Galatia Channel:Murphysboro Coal and Oraville Channel

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The Murphysboro Coal, in the upper Tradewater Formation, presents some similarities to the Colchester, Springfield, Herrin, and Danville Coals in that thick, low-sulfur coal is associated with a gray shale “wedge” and a contemporaneous channel. However, the Murphysboro is highly lenticular and has been less thoroughly studied than the other examples, so the relationship of coal to gray shale and the channel is not completely understood.

Jacobson (1983)[1] documented that thick, low-sulfur Murphysboro Coal in southwestern Illinois flanks a feature that he named the Oraville channel (Figures 39 and 47). In fact, coal of mineable thickness (up to 8.2 ft [2.5 m]) is confined to a small area near the channel. Sulfur content is low to moderate (1% to 2.5%) near the channel where thick, nonmarine gray mudstone (unnamed) overlies the coal. Elsewhere, the coal is topped by marine black shale and limestone, and its sulfur content is greater than 3% (Jacobson 1983). Away from the Oraville channel, the Murphysboro has a highly patchy distribution (Treworgy and Bargh 1984)[2]. Only small, isolated areas of thick coal are known. Little significant mining has taken place away from the channel.

  • Figure 39 Map of the Illinois Basin showing channels and gray shale wedges affecting the Murphysboro, Colchester, Herrin, Baker, and Danville Coals.
  • Figure 47 Map showing the thickness of the Murphysboro Coal near the Oraville channel in Jackson and Perry Counties, southwestern Illinois. From Jacobson (1983)[3]

The Murphysboro undergoes dramatic splitting near the Oraville channel margins, where underclay is absent or weakly developed (Figure 48). Upright lycopsid tree stumps are common above the lower coal bench. The gray mudstone exhibits tidal rhythmites and bears a prolific, well-preserved flora dominated by Macroneuropteris scheuchzeri, a plant believed to have been tolerant of coastal, perhaps brackish-water, conditions (Falcon-Lang 2009)[4]. The Oraville channel follows the downthrown side of a monocline that was active during deposition of the Murphysboro Coal (Nelson et al. 2011)[5].

  • Figure 48 Interpretive cross section of the Oraville channel.

Ostensibly, the Oraville is another fluvial channel that became an estuary, like the Galatia and Walshville channels. However, nothing is known of the presumed fluvial “precursor” channel, and the nature of “splitting” coal is poorly understood. Further study of the Murphysboro is required to integrate this unit into a general model.

Primary Source

Nelson, W.J., S.D. Elrick, W.A. DiMichele, and P.R. Ames, 2020, Evolution of a peat-contemporaneous channel: The Galatia channel, Middle Pennsylvanian, of the Illinois Basin: Illinois State Geological Survey, Circular 605, 85 p., 6 pls.

References

  1. Jacobson, R.J., 1983, Murphysboro Coal, Jackson and Perry Counties: Resources with low to medium sulfur potential: Illinois State Geological Survey, Illinois Mineral Notes 85, 19 p.
  2. Treworgy, J.D., and M.H. Bargh, 1984, Coal resources of Illinois, Herrin (No. 6) Coal: Illinois State Geological Survey, 1 map sheet, 1:500,000.
  3. Jacobson, R.J., 1983, Murphysboro Coal, Jackson and Perry Counties: Resources with low to medium sulfur potential: Illinois State Geological Survey, Illinois Mineral Notes 85, 19 p.
  4. Falcon-Lang, H.J., 2009, A Macroneuropteris scheuchzeri tree preserved in growth position in the Middle Pennsylvanian Sydney Mines Formation, Nova Scotia, Canada: Atlantic Geology, v. 45, p. 74–80.
  5. Nelson, W.J., J.A. Devera, L.M. Williams, and J.R. Staub, 2011, Bedrock geology of Oraville Quadrangle: Illinois State Geological Survey, Illinois Geologic Quadrangle Map IGQ Oraville-BG, 2 sheets, 1:24,000.