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the Creative Commons Attribution 4.0 License.
| 07 Dec 2021
Terrestrial records of glacial terminations V and IV and insights on deglacial mechanisms
Abstract. 40Ar/39Ar geochronology constraints to aggradational phases and grainsize variations show that the sedimentary filling of the Liri fluvial-lacustrine basin (central Italy) recorded the occurrence of deglaciation events associated with global meltwater pulses.
Integrating these data with those from the Tiber River catchment basin, we find a precise match between the ages of gravel deposition and the occurrence of moderate sea-level rise events which anticipate those more marked during the glacial termination V and IV in the Red Sea relative sea level curve.
Such correspondence suggests that gravel deposition is facilitated by melting of Apennine mountain range glaciers, which provide the water transport energy and a surplus of clastic input to the rivers draining the mountain regions and flowing into the Tyrrhenian Sea. Therefore, the thick gravel beds intercalated in the sedimentary filling of the catchment basins of the major rivers in central Italy may be regarded as an equivalent proxy of large deglaciation events, similar to the ice-rafted debris in northern Atlantic.
Consistent with this hypothesis, we also show the close correspondence between the occurrence of particularly mild (warmer) minima of the mean summer insolation at 65° N and these early aggradational phases, as well as with other anomalous early sea-level rises occurred 750 ka and 540 ka at the onset of glacial termination VIII and VI, and 40 ka at the onset of the so-called Heinrich events.
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Interactive discussion
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RC1: 'Comment on cp-2021-161', Anonymous Referee #1, 12 Jan 2022
I read with interest the manuscript “Terrestrial records of glacial terminations V and IV and insights deglacial mechanism” by Marra and co-authors. This work shows some advances in the knowledge of the Liri basin but in my opinion it lacks of alternative interpretations of the sedimentary data and consequently of the sedimentary evolution. The interpretation seems to be equalize to a single hypothesis, the most unlikely, in order to be suitable for the Journal. I think that the work has to be rejected; it needs to be completely reconsidered and then submitted to another journal focusing not only on climate but also on geodynamics and basin analysis.
I list the reasons why I made this decision as follow.
- In the title the Authors clearly stated that the discussion will be about deglacial mechanism during terminations. But, first of all, where are the glaciated areas? No figures show them, no mentions in the geological background. In the Liri catchment, according to Giraudi (2011) evidence of glaciations can be ascribed to the LGM, older glaciations are lacking, or not yet studied. Anyhow, potential glaciers could be inferred in the Ernici, Meta, and Serralunga mounts. These are characterized by karstic environments, so the potential meltwater could have been captured by karstic circulation (for the argument see Zebre and Stepisnik, 2014 ESPL). Moreover, the supposed meltwater streams, before reaching the study area, could have been deposited in upstream basins, like Sora and Atina. For example, the Pescosolido alluvial fan. So, for having deglaciation, it needs glaciers, and these are not reported. This question can alone show the weakness of the work.
- Geological background. The Liri catchment is characterized by several mountain basins that can act as sediment trap. The geological background is focused only in the Latin Valley, skipping the innermost sectors towards N and NE. A better framework of the tectono-geological and geomorphological evolution of the catchment, including Roveto valley, is basic for understanding the sedimentary evolution of the drainage, and the possible presence of meltwater streams. This information can also help to understand the presence of lacustrine basins and their fading into fluvial environments. In Muttoni et al (2009 EPSL, fig 1) the presence of damming ridges were supposed. Considering the presence of the wide lacustrine basin of Sora just upstream, a break of the threshold (see Carrara 1991 Il Quaternario) could have completely renewed also the downstream sectors between Ceprano and the confluence with the Garigliano river. After the junction, the river flows through the southern sector of the Volsci range at the boundary with the Roccamonfina volcano, this before arriving at sea. I wonder if such volcanic structure took a part in the upstream basins’ evolution. Active faults are also documented (Bidittu et al. 2012). Moreover, tectonic structures reported in figure 2, especially faults A and B are not reported in the recent geological map (Ceccano Sheet) at the scale 1:50.000 (Centamore and Dramis, 2015) (http://www.isprambiente.gov.it/Media/carg/402_CECCANO/Foglio.html). How the sedimentary evolution described in chapter 5.1 and figures 6 and 7 can be presented with supposed fault?
- Sediment characterization. The sedimentology is related to previous works. The reinterpretation of the geological sections needs to be justified. For example, Isoletta section showed in the supporting material (figure S7) shows a layer of gravels that in Pereira et al (2018 QSR) are not reported but only sand layers, with volcanoclastic facies in the lower part. The gravels drilled in Ceprano cores, at -34-38 m, are described in Muttoni et al (2009 EPSL) as “subangular” and ascribed to an alluvial fan. Are these related to the Liri? Or to a stream flowing down the nearby Volsci mounts? Any provenance analysis? For example, in Devoto (1965 GR) there is a rough description of the gravel succession in Ceprano and S. Giorgio al Liri, pointing to a mix of volcanoclatic clasts and carbonates, with abundant quartz in the sands. The correlation across the basin of gravel units, actually very thin, must take into consideration facies and provenance. They can be simply different sedimentary episodes not strictly related. Also the development of volcanoes in the Volsci can have contributed in some way to geomorphological modifications, including the availability of volcanoclastic sediments, as reported by Pereira et al. (2018 QSR).
- The 8 new datings provided in this work are reported in different way in the text. Especially CE-1 and CE-2 have to be considered as post quem ages as reported in some figures but not in the table, in figure 8 or in the text at lines 293 and 295. The assumption at line 295-297 is not acceptable because they take into consideration just a single grain and there is no reason to think to the possibility that also younger crystals can be found in such reworked sediments. In this perspective, CE-1 indicates that the age of the gravel GH1 can be 452 ka to about 400 ka, the sedimentation of such thin gravel bed can be instantaneous geologically speaking, in respect to the overlying lacustrine deposits. CE-2 is again post quem and may be younger. The age of GH-2 is based on two post quem datings (Fig.6) and at Isoletta the original description (Pereira et al. 2018 QSR) shows sand and not gravels. The sedimentation rate of figure 4 has no mean because it is referred to 2 points that are post quem ages, the sedimentation rate reported in Muttoni et al (2009 EPSL) can be taken into consideration, but the new ages suggest a re-discussion. I also ask why the information given by pollen analysis of the Ceprano 1 core reported in Manzi et al. (2010 JHE) is not discussed for matching to your climatic discussion. The Pignataro Interamna upper lacustrine is tentatively ascribed to the fluvial unit upstream, but no chronology is provided for such correlation. In this way the chronology is too poorly detailed for very tight climate discussion.
- Alternative driver mechanisms. In such complex structural and geomorphological sector of the Apennines, the only hypothesis considered for depicting the evolution of the Latin valley (Fig. 7) is the most unlikely: the deglaciation from unknown glaciers and the relationship with sea-level changes of a coastline located far away and separated from the basin by a range and the Roccamonfina Volcano. The presence of gravel layers cutting lacustrine deposits (GH1) can be also determined alternatively by the failure of a dam or a threshold, and this can be ascribed to fault activity, threshold erosion, river piracy, etc. The gravel progradation can be ascribed to upstream reorganization of the catchment due to uplift, drainage changes, volcanic activity, etc. The abundance of travertine units (see Carrara 1991 Il Quaternario) could have also played a role. The presence of sand and gravels in a fluvio-lacustrine environment, such as the middle and upper succession can be simply related to channel avulsions. It is possible that all these drivers can be discarded, but it would be important to know why. The relationship to sea-level changes is related also to the Tiber valley (also too largely described in the setting), but I personally think that the geological/geomorphological framework is quite different. Anyhow for a robust correlation to sea-level changes and discussing about climate cycles, and also about depositional sequences, the availability of coastal successions in connection to the continental would be basic. No mention is provided about the coastal succession and they connection to those of the Latin valley. Here the separation from the coast area by a range with an active volcano hamper any consideration. Let’s why I think that chapter 5.3 is, in this perspective, a nonsense, especially the recognizing of early phases of se-level rising.
- Introducing figures need to be more informative (like in Pereira et al., 2018 QSR for example), especially figure 2 that would include all the information for understanding the complexity of the area. Figure 6 is key for understanding the correlations, some logs (also those provided in the supplemental data) are different from the original ones. What are the dashed lines? Basal surfaces? What represents the blue one? Why some of them cross the travertine in Pontecorvo? The Pignataro Interamna upper lacustrine correlation with fluvial unit of Isoletta looks a bit forced. Figure 7 is quite rough and many steps are unclear (also following the text).
best wishes
Citation: https://doi.org/10.5194/cp-2021-161-RC1 -
AC1: 'Reply on RC1', Fabrizio Marra, 13 Jan 2022
Our paper deals with the deglaciation signal at global scale and the possible forcing mechanisms based on a sedimentary record spanning 450 - 350 ka. In contrast, the reviewer discusses details of the local geology which represent the effect of the morphotectonic processes acting after the Last Glacial Maximum and have no relation with those responsible for the emplacement of thick horizons of coarse gravel during time spans precisely bracketed by 40Ar/39Ar age constraints and coinciding with the glacial terminations V and IV.
We apologize for not having referred to the local literature which described the evidence of glaciation in the central Apennines. We have given it for granted that a significant ice sheet would had occurred during the glacial maxima on a mountain range culminating above 2000 m; however, this is not a justification for not having cited the valuable and detailed work by Giraudi (2011) and we make amend.
Once this is acknowledged, we must say that we have found the comments by this anonymous reviewer contradictory at places, and biased by a complete lack of perspective.
Indeed, the reviewer says that the paper should be rejected because it does not provide any evidence of the presence of the glaciers, except to point out him/herself on the widespread evidence of glacial forms in this region reported in the local literature.
Moreover, the reviewer throughout his/her excursus mentions a series of very local sedimentary processes and several morpho-structural features characterizing the post Last Glacial Maximum Liri basin, without considering that, due to an extremely intense extensional tectonic phase coupled with a regional uplift in the order of hundreds of meters occurred in the last 250 ky, the present features may be very different from those which characterized this region 450.000 and 350.000 years ago.
For example, the reviewer completely ignores the fact that there is no evidence for gravel deposition within the Liri Basin after 350 ka, as shown by the geologic record that we have precisely dated. Therefore, it is clear that the present-day morpho-tectonic and hydrographic features that the reviewer describes have no relationship at all with those characterizing this region 450 through 350 ka.
Indeed, the subject of our paper is represented by two several meters thick and several tens of kms wide coarse gravel horizons which the provided geochronologic constraints demonstrate are deposited during well circumscribed time spans, at 450 and 350 ka, broadly coinciding with the glacial terminations V and IV.
As a matter of fact, large glaciers were surely present (as also the reviewer agree) and, despite all the possible traps and accidents that affect the present day basin, huge amounts of very coarse gravel were transported from the higher portions of the basin and deposited in two ~4 m thick layers in an area stretching up to 30 km within the basin.
Therefore, we believe that all the objections raised by the reviewer are superseded by these facts, and his/her criticism relies on discussing hypothetical minor aspects of the sedimentary processes and of the present-day hydrographic and geomorphologic features of the basin which have no relation with the large-scale processes investigated in our paper, and which have no consequence and impact at a global scale.
Therefore, his/her comments must be rejected, apart from some useful indications for improving the clarity of the text and of the figures.
While believing that the considerations above are sufficient to highlight the inconsistency of the reviewer's arguments, and a hassle on the details of the local geology would not interest an international audience, a point-by-point rebuttal of all the sometimes finicky issues raised by the reviewer in his/her detailed comments will be posted in a while, for those who are concerned. Here we just remark that many objections, like that on the post-quem character of the ages and on the sedimentation rate, do not take into account the explanation and the argumentation provided in the text and seem to arise from an inaccurate reading or lack of understanding.
Citation: https://doi.org/10.5194/cp-2021-161-AC1
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AC2: 'Comment on cp-2021-161', Fabrizio Marra, 01 Feb 2022
Point by point answers to Reviewer #1's comments
- Evidence for glaciers in the Apennines. The reviewer states that the weakness of the paper is that for having glaciations it needs glaciers and these are not reported. We will report the evidence of glaciations according to Giraudi (2011) in Figure 1 and add reference to this work.
- Geological background. All the long paragraph in which the reviewer describes in detail the features of the Present-day Liri catchment basins are irrelevant with respect to the topics of our work which is focused on the fluvial-lacustrine deposits emplaced 450 and 350 ka within a completely different morpho-structural basin. As a matter of facts, two several meter-thick coarse gravel horizons were emplaced within the Liri basin 450 ka and 350 ka, as evidenced by the 40Ar/39Ar age constraints provided in the paper.
Regarding the hypothesized tectonic structures, most of those reported in Figure 1 are based on a wide literature (e.g., Cardello et al., 2020; Centamore t al., 2010; Sani et al., 2004). For what concerns faults A and B, the fact that they are not reported in the recent geological map doesn't necessary imply that they do not exist. The 1:50.000 geologic map is based on the survey of surface evidence; in contrast, the inferred faults are hypothesized based on the interpretation of original subsurface chronostratigraphic data provided in our work.
The surface effects of these faults, even if they were active until 250 ka, only (that's during the climax of the extensional phase that affected this portion of the Apennines and was followed by a steady tectonic uplift since 250 ka), can be detected in the morpho-structural features of the Liri basin highlighted in Figure 1a.
