Geochemical and climatic effects of increased marine organic carbon burial at the Cenomanian/Turonian boundary

;
• Dean, Walter E.
;
• Pratt, Lisa M.

Abstract

Perhaps the most significant event in the Cretaceous record of the carbon isotope composition of carbonate^1,2, other than the 1-2.5 ‰ negative shift in the carbon isotope composition of calcareous plankton at the Cretaceous/Tertiary boundary³, is the rapid global positive excursion of ~2 ‰ (¹³C enrichment) which took place between ~91.5 Myr and 90.3 Myr (late Cenomanian to earliest Turonian (C/T boundary event))^1,4,5. This excursion has been attributed to a change in the isotope composition of the marine total dissolved carbon (TDC) reservoir resulting from an increase in rate of burial of ¹³C-depleted organic carbon, which coincided with a major global rise in sea level⁵ during the so-called C/T oceanic anoxic event (OAE)⁶. Here we present new data, from nine localities, which demonstrate that a positive excursion in the carbon isotope composition of organic carbon at or near the C/T boundary^7,8 is nearly synchronous with that for carbonate and is widespread throughout the Tethys and Atlantic basins (Fig. 1), as well as in more high-latitude epicontinental seas. The postulated increase in the rate of burial of organic carbon may have had a significant effect on CO₂ and O₂ concentrations in the oceans and atmosphere, and consequent effects on global climate and sedimentary facies.