## 6 Conclusions  
(1) There are mainly four lithofacies types of MSRs. As the terrigenous element content decreases, the water depth of deposition increases. Sandy dolostone develops in the subtidal zone under the influenced of storms. The mixing degree index was calculated based on the minor component proportions derived from mineral compositions interpreted from well logging. The B2, B3-1, B3-2, and B4 sublayers show a higher proportion of MSRs with high mixing degrees compared to other sublayers in the southern region.  
(2) The pore and throat patterns of MSRs reservoirs change with the mixing degree index. Sandstone and sandstone-bearing dolomites have the highest porosity and perme  
Figure 11: Distribution of MSR reservoirs across different mixed microfacies. (**a**) Distributary channel mixed with sandy flat; (**b**) sandy flat and dolomitic flat mixed with sandy dolomitic flat; (**c**) dolomitic flat and tidal shoul mixed with sandy dolomitic flat.  
ability among the MSRs, followed by dolostone, sandy dolostone, and dolomitic sandstone. Sandy dolostone exhibits the poorest reservoir quality. When the dolomite content in sandstone exceeds 25%, the pore-throat structure changes significantly. However, a small amount of sand in dolostone has little effect on the pore-throat structure.  
(3) The mechanisms driving mixed sedimentation include proximal reworked mixing and distal transported mixing. Proximal reworked mixing of distributary channel sands under tidal influence occurs in the transitional zone between distributary channels of the delta and the mixed tidal flat. The distal transported mixing model develops in the intertidal and subtidal zones of the mixed tidal flat under tidal influence.  
(4) The distribution of MSRs reservoirs is mainly controlled by provenance supply and tidal currents. The distance from the provenance area and paleo-topographic features determine the degree of mixing. Tidal currents directly rework terrigenous clastic particles and determine their final deposition locations. Mixed sandstone reservoirs are distributed on both sides of distributary channels and mouth bar. Dolostone-bearing sand reservoirs occur in the transition zone between sandy flat and dolomitic flat. Sandy dolostone deposits are typically thin and isolated, primarily due to storm activity.  
Formal analysis, writing--original draft preparation, J.H.; resources, writing--review and editing, funding acquisition, L.Y.; methodology, supervision, C.H.; project administration, B.Z.; visualization data, curation M.F.; investigation, W.Z., software, Y.F. All authors have read and agreed to the published version of the manuscript.  
Major Science and Technology Projects of CNOOC Limited under the 14 th Five-Year Plan (KJGG2022-0905).  
Not applicable.  
The original contributions presented in this study are included in the article.  
We thank China National Offshore Oil International Limited for providing rock samples. We thank the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation in China for the measurement. We thank reviewers for their constructive reviews of this manuscript.  
Author [PERSON], [PERSON], [PERSON] and [PERSON] were employed by the company China National Offshore Oil International Limited. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. [PERSON], [PERSON], [PERSON] and [PERSON] are employees of China National Offshore Oil International Limited, who provided funding and technical support for the work. The funder had no role in the design of the study; in the collection, analysis, or interpretation of data, in the writing of the manuscript, or in the decision to publish the results.