- Regarding the concerns about sedimentologic characterization, it is clearly stated in the paper:
Also due to the fact that several geologic sections that are included in this study are no longer exposed and stratigraphic data have been obtained from the literature, here we adopt a relatively simple but effective sedimentological approach based on the identification of three main granulometric classes, aimed at providing information on the energy of transport and the related sedimentary environments within the Sacco-Liri catchment basin:
- coarse gravel (max diameter of pebbles >2 cm), tractive fluvial environment of high transport energy;
- coarse sand with sparse fine gravel (max diameter of pebbles ≤2 cm), fluvial environment of mid transport energy;
iii. silt, clay and carbonate-rich mud; lacustrine and, subordinately, alluvial environment of low transport energy.
However, for assurance of the reviewer, author Italo Biddittu originally investigated all the geologic sections reported in previous literature, providing a detail documentation of their stratigraphy, which is far enough to accomplish the goals of the present study, and can report on the correctness of the descriptions provided in the paper.
Moreover, myself, Fabio Florindo and Giovanni Muttoni have re-analyzed cm by cm the sedimentologic features of the cores of the two boreholes previously described in Muttoni et al. (2009) and presently hosted at the Milano University.
Finally, all the sedimentologic details that the reviewer mentions have no direct implication on the topics of our study.
- Geochronology. The reviewer is evidently not a geochronologist and has not carefully read the explanation of the principles on which the detrital sanidine method is based. Indeed, the accuracy, as well as the limitations of the 40Ar/39Ar ages are clearly and thoroughly discussed in a dedicated section (3.3 Detrital sanidine dating approach). Moreover, all the dated samples are discussed one by one in a dedicated supplementary text (Supplementary Material #1B - Age data and interpretations).
We briefly report here some considerations:
The youngest crystal (or the youngest crystal population in case two or more crystals yield consistent ages at two sigma) in the sedimentary samples provides a maximum age (terminus post quem) to the time of deposition of the sediment (i.e., the age of the sediment must be younger or equal to that of the youngest crystal(s)). However, as discussed in Marra et al. (2019), the occurrence of continuous eruptive activity throughout the Middle-Upper Pleistocene in the volcanic districts of central Italy allows to assume the lack of younger ages corresponding to known, large eruptions as a relative upper age-constraint. Indeed, incorporation of crystals from the youngest, stratigraphically higher eruption has higher probability with respect to those of older eruptions, and their absence should be considered statistically improbable when a large number of crystals (e.g., ~30) is dated. Therefore, it is reasonable to assume that the time of emplacement must be close to the youngest population age.
Also regarding the sedimentation rates, the reviewer seems to have not read the supplementary material in which this issue is discussed in detail. We report here the full discussion of the ages of the two samples collected in the Ceprano boreholes and their implication on the sedimentation rate:
Samples CE-1, CE-2 (this work)
Sample CE-1 was collected in borecore Ceprano 1 at 39.3 m depth within a coarse gravel layer with abundant sand matrix. The youngest crystal out of a population of 30 extracted from this sediment yielded a 40Ar/39Ar age of 452.4±1.8 ka (2 uncertainty). Sample CE-2 was collected at 15.1 m depth in borehole Ceprano 2, at the base of a coarse sand layer and yielded a youngest crystal date of 389.6±2.7 ka (2 uncertainty).
These two maximum ages can be regarded as statistically significant even if based on one single crystal. The Ceprano boreholes were drilled in Campogrande which is located on the left hydrographic side of the Sacco catchment basin, a sector draining the most active and densely vent-populated volcanic area of the Volsci Volcanic Field. A climactic eruptive phase occurred at the VVF in the interval 420 - 350 ka9, so the lack of crystals younger than 453 ka is strongly suggesting that the emplacement of the sand deposit occurred before the start of this volcanic phase. Consistent with this hypothesis, there is one crystal of 428±10 ka along one youngest crystal of 390±3.6 ka in the sample stratigraphically above. Moreover, these two ages along with that of 350.8±8 ka on the primary layer occurring at the top of the sedimentary succession recovered in the Ceprano boreholes10 provide a constant sedimentation rate of 38 cm/ky (see Figure 4 in the main text), which accounts for the exactness of these ages.
Therefore, it is reasonable to assume that also the maximum ages derived from reworked sanidine crystals can be regarded as providing precise time constraints to sediment deposition, as the one on the primary volcanic layer.
Indeed, and age close to 453 ka for the gravel deposition during MIS 11 is in perfect agreement with the constraints provided from the Paleo-Tiber aggradational successions, which bracket it between 451±2 and 445±3 ka11 (Figure 8 in the main text).
- Forcing mechanism on gravel deposition. The reviewer states that the hypothesis considered for gravel deposition, i.e.: deglaciation process, is the most unlikely. However, 25 years of dedicated literature contradict this statement:
Alvarez, W., Ammerman, A.J., Renne, P.R., Karner, D.B., Terrenato, N., Montanari, A., 1996. Quaternary fluvial-volcanic stratigraphy and geochronology of the Capitoline hill in Rome. Geology 24, 751-754.
Karner, D.B., Marra, F., 1998. Correlation of fluviodeltaic aggradational sections with glacial climate history: A revision of the Pleistocene stratigraphy of Rome. Geological Society of America Bulletin 110, 748–758.
Karner, D.B., Renne, P.R., 1998. 40Ar/39Ar geochronology of Roman volcanic province tephra in the Tiber River valley: Age calibration of middle Pleistocene sea-level changes. Geological Society of America Bulletin 110, 740-747.
Marra, F., Florindo, F., Karner, D.B.,1998. Paleomagnetism and geochronology of early Middle Pleistocene depositional sequences near Rome: comparison with the deep sea 18O climate record. Earth and Planetary Science Letters, 159, 147-164.
Florindo, F., Karner, D.B., Marra, F., Renne, P.R., Roberts A.P., Weaver, R., 2007. Radioisotopic age constraints for Glacial Terminations IX and VII from aggradational sections of the Tiber River delta in Rome, Italy. Earth and Planetary Science Letters 256, 61-80. doi: 10.1016/j.epsl.2007.01.014.
Marra, F., Florindo, F., Boschi, E., 2008. History of glacial terminations from the Tiber River, Rome: Insights into glacial forcing mechanisms. Paleoceanography 23, 1-17. doi:10.1029/2007PA001543
Marra, F., Bozzano, F., Cinti, F.R., 2013. Chronostratigraphic and lithologic features of the Tiber River sediments (Rome, Italy): implications on the Post-glacial sea-level rise and Holocene climate. Global and Planetary Change. https://doi.org/10.1016/j.gloplacha.2013.05.002
Grant, K.M., Rohling, E.J., Ramsey, C.B., Cheng, H., Edwards, R.L., Florindo, F., Heslop, D., Marra, F., Roberts, A.P., Tamisiea, M.E., Williams, F., 2014. Sea-level variability over five glacial cycles. Nature Communications 5, 5076. doi:10.1038/ncomms6076
Marra, F., Rohling, E.J., Florindo, F., Jicha, B., Nomade, S., Pereira, A., Renne, P.R., 2016a. Independent 40Ar/39Ar and 14C age constraints on the last five glacial terminations from the aggradational successions of the Tiber River, Rome (Italy). Earth Planet Sci. Lett. 449, 105-117. doi:10.1016/j.epsl.2016.05.037
Marra, F., Florindo, F., Anzidei, M., & Sepe, V., 2016b. Paleo-surfaces of glacio-eustatically forced aggradational successions in the coastal area of Rome: assessing interplay between tectonics and sea-level during the last ten interglacials. Quaternary Science Reviews 148, 85-100. http://dx.doi.org/10.1016/j.quascirev.2016.07.003
Marra, F., Jicha, B., Florindo, F., 2017. 40Ar/39Ar dating of Glacial Termination VI: constraints to the duration of Marine Isotopic Stage 13. Scientific Reports 7, 8908. doi:10.1038/s41598-017-08614-6
Luberti, G.M., Marra, F., Florindo, F., 2017. A review of the stratigraphy of Rome (Italy) according to geochronologically and paleomagnetically constrained aggradational successions, glacio-eustatic forcing and volcano-tectonic processes. Quaternary International, 438, 40-67. http://dx.doi.org/10.1016/j.quaint.2017.01.044
Marra, F. Costantini, L., Di Buduo, G.M. Florindo, F., Jicha, B.R., Monaco, L., Palladino, D.M., Sottili, G., 2019. Combined glacio-eustatic forcing and volcano-tectonic uplift: geomorphological and geochronological constraints on the Tiber River terraces in the eastern Vulsini Volcanic District (central Italy). Global and Planetary Change 182,103009. doi:10.1016/j.gloplacha.2019.103009.
Pereira, A., Monaco, L., Marra, F., Nomade, S., Gaeta, M., Leicher, N., Palladino, D.M., Sottili, G., Guillou, H., Scao, V., Giaccio, B., 2020. Tephrochronology of the central Mediterranean MIS 11c interglacial (~425-395 ka): new constraints from Vico volcano and Tiber delta, Central Italy. Quaternary Science Reviews 243: 106470.
Giaccio, B., Marino, G., Marra, F., Monaco, L., Pereira, A., Zanchetta, G., Gaeta, M., Leicher, N., Nomade, S., Palladino, D.M., Sottili, G., Guillou, H., Scao, V., 2021. Tephrochronological constraints on the timing and nature of sea-level change prior to and during glacial termination V. Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2021.106976
Marra, F., Pereira, A., Boschian, G., Nomade, S., 2021a. MIS 13 and MIS 11 aggradational successions of the Paleo-Tiber delta: geochronological constraints to sea-level fluctuations and to the Acheulean sites of Castel di Guido and Malagrotta (Rome, Italy), Quaternary International, in press. https://doi.org/10.1016/j.quaint.2021.12.016
- Figures. We will take into account the suggestions to improve clarity of the figures.
Citation: https://doi.org/10.5194/cp-2021-161-AC2 -
CC1: 'Comment on cp-2021-161', Gianluca Marino, 19 Feb 2022
Marra et al. present new, valuable chronological (40Ar/39Ar) constrains on the timing of rapid ice-sheet melting/sea-level rise prior and at glacial terminations V and VI from the Liri fluvial-lacustrine basin in central Italy. The timing of rapid ice-sheet melting (at glacial terminations) is an essential piece of information, especially when this can be radiometrically constrained because it allows unambiguous comparison with the timing of insolation changes. Addressing the relationship between ice-sheet melting and insolation changes is one of the scopes of the study by Marra et al. and a key question in palaeoclimatology.
The “sedimentological” approach presented in the manuscript was used previously and successfully by Marra and his group both in the coastal and more inland sections of the Tiber catchment basin. Although it does not provide a quantitative sea-level reconstruction their approach is valuable, in that these sedimentary successions are sensitive “detectors” of past episodes of rapid sea-level rise (melt-water pulses), while the 40Ar/39Ar dating ensures firm constraints on the timing of these melt-water pulses.
The timing of meltwater pulses at the two terminations are consistent with previous studies centred on the Tiber catchment basin, which lends confidence to the reconstructions presented in this study. The most interesting (and to some extent surprising) finding of the manuscript is the occurrence of meltwater pulses/events during the glacial maxima that preceded both T-V and T-IV. The two intervals (glacial-interglacial cycles) have very different glacial histories (MIS 12 was plausibly way more glaciated than MIS 10, e.g., Spratt & Lisiecki, 2016 [Climate of the Past]) and insolation forcing. It is also worth mentioning that T-V and T-IV are very different terminations with the rates of ice-sheet melting/sea-level rise for the former (latter) being slower (faster) that for most (all) of the last five terminations (Grant et al., 2014 [Nature Communications]). I think the manuscript would benefit from a deeper discussion on this aspect prior to discussing the “mild insolation minima” mechanism (section 5.3). Glacial maxima are generally considered relatively stable intervals in which ice sheets are close to equilibrium with the forcing before their supercritical size makes them more sensitive to rising insolation (Raymo, 1997 [Paleoceanography]; Abe-Ouchi et al., 2013 [Nature]). Figure 9 shows that these events coincided with episodes of millennial-scale variability/Heinrich events. Do the authors think that these events of millennial-scale variability/meltwater pulse are entirely orbitally controlled?
Finally, the manuscript brings together a wealth of chronostratigraphic information from various locations of the Liri fluvial-lacustrine basin that is instrumental to the determining the timing of past meltwater pulses around T-V and T-IV. In its present form the results are hard to read. I would recommend to better integrate and make more concise this section of the manuscript.
Citation: https://doi.org/10.5194/cp-2021-161-CC1 -
AC3: 'Reply on CC1', Fabrizio Marra, 19 Feb 2022
We thank Gianluca Marino for his kind review and the useful suggestions to improve the completeness and clarity of the paper.
We realize that our paper, as it is, only provides a qualitative approach to the possible explanation of the occurrence of meltwater pulses events during the glacial maxima that precede the glacial termination. We provide geochronologic constraints to these events and we show that they are broadly coincident with several Heinrich-like events, as well as, with particularly moderate (mild) insolation minima. Moreover, such double correlation generate a "short circuit", implying, as Gianluca Marino remarks, that episodes of millennial-scale variability/Heinrich events might be entirely orbitally controlled. A fact that most of the paleoclimate community wouldn't welcome, and that we didn't even intend to claim.
Therefore, while we believe that our paper not necessarily has to establish the triggering mechanism for the detected episodes of deglaciation, we strongly agree that this aspect needs a more in depth, and clear discussion.
