Taking stock of a microcontinent

17.01.2013
Researchers acquired geological samples from the Jan Mayen Ridge in the North Atlantic this summer using a remotely operated vehicle (ROV) with an installed saw. The method is new – and the results make a useful contribution to existing knowledge.
  • Bente Bergøy Miljeteig and Robert W Williams (photos)

Chain saw

Chain saw.
A remotely operated vehicle (ROV) at work in the depths with a hydraulic
chain saw attached. The mechanics adjusted the saw a little and replaced
some hoses before installing it on the unit. On the right, the ROV is
ready for its first excursion.

 

“This is the most fun thing I‘ve done as a geologist,” says Robert W Williams at the NPD, who took part in the voyage on the G O Sars research vessel.

A collaboration between the directorate and the University of Bergen’s centre for geobiology, this expedition was led by professor Rolf-Birger Pedersen from the latter facility.

It left Akureyri in northern Iceland on 4 August. Over two weeks, geological material was acquired from five locations in the steep underwater cliffs of the ridge. These covered both the Norwegian and the Icelandic sides.

Williams says that the expedition will provide considerable new knowledge about the geology off Jan Mayen, but that it is too early to say whether oil or gas could be there.

He adds that the findings match existing seismic data from the area perfectly – but that the surveys have also entailed some surprises.

“I hadn’t expected there to be so much sandstone there, for example. Over basalt (volcanic) layers roughly 250 metres deep, we measured sandstone layers more than 250 metres thick.”

The Jan Mayen Ridge was formed in the Oligocene epoch roughly 30 million years ago, and Williams describes the geology there as a mirror image of Greenland.

Jan Mayen island itself lies to the north of Iceland, between Norway and Greenland – which used to be much closer together than Norway and the UK are today.

The Norwegian and Greenland Seas were formed during two major rifting episodes, with the Norwegian Sea initially separating Greenland and Jan Mayen from Norway.

Then Jan Mayen was split off from Greenland, forming a separate microcontinent, when the Greenland Sea opened.

Water depths in the surveyed area vary from 600 to 2 000 metres. Little is known about the geology, with existing data derived from scattered seismic surveys conducted in the 1980s and shallow boreholes from 1974.

The NPD shot two-dimensional seismic lines off Jan Mayen this summer, but the data have yet to be interpreted.

 

Innovative

This year’s expedition took some innovative steps to improve the tooling of the ROV in order to obtain samples directly from the solid bedrock.

Samples were also collected with an ROV on Ridge last year. Since that vehicle only carried a grab, however, it gathered almost entirely loose material. This made it difficult to determine the age of the rock.

“We couldn’t know for certain if the samples really originated locally or whether they were foreign rocks brought with icebergs from Greenland,” Williams explains.

Icebergs can carry rocks, sand and gravel with them from the land where they originated. This material is sometimes released on the seabed far from its origin, and can be found scattered across the North Atlantic.

”Pedersen went to a building supplies store and bought a large hydraulic chainsaw, which is actually intended for foundation work,” says Williams. “The mechanics replaced some hoses, made a few adjustments and installed it on the ROV.”

This solution worked as the researchers had hoped, and a total of nearly 40 samples were collected. The largest stone block retrieved weighed 40-50 kilograms.

“We’ve learnt a lot, and understand the geology much better now than last year,” Williams concludes.

The basalt samples will now be analysed at the University of Bergen, while the NPD is responsible for dating the sedimentary rocks.


Topics: Geology