During which geologic periods were many source rocks for major natural gas deposits formed?

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natural gas The Troll A natural gas production platform in the North Sea, 80 km (50 miles) northwest of Bergen, Norway. Troll A, the largest movable structure ever built, rests on the seafloor some 300 metres (990 feet) below the surface and rises more than 100 metres (330 feet) above the sea. The platform regulates the recovery of gas from 40 wells located on the seafloor.

Many source rocks for significant natural gas deposits are associated with the worldwide occurrence of coal that formed during the Carboniferous Period and the Early Permian Period, a timeframe spanning roughly 358.9 million to 273 million years ago.1

Because natural gas is derived from both land plants and aquatic organic matter, it is more ubiquitous than oil and can be generated from all source rocks. While many major gas fields are located at intermediate or deeper levels where older reservoirs exist, gas generation can occur above, throughout, and below the oil window through both biogenic and thermal processes.12