Dear Jingzhe Li and co-authors,

Thank you for your revised manuscript. As you will have seen, reviewer 1 was satisfied that you had addressed their concerns. I had to bring in a third reviewer because the previous reviewer 2 was no longer available. This new reviewer is supportive of the manuscript being published if the following issues can be addressed thoroughly. I agree with the reviewers points, and would also like to suggest that you highlight more clearly the fact that this model is open source as an aspect that differentiates the work from many of the 'competing' models.

I copy the reviewers comments below. Please can I ask you to provide a revise manuscript addressing these issues.

Kind regards,
Paul Halloran, Topical Editor

Comments:

Two main features of Sedapp v2021 are put forward in this paper as major contributions to the field of Forward Stratigraphic Modelling: (1) The use of the distance from estuary as a parameter controlling sediment transport in shallow water environments and (2) an interplay between sedimentation and erosion controlled by a complex interaction between several lithological and environmental aspects simulated in the numerical model. While the first point was, in my opinion, was satisfactorily addressed and exemplified in the paper, the second point was only hinted in the introduction section and briefly mentioned in the methodology section. My main criticism of the work presented here is the lack of an in-depth explanation on how exactly erosion is handled by Sedapp v2021. Furthermore, none of the presented models show any visible effect of erosion affecting the simulated stratigraphic unities simulated. As this is mentioned as a major feature of Sedapp v2021, I truly believe the subject of how erosion is handled by this tool should be better detailed, especially concerning how lithologies that are more easily erodible are distinguished from "hardgrounds", and there should be at least one model clearly illustrating the effect of erosion in a simulated stratigraphic succession.

Major points on the paper:

1 - Line 47: Why “especially in the shallow marine environments”? There are several published papers about Forward Stratigraphic Modeling in continental and deep marine environments that attest to the applicability of this method in a variety of sedimentary environments. I think it would be better to cut off this statement to avoid the risk of misleading the reader to believe that Forward Stratigraphic Modeling is a method limited to shallow marine environments.

2 - Line 72: It is unclear to me what the authors meant by “fractal stratigraphic theory” and, unfortunately, I do not have access to the book they cited. Is it somehow related to Schlager’s (2004) scale-invariant fractal model for sequence stratigraphy? If so, I am not sure what would be the use of this citation here in reference to the formation of hardgrounds. I suggest rewriting that sentence to make clear what kind of hardgrounds the authors want to mention or finding a better example for the formation of strata resistant to erosion.

3 - Lines 72 and 73: By “This is actually a reflection of the efficiency ratio of deposition to erosion. This is less involved in the existing FSM models.” seem to imply that the existing FSM models do not take into consideration the dynamic between deposition and erosion. This would be simply not true as the dynamic between deposition vs. erosion according to the efficiency of sediment transport and sediment supply is part of the fundamental principles of some of the most used FSM tools. I think the authors should rephrase this part to make clear what they mean by “efficiency ratio of deposition to erosion” if they really think that it is something missing in other FSM tools.

4 - Line 115: What the authors mean by “hydraulic characteristic energy” in terms of oceanographic and sedimentological processes? And how does it differ from the environment energy represented by ε? I think it is important to mention what exactly E and ε were designed to simulate.

5 - Line 133: How exactly the model differentiates “hardground” from easily erodible layers? Is it somehow user-defined for cells in the model? Or is it automatically calculated for each cell in the model? If so, how is it calculated for each cell? In subtopic 3.2 the authors mention that a variety of lithological and environmental factors affect erosion rate in Sedapp v2021, but how exactly these factors are taken into consideration? As the “efficiency ratio of deposition to erosion” was mentioned as an innovative aspect of Sedapp v2021, I think it is important to understand how all parameters related to erosion work in Sedapp.

6 - Line 183: The proportions of sediment classes were changed between figures 3a, 3b, and 3c? I think it would be better to keep the same sediment proportions in a, b, and c to illustrate the effect of different depth-porosity curves alone. Might also be interesting to show the effect in compaction of varying the sediment proportions and keeping the same depth-porosity curve. But if for the sake of simplicity, the authors prefer to only show an example where both the depth-porosity curves and sediment proportions change, they must indicate in the figure legend what is the sediment proportion variation between 3a, 3b, and 3c.

