Fig. 1: Coal ball sample locations and stratigraphic context.
From: A marine origin of coal balls in the Midland and Illinois basins, USA
a Late Pennsylvanian (310 Ma) paleogeographic reconstruction of Scotese (ref. 34) showing Pennsylvanian basins with coal balls (white circles). Supplementary Data documents the presence of marine sediments overlying coals with coal balls, or the presence of marine invertebrates in coal balls in all coalball basins except the Stellarton Basin of Maritime Canada (white asterisk). Partial country boundaries and US state boundaries in black. b Late Pennsylvanian (310 Ma) paleogeographic map of North America (ref. 34) showing the location of marine facies as white triangles (ref. 15) and coal balls with echinoderm stereom as black triangles in white circles. Localities: 1— Pittsburg, KS; 2—Dalton coal, Palo Pinto Co., TX; 3—Calhoun Coal, Berryville, IL; 4—Holder Fm., Dry Canyon, NM; 5—Palo Pinto Co., TX.; 6—Pontotoc Co., OK. Partial US state boundaries in black. c Pennsylvanian stratigraphic column with coal-ball (black triangles in white circles) and marine facies (white triangles) localities.
