Abstract

Bitumen deposits are known to be present in sedimentary rocks of all geological ages throughout the world. The optical properties of bitumen (reflectance and fluorescence) have been used to estimate the level of thermal maturity of host rocks, particularly those of lower Paleozoic age due to absence of vitrinite. In addition, a linear relationship has been developed between bitumen and vitrinite reflectance as well as the reflectance of other organic fossils (i.e. graptolites, chitinozoa and scolecodonts).

Bitumen may occur in source rocks or reservoir rocks in concentrated or disseminated form and indicates the generation and/or migration of hydrocarbons. Among three or more bitumen populations in rocks, the one with the lowest non-migrated reflectance represents most closely the degree of thermal maturity of the sediment. However, the use of bitumen reflectance as a thermal maturity indicator is further complicated by the presence of primary (autochthonous) and migrated (allochthonous) bitumen in a succession. It has been documented that the reflectance of primary bitumen increases with increasing depth of burial while the reflectance of migrated bitumen remains unchanged under the same conditions.

Bitumen reflectance has been used successfully in studying the effect of igneous intrusions on organic matter, the regional thermal maturity of lower Paleozoic successions in the Canadian Arctic Islands, the presence of generated and/or migrated hydrocarbons and in estimating the amount of eroded section lost due to regional unconformities.