In particular, a more comprehensive spectrum of possible mechanisms should be discussed, for example the instability of the ice-sheets when approaching their supercritical size, as suggested by Gianluca Marino. Moreover, we agree that a disambiguation on the coincidence between Heinrich events and "mild" minima is necessary, with a more detailed information on the model published in Paleoceanography by Marra et al. (2008).
For what concerns the chronostrarigraphic information provided in the paper, if the Editor will ask us to resubmit a revised manuscript, we will have care to shorten and clarify this section, leaving only the information that is functional to the aims of our study, and moving the detail of the stratigraphy and the tectonic evolution in the supplements.
Citation: https://doi.org/10.5194/cp-2021-161-AC3
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AC3: 'Reply on CC1', Fabrizio Marra, 19 Feb 2022
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RC2: 'Comment on cp-2021-161', Anonymous Referee #2, 24 Feb 2022
I have carefully read the article entitled "Terrestrial records of glacial terminations V and IV and insights on deglacial mechanisms".
From a formal point of view, the overall presentation is well structured and clear, the language used by the authors is fluent and precise and the manuscript is easy to read. The references are up-to-date, including recent ones.
However, although it provides new chronological data on sedimentation events that may help reconstructing a palaeoclimatic interpretation in the basin, there is important stratigraphical and sedimentological information missing in order to back up the palaeoclimatic inferences presented in the article. Therefore, I think that the article should be accepted after major revisions have been undertaken.
In terms of the content, as I am not familiar with the geology of the region on which the study is focused nor with the references or previous geological work developed in the area, I have approached this revision purely as a stratigrapher and sedimentologist, looking at the formal aspects of the manuscript, at the type of data supplied by the authors and checking whether the discussion and conclussions they provide are soundly supported by the data they present and if they fit into the scope of the journal.
I will start with a general overview, to then land onto the specific comments addressing questions or issues that have arosen while reading the manuscript.
General overview
Although the article shows a thorough chronological study, proper stratigraphical and sedimentological interpretation of the sections is missing in order to provid a solid background for their conclusions regarding the past climate in the studied area.
From my point of view, the basis for a proper chronostratigraphical framework in any basin requires a previous solid stratigraphical framework to correclty locate the beds into all the sequences, which needs a detailed correlation among the different sections, that in turn requires a characterisation of the facies and an interpretation of the different subenvironments that they represent. Without this, the reliabiliy of the chronological frame is at risk.
From a sedimentological point of view, the article is lacking a proper study on the facies nature and their environmental (climatic) interpretation. They mention at the beginning three granulometric classes that they propose, which from a palaeoenvironmental point of view is too simplistic, but then they use an old classification by Devoto, 1965 when describing the stratigraphical sections, an old paper that is inaccessible to most readers. Apart from a very vague description of the three types of sediments that Devoto mentions, no real facies analysis is performed. Moreover, a detailed facies interpretation may provide valuable climatic information that has been disregarded in the present study.
Even when the authors have nine stratigraphical sections available, the correlation panel shown and the palaeogeographical reconstruction of the basin in different moments are too basic, so the reader does not know what kind of depositional environment is represented by each section nor is able to determine whether the correlation among different gravel beds has been properly carried out, which directly affects the dates that the authors present as the base of their work.
Regarding the linking of these continental gravels with sea-level changes, I personally think that without first establishing a proper stratigraphical frame for the continental area and without detailed correlations with other sections in coastal areas, it is too risky to interpret variations in potentially fluvial grain size as sea-level changes due to glacial terminations. Upstream sedimentology may be affected by tectonism, climate and base-level changes. If there was a lake damming the water at some point in the basin between the upstream facies (potentially related to glaciation/deglaciation events) and the mouth of the river (where sea level changes would have a direct record), the lake would act as a local base level, its fluctuations affecting the behaviour of the sediments upstream, and thus disconnecting their response to the sea level changes. The authors keep mentioning the word "lacustrine" whithout properly describing the facies or the subenvironments in which they appear, not considering whether there was a lake, several lakes, wetlands or ponds (something relevant regarding the potential existence of a local base level) or the type of river that deposits the coarser sediments (which could also be relevant for climatic inferences).
Apart from other potential issues related to the presence or not of glaciers in the source area, which is also something that should be properly addressed and discussed, a proper facies analysis must be done, the depositional environments should be properly interpreted and their potential influence in the relation with the sea level changes should be considered as part of the discussion of the ages of the events dated, something that right now is missing in the article.
Specific comments
pp.7, lines 164, Section 3.1. I don't see the connection of the three lacustrine facies described by Devoto (1965) and the three main granulometric classes proposed by the authors. There is no correspondence in grain size nor type of sediment. I think the authors should explain how this old facies description fits in their new sedimentary frame. In fact, when going further into the manuscript, the authors do use again these three lacustrine facies to characterise the sequences, but there is no clarification on how they correlate to the three main granulometric classes. I believe some kind of scheme or table should be provided, to show how these different classifications relate to each other, both in general and for each of the stratigraphical sections. This would be helpful information, especially taking into account that the three so-called "lacustrine facies" lack a proper sedimentological characterisation in the current article. Moreover, the three main granulometric classes are not used again throughout the manuscript, so I do not see the point of explaining them in the first place.
For a reader not familiar with the region, so many names of sections make it difficult to follow the text and to mentally situate each one, and figure 2 size does not help at all. This figure should occupy a full page (if it is the responsibility of the journal, I strongly ask them to rethink the size of this figure), the dots were each stratigraphical section is located should be easier to spot (and maybe represented different if they are newly studied sections or re-analysed sections from the literature), and the names of the sections should be readable without needing to zoom in. If the reader is somewhere else in the manuscript and needs to go back to this figure to check these locations, it should not be so difficult as it is now.
pp.7, line 182. References are needed here about these previously produced datings
- 7, lines 183-184. The names of the sections that are no longer exposed should be mentioned here in the main text (I assume these would be the Cava Pompi, Colle Avarone, Isoletta, Lademagne and Ponte Corvo, shown in Supplementary Material #3) and the references from which these sections have been obtained as well, independently of this information being or not already in the supplementary data.
Regarding these supplementary data, the authors show no stratigraphical section of Ponte Corvo, just a photograph in which no gravel layer can be seen. If this is all the information available on this outcrop, I do not see how this outcrop can be properly correlated to the other sections from a sedimentological point of view without proper information about the relative position and thickness of the supposedly present gravel beds with regards to the tephra layers. I think more information and a propper stratigraphical section of this outcrop is needed if these two datings are to be included in the general correlation scheme. Without it, I do not see the point in including this section in the present study.
pp.7, line 190. I am not sure that from a sedimentological point of view, the interpretation of the third granulometric class proposed by the authors is appropriate. They do characterise the facies regarding the energy of the environment producing them, but in terms of the depositional environment, a distinction should be made whether the sediment belongs to the floodplain of the river, to an alluvial flat (I have seen no mention of alluvial fans at all, but I would imagine there would be some coming down from the Apenines and potentially reaching the main valley from time to time) or to palustrine/lacustrine facies. This distinction may be useful for later climatic interpretations.
pp.13, line 310. How do the authors know that these lacustrine sediments have a relatively constant sedimentation rate? First of all, there is no discussion on the nature of these facies, so they could either be palustrine or lacustrine in nature. If they were palustrine, frequent pauses in sedimentation may occur, as palustrine facies are often dried up and then flooded again some time later, generating a discontinuous record that would not have a constant sedimentation rate.
Figure 4. I would think that "white carbonatic mud" is a too vague term. Is it a marl or a calcilutite? It does make a difference, as the lack of any proper limestone facies makes me think this is no lake, but maybe just a shallow pond (and this has implications for the sedimentation rates and the environmental interpretation, as well as for the way the authors use the term "lacustrine" throughout the article).
- 13, line 330 and pp.14, line 356. These sentence sounds as if the authors lack enough information about the sediments. This description sounds rather vague (I don't even think the word "travertinaceous" is correct) and a rock that looks "something like a travertine" could also be a laminar calcrete. Given the lack of facies analysis in the article, I worry the authors may be mistaking one for another. Travertine deposition, following the current terminology (e.g. Arenas et al., 2010) requires the presence of a hot spring, which could happen, being in a volcanic zone, and would be independent of the climate. However, a calcareous tufa (also a laminated carbonate, see Arenas et al., 2010 for a further description) would usually imply warmer conditions of deposition, and they have in fact been used as indicators of interglaciar conditions in temperate areas (e.g.Pedley et al., 1996). On the other hand, a calcrete requires an arid climate and no sedimentation, and may have local, or sometimes basin-scale implications in terms of the sedimentary processes taking place. My point is that these three possibilities would have different climatic implications. I think if the authors want to establish climatic patterns, they should be taking a closer look to the sediments and not just focusing on the gravel layers. If they have already done so, I strongly recommend them to include proper descriptions and photographs of the different facies, as it is impossible to know if this has been done with the information provided in the current article.
Figures 4 and 5. The patterns used by the authors to characterise the different facies in the drawn sections are difficult to distinguish from each other. I would recommend to widen the pattern to make it easier to read and.
Figure 6a. I do not understand the criteria behind this correlation, when a proper sedimentological analysis is missing. Although in the figure caption the authors refer to the text for further explanations, I have not found them. I think this correlation is too simplistic to capture any nuances related to climate changes in the basin. The authors do not even refer to the three facies types of Devoto (1965), they just generalise and divide the sections into a lower, middle and upper lacustrine successions, without really providing information on how they have decided on this division and without providing the sedimentological features and palaeoenvironmental interpretation of these three sucessions, which could significantly alter the correlation among layers of different successions and therefore, the relative position of the dated beds, thus changing their chronostratigraphical scheme. Moreover, they add some dotted lines to correlate beds within those three successions, without a clear stratigraphical or correlational reason to it (for example, the darker blue dotted line connects the bottom of the Ceprano sequence with the apparent top of the same succession in Ponte Corvo section and then with a seemingly random point within the same lower lacustrine succession in the S. Giorgio a Liri sequence. I believe a detailed correlation scheme, based on sedimentological and stratigraphical evidence, clearly explained and shown, should be provided by the authors, in order to support the relative locations of the dated beds.
Figure 7. The authors show the sedimentary evolution of the basin, but if their intention is to propose climatic conclusions to their work, I believe this interpretation is too simplistic, and I don't mean to make the figure more complex. It is ok to visually simplify the figures and to generalise stratigraphical events to represent the different stages in the evolution of the basin. However, the information presented in the figure is incorrect.
First of all, the authors assign a 31cm/kyr sedimentation rate to the lower lacustrine succession. That is an unprecedented rate for these type of sediments and therefore should be well justified. Earlier in the text, they did give this same number for the sedimentation rate of the gravel beds (which would make sense), but I do not believe that this could also be the sedimentation rate for a lacustrine environment (e.g. a sedimentation rate up to 5cm/kyr was obtained for the depocentre of a fluvio-lacustrine basin in Southern Spain in Pla-Pueyo et al., 2011).
In stage C, they propose lacustrine to fluvial aggradation. They have not mentioned at all before what kind of facies changes support this evolution. Moreoever, they have described all of the sequences as lacustrine, but then they have not properly discussed what parts are fluvial and what parts are lacustrine.
From stage C onwards the figure shows the sediments thining towards the right side (which by the way, should be indicated as a cardinal point, there is no orientation to the figure) but I do not see what kind of feature could be forcing lacustrine sediments to end laterally in this manner if there is no erosion at that precise time (subsidence would not make lakes end laterally in that way, but would probably cause a change in the drainage pattern, preventing the water from forming lakes and maybe causing the sediments to move downwards, forming alluvial fans or deltas. I do not see the logic of this right slope.
In Stage G, the authors propose erosion and travertines progradation. As I understand, this is based on Devoto (1965), but due to the obvious difficulty of accesing such paper, and that this carbonate is supposed to bear cold fauna (Pentecost, 1995) I would strongly recommend the authors to provide photographs of hand samples and thin sections. If not, there is always the possibility of them being confused with a different type of carbonate with a different climatic meaning.
The information about the sedimentation rates in figure 7 is also contradictory to the one provided in pp.24, line580, where a sedimentation rate of 2.3mm/Kyr is assumed for the gravel aggradational sequence. It does not make sense that for a lacustrine sequence, the authors obtain a rate s large and for a gravel sequence, that supposedly deposited quite fast, the rate is below the one calculated for silts and clay in a fluvial environment (Pla-Pueyo et al., 2011). I strongly recommend the authors to recalculate all the sedimentation rates in the paper, not just for the gravel beds, but also to all the sedimentary intervals that appear in the different sequences, once they have made a detailed stratigraphical correlation, and to make sure that these rates are coherent with the type of sediment, the subsidence rate and the expected processes in the place for which the rate is calculated.
Section 5.3. I honestly don't think the authors have enough data nor are working in the right place to propose any triggering mechanisms for deglaciation, as this would have to do with whatever processes are taking place in the Apenines, and on a wider scale affecting all of the basins, not just the studied basin itself. I would totally avoid this section in the article, unless the authors are able to provide information of the same quality proving the existence of the same events in all of the affected basins and link it with proof from the Apenines themselves.
As the conclusions of the article are directly affected by all my other observations, I see no point in repeating myself.
Technical corrections
The authors should agree on the term to refer to the Latin valley and stick to it throughout the manuscript, as sometimes it is spelled as Latina (for example, in figure 2 caption or in line 150) and others is spelled Latin.
