2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 8
Presentation Time: 3:30 PM


CRAMER, Bradley D., Geological Sciences, The Ohio State Univ, 170 Mendenhall Laboratory, 125 S. Oval Mall, Columbus, OH 43210 and SALTZMAN, Matthew R., Geological Sciences, Ohio State Univ, 275 Mendenhall Laboratory, 125 South Oval Mall, Columbus, OH 43210, cramer.70@osu.edu

A major early Silurian positive carbon isotope excursion began at or near the top of the Pterospathodus amorphognathoides conodont biozone (herein referred to as the Ireviken Excursion), and is recorded in sections in Europe, Australia and North America. We have documented the shift in carbonate carbon in three successions in the mid-continent of North America, also conducting paired carbon isotope analyses of carbonate and organic carbon on the section of the Wayne Formation in central Tennessee. The results indicate that a positive shift in δ13Ccarb of +3.9‰ coincided with a minimum in δ13Corg of -30.1‰. This data indicate that pCO2 was increasing during the onset of the Ireviken Excursion. Subsequently, the δ13Ccarb curve decreased to a stable baseline near +1‰ in the upper part of the Maddox, while the δ13Corg curve increased back to baseline. The rate and timing of changes in the two isotopic records reveal a complex, counter-intuitive relationship suggesting that high organic carbon burial initially coincided with increasing pCO2 during the early Silurian Ireviken Excursion. This is proposed to reflect warming in polar regions that switched the site of deep water formation to low latitudes. As a result, organic carbon burial increased in the anoxic deep oceans, which provided a negative feedback on rising pCO2 levels. The alteration of deep ocean circulation also lowered nutrient availability in shelf environments, which severely affected the biota and allowed a healthy carbonate factory to develop throughout the tropics.