the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Jul 2026
Astronomical pacing and impact of the Middle Maastrichtian warming event on the Maastrichtian upwelling system of the southern Neo-Tethys Ocean margin (Jordan)
Abstract. The southern NeoTethys Ocean margin was the site of one of the most organically rich Early Maastrichtian global upwelling systems, with organic matter concentrations reaching>20 % TOC, which came to an abrupt end in the Late Maastrichtian, when sedimentation changed to pure chalk deposits. The integration of biostratigraphy, climate and depositional environment proxies, and cyclostratigraphy demonstrated that this change from organic to carbonate-dominated productivity occurred around the Early-Late Maastrichtian and was time equivalent to a climatic change from cooler to warmer conditions. The smaller scale productivity variations were paced by the eccentricity modulated precession orbital cycles. The integration of calcareous nannofossil and dinoflagellate cyst biostratigraphy, radiolarian paleoecology, stable isotope geochemistry (δ¹³Ccarb, δ¹³Corg, δ¹⁸O and δ¹⁵Norg), and organic geochemical proxies from two closely spaced shallow cores (139 m and 71 m thickness) in Central Jorden were used to reconstruct the evolution of the Maastrichtian upwelling system manifest along the Levant margin of the southern NeoTethys Ocean. Integrated biostratigraphic and chemostratigraphic data constrain deposition of the oil shale interval to the Early Maastrichtian (72.7–68.2 Ma), representing ~4.5 Myr of accumulation with sedimentation rates of ~1.5–2.2 cm kyr⁻¹. Pronounced lithological and geochemical cyclicity reveals a dominant precession signal modulated by short eccentricity (~100 kyr), suggesting that eccentricity-paced insolation forcing regulated migration of the Intertropical Convergence Zone (ITCZ), regional wind intensity, and coastal upwelling strength. These orbitally forced changes controlled nutrient delivery, marine productivity, as expressed in the calcareous nannofossil, dinoflagellate cyst, and radiolarian assemblages, and cyclic accumulation of organic-rich sediments. Combined δ¹³Ccarb, δ¹³Corg, and calcareous nannofossil records place the Middle Maastrichtian Carbon Isotope Event within the upper part of the oil shale succession. δ¹⁸O trends and nannofossil assemblage variations indicate cooling during the Early Maastrichtian, followed by warming during the early Late Maastrichtian. Low total organic nitrogen values, elevated C/N ratios, depleted δ¹³Corg values, and enriched δ¹⁵Norg signatures indicate intense diagenetic recycling of nitrogen-rich organic matter under persistent oxygen-deficient conditions, likely involving denitrification within an expanded oxygen minimum zone. Our findings demonstrate the coupled influence of orbital forcing and climate change on upwelling dynamics, marine productivity, and biogenic sedimentation during the Early Maastrichtian.
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RC1: 'Comment on egusphere-2026-3135', Baptiste Suchéras-Marx, 29 Jul 2026
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AC2: 'Reply on RC1', jihede haj messaoud, 30 Sep 2026
We sincerely thank both reviewers for their careful and constructive evaluations. Their comments prompted substantial revisions that improved the clarity, methodological transparency, and robustness of the manuscript. Pasted markdown
Major revisions include: improved figure readability and consistency; expanded geological and paleogeographic context; a more detailed and reproducible cyclostratigraphic workflow; independent evaluation of GR cyclicity using sedimentological and geochemical proxies; and explicit consideration of variable sedimentation rates and changing cycle thickness. Pasted markdown
We also strengthened the age model using integrated biostratigraphy, chemostratigraphy, and cyclostratigraphy; clarified the significant hiatus across the K/Pg interval; and revised identification of the mid-Maastrichtian Event (MME) using carbon-isotope features, nannofossil bioevents, and cyclostratigraphic constraints. Pasted markdown
The paleoenvironmental discussion has been reorganized to link interpretations more directly to the Jordanian datasets, including GR, TOC, nannofossils, stable isotopes, detrital proxies, sedimentation rates, and the sequence-stratigraphic framework. Terminology and the distinction between observations and interpretations have also been standardized throughout. Pasted markdown
Overall, these revisions provide a clearer stratigraphic framework, a more reproducible analytical workflow, a more conservative orbital interpretation, and a stronger multi-proxy basis for the MME and paleoenvironmental reconstruction.
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AC2: 'Reply on RC1', jihede haj messaoud, 30 Sep 2026
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RC2: 'Comment on egusphere-2026-3135', Sietske Batenburg, 06 Aug 2026
Dear authors and editor,
Thank you for the manuscript “Astronomical pacing and 1 impact of the Middle Maastrichtian warming event on the Maastrichtian upwelling system of the southern Neo-Tethys Ocean margin (Jordan)” by Messaoud and co-authors. The manuscript provides new data from the Tethyan margin which can provide new insights. However, the presentation of the data is not adequate to evaluate the manuscript. The resolution of the figures is too low. While the authors prepare better resolution figures, I encourage them to consider incorporating other elements.
Geologic setting
Consider including a paleogeographic map of the Tethyan margin area. Are the 7 wells in figure 1 indicated on the map, and do these include the studied wells?
