A marine origin of coal balls in the Midland and Illinois basins, USA Academic Article uri icon


  • AbstractCoal balls are carbonate concretions that preserve peat in cellular detail. Despite their importance to paleobotany, the salinity of coal-ball peat remains controversial. Pennsylvanian coal balls from the Midland and Illinois basins contain echinoderms and early high-magnesium calcite cement. Echinoderm skeletons reflect the Mg/Ca ratio of the seawater in which they grew. Here we show that well-preserved echinoderms in coal balls and North American Pennsylvanian marine facies have similar average mole % MgCO3; 10.212.3 and 9.912.5 respectively. Coal-ball echinoderms reflect the magnesium content of the adjacent epicontinental seawater. Early high-magnesium calcite cement in coal balls has the same, or more magnesium than echinoderms from the same deposit, and high Sr/Ca and Na/Ca, consistent with formation in marine or brackish water. Subsequent coal-ball cement is low-magnesium calcite, suggesting freshwater diagenesis and cementation followed formation of marine high-magnesium calcite. Coal balls likely formed in the marine-freshwater mixing zone.

published proceedings


altmetric score

  • 0.75

author list (cited authors)

  • Chrpa, M. E., Raymond, A., Lamb, W. M., & Laya, J.

citation count

  • 0

complete list of authors

  • Chrpa, Michelle E||Raymond, Anne||Lamb, William M||Laya, Juan-Carlos

publication date

  • 2023