Depositional Framework of the Baker Coal in the Illinois Basin
John W. Nelson1, Scott Elrick1, and Phil Ames2
1Illinois State Geological Survey, Champaign, IL, [email protected]
2Peabody Energy, St. Louis, MO
The Baker Coal is confined to the southeastern Illinois Basin, where it locally exceeds 3 m thick and is relatively low sulfur. The Baker Coal has been called Allenby Coal in Illinois and Lower Millersburg in Indiana; the name Baker has priority. In Indiana the Baker was incorrectly identified Hymera Coal. Thick Baker Coal is concentrated along both margins of a contemporaneous channel (called Winslow in Indiana and Henderson in Kentucky). The coal is commonly split with layers of claystone and carbonaceous shale close to the channel and tends to thicken into pre-existing channels beneath the coal.
Unlike the Murphysboro, Springfield, and Herrin Coals, the Baker Coal lacks a thick estuarine gray shale roof close to its contemporaneous channel. Instead, the Baker is overlain everywhere by non-marine strata, largely flood plain but also fresh-water lake deposits.
We propose that a prolonged low stand of sea level set the stage for Baker Coal deposition. The basin was exposed, soils formed, and fluvial channels eroded into underlying strata. As base level rose, thick peat developed in low-lying areas, particularly along the edges of the Winslow- Henderson channel. During a shift toward more seasonal climate, sea level rose, but remained low relative to the Illinois Basin such that non-marine sediments covered Baker peat. Not until the end of the next higher coal deposit was there complete de-glaciation and sea-level rise, giving marine units above the Danville coal.
AAPG Search and Discovery Article #90095©2009 AAPG Eastern Section Meeting, Evansville, Indiana, September 20-22, 2009