To the Editor of

Earth System Science Data

Manuscript Number: essd-2023-65

Title: Subsurface geological and geophysical data from the Po Plain and the northern Adriatic Sea (north Italy)

Authors: Michele Livani et al.

REVIEWER SCORE: minor revisions

Respected Editor,

Dear Authors,

I reviewed the manuscript by Michele Livani and co-authors. The paper collects published and publicly available subsurface data of four (five) stratigraphic horizons and analyze them in order to provide a 3D reconstruction of them throughout the almost entire Po Plain. The 3D reconstruction is associated to a quantitative analysis of data accuracy and provide an interesting and useful evaluation of them, allowing the readers/users to evaluate the reconstruction accuracy and reliability.

I think that, given the journal purposes and its readership, the paper is suitable for publication and can be of help for a number of uses.

I have a main general comment and other minor/specific points that I hope the authors can consider and discuss; in some cases probably minor issues can be solved by rephrasing parts of the text and/or by better clarifying what the authors mean.

Given the wide scientific literature and dataset on the Po Plain, a paper where references and available data are homogenized and well organized is appropriate for ESSD.

In the following parts I list some general comments and more detailed/specific ones.

GENERAL COMMENTS

A general question is relative to the study area extent and to the choice of the available dataset. The authors include in their reconstructions and analysis only a slight part of the Venetian Friulian basin (east of the Schio-Vicenza fault). There are available data for at least three of their five analyzed horizons that cover the entire extent of this basin. Toscani et al., 2016 (Ital. J. Geosci., Vol. 135, No. 3), provide both isobath maps and geological cross sections of this basin. Also the cited paper of Nicolich et al., 2004 provide nice and complete data about some of the considered horizons in the Venetian basin subsoil. Moreover, the paper by Pola et al., 2014 (Ital. J. Geosci. (Boll. Soc. Geol. It.), Vol. 133, No. 2) provides a set of geological cross sections derived from seismic reflection profiles and well data that could allow to connect the surfaces through the Schio-Vicenza lineament (that apparently shouldn’t be an “obstacle” for the interpolation process and reconstruction, given that it is a subvertical mainly strike slip fault and the authors declare that in their reconstructions fault displacements are treated as vertical steps).

The same happens for the subsurface maps provided by Amadori et al., 2019; also in this paper 2 of the 5 analyzed horizons are considered and coherently reconstructed throughout a wide area of the Po Plain, also covering the area of the GEOMOL project.

Lastly, the authors do not consider and do not cite the outputs of the “Hotlime project” (see https://geoera.eu/projects/hotlime6/). In this case a depth converted surface of the top of the carbonates is provided almost all over the studied area but, surprisingly, it these relatively recent and well constrained data are not considered.

Apparently, the choice of the authors was to consider only dataset containing ALL the stratigraphic surfaces they decided to analyze? This is the case, for example, of the outputs of GEOMOL project, but, if this is the case, its reason appears to me obscure and questionable for the following reasons:

1. In this way the authors exclude from their study wide and potentially useful datasets (in particular on one of the less constrained stratigraphic horizon, top of the Carbonates, given the few number of wells surveying it)

2. IF the reason for not considering these dataset is that they provide just one stratigraphic horizon, this is apparently in contrast with the following procedures and quantitative analysis that consider the single surfaces.

3. It is not immediately clear the choice of not considering the previously cited dataset, given that in ch. 4.3 a list of the considered subsurface maps is provided

In my opinion, the authors should better explain and clarify their choice and clarify it in the text by correcting or supplementing their statement (lines 108-109) “In this work, we refined the previous regional 3D geological models extending the literature used to define the geometry of the geological surfaces”.

Another comment/request of clarification deals with the data selection and their preliminary analysis. The authors declare that they graphically rearranged the sections, imperfections were reduced, parts of the sections were re-positioned and (line 364) they declare that some sections have been excluded in case of inconsistencies with the contiguous ones. In my opinion, the criteria at the base of this selection should be clarified or explained providing a couple of examples, because in this way it is not clear which section(s) they decide is “wrong” and if there’s a quantitative parameter to define them as wrong (different depths of the horizons? Of all horizons or on one only? Which is the inconsistency amount to exclude a section? May be that on different sections there are big inconsistences on the carbonate top, but the Pleistocene base are comparable. How are treated the sections in this case? And which of the two is excluded?

I think that with a couple of examples, the reader could easily understand this point that quite heavily affects the dataset.

A request of clarification is relative to the assumptions that are always connected with data choice and selection. All the subsurface maps and cross sections considered in this paper are depth converted yet. The depth conversion process of seismic reflection profiles is based on a velocity model that strongly affects the final result. In the framework of a so detailed and quantitative data analysis, it sounds a bit strange to me that the authors do not cite and do not consider at all the possible inconsistencies, differences and may be errors given by the native velocity models on whom sections and maps are based. The authors could consider to add a brief paragraph (or a table in the supplementary material) indicating the range of the velocity values (if and when available) used in the original papers from where they selected sections and maps.

