高分辨率碳氧同位素应用及西藏岗巴地区白垩纪中期Cenomanian-Turonian期碳同位素偏移

Applications of high-resolution carbon-and oxygen-isotopes: Results from Cenomanian-Turonian in Gamba, Tibet.

介绍了高分辨率碳氧同位素的应用成果;指出半远洋、远洋碳酸盐全岩高分辨率碳同位素高值正偏可作为甄别大洋缺氧事件的指示剂和分析古气候变化的指针,碳同位素偏移型式可为长期海平面变化和短期海平面波动提供参照对比的依据。西藏南部岗巴地区的高分辨率偏移曲线显示,碳同位素Cenomanian Tu ronian界线时期的正偏幅度达2.90‰,Turonian期长期持续负偏,并在M. sigali带中、下部呈现两个负偏凹陷区。这表明,该区白垩纪中期Cenomanian Turonian期存在可以在特提斯甚至全球类比的碳同位素变化趋势,表现为Cenomanian Turonian界线时期的缺氧事件、Turonian期的长期海平面下降趋势和Turonian晚期短暂气候变冷的响应。

Applications of high-resolution carbon- and oxygen-isotopes in geology are reviewed.We report the results of carbon- and oxygen determinations from the Cenomanian-Turonian in southern Tibet. High-resolution analyses of bulk samples show extremely positive or negative (δ^(13)C) excursions. These are interpreted as indicating an oceanic anoxic event and a palaeoclimatic change . The (δ^(13)C) curve reflects the long-term change and short-term fluctuation of sea level. The (δ^(13)C) values from the Gamba-Zongshan section in Tibet show an abrupt positive excursion of 2.9‰ at the Cenomanian-Turonian boundary. A long-term negative (δ^(13)C) excursion occurs in whole Turonian, in which two pronounced negative troughs occur in the middle and lower M. sigali zone. The pattern of the (δ^(13)C) excursion displays that the trend of the curve is similar to that in Tethys and even to that of the global curve, which reveals the OAE2 at the Cenomanian-Turonian boundary, a long-term sea-level falling in the Turonian, and a climate cooling in the northern Indian passive margin, i.e., in southeastern Tethys Sea.