| Popis: |
This paper demonstrates a process-based method of graphic logging and stratigraphic interpretation that is based on a new, texturally based classification of clastic sediment which is independent from composition, cementation, and geologic environment. The method integrates facies analysis with sequence stratigraphy because it requires identifying surfaces, compiling vertical changes in texture and attributes between surfaces, and uses these parameters to identify facies units and interpret continuously deposited intervals. Four clastic shelf to shoreface successions from the Atlantic Coastal Plain Province (Cretaceous to Holocene in age) with established chronostratigraphic and sequence stratigraphic frameworks provide examples of the application of this method. For each, graphic logs standardized for texture show the facies and bounding surfaces that define the thickness and hierarchy of event strata (e.g., sequences, beds, bedsets, parasequences, parasequence sets); these are directly compared with gamma-ray log response patterns and the distribution of factors that impact potential permeability. Shelf to shoreface successions were chosen because these facies exhibit the greatest diversity in composition (siliciclastic, carbonate, and glauco-phosphatics), but, in spite of this, exhibit comparable and predictable graphic and gamma-ray response patterns if systematically logged using this method. For the process–response model examined, texture, i.e., principal grain size, controls the amplitude (width) of the graphic log; its shape is constant, and independent from composition. The pattern in the correlated gamma-ray log parallels the log of principal grain size, except that an inverse response is associated with coarser lags; the amplitude of the gamma log is controlled by composition. A proxy for permeability developed from standardized textural fields is applied to two of the examples, to shows how aquifer or reservoir potential is systematically tied to stratigraphic and sedimentologic parameters. |