Methodology
Please provide more information on how the GR data were collected for the different cores or wells and how they were made into a composite record (Fig. 9).
Include information on how time series analysis was performed, such as the software used and the settings applied. Consider performing time series analyses on the TOC data.
Explain how the tuning was performed.
Results
Display the results of the SA-01 core where they are described (before figure 3). Line 254 suddenly mentions cycles, indicate what this refers to. The subscript of figure 2 discusses non displayed items from line 271 onwards.
Consider presenting an age-depth plot for both cores, with all the available age information, including the biostratigraphic datums, d13C events and the cyclostratigraphic tuning.
Section 4.7 might be better suited for the discussion, and the authors should discuss how the position of the K/Pg boundary is inferred, or whether there is a hiatus. Discuss whether you think that the entire record is (biostratigraphically) complete.
Provide data tables.
Cyclostratigraphy:
Discuss if there is a rhythmic alternation of lithologies and whether this is reflected in the GR record. The text mentions an estimated sedimentation rate, please explain how this rate was obtained. The GR series is tuned, but any information on how this was done is lacking. The MTM spectrum of the tuned GR series looks less convincing than the spectral analysis in the depth domain. The colourmap of the wavelet does not allow identification of dominant periodicities.
Some observations on the variations in the GR data: Prominent peaks around 80 m follow a longer periodicity in the depth domain than peaks around 130 m, yet all are interpreted as short eccentricity (figure 12). They may be driven by other periodicities, or there might be changes in sedimentation rate.
Discussion
The identification of the mid Maastrichtian event is critical for this paper, yet not an easy feat and the main figure (10) can be improved. Why are there two panels, and why does the d13C curve of Gubbio look different in the two panels?
Section 5.5 has a lot of paleoenvironmental mechanisms, but these are not clearly linked to the own data.
Generally, the manuscript would benefit from a slight restructuring. Several figure captions detail the paleoenvironmental interpretation, which is better suited for the main text. Elements are missing, and a figure should be moved, as discussed above. Please pay attention to the capitalisation and correct use of early/late, lower/upper, and write mid-Maastrichtian event.
Citation: https://doi.org/10.5194/egusphere-2026-3135-RC2 -
AC1: 'Reply on RC2', jihede haj messaoud, 30 Sep 2026
Dear Editor and Reviewers,
We sincerely thank both reviewers for their careful, constructive, and detailed evaluations of our manuscript. Their comments were highly valuable and prompted a substantial revision of the manuscript. In particular, the reviews highlighted the need to improve figure readability, strengthen methodological transparency, clarify the stratigraphic terminology and age control, make the cyclostratigraphic workflow fully reproducible, refine the identification of the mid-Maastrichtian Event (MME), clarify the nature of the K/Pg interval, and link the paleoenvironmental interpretations more directly to the measured Jordanian datasets.
We have reorganized several parts of the manuscript, revised the principal figures, expanded the Methods and Results, and made the Discussion more explicitly data-driven. Our aim throughout the revision was to distinguish more clearly between direct observations, stratigraphic correlations, and paleoenvironmental interpretations, while retaining the integrated multi-proxy approach that forms the basis of the study.
Major revisions made in response to the reviewers
- Figures and graphical presentation. All main figures have been reconsidered for publication-scale readability. Text, axes, species names, scale bars, symbols, and legends are being enlarged or reorganized where necessary, and pixelized/rasterized text is avoided where possible. Figures 4 and 5 are being standardized so that comparable datasets are displayed using a consistent graphical architecture and scale. Captions are also being revised to remain descriptive rather than interpretative.
- Geological and paleogeographic framework. The geological-setting section has been strengthened by separating regional paleogeographic context from the local well and correlation framework. The revised presentation includes a Maastrichtian paleogeographic reconstruction of the southern Neo-Tethyan margin and a geological map/correlation figure that explicitly identifies the studied SA-01 and AJ-02 wells and distinguishes them from additional wells or sections used only for regional correlation.
- Cyclostratigraphic methodology and reproducibility. A dedicated cyclostratigraphic Methods subsection has been added and expanded. It now describes the origin and construction of the gamma-ray records, preprocessing and interpolation, detrending, MTM spectral analysis, the background-noise model and significance testing, evolutionary/wavelet analysis, filtering, orbital-band evaluation, astronomical tuning, and age-model construction. The revised workflow presents the untuned depth-domain analysis before the tuned time-domain analysis, because the former provides the primary evidence for sedimentary cyclicity.
- Independent testing of cyclicity. Following Reviewer 2's suggestion, the cyclicity identified in the gamma-ray record is evaluated against independent sedimentological and geochemical proxies, including TOC and other compositional records. This provides an additional test of whether the observed spectral structure reflects depositional cyclicity rather than being an artifact of a single proxy.
