CO2, organic carbon burial, and global climate change in the Wenlock (Silurian):waired 13 Ccarb and 13 Corg analyses of marine carbonates
Final Report Abstract
At present only four widely used palaeo-pCO2 proxies for pre-Quaternary rocks exist: ?13C of pedogenic carbonates, paired ?13Ccarb and ?13Corg analyses of marine sediment, density of stomata on the leaves of C3 plants, and ?11B of planktic foraminiferans. Among these, only paired analyses of ?13Ccarb and ?13Corg can be used to reconstruct the palaeo-pCO2 of the Early Palaeozoic because vascular plants and planktic foraminiferans had not yet evolved. Paired analyses of ?13Ccarb and ?13Corg (??13C) can be used as a proxy for the pCO2 of the atmosphere because the ??13C values are to a large degree controlled by photosynthetic fractionation (ep), which is in part dependent on the concentration of dissolved CO2 in sea water (there is, however, an ongoing discussion on the applicability of this proxy). The time interval from Late Ordovician to latest Silurian is characterised by several pronounced ?13Ccarb excursions. For the present study, 4 out of 9 sections, which include 5 of these excursions (Hirnantian, early Sheinwoodian, late Homerian, late Ludfordian), have been investigated with respect to both their ?13Ccarb and ?13Corg isotope values. Our results (and a survey of all published data) indicate that each of the ?13Ccarb excursions is also characterised by increased ?13Corg values, although mostly with lower amplitudes and more “noise”. Consequently, also the ??13C values show positive excursions indicating enhanced pCO2 values. This is in conflict with oxygen isotope data which indicate lower sea-surface temperatures, and, consequently, a lower CO2 content of the atmosphere.
Publications
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(2009): New biostratigraphic and chemostratigraphic data from the Chicotte Formation (Llandovery, Anticosti Island, Laurentia) compared with the Viki core (Estonia, Baltica). Estonian Journal of Earth Sciences, 58(3), 159-169
Munnecke, A. & Männik, P.
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(2010): Paleobiogeography, high-resolution stratigraphy, and the future of Paleozoic biostratigraphy: Fine-scale biostratigraphic diachroneity of the Wenlock (Silurian) conodont Kockelella walliseri. Palaeogeography, Palaeoclimatology, Palaeoecology, 294, 232-241
Cramer, B.D., Kleffner, M.A., Brett, C.E., McLaughlin, P.I., Jeppsson, L., Munnecke, A. & Samtleben, C.
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(2010): Testing the limits of Paleozoic chronostratigraphic correlation via highresolution (<500 kyr) integrated conodont, graptolite, and carbon isotope (d13Ccarb) biochemostratigraphy across the Llandovery-Wenlock (Silurian) boundary: Is a unified Phanerozoic timescale achievable? GSA Bulletin, 122, 1700-1716
Cramer, B.D., Loydell, D.K., Samtleben, C., Munnecke, A., Kaljo, D., Männik, P., Martma, T., Jeppsson, L., Kleffner, M.A., Barrick, J.E., Johnson, C.A., Emsbo, P., Joachimski, M.M., Saltzman, M.R.
