Detailed isotope stratigraphies for the Carboniferous are presented based on brachiopod shell calcite from the mid-continent region of North America. Evidence for shell calcite preservation includes (1) preservation of shell microstructure, (2) lack of cathodoluminescence, (3) low Si, Al, Fe, and Mn contents, (4) Na, Sr, and S contents comparable to those of modern brachiopod shells, and (5) d¹³C and d¹⁸O values higher than those of associated cements and matrix.

    The Carboniferous d¹³C record for North America is characterized by three isotopic stages. The earliest stage, C1, follows a 2.0‰ increase in the Kinderhookian (early Tournaisian), from 1.5‰ to 3.5‰, and includes a brief and perhaps local late Kinderhookian excursion to 5.4‰. The d¹³C values remain stable at 3.5 to 4‰ during Stage C1, then decrease about 1‰ near the Meramecian-Chesterian boundary (Visean) to 2 - 3‰ (Stage C2). Stage C2 ends with a 1 - 2‰ increase (C2/C3 transition) between the mid Chesterian and early Morrowan (Serpukhovian-Bashkirian). Stage C3 values remain mostly between 3 and 4.5‰ up section to the Virgilian (Gzhelian). Increases in d¹³C probably reflect global increases in sedimentary organic carbon burial and suggest pCO₂ declines in the earliest and middle Carboniferous. The mid-Carboniferous d¹³C shift of B. Popp, T. Anderson, and P. Sandberg (1986a), a roughly 3‰ increase in European sections, occurs in North America (C2/C3 transition) but is limited to roughly 1.5‰. This 1.5‰ increase was probably caused by increased organic carbon burial, whereas the additional ~1.5‰ shift in European sections likely reflects changes in ocean circulation patterns associated with the closing of the Equatorial Seaway. Based on the timing of the d13C divergence between North America and Europe, the isolation of the Paleotethys began in the late Chesterian (Serpukhovian).

    The d¹⁸O record can also be separated into the three stages. There is a 3‰ increase during the Kinderhookian-Osagean (Tournaisian), corresponding to the Devonian-to-Carboniferous transition to Stage C1, a 3‰ decrease during the Meramecian-early Chesterian (Visean; C1/C2 transition), then a 2‰ increase in the late Chesterian-early Morrowan (Serpukhovian-Bashkirian; C2/C3 transition). The d¹⁸O values then fluctuate between -1 and -3‰ (C3 stage) up section to the Virgilian (Gzhelian). If global, the 2 to 3‰ d¹⁸O shifts are compelling evidence for cooling and glaciation in the Early Mississippian, warming and deglaciation in the Late Mississippian, and a return to cool, glacial conditions in the earliest Pennsylvanian. The general correlation between d¹³C and d¹⁸O shifts suggests cooling is associated with drawdown of atmospheric CO₂.