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I was involved in Illinois Basin coals primarily and found many of the seams had similar features. Almost all had been subject to ground shifting forces that caused seams to "roll" as much as several feet. I don't know if this is evidence of tectonics but its possible. Coals in Missouri, Iowa and central Illinois and Indiana exhibited "bands" of sulfur, steaks of fools gold, at various levels. Southern Illinois pyrites were often flat dollar coin sized deposits, without the bands. These coals also had a rather oily appearance. In one Illinois county there was an exception to this, known as the "Quality Circle." BTUs and ash fusion temperature (when burned) were higher and sulfur was much lower.
In the Powder River Basin of Wyoming, the source of 60 percent of American production, pyrite sulfur is almost unknown and inherent sulfur is quite low, less than 1/2 percent in some cases. PRB coals are "younger" beds, and are referred to as "sub-Bituminous coal. BTUs run about 8250 to 8400/lb. Midwest coals are 10,500 to 13,000 BTUs/lb.