Are coal balls rare? A cyclostratigraphic analysis of coalball ...
WEBApr 1, 2019 · From the perspective of Phanerozoic time, coal balls are rare, apparently limited to a 24 interval (323–299 Ma) in the Pennsylvanian and earliest within this interval, coal balls occur in many coals. Approximately 82 transgressiveregressive sedimentary cycles have been described for the Midcontinent, Illinois and .