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Making New Zealand vol 01 no 01: The Beginning

The Era of Modern Life

page 14

The Era of Modern Life

Limestone formation in Castle Hill Basin, Canterbury. Thelma R. Kent

Limestone formation in Castle Hill Basin, Canterbury. Thelma R. Kent

The next era, the Tertiary, though it began some sixty million years ago, is described as 'modern' by the geologist, since, during its course, many forms of life known to us began to appear. In New Zealand it commenced with a gradual advance of the sea over the old land-surface of Mesozoic times. The spoil then carried down from the uplands formed coarse-grained grits, conglomerates, and sandstones. These were succeeded by coal-measures similar in origin to those of Upper Cretaceous times. As the sea advanced farther, shallow-water greensands were laid down,
Shark's tooth of Tertiary age. F. Chapman

Shark's tooth of Tertiary age. F. Chapman

Microscopic fossils—primitive plants and animals from the Oamaru district. J. Park

Microscopic fossils—primitive plants and animals from the Oamaru district. J. Park

and finally accumulations of the hard parts of sea animals were built up in water too far removed from the land to contain sand or mud. These are termed limestones, and they are so widespread in Middle Tertiary formations that very little land could have remained above the sea.

That some land did survive, however, is proved by fresh-water deposits containing impressions of plants. These are quite modern in type, showing that flowering plants had now replaced the fern-like and conifer plants of the Mesozoic Era.

After Middle Tertiary times the downward movement of the New Zealand area was reversed, and the land began to rise. Limestone continued to be formed, particularly in parts of the North Island, but as the waters became shallower, there gradually appeared different deposits. These were fine-grained muds and sands washed into the sea from the emerging land.

The uplift of most of the South Island ended marine sedimentation, but in Marlborough and page 15 Tertiary Era
'Papa,' of blue mudstone, deeply carved by water, is a familiar formation in the North Island. This photograph shows the RangItikei River, near Mangaweka. New Zealand Railways

'Papa,' of blue mudstone, deeply carved by water, is a familiar formation in the North Island. This photograph shows the RangItikei River, near Mangaweka. New Zealand Railways

Tertiary foraminifera, marine fossils which help geologists in their search for petroleum. The pictures of these fossils are greatly enlarged. H. J. Finlay

Tertiary foraminifera, marine fossils which help geologists in their search for petroleum. The pictures of these fossils are greatly enlarged. H. J. Finlay

Lamp-shells in limestone, Kakanui, Otago. J. Boehm

Lamp-shells in limestone, Kakanui, Otago. J. Boehm

over much of the North Island it continued to a later date. The spoil worn down from the granite mountains of Nelson and northern Westland was carried north by ocean currents and spread over Taranaki, Wellington, and Hawke's Bay to form the widespread blue mudstones, or 'papa,' which are the youngest Tertiary strata in those areas.

Throughout the Tertiary Era there was a gradual change in climate, a change that was to culminate in a severe ice age in the next era. In Early and Middle Tertiary times, however, the climate in New Zealand was much warmer than at present, and in the shallow seas which flooded the land there flourished a rich and varied animal life, including some forms now found only in warm-temperate and tropical climates. From sands, limestones, and mudstones formed in these times, therefore, many well-preserved fossils can be collected. The specimens from the earliest strata belong to extinct kinds, but as we pass to higher strata, there is a gradual increase in the number of species which are identical with the life in New Zealand seas to-day.

The fossils of the marine beds belong to many groups. The lowly, single-celled Foraminifera, found in great numbers, are of great value to geologists when seeking for petroleum in commercial quantities. The spicules, which form the framework of sponges, are numerous in the famous chalk-like deposits of the Oamaru district. These also contain exquisitely constructed primitive plants called diatoms and lowly animals known as radiolaria. Among the larger fossils the most important are shells of many varieties, while corals, barnacles, and crabs are found in smaller numbers. Vertebrates (animals with a spinal column) are rare, but occasionally fragments of fossil reptiles and whales have been discovered. Fossil bones of a gigantic penguin are known, and sharks' teeth are comparatively common. Altogether, these Tertiary deposits provide a wonderful hunting-ground for the geologist, amateur or professional.