Overall, this paper represents a useful addition to the carbonate geochronology special issue. This paper represents a useful guide for those interested in the limits of U-Pb carbonate geochronology and will be of interest for those wondering whether their samples will be suitable for analysis. It also will be a useful methodological paper for those interested in choosing a mass spec to use for carbonate (and other common Pb bearing phases) geochronology. The spot size discussion and modelling at the end of the paper is also a helpful addition and discussion for those analysts keen on improving their carbonate geochronology data.

I am happy that the authors have addressed the reviewers comments where appropriate and I thank the authors for their considered response. As the authors have commented, the benefit of a completely open access journals that the dialogue between the reviewer and author can be seen by all. Some excellent points and discussion have been brought up in the comments to reviewers and it is a bit of a shame that not all of these have made it into the final paper, but I can see that it is somewhat beyond the scope to go into so much detail. I hope that interested readers will also delve into this published resource.

I only have a couple of minor additional comments:

Lines 104-110 calcite sample ages are reported in the analytical setup- this seems a bit unusual, would it be better to leave reporting the data until the results section? Or have the dates of these samples already been published in which case can you cite where these dates come from?

Nuriel et al., (in review) is now published so please update the reference.

Dear Andrew
your paper is now in excellent shape and ready to be accepted. There is only one point that has to be considered. As pointed out by the Associate Editor the paper Nuriel et al is published and should be referenced properly. The AE is a bit surprised that the data is presented a bit early in the paper. If you agree, you can move the table further down where it would be in a more appropriate place. However, this modfication is not essential and I leave it to your discretion.
Thanks a lot for submitting such a nice paper to our new journal. I hope it will help us all to establish a good reputation for GEOCHRNOLOGY.

Greetings
KLaus