Petroleum Geology and Play Assessment, Bornholm Area, Denmark

Niels Balsley Joergensen

The Bornholm area is in the easternmost part of the Danish license area of northwest Europe, where it is part of the mobile border zone between the stable Fennoscandian shield and the subsiding Danish-Polish trough.

The Bornholm area is dominated by a complicated pattern of grabens and uplift horst blocks, of which the island of Borhnolm is one. The horst blocks are parallel with the general northwest-southeast trend of the border zone, but major grabens arc perpendicular to this trend. The most prominent one is the Ronne graben, in which up to 2 km of Paleozoic and Mesozoic sediment are present.

Cambrian-Silurian rocks are present over most of the Bornholm area, whereas substantial thicknesses of Mesozoic sediments are more or less restricted to the southwestern part. Devonian-Early Triassic rocks are not seen in outcrop but may be present in the deeper grabens. During the Late Cretaceous-early Tertiary Laramide orogeny, part of the area was uplifted as much as 1-2 km.

Source rocks are probably lower Paleozoic, high-TOC, shelf mudstones, and possibly Upper Carboniferous coal measures, and Jurassic coal measures.

Due to its proximity to the Fennoscandian shield, clastic sediment has been supplied to the Bornholm area throughout geologic history. A wide range of structural traps resulted from normal extension, strikeslip faulting, and inversion.

Although the Bornholm area is virtually unexplored for hydrocarbons, the presence of surrounding, structurally related oil and gas provinces makes the area a logical target for exploration today.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.