## 9 Conclusions  
On the basis of the analysis of sequence stratigraphy and seismic sedimentology of the Dainan Formation in the Gaoyou Sag, the developmental types and spatio-temporal evolution of depositional systems in each system tract in the faulted lake basin are discussed.  
1. Based on the relationships of seismic reflection terminations and sedimentary cyclic characteristics in the Dainan Formation of the Gaoyou Sag, the Paleogene Dainan Formation can be divided into three third-order sequences, each comprising corresponding LST, TST, and HST system tracts. The sediment thickness of each third-order sequence ranges from 300 to 500 m, with the stratigraphic distribution primarily controlled by the boundary faults of the sag, intra-basin fault activity, and fluctuations in lake level.
2. The Dainan Formation in the Gaoyou Sag comprises five sedimentary types: normal deltas, fan deltas, nearshore subaqueous fans, slump turbidite fans, and lake deposits. The distribution and characteristics of these sedimentary facies are influenced by the tectonic activities of the lake basin and the various stages of tectonic evolution. Specifically, the steep slope zone is dominated by nearshore subaqueous fans and fan deltas, while the gentle slope zone primarily develops normal deltas. Shallow lacustrine facies are distributed along the margins of the lake basin, whereas deep to semi-deep lake and slump turbidite fans are found in the central regions of the faulted lake basin.
3. The optimal seismic tuning frequency for sandstone thickness in the Dainan Formation of the Gaoyou Sag is between 16 and 24 Hz, based on the methods of seismic sedimentology. Amplitude-based seismic attributes effectively characterize the morphology of sandstone bodies and the distribution features of depositional systems in the northern gentle slope, southern steep slope, and central deep trough across different system tracts. Specifically, during the LST and HST deposition periods, the northern gentle slope zone develops multiple lobe-shaped deltas, while the southern steep slope zone is primarily characterized by fan deltas or nearshore subaqueous fans. Slump turbidite fans are primarily distributed in the deep trough. In contrast, during the TST deposition period, the scale of deltas in both the northern gentle slope and southern steep slope zones decreases significantly, while the deep trough develops deeper lake deposits.  
Conceptualization, X.Z. and Q.Z.; Methodology, X.Z. and X.H.; Software, X.H.; Validation, Y.X.; Formal Analysis, X.H., Y.D. and Q.Z.; Investigation, X.H.; Resources, X.Z.; Data Curation, X.H., Y.D. and X.W.; Writing--Original Draft Preparation, X.Z., X.H., Y.D. and X.W.; Writing--Review & Editing, X.Z., Y.D., X.W. and Y.X.; Visualization, Q.Z.; Supervision, X.Z.; Project Administration, X.Z.; Funding Acquisition, Y.X. All authors have read and agreed to the published version of the manuscript.  
Funding: This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The raw data supporting the conclusions of this article will be made available by the authors on request.  
**Acknowledgments:** We want to express our thanks to Jiangsu Oilfield Company, SINOPEC. They allowed us to use their geological and geophysical data. Many special thanks are given to [PERSON], who provided earnest guidance and support. We also thank [PERSON] for polishing the article and the reviewers for their constructive comments.  
**Conflicts of Interest:** The authors declare no conflict of interest.