Tuatara: Volume 16, Issue 1, April 1968
Cenozoic Marine Temperatures Indicated by the Scleractinian Coral Fauna of New Zealand
Cenozoic Marine Temperatures Indicated by the Scleractinian Coral Fauna of New Zealand
In 1958, Squires published a major systematic analysis of the Cretaceous and Tertiary coral fauna of New Zealand. From his data he was able to prepare a temperature graph for the New Zealand Tertiary based on the presence of coral genera in each stage for which the present day broad temperature tolerances are known, supported by the temperature indications obtained from other fossil groups. This paper is an attempt to examine the temperature graph that the Scleractinian corals alone appear to indicate for the Cenozoic, utilising the increased published and unpublished data that has become available since 1958. In view of the limitations on space this article is a summary of evidence only with selected bibliography rather than a full documentation.
Method of Faunal Analysis
The assumption is made that the presence in the fossil record of genera now only found living in warmer waters is evidence that similar higher temperatures existed in New Zealand for the duration of the record of these genera. Present day latitudinal distribution of the fauna can be unreliable for temperature guides unless additional factors like depth and sub-surface temperatures are known. To rationalise all variable factors is difficult, but by use of records where some of these factors are known does provide a basis for classifying certain genera as warm, temperate or cold water forms. This provides the analogy with which the fossil fauna is compared and a temperature curve thus produced. The analysis of the fossil Scleractinian coral fauna is on a generic and subgeneric basis as this enables the plotting of more positive ranges than can be done with individual species. In some cases, however, it is necessary to take into account the ranges of separate species which are naturally zoned into distinct warm or cold water geographic elements for at a generic level their significance would be overlooked. All minor gaps occurring within ranges have been bridged, while major gaps have been treated as absences prior to recolonisation. Because New page 22 Zealand fossil corals appear to show little overall provincialism in their distribution the fauna is treated as one entity without recognition of any geographic zonation. The coral faunas for certain ages (Cretaceous, Dannevirke and Wanganui Series), though poorly known due to facies and preservation problems, are nevertheless treated as representational.
Temperature Curve Assessment
Knowledge of the New Zealand Cretaceous coral fauna is poor, being derived from the presence of six ahermatypic genera. One is endemic while the others appear to be a mixture of wide-ranging forms of cold to warm water tolerances. Fleming (1962:66) interprets the Upper Cretaceous as “warm temperate, warmer than the present’, and this is used as a suitable temperature level at which to begin the temperature curve (Fig. 1).
The end of the Cretaceous spells the extinction of the Mesozoic coral fauna, only one genus (Dasmosmilia) surviving into the Eocene. The recovery of the fauna during Dannevirke times appears slow, suggesting that temperatures and conditions may have been largely against any rapid reinvasion of Indo-Pacific forms. Immigrant genera include Lochmaeotrochus, Notocyathus (Paradeltocyathus), Balanophyllia (B.), B. (Eupsammia), indicating that temperatures were about warm temperate level. Dannevirke conditions, therefore, are interpreted as having remained largely similar to those at the end of the Cretaceous, but showed a gradual rise during the Porangan.
Bortonian time marks the major recovery of the fauna after the Cretaceous with a rapid influx of Indo-Pacific genera. Long ranging cosmopolitan forms which were to form major constituents of the Tertiary fauna appeared and warm water forms like Oculina, Conocyathus, Asterosmilia, some species of the Flabellum group and Balanophyllia appear to attest to warmer conditions. The presence of Madracis in the South Island, the earliest - known apparently hermatypic coral from the New Zealand fossil record supports at least warm temperate conditions. The apparent extinction of some genera like Madracis and the end of the Bortonian and others during the Kaiatan suggests that the distinct warming trend developed at the beginning of the Bortonian was not sustained for the rest of the Arnold, though overall conditions were warmer than the Dannevirke.page 23
Temperatures appear to have been largely similar to those of the upper Arnold Series, and most genera that appeared during the Arnold continued. Three immigrant genera appeared during the Whaingaroan (one, Notocyathus (N.) being a warm water form), and four during the Duntroonian, but most forms can be regarded as temperate.
The Otaian Stage is the most significant in mid-Tertiary stratigraphy as it records the greatest number of generic incomings (23), and the greatest number of extinctions (22) in the coral fauna for any one stage. 17 Indo-Pacific genera of hermatypic corals appear in the record, including Porites and Turbinaria, which are regarded as being significant reef-building genera. These hermatypic forms are restricted to localities in the Northland Peninsula and East Cape, and all evidence suggests that these specimens are detrital material (Squires, 1962) from shallow water reef structures that lived within an estimated temperature range of 19 to 28°C (Squires, 1962a). Nearly all the genera are known to be present on the Great Barrier Reef today. Incoming ahermatypic page 24 genera are all cool to warm temperate forms but the presence of hermatypic corals for only one Stage indicates that tropical or at very least marginal tropical conditions were achieved for the Otaian in more northern areas.
