Abstract

Gamma-gamma logs were used to study the density of sedimentary rocks and formations in the Western Canada basin. The frequency distributions of density of all the main rock types have negative skewness, a characteristic that seems to be a general feature of density distributions of rocks based on well logging. The frequency distributions of density for sandstone and limestone were not found to be different from those of shale and dolomite, respectively, at the 0.01 level of significance.Several density-depth functions were applied to the shale samples. Athy's (1930) exponential function provided the best fit to observed values. Using this function, the average thickness of sediments removed by denudation in south and central Alberta was calculated to be 4400 or 3600 ft on the assumption that the density of the original surface clay was 1.4 or 1.6 g/cm 3 , respectively.Maps of average density for six formations in Alberta and Saskatchewan indicate only a partial correlation with lithology and depth. A large scattering of density with depth was found in the case of four Cretaceous formations in which density was observed to be independent of the sandstone/shale ratio. In the case of one formation containing predominantly shale, no obvious dependence on depth was found. Also, no relationship between density and the occurrence of oil and gas fields was apparent.

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