- Variable sedimentation rates and cycle thickness. We no longer imply that a given orbital component must have a constant thickness throughout the core. The revised sedimentation-rate reconstruction documents substantial stratigraphic variability, including rates of approximately 3 cm kyr-1 between 139 and 128 m, approximately 1.8-2.0 cm kyr-1 between 128 and 110 m, an increase to approximately 4.2 cm kyr-1 around 106 m, and an upward decrease toward approximately 2.1-2.3 cm kyr-1. This variability provides an important explanation for changing cycle thickness in the depth domain. Consequently, individual GR peaks are not assigned to short eccentricity solely on the basis of spacing; the orbital interpretation is instead based on the overall spectral hierarchy, stratigraphic evolution of spectral power, independent age constraints, sedimentation-rate changes, and recurrence in other proxies.
- Age control and stratigraphic completeness. The age framework has been clarified by integrating biostratigraphic constraints, chemostratigraphic events, and the cyclostratigraphic model. Age-depth relationships for the studied cores are presented more explicitly, including intervals of condensation. We also expanded the discussion of stratigraphic completeness rather than assuming that the succession is continuous.
- K/Pg interval and hiatus. The revised manuscript explicitly recognizes that the K/Pg boundary itself is not continuously preserved in SA-01. The uppermost Cretaceous samples contain a late Maastrichtian assemblage assigned to upper UC20b, whereas the first clearly identified Paleogene assemblage is attributable to NP3 near 53 m. The intervening UC20c-UC20d and NP1-NP2 assemblages are not recorded. We therefore interpret a substantial hiatus spanning the latest Maastrichtian, the K/Pg boundary, and part of the early Danian. Accordingly, the physical surface is described as a disconformity/hiatus and is not itself labelled as the K/Pg boundary.
- Identification of the mid-Maastrichtian Event. Because identification of the MME is central to the manuscript, its stratigraphic placement has been made more explicit and conservative. The revised interpretation does not rely on visual similarity of a single carbon-isotope curve. Instead, the MME is identified using the combined M1+, M1-, M2+, M2-, and M3+ carbon-isotope features together with the succession of calcareous nannofossil bioevents, including Uniplanarius trifidus, Broinsonia parca constricta, Tranolithus orionatus, Reinhardtites levis, Micula praemurus, and Lithraphidites quadratus, and the cyclostratigraphic framework. We also distinguish the broader approximately 69.5-67.5 Ma mid-Maastrichtian climatic perturbation from the shorter approximately 570 kyr MME sensu stricto following Dubicka et al. (2024).
- Revised MME correlation figure. The previous two-panel presentation is replaced by a single internally consistent correlation panel using the same Gubbio reference dataset and scaling throughout. The revised figure emphasizes the diagnostic carbon-isotope features and independent nannofossil bioevents used to constrain the Jordanian record, thereby removing the apparent inconsistency between the two former panels.
- Paleoenvironmental interpretation anchored to the data. The Discussion has been reorganized so that interpretations of productivity, oxygenation, organic-carbon burial, climate, sea level, and upwelling are directly connected to the measured datasets. Particular emphasis is placed on GR and TOC cyclicity, the transition from organic-rich to carbonate-rich facies, changes in cool-water nannofossil taxa and Watznaueria, the oxygen-isotope trend, detrital proxies such as Al2O3 and Ti, reconstructed sedimentation rates, and the independently developed sequence-stratigraphic/relative sea-level framework. Interpretations that cannot be directly demonstrated by the Jordanian data have been softened.
- Nannofossil and dinocyst presentation. The nannofossil percentage scales and counting approach are clarified, and uncertainty estimates are added for the cool-water taxon percentages. Where dinocyst assemblages and the peridinioid/gonyaulacoid ratio are used as a central argument, the underlying data are displayed and described in the Results before being interpreted in the Discussion.
- Terminology and distinction between observation and interpretation. Terminology has been standardized throughout the manuscript. 'Middle Maastrichtian' is replaced by 'mid-Maastrichtian'; Early/Late is used for geochronologic time and Lower/Upper where appropriate for chronostratigraphic usage. The term 'sequence boundary' is replaced by the observational term 'disconformity' where the physical surface is documented, with sequence-stratigraphic interpretation reserved for the text. Similarly, overly strong language such as 'exceptional preservation' is replaced by more precise wording concerning enhanced net organic-carbon burial or accumulation.
- Carbon-isotope interpretation. The interpretation of the weak relationship between delta13Ccarb and delta13Corg has been revised. Because the carbonate signal may be affected by diagenetic modification, the manuscript no longer treats the weak correlation as direct evidence for primary carbon-reservoir decoupling. Instead, it is presented more cautiously as evidence that the two records did not respond identically, while explicitly acknowledging the limitations imposed by carbonate alteration.
- Results organization and supplementary data. Background material derived primarily from previous studies has been moved from the Results to the Geological Setting/Stratigraphy section. The SA-01 observations are introduced before interpretation and comparison with AJ-02, sample identifiers are standardized, abbreviations such as amorphous organic matter (AOM) are defined at first use, and numerical data tables are provided as supplementary Excel files.
Overall outcome of the revision
Taken together, these revisions substantially strengthen the manuscript. The revised version presents the stratigraphic framework and analytical workflow more transparently, treats orbital interpretations more conservatively, makes the MME correlation explicitly multi-proxy, recognizes the important hiatus across the K/Pg interval, and grounds the paleoenvironmental discussion more directly in the Jordanian observations. We believe these changes address the central concerns raised by both reviewers while improving the clarity, reproducibility, and robustness of the manuscript.
