Observations from mines and boreholes through the Galatia channel and related features, as well as similar channels associated with older and younger coal beds, indicate that the old model of a Mississippi-style delta having natural levees and crevasse splays is due for revision. Combined with a better understanding and climate influences not available to earlier workers, these observations lead to a new model of channel development that has connotations for larger concepts of cyclic sedimentation.
Model of Channel Development
Linkage of Climate and Eustasy
Peat Developed at Lowstand
Rapid Transgression, Gradual Regression
Relationship of Effingham and Galatia Channels
The Effingham channel clearly was cut, filled, and abandoned prior to development of the Galatia channel. In fact, the Galatia channel crosses the Effingham at a right angle. Thus, the two channels represent separate cycles of sedimentation. Previously, all strata between the Houchin Creek and Springfield Coals were assumed to belong to a single cycle (Summum cyclothem), reflecting a single episode of marine transgression and regression.
In the Midcontinent Basin, the correlative interval contains two cyclothems. The minor Upper Blackjack Creek cycle (Figure 61) falls between the major Lower Fort Scott (Excello Shale) and Upper Fort Scott (Little Osage Shale, correlative with Turner Mine Shale) cycles (Heckel 1994, 2002, 2013). As Heckel (2002, p. 110) stated, “The upper part of the Blackjack Creek Limestone extends as a bed into the upper part of the Morgan School Shale in Iowa, where it contains moderately abundant conodonts [and] thus apparently represents a minor transgression.” Heckel further noted that “the Lower Fort Scott cyclothem loses both its lower and upper bounding paleosols a short distance south of the Kansas border in northern Oklahoma [see Figure 11 on p. 20 in Heckel 2013]. This supports the idea that the lower part of the Midcontinent shelf in southern Kansas and northern Oklahoma was at a lower Pennsylvanian elevation that the entire Illinois Basin” (P.H. Heckel, written communication to W.J. Nelson, June 6, 2014).
We propose the following scenario: During late highstand and early regression of the major Lower Fort Scott cycle, deltaic sediments of the Delafield Member essentially filled the Illinois Basin. As the sea level continued to fall, the Effingham channel became incised and established a meander belt. Then came the minor Upper Blackjack Creek transgression, drowning the Effingham channel and backfilling it with sediment. When sea level again declined, a new fluvial system—the Galatia channel—became established on the exposed shelf. No limestone or marine fossiliferous shale marks the Upper Blackjack Creek event in this basin because the sea-level rise was relatively brief and low in amplitude. Tidal rhythmites in the upper Effingham channel fill in the Elysium core and local, thin coal in other boreholes points to estuarine conditions, not fully marine.
As an alternate hypothesis, an autocyclic process or tectonic movement in the basin might have led to the abandonment of one channel (Effingham) and the establishment of another (Galatia) during a single eustatic cycle. Earth movements might have changed the regional gradient from southeast to southwest, inducing a change in channel orientation. This idea is not far fetched because both the Springfield and Herrin Coals thin across the La Salle Anticlinorium and other basin structures, indicating syndepositional tectonism. The channel-forming process clearly was complex and required a substantial amount of time.
W. John Nelson, Scott D. Elrick, William A. DiMichele, and Philip R. Ames xxxx, Evolution of a Peat-Contemporaneous Channel: The Galatia Channel, Middle Pennsylvanian, of the Illinois Basin FINISH CITATION