7 - Line 219: I believe there is a missing reference to figure 7 by the end of this phrase.

8 - Line 221: The way geological time is counted in this paragraph and in figure 7 is very confusing from the point of view of a geologist. In geology, time is always counted backward as “years ago” or “years before present”. For geologists “Ma” always means “millions of years ago”. Sometimes “Myr” is used to indicate a time span in million years from one moment to another, rather than the “Ma” that is always in reference to the present day. So, in this paragraph and figure 7, it is like all ages are inverted from a geological point of view. I suggest using “Myr” instead of “Ma” if the author prefer to count time forwardly despite of the geological nature of the paper or even better invert all ages and use: t = 0 (10 Ma); t = 4 (8 Ma); t = 8 (6 Ma); t = 12 (4 Ma); t = 18 (2 Ma) and t = 20 (0 Ma). The same is valid for all ages in the following figures and paragraphs mentioning geological time.

9 - Line 229: I believe there is a missing reference to figure 8 by the end of this phrase.

10 - Line 277: I suppose there are things that Sedapp v2021 do better than the Sedpak model used by Li et al., 2018, hence the reason to publish this paper. How do Model 2 presented in this paper compare to the model presented by Li et al., 2018? What is the advantage of using Sedapp v2021? I think there is a good opportunity here to clearly state the contribution of Sedapp v2021 to Forward Stratigraphic Modeling. Please elaborate more.

11 - Lines 278 to 282: This part seems much more like results that should be presented in the previous section than Discussion. All models shown in figure 12 were made using Sedapp v2021? If so, this part of the text and figure 12 must be moved to the “Verification of Sedapp” section. Furthermore, it must be stated how exactly model 12a differs from 12b and model 12c differs from 12d. Is it only a matter of turning on and off the diffusive transport as a function of distance to shore? Or these models differ between them in another way?

12 - Lines 282 to 284: The statement about the preservation of shoreface profile angle seems misplaced in this paper. To the extent of my knowledge, the preservation of shoreface profile is always discussed in the context of the action of processes that do not seem to be simulated in Sedapp v2021, such as sediment reworking above the wave base and sediment collapse when a clinoform reaches a critical slope. There are plenty of examples in the literature about varying shoreface profiles during regressive system tracts when processes like these do not affect sediment deposition and preservation significantly. I do not see the point in discussing the preservation of shoreface profile if the processes that allow it are not taken into consideration individually by the models presented in this paper. Suffice to point out that in figure 12d the sigmoidal shape of the deltaic layers persists during the progradation of subsequent stratigraphic layers and that the slope break is never located landward of the shoreline (which is the true issue in figure 12c).
13 - Line 352: Missing year of publication?

14 - Figure 7: What are the min and max values of the color scale? It should be at least mentioned in the figure’s legend if not plotted on the figure.

Suggestions about minor points:
1 – Line 31: The word “archive” is used three times in the first paragraph to describe sedimentary deposits. I find the use of this word very unusual in this context. The meaning is clear, so I suppose that there is no problem in using the word “archive” there, but I would rather say something like: The sedimentary successions formed in these areas are an important record of the past interactions. In addition, shallow marine stratigraphic record itself can be an ideal hydrocarbon accumulation place. From this record, many theoretical and field studies have made great achievements and accumulated a wealth of data in the past decades.

2 – Line 43: I think there is a missing reference here. In my opinion, it would be appropriate to include here at least one citation about Dionisos. It is free for academic use and it pioneered the field of Forward Stratigraphic Modeling with a considerable contribution through dozens of published scientific works during the last 20 years. I suggest adding to the references either Granjeon and Joseph (1999) or Granjeon (2014) as these papers are more methodological.