Figure 2. First of all, the fact that the regional map is called B and the local map is called A is counterintuitive and leads to confusion. I would recommend the authors to change the labelling.
Secondly, and this may be a not for the editors rather than the authors, the size of the whole figure is too small and the legend is almost impossible to read, it requires so much zoom that when you are able to read it, you miss the image in the screen. I would recommend to use a full page if possible or at least, to increase the font of the legend to make it easier to read.
Third, following the legend, the colours used in figure 2A are confusing. On one hand, they are supposed to represent topographical height (which I am not sure is so relevant, I think a geological map would be more useful than a topographical one) while on the other hand, the same colours are used to represent the Meso-Caeonozoic limestones and flysch.
Citation: https://doi.org/10.5194/cp-2021-161-RC2 -
AC4: 'Reply on RC2', Fabrizio Marra, 25 Feb 2022
We are really puzzled with this second review. It replicates, almost point by point, previous comments by anonymous Reviewer #1, which also was a sedimentologist and not an expert on paleoclimatology. It seems like the second reviewer didn't read the reply to the former one.
First of all, ours is not a sedimentologic work and Climate of the Past is not a sedimentology journal. It is not the aim of our work describing in detail the stratigraphy of the Liri Lacustrine Basin which has been already documented in great detail by Devoto (1965). It is ridiculous to state that this paper is not easily accessible and therefore we should replicate the study performed by this author.
Moreover, we don't understand which kind of facies analysis should be performed on this very localized fluvial-lacustrine sections which may add useful information for the scope of this paper.
The facies analysis that the Reviewer #2 claims for cannot be carried out on the borecores and on most of the described sections which are no more exposed; in any case, it would not add anything to this work which is based on a very simple, yet straightforward principle:
<< here we adopt a relatively simple but effective sedimentological approach based on the identification of three main granulometric classes, aimed at providing information on the energy of transport and the related sedimentary environments within the Sacco-Liri catchment basin:
- coarse gravel (max diameter of pebbles >2 cm), tractive fluvial environment of high transport energy;
- coarse sand with sparse fine gravel (max diameter of pebbles ≤2 cm), fluvial environment of mid transport energy;
iii. silt, clay and carbonate-rich mud; lacustrine and, subordinately, alluvial environment of low transport energy.>>
Our scientific approach relies on the changes in the energy of the fluvial-lacustrine basin which is expressed by the water capacity of transport. Our stratigraphic study evidences the occurrence of two coarse gravel layers the continuity of which is very well documented and supported by the geochronologic constraints provided through 40Ar/39Ar dating.
Scope of this paper is demonstrating that the coarse gravel input which occurs twice within the basin is originated by melting of the Apennine glaciers, and investigating the possible orbital trigger of these events.
To do so, we correlate stratigraphically two gravel layers 3-4 m thick, occurring at the same elevation through a 20 km wide area. We provide very precise radiometric ages to these gravel layers supporting the reconstruction in an objective way, as opposed to to facies analysis which cannot provide age constraints for correlation.
By doing so, we demonstrate that emplacement of these gravel layers is also coincident with the emplacement of identical gravel beds in the Tiber River basin, for which the direct link with the deglacial process has been demonstrated in previous literature.
We don't think that the lengthy specific comments on sedimentologic aspects by Reviewer #2 need a reply, since they are identical to those provided by Reviewer #1 and in any point they affect the scientific approach, the interpretations and the conclusion of our paleoclimatic study.
Citation: https://doi.org/10.5194/cp-2021-161-AC4
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AC5: 'Comment on cp-2021-161', Fabrizio Marra, 03 Mar 2022
Dear Editor,
I'm sorry that the research for available reviewers for our submitted paper didn't provide a more profitable outcome, so far.
Indeed, the two reviewers who accepted to do the review were evidently two sedimentologists who didn't caught the real focus of our paper and the aims of the Journal.
Our work is at not extent a sedimentologic work and the sedimentology of the Liri Basin is not the subject of our study.
As I had the chance to say in both replies, our paper deals with the deglaciation signal at global scale and the possible forcing mechanisms based on a sedimentary record represented by two several meters thick and several tens of kms wide coarse gravel horizons which the provided geochronologic constraints demonstrate are deposited during well circumscribed time spans, at 450 and 350 ka, broadly coinciding with the glacial terminations V and IV.
These chronological constraints demonstrate that these gravels originated from melting of the Apennine's glaciers and therefore represent a proxy of the deglaciation process, similar to the ice-drafted debries in Northern Atlantic.
We believe that these data, and the possible triggering mechanisms proposed, may be of great interest for the scientific community and may represent an input for future studies based on similar datasets all over the world.
We hope that you will agree with these considerations and with the only comment posted by the community.
In the absence of other reviews, we wonder whether you would like to review the paper yourself, providing your comments and the indications to resubmit a revised version that may be accepted for publication.
Thank you very much for your kind attention also on behalf the co-authors,
Fabrizio Marra
Citation: https://doi.org/10.5194/cp-2021-161-AC5 -
EC1: 'Reply on AC5', Alberto Reyes, 08 Mar 2022
Dear Dr. Marra,
I have extended the discussion period for your manuscript, to allow me to provide my own formal review for the record. I will endeavour to do this quickly—certainly in less than a week—after which the discussion period can be closed.
Sincerely,
Alberto Reyes
Citation: https://doi.org/10.5194/cp-2021-161-EC1 -
AC6: 'Reply on EC1', Fabrizio Marra, 08 Mar 2022
Dear Alberto,
thank you very much for your communication.
I'm looking forward to the completion of the review process.
Kind regards,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC6 -
CC2: 'Reply on EC1', Fabio Florindo, 04 May 2022
Dear Editor,
I am coauthor of ms "Terrestrial records of glacial terminations V and IV and insights on deglacial mechanisms". I am contacting you to be updated about the status of our manuscript.
Sincerely, Fabio Florindo
Citation: https://doi.org/10.5194/cp-2021-161-CC2
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AC6: 'Reply on EC1', Fabrizio Marra, 08 Mar 2022
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EC1: 'Reply on AC5', Alberto Reyes, 08 Mar 2022
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AC7: 'Comment on cp-2021-161', Fabrizio Marra, 24 Apr 2022
Dear Alberto,
I would kindly like to know if you have had the opportunity to form a final opinion on our work and what your decision is.
Thank you,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC7 -
AC8: 'Comment on cp-2021-161', Fabrizio Marra, 06 May 2022
Dear Alberto,
two months ago you told us that you would have provided your own formal review in less than a week, after which the discussion period will be closed.
No comment has been posted since then and you certainly have been prevented by important reasons.
However, we truly hope that the paper will not be rejected after this long wait and you will provide us with insightful review and instructions.
Kind regards,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC8 -
RC3: 'reviewer/editor comment on cp-2021-161', Alberto Reyes, 12 May 2022
The manuscript by Marra et al. was reviewed formally by two anonymous referees, together with a community comment.
On the positive side, the community comment from Gianluca Marino notes that radiometric dates for intervals of rapid sea-level rise are valuable, particularly for Middle Pleistocene glacial terminations that are not as well studied as T1 and T2. Dr. Marino also noted the puzzling conclusion in the Marra manuscript regarding meltwater pulses during the glacial maxima preceding T5 and T4, and recommended better integration of the results and discussion in order enhance the readability of the manuscript.
The two anonymous reviewers were more critical. Both reviewers felt that important details of geological setting and—in particular—the stratigraphic/sedimentological framework were lacking. In turn, the reviewers argued that the lack of detail made it impossible for readers to consider alternative explanations and evaluate the suggested correlations within the basin. One of the reviewers also highlighted interpretive concerns with respect to the interpreting minimum/maximum/direct ages for sedimentary units based on the Ar-Ar dates and some inconsistencies between lithostratigraphic description of key sites between the Marra manuscript and the original publications. Finally, both reviewers felt the manuscript lacked polish. The author responses to the reviewer comments were largely dismissive; the authors requested an additional assessment, which I am providing as editor but also as a geoscientist with a background in Quaternary stratigraphy, geochronology, and paleoclimate.
Though the objective of the manuscript is indeed to shed light on global-scale sea-level rise during deglaciation, the story relies on outcrop-scale lithostratigraphy and correlation within a basin. As such, I don’t think it’s unreasonable to expect: (1) a decent level of lithostratigraphic description, including nature of contacts between units; (2) justification of correlations made across the basin; (3) justification of any deviations from published interpretations/description on those same sediments. Unfortunately I find myself agreeing with the two reviewers on these issues. The lithostratigraphic descriptions are not sufficient for readers to evaluate the significance of the coarse units with respect to a region deglaciation signal. The correlations of relatively thin coarse units across >10 km are similarly not well described/justified. Rev 1 points out some discrepancies between published accounts and description in this manuscript for key sediments at Isoletta and Ceprano boreholes, and I agree that these discrepancies are potentially non-trivial for interpreting the significance of the coarse horizons. I also agree that the sedimentation rate calculations don’t seem appropriate here, given the mix of lacustrine and fluvial sedimentation and what appear from the figures to be some scour surfaces.
I have no doubt that the geochronology analyses are solid, but I do share some concerns with interpretation of these radiometric dates. Ages for several key samples (e.g. CE-1, CE-2) are based on clusters of only two young crystals; these are important dates which unpin much of the discussion. But then the reader is asked to just dismiss a coherent cluster of five too-young ages for sample BL-5 at San Giorgio al Siri, with little justification. I also can’t agree with the assumption that the maximum ages based on single crystal ages should be regarded as direct ages, which is provided on lines 286-287 and p9/line19 of the supporting materials with limited justification. Of course I don’t need to agree, but more justification should be provided when pushing detrital mineral chronologies so hard.
WIth all these uncertainties, the discussion section that relates the evolution of basin fill aggradation and erosion to glacial/interglacial sea-level change starts to feel overly ambitious, particularly when assessed at very optimistic temporal resolution against the insolation record. I do think the ultimate conclusion, made on lines 537-543 re: regional similarity of the aggradational successions, is pretty cool. And I think this approach is a clever way to indirectly date episodes of deglacial sea-level rise. But unfortunately it is very hard for a reader to tease out this story from the manuscript, and I don’t think the conclusion is yet adequately supported by the data and observations.
There are, finally, some smaller points that are easily fixed but numerous enough that they detract significantly from the reader’s ability to easily piece this story together. Some examples:
-It is not easy for readers to link locality names to individual dates across text, figures, and Table 1.
-Numerous references are presented as superscript numbers in tables and figures, but nowhere are the citations association with the superscript numbers
-Supplemental figure callout citations in the main text are commonly incorrect (e.g. line 317 Fig S1 seemingly should be S5; line 332 Fig S2 should be S6; line 340 no callout to Fig S7 for Isoletta)
-Inconsistencies in ages reported for the same sample at different points in manuscript (e.g. for BL-5 at San Giorgio al Liri, reported as 310+-12 at line 501, 300+-12 in Table 1, and <305 in Fig 5. Another: dates reported on Line 541 and 548 don’t appear in Fig 8 in spite of a callout to that figure.
-The important Fig 6 is very hard to decipher.
The author responses suggest that these criticisms of the manuscript are not appropriate because the study is intended to tell a paleoclimate/deglaciation story, rather than a stratigraphic/sedimentological one. But I fundamentally disagree: the proxy here is the sedimentary record, and no matter how good the geochronology might be, readers clearly want to see better justification provided for this basin’s sedimentary record of response to glacial/interglacial sea-level change.
Though I think the topic is important and there’s potential here for a very interesting paper, at this point my recommendation is that the manuscript is not suitable for publication in Climate of the Past in its present form.
Citation: https://doi.org/10.5194/cp-2021-161-RC3 -
AC9: 'Reply on RC3', Fabrizio Marra, 27 May 2022
I consider the outcome of the review process to be deeply unfair.
The Editor based his judgment on two reviewers whose responses were sort of a "past-and-copy" of incorrect comments based on misleading claims intended solely to have the work rejected. The first one also had the bad taste to close his acrimonious review with "best wishes". Unfortunately, I know these two Italian sedimentologists who have not the heart to sign their reviews.
The Editor, after the open discussion was extended twice due to not being able to find competent reviewers, took another two months (!) just to reiterate the two reviewers' objections. I think that in the replies we had explained in depth the inconsistency of their statements and their total irrelevance to the content of the work.
In reiterating the remarks of the reviewers, without ever entering the specific context of the work, the Editor has shown, in my opinion, his inability to understand and to discuss the actual subject of the submitted work and opted for a shortcut: to share the bad faith and prejudice of the reviewers totally inadequate he had chosen.
The objections at points (1), (2), (3) are ridiculous and somewhat offensive. The editor states that there is no "decent" level of stestigraphic decription, no justification of correlation made across the basin and of deviations (?) from published interpretatioin/description (which ones?).
And which are these "alternative" descriptions, correlations and interpretsations? Those that the reviewers have proposed based on the features of the Holocene Liri-Lacustrine basin, when we are describing those of the 600-350 ka interval, or those that they didn't even mention?
The statement: "the lithostratigraphic descriptions are not sufficient for readers to evaluate the significance of the coarse units with respect to a region deglaciation signal" is simply false. What is the difficulty in understanding the difference in water transport energy between a suite of silty-clay lacustrine sediments and the intercalated, 3-4 m thick, 10-20 km wide, beds of coarse gravel (diameter of pebbles >5-10 cm)?
