A New Paleobathymetric Approach Based on Shoreline Trajectory: An  example from Dongying delta in the third member of Paleogene Shahejie Formation

Key words: 
• paleobathymetry /
• shoreline trajectory /
• accommodation /
• Dongying Depression /
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Abstract: 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 (Es3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 Es32 where nine sets of progradation are developed, showing that the deepest water occurs in t3 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.