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Geologic studies have shown that many parameters of coal beds (thickness, continuity, roof and floor rock, sulfur and trace-element content, and ash) can be attributed to the depositional environment in which the peat beds formed and to the tectonic setting at the time of deposition. With an understanding of the depositional setting of the coal seam and contemporaneous tectonic influences, the characteristics and variability of many of these parameters can be predicted.
On a regional scale, depositional models can be used to predict the trends of coal bodies. At the lease-tract level, coal thickness variations are closely related to the preexisting depositional topography. In addition, the
shape of the coal body is modified by coexisting and postdepositional environments such as channels.
Iron disulfides are present in coals either as marcasite or pyrite and are the major cause of sulfur variation within the seam. High sulfur contents in the form of disseminated framboidal pyrite are present in coals that were transgressed by marine to brackish-water environments. The only exception is where a sufficient thickness of sediment is introduced early enough to shield the peat from marine to brackish waters. Thus, the environments of deposition that overlie the coal are more important to the distribution of the type and amount of sulfur in the coal than the environments of deposition of the sediment on which the coal developed.
Roof quality in underground mines is dependent on the interrelations of rock types, syndepositional structures, early postdepositional compactional traits, and later tectonic features. Most of the features of roof conditions can be related to depositional or early-stage compactional processes of the environments overlying the coal. Later tectonic events may accentuate these early traits, but the basic characteristics seem to have been established during or shortly after the sediments were deposited.
Superposed on changes in seam character attributed to variations in environments of depositions are contemporaneous tectonic influences. Rapid subsidence during sedimentation generally results in rapid variation in coal seams but favors lower sulfur and trace-element content, whereas slower subsidence favors greater lateral continuity by higher content of chemically precipitated material.
Knowledge of depositional environments and of their tectonic setting is a valid and viable tool in the search for and development of coal resources.
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