东营凹陷中晚始新世古气候演化特征及其意义——以Hk1井为例

始新世中晚期是东亚地区古近纪气候的关键转变期，其古气候演化过程及影响因素非常复杂。以往主要是依据中国中西部地区的沉积资料对这一时期的古气候演化进行研究，但是中国东部缺少广泛分布的沉积地层证据，使得这一时期的古气候演化仍然是争论的焦点。位于中国东部的东营凹陷中晚始新世发育有一套连续的红层—膏盐层—湖相泥岩沉积序列，对古气候变化非常敏感。以东营凹陷Hk1井沙四段为研究对象，综合利用沉积学资料和Na/Al比值、化学变化指数（CIW’）等地球化学指标，探讨了其中晚始新世古气候演化特征及其意义。研究表明:中国东部中晚始新世气候演化分为五个阶段，其中，第1~3阶段古气候变化与中国中西部古气候变化基本一致，即长周期的干冷趋势中出现一个短暂的急剧变暖过程（MECO）；第4~5阶段古气候演化与中国中西部古气候变化趋势出现明显差异。第4阶段沉积时期，中国东部古气候变得湿润，纬向分带古气候开始格局被打破；第5阶段时期，古气候整体转变为东湿西干的气候格局，东亚季风开始盛行并成为中国东部地区气候的主导因素。

Mid-late Eocene Paleoclimate Characteristics and Significance in the Dongying Depression: An example from well Hk-1

The mid?late Eocene with complex paleoclimate change is a key period for understanding the evolution of Paleogene paleoclimate in East Asia. Previous studies focused on this period were mainly based on sedimentological data from central and western China， but the paucity of sedimentary stratigraphic evidence from eastern China make the mid?late Eocene climate evolution a continuing area of research interest. The sediments of the Dongying Depression in eastern China provide a stratigraphic sequence of red-bed clastic rocks， gypsum-salt rocks and shallow-semi-deep lacustrine mudstones during the mid-late Eocene， which was a period highly sensitive to paleoclimate change. Selecting the Fourth member of the Shahejie Formation （Es₄） of the Hk1 well as the study object， the evolutional characteristics and corresponding significance of the mid?late Eocene climate are discussed with relation to a comprehensive analysis of sedimentological data and geochemical indicators （e.g.， Na/Al ratio and the Chemical Index of Weathering （CIW’））. The results indicate that the mid?late Eocene paleoclimate evolution in eastern China may be divided into five stages， in which the trends of paleoclimate change in stages 1?3 were similar to those in central and western China: long-term drying and cooling trend with the Middle Eocene Climate Optimum （MECO）. The trends in stages 4 and 5 were clearly distinct from those in central and western China. The climate in eastern China became relatively humid and the latitudinal zonal paleoclimate pattern was beginning to be broken during stage 4. The paleoclimate pattern change from latitudinal zones to east/humid and west/arid during stage 5 suggest that the East Asian summer monsoon became prevalent and dominated the climate in eastern China at that time.