Disrupted coal and carbonate facies within two Pennsylvanian cyclothems, southern Illinois basin, United States

Carol B. De Wet, Stephen O. Moshier, James C. Hower, Andrew P. De Wet, Sean T. Brennan, Charles T. Helfrich, Anne L. Raymond

Research output: Contribution to journalArticlepeer-review

25 Scopus citations


Two cyclothems contain an unusual suite of disrupted fabrics. This study's interdisciplinary integration of coal macerai and sedimentological information offers significant new interpretations of coal-limestone interchange, both depositionally and diagenetically. Disrupted fabrics within the Herrin Coal and Providence Limestone are interpreted as representing previously undocumented interactive processes between coals and limestones. The Herrin Coal contains brecciated beds that are the result of marine transgression over a coastal-plain mire, representing high-energy conditions at the swamp-beach interface. This interface has rarely been documented in detail. Peat is inherently unstable prior to its conversion to coal, and we document this by interpreting conglomeratic beds in overlying strata. Differential compaction of Herrin peats generated subaqueous debris flows in the overlying Providence Limestone. This mechanism for syndiagenetic and early diagenetic sediment deformation has not been previously recognized. In addition, near-surface and surface processes produced other disrupted fabrics in the Providence Limestone, such as in situ mosaic breccias, nodular fabrics, and calcrete horizons. This study also documents that stratigraphically adjacent, alkaline carbonate sediments were further altered by undersaturated acidic pore waters, derived from compacting peats during early diagenesis. Our interdisciplinary approach to distinguishing and interpreting all of these disrupted fabrics led to a new appraisal of the importance of depositional and postdepositional interactions between coal and limestone. The presence of mire deposits can have a significant influence on the thickness, distribution, and fabrics in overlying strata. In cyclothems, climatic and eustatic changes may control overall depositional patterns, but peat compaction may determine certain facies.

Original languageEnglish
Pages (from-to)1231-1248
Number of pages18
JournalBulletin of the Geological Society of America
Issue number10
StatePublished - Oct 1997

ASJC Scopus subject areas

  • Geology


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