Characterization of the negative carbon isotope shift in segment C2, its global implications as a harbinger of OAE1a

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• 作者：Jander Socorro ; Florentin J.-M. R. Maurrasse…
• 关键词：Oceanic Anoxic Event 1a (OAE1a) ; Aptian ; Organyà Basin ; Chemostratigraphy ; Pyrenees
• 刊名：Science China Earth Sciences
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：60
• 期：1
• 页码：30-43
• 全文大小：5827KB
• 刊物主题：Earth Sciences, general;
• 出版者：Science China Press
• ISSN：1869-1897
• 卷排序：60

文摘

Lower Cretaceous C-isotope records show intermittent negative/positive spikes, and consistent patterns of coeval chemostratigraphic curves thus document shifts that signal simultaneous responses of temporal changes in the global carbon reservoir. The standard pattern registered by the δ13C_org and δ13C_carb in Lower Aptian sediments includes distinct isotope segments C1 to C8 (Menegatti et al., 1998). In the El Pui section, Organyà Basin, Spain, C-isotope segment C2 is the longest interval preceding segments C3–C6 associated with oceanic anoxic event 1a (OAE 1a), and reveals a distinct negative shift of ~1.8‰ to ~2.23‰ defining the C-isotope pattern within that interval. Total inorganic carbon (TIC), total organic carbon (TOC), δ13C_org, microfacies, n-alkanes show no difference before, during, or after the negative inflection. The biomarkers indicate that organic matter (OM) mainly originates from algal/microbial sources because short-chain length homologues (≤nC₁₉) dominate. nC₂₀ through nC₂₅ indicate some contribution from aquatic vegetation, but little from higher plants (>nC₂₅), as also suggested by the terrestrial/aquatic ratio of n-alkanes or (TAR) = [(nC₂₇+nC₂₉+nC₃₁)/(nC₁₅+nC₁₇+nC₁₉)] (averages 0.085). We suggest that conjoint pulses of contemporaneous LIPs (Ontong Java) and massive explosive volcanism in northeast Asia, the Songliao Basin (SB-V), best conform to plausible causes of the negative intra-C2 carbon isotopic excursion (CIE) at that time. Because of its apparent common occurrence the intra-C2 inflection could be a useful marker harbinger to the more pronounced CIE C3, the hallmark of OAE1a.