The last point deals with the chronostratigraphic subdivision (lines 189-200 in the manuscript). What the authors declare (pre- and post-2009 age of quaternary sediments) is true and can cause misunderstandings but I think that maintaining a pre-2009 subdivision in a paper published in 2023 will cause more misunderstandings and is formally wrong. In this case I warmly suggest to the authors to do an effort and to use the current stratigraphic subdivision.

MINOR/SPECIFIC POINTS (when possible, they will be listed referring to the line numbers of the manuscript)

LINE 28: in my opinion “strategies to ensure the safety of urbanized areas and human activities” usually need much more detailed studies at a different scale. I would say that this study can be of help in defining and highlighting areas where data collection and more detailed studies are needed for…

LINE 47: add Cassano et al to the references cited

LINE 87: same comment of line 28

LINE 128: probably Turrini et al., 2016 could be added to the references cited

LINE 130: in my opinion the best sections showing the outermost buried fronts of the two thrust belts are from Fantoni and Franciosi 2010 and Toscani et al., 2014).

LINES 129-132: if you change the order of the two sentences the pictures (2a and 2b) will be cited in the right order (2a before 2b) without any change in the general meaning of the paragraph.

LINES 140-143: a clarification of this paragraph would be of help. Probably the upper cycle is fed by the Apennine chain (as stated by the authors) close to the outcropping Northern Apennines, but throughout the Plio-Plesitocene the Alps are still providing sediments. In figs. 18, 20 and 21 of Ghielmi et al., 2013 all the entry points of the main sand systems are located close to the southern alps.

LINE 150: in the reference list, and in general in the paper, it should be added Fantoni et al., 2004 (Boll. Soc. Geol. It., 123 (2004), 463-476) where, in my opinion, one of the best stratigraphic sketch of the Southern Alps is presented.

LINE 174; I think other papers dealing with recent tectonic activity of the Po Plain should be cited (Livio et al., 2009; Zuffeti and Bersezio, 2020; Bresciani and Perotti, 2014)

LINES 209-211: I think this part should be moved at the beginning of the paper in order to declare since the beginning the possible lack of data

TABLE 2 AND FIG4A: it would be useful to highlight which wells drills the 4 horizons considered in the study. Different colors (and symbols in the table) for wells drilling the carbonates, for wells drilling the base of the Pliocene etc could be provided.

LINE 364: if I understand correctly , this means that you have a dataset of all collected sections but then on each of them you exclude the horizons that for different reasons are not usable. This means that the stratigraphic horizons have been reconstructed using a non-homogeneous dataset. Why not providing four maps reporting ONLY the sections used for a given horizon?

LINE 371-372: why not considering the surfaces from Amadori et al., 2029?

LINE 377: even if you provide a detailed analysis of data accuracy, it would be useful to provide some examples and values of this check. For example taking a well far from the digitized sections and not included in the interpolation process and check at which vertical distance the reconstructed horizon is from the values indicated in the logs. Possibly taking a well placed on the top of an anticline and another one along the monocline.

FIG. 9: just a suggestion (after a trial, the authors will decide if to follow this suggestion or not). Why not plotting on this map the section traces and the map polygons? If graphically possible, this would help in providing the readers an immediate view of the correspondence between digitized sections and maps and the reconstructed surfaces.

Paragraph 5.3 LINES 472-483: this part and its significance should be reorganized/rewritten and better clarified. I agree that if you have two (or more) vertical values in correspondence of a node, you can calculate the maximum and  minimum depth of the horizon in correspondence of the node, but it is not that clear why the range of depths at the nodeS (you mean all nodes?) quantifies the uncertainty of the level. I think that the uncertainty is associated with a single point. On a given level you could have nodes with different values along the vertical, and nodes where the vertical values are coincident. This means, in my opinion, that in the first point the uncertainty is high, while in the second is low. The level of uncertainty is different along the level.

Secondly, I would provide a percentage of these variations with respect to the maximum and minimum depth. The small (or big) variations in depth of different horizons should be evaluated with respect to the depth of the horizon. 2 km of variations on an horizon that reaches a maximum depth of 2 km is a 100% of variation; the same value (2km) if referred to a very deep horizon could be a 20% of variation so indicating a better coherence between different guesses.

FINAL REMARKS

As stated before, I found the paper of interest and I think it deserves to be published Earth System Science Data after minor changes that can be evaluated by the Editor without a second round of revisions.

I hope the previous suggestions/criticisms will be accepted as constructive and positively considered by the Authors and will encourage them to do few additional efforts to make the manuscript even more complete, readable and of wide interest.

Dear Authors,

Your article is welcome as it makes a great effort in collecting, organizing and homogenizing a large amount of data from the Po Plain subsurface, gathered over the last 70 years. Undoubtedly other projects pursued the same goal, however focusing to specific areas or specific stratigraphic intervals. The merit of this work lies on having produced a consistent analysis extended to the whole Po Plain and represents a useful database for future quantitative studies related to land management, seismic hazard etc. The assessment of the spatial accuracy of the dataset is remarkable and allows to inspect the quality of the results.

Considering the journal's target audience, this study certainly deserves publication.

There are some deficiencies that can be remedied to make the dataset more complete and accurate. Here are my comments.

