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Creating Hydrocarbons

Fossil leaves. Image from Julian Thomson.

Fossil leaves. Image from Julian Thomson.

New Zealand’s fossil resources (oil, gas and coal) are mainly derived from land plants that would have grown as dense forests, in a favorable climatic setting, when much of Zealandia was just above sea level 30–70 million years ago (Palaeogene and Late Cretaceous). As the plants died in these forests, some would be buried over millions of years to form thick layers of undecayed woody gelatinous (‘jelly like’) material. These were progressively buried by more sediment to depths of several kilometres where they were ‘pressure cooked’ at temperatures of more than 130°C.