The expression of the Cenomanian–Turonian oceanic anoxic event in Tibet
The expression of the Cenomanian–Turonian oceanic anoxic event in Tibet
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DOI：
10.1016/j.palaeo.2012.11.011
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
B. Bomou;T. Adatte;A. Tantawy;Haydon P. Mort;D. Fleitmann;Yongjian Huang;K. Föllmi
中科院分区：
文献类型：
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作者：
B. Bomou;T. Adatte;A. Tantawy;Haydon P. Mort;D. Fleitmann;Yongjian Huang;K. Föllmi
中国西藏贡扎地段位于印度板块（特提斯东南部）北缘，以半远洋灰色泥灰岩和泥灰岩、浅灰色灰岩和粉砂质灰岩为特征，但无富含有机质沉积物。高分辨率生物地层学揭示了扩大的塞诺曼阶-土伦阶 (CT) 边界区间，δ13C 记录包括表征 CT 海洋缺氧事件的经典正碳同位素偏移的主要特征。从有孔虫推断出的生物反应表明，从有氧到缺氧条件普遍存在，除了以异螺旋峰丰度为标志的短时间间隔外，这表明在 δ13C“b”峰偏移期间存在明显的缺氧环境。在δ13C最大偏移期间，氧化还原敏感微量元素（RSTE）的总体下降趋势证实了贡扎断面不存在明显的长期缺氧。 RSTE 的富集与碎屑输入增加的阶段有关。化学风化指数表明，塞诺曼阶上部沉积物在日益炎热和潮湿的气候下积累，并在 CT 边界附近达到顶峰。土伦纪早期较低的风化指数表明气候温暖、干燥，大陆径流减少。磷质量积累率在 δ13C 正偏移开始时显示出显着的峰值，随后下降到基底土伦阶。这种模式与碎屑指数的长期下降呈正相关，在许多其他 CT 边界断面（例如伊斯特本、普韦布洛和 Whadi El Ghaib、西奈）也观察到这一点。因此，贡扎地段磷的长期积累与碎屑输入的变化有关。碎屑输入总体减少的原因可以解释为，由于塞诺曼纪末的大规模海侵，大陆来源越来越偏远，加上与日益干旱的气候条件相关的大陆风化强度的变化。
The Gongzha section of Tibet, China is located at the northern margin of the Indian Plate (SE Tethys) and is characterized by hemipelagic grey marls and marly limestones, light grey limestones and silty limestones, but no organic-rich sediments. High-resolution biostratigraphy reveals an expanded Cenomanian–Turonian (CT) boundary interval and the δ13C record includes the main features of the classical positive carbon-isotope excursion that characterizes the CT oceanic anoxic event. The biotic response inferred from the foraminifera suggests that oxic to dysoxic conditions prevailed, except for a short interval marked by peak abundance of Heterohelix that indicates a significantly dysoxic environment during the δ13C “b” peak excursion. The overall decreasing trend in redox-sensitive trace elements (RSTE) during the maximum δ13C excursion confirms the absence of significant longer-lasting anoxia in the Gongzha section. Enrichments in RSTE are linked to phases of increased detrital input. Chemical weathering indices suggest that the upper Cenomanian sediments accumulated under an increasingly hot and humid climate that culminated near the CT boundary. In the early Turonian lower weathering indices suggest a warm, drier climatic regime with reduced continental runoff. Phosphorus mass-accumulation rates show a significant peak at the onset of the positive δ13C excursion, followed by a decrease up to the basal Turonian. This pattern is positively correlated with the long-term decrease in detrital index as also observed in numerous other CT boundary sections (e.g., Eastbourne, Pueblo, and Whadi El Ghaib, Sinaï). Long-term phosphorus accumulation in the Gongzha section is therefore associated with changes in detrital input. The overall decreased detrital input can be explained by the increasingly remote continental sources due to the major transgression at the end of Cenomanian, coupled with changes in continental weathering intensity linked to increasingly more arid climate conditions.