Since the late 1960s, geologists working in the Illinois Basin have recognized that deposits of thick coal having a relatively low sulfur content (less than 2%) are associated with thick, nonmarine gray mudstone and siltstone overlying the coal. Moreover, these thick, gray sediments are associated with paleochannels that existed during peat formation. Channels contemporaneous with the Herrin and Springfield Coals, the two most important economic seams in the basin, have been identified and mapped in detail. Similar relationships involving the Murphysboro, Colchester, Baker, and Danville Coals also have been documented (Treworgy and Jacobson 1979).
Previous authors have explained these relationships by using a model based on the modern Mississippi delta. They envisioned a channel that periodically broke through its natural levees and discharged sediment-laden water into flanking peat swamps. Resulting “crevasse splays” created clastic “splits” within the peat along the channel margins. However, no natural levees have been found along the paleochannels, significant evidence exists for tidal sedimentation, and further research has shown that the Mississippi delta is probably not a good analogue for Pennsylvanian coal deposits. Hence, the model is in need of revision.
This study describes and explains the Galatia channel, one of the best-known examples of a paleochannel contemporaneous with peat accumulation. Such paleochannels yield key insights into the ways eustasy and climate influence sedimentation, and they add complexity to generalized models of cyclic sedimentation. A new model is presented here, which takes in the complete history of development of the Galatia channel and the landscapes of which it was a part. This model is then applied to other paleochannels in the Illinois Basin, and likely can be applied in other basins.
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.
- Treworgy, C.G., and R.J. Jacobson, 1979, Paleoenvironments and distribution of low-sulfur coal in Illinois, in A.T. Cross, ed., Economic geology: Coal, oil and gas: Ninth International Congress on Carboniferous