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Geologic data from Mesaverde Group (Upper Cretaceous) strata in the Rocky Mountain region indicate that two major depositional models can be used to evaluate the geology and mining conditions of many western coal deposits. Marine and continentally deposited strata that enclose coal seams are characterized by physical and chemical characteristics which, if recognized, will permit more efficient mine planning and development. These characteristics impact selectively and differently on underground coal mining including longwall and room-and-pillar methods.
Continentally deposited strata in the roof and floor of coal seams require closely spaced data points for predicting geologically related mining conditions due to the lenticularity of the component beds. Fluvial sandstones are commonly associated with "wants," rolls, water inflows, and thinned coal. Channel-margin strata are notorious for roof control problems. Mudstones deposited in interchannel areas are prone to rapid decomposition with the introduction of water, humidity, and stress release.
Marine-deposited strata enclosing coal seams require less closely spaced data points than continentally deposited strata for predicting mining conditions because of the lateral continuity of such strata. Roof and floor strata and mining conditions are characteristically uniform over wide areas except near the termination of strata. Shoreline sandstones form very competent roofs and floors although they are locally associated with reduced seam thicknesses. The immediate association of marine-deposited strata and coal commonly results in higher sulfur values at the contacts of these strata.
Where marine and continental strata interfinger, the prediction of mining conditions becomes complex and requires an understanding of the depositional and erosive capabilities of the associated facies.
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