As we have explained in our replies, the subject of the work is not sedimentology, but the direct correlation, demonstrated by 40Ar / 39Ar dating, between the deposition of extensive gravel beds in the catchment basins of the major rivers of central Italy and the deglacial process at global scale.
This has been appreciated by the paleoclimate community, as the nearly 1,000 reads demonstrate, but is evidently irrelevant for the Editor of the journal, who prefers that the work will be published in another venue.
Fabrizio Marra
Citation: https://doi.org/10.5194/cp-2021-161-AC9
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AC9: 'Reply on RC3', Fabrizio Marra, 27 May 2022
Interactive discussion
Status: closed
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RC1: 'Comment on cp-2021-161', Anonymous Referee #1, 12 Jan 2022
I read with interest the manuscript “Terrestrial records of glacial terminations V and IV and insights deglacial mechanism” by Marra and co-authors. This work shows some advances in the knowledge of the Liri basin but in my opinion it lacks of alternative interpretations of the sedimentary data and consequently of the sedimentary evolution. The interpretation seems to be equalize to a single hypothesis, the most unlikely, in order to be suitable for the Journal. I think that the work has to be rejected; it needs to be completely reconsidered and then submitted to another journal focusing not only on climate but also on geodynamics and basin analysis.
I list the reasons why I made this decision as follow.
- In the title the Authors clearly stated that the discussion will be about deglacial mechanism during terminations. But, first of all, where are the glaciated areas? No figures show them, no mentions in the geological background. In the Liri catchment, according to Giraudi (2011) evidence of glaciations can be ascribed to the LGM, older glaciations are lacking, or not yet studied. Anyhow, potential glaciers could be inferred in the Ernici, Meta, and Serralunga mounts. These are characterized by karstic environments, so the potential meltwater could have been captured by karstic circulation (for the argument see Zebre and Stepisnik, 2014 ESPL). Moreover, the supposed meltwater streams, before reaching the study area, could have been deposited in upstream basins, like Sora and Atina. For example, the Pescosolido alluvial fan. So, for having deglaciation, it needs glaciers, and these are not reported. This question can alone show the weakness of the work.
- Geological background. The Liri catchment is characterized by several mountain basins that can act as sediment trap. The geological background is focused only in the Latin Valley, skipping the innermost sectors towards N and NE. A better framework of the tectono-geological and geomorphological evolution of the catchment, including Roveto valley, is basic for understanding the sedimentary evolution of the drainage, and the possible presence of meltwater streams. This information can also help to understand the presence of lacustrine basins and their fading into fluvial environments. In Muttoni et al (2009 EPSL, fig 1) the presence of damming ridges were supposed. Considering the presence of the wide lacustrine basin of Sora just upstream, a break of the threshold (see Carrara 1991 Il Quaternario) could have completely renewed also the downstream sectors between Ceprano and the confluence with the Garigliano river. After the junction, the river flows through the southern sector of the Volsci range at the boundary with the Roccamonfina volcano, this before arriving at sea. I wonder if such volcanic structure took a part in the upstream basins’ evolution. Active faults are also documented (Bidittu et al. 2012). Moreover, tectonic structures reported in figure 2, especially faults A and B are not reported in the recent geological map (Ceccano Sheet) at the scale 1:50.000 (Centamore and Dramis, 2015) (http://www.isprambiente.gov.it/Media/carg/402_CECCANO/Foglio.html). How the sedimentary evolution described in chapter 5.1 and figures 6 and 7 can be presented with supposed fault?
- Sediment characterization. The sedimentology is related to previous works. The reinterpretation of the geological sections needs to be justified. For example, Isoletta section showed in the supporting material (figure S7) shows a layer of gravels that in Pereira et al (2018 QSR) are not reported but only sand layers, with volcanoclastic facies in the lower part. The gravels drilled in Ceprano cores, at -34-38 m, are described in Muttoni et al (2009 EPSL) as “subangular” and ascribed to an alluvial fan. Are these related to the Liri? Or to a stream flowing down the nearby Volsci mounts? Any provenance analysis? For example, in Devoto (1965 GR) there is a rough description of the gravel succession in Ceprano and S. Giorgio al Liri, pointing to a mix of volcanoclatic clasts and carbonates, with abundant quartz in the sands. The correlation across the basin of gravel units, actually very thin, must take into consideration facies and provenance. They can be simply different sedimentary episodes not strictly related. Also the development of volcanoes in the Volsci can have contributed in some way to geomorphological modifications, including the availability of volcanoclastic sediments, as reported by Pereira et al. (2018 QSR).
- The 8 new datings provided in this work are reported in different way in the text. Especially CE-1 and CE-2 have to be considered as post quem ages as reported in some figures but not in the table, in figure 8 or in the text at lines 293 and 295. The assumption at line 295-297 is not acceptable because they take into consideration just a single grain and there is no reason to think to the possibility that also younger crystals can be found in such reworked sediments. In this perspective, CE-1 indicates that the age of the gravel GH1 can be 452 ka to about 400 ka, the sedimentation of such thin gravel bed can be instantaneous geologically speaking, in respect to the overlying lacustrine deposits. CE-2 is again post quem and may be younger. The age of GH-2 is based on two post quem datings (Fig.6) and at Isoletta the original description (Pereira et al. 2018 QSR) shows sand and not gravels. The sedimentation rate of figure 4 has no mean because it is referred to 2 points that are post quem ages, the sedimentation rate reported in Muttoni et al (2009 EPSL) can be taken into consideration, but the new ages suggest a re-discussion. I also ask why the information given by pollen analysis of the Ceprano 1 core reported in Manzi et al. (2010 JHE) is not discussed for matching to your climatic discussion. The Pignataro Interamna upper lacustrine is tentatively ascribed to the fluvial unit upstream, but no chronology is provided for such correlation. In this way the chronology is too poorly detailed for very tight climate discussion.
- Alternative driver mechanisms. In such complex structural and geomorphological sector of the Apennines, the only hypothesis considered for depicting the evolution of the Latin valley (Fig. 7) is the most unlikely: the deglaciation from unknown glaciers and the relationship with sea-level changes of a coastline located far away and separated from the basin by a range and the Roccamonfina Volcano. The presence of gravel layers cutting lacustrine deposits (GH1) can be also determined alternatively by the failure of a dam or a threshold, and this can be ascribed to fault activity, threshold erosion, river piracy, etc. The gravel progradation can be ascribed to upstream reorganization of the catchment due to uplift, drainage changes, volcanic activity, etc. The abundance of travertine units (see Carrara 1991 Il Quaternario) could have also played a role. The presence of sand and gravels in a fluvio-lacustrine environment, such as the middle and upper succession can be simply related to channel avulsions. It is possible that all these drivers can be discarded, but it would be important to know why. The relationship to sea-level changes is related also to the Tiber valley (also too largely described in the setting), but I personally think that the geological/geomorphological framework is quite different. Anyhow for a robust correlation to sea-level changes and discussing about climate cycles, and also about depositional sequences, the availability of coastal successions in connection to the continental would be basic. No mention is provided about the coastal succession and they connection to those of the Latin valley. Here the separation from the coast area by a range with an active volcano hamper any consideration. Let’s why I think that chapter 5.3 is, in this perspective, a nonsense, especially the recognizing of early phases of se-level rising.
- Introducing figures need to be more informative (like in Pereira et al., 2018 QSR for example), especially figure 2 that would include all the information for understanding the complexity of the area. Figure 6 is key for understanding the correlations, some logs (also those provided in the supplemental data) are different from the original ones. What are the dashed lines? Basal surfaces? What represents the blue one? Why some of them cross the travertine in Pontecorvo? The Pignataro Interamna upper lacustrine correlation with fluvial unit of Isoletta looks a bit forced. Figure 7 is quite rough and many steps are unclear (also following the text).
best wishes
Citation: https://doi.org/10.5194/cp-2021-161-RC1 -
AC1: 'Reply on RC1', Fabrizio Marra, 13 Jan 2022
Our paper deals with the deglaciation signal at global scale and the possible forcing mechanisms based on a sedimentary record spanning 450 - 350 ka. In contrast, the reviewer discusses details of the local geology which represent the effect of the morphotectonic processes acting after the Last Glacial Maximum and have no relation with those responsible for the emplacement of thick horizons of coarse gravel during time spans precisely bracketed by 40Ar/39Ar age constraints and coinciding with the glacial terminations V and IV.
We apologize for not having referred to the local literature which described the evidence of glaciation in the central Apennines. We have given it for granted that a significant ice sheet would had occurred during the glacial maxima on a mountain range culminating above 2000 m; however, this is not a justification for not having cited the valuable and detailed work by Giraudi (2011) and we make amend.
Once this is acknowledged, we must say that we have found the comments by this anonymous reviewer contradictory at places, and biased by a complete lack of perspective.
Indeed, the reviewer says that the paper should be rejected because it does not provide any evidence of the presence of the glaciers, except to point out him/herself on the widespread evidence of glacial forms in this region reported in the local literature.
Moreover, the reviewer throughout his/her excursus mentions a series of very local sedimentary processes and several morpho-structural features characterizing the post Last Glacial Maximum Liri basin, without considering that, due to an extremely intense extensional tectonic phase coupled with a regional uplift in the order of hundreds of meters occurred in the last 250 ky, the present features may be very different from those which characterized this region 450.000 and 350.000 years ago.
For example, the reviewer completely ignores the fact that there is no evidence for gravel deposition within the Liri Basin after 350 ka, as shown by the geologic record that we have precisely dated. Therefore, it is clear that the present-day morpho-tectonic and hydrographic features that the reviewer describes have no relationship at all with those characterizing this region 450 through 350 ka.
Indeed, the subject of our paper is represented by two several meters thick and several tens of kms wide coarse gravel horizons which the provided geochronologic constraints demonstrate are deposited during well circumscribed time spans, at 450 and 350 ka, broadly coinciding with the glacial terminations V and IV.
As a matter of fact, large glaciers were surely present (as also the reviewer agree) and, despite all the possible traps and accidents that affect the present day basin, huge amounts of very coarse gravel were transported from the higher portions of the basin and deposited in two ~4 m thick layers in an area stretching up to 30 km within the basin.
Therefore, we believe that all the objections raised by the reviewer are superseded by these facts, and his/her criticism relies on discussing hypothetical minor aspects of the sedimentary processes and of the present-day hydrographic and geomorphologic features of the basin which have no relation with the large-scale processes investigated in our paper, and which have no consequence and impact at a global scale.
Therefore, his/her comments must be rejected, apart from some useful indications for improving the clarity of the text and of the figures.
While believing that the considerations above are sufficient to highlight the inconsistency of the reviewer's arguments, and a hassle on the details of the local geology would not interest an international audience, a point-by-point rebuttal of all the sometimes finicky issues raised by the reviewer in his/her detailed comments will be posted in a while, for those who are concerned. Here we just remark that many objections, like that on the post-quem character of the ages and on the sedimentation rate, do not take into account the explanation and the argumentation provided in the text and seem to arise from an inaccurate reading or lack of understanding.
Citation: https://doi.org/10.5194/cp-2021-161-AC1
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AC2: 'Comment on cp-2021-161', Fabrizio Marra, 01 Feb 2022
Point by point answers to Reviewer #1's comments
- Evidence for glaciers in the Apennines. The reviewer states that the weakness of the paper is that for having glaciations it needs glaciers and these are not reported. We will report the evidence of glaciations according to Giraudi (2011) in Figure 1 and add reference to this work.
- Geological background. All the long paragraph in which the reviewer describes in detail the features of the Present-day Liri catchment basins are irrelevant with respect to the topics of our work which is focused on the fluvial-lacustrine deposits emplaced 450 and 350 ka within a completely different morpho-structural basin. As a matter of facts, two several meter-thick coarse gravel horizons were emplaced within the Liri basin 450 ka and 350 ka, as evidenced by the 40Ar/39Ar age constraints provided in the paper.
Regarding the hypothesized tectonic structures, most of those reported in Figure 1 are based on a wide literature (e.g., Cardello et al., 2020; Centamore t al., 2010; Sani et al., 2004). For what concerns faults A and B, the fact that they are not reported in the recent geological map doesn't necessary imply that they do not exist. The 1:50.000 geologic map is based on the survey of surface evidence; in contrast, the inferred faults are hypothesized based on the interpretation of original subsurface chronostratigraphic data provided in our work.
The surface effects of these faults, even if they were active until 250 ka, only (that's during the climax of the extensional phase that affected this portion of the Apennines and was followed by a steady tectonic uplift since 250 ka), can be detected in the morpho-structural features of the Liri basin highlighted in Figure 1a.
- Regarding the concerns about sedimentologic characterization, it is clearly stated in the paper:
Also due to the fact that several geologic sections that are included in this study are no longer exposed and stratigraphic data have been obtained from the literature, here we adopt a relatively simple but effective sedimentological approach based on the identification of three main granulometric classes, aimed at providing information on the energy of transport and the related sedimentary environments within the Sacco-Liri catchment basin:
- coarse gravel (max diameter of pebbles >2 cm), tractive fluvial environment of high transport energy;
- coarse sand with sparse fine gravel (max diameter of pebbles ≤2 cm), fluvial environment of mid transport energy;
iii. silt, clay and carbonate-rich mud; lacustrine and, subordinately, alluvial environment of low transport energy.
However, for assurance of the reviewer, author Italo Biddittu originally investigated all the geologic sections reported in previous literature, providing a detail documentation of their stratigraphy, which is far enough to accomplish the goals of the present study, and can report on the correctness of the descriptions provided in the paper.