Detailed responses to every comment are provided in two separate point-by-point documents: one for Reviewer 1 (Baptiste Suchéras-Marx) and one for Reviewer 2 (Sietske). In those documents, each reviewer comment is reproduced and followed by our response, including the specific figure, methodological, stratigraphic, or interpretative changes made in the revised manuscript.
We again thank the Editor and both reviewers for the time and care devoted to evaluating our work. Their comments have helped us improve the presentation and scientific argument of the manuscript substantially. We hope that the revised manuscript and the accompanying detailed responses satisfactorily address all of the concerns raised.
The new figures are at the end of the PDF attached below.
Sincerely,
The Authors
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AC1: 'Reply on RC2', jihede haj messaoud, 30 Sep 2026
Status: closed
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RC1: 'Comment on egusphere-2026-3135', Baptiste Suchéras-Marx, 29 Jul 2026
Dear editor,
I have read on your request the manuscript from Jihede Haj Messaoud and I have some comments.
I would whether ask for major revision or rejection of the manuscript. The first and main reason is that the figures are barely readable hence it is almost impossible to evaluate properly the manuscript. I have printed the draft but I also check on the pdf version but in both case, it is very difficult to see many aspects of the figures. Secondly, there are many uncertainties on some aspects of the manuscript that make the study difficult to understand. Below, you’ll find more specific comments.
Sincerely,
Baptiste Suchéras-Marx
Figure 1: a. text is not readable. b. wells and outcrops name are not readable. c. almost nothing is readable. The facies legend is missing. The description speaks about Group and Formation that are not shown on the figure.
Figure 2: I like to see the core but it would be more interesting to have a figure similar to figure 3 here and keep the current figure 2 for supplementary material.
Figure 3: TS curve is very difficult to see. Text is very pixelized. The term of “sequence boundary” seems very interpretative, I would rather use “disconformity”.
Figure 4: Nothing is readable. For what I supposed it is calcareous nannofossils, I don’t understand the scale.
Figure 5: Almost nothing is readable. And I don’t understand why this figure is not constructed the same way as figure 4. Also, I don’t get why the cool interval goes down to the Campanian whereas the cool-water taxa have the same percentage as in the warm interval. And the blue line in the middle is not defined.
Figure 6: Missing scale for photos 1 to 12. On photo 3, I don’t see the coccolith. On photo 5, I doubt it is a Watznaueria biporta.
Figure 7: Many species names are too small. And scale bar numbers too.
Figure 8: text is too small and scales too.
Figure 9: I don’t get why the tuned is before the untuned spectra. It is not logic. And so panel don’t have numbering/letters.
Figure 10: The dark band on the top figure is problematic because it seems to be a time line but it doesn’t correlate with the Campanian-Maastrichtian boundary. Again, text is too small. And please be more specific on the material analyzed for the δ13C whether it is δ13CTOC, δ13Cbulk carb or δ13Cforam/belem/brachio/etc
Figure 11: not called in the text hence useless.
Figure 12: This could be interesting but the authors never talk about the hiatus shown on this figure. So not fully exploited.
For all figures: the captions are way too interpretative. In many cases, some of the text there should be in the discussion and not the caption. For example, figure 9 which is in the Results section.
Authors should exclude the use of Middle Maastrichtian which does not exist. Please use the term of mid Maastrichtian. Moreover, you use Early/Late and Lower/Upper and early/late and lower/upper without considering that those have a meaning. Early/Late is use for time whereas Lower/Upper for stratigraphic interval. lower/upper is also for stratigraphic interval that were not formely defined by the ICS.
Method:
- Add a sub-section for the cyclostratigraphic analysis (software, algorithm, etc).
- section 3.2: you don’t say on which well you worked. The reader can only understand in the Results section. And add the magnification you have been using.
Results:
- section 4.1.1: the description is mostly derived from a published work. Hence it is not Results but rather Geological settings then.
- line 330: what mean “low to moderate”? Before, you gave numbers.
- line 356-357: do you mean oligotrophic conditions? If yes, say so.
- you show and use cool-water taxa (%). Please add the percentage uncertainties on those results for the reader to evaluate the importance of the change.
- section 4.3: in line 452, you give the name of the sample. But you don’t so for others. Please be consistent and do it for all level.
- line 434: Please define here “AOM”.
- line 494: You say “Late Campanian” but – and it is actually very difficult due to low quality of the figures – it seems to be in contradiction with the figures.
- section 4.8: this section should have some information in Methods. Moreover, you just don’t explain how you tuned the dataset which is highly critical for the interpretation. You give a sedimentation rates range but how did you came to these values? And I disagree with the statement that the 6.8 m cycle is persistent. On the wavelet, it is clear that it tends to split sometimes and that it is very weak in the chalk interval. It should be discussed then in term of sedimentation dynamics.
