【作者】 刘建平； 鲜本忠； 纪友亮； 龚承林； 王俊辉； 王震； 陈鹏；

【Author】 Jianping Liu;Benzhong Xian;Youliang Ji;Chenglin Gong;Junhui Wang;Zhen Wang;Peng Chen;College of Geosciences,China University of Petroleum;State Key Laboratory of Petroleum Resources and Prospecting;School of Energy Resources,China University of Geosciences;

【机构】 中国石油大学(北京)地球科学学院； 油气资源与探测国家重点实验室； 中国地质大学(北京)能源学院；

【摘要】 气候波动、基准面变化及沉积物供给的交互作用控制了陆源碎屑向湖盆深水区的输送过程。发育于研究区东营凹陷始新世的大型前积体(厚可达～700m)提供了良好的机会以建立湖相环境中深水沉积物分散和前积体结构、滨线轨迹之间的联系。基于地震反射结构特征识别,始新世东营三角洲复合体由多期交替出现、具不同滨线轨迹特征的加积型(aggradatioinalclinothem)和前积型(progradationalclinothem)前积体叠置而成。进一步引入滨线轨迹角(shelf–edge trajectory angle)、前积体趾部距离(clinothem toe distance)、加积高度(aggradational height)和前积距离(progradational distance)等参数对前积体结构进行定量表征。加积型前积体以上升型滨线轨迹(平均轨迹角3.88°)、明显的顶积层(平均厚度85 m),较短的前积距离(平均1.5 km)和厚层、广泛分布的富砂质底积层(延伸可达数十公里,厚可达200m)为特征,指示了碎屑物质向远端湖底环境的高效率输送过程。前积型前积体以近于水平或弱下降型滨线轨迹(轨迹角介于-1.5-0.5°)、较远的前积距离(平均4.0km)为特征,通常缺乏底积层。上升型和近于水平或弱下降型滨线轨迹的交替出现表明了湖平面的频繁波动。进一步运用地震成像技术和地震地貌学开展分析,表明湖底厚层加积的底积层通常由湖底水道-朵体系统构成,而滑动-滑塌块体更易发育于前积型前积体的斜坡-斜坡脚环境。这一特征指示了响应于不同前积体结构和滨线轨迹的深水沉积物搬运过程的差异。温润-干旱气候驱动下的湖平面、沉积物供给及水体盐度/密度变化被认为是控制前积体叠置样式和深湖区沉积物分散的主导因素。在温润气候时期,河流补给和降水量的增加促进了湖平面上升以及湖盆水体盐度/密度的下降,伴随着河流能量和沉积物浓度的增大,洪水频发,陆源碎屑可通过湖底异重流水道向更远端的底积层区域直接供给。干旱气候期间,河流流量小、蒸发量大,在近于稳定或下降的湖平面条件下发育前积型前积体,河流供给碎屑物质在河口区聚集,由于过负载发生垮塌,沉积物以滑动-滑塌的方式向前搬运并在斜坡脚形成堆积。本文揭示了两种不同的深湖沉积物的输送过程及其与气候波动、基准面变化及沉积物供给之间的联系,这一认识有望为研究湖相深水沉积体系提供新思路。更多还原

【Abstract】 The process of sediment dispersal into deep-water can be significantly different in lacustrine basins from their well-studied marine counterparts in response to the interplay of climate change, lake-level fluctuation and sediment supply. The seismical well-imaged lacustrine clinothems in the Eocene Dongying Depression provide a good opportunity to bridge the deep-water sediment partitioning with clinothem architecture and shelf-edge trajectories. In the study area, the Eocene Dongying delta-complex is composed of alternating aggradational(AC) and progradationalclinothems(PC1) with diagnostic shelf-edge trajectories in terms of seismic reflectionarchitecture. Additionally, shelf–edge trajectory angle(θsht), clinothem toe distance(Td), aggradational height(Ah) and progradational distance(Pd) are introduced to quantify clinothem architecture. Aggradationalclinothems are characterized by ascending shelf-edge trajectories with thick and widespread sand-prone bottomsets, suggesting higher efficiency of sediment deliver into distant lake floor. Whereas progradationalclinothems are characterized by flat to slightly descending trajectories and generally lack bottomsets. Alternations of rising and flat to slightly descending trajectories accompanied with different clinothem types probably indicate frequently relative lake level changes. Further analysis of seismic images suggest the distally aggradationalbottomsets are generally consist of sub-lacustrine channel-lobe systems, whereas sediment slide, slump blocks occur in progradational-clinothem slope to slope toe areas, which indicate varied processes of deep-water sediment transport associated with different clinothem types and shelf-edge trajectories. Lake-level, sediment supply and water salinity/density change induced by humid-arid climate cycle are suggested to be main factors controlling clinothems stacking pattern and sediment dispersal into deep-lacustrine. Humid climate are considered to be related with agggradationalclinothems, during which increased water influx and precipitation prompt rising of lake level and decreasing in ambient water salinity/density, thus sediment can be directly transport to the distant bottomset areas through hyperpycnal channels due to increased sediment concentration and energy in river discharge. Whereas during dry periods, progradationalclinothems start to built under stillstand or falling lake level conditions, sediment generally accumulate at river mouth and collapse due to sediment overload. Therefore, a relationship between deep-lacustrine depositional process and climatic signature was established which may provide new thoughts in the study of deep-water depositional systems in lacustrine basins.更多还原