Moreover, myself, Fabio Florindo and Giovanni Muttoni have re-analyzed cm by cm the sedimentologic features of the cores of the two boreholes previously described in Muttoni et al. (2009) and presently hosted at the Milano University.
Finally, all the sedimentologic details that the reviewer mentions have no direct implication on the topics of our study.
- Geochronology. The reviewer is evidently not a geochronologist and has not carefully read the explanation of the principles on which the detrital sanidine method is based. Indeed, the accuracy, as well as the limitations of the 40Ar/39Ar ages are clearly and thoroughly discussed in a dedicated section (3.3 Detrital sanidine dating approach). Moreover, all the dated samples are discussed one by one in a dedicated supplementary text (Supplementary Material #1B - Age data and interpretations).
We briefly report here some considerations:
The youngest crystal (or the youngest crystal population in case two or more crystals yield consistent ages at two sigma) in the sedimentary samples provides a maximum age (terminus post quem) to the time of deposition of the sediment (i.e., the age of the sediment must be younger or equal to that of the youngest crystal(s)). However, as discussed in Marra et al. (2019), the occurrence of continuous eruptive activity throughout the Middle-Upper Pleistocene in the volcanic districts of central Italy allows to assume the lack of younger ages corresponding to known, large eruptions as a relative upper age-constraint. Indeed, incorporation of crystals from the youngest, stratigraphically higher eruption has higher probability with respect to those of older eruptions, and their absence should be considered statistically improbable when a large number of crystals (e.g., ~30) is dated. Therefore, it is reasonable to assume that the time of emplacement must be close to the youngest population age.
Also regarding the sedimentation rates, the reviewer seems to have not read the supplementary material in which this issue is discussed in detail. We report here the full discussion of the ages of the two samples collected in the Ceprano boreholes and their implication on the sedimentation rate:
Samples CE-1, CE-2 (this work)
Sample CE-1 was collected in borecore Ceprano 1 at 39.3 m depth within a coarse gravel layer with abundant sand matrix. The youngest crystal out of a population of 30 extracted from this sediment yielded a 40Ar/39Ar age of 452.4±1.8 ka (2 uncertainty). Sample CE-2 was collected at 15.1 m depth in borehole Ceprano 2, at the base of a coarse sand layer and yielded a youngest crystal date of 389.6±2.7 ka (2 uncertainty).
These two maximum ages can be regarded as statistically significant even if based on one single crystal. The Ceprano boreholes were drilled in Campogrande which is located on the left hydrographic side of the Sacco catchment basin, a sector draining the most active and densely vent-populated volcanic area of the Volsci Volcanic Field. A climactic eruptive phase occurred at the VVF in the interval 420 - 350 ka9, so the lack of crystals younger than 453 ka is strongly suggesting that the emplacement of the sand deposit occurred before the start of this volcanic phase. Consistent with this hypothesis, there is one crystal of 428±10 ka along one youngest crystal of 390±3.6 ka in the sample stratigraphically above. Moreover, these two ages along with that of 350.8±8 ka on the primary layer occurring at the top of the sedimentary succession recovered in the Ceprano boreholes10 provide a constant sedimentation rate of 38 cm/ky (see Figure 4 in the main text), which accounts for the exactness of these ages.
Therefore, it is reasonable to assume that also the maximum ages derived from reworked sanidine crystals can be regarded as providing precise time constraints to sediment deposition, as the one on the primary volcanic layer.
Indeed, and age close to 453 ka for the gravel deposition during MIS 11 is in perfect agreement with the constraints provided from the Paleo-Tiber aggradational successions, which bracket it between 451±2 and 445±3 ka11 (Figure 8 in the main text).
- Forcing mechanism on gravel deposition. The reviewer states that the hypothesis considered for gravel deposition, i.e.: deglaciation process, is the most unlikely. However, 25 years of dedicated literature contradict this statement:
Alvarez, W., Ammerman, A.J., Renne, P.R., Karner, D.B., Terrenato, N., Montanari, A., 1996. Quaternary fluvial-volcanic stratigraphy and geochronology of the Capitoline hill in Rome. Geology 24, 751-754.
Karner, D.B., Marra, F., 1998. Correlation of fluviodeltaic aggradational sections with glacial climate history: A revision of the Pleistocene stratigraphy of Rome. Geological Society of America Bulletin 110, 748–758.
Karner, D.B., Renne, P.R., 1998. 40Ar/39Ar geochronology of Roman volcanic province tephra in the Tiber River valley: Age calibration of middle Pleistocene sea-level changes. Geological Society of America Bulletin 110, 740-747.
Marra, F., Florindo, F., Karner, D.B.,1998. Paleomagnetism and geochronology of early Middle Pleistocene depositional sequences near Rome: comparison with the deep sea 18O climate record. Earth and Planetary Science Letters, 159, 147-164.
Florindo, F., Karner, D.B., Marra, F., Renne, P.R., Roberts A.P., Weaver, R., 2007. Radioisotopic age constraints for Glacial Terminations IX and VII from aggradational sections of the Tiber River delta in Rome, Italy. Earth and Planetary Science Letters 256, 61-80. doi: 10.1016/j.epsl.2007.01.014.
Marra, F., Florindo, F., Boschi, E., 2008. History of glacial terminations from the Tiber River, Rome: Insights into glacial forcing mechanisms. Paleoceanography 23, 1-17. doi:10.1029/2007PA001543
Marra, F., Bozzano, F., Cinti, F.R., 2013. Chronostratigraphic and lithologic features of the Tiber River sediments (Rome, Italy): implications on the Post-glacial sea-level rise and Holocene climate. Global and Planetary Change. https://doi.org/10.1016/j.gloplacha.2013.05.002
Grant, K.M., Rohling, E.J., Ramsey, C.B., Cheng, H., Edwards, R.L., Florindo, F., Heslop, D., Marra, F., Roberts, A.P., Tamisiea, M.E., Williams, F., 2014. Sea-level variability over five glacial cycles. Nature Communications 5, 5076. doi:10.1038/ncomms6076
Marra, F., Rohling, E.J., Florindo, F., Jicha, B., Nomade, S., Pereira, A., Renne, P.R., 2016a. Independent 40Ar/39Ar and 14C age constraints on the last five glacial terminations from the aggradational successions of the Tiber River, Rome (Italy). Earth Planet Sci. Lett. 449, 105-117. doi:10.1016/j.epsl.2016.05.037
Marra, F., Florindo, F., Anzidei, M., & Sepe, V., 2016b. Paleo-surfaces of glacio-eustatically forced aggradational successions in the coastal area of Rome: assessing interplay between tectonics and sea-level during the last ten interglacials. Quaternary Science Reviews 148, 85-100. http://dx.doi.org/10.1016/j.quascirev.2016.07.003
Marra, F., Jicha, B., Florindo, F., 2017. 40Ar/39Ar dating of Glacial Termination VI: constraints to the duration of Marine Isotopic Stage 13. Scientific Reports 7, 8908. doi:10.1038/s41598-017-08614-6
Luberti, G.M., Marra, F., Florindo, F., 2017. A review of the stratigraphy of Rome (Italy) according to geochronologically and paleomagnetically constrained aggradational successions, glacio-eustatic forcing and volcano-tectonic processes. Quaternary International, 438, 40-67. http://dx.doi.org/10.1016/j.quaint.2017.01.044
Marra, F. Costantini, L., Di Buduo, G.M. Florindo, F., Jicha, B.R., Monaco, L., Palladino, D.M., Sottili, G., 2019. Combined glacio-eustatic forcing and volcano-tectonic uplift: geomorphological and geochronological constraints on the Tiber River terraces in the eastern Vulsini Volcanic District (central Italy). Global and Planetary Change 182,103009. doi:10.1016/j.gloplacha.2019.103009.
Pereira, A., Monaco, L., Marra, F., Nomade, S., Gaeta, M., Leicher, N., Palladino, D.M., Sottili, G., Guillou, H., Scao, V., Giaccio, B., 2020. Tephrochronology of the central Mediterranean MIS 11c interglacial (~425-395 ka): new constraints from Vico volcano and Tiber delta, Central Italy. Quaternary Science Reviews 243: 106470.
Giaccio, B., Marino, G., Marra, F., Monaco, L., Pereira, A., Zanchetta, G., Gaeta, M., Leicher, N., Nomade, S., Palladino, D.M., Sottili, G., Guillou, H., Scao, V., 2021. Tephrochronological constraints on the timing and nature of sea-level change prior to and during glacial termination V. Quaternary Science Reviews, https://doi.org/10.1016/j.quascirev.2021.106976
Marra, F., Pereira, A., Boschian, G., Nomade, S., 2021a. MIS 13 and MIS 11 aggradational successions of the Paleo-Tiber delta: geochronological constraints to sea-level fluctuations and to the Acheulean sites of Castel di Guido and Malagrotta (Rome, Italy), Quaternary International, in press. https://doi.org/10.1016/j.quaint.2021.12.016
- Figures. We will take into account the suggestions to improve clarity of the figures.
Citation: https://doi.org/10.5194/cp-2021-161-AC2 -
CC1: 'Comment on cp-2021-161', Gianluca Marino, 19 Feb 2022
Marra et al. present new, valuable chronological (40Ar/39Ar) constrains on the timing of rapid ice-sheet melting/sea-level rise prior and at glacial terminations V and VI from the Liri fluvial-lacustrine basin in central Italy. The timing of rapid ice-sheet melting (at glacial terminations) is an essential piece of information, especially when this can be radiometrically constrained because it allows unambiguous comparison with the timing of insolation changes. Addressing the relationship between ice-sheet melting and insolation changes is one of the scopes of the study by Marra et al. and a key question in palaeoclimatology.
The “sedimentological” approach presented in the manuscript was used previously and successfully by Marra and his group both in the coastal and more inland sections of the Tiber catchment basin. Although it does not provide a quantitative sea-level reconstruction their approach is valuable, in that these sedimentary successions are sensitive “detectors” of past episodes of rapid sea-level rise (melt-water pulses), while the 40Ar/39Ar dating ensures firm constraints on the timing of these melt-water pulses.
The timing of meltwater pulses at the two terminations are consistent with previous studies centred on the Tiber catchment basin, which lends confidence to the reconstructions presented in this study. The most interesting (and to some extent surprising) finding of the manuscript is the occurrence of meltwater pulses/events during the glacial maxima that preceded both T-V and T-IV. The two intervals (glacial-interglacial cycles) have very different glacial histories (MIS 12 was plausibly way more glaciated than MIS 10, e.g., Spratt & Lisiecki, 2016 [Climate of the Past]) and insolation forcing. It is also worth mentioning that T-V and T-IV are very different terminations with the rates of ice-sheet melting/sea-level rise for the former (latter) being slower (faster) that for most (all) of the last five terminations (Grant et al., 2014 [Nature Communications]). I think the manuscript would benefit from a deeper discussion on this aspect prior to discussing the “mild insolation minima” mechanism (section 5.3). Glacial maxima are generally considered relatively stable intervals in which ice sheets are close to equilibrium with the forcing before their supercritical size makes them more sensitive to rising insolation (Raymo, 1997 [Paleoceanography]; Abe-Ouchi et al., 2013 [Nature]). Figure 9 shows that these events coincided with episodes of millennial-scale variability/Heinrich events. Do the authors think that these events of millennial-scale variability/meltwater pulse are entirely orbitally controlled?
Finally, the manuscript brings together a wealth of chronostratigraphic information from various locations of the Liri fluvial-lacustrine basin that is instrumental to the determining the timing of past meltwater pulses around T-V and T-IV. In its present form the results are hard to read. I would recommend to better integrate and make more concise this section of the manuscript.
Citation: https://doi.org/10.5194/cp-2021-161-CC1 -
AC3: 'Reply on CC1', Fabrizio Marra, 19 Feb 2022
We thank Gianluca Marino for his kind review and the useful suggestions to improve the completeness and clarity of the paper.
We realize that our paper, as it is, only provides a qualitative approach to the possible explanation of the occurrence of meltwater pulses events during the glacial maxima that precede the glacial termination. We provide geochronologic constraints to these events and we show that they are broadly coincident with several Heinrich-like events, as well as, with particularly moderate (mild) insolation minima. Moreover, such double correlation generate a "short circuit", implying, as Gianluca Marino remarks, that episodes of millennial-scale variability/Heinrich events might be entirely orbitally controlled. A fact that most of the paleoclimate community wouldn't welcome, and that we didn't even intend to claim.
Therefore, while we believe that our paper not necessarily has to establish the triggering mechanism for the detected episodes of deglaciation, we strongly agree that this aspect needs a more in depth, and clear discussion.
In particular, a more comprehensive spectrum of possible mechanisms should be discussed, for example the instability of the ice-sheets when approaching their supercritical size, as suggested by Gianluca Marino. Moreover, we agree that a disambiguation on the coincidence between Heinrich events and "mild" minima is necessary, with a more detailed information on the model published in Paleoceanography by Marra et al. (2008).
For what concerns the chronostrarigraphic information provided in the paper, if the Editor will ask us to resubmit a revised manuscript, we will have care to shorten and clarify this section, leaving only the information that is functional to the aims of our study, and moving the detail of the stratigraphy and the tectonic evolution in the supplements.
Citation: https://doi.org/10.5194/cp-2021-161-AC3
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AC3: 'Reply on CC1', Fabrizio Marra, 19 Feb 2022
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RC2: 'Comment on cp-2021-161', Anonymous Referee #2, 24 Feb 2022
I have carefully read the article entitled "Terrestrial records of glacial terminations V and IV and insights on deglacial mechanisms".
