Other formats

    TEI XML file   ePub eBook file  


    mail icontwitter iconBlogspot iconrss icon

Tuatara: Volume 16, Issue 1, April 1968

General Discussion

page 80

General Discussion

Dr. J. W. Dawson. I would like to suggest two fields of botanical research that could assist in evaluating our past climates. The first one is the study of leaf fossils. Near the tropics there is a preponderance of rain forest species with large leaves whereas in our present rain forests we have mainly small leaves. A study of the sizes of leaves at various times could give an idea of the climate variations. I haven't looked at this closely, but what leaf fossils I have seen from the New Zealand Tertiary all seem about the same size as today. The second field is the study of epiphytes — the epiphytes of our rain forests are quite different from those of the tropical lowlands. In New Caledonia the lowland forest has a range of tropical epiphyte species, but above about 2000 feet the assemblage is like New Zealand. I don't think there have been many, if any, tropical epiphytes recorded as Tertiary plant fossils in New Zealand. By and large I think this suggests that the Tertiary climate in New Zealand was never truly tropical.

Mr. I. Devereux. Would anyone like to comment on the concept of latitude variations during the Tertiary. Is everyone more or less in agreement that there were definite latitude temperature differences throughout the Tertiary?

Mr. P. A. Maxwell. The Bortonian seems to be very even throughout New Zealand. During the Otaian-Hutchnisonian there seemed to be marked differences between Northland and Canterbury/ Otago.

Mr. I. Devereux. From the evidence presented it seems that the latitude differences are more apparent in the cooler periods. In the warmer times the whole country was warm and latitude differences are harder to recognise.

Dr. N. deB. Hornibrook. The position of the Sub-Antarctic convergance could have an effect.

Mr. I. Devereux. I think we could move on to comparing the results from each paper and seeing if we can come to any agreement. Professor P. VELLA. The drop in temperature at the Eocene/ Oligocene is one of the major agreements from all the papers presented. I think we could really concentrate on this boundary in New Zealand. We have an opportunity to do something really worthwhile for world stratigraphy.

Dr. N. deB. Hornibrook. At the Pan Pacific Science Congress paleobotanical evidence was presented which suggested a cooling during the Oligocene, so it would seem that this cooling was a worldwide event.

Dr. D. G. Jenkins. I think that the most significant thing that has come out of the Conference is that you have to pick a sensitive page 81 subject to work with. Mr. Lewis's flemingi is undoubtably a very sensitive animal and so are the planktonic foraminifera and nannoplankton. However the Mollusca are a broad group and tend to give a broad picture. It would seem to be a good idea to select a more sensitive group from the Mollusca. The land plants also seemed to be fairly insensitive. I think the other significant thing was the good agreement between the isotope results from New Zealand and Australia.

Mr. V. Neall. One point that has struck me during the conference is that everyone has worked from tropical affinities. There would seem to be a good field in looking at cold water affinities, especially in echinoids, crabs and brachiopods.

Dr. P. Webb. It is said that some species of animals become more ornate in the tropics. I wonder if Dr Jenkins could say if this is the case with planktonic foraminifera and if so could this be used for climate studies?

Dr. D. G. Jenkins. I believe this is the case with some molluscs but I don't know of any species of foraminifera where this occurs. Dr. N. deB. HORNIBROOK. To get away from purely biological things, there is a field that has not yet been touched in New Zealand. That is the colour of sediments and microfacies studies. I wonder if Dr. Webb could tell us what is being done in Europe in this sort of thing?

Dr. P. Webb. This is a very wide field. Formation of phosphates, glauconites, and gypsum all have some climatic inference and could be used for climate indicators.

Mr. I. Devereux. Professor Wellman has told me that on the East Coast of the North Island there is a sudden change in the colour of the sediments at the top of the Runangan.

Dr. P. Suggate. In the West Coast of the South Island there are light colours in the Runangan and much lighter again in the Landon Sediments. This is associated with increasing lime content — the Landon tends to be limestones. Presumably this factor has a climatic association.

Professor P. Vella. This is a question for the sedimentologists and unfortunately we have a lack of sedimentologists in New Zealand.

Mr. I. Devereux. I wonder if anyone has any information on experiments either in tanks or by observation of natural communities, where the effects of altering the temperature are tabulated. Do some things die out while others hang on?

Professor P. Vella. Off South America there are a lot of sea birds dying. I'm not sure whether this is caused by over-fishing or a change in the Humboldt current or some other factor. I don't know whether this is being carefully watched.

Dr. D. F. Squires. The trouble with experiments is that marine organisms seem hard enough to keep alive in tanks without trying experimenting with them. With natural environments it is difficult page 82 to tell what are short term effects and what are long term effects and so it is difficult to know what any change means.

Dr. I. Speden. The problem of what causes animal populations to change is not a simple one. People here have been stressing temperature changes but there are other factors which are probably just as important: turbidity, oxygen concentration, salinity, competition, etc.

Dr. D. F. Squires. I'd like to comment on that. Since I was here in 1959 I have wondered why there aren't reef corals in Northland. Maybe there are but nobody has reported them. The temperatures are alright, but marginal, but there are other things working against them; isolation, turbidity, and probably seasonal temperature fluctuations.

Mr. I. Devereux. I think I might attempt to summarise the results in a broad way, say Series by Series.

Dannevirke Series: Not a very good record from this time with the planktonic foraminifera probably providing the most valuable information. The general feeling is that it was a little warmer than today but cooler than the following series.

Arnold Series: From this time on there has been very good agreement. The Arnold would seem to be markedly warmer than today, being marginally tropical over most of New Zealand and there is a strong suggestion that it may have been the warmest period of the Tertiary.

Landon Series: A definite cooling seems to have taken place at the beginning of this time although the extent of this cooling is not completely clear.

Pareora Series: A warming again after the cooler Landon, with temperatures becoming marginally tropical especially in the North Island.

Southland Series: A very warm period at the beginning which may be the warmest time of the Tertiary rather than the Pareora which has been accepted till now as the Tertiary temperature peak. A definite cooling appears to have set in almost from the beginning of this time.

Taranaki Series: Cooling probably continued through this time also.

Wanganui Series: The cooling of the previous times may have continued right through to the Pleistocene but there is some suggestion that the temperatures of the Pliocene were fairly uniform and about the same as today. It has been suggested though that the temperature fluctuations that are the feature of the Pleistocene may have begun in the Pliocene.

Conference closed.

page breakpage break