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The Sameness of Rocks, the Uniqueness of Earth History

Since the publication of Lyell’s Principles of Geology, there has been a clear realisation that although uniformitarianism based on consistency of physical laws is a valid and useful approach to earth science, there are also “directional” trends, cycles of change or “events” in the earth’s history which make the geological record far from simply a monotonous repetition of the consequences of those actual causes we can infer from direct observation.

The hydrocarbon industry has in general been at the Lyellian, uniformitarianist, end of the spectrum when it comes to sub-surface interpretation. The success of facies sedimentology as a basis for clastic reservoir modeling is a good example. Irrespective of geological age, reservoir modelers feel confident that they can make sensible subsurface models of the complete range of depositional environments.

Carbonate geologists are more circumspect, being well aware that dealing with the consequences of organic evolution and changing sea water chemistry that they need to modify conclusions based on actualistic examples to apply them to the rock record. In general however temporal effects are treated at best as second order.

Recently there has been a major increase in studies of earth systems. For example of climatic and oceanic circulation changes in response to plate tectonics and mountain building, eustatic sea level change as a result of multiple causes, physical and chemical effects of the biosphere through organic evolution, extra-terrestrial events, and the consequent feedback loops between all of the above as reflected in changes atmospheric and oceanic chemistry. These studies reveal a picture whereby the convolution of the time-series of “signals” (for example record of sea level, atmospheric C02, atmospheric pressure, average global temperature, pole-to equator temperature gradients) results in a picture whereby each geological interval, at the resolution of a stage or lower, can usefully be considered distinct. Does all this “distinctiveness” really have little impact on our understanding of hydrocarbon accumulations? Or does it deserve more attention from industry professionals?

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Bruce Levell (Shell)


Bruce is a Geologist who has spent his working life in Petroleum Exploration. He graduated from Oxford University with a BA and PhD in Geology in 1978, specializing in sedimentology.

Bruce has worked for Shell Exploration and Production for 30 years. He began in Research with assignments in seismic and sequence stratigraphy, stratigraphic and basin modeling and regional geology. Operational assignments followed as an exploration geologist in Sabah, and Sarawak, Malaysia; Manager of Geology for the Mid Continent Division of the USA (principally Texas, Oklahoma, Michigan); Head of Geological Services for the North Sea; Team leader responsible for UK/Irish Atlantic Margin exploration, and Exploration Manager in Oman.

From 2003 to 2008 Bruce was Vice President responsible for New Ventures in Shell’s Global Exploration unit. In September of 2008 he was appointed Chief Scientist: Geology for Shell, based in The Netherlands.