Making New Zealand vol 01 no 01: The Beginning

The Oldest Fossils in New Zealand

A slab of fossils of attractive form found in the Wairoa Gorge, Nelson. These shells are widespread in rocks of the Triassic Period mentioned on page 9. Wm. C Davies. Cawthron Institute

How old is New Zealand? The land as we know it is of comparatively recent origin, but in remote places at both ends of the South Island geologists have discovered traces of life which existed in the Ordovician Period, some 450 million years ago. At Preservation Inlet and Cape Providence in Fiordland and in the Mount Arthur and West Haven districts in the north are found the oldest fossils in New Zealand, the most numerous of which are the graptolites.

The graptolites were surface-dwellers in the oceans of that ancient period. After death their skeletons rained down into the bottom sediments or were swept by winds and currents into bays, to be preserved in black muds, where no scavengers could live to destroy them. Hence their fossil remains are usually found in dark-coloured mud-stones or slates, forming a white, flattened impression on a dark ground. The graptolites were quite unlike any marine animals of to-day and they left no descendants. But the fossil remains of these creatures are of great value to the geologist as signs of that remote period so many million years ago.

There followed a long interval of time during which the history of New Zealand is unknown. Then another episode in the story is revealed by rocks exposed at Reefton and farther north in the Baton and Wangapeka Valleys of Nelson. In these places there are mudstones and sandstones rich in marine fossils, the most abundant being ancestors of the modern lamp-shells. These creatures are comparatively rare and unimportant in modern seas, but in ancient oceans they were dominant. The local fossils are closely related to those which are found in Devonian rocks in parts of Europe. For this reason it has been suggested that they migrated here by means of an ancient sea-way, called Tethys, separating Eurasia from Africa and now reduced to a small remnant in the Mediterranean Sea.

The rocks at Reefton provide yet another link in the story. Here the lower beds with lamp-shells are followed by dark-coloured limestones containing corals of varied size and character. These belong to the middle part of the Devonian Period, and the seas in which the corals lived also flooded Eastern Australia where similar forms are known.

The seas of the Devonian Period finally retreated, and there followed another lengthy period not represented by rocks in New Zealand. In the page 7

Palaeozoic Era Ordovician Period Devonian Period

This title refers to the era and period shown by the time-scale on page 5. It will assist the reader to note the relation of this and the eleven succeeding titles to the time-scale.

Northern Hemisphere at this time flourished the great forests of the Carboniferous Period which were to form widespread coal-measures, but these are completely absent in New Zealand. Our local coal-fields are much younger.

Before the Palaeozoic Era finally closed, seas again invaded this area, as we know from a few poorly preserved fossils of Permian age found in Nelson and at Clinton in Otago. These are the last remnants of that ancient era, so scantily developed in New Zealand.