From a formal point of view, the overall presentation is well structured and clear, the language used by the authors is fluent and precise and the manuscript is easy to read. The references are up-to-date, including recent ones.
However, although it provides new chronological data on sedimentation events that may help reconstructing a palaeoclimatic interpretation in the basin, there is important stratigraphical and sedimentological information missing in order to back up the palaeoclimatic inferences presented in the article. Therefore, I think that the article should be accepted after major revisions have been undertaken.
In terms of the content, as I am not familiar with the geology of the region on which the study is focused nor with the references or previous geological work developed in the area, I have approached this revision purely as a stratigrapher and sedimentologist, looking at the formal aspects of the manuscript, at the type of data supplied by the authors and checking whether the discussion and conclussions they provide are soundly supported by the data they present and if they fit into the scope of the journal.
I will start with a general overview, to then land onto the specific comments addressing questions or issues that have arosen while reading the manuscript.
General overview
Although the article shows a thorough chronological study, proper stratigraphical and sedimentological interpretation of the sections is missing in order to provid a solid background for their conclusions regarding the past climate in the studied area.
From my point of view, the basis for a proper chronostratigraphical framework in any basin requires a previous solid stratigraphical framework to correclty locate the beds into all the sequences, which needs a detailed correlation among the different sections, that in turn requires a characterisation of the facies and an interpretation of the different subenvironments that they represent. Without this, the reliabiliy of the chronological frame is at risk.
From a sedimentological point of view, the article is lacking a proper study on the facies nature and their environmental (climatic) interpretation. They mention at the beginning three granulometric classes that they propose, which from a palaeoenvironmental point of view is too simplistic, but then they use an old classification by Devoto, 1965 when describing the stratigraphical sections, an old paper that is inaccessible to most readers. Apart from a very vague description of the three types of sediments that Devoto mentions, no real facies analysis is performed. Moreover, a detailed facies interpretation may provide valuable climatic information that has been disregarded in the present study.
Even when the authors have nine stratigraphical sections available, the correlation panel shown and the palaeogeographical reconstruction of the basin in different moments are too basic, so the reader does not know what kind of depositional environment is represented by each section nor is able to determine whether the correlation among different gravel beds has been properly carried out, which directly affects the dates that the authors present as the base of their work.
Regarding the linking of these continental gravels with sea-level changes, I personally think that without first establishing a proper stratigraphical frame for the continental area and without detailed correlations with other sections in coastal areas, it is too risky to interpret variations in potentially fluvial grain size as sea-level changes due to glacial terminations. Upstream sedimentology may be affected by tectonism, climate and base-level changes. If there was a lake damming the water at some point in the basin between the upstream facies (potentially related to glaciation/deglaciation events) and the mouth of the river (where sea level changes would have a direct record), the lake would act as a local base level, its fluctuations affecting the behaviour of the sediments upstream, and thus disconnecting their response to the sea level changes. The authors keep mentioning the word "lacustrine" whithout properly describing the facies or the subenvironments in which they appear, not considering whether there was a lake, several lakes, wetlands or ponds (something relevant regarding the potential existence of a local base level) or the type of river that deposits the coarser sediments (which could also be relevant for climatic inferences).
Apart from other potential issues related to the presence or not of glaciers in the source area, which is also something that should be properly addressed and discussed, a proper facies analysis must be done, the depositional environments should be properly interpreted and their potential influence in the relation with the sea level changes should be considered as part of the discussion of the ages of the events dated, something that right now is missing in the article.
Specific comments
pp.7, lines 164, Section 3.1. I don't see the connection of the three lacustrine facies described by Devoto (1965) and the three main granulometric classes proposed by the authors. There is no correspondence in grain size nor type of sediment. I think the authors should explain how this old facies description fits in their new sedimentary frame. In fact, when going further into the manuscript, the authors do use again these three lacustrine facies to characterise the sequences, but there is no clarification on how they correlate to the three main granulometric classes. I believe some kind of scheme or table should be provided, to show how these different classifications relate to each other, both in general and for each of the stratigraphical sections. This would be helpful information, especially taking into account that the three so-called "lacustrine facies" lack a proper sedimentological characterisation in the current article. Moreover, the three main granulometric classes are not used again throughout the manuscript, so I do not see the point of explaining them in the first place.
For a reader not familiar with the region, so many names of sections make it difficult to follow the text and to mentally situate each one, and figure 2 size does not help at all. This figure should occupy a full page (if it is the responsibility of the journal, I strongly ask them to rethink the size of this figure), the dots were each stratigraphical section is located should be easier to spot (and maybe represented different if they are newly studied sections or re-analysed sections from the literature), and the names of the sections should be readable without needing to zoom in. If the reader is somewhere else in the manuscript and needs to go back to this figure to check these locations, it should not be so difficult as it is now.
pp.7, line 182. References are needed here about these previously produced datings
- 7, lines 183-184. The names of the sections that are no longer exposed should be mentioned here in the main text (I assume these would be the Cava Pompi, Colle Avarone, Isoletta, Lademagne and Ponte Corvo, shown in Supplementary Material #3) and the references from which these sections have been obtained as well, independently of this information being or not already in the supplementary data.
Regarding these supplementary data, the authors show no stratigraphical section of Ponte Corvo, just a photograph in which no gravel layer can be seen. If this is all the information available on this outcrop, I do not see how this outcrop can be properly correlated to the other sections from a sedimentological point of view without proper information about the relative position and thickness of the supposedly present gravel beds with regards to the tephra layers. I think more information and a propper stratigraphical section of this outcrop is needed if these two datings are to be included in the general correlation scheme. Without it, I do not see the point in including this section in the present study.
pp.7, line 190. I am not sure that from a sedimentological point of view, the interpretation of the third granulometric class proposed by the authors is appropriate. They do characterise the facies regarding the energy of the environment producing them, but in terms of the depositional environment, a distinction should be made whether the sediment belongs to the floodplain of the river, to an alluvial flat (I have seen no mention of alluvial fans at all, but I would imagine there would be some coming down from the Apenines and potentially reaching the main valley from time to time) or to palustrine/lacustrine facies. This distinction may be useful for later climatic interpretations.
pp.13, line 310. How do the authors know that these lacustrine sediments have a relatively constant sedimentation rate? First of all, there is no discussion on the nature of these facies, so they could either be palustrine or lacustrine in nature. If they were palustrine, frequent pauses in sedimentation may occur, as palustrine facies are often dried up and then flooded again some time later, generating a discontinuous record that would not have a constant sedimentation rate.
Figure 4. I would think that "white carbonatic mud" is a too vague term. Is it a marl or a calcilutite? It does make a difference, as the lack of any proper limestone facies makes me think this is no lake, but maybe just a shallow pond (and this has implications for the sedimentation rates and the environmental interpretation, as well as for the way the authors use the term "lacustrine" throughout the article).
- 13, line 330 and pp.14, line 356. These sentence sounds as if the authors lack enough information about the sediments. This description sounds rather vague (I don't even think the word "travertinaceous" is correct) and a rock that looks "something like a travertine" could also be a laminar calcrete. Given the lack of facies analysis in the article, I worry the authors may be mistaking one for another. Travertine deposition, following the current terminology (e.g. Arenas et al., 2010) requires the presence of a hot spring, which could happen, being in a volcanic zone, and would be independent of the climate. However, a calcareous tufa (also a laminated carbonate, see Arenas et al., 2010 for a further description) would usually imply warmer conditions of deposition, and they have in fact been used as indicators of interglaciar conditions in temperate areas (e.g.Pedley et al., 1996). On the other hand, a calcrete requires an arid climate and no sedimentation, and may have local, or sometimes basin-scale implications in terms of the sedimentary processes taking place. My point is that these three possibilities would have different climatic implications. I think if the authors want to establish climatic patterns, they should be taking a closer look to the sediments and not just focusing on the gravel layers. If they have already done so, I strongly recommend them to include proper descriptions and photographs of the different facies, as it is impossible to know if this has been done with the information provided in the current article.
Figures 4 and 5. The patterns used by the authors to characterise the different facies in the drawn sections are difficult to distinguish from each other. I would recommend to widen the pattern to make it easier to read and.
Figure 6a. I do not understand the criteria behind this correlation, when a proper sedimentological analysis is missing. Although in the figure caption the authors refer to the text for further explanations, I have not found them. I think this correlation is too simplistic to capture any nuances related to climate changes in the basin. The authors do not even refer to the three facies types of Devoto (1965), they just generalise and divide the sections into a lower, middle and upper lacustrine successions, without really providing information on how they have decided on this division and without providing the sedimentological features and palaeoenvironmental interpretation of these three sucessions, which could significantly alter the correlation among layers of different successions and therefore, the relative position of the dated beds, thus changing their chronostratigraphical scheme. Moreover, they add some dotted lines to correlate beds within those three successions, without a clear stratigraphical or correlational reason to it (for example, the darker blue dotted line connects the bottom of the Ceprano sequence with the apparent top of the same succession in Ponte Corvo section and then with a seemingly random point within the same lower lacustrine succession in the S. Giorgio a Liri sequence. I believe a detailed correlation scheme, based on sedimentological and stratigraphical evidence, clearly explained and shown, should be provided by the authors, in order to support the relative locations of the dated beds.
Figure 7. The authors show the sedimentary evolution of the basin, but if their intention is to propose climatic conclusions to their work, I believe this interpretation is too simplistic, and I don't mean to make the figure more complex. It is ok to visually simplify the figures and to generalise stratigraphical events to represent the different stages in the evolution of the basin. However, the information presented in the figure is incorrect.
First of all, the authors assign a 31cm/kyr sedimentation rate to the lower lacustrine succession. That is an unprecedented rate for these type of sediments and therefore should be well justified. Earlier in the text, they did give this same number for the sedimentation rate of the gravel beds (which would make sense), but I do not believe that this could also be the sedimentation rate for a lacustrine environment (e.g. a sedimentation rate up to 5cm/kyr was obtained for the depocentre of a fluvio-lacustrine basin in Southern Spain in Pla-Pueyo et al., 2011).
In stage C, they propose lacustrine to fluvial aggradation. They have not mentioned at all before what kind of facies changes support this evolution. Moreoever, they have described all of the sequences as lacustrine, but then they have not properly discussed what parts are fluvial and what parts are lacustrine.
From stage C onwards the figure shows the sediments thining towards the right side (which by the way, should be indicated as a cardinal point, there is no orientation to the figure) but I do not see what kind of feature could be forcing lacustrine sediments to end laterally in this manner if there is no erosion at that precise time (subsidence would not make lakes end laterally in that way, but would probably cause a change in the drainage pattern, preventing the water from forming lakes and maybe causing the sediments to move downwards, forming alluvial fans or deltas. I do not see the logic of this right slope.
In Stage G, the authors propose erosion and travertines progradation. As I understand, this is based on Devoto (1965), but due to the obvious difficulty of accesing such paper, and that this carbonate is supposed to bear cold fauna (Pentecost, 1995) I would strongly recommend the authors to provide photographs of hand samples and thin sections. If not, there is always the possibility of them being confused with a different type of carbonate with a different climatic meaning.
The information about the sedimentation rates in figure 7 is also contradictory to the one provided in pp.24, line580, where a sedimentation rate of 2.3mm/Kyr is assumed for the gravel aggradational sequence. It does not make sense that for a lacustrine sequence, the authors obtain a rate s large and for a gravel sequence, that supposedly deposited quite fast, the rate is below the one calculated for silts and clay in a fluvial environment (Pla-Pueyo et al., 2011). I strongly recommend the authors to recalculate all the sedimentation rates in the paper, not just for the gravel beds, but also to all the sedimentary intervals that appear in the different sequences, once they have made a detailed stratigraphical correlation, and to make sure that these rates are coherent with the type of sediment, the subsidence rate and the expected processes in the place for which the rate is calculated.
Section 5.3. I honestly don't think the authors have enough data nor are working in the right place to propose any triggering mechanisms for deglaciation, as this would have to do with whatever processes are taking place in the Apenines, and on a wider scale affecting all of the basins, not just the studied basin itself. I would totally avoid this section in the article, unless the authors are able to provide information of the same quality proving the existence of the same events in all of the affected basins and link it with proof from the Apenines themselves.
As the conclusions of the article are directly affected by all my other observations, I see no point in repeating myself.
Technical corrections
The authors should agree on the term to refer to the Latin valley and stick to it throughout the manuscript, as sometimes it is spelled as Latina (for example, in figure 2 caption or in line 150) and others is spelled Latin.
Figure 2. First of all, the fact that the regional map is called B and the local map is called A is counterintuitive and leads to confusion. I would recommend the authors to change the labelling.
Secondly, and this may be a not for the editors rather than the authors, the size of the whole figure is too small and the legend is almost impossible to read, it requires so much zoom that when you are able to read it, you miss the image in the screen. I would recommend to use a full page if possible or at least, to increase the font of the legend to make it easier to read.
Third, following the legend, the colours used in figure 2A are confusing. On one hand, they are supposed to represent topographical height (which I am not sure is so relevant, I think a geological map would be more useful than a topographical one) while on the other hand, the same colours are used to represent the Meso-Caeonozoic limestones and flysch.
