滇西兰坪-思茅盆地白垩纪中期内陆沙漠沉积记录与气候变化研究

The mid-Cretaceous (Cenomanina-Turonian) is a period of extreme warm and dry in the earth’s history, accurate understanding the global climate evolution behavior of this interval is thus one of the major issues in paleoclimatology research. Multiple climate proxies show that the equator-polar geothermal gradient during the Cretaceous ‘Supergreen house’ is extremely low compared with the current earth, meaning much heat of atmospheric or oceanic circulation is meridional transported. However, the pattern of the mid-Cretaceous atmospheric circulation is still poorly understood due to the absence of direct geological evidence, especially from the terrestrial-atmospheric system. Wide deserts sediments in the mid-low latitude regions of the northern hemisphere often occurred in form of desert basin groups during the mid-Cretaceous period, providing unique information of prevailing winds and paleoclimate of mid-Cretaceous. In this study we use desert sediment records as monitor for the mid-Cretaceous greenhouse climate to reconstruct the spatial configuration of desert sediment in the Lanping-Simao basin, to identify the type of prevailing wind and reconstruct the general circulation patterns by combining with the paleo-wind direction, and to verify the synchronization and asynchronization among events of desert deposition in low-latitude basins, sediment transition and wind-direction changes via changes of desert sedimentary system and wind vectors. Our study will improve our knowledge of short-term climate change in the mid-Cretaceous “greenhouse” from a new angle of view and provide the reference to human to realize the current environmental problems such as "greenhouse effect" .

白垩纪中期（森诺曼阶-土仑阶）是地质历史上极端温暖干旱时期，了解该时期全球气候演变行为是古气候学研究的重大课题之一。众多气候替代指标表明，与现代赤道至极地的温度梯度相比，白垩纪“超级温室气候期”赤道-极地地温梯度幅度极低，这意味着大量的大气或海洋环流的热量沿纬线传输。然而，白垩纪中期大气环流格局的重建仍然缺乏大气-陆地系统的直接地质证据。白垩纪中期，北半球中低纬度广泛发育沙漠而形成沙漠群，从这些沙漠沉积中可提取出大量盛行风及气候信息。本研究以滇西地区兰坪-思茅盆地白垩纪沙漠沉积记录作为温室期气候演变的监测器，研究沙漠沉积时空分布特征，恢复古风向并判断所属盛行风性质，重塑滇西地区大气环流分配样式。根据沙漠沉积体系及矢量风向组的变化和转型事件，探讨中低纬度盆地群沙漠事件、沉积转型、古风向转变的同步性或差异性，更新我们对白垩纪中期短周期温室气候变化的认识。

本研究以风成沉积体系理论为指导，以兰坪-思茅盆地白垩系巨厚红色碎屑岩层为研究对象，开展了岩石学特征研究，风成沙丘建筑学分析，总结风成沉积时空分布规律，恢复古风向和判定其所属盛行风性质。基于以上研究内容和结果，分析了兰坪-思茅盆地白垩纪风成沉积堆积、保存的控制因素，探讨白垩纪中期东亚古风向展布和大气环流格局，总结了风成-干盐湖沉积体系对思茅盆地钾盐成藏作用的约束，并试论大陆性沙漠气候对无冰期短周期海平面变化的影响。研究表明：兰坪-思茅盆地在白垩中期处于副高的笼罩之下，气流下沉，气候干旱。同时随着中特提斯洋的关闭东亚地区西南缘造山运动的持续叠加作用，在北半球中低纬度发生了一次剧烈的沙漠化事件。其次，指出勐野井组与围岩曼岗组可能为指状交叉接触，二者为白垩纪中期干旱气候条件下中纬度低海拔沙漠环境中的同时异相沉积。含钾盐矿层的干盐湖沉积体展现为一个个巨大透镜状的隐伏盐体，这是风成沙丘周期性迁移覆盖于干盐湖沉积之上所致。该认识可能为固体钾盐勘查提供了新的视角。再者，根据白垩纪中期四川盆地，兰坪-思茅盆地，泰国呵叻盆地的古风向，三者形成了一个向外发散、顺时针旋转的封闭环流形态。这与控制撒哈拉和澳大利亚沙漠的高压单体较为类似。高压单体促进了内陆半封闭和封闭盆地干旱条件增强，内陆荒漠化、沙漠化开始盛行并伴随蒸发岩沉积。