Discussion:
- One major concern in this discussion is the mechanism associated with the switch from cool to warm. It seems not logic to have more oxygeneous conditions with warmer conditions. Moreover, you discuss saying that in the warmer interval, runoff is more important with more terrestrial organic matter. If the runoff is more important and it is warmer, the logic would be more stratified conditions. But the preservation of the organic matter is better in the cool interval. You need to expand these points because it is conter-intuitive.
- section 5.2: you discuss dinocysts assemblages and peridinioid/gonyaulacoid ratio. Please show it on a figure.
- line 720: “Early-Middle Maastrichtian boundary” there is no “Middle Maastrichtian”.
- line 726: “that nutrient enrichment in the chalky marls unit” I guess you wish to discuss about “source” rather than enrichment. Probably need to rephrase because it is not clear.
- line 748: “The weak correlation between δ¹³C₍carb₎ and δ¹³C₍org₎ indicates partial decoupling of inorganic and organic carbon reservoirs.” It is clearly not logic with the beginning of the paragraph where you say that there is important diagenesis on δ¹³C₍carb₎. Please consider rewriting.
- line 840: I don’t understand this sentence.
- line 841: “promoted exceptional preservation of marine organic matter” is not true because you said that the organic matter was transformed with loss of N. Hence it cannot be “exceptional preservation”. Please consider finding another term.
- lines 894-909: this part is very important and explain a lot. It enjoyed it.
You talk about “K/Pg boundary” but this boundary has a clear meaning. You don’t have the K/Pg boundary because you have a disconformity. So please, don’t use this term.
Citation: https://doi.org/10.5194/egusphere-2026-3135-RC1 -
AC2: 'Reply on RC1', jihede haj messaoud, 30 Sep 2026
We sincerely thank both reviewers for their careful and constructive evaluations. Their comments prompted substantial revisions that improved the clarity, methodological transparency, and robustness of the manuscript. Pasted markdown
Major revisions include: improved figure readability and consistency; expanded geological and paleogeographic context; a more detailed and reproducible cyclostratigraphic workflow; independent evaluation of GR cyclicity using sedimentological and geochemical proxies; and explicit consideration of variable sedimentation rates and changing cycle thickness. Pasted markdown
We also strengthened the age model using integrated biostratigraphy, chemostratigraphy, and cyclostratigraphy; clarified the significant hiatus across the K/Pg interval; and revised identification of the mid-Maastrichtian Event (MME) using carbon-isotope features, nannofossil bioevents, and cyclostratigraphic constraints. Pasted markdown
The paleoenvironmental discussion has been reorganized to link interpretations more directly to the Jordanian datasets, including GR, TOC, nannofossils, stable isotopes, detrital proxies, sedimentation rates, and the sequence-stratigraphic framework. Terminology and the distinction between observations and interpretations have also been standardized throughout. Pasted markdown
Overall, these revisions provide a clearer stratigraphic framework, a more reproducible analytical workflow, a more conservative orbital interpretation, and a stronger multi-proxy basis for the MME and paleoenvironmental reconstruction.
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AC2: 'Reply on RC1', jihede haj messaoud, 30 Sep 2026
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RC2: 'Comment on egusphere-2026-3135', Sietske Batenburg, 06 Aug 2026
Dear authors and editor,
Thank you for the manuscript “Astronomical pacing and 1 impact of the Middle Maastrichtian warming event on the Maastrichtian upwelling system of the southern Neo-Tethys Ocean margin (Jordan)” by Messaoud and co-authors. The manuscript provides new data from the Tethyan margin which can provide new insights. However, the presentation of the data is not adequate to evaluate the manuscript. The resolution of the figures is too low. While the authors prepare better resolution figures, I encourage them to consider incorporating other elements.
Geologic setting
Consider including a paleogeographic map of the Tethyan margin area. Are the 7 wells in figure 1 indicated on the map, and do these include the studied wells?
Methodology
Please provide more information on how the GR data were collected for the different cores or wells and how they were made into a composite record (Fig. 9).
Include information on how time series analysis was performed, such as the software used and the settings applied. Consider performing time series analyses on the TOC data.
Explain how the tuning was performed.
Results
Display the results of the SA-01 core where they are described (before figure 3). Line 254 suddenly mentions cycles, indicate what this refers to. The subscript of figure 2 discusses non displayed items from line 271 onwards.
Consider presenting an age-depth plot for both cores, with all the available age information, including the biostratigraphic datums, d13C events and the cyclostratigraphic tuning.
Section 4.7 might be better suited for the discussion, and the authors should discuss how the position of the K/Pg boundary is inferred, or whether there is a hiatus. Discuss whether you think that the entire record is (biostratigraphically) complete.
Provide data tables.
Cyclostratigraphy:
Discuss if there is a rhythmic alternation of lithologies and whether this is reflected in the GR record. The text mentions an estimated sedimentation rate, please explain how this rate was obtained. The GR series is tuned, but any information on how this was done is lacking. The MTM spectrum of the tuned GR series looks less convincing than the spectral analysis in the depth domain. The colourmap of the wavelet does not allow identification of dominant periodicities.
