Recent studies in the coal measures of the Carboniferous, Cretaceous, and Tertiary have shown that one of the most critical determinants of seam parameters is the depositional environment of the coal and enclosing strata. Although some of the differences between the Cretaceous-Tertiary and Carboniferous coals can be explained by their different ages and depth of burial (Btu, moisture content), many of the coal parameters (thickness and continuity, sulfur and trace-element content, ash content, roof and floor conditions) can be attributed to their depositional setting and the effect of energy conditions in the depositional basin on the environments of peat accumulation.

Because of the wave energy in the western Cretaceous seaway, many of the deltas have sandstones that were reworked into interchannel areas from contemporaneous distributary mouth bars. These delta-front sheet sandstones formed platforms upon which widespread coals developed. In contrast, the most laterally continuous Carboniferous coals of the Appalachians accumulated in the upper reaches of the lower delta plain. Because of the low wave energies at the delta front, the only sites for coals to amass were on the levee and splay deposits adjacent to distributary channels which were separated by large interdistributary bay sequences.

Previous studies have related the sulfur content of coals to the occurrence of marine and brackish roof rock. Western coals are considered to be lower in sulfur than eastern coals. Since a significant part of the western reserves are in fluvially related Tertiary coals while most of the low-sulfur fluvial coals of the Appalachian Carboniferous have already been mined, this statement is true in generalities. However, the Cretaceous-Tertiary coals of the west that developed in marginal marine environments are as high in sulfur as the Appalachian Carboniferous coals that accumulated in similar environments.

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