Short measures on land

28/03/2006 The world’s coal deposits far outstrip its petroleum resources, and are mined on every continent. Norway also has a share of this fuel – but only under the sea.

This article was first published in Norwegian Continental Shelf no. 3-2005

This article was first published in Norwegian Continental Shelf no. 3-2005

Ranked as one of the leading energy sources after oil and gas, coal can be found in larger or smaller quantities in every sedimentary rock with the remains of land plants. But such vegetation is a fairly recent phenomenon. Land plants had not developed enough to form coal in interesting quantities until the Carboniferous period 300-330 million years ago. Almost all the sedimentary rocks in mainland Norway pre-date the Carboniferous, so no coal measures occur there.

But the country has had its own short-lived “coal fever”. This occurred after coal fragments were discovered in glacier-deposited moraine clays on the Jæren plains south of Stavanger in the 1870s. Drilling to locate these deposits was led by Tellef Dahl, head of the Norwegian Geological Survey at the time, who submitted daily reports to the Stavangeren newspaper. When the bit finally penetrated to the basement rock, hopes of finding coal measures in the solid sediments evaporated. The fever abated, and the investors lost their stake.

Fossil plants in the coal found on Jæren and the island of Karmøy further north date from the early Jurassic, 170-200 million years ago. At that time, northern Europe and the whole of its continental shelf were a continuous low-lying plain, with only a few modest hills rising above it. Huge rivers ran sluggishly through this landscape, the climate was warm and moist, and a rich vegetation became the source of coal measures from buried peat, leaves and tree trunks.

The process of converting these deposits to coal is similar to making charcoal, apart from the low temperature involved – in the order of 100°C – and a timescale of several million years. On a world scale, coal resources far outstrip petroleum assets and a new Norwegian coal fever at some time in the future is not inconceivable. That is because Jurassic coal measures lie under the Norwegian continental shelf, from near the coast to beyond the oil and gas fields. But no deposits of any significance from other periods have been proven.

In earlier ages, the local climate was dry and provided poor growth conditions for the necessary land plants. The whole area was flooded by the sea at the end of the Jurassic. Since then, the continental shelf has been largely under water – again eliminating the vegetation needed to form coal. In fact, the Barents Sea region was covered by the sea even before the Jurassic.

Coal deposits from the late Triassic and Jurassic can be found on the whole NCS, from the North Sea in the south to the Barents Sea in the north. On land, however, resources are confined to bits and pieces from these periods along the whole coast. Younger strata on the continental shelf contain insignificant amounts of coal because they were deposited in water and have not contained land plants.

The Trondheim and Beitstad Fjords in mid Norway were once filled with Jurassic sediments, but these eroded away during the ice ages and are now found only on the bed of the Beitstad Fjord. Jurassic strata are exposed on the island of Andøya in northern Norway, but coal measures there can only be found by mining or drilling.

 

Updated: 14/12/2009