An alternative model for positive shifts in shallow-marine carbonate δ13C and δ18O
Article first published online: 27 AUG 2003
Volume 50, Issue 5, pages 953–959, October 2003
How to Cite
Immenhauser, A., Della Porta, G., Kenter, J. A. M. and Bahamonde, J. R. (2003), An alternative model for positive shifts in shallow-marine carbonate δ13C and δ18O. Sedimentology, 50: 953–959. doi: 10.1046/j.1365-3091.2003.00590.x
- Issue published online: 27 AUG 2003
- Article first published online: 27 AUG 2003
- Manuscript received 30 January 2003; revision accepted 15 May 2003.
- epeiric seas;
Abstract Positive shifts in global seawater δ13CDIC are related to changes in the ratio of organic relative to inorganic carbon burial in oceanic basins, whereas factors such as climatic cooling and the accumulation of polar ice are known to cause positive shifts in δ18O. Here, an alternative model is proposed for the formation of local positive isotope shifts in shallow-marine settings. The model involves geochemically altered platform-top water masses and the effects of early meteoric diagenesis on carbonate isotopic composition. Both mechanisms are active on modern (sub)tropical carbonate platforms and result in low carbonate δ13C and δ18O relative to typical oceanic values. During high-amplitude transgressive events, the impact of isotopically light meteoric fluids on the carbonate geochemistry is much reduced, and 13C-depleted platform-top water mixes with open oceanic water masses having higher isotope values. Both factors are recorded as a transient increase in carbonate 13C and 18O relative to low background values. These processes must be taken into consideration when interpreting the geochemical record of ancient epeiric seas.