Some observations on the variations in the GR data: Prominent peaks around 80 m follow a longer periodicity in the depth domain than peaks around 130 m, yet all are interpreted as short eccentricity (figure 12). They may be driven by other periodicities, or there might be changes in sedimentation rate.
Discussion
The identification of the mid Maastrichtian event is critical for this paper, yet not an easy feat and the main figure (10) can be improved. Why are there two panels, and why does the d13C curve of Gubbio look different in the two panels?
Section 5.5 has a lot of paleoenvironmental mechanisms, but these are not clearly linked to the own data.
Generally, the manuscript would benefit from a slight restructuring. Several figure captions detail the paleoenvironmental interpretation, which is better suited for the main text. Elements are missing, and a figure should be moved, as discussed above. Please pay attention to the capitalisation and correct use of early/late, lower/upper, and write mid-Maastrichtian event.
Citation: https://doi.org/10.5194/egusphere-2026-3135-RC2 -
AC1: 'Reply on RC2', jihede haj messaoud, 30 Sep 2026
Dear Editor and Reviewers,
We sincerely thank both reviewers for their careful, constructive, and detailed evaluations of our manuscript. Their comments were highly valuable and prompted a substantial revision of the manuscript. In particular, the reviews highlighted the need to improve figure readability, strengthen methodological transparency, clarify the stratigraphic terminology and age control, make the cyclostratigraphic workflow fully reproducible, refine the identification of the mid-Maastrichtian Event (MME), clarify the nature of the K/Pg interval, and link the paleoenvironmental interpretations more directly to the measured Jordanian datasets.
We have reorganized several parts of the manuscript, revised the principal figures, expanded the Methods and Results, and made the Discussion more explicitly data-driven. Our aim throughout the revision was to distinguish more clearly between direct observations, stratigraphic correlations, and paleoenvironmental interpretations, while retaining the integrated multi-proxy approach that forms the basis of the study.
Major revisions made in response to the reviewers
- Figures and graphical presentation. All main figures have been reconsidered for publication-scale readability. Text, axes, species names, scale bars, symbols, and legends are being enlarged or reorganized where necessary, and pixelized/rasterized text is avoided where possible. Figures 4 and 5 are being standardized so that comparable datasets are displayed using a consistent graphical architecture and scale. Captions are also being revised to remain descriptive rather than interpretative.
- Geological and paleogeographic framework. The geological-setting section has been strengthened by separating regional paleogeographic context from the local well and correlation framework. The revised presentation includes a Maastrichtian paleogeographic reconstruction of the southern Neo-Tethyan margin and a geological map/correlation figure that explicitly identifies the studied SA-01 and AJ-02 wells and distinguishes them from additional wells or sections used only for regional correlation.
- Cyclostratigraphic methodology and reproducibility. A dedicated cyclostratigraphic Methods subsection has been added and expanded. It now describes the origin and construction of the gamma-ray records, preprocessing and interpolation, detrending, MTM spectral analysis, the background-noise model and significance testing, evolutionary/wavelet analysis, filtering, orbital-band evaluation, astronomical tuning, and age-model construction. The revised workflow presents the untuned depth-domain analysis before the tuned time-domain analysis, because the former provides the primary evidence for sedimentary cyclicity.
- Independent testing of cyclicity. Following Reviewer 2's suggestion, the cyclicity identified in the gamma-ray record is evaluated against independent sedimentological and geochemical proxies, including TOC and other compositional records. This provides an additional test of whether the observed spectral structure reflects depositional cyclicity rather than being an artifact of a single proxy.
- Variable sedimentation rates and cycle thickness. We no longer imply that a given orbital component must have a constant thickness throughout the core. The revised sedimentation-rate reconstruction documents substantial stratigraphic variability, including rates of approximately 3 cm kyr-1 between 139 and 128 m, approximately 1.8-2.0 cm kyr-1 between 128 and 110 m, an increase to approximately 4.2 cm kyr-1 around 106 m, and an upward decrease toward approximately 2.1-2.3 cm kyr-1. This variability provides an important explanation for changing cycle thickness in the depth domain. Consequently, individual GR peaks are not assigned to short eccentricity solely on the basis of spacing; the orbital interpretation is instead based on the overall spectral hierarchy, stratigraphic evolution of spectral power, independent age constraints, sedimentation-rate changes, and recurrence in other proxies.
- Age control and stratigraphic completeness. The age framework has been clarified by integrating biostratigraphic constraints, chemostratigraphic events, and the cyclostratigraphic model. Age-depth relationships for the studied cores are presented more explicitly, including intervals of condensation. We also expanded the discussion of stratigraphic completeness rather than assuming that the succession is continuous.
- K/Pg interval and hiatus. The revised manuscript explicitly recognizes that the K/Pg boundary itself is not continuously preserved in SA-01. The uppermost Cretaceous samples contain a late Maastrichtian assemblage assigned to upper UC20b, whereas the first clearly identified Paleogene assemblage is attributable to NP3 near 53 m. The intervening UC20c-UC20d and NP1-NP2 assemblages are not recorded. We therefore interpret a substantial hiatus spanning the latest Maastrichtian, the K/Pg boundary, and part of the early Danian. Accordingly, the physical surface is described as a disconformity/hiatus and is not itself labelled as the K/Pg boundary.
