Making New Zealand vol 01 no 01: The Beginning
The Era of Modern Life
The Era of Modern Life
Limestone formation in Castle Hill Basin, Canterbury. Thelma R. Kent
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.
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.
'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
Lamp-shells in limestone, Kakanui, Otago. J. Boehm
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.