【摘要】 西藏南部上白垩统半远洋沉积高分辨率碳、氧同位素实验结果显示δ13C值在Cenomanian末期正偏并形成正偏“高原”,从Turonian期开始总体呈现长期持续负偏,到Campanian早期负偏达到最低值。这种长期变化格局与世界有关地区的碳同位素偏移和同期全球海侵—海退旋回型式匹配性甚好,印证了晚白垩世δ13C值长期偏移趋势可作为大区域乃至全球海平面变化的指针。短期δ13C值波动方面,Cenomanian末期、Turonian中—晚期、Turoni-an—Santonian界线时期、Campanian期都存在与世界相关地区的可比性,但Coniacian—Santonian期全球碳同位素偏移型式存在较大差异。更多还原

【Abstract】 Bulk samples of carbon and oxygen isotopes taken from Tingri and Gamba of southern Xizang(Tibet) are analyzed in this study. All the samples were taken as fresh as possible in field, and the samples with much diagenetic overprint, calcite-filled microcrack and bioturbation fabrics are carefully avoided to use for isotope analyses. At last, 611 samples in 250 m thick section from Tingri, ca. 45.8 ka interval between two samples, were analyzed at Oxford University, and 170 samples in 381 m thick section from Gamba, ca. 164.7 ka intervals, were experimented at Tongji University in Shanghai. The results of carbon isotope ratios from Tingri indicate an extreme positive excursion of δ 13 C values occurs at the Cenomanian—Turonian boundary, and afterwards, a secular long-term negative excursion goes on to a lowest horizon at the early Campanian. This long-term δ 13 C change trend is correlative with those in southern England and Russian Far East, and so be with the global transgressive—regressive cycle. However, it is not so compatible by the δ 13 C values from Gamba, which may result from sample preparation. In aspect of short-term fluctuation, the excursion patterns of δ 13 C values of the Cenomanian—Turonian boundary passage, middle—late Turonian, Turonian—Santonian boundary beds, and Campanian in southern Xizang(Tibet), are similar with the coeval periods in Mediterranean Tethys and Europe. Of them, three patterns of δ 13 C excursion during Coniacian—Santonian are summarized, which could be resulted from different basin and lithofacies; and a long-term positive excursion in the middle Campanian may be a response of highest stand of sea-level or largest transgression since Cenomanian. Other more, three troughs of the δ 13 C values in Tingri occurring at the base of Campanian,middle Lower Campanian, the boundary of Lower and Upper Campanian, may represent three carbon isotope excursion events, and they could correspond to the lowstands of the short-term sea-level fluctuations in globe by the Haq curve.更多还原