干旱区生态环境知识资源中心

Carbon isotope (delta(13)C(org)) analyses of neritic carbonates and block shales spanning the Silurian-Devonian transition are compared from two richly fossiliferous sequences in Zoige County (West Qinling Region) of Sichuan Province, China. The two sections. Putonggou and Yanglugou sections in West Qinling, reveal positive delta(13)C(org) shifts happening in the upper Pridoli and lower Devonian and reaching peak values as heavy as -19.9 parts per thousand (Putonggou) and -19.7 parts per thousand (Yanglugou) in the lowermost Lochkovian following the first occurrence of the Protathyris-Lanceomyonia brachiopod fauna and the conodont Icriodus woschmidti woschmidti. These results replicate a globally known positive shift in delta(13)C(org) from the uppermost Silurian to the lowermost Devonian. The isotopic trend for organic carbon across the Silurian-Devonian Boundary (SDB) offers an approach to a potential correlation of the SDB from different sedimentary facies. The delta(13)C(org) variations across the Silurian-Devonian transition at the two sections in West Qinling exhibit a similar shift in their carbon isotopic composition as the detailed SDB curves from the borehole Klonk-1 drilled at top of the Klonk GSSP in the Prague Basin, Czech Republic. This suggests that the SOB in West Qinling is located at the upper part of the Yanglugou Formation (between ZY-07 and ZY-06) in the Yanglugou Section and the lower part of the Xiaputonggou Formation (between ZP-09 and ZP-10) in the Putonggou Section. More data will help to reveal individual causes for the isotopic shift, such as enhanced carbon burial due to anoxic conditions and/or increased productivity, alternating arid and humid periods, or changes in the composition of primary producers.