- Identification of the mid-Maastrichtian Event. Because identification of the MME is central to the manuscript, its stratigraphic placement has been made more explicit and conservative. The revised interpretation does not rely on visual similarity of a single carbon-isotope curve. Instead, the MME is identified using the combined M1+, M1-, M2+, M2-, and M3+ carbon-isotope features together with the succession of calcareous nannofossil bioevents, including Uniplanarius trifidus, Broinsonia parca constricta, Tranolithus orionatus, Reinhardtites levis, Micula praemurus, and Lithraphidites quadratus, and the cyclostratigraphic framework. We also distinguish the broader approximately 69.5-67.5 Ma mid-Maastrichtian climatic perturbation from the shorter approximately 570 kyr MME sensu stricto following Dubicka et al. (2024).
- Revised MME correlation figure. The previous two-panel presentation is replaced by a single internally consistent correlation panel using the same Gubbio reference dataset and scaling throughout. The revised figure emphasizes the diagnostic carbon-isotope features and independent nannofossil bioevents used to constrain the Jordanian record, thereby removing the apparent inconsistency between the two former panels.
- Paleoenvironmental interpretation anchored to the data. The Discussion has been reorganized so that interpretations of productivity, oxygenation, organic-carbon burial, climate, sea level, and upwelling are directly connected to the measured datasets. Particular emphasis is placed on GR and TOC cyclicity, the transition from organic-rich to carbonate-rich facies, changes in cool-water nannofossil taxa and Watznaueria, the oxygen-isotope trend, detrital proxies such as Al2O3 and Ti, reconstructed sedimentation rates, and the independently developed sequence-stratigraphic/relative sea-level framework. Interpretations that cannot be directly demonstrated by the Jordanian data have been softened.
- Nannofossil and dinocyst presentation. The nannofossil percentage scales and counting approach are clarified, and uncertainty estimates are added for the cool-water taxon percentages. Where dinocyst assemblages and the peridinioid/gonyaulacoid ratio are used as a central argument, the underlying data are displayed and described in the Results before being interpreted in the Discussion.
- Terminology and distinction between observation and interpretation. Terminology has been standardized throughout the manuscript. 'Middle Maastrichtian' is replaced by 'mid-Maastrichtian'; Early/Late is used for geochronologic time and Lower/Upper where appropriate for chronostratigraphic usage. The term 'sequence boundary' is replaced by the observational term 'disconformity' where the physical surface is documented, with sequence-stratigraphic interpretation reserved for the text. Similarly, overly strong language such as 'exceptional preservation' is replaced by more precise wording concerning enhanced net organic-carbon burial or accumulation.
- Carbon-isotope interpretation. The interpretation of the weak relationship between delta13Ccarb and delta13Corg has been revised. Because the carbonate signal may be affected by diagenetic modification, the manuscript no longer treats the weak correlation as direct evidence for primary carbon-reservoir decoupling. Instead, it is presented more cautiously as evidence that the two records did not respond identically, while explicitly acknowledging the limitations imposed by carbonate alteration.
- Results organization and supplementary data. Background material derived primarily from previous studies has been moved from the Results to the Geological Setting/Stratigraphy section. The SA-01 observations are introduced before interpretation and comparison with AJ-02, sample identifiers are standardized, abbreviations such as amorphous organic matter (AOM) are defined at first use, and numerical data tables are provided as supplementary Excel files.
Overall outcome of the revision
Taken together, these revisions substantially strengthen the manuscript. The revised version presents the stratigraphic framework and analytical workflow more transparently, treats orbital interpretations more conservatively, makes the MME correlation explicitly multi-proxy, recognizes the important hiatus across the K/Pg interval, and grounds the paleoenvironmental discussion more directly in the Jordanian observations. We believe these changes address the central concerns raised by both reviewers while improving the clarity, reproducibility, and robustness of the manuscript.
Detailed responses to every comment are provided in two separate point-by-point documents: one for Reviewer 1 (Baptiste Suchéras-Marx) and one for Reviewer 2 (Sietske). In those documents, each reviewer comment is reproduced and followed by our response, including the specific figure, methodological, stratigraphic, or interpretative changes made in the revised manuscript.
We again thank the Editor and both reviewers for the time and care devoted to evaluating our work. Their comments have helped us improve the presentation and scientific argument of the manuscript substantially. We hope that the revised manuscript and the accompanying detailed responses satisfactorily address all of the concerns raised.
The new figures are at the end of the PDF attached below.
Sincerely,
The Authors
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AC1: 'Reply on RC2', jihede haj messaoud, 30 Sep 2026
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- 1
Dear editor,
I have read on your request the manuscript from Jihede Haj Messaoud and I have some comments.
I would whether ask for major revision or rejection of the manuscript. The first and main reason is that the figures are barely readable hence it is almost impossible to evaluate properly the manuscript. I have printed the draft but I also check on the pdf version but in both case, it is very difficult to see many aspects of the figures. Secondly, there are many uncertainties on some aspects of the manuscript that make the study difficult to understand. Below, you’ll find more specific comments.
