SOURCE ROCKS IN A SEQUENCE STRATIGRAPHIC CONTEXT

Waples, D. W.
Consultant, Evergreen, Colorado, USA

        Application of sequence stratigraphy in understanding and predicting source-rock occurrence is still in an early stage. Models proposed for marine source rocks have mainly focused on the TST or the "condensed section." However, numerous other factors, including oxygen levels in bottom waters, biological productivity, water depth, and geologic age play important roles in determining whether source rocks exist, how rich they are, and what type of kerogen they will contain.

        Lacustrine source rocks can be analyzed in a similar way, although the proximal/distal issues in TST’s are replaced by questions of water depth during source-rock deposition. Once again other factors, including productivity and surrounding topography, are at least as important as the sequence-stratigraphic position.

        Coals and coaly shales, in contrast, which are important source rocks in SE Asia, do not fit into either of these models. Those facies are deposited during HST and LST. Development of coals is strongly controlled by geologic age, as land plants proliferated during the Carboniferous and angiosperms and grasses dominated during the Tertiary.