江陵凹陷始新世早期古气温：来自无水芒硝流体包裹体的证据

摘要

江陵凹陷古新统沙市组和始新统新沟嘴组下段沉积为一套巨厚含盐岩系。对始新世早期新沟嘴组下段沉积的无水芒硝中的原生单一液相流体包裹体采用冷冻法进行均一温度测定。原生流体包裹体是在矿物沉积的过程中被捕获的，矿物生长过程中所圈闭的流体（即古盐湖卤水）保存了当时地质环境的各种地质地球信息，可以为研究古温度、古水体成分、古大气成分以及生物的演化等方面提供可靠的定量数据。测温结果显示，其均一温度范围是17．6～38．5℃，均值为27．2℃。这可能说明，江陵凹陷早始新世新沟嘴组下段的古气温在27．2℃左右，极端情况下，当时的古气温可达38．5℃。通过与前人的研究比对发现江陵凹陷自沙市组上段到新沟嘴组下段有明显降温趋势。由于古新世—始新世的升温事件（PETM）使全球气温普遍升高，可以看出江陵凹陷自新沟嘴底部虽已进入 PETM 事件后的降温期但气候依然以炎热干旱为主要特征。%Shashi Formation and the lower section of Xingouzui Formation in the Jinangling Depression deposited a thick rock series of salt.The homogenization temperatures of primary fluid inclusions in thenardite from the lower section of Xingouzui Formation of Early Eocene were measured by freezing method.The samples were placed in a freezer at -18℃ for one or two weeks.This temperature was not cold enough to freeze the fluid inclusions.Once removing the sample in a Linkam THMS600 heating/freezingstage when we observed the fluid inclusions in a sample produced vapor bubbles.Then the sample was slowly heated until the bubbles disappeared.The current temperature was the homogenization temperature.Temperature results show that the homogenization temperature range is 17.6 ~38.5℃,with the average of 27.2℃. This maybe show that,the paleotemperature of lower section of Xingouzui Formation in Jinangling Depression of Early Eocene was around 27.2℃.In extreme cases,the paleotemperature can reach 38.5 ℃. By comparison with previous studies,we found a significant cooling trend from the upper section of Shashi Formation to the the lower section of Xingouzui Formation in the Jinangling Depression.However,due to PETM(Paleocene-Eocene Thermal Maximum)events,global temperatures were generally higher at that time.It can be conduded that although the lower section of the Xinggouzui Formation entered the cooling period after the PETM event,the climate was still parched.