Citation: https://doi.org/10.5194/cp-2021-161-RC2 -
AC4: 'Reply on RC2', Fabrizio Marra, 25 Feb 2022
We are really puzzled with this second review. It replicates, almost point by point, previous comments by anonymous Reviewer #1, which also was a sedimentologist and not an expert on paleoclimatology. It seems like the second reviewer didn't read the reply to the former one.
First of all, ours is not a sedimentologic work and Climate of the Past is not a sedimentology journal. It is not the aim of our work describing in detail the stratigraphy of the Liri Lacustrine Basin which has been already documented in great detail by Devoto (1965). It is ridiculous to state that this paper is not easily accessible and therefore we should replicate the study performed by this author.
Moreover, we don't understand which kind of facies analysis should be performed on this very localized fluvial-lacustrine sections which may add useful information for the scope of this paper.
The facies analysis that the Reviewer #2 claims for cannot be carried out on the borecores and on most of the described sections which are no more exposed; in any case, it would not add anything to this work which is based on a very simple, yet straightforward principle:
<< here we adopt a relatively simple but effective sedimentological approach based on the identification of three main granulometric classes, aimed at providing information on the energy of transport and the related sedimentary environments within the Sacco-Liri catchment basin:
- coarse gravel (max diameter of pebbles >2 cm), tractive fluvial environment of high transport energy;
- coarse sand with sparse fine gravel (max diameter of pebbles ≤2 cm), fluvial environment of mid transport energy;
iii. silt, clay and carbonate-rich mud; lacustrine and, subordinately, alluvial environment of low transport energy.>>
Our scientific approach relies on the changes in the energy of the fluvial-lacustrine basin which is expressed by the water capacity of transport. Our stratigraphic study evidences the occurrence of two coarse gravel layers the continuity of which is very well documented and supported by the geochronologic constraints provided through 40Ar/39Ar dating.
Scope of this paper is demonstrating that the coarse gravel input which occurs twice within the basin is originated by melting of the Apennine glaciers, and investigating the possible orbital trigger of these events.
To do so, we correlate stratigraphically two gravel layers 3-4 m thick, occurring at the same elevation through a 20 km wide area. We provide very precise radiometric ages to these gravel layers supporting the reconstruction in an objective way, as opposed to to facies analysis which cannot provide age constraints for correlation.
By doing so, we demonstrate that emplacement of these gravel layers is also coincident with the emplacement of identical gravel beds in the Tiber River basin, for which the direct link with the deglacial process has been demonstrated in previous literature.
We don't think that the lengthy specific comments on sedimentologic aspects by Reviewer #2 need a reply, since they are identical to those provided by Reviewer #1 and in any point they affect the scientific approach, the interpretations and the conclusion of our paleoclimatic study.
Citation: https://doi.org/10.5194/cp-2021-161-AC4
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AC5: 'Comment on cp-2021-161', Fabrizio Marra, 03 Mar 2022
Dear Editor,
I'm sorry that the research for available reviewers for our submitted paper didn't provide a more profitable outcome, so far.
Indeed, the two reviewers who accepted to do the review were evidently two sedimentologists who didn't caught the real focus of our paper and the aims of the Journal.
Our work is at not extent a sedimentologic work and the sedimentology of the Liri Basin is not the subject of our study.
As I had the chance to say in both replies, our paper deals with the deglaciation signal at global scale and the possible forcing mechanisms based on a sedimentary record represented by two several meters thick and several tens of kms wide coarse gravel horizons which the provided geochronologic constraints demonstrate are deposited during well circumscribed time spans, at 450 and 350 ka, broadly coinciding with the glacial terminations V and IV.
These chronological constraints demonstrate that these gravels originated from melting of the Apennine's glaciers and therefore represent a proxy of the deglaciation process, similar to the ice-drafted debries in Northern Atlantic.
We believe that these data, and the possible triggering mechanisms proposed, may be of great interest for the scientific community and may represent an input for future studies based on similar datasets all over the world.
We hope that you will agree with these considerations and with the only comment posted by the community.
In the absence of other reviews, we wonder whether you would like to review the paper yourself, providing your comments and the indications to resubmit a revised version that may be accepted for publication.
Thank you very much for your kind attention also on behalf the co-authors,
Fabrizio Marra
Citation: https://doi.org/10.5194/cp-2021-161-AC5 -
EC1: 'Reply on AC5', Alberto Reyes, 08 Mar 2022
Dear Dr. Marra,
I have extended the discussion period for your manuscript, to allow me to provide my own formal review for the record. I will endeavour to do this quickly—certainly in less than a week—after which the discussion period can be closed.
Sincerely,
Alberto Reyes
Citation: https://doi.org/10.5194/cp-2021-161-EC1 -
AC6: 'Reply on EC1', Fabrizio Marra, 08 Mar 2022
Dear Alberto,
thank you very much for your communication.
I'm looking forward to the completion of the review process.
Kind regards,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC6 -
CC2: 'Reply on EC1', Fabio Florindo, 04 May 2022
Dear Editor,
I am coauthor of ms "Terrestrial records of glacial terminations V and IV and insights on deglacial mechanisms". I am contacting you to be updated about the status of our manuscript.
Sincerely, Fabio Florindo
Citation: https://doi.org/10.5194/cp-2021-161-CC2
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AC6: 'Reply on EC1', Fabrizio Marra, 08 Mar 2022
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EC1: 'Reply on AC5', Alberto Reyes, 08 Mar 2022
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AC7: 'Comment on cp-2021-161', Fabrizio Marra, 24 Apr 2022
Dear Alberto,
I would kindly like to know if you have had the opportunity to form a final opinion on our work and what your decision is.
Thank you,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC7 -
AC8: 'Comment on cp-2021-161', Fabrizio Marra, 06 May 2022
Dear Alberto,
two months ago you told us that you would have provided your own formal review in less than a week, after which the discussion period will be closed.
No comment has been posted since then and you certainly have been prevented by important reasons.
However, we truly hope that the paper will not be rejected after this long wait and you will provide us with insightful review and instructions.
Kind regards,
Fabrizio
Citation: https://doi.org/10.5194/cp-2021-161-AC8 -
RC3: 'reviewer/editor comment on cp-2021-161', Alberto Reyes, 12 May 2022
The manuscript by Marra et al. was reviewed formally by two anonymous referees, together with a community comment.
On the positive side, the community comment from Gianluca Marino notes that radiometric dates for intervals of rapid sea-level rise are valuable, particularly for Middle Pleistocene glacial terminations that are not as well studied as T1 and T2. Dr. Marino also noted the puzzling conclusion in the Marra manuscript regarding meltwater pulses during the glacial maxima preceding T5 and T4, and recommended better integration of the results and discussion in order enhance the readability of the manuscript.
The two anonymous reviewers were more critical. Both reviewers felt that important details of geological setting and—in particular—the stratigraphic/sedimentological framework were lacking. In turn, the reviewers argued that the lack of detail made it impossible for readers to consider alternative explanations and evaluate the suggested correlations within the basin. One of the reviewers also highlighted interpretive concerns with respect to the interpreting minimum/maximum/direct ages for sedimentary units based on the Ar-Ar dates and some inconsistencies between lithostratigraphic description of key sites between the Marra manuscript and the original publications. Finally, both reviewers felt the manuscript lacked polish. The author responses to the reviewer comments were largely dismissive; the authors requested an additional assessment, which I am providing as editor but also as a geoscientist with a background in Quaternary stratigraphy, geochronology, and paleoclimate.
Though the objective of the manuscript is indeed to shed light on global-scale sea-level rise during deglaciation, the story relies on outcrop-scale lithostratigraphy and correlation within a basin. As such, I don’t think it’s unreasonable to expect: (1) a decent level of lithostratigraphic description, including nature of contacts between units; (2) justification of correlations made across the basin; (3) justification of any deviations from published interpretations/description on those same sediments. Unfortunately I find myself agreeing with the two reviewers on these issues. The lithostratigraphic descriptions are not sufficient for readers to evaluate the significance of the coarse units with respect to a region deglaciation signal. The correlations of relatively thin coarse units across >10 km are similarly not well described/justified. Rev 1 points out some discrepancies between published accounts and description in this manuscript for key sediments at Isoletta and Ceprano boreholes, and I agree that these discrepancies are potentially non-trivial for interpreting the significance of the coarse horizons. I also agree that the sedimentation rate calculations don’t seem appropriate here, given the mix of lacustrine and fluvial sedimentation and what appear from the figures to be some scour surfaces.
I have no doubt that the geochronology analyses are solid, but I do share some concerns with interpretation of these radiometric dates. Ages for several key samples (e.g. CE-1, CE-2) are based on clusters of only two young crystals; these are important dates which unpin much of the discussion. But then the reader is asked to just dismiss a coherent cluster of five too-young ages for sample BL-5 at San Giorgio al Siri, with little justification. I also can’t agree with the assumption that the maximum ages based on single crystal ages should be regarded as direct ages, which is provided on lines 286-287 and p9/line19 of the supporting materials with limited justification. Of course I don’t need to agree, but more justification should be provided when pushing detrital mineral chronologies so hard.
WIth all these uncertainties, the discussion section that relates the evolution of basin fill aggradation and erosion to glacial/interglacial sea-level change starts to feel overly ambitious, particularly when assessed at very optimistic temporal resolution against the insolation record. I do think the ultimate conclusion, made on lines 537-543 re: regional similarity of the aggradational successions, is pretty cool. And I think this approach is a clever way to indirectly date episodes of deglacial sea-level rise. But unfortunately it is very hard for a reader to tease out this story from the manuscript, and I don’t think the conclusion is yet adequately supported by the data and observations.
There are, finally, some smaller points that are easily fixed but numerous enough that they detract significantly from the reader’s ability to easily piece this story together. Some examples:
-It is not easy for readers to link locality names to individual dates across text, figures, and Table 1.
-Numerous references are presented as superscript numbers in tables and figures, but nowhere are the citations association with the superscript numbers
-Supplemental figure callout citations in the main text are commonly incorrect (e.g. line 317 Fig S1 seemingly should be S5; line 332 Fig S2 should be S6; line 340 no callout to Fig S7 for Isoletta)
-Inconsistencies in ages reported for the same sample at different points in manuscript (e.g. for BL-5 at San Giorgio al Liri, reported as 310+-12 at line 501, 300+-12 in Table 1, and <305 in Fig 5. Another: dates reported on Line 541 and 548 don’t appear in Fig 8 in spite of a callout to that figure.
-The important Fig 6 is very hard to decipher.
The author responses suggest that these criticisms of the manuscript are not appropriate because the study is intended to tell a paleoclimate/deglaciation story, rather than a stratigraphic/sedimentological one. But I fundamentally disagree: the proxy here is the sedimentary record, and no matter how good the geochronology might be, readers clearly want to see better justification provided for this basin’s sedimentary record of response to glacial/interglacial sea-level change.
Though I think the topic is important and there’s potential here for a very interesting paper, at this point my recommendation is that the manuscript is not suitable for publication in Climate of the Past in its present form.
Citation: https://doi.org/10.5194/cp-2021-161-RC3 -
AC9: 'Reply on RC3', Fabrizio Marra, 27 May 2022
I consider the outcome of the review process to be deeply unfair.
The Editor based his judgment on two reviewers whose responses were sort of a "past-and-copy" of incorrect comments based on misleading claims intended solely to have the work rejected. The first one also had the bad taste to close his acrimonious review with "best wishes". Unfortunately, I know these two Italian sedimentologists who have not the heart to sign their reviews.
The Editor, after the open discussion was extended twice due to not being able to find competent reviewers, took another two months (!) just to reiterate the two reviewers' objections. I think that in the replies we had explained in depth the inconsistency of their statements and their total irrelevance to the content of the work.
In reiterating the remarks of the reviewers, without ever entering the specific context of the work, the Editor has shown, in my opinion, his inability to understand and to discuss the actual subject of the submitted work and opted for a shortcut: to share the bad faith and prejudice of the reviewers totally inadequate he had chosen.
The objections at points (1), (2), (3) are ridiculous and somewhat offensive. The editor states that there is no "decent" level of stestigraphic decription, no justification of correlation made across the basin and of deviations (?) from published interpretatioin/description (which ones?).
And which are these "alternative" descriptions, correlations and interpretsations? Those that the reviewers have proposed based on the features of the Holocene Liri-Lacustrine basin, when we are describing those of the 600-350 ka interval, or those that they didn't even mention?
The statement: "the lithostratigraphic descriptions are not sufficient for readers to evaluate the significance of the coarse units with respect to a region deglaciation signal" is simply false. What is the difficulty in understanding the difference in water transport energy between a suite of silty-clay lacustrine sediments and the intercalated, 3-4 m thick, 10-20 km wide, beds of coarse gravel (diameter of pebbles >5-10 cm)?
As we have explained in our replies, the subject of the work is not sedimentology, but the direct correlation, demonstrated by 40Ar / 39Ar dating, between the deposition of extensive gravel beds in the catchment basins of the major rivers of central Italy and the deglacial process at global scale.
This has been appreciated by the paleoclimate community, as the nearly 1,000 reads demonstrate, but is evidently irrelevant for the Editor of the journal, who prefers that the work will be published in another venue.
Fabrizio Marra
Citation: https://doi.org/10.5194/cp-2021-161-AC9
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AC9: 'Reply on RC3', Fabrizio Marra, 27 May 2022
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Fabrizio Marra
Alison Pereira
Brian Jicha
Sebastien Nomade
Italo Biddittu
Fabio Florindo
Giovanni Muttoni
Elizabeth Niespolo
Paul Renne
Vincent Scao
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