Surprises on ROV Expedition in the Norwegian Sea

"We knew there was basalt in the Norwegian Sea – but we were still surprised when we found 100-metre thick columnar basalt underneath the extrusive basalt which covers large areas in the western Norwegian Sea," says an excited Robert W. Williams, paleontologist in the Norwegian Petroleum Directorate.

 The ROV expedition (ROV = remotely operated vehicle) was carried out in the final week of August last year. Williams was the NPD's representative on the Seabed Worker vessel. Professor Rolf Birger Pedersen from the University of Bergen was in charge of the expedition and Nils Rune Sandstå was the project manager.

"We took samples from the southern extension on the Gjallar Ridge, at depths from 2200 to 2900 metres, and from Vøringsutstikkeren, at depths from 2800 to 3550 metres," says Robert W. Williams.

Photo: Columnar Basalt

They found the columnar basalt in the south-western part of the Gjallar Ridge in the western Norwegian Sea, and it is similar to what can be found at the tourist attractions Giant's Causeway in Northern Ireland and Devil's Tower in the US. Early in the formation of the North Atlantic, lava penetrated the surrounding sedimentary mudstone and then cooled, forming columnar basalt. "The sedimentary rocks were not impacted significantly by the heat from the volcanic incident," says Williams.

Both the Gjallar Ridge and Vøringsutstikkeren are connected to the Jan Mayen fracture zone. The exposed ridge sequence that was examined is remarkable, since this is the conjugated margin (conjugated = binding two things together) after the separation from what was then the northern part of Jan Mayen on eastern Greenland in the Paleocene/Eocene.

"The examined areas are characterized by steep terrain and deep water. They are relatively unexplored, and this is the first time this area has been filmed. There is less benthic life there than what we saw on the seabed along the Jan Mayen ridge," says Williams.
The deepest sample that could be dated (water depth of 2900 metres) is Campanian (Upper Cretaceous) from the southern part of the Gjallar Ridge. The material which has been dated is mudstone from an open marine environment. All the material collected near the Gjallar Ridge is located 'sub-basally', i.e. beneath the extrusive basalt that was formed when lava flowed onto the seabed 56 million years ago, in the transition from Paleocene to Eocene.

The samples were taken with an ROV fitted with a chain saw. The chain saw is actually intended for the concrete industry, but works excellently in deep waters. This tool was also used to collect material from the seabed off Jan Mayen in 2012. A powerful grab was used in some locations to collect rocks.

"Overall, we collected material from 39 unique sub-basalt levels in seven dives on the southern Gjallar Ridge, and 26 samples in three dives near Vøringsutstikkeren," says Nils Rune Sandstå.

The sedimentary material is being analyzed for fossil microplankton by Robert W. Williams at the Norwegian Petroleum Directorate. Geochemical samples, test analyses and dating of columnar basalt will be handled by the University of Bergen. The results are expected to be ready this spring, and will then be published.