Carboniferous isotope stratigraphies of North America; implications for Carboniferous paleoceanography and Mississippian glaciation
Carboniferous isotope stratigraphies of North America; implications for Carboniferous paleoceanography and Mississippian glaciation
Geological Society of America Bulletin (July 1999) 111 (7): 960-973
- alkali metals
- C-13/C-12
- calcite
- carbon
- carbon dioxide
- carbonates
- Carboniferous
- chemostratigraphy
- cooling
- deglaciation
- diagenesis
- errors
- glacial environment
- glacial geology
- glaciation
- isotope ratios
- isotopes
- metals
- minor elements
- Mississippian
- North America
- O-18/O-16
- ocean circulation
- organic carbon
- oxygen
- paleo-oceanography
- paleoatmosphere
- paleoclimatology
- Paleozoic
- preservation
- shells
- sodium
- stable isotopes
- sulfur
- trace elements
We present detailed isotope stratigraphies for Carboniferous time based on brachiopod shell calcite from the midcontinent 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) delta (super 13) C and delta (super 18) O values higher than those of associated cements and matrix. The Carboniferous delta (super 13) C record for North America is characterized by three isotopic stages. The earliest stage, C1, follows a 2.0 per mil increase in Kinderhookian time (early Tournaisian), from 1.5 per mil to 3.5 per mil, and includes a brief and perhaps local late Kinderhookian excursion to 5.4 per mil. The delta (super 13) C values remain stable at 3.5 per mil to 4 per mil during stage C1, then decrease about 1 per mil near the Meramecian-Chesterian boundary (Visean) to 2 per mil-3 per mil (stage C2). Stage C2 ends with a 1 per mil-2 per mil increase (C2-C3 transition) between middle Chesterian and early Morrowan time (Serpukhovian-Bashkirian). Stage C3 values remain mostly between 3 per mil and 4.5 per mil upsection to Virgilian strata (Gzhelian). Increases in delta (super 13) C probably reflect global increases in sedimentary organic carbon burial and suggest that pCO (sub 2) declines in the earliest and middle Carboniferous strata. The middle Carboniferous delta (super 13) C shift of B. Popp, T. Anderson, and P. Sandberg, an approximately 3 per mil increase in European sections, occurs in North America (C2-C3 transition) but is limited to approximately 1.5 per mil. This 1.5 per mil increase was probably caused by increased organic carbon burial, whereas the additional approximately 1.5 per mil 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 delta (super 13) C divergence between North America and Europe, the isolation of the Paleotethys began in late Chesterian time (Serpukhovian). The delta (super 18) O record can also be separated into the three stages. There is a 3 per mil increase during Kinderhookian-Osagean time (Tournaisian), corresponding to the Devonian to Carboniferous transition to stage C1, a 3 per mil decrease during Meramecian-early Chesterian time (Visean; C1-C2 transition), then a 2 per mil increase in late Chesterian-early Morrowan time (Serpukhovian-Bashkirian; C2-C3 transition). The delta (super 18) O values then fluctuate between -1 per mil and -3 per mil (C3 stage) upsection to the Virgilian strata (Gzhelian). If global, the 2 per mil to 3 per mil delta (super 18) O shifts are compelling evidence for cooling and glaciation in Early Mississippian time, warming and deglaciation in Late Mississippian time, and a return to cool, glacial conditions in earliest Pennsylvanian time. The general correlation between delta (super 13) C and delta (super 18) O shifts suggests that cooling is associated with drawdown of atmospheric CO (sub 2) .