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Upper Jurassic methane seeps from Svalbard (Spitsbergen, inner Isfjorden area)

Methane seeps represent one of the most exciting discoveries in marine science in the last 2-3 decades. Such natural gas seeps are fairly common in today's oceans, and are found also on the Norwegian continental shelf. Methane seeps are sometimes associated with mounds or columns of limestone that precipitates in the unusual environment. The may also form the basis for exotic microbial communities that use methane as their energy source. Such microbes can live symbiotically with specialized organisms such as bivalves and worms. The result can be a whole ecosystem based on methane instead of solar light as the primary source of energy. Some methane seeps are strange 'underwater oases' teeming with life. In recent years some fossil methane seeps have been found around the world. They often appear as 'lumps' of limestone, sometimes the size of houses, in black, organic-rich shales. The limestones have particular layering connected with microbial activity, and many other diagnostic structures. The carbon isotope signature is very different from that of other limestones. And finally the fossil methane seep is often extremely rich in fossils, with large numbers of bivalves and other organisms that lived at the seep site. Such finds are of great interest because they give information about how these peculiar ecosystems have evolved through geological time.

The methane seeps newly discovered during the NHM expeditions to Svalbard are exceptional. They are among the oldest typical methane seeps (late Jurassic), well preserved and very fossil rich. They display all the characteristics mentioned above. The most common fossils are numerous species of bivalves, but we also find many ammonites that by chance landed on the seep after death. Brachiopods, crinoids, snails and tube worms are rarer. So far we have found four seeps - one of considerable size - in the same strata as the spectacular marine reptile fossils. We have collected some fossils and geochemical data, but we have many unanswered questions. Is the co-occurrence of methane seeps and unusual vertebrate preservation coincidental? If not, could this be a method for finding areas of such preservation? Where did the gas come from, and how did it escape from depth (perhaps through a fault zone)? Are there methane seeps of the same age elsewhere in Svalbard? If not - what is special about this area? How can the fauna be compared with other contemporary and younger seeps, and what can this tell us about biogeography and evolution? Is the fauna very different from the one found (much less well preserved) in the surrounding shale? These methane seeps can give material for exciting research for many years to come. Together with the finds of marine reptiles they also show that great discoveries can still be made in the geology of Svalbard.

Yellowish carbonate rocks ("methane seep carbonates") in the black shale, Agardhfjellet Formation, Knorringfjellet area
Polished surface of a methane seep carbonates sample

References

  • Nakrem, H.A., Hammer, Ø. & Hurum, J.H. 2008. Late Jurassic chemosynthetic carbonate mounds of Svalbard (arctic Norway) - preliminary results. International Geological Congress (IGC), August 2008, Oslo.
  • Nakrem, H.A., Hammer, Ø. & Hurum, J.H. 2009. Upper Jurassic hydrocarbon seeps ('cold seeps') from Western Spitsbergen, Svalbard. NGF Abstracts and Proceedings of the Geological Society of Norway 1 (2009), p. 83. ISBN: 978-82-92394-48-9
  • Nakrem, H.A., Hammer, Ø., Hurum, J.H. & Little, C.T.S. 2010. A hydrocarbon seep fauna from the uppermost Jurassic of Spitsbergen, Svalbard. Programme and Abstract, 3rd International Palaeontological Congress, London, June 28 – July 3, p. 291
  • Hammer, Ø. & Nakrem, H.A 2010. Carbon isotope chemostratigraphy of the Upper Jurassic of Svalbard, Norway. NGF Abstracts and Proceedings of the Geological Society of Norway 1 (2010), p. 61-62. ISBN: 978-82-92394-56-4
  • Hammer, Ø., Nakrem, H.A., Little. C.T.S., Hryniewicz, K., Sandy, M.R., Druckenmiller, P., Knutsen, E.M., Hurum, J.H. & Høyberget, M. 2011. Hydrocarbon seeps from close to the Jurassic–Cretaceous boundary, Svalbard. Palaeogeography, Palaeoclimatology, Palaeoecology 306, 15-26.
Published Sep. 14, 2015 11:58 AM - Last modified Sep. 29, 2015 11:00 AM

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