The decline from this highest point reached in the Tertiary appears as steep as its inclination, suggesting that this rise in the Otaian was more a temperature fluctuation rather than the crest of a curve. For the rest of the Pareora temperatures appear to have returned to a level similar to those for the end of the Landon.
The Altonian appears to possibly reflect a sharp minor rise in temperature before a decreasing trend set in for the rest of the Southland Series. The warm water genus Cladangia and the sub-genus Trochocyathus (Platycyathus) appeared during this Stage as well as further records of hermatypic genera — Plesiastrea and Turbinaria from Muriwai, but all did not extend beyond it. In all six genera became extinct at the end of this Stage, and three further genera for the rest of this Series, including two long-surviving temperate forms. This suggests a marked temperature decline from the Altonian.
Two cool water immigrant genera (Oulangia and Lophelia) are known for this Series, but in the Tongaporutuan five noticeable extinctions of long-ranging genera, including several cool water cosmopolitan forms, took place, continuing the marked downward temperature trend begun in the Southland. In the Kapitean two species of long-ranging genera were extinguished.
In the Opoitian five cool species appear for five genera previously recorded in the Tertiary record. These forms (like Flabellum rubrum, especially) represent the prominence of distinct cold water elements. The onset of apparently markedly cooler conditions during the Opoitian also marks the extinction of representatives of three long-ranging Tertiary genera. The end of the Waitotaran sees the further removal of four genera, including two long-ranging forms. In the Nukumaruan a cold water species that made its appearance during the Opoitian is extinguished, though the genus Culicia makes an appearance. In the Okehuan Astrangia also appears.
The only forms which appear to have survived the low climatic range and fluctuations of the Pleistocene are Flabellum rubrum and possibly Culcicia rubeola, for both are found as extant species. The reappearance of an abundant Recent fauna of 16 genera illustrates the rapid reinvasion of Indo-Pacific forms when temperatures rose after the end of the Pleistocene. As the Pleistocene virtually extinguished all Tertiary lineages, the Recent fauna can be regarded as a new one.
Dr. D. G. Jenkins. I think the graph appears to be very low in the Pliocene.
Mr. I. W. Keyes. At that time several long ranging genera died out and it would seem that conditions deteriorated considerably. Professor P. VELLA. Did they die out at the end of the Miocene or gradually?
Mr. I. W. Keyes. A range chart of genera would show a steady decrease in numbers from late Miocene to the Wanganui Series. Dr. N. deB. HORNIBROOK. It is possible though that the temperature would not needed to have dropped to such a degree to get these changes?
Mr. I. W. Keyes. That is possible but we are losing cool-temperate to cold water forms and so a considerable drop is indicated.
Dr. D. G. Jenkins. Are they replaced with any cold water or Antarctic forms?
Mr. I. W. Keyes. Warm water species tend to die out and cold water species come in. Some of the warm water ones remain however.
Dr. I. Speden. Is the 2°C rise in the Bortonian significant?
Mr. I. W. Keyes. There is a large influx at the beginning of the Arnold of warm water forms.
Professor P. Vella. What is the method of dispersal of the corals? If they were wiped out could they easily repopulate from say Australia?
Dr. D. F. Squires. We have found recently that the larval life of the ahermatypic types are longer than previously thought and may be several days. The tropical ones are probably longer; they spawn regularly and profusely, so repopulation should not be too difficult.
Mr. K. Lewis. I am wondering if you have allowed for latitude differences in your samples? There seems to be some fairly small kinks on your curve that could be due to this cause.
Mr. I. W. Keyes. This is possible, as I have treated the country as a whole and not treated the South Island separately from the North.
Fleming, C. A., 1962. New Zealand Biogeography: A Paleontologist's Approach. Tuatara 10 (2): 53-108.
Squires, D. F., 1958. The Cretaceous and Tertiary Corals of New Zealand. N.Z. geol. Surv. paleont. Bull. 29. 107 pp.
—— 1962. A Scleractinian Coral Faunule from Cape Rodney. N.Z. J. Geol. Geophys. 5 (3): 508-14.
—— 1962a. Additional Cretaceous and Tertiary Corals from New Zealand. Trans. Roy. Soc. N.Z. Geology 1 (9): 133-150.