It is difficult to estimate paleobathymetry in sedimentary study.The modes of ＂indicator-paleowater depth＂ have been used as qualitative or semi-quantitative methods,but with challenges from hard samples requirement and low predicting precision.A new geometric approach-shoreline trajectory for quantitatively paleobathymetric analysis has been proposed based on the study of Dongying delta,middle part of third member of Paleogene Shahejie Formation（Es3-2） in the Donying depression.Shoreline trajectory is used to obtain the variation principle of accommodation and sediment supply under a point sediment supply.Backstripping and forwarding methods are combined to acquire the initial sediment thickness and the increment of accommodation in the top layer of each unit,respectively.The water depth in under-compensation areas in deltaic front facies can be expressed as the value of sediment thickness subtracted by accommodation.Both differential tectonic subsidence and sediment supply tendency are considered in this method,making it an accurate approach to predict water-depth variation in deltaic areas.This method is successfully applied in Dongying deltaic areas of Es3-2 where nine sets of progradation are developed,showing that the deepest water occurs in t3 with the maximum water depth up to 180 m.This method reveals the variation of water depth in deltaic area in detail,providing an effective way for quantitatively predicting the Spatial distribution of sediment.%古水深确定是沉积学分析中难点问题,目前主要依据＂标志物—水深＂的定性—半定量方法确定,但存在原始样品获取难、预测精度低等诸多问题。该方法依据滨线轨迹迁移规律获取在点物源背景条件下一个三级层序内可容纳空间与沉积物供给速率之间变化关系或定量函数,进而采用回剥法和正演法相结合获取不同点原始沉积物厚度和相应的可容空间,其中回剥法获取每个单元原始沉积厚度,正演法获取每个单元随沉积物覆盖后顶层可容空间增量。三角洲平原区为补偿区,其原始沉积物厚度等于可容纳空间增量,三角洲前缘区为欠补偿区,其水深等于可容空间增量与原始沉积物厚度之差。这一新方法不仅考虑到不同点构造沉降差异,而且还考虑了三级层序内沉积物供给速率的变化趋势,因而,较为准确地预测三角洲区的古水深变化。该方法成功地应用于东营地区三角洲沉积区水深变化,该区沙三中（Es3-2）共发育9期进积体,最大水深为180 m,出现于t3时刻。该方法揭示了9期三角洲朵体发育时期水深变化,为该区沉积体空间展布预测提供了有效的定量预测方法。
展开▼
