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by the fact that it is unusually radioactive, and also hot. Hbritier et al. (1981,
p. 381) reported that the Frigg discovery well penetrated 77 m of oil shale of
Kimmeridgian age that registered 250 API units of gamma radiation at. about
4200 m (but they do not regard it as the source rock for the Frigg petroleum
because the vitrinite reflectance is only 1%).
From these examples, it is clear that attention must be paid to the geo-
physical properties of the fine-grained rocks that might be petroleum source
rocks. Source rocks generating petroleum may also generate local abnormality
of pressure, resistivity, sonic velocity, and their temperatures may well pro-
vide more direct evidence of the requirements for oil and gas generation.

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