GENERAL COMMENTS

I understand the difficulty of resuming the regional geology, but there are several imprecisions that may have a strong impact on the definition of the mapped surfaces. For example, where it is incorrectly written that the carbonate substratum is Triassic to middle Eocene, you are neglecting the early phase of Alpine Orogeny (Aptian-Maastrichtian), which in turn provides one of the most evident stratigraphic and seismic horizons in the Po Plain subsurface (top of Maiolica Fm). Actually, apart few isolated carbonate platforms in the distal foreland (e.g., Bagnolo platform), since the Aptian the Po Plain Alpine foredeep sedimentation is mostly characterized by marls (e.g., Di Giulio et al., 2001; Tremolada et al., 2008; Sciunnach et al., 2023). What you mean as Carbonate succession top is actually the top of Scaglia Fm, (Scaglia is marl to claystone sediment) and it marks the onset of full Alpine collision (e.g., a tectono-stratigraphic sequence boundary).

It is understandable, as correctly written in the text, the need of focussing on the main previous studies, selected for extension and detail, however I’ve missed the pioneering studies on the Po Plain shallow aquifers (ENI-RER, 1998; ENI-RL, 2002; Irace et al., 2010), which had a great importance in the definition of the most recent surfaces, whose one is possibly your base of the coarse-grained alluvial deposits. Various papers have also been published about this surface (R-surface, e.g., Muttoni et al., 2003; Garzanti et al., 2011; Scardia et al., 2012; Ghielmi et al., 2013).

About the surfaces you chose to focus on, I’ve found the stratigraphic approach not accurate: you define them as geological or lithostratigraphic surfaces, the former term being imprecise and the latter incorrect or not clear. Are they operational surfaces adequate for practical applications or have they been chosen because are more easily recognizable in well and geophysical data? I believe in the second hypothesis, but on the whole the stratigraphic meaning of these surfaces should be addressed more clearly and your choice (lithostratigraphic vs other kind) should be discussed according to the expected application of your dataset.

Specifically, the recognized surfaces can be considered as sequence boundaries with chronostratigraphic value. In this sense, the reference to Ricci Lucchi (1986) is misleading and obsolete, because it is based on lithostratigraphic units established for ENI operational purposes, and in my opinion not very useful in defining stratigraphic surfaces with chronostratigraphic value or regional extension. It would be more useful to rely on the more recent syntheses of Fantoni and Ghielmi, which frame the old ENI lithostratigraphic units into the modern sequence stratigraphy.

For example, the top of the carbonates, even if associated to the top of Maiolica Fm (see my previous comment) or to the top of the Scaglia, can be considered a tectono-stratigraphic sequence boundary produced by the onset of an Alpine tectonic phase (eoAlpine or neoAlpine, respectively) and the associated pulses of terrigenous input into the basin. Also the base of Pliocene is a tectono-stratigraphic surface (e.g., Ghielmi et al., 2013), which documents the effect of Apennine tectonics on the Po Plain, modifying the geometry of the previous basin.

The most recent surface, which deserves a more detailed discussion, is a climate sequence boundary (R-surface), well defined in the works of the Po Plain aquifers and in the already mentioned following scientific articles.

SPECIFIC COMMENTS

The magnetic basement is called Variscan (line 307) or Hercinian (lines 148, 152; Fig. 2): the former is preferable and should be used consistently in the text.

For the alluvial deposits you mention as youngest surface the correct term would be “coarse-grained” (not just coarse) and, if we use a sequence stratigraphy approach (R-surface of Muttoni et al., 2003), at east of Ferrara they pass to shallow-water fine-grained marine sediments (Scardia et al., 2012; Ghielmi et al., 2013;) and at Venice they are prodelta turbidites (Muttoni et al., 2018). Lithostratigraphically they would be different units but apparently you are putting them altogether into a same sequence. This is another example about the importance of defining and justifying the stratigraphic approach you want to use and applying it correctly.

Line 104: “geological maps”. Perhaps you mean stratigraphic maps or isobath maps, or better use just maps.

Line 146: carbonate substratum. See my comments about Maiolica and Scaglia.

Line 196: what do you mean with the reference to ENI S.P.A.? It is not in the reference list and it is not clear. Anyway, I agree with your discussion about the formal base of the Quaternary period, but the point here is how ENI defined the base of Quaternary in its wells. As far as I know, ENI’s base of Quaternary was defined by the FO of Hyalinea balthica in the Mediterranean Sea following the recommendations of the 18^th International Geological Congress (London, 1948; see for example discussion in Gradstein et al., 2012, p. 980). By the way, the FO of H. Balthica in the Po basin has been recently dated at ca. 1.9 Ma (Monesi et al., 2018) in the Arda River series. On the whole, you should discuss what you use actually as base of Quaternary also according to the stratigraphic data you’re including in your dataset.

Line 213: geologic maps, see my previous comment

Line 547: the typical Carbonate succession top in the Po basin is the top of Maiolica Fm (e.g., Fantoni and Franciosi (2010). The one you are using is the top of Scaglia Rossa. Actually, the Gallare Marls are also known as Scaglia Cinerea/Variegata on correlated exposures in the Alps and Apennines.