Sincerely,
Baptiste Suchéras-Marx
Figure 1: a. text is not readable. b. wells and outcrops name are not readable. c. almost nothing is readable. The facies legend is missing. The description speaks about Group and Formation that are not shown on the figure.
Figure 2: I like to see the core but it would be more interesting to have a figure similar to figure 3 here and keep the current figure 2 for supplementary material.
Figure 3: TS curve is very difficult to see. Text is very pixelized. The term of “sequence boundary” seems very interpretative, I would rather use “disconformity”.
Figure 4: Nothing is readable. For what I supposed it is calcareous nannofossils, I don’t understand the scale.
Figure 5: Almost nothing is readable. And I don’t understand why this figure is not constructed the same way as figure 4. Also, I don’t get why the cool interval goes down to the Campanian whereas the cool-water taxa have the same percentage as in the warm interval. And the blue line in the middle is not defined.
Figure 6: Missing scale for photos 1 to 12. On photo 3, I don’t see the coccolith. On photo 5, I doubt it is a Watznaueria biporta.
Figure 7: Many species names are too small. And scale bar numbers too.
Figure 8: text is too small and scales too.
Figure 9: I don’t get why the tuned is before the untuned spectra. It is not logic. And so panel don’t have numbering/letters.
Figure 10: The dark band on the top figure is problematic because it seems to be a time line but it doesn’t correlate with the Campanian-Maastrichtian boundary. Again, text is too small. And please be more specific on the material analyzed for the δ13C whether it is δ13CTOC, δ13Cbulk carb or δ13Cforam/belem/brachio/etc
Figure 11: not called in the text hence useless.
Figure 12: This could be interesting but the authors never talk about the hiatus shown on this figure. So not fully exploited.
For all figures: the captions are way too interpretative. In many cases, some of the text there should be in the discussion and not the caption. For example, figure 9 which is in the Results section.
Authors should exclude the use of Middle Maastrichtian which does not exist. Please use the term of mid Maastrichtian. Moreover, you use Early/Late and Lower/Upper and early/late and lower/upper without considering that those have a meaning. Early/Late is use for time whereas Lower/Upper for stratigraphic interval. lower/upper is also for stratigraphic interval that were not formely defined by the ICS.
Method:
- Add a sub-section for the cyclostratigraphic analysis (software, algorithm, etc).
- section 3.2: you don’t say on which well you worked. The reader can only understand in the Results section. And add the magnification you have been using.
Results:
- section 4.1.1: the description is mostly derived from a published work. Hence it is not Results but rather Geological settings then.
- line 330: what mean “low to moderate”? Before, you gave numbers.
- line 356-357: do you mean oligotrophic conditions? If yes, say so.
- you show and use cool-water taxa (%). Please add the percentage uncertainties on those results for the reader to evaluate the importance of the change.
- section 4.3: in line 452, you give the name of the sample. But you don’t so for others. Please be consistent and do it for all level.
- line 434: Please define here “AOM”.
- line 494: You say “Late Campanian” but – and it is actually very difficult due to low quality of the figures – it seems to be in contradiction with the figures.
- section 4.8: this section should have some information in Methods. Moreover, you just don’t explain how you tuned the dataset which is highly critical for the interpretation. You give a sedimentation rates range but how did you came to these values? And I disagree with the statement that the 6.8 m cycle is persistent. On the wavelet, it is clear that it tends to split sometimes and that it is very weak in the chalk interval. It should be discussed then in term of sedimentation dynamics.
Discussion:
- One major concern in this discussion is the mechanism associated with the switch from cool to warm. It seems not logic to have more oxygeneous conditions with warmer conditions. Moreover, you discuss saying that in the warmer interval, runoff is more important with more terrestrial organic matter. If the runoff is more important and it is warmer, the logic would be more stratified conditions. But the preservation of the organic matter is better in the cool interval. You need to expand these points because it is conter-intuitive.
- section 5.2: you discuss dinocysts assemblages and peridinioid/gonyaulacoid ratio. Please show it on a figure.
- line 720: “Early-Middle Maastrichtian boundary” there is no “Middle Maastrichtian”.
- line 726: “that nutrient enrichment in the chalky marls unit” I guess you wish to discuss about “source” rather than enrichment. Probably need to rephrase because it is not clear.
- line 748: “The weak correlation between δ¹³C₍carb₎ and δ¹³C₍org₎ indicates partial decoupling of inorganic and organic carbon reservoirs.” It is clearly not logic with the beginning of the paragraph where you say that there is important diagenesis on δ¹³C₍carb₎. Please consider rewriting.
- line 840: I don’t understand this sentence.
- line 841: “promoted exceptional preservation of marine organic matter” is not true because you said that the organic matter was transformed with loss of N. Hence it cannot be “exceptional preservation”. Please consider finding another term.
- lines 894-909: this part is very important and explain a lot. It enjoyed it.
You talk about “K/Pg boundary” but this boundary has a clear meaning. You don’t have the K/Pg boundary because you have a disconformity. So please, don’t use this term.