Paired δ13Ccarb and δ13Corg records of Upper Ordovician (Sandbian–Katian) carbonates in North America and China: Implications for paleoceanographic change

Late Sandbian–Early Katian marine carbonates from two sections in North America and one in south China were analyzed for paired δ13Ccarb and δ13Corg, and revealed similar δ13Ccarb but varying trends in δ13Corg stratigraphy while all sections recorded a well-known positive δ13Ccarb shift. These δ13Corg records are the first through the Guttenberg δ13Ccarb excursion (GICE) in China, Oklahoma, and West Virginia. In south China a positive excursion in δ13Corg is associated with the latter part of the positive δ13Ccarb excursion and closely resembles trends from Iowa and Pennsylvania that have been interpreted to reflect a lowering of atmospheric pCO2 levels. The δ13Corg trends from Oklahoma and West Virginia differ significantly from what is observed in China. This likely indicates that local changes in nutrient cycling and phytoplankton growth rates were the dominant control on 12C fractionation in Oklahoma and West Virginia, masking a possible global signal of lowered atmospheric pCO2 levels observed in China.