For many people fossils are intriguing and beautiful objects. They are collected because of their shape, texture or colour.
Serving science and industry
To geologists fossils help solve problems about origins, age and relationships of sedimentary rock layers. To paleontologists they are a history of life, showing what previous organisms looked like and how they functioned and evolved. To geochemists, fossils are time capsules. Some fossils provide stable isotopes of oxygen, carbon and strontium, which provide insights into what past climates and environments were like, and how extinctions occurred.
Some rocks such as limestone are almost entirely made up of fossils. Limestone is a biogenic rock – it has formed from the skeletal remains of once-living creatures. Limestone is used to make cement, for building (such as Ōamaru stone), and is also crushed and applied to farmland as fertiliser.
Pollen, along with sand grains and organic debris found at crime scenes, in car mudguards or clothing is used by the police in forensic work, as different localities have unique pollen profiles due to the particular mix of plants that grow there.
Coal is another biogenic rock. Originally it accumulated as plant material in swamps and forests, before being buried. Oil and gas are derived from the slow pressure-cooking of organic matter buried at great depths (normally more than 5 kilometres).
Underground exploration for oil, gas, coal or water makes use of microfossils. As they provide information on the age, origins and relationships of rock layers they provide geologists with clues as to where coal, oil or gas is likely to be found – usually porous rocks that were once coastal sands.
Paleontologists are trained fossil hunters. Subtle features on rock surfaces, changes in texture or colour, or strange shapes attract their eye. Most collecting requires only keen eyes, a geological hammer and a cold chisel. Collectors rarely dig with spades, unless sediments are exceptionally soft. In New Zealand such sediments would usually be very young (formed less than 2 million years ago). Bigger fossils require more equipment – for large vertebrate fossils (dinosaurs and whales), power tools and heavy machinery are often needed.
Location and scientific discovery
In 1946 geologist Harold Wellman established the Fossil Record File – a New Zealand-wide register of fossil localities recorded by members of the geological community. The only national database of fossil localities in the world, it is now administered by the Geological Society of New Zealand.
Serious collectors carry notebooks to record new localities, preferably using a Global Positioning System (GPS) instrument. Very precise details are also required of the actual rock layer that holds the fossils. Each fossil is unique. Once collected, fossils are carefully wrapped in newspaper and placed in labelled bags. A small, sturdy backpack is used to carry fossils back to the car.
GNS Science, at Avalon in the Hutt Valley, holds the national paleontology collection, the country’s largest. Other major collections are held at universities, museums, and by private collectors. Otago Museum has the largest public exhibit of New Zealand fossils, and the University of Otago’s geology department museum the second largest.
Where to collect fossils
The best places to look for fossils are along shore platforms and coastal cliffs where there are outcrops of sedimentary rock. Most shorelines are publicly accessible and are open to collecting. Exceptions are beaches within National Parks, Department of Conservation reserves, land owned by Māori tribes, land designated as Geological Reserves and private land. It is essential to check the tides and watch out for waves when collecting on the coast.
Coastal and river valley exposures of fossil-bearing rock are constantly eroded by wind, sand and water. If visible fossils are not collected, then nature will slowly destroy them.
Acknowledgements to Richard Cook (GNS Science)