Geoscientist Online

Geoscientist 17.4 April 2007

The first "Local Heroes" event celebrates Bill Ramsbottom, whose ideas anticipated sequence stratigraphy, writes Joe Cann (right)

The first of what promises to be 25 to 30 "Local Heroes" events took place in Leeds on 20 January. The Local Hero in question was Bill Ramsbottom, a pioneer in the use of global changes in sea level for stratigraphic correlation. This technique has now become very important in oil exploration around the world.

Bill Ramsbottom (1926-2004) was an officer of the British Geological Survey, working in the Leeds office, and expert on the palaeonotology and stratigraphy of the Carboniferous. He combined the attention to detail that every successful palaeontologist needs with a breadth of vision that allowed him to recognise stratigraphic relationships on a global scale. He saw that correlating the complex lithologies of the British Carboniferous could be simplified by using “mesothems”, units of strata defined by changing sea level, and set out the ideas behind this in a series of papers in the 1970s and 80s.

At the same time, seismic stratigraphy, defined from interpretations of the stratigraphic record seen on seismic traces in terms of changing sea level, was being developed by Vail and colleagues in the USA. This evolved through the 1980s into sequence stratigraphy, in which a geological dimension was given to seismic stratigraphy, and the link to changing sea level made more explicit. Ramsbottom’s work prefigured these ideas, which were mainly developed using Mesozoic and Cenozoic examples. Sequence stratigraphy is now widely used in the interpretation of sedimentary units, and is fundamental to much present-day hydrocarbon exploration. A tool for basic correlation of sedimentary rocks has turned into a technique of enormous economic importance.

Caption: Bill Ramsbottom examining the Goniatite Bed at the top of the Caswell Bay Oolite and the junction with the overlying Caswell Bay Mudstone, both of Chadian age, in Three Cliffs Bay, Gower, South Wales: 6 August 1971. The slide was taken during a 
visit to South Wales by the Geological Society's "Dinantian Working 
Group".
 It was immediately after this visit that Bill recognised that variations of water depth in the Carboniferous Limestones of Gower (first noted by E E L Dixon in 1912) could be used to define a sequence of major cycles to subdivide and, with their contained faunas, correlate the Dinantian rocks of Britain.

The meeting in Leeds was organised at the University of Leeds by the Yorkshire Geological Society and the Leeds Geological Association, with support from the Geological Society of London, and was attended by over 100 people, ranging from ex-colleagues of Ramsbottom from the British Geological Survey to amateur geologists and members of the general public.

There were four speakers at the Leeds meeting. The first was Bilal Haq, (National Science Foundation, Washington DC) one of the pioneers in the development of sequence stratigraphy. He gave an eloquent tribute to Ramsbottom, showing how Ramsbottom’s work had anticipated almost all of the fundamental ideas of sequence stratigraphy. He then went on the discuss the problems still facing the determination of past sea levels, concentrating on the Palaeozoic, and highlighting the difficulties of back stripping the sedimentary record to yield the environment at the time of deposition. The hardest problem turns out to be estimating the water depth at which sediment had been formed.

Mike Simmons and colleagues (Neftex) presented the results of their detailed analysis of sequences around the world, with the identification of 114 first, second and third order maximum flooding surfaces and associated sequence boundaries. His group is convinced that the major control on sea level is by freezing and melting of continental ice sheets, even in the periods in the Mesozoic which have traditionally been thought to be ice-free.

Tony Hallam, (University of Birmingham) took a sceptical point of view, looking back into the history of geology at the recognition of sea level change in the geological record, and at the geological evidence for sequences based in fluctuating sea level. He emphasised the need to look very carefully at the sources of data to exclude biases introduced by regional tectonics. His examination of the Jurassic sedimentary record suggested that some claims for falling sea level might be mistaken, indicating how difficult it can be to determine past sea levels precisely from the sedimentary record.

The last speaker was Paul Wignall (University of Leeds) examining the evidence for correlation between global sea level changes and mass extinction events. While the basic idea is attractive, his detailed analysis of five mass extinction events turned up only one - the end-Triassic event - in which the extinction event could clearly be correlated with a major global low-stand in sea level. While he remained optimistic about a possible link in other cases, his analysis of the available data was sceptical.

The meeting was a fine example of the essential idea behind Local Heroes. An honorary Yorkshireman, though Lancashire-born, Ramsbottom was celebrated in the city where he had worked for many years for his fundamental contribution to geology at the global scale through his visionary work on the Carboniferous of northern England.