A rapid hydroclimate change and its influence on the Songliao Basin during the Santonian-Campanian transition as recorded by compound-specific isotopes
A rapid hydroclimate change and its influence on the Songliao Basin during the Santonian-Campanian transition as recorded by compound-specific isotopes
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DOI：
10.1016/j.palaeo.2020.109674
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发表时间：
2020-05
期刊：
影响因子：
--
通讯作者：
Li Wang;Yankuan Tian;Jiaju Zhao
中科院分区：
文献类型：
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作者：
Li Wang;Yankuan Tian;Jiaju Zhao
恢复松辽盆地古气候和古环境，对于揭示白垩纪温室气候条件下的区域大陆性气候特征和大陆有机质的聚集具有重要的理论和现实意义。本文报道了松辽盆地嫩江组沉积物中生物标志化合物组成和正构烷烃的碳、氢稳定同位素组成，为研究晚白垩世生物来源、古环境和古气候变化提供了信息。正构烷烃的氢同位素记录显示出显著的负移，表明在Santonian-Campanian过渡期发生了一个非常潮湿的气候。潮湿的气候，如在一个长时间的降雨事件，对湖泊产生了重大影响，并导致在此期间，湖泊水位上升，地表水的盐度下降。但淡水输入增加了上、下层的盐度差，使湖泊出现稳定的水体分层。此外，高的总有机碳（TOC）含量表明高初级生产力，因为增加的降水携带更多的陆源营养物质进入湖泊，导致富营养化在此期间。值得注意的是，增加的芳基类异戊二烯的比例和isorenieratane的出现表明，透光带euxinia（PZE）增强在Santonian-Campanian过渡，这可能是由于在水文气候的急剧变化。我们推测，大量的淡水输入促进了湖泊中PZE的形成。其次，PZE限制了好氧生物的栖息地，对湖泊生态系统产生了致命的影响。
Reconstruction of the paleoclimate and paleoenvironment of the Songliao Basin has important theoretical and practical significance to reveal the regional continental climate characteristics and continental organic matter accumulation under the Cretaceous greenhouse climate conditions. Here, we report the composition of biomarkers and the stable carbon and hydrogen isotope compositions ofn-alkanes from Nenjiang Formation sediments in the Songliao Basin, which provide information on the source of organisms, paleoenvironmental conditions, and paleoclimate changes during the Late Cretaceous. Our hydrogen isotope records ofn-alkanes displayed a significantly negative shift, indicating that a dramatically wet climate occurred during the Santonian-Campanian transition. A wet climate, such as that during a prolonged rainfall event, had a significant impact on the lake and resulted in the lake level increasing and the salinity decreasing in the surface water during this period. However, the freshwater input increased the salinity difference between the upper and lower water layers, which caused stable water stratification to occur in the lake. In addition, the high total organic carbon (TOC) content indicates high primary productivity because of increased precipitation carrying more terrigenous nutrients into the lake, which resulted in eutrophication during this period. Notably, the increased aryl isoprenoid ratios and the occurrence of isorenieratane indicates that photic zone euxinia (PZE) was enhanced during the Santonian-Campanian transition, which was possibly due to the dramatic change in the hydroclimate. We speculate that the large freshwater input promoted the formation of PZE in the lake. Then, PZE restricted the habitat available for aerobic organisms, which had fatal effects on the lake ecosystem.