Stable carbon isotope stratigraphy in the Ordovician of South China

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• 作者：Axel Munnecke^a ; ^{axel.munnecke@gzn.uni-erlangen.de"" rel=""nofollow} ; Yuandong Zhang^b ; ^{ydzhang@nigpas.ac.cn"" rel=""nofollow} ; Xiao Liu^b ; Junfeng Cheng^b
• 关键词：Ordovician ; South China ; Stable carbon isotopes ; Stratigraphy ; Graptolites
• 刊名：Palaeogeography, Palaeoclimatology, Palaeoecology
• 出版年：2011
• 出版时间：1 July 2011
• 年：2011
• 卷：307
• 期：1-4
• 页码：17-43
• 全文大小：9747 K

文摘

About 500 samples from 11 Ordovician sections in South China have been analysed for their δ¹³C_carb composition. Four sections are located in the Yangtze platform region, the remaining seven sections in the Jiangnan slope region. The sections span more or less the entire Ordovician, but the sample resolution in its lower part (Tremadocian to Dapingian) is lower than in its upper part (Darriwilian to Hirnantian). Overall, the data show a good correlation with the published global isotope curve. At the Cambrian–Ordovician boundary positive values are observed. In the succeeding Tremadocian the values decrease and remain negative into the early Floian. In the late Floian, the values increase to slightly positive. The correlation of Dapingian rocks between the Yangtze and the Jiangnan regions is somewhat problematic which might be due to high siliciclastic input in the Yangtze section. In the Darriwilian a small positive excursion is observed in the Yangtze platform area, however, it is missing in the Jiangnan slope area. This excursion probably correlates with the mid-Darriwilian excursion (MDICE) reported from Baltoscandia. Both chemostratigraphy and conodont biostratigraphy indicate a possible gap between the Shihtzupu Formation and the Pagoda Formation, i.e. most of the Sandbian is probably not represented in the Upper Yangtze region. The earliest Katian is characterised by a pronounced positive excursion correlating with the well-known global Guttenberg excursion (GICE). In the late Katian at least one additional positive excursion was determined. The precise biostratigraphy, however, is not clear, and therefore it is not known which of the known four to five remaining Katian δ¹³C excursions identified in Baltica correlate(s) with the one(s) observed in the present study, and further biostratigraphic study is required. The lower part of the Hirnantian excursion (HICE) is probably not preserved, with only small remnants of the HICE observed near the base of the Kuanyinchiao Bed.