oligocene and Miocene, are considered to be indicators of warm climates. They occur in great abundance in rocks of the equatorial belt, but their occurrence in New Zealand is more sporadic and they are smaller and less abundant, suggesting subtropical to only marginally tropically conditions.
The following is a summary of the occurrence of larger Foraminifera in the New Zealand Tertiary:
Mangaorapan: Asterocyclina abundant, and Sphaerogypsina (Eyre River Sand, S. Canterbury and Chatham Is.).
Kaiatan: Halkyardia, large, abundant Amphistegina - Astejgerina (N. Otago and Westland).page 14
Runangan: Peneroplis, (Westland); Asterocyclina (small sp.), Sphaerogypsina (N. Otago). Amphistegina-Asterigerina large and abundant in both areas.
Whaingaroan: Operculina, Amphistegina-Asterigerina, “Calcarina’ (Southland, etc.). No Lepiodocyclinidae.
Duntroonian: “Calcarina’, Amphistegina (Southland, etc.); Operculina (Waikato). No Lepidocyclinidae.
Waitakian: Amphistegina (Southland, E. Coast North Island and Waikato); Lepidocyclina locally abundant (E. Coast North Island and King Country); Amphistegina infrequent and Lepidocyclinidae absent from E. Coast South Island.
Otaian: Lepidocyclinidae, Miogypsina and abundant Amphistegina, North Island.
Upper Otaian-Hutchinsonian: Amphistegina (Southland), Lepidocyclina, Miogypsina, Amphistegina, Heterostegina, locally abundant (Northland).
Awamoan: Amphistegina rare E. Coast South Island.
Altonian: Amphistegina, Heterostegina, Planorbulinella abundant throughout Southland and Westland. Rare Cycloclypeus and Lepidocyclina in Southland; more abundant in Nelson and N. Island.
Clifdenian: Abundant Lepidocyclinidae, Amphistegina, Cycloclypeus, Heterostegina, Planorbulinella (Westland).
Lilburnian: Lepidocyclina in Southland; unsuitable facies elsewhere.
Waiauan: Abundant large Amphistegina, Heterostegina, Cycloclypeus Operculina mbalavuensis Cole (described Fiji), Lepidocyclina s.l., Sphaerogypsina, Planorbulinella, in Northland; the same assemblage in E. Dannevirke with Marginopora. Amphistegina present in Southland.
Tongaporutuan: Amphistegina present locally, E. Coast North Island.
Kapitean: Amphistegina present locally, E. Cape.
Waitotaran: Amphistegina sporadic, Hawkes Bay.
Absence of Lepidocyclinidae in Whaingaroan and Duntroonian.
Absence of many warm water Foraminifera from E. coast South Island from Waitakian to Awamoan, suggestive of a locally cool current as at present.
Large Foraminifera well established from Otaian to Waiauan, indicating fairly continuous warm climate, probably marginally tropical in Northland.
Absence of most larger Foraminifera above Tongaporutuan, indicating cooling.page 15
Larger Foraminifera being essentially shallow water organisms are pretty much restricted to particular facies. Their occurrence is sporadic and they record only the warm periods in the Tertiary.
Mr. K. Lewis. Amphistegina is a shallow water foram and I am wondering whether it is possible that since the last ice age it has not been able to bridge the gap back to New Zealand. This would make the present distribution atypical.
Dr. N. deB. Hornibrook. There is some possibility but this is not likely. These animals seem to be able to get about very easily. Some estuarine Foraminifera for instance have a very wide distribution.
Dr. C. A. Fleming. The distribution through the islands of the Pacific suggests it can cross barriers and its absence south of Sydney confirms your interpretation.
Dr. I. Speden. Have you any comments on “change of diversity’ in the Foraminifera through the Tertiary? Some people hold that the degree of diversity of the fauna decreases as you approach the poles.
Dr. N. deB. Hornibrook. The absence of these Foraminifera at certain times means that the fauna is less diverse. As a generalisation I would say that as the Wanganui is approached the fauna becomes less diverse.
Garner, D. M., 1954. Sea Surface Temperatures in the South-west Pacific Ocean, from 1949 to 1952. N.Z.J. Sci. Tech. B36 (1): 285-303.
—— and Ridgway, N. M., 1965. Hydrology of New Zealand Offshore Waters. N.Z.D.S.I.R. Bull. 162: 63 pp.
Heron-Hallen, E., and Earland, A., 1924. The Foraminifera of Lord Howe Islands, South Pacific. J. Linn. Soc. Zool. 35: 599-647.
Hornibrook, N. de B., 1967. New Zealand Tertiary Microfossil Zonation, Correlation and Climate, pp. 29-39, (in) Hatai (Ed.), Tertiary Correlations and Climatic Changes in the Pacific, 102 pp.: Sasaki Printing and Publishing Co., Sendai.
Wisely, B., 1959. Factors influencing the settling of the principal marine fouling organisms in Sydney Harbour. Aust. J. Mar. and Fresh Wat. Res. 10: 30-44.