3 – Line 76: This phrase seems a little too bold to me. Forward Stratigraphic Modeling has been evolving significantly in the last two decades, but it is true that the existing FSM tools still have many shortcomings. That said, although Sedapp v2021 appears to propose some clever solutions, it surely will not overcome all shortcomings of the existing models. I think “… is expected to overcome some of the shortcomings of the existing models” would be more appropriate.

3 – Lines 86; 104: I suppose the authors meant “class of sediment” instead of “class of lithology”.

4 – Line 153: What is “c”? I suppose c is the variable used in equation 9 in the previous topic to differentiate the characteristics of different sediment types, but this chapter is too far from the last mention of c. I had to go back in the text to understand what it was. I think it would be a good idea to reference equation 9 here to help a reader like me find where c was described.

5 – Line 160: I think “underlying strata” would be more appropriate than “lower strata”.

6 – Line 206: It would be nice to add a line in figures 5a and 5b representing the boundary between these two cycles as a visual reference for readers that are not used to analyze this kind of results. It would make it easier to identify the aspects of figure 5 mentioned in this paragraph.

7 – Line 263: What do the authors mean by “guide us to keep the general direction”? Validate the previously proposed conceptual model? This sentence is not clear. I suggest rewriting it.

8 - Line 264: This information is repeated in the following discussion section. I believe the comparison between the results presented in the present paper and previously published models should be left to the discussion section.

9 - Figures 8 and 9: Why there are blank spaces between layers? Is it a choice for displaying the model? If so, why is it presented like that? What were the criteria to display intervals with filled colors or as blank intervals? Why the blank intervals are sometimes thick in relation to the adjacent colored intervals and sometimes this relation is inverted?

My main criticism of the work presented here is the lack of an in-depth explanation on how exactly erosion is handled by Sedapp v2021. Furthermore, none of the presented models show any visible effect of erosion affecting the simulated stratigraphic unities simulated. As this is mentioned as a major feature of Sedapp v2021, I truly believe the subject of how erosion is handled by this tool should be better detailed, especially concerning how lithologies that are more easily erodible are distinguished from "hardgrounds", and there should be at least one model clearly illustrating the effect of erosion in a simulated stratigraphic succession.

Dear Shuyu Sun, Jingzhe Li and co-authors,

Thank you for your revision and response. I am pleased to say that I would like to accept your manuscript after the following minor changes have been made.

The changes you make In response to the comment around efficiency ratio of deposition to erosion are useful, but to my mind you do not yet answer the part fo the question about what the phrase “efficiency ratio of deposition to erosion” means. Please could you define what you mean by this, i.e. what efficiency means in this context?

Your response to the reviewer regarding the comment beginning “What the authors mean by “hydraulic characteristic energy”…” is useful. Please could you integrate this explanation in to the manuscript.

Your response to the author’s comment beginning “I suppose there are things that Sedapp v2021 do better than the Sedpak model…” is again very useful, but not reflected in the manuscript. As a model development paper it is valuable to contrast with alternative tools. Please can you incorporate this response in to the paper, making sure you evidence the points being made.

Your response to the reviewer comment beginning “Figures 8 and 9: Why there are blank spaces between layers…” is again something that would be useful to the reader. Could this be included in the figure caption?

Kind regards,
Paul Halloran, Topical Editor

Dear Shuyu Sun and co-authors,

Thank you for your minor revisions. I would like to accept the manuscript after one final extremely minor technical revision.

The two new sentences “This seems to have little thing to do with the transportation capability originated from the river injection. It’s more like the energy inherent in the basin that carries the sediments to the basin center.” Read a little awkwardly, and are not completely clear to me.

Can I suggest that you modify the 1st sentence to something like:

“This seems to have little to do with the transportation capability originated from the river injection.”

Then the 2nd sentence (“It’s more like the energy inherent in the basin that carries the sediments to the basin center.") is not completely clear to me, and I think it is saying almost the same thing as the final sentence in the paragraph. If I have understood what you are trying to say, perhaps the end of the paragraph could read:

This seems to have little to do with the transportation capability originated from the river injection, instead the most appropriate description is as the energy inherent in the basin that carries the sediments to the basin centre.

Many thanks for making these final changes. Kind regards,
Paul Halloran