| 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.
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.