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All aboard the warming express

Eurostar passes through Scalers Hill

Channel Tunnel Rail Link exposes clues to global warming 55 million years ago, reports Adler deWind

Geoscientist Online 10 October 2007

The Paleocene/Eocene thermal maximum (PETM), a period of intense global warming about 55 million years ago, has been attributed to a rapid rise in greenhouse gas levels. Uniquely the new channel tunnel rail link, recently opened, cut through a section of rock known as the Cobham Lignite.

Traditionally the rapid rise in greenhouse gasses has been attributed to dissociation of marine methane hydrates. However, it has also been suggested that high-latitude methane emissions from terrestrial environments could have enhanced the warming effect, but direct evidence for an increased methane flux from wetlands was lacking.

In a recent issue of the journal Nature (20 September), the group reports results from the analyses of organic compounds in the Cobham Lignite, led by Rich Pancost (University of Bristol). They observed very high abundances of hopanoids - biomarkers derived from bacteria - in the mire sediment from Cobham. Critically, the carbon isotope values of these hopanoids decrease at the onset of the PETM interval, a geochemical signature suggesting an increase in bacteria that feed on methane (methanotrophs).

The outcrop of the Cobham Lignite The authors propose that this reflects an increase in methane production, possibly driven by a warmer, wetter climate. They suggest that release of methane from the terrestrial biosphere increased – acting as a positive feedback mechanism to global warming. Says Pancost: “Although we must be careful not to over interpret data from a single site, this does provide insight into how some ecosystems could respond to rapid, warming-induced changes in climate.” However, as Professor Andrew Scott (Royal Holloway) cautions: “We can not use this section as an exact model for interpreting future global warming as the initial climate was very much warmer than that of today.”

“There were other important changes in the terrestrial system seen in the Cobham sequence”, explains Scott. In a paper published earlier in the year the same researchers showed (from qualitative and quantitative coal petrological analyses undertaken on the laminated lignite at the base of the Cobham Lignite Bed) the presence of abundant charcoal derived from wildfires. They considered that charcoal-rich and charcoal-poor layers were indicative of episodic fires and post-fire erosion. Charcoal clasts were derived from living or recently dead plants, and were dominated by the leaf stalks of herbaceous ferns and wood fragments from flowering plants. This charcoal assemblage reflected a low-diversity flora, possibly one adapted to disturbance by fire, derived from a source vegetation subjected to seasonal surface wildfires. The environmental conditions leading up to and across the onset of the PETM were interpreted as incorporating a persistent fire regime with episodic wildfires followed by rainfall and runoff events. They further showed that the fire regime suddenly stops, probably as a result of increased rainfall.

“We have been surprised at the amount of information that we could obtain from such a short section of the rail cutting and were fortunate that the rocks were of an age to help us unravel some of the secrets of this period of rapid global warming”, Professor Scott added. Unfortunately this section is now entombed in concrete!

The Cobham Lignite Bed, from Scalers Hill, Kent, England was the subject of a study, supported by the Leverhulme Trust, by researchers at Royal Holloway University of London (Geology), the Natural History Museum (Palaeontology) and the University of Bristol (Chemistry) led by Professor Margaret Collinson of the Geology Department at Royal Holloway, with Dr David Steart as Post Doctoral assistant.


  • Collinson, M.E. Steart, D., Scott, A.C., Glasspool, I.J. and Hooker, J.J. 2007. Fire and episodic runoff and deposition at the Paleocene-Eocene boundary. Journal of the Geological Society, London 164, 87-97.
  • Collinson, M.E. Steart, D., Scott, A.C., Glasspool, I.J. & Hooker, J.J. 2007. Palaeobotany as revealed by petrology of two contrasting lignites on either side of the Paleocene-Eocene Thermal Maximum. Acta Palaeobotanica 47(1), 109-125
  • Pancost, R.D., Steart, D.S., Handley, L., Collinson, M.E., Hooker,J.J., Scott, A.C., Grassineau N.J. and Glasspool, I.J. 2007 Increased terrestrial methane cycling at the Paleocene-Eocene Thermal Maximum . Nature 449