the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 27 May 2026
Milankovitch Forcing and Nonlinear Climate Variability during the Late Givetian (Appalachian Basin, New York, USA)
Abstract. Astronomical forcing is a major driver of Earth's climate variability, yet the linear and nonlinear climate responses to this forcing under warmer-than-present conditions remain poorly constrained. We use cyclostratigraphy of the Sherburne Formation, a Givetian record from the Appalachian Basin, to characterize Milankovitch cyclicity and evaluate the complex climatic behavior inferred from the sedimentary record. A new cyclostratigraphic age model refines the timing of the regional Fir Tree, Hubbard Quarry and Lodi events and places the onset of the global Frasnes Crisis (represented by the regional Lodi Event) into an astronomically calibrated framework. Our results reveal precession-eccentricity-paced detrital influx, obliquity amplification, precession-obliquity interference patterns, half-precessional cyclicity, and nonlinear climate-sediment dynamics. These findings show how pantropical late Givetian climate variability is shaped by high- and low-latitude climatic and hydrologic teleconnections and highlight the sensitivity of Devonian climate to orbital variability.
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- RC1: 'Comment on egusphere-2026-2034', Anonymous Referee #1, 30 Jul 2026 reply
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General comments:
This study concerns the cyclostratigraphic investigation of a late Givetian core from the Appalachian Basin, US. The authors apply robust cyclostratigraphic techniques to construct an astrochronological framework for the core, constraining the duration of several lithological units as well as regional and global events. Their analysis reveals potential sub-Milankovitch forcing, including half-precession cycles, something that has rarely been demonstrated in the Devonian as of yet.
The minimal tuning approach is appropriate for the presented record, which has limited independent age control and lacks exact durations for precession and obliquity. This minimal 405-kyr based tuning is complemented by a precession-based age model that takes into account high-frequency sedimentation rate changes. The manuscript integrates cyclo- and sequence stratigraphic interpretations and takes the depositional context into consideration. The description of the cyclostratigraphic approach is sufficiently detailed.
The authors provide an excellent explanation of nonlinear interactions, including Figure 8. In general, the figures are clear and informative.
The only aspect that appears lacking at times is a detailed explanation of the climatic and depositional mechanisms that underly the transfer of the detected astronomical signals to the sedimentary record, particularly regarding phase relationships. This is kept vague; perhaps intentionally, to avoid speculation, but it feels lacking nonetheless.
Overall, this is a well-written, valuable contribution to the field of Devonian cyclostratigraphy and paleoclimatology. I do have several specific comments, as well as a few technical corrections, which are provided below. Addressing these concerns constitutes minor revisions.
Kind regards.
Specific comments:
Line 84, section 2 in general: Figure 1b indicates the Genesee, Tully, and Hamilton Groups, but nowhere in this section does it state to which of these groups the Sherburne Fm belongs. This should be clarified somewhere in the first paragraph.
Figure 2: While I understand the aim behind it, only showing selected depth intervals at lithological boundaries makes the figure somewhat harder to read, especially regarding the scale of the cyclicity in GRS and MS. I suggest just adding a continuous depth scale instead. The auloporid indicators are also very hard to see.
Line 200-203: Please elaborate on how it was established that the gamma ray signal mostly tracks detrital input in the core. Did the authors compare silt/clay content with the gamma ray signal across selected intervals? This information is not visible from the litholog in Figure 2, which does not show much detail.
Line 218: The Bonferroni correction is carried out and displayed in Figure S1, but many peaks that are not significant after the Bonferroni correction are still used and discussed in a cyclostratigraphic context (e.g. the 0.32-0.69 m peaks in Fig. S1a, 6.5 and 3.0 m peaks in panel b, and most of sub-Milankovitch peaks in panels e and f). While I do not think that this is fundamentally a problem – there are other lines of evidence aside from statistical significance – if this correction is included, it should at least be addressed how and why exactly it is used, and in which cases the authors decide to disregard it (in favour of other evidence).
Line 220: I suggest adding ‘e.g.’ to the ‘Arts, 2023; Arts et al., 2024’ citation, as this is not the first use of CWT for cyclostratigraphic purposes and the authors do not specifically refer to the use of WaverideR here.
Figure 3: I would add the bandpass widths rather than just giving an average (e.g. ~1.0 m), it is more transparent.
Line 295-296: The specific durations of the astronomical parameters in the Givetian require a reference.
Line 302: Why was TimeOpt only run up to 4.0 cm/kyr when the initial hypothesis is pretty close to that maximum (3.0 cm/kyr), rather than, say, up to 5 or 6 cm/kyr? Especially since the max envelope r2 for one of the cases (MS, short and long eccentricity) is very close to 4 cm (3.94 cm/kyr; Fig. S4). Is it a mathematical constraint arising from the length of the record? Please elaborate and, if possible, increase the permitted sedimentation rate, at least for the precession-short eccentricity combination. In addition, have the authors considered running TimeOptSim in order to assess the robustness of these results? Finally, what error margins were used for the input astronomical frequencies in TimeOpt? This can be found in the code, but it’d be easier for readers to just place this in information in the caption.
Line 309: The absolute age estimates of the conodont zones in Becker et al. 2020 are only estimates; while I agree that the order of magnitude is likely correct and agrees with the cyclostratigraphic interpretation obtained here, this duration should be presented a bit more carefully.
Line 334: Not sure if I agree with the ± 29 kyr being a realistic error margin. It does not include any other sources of error such as the miscounting of precession cycles; for example at the boundary between the different members where you have the signal ‘jump’; or in broad peaks that could either be interpreted as a double or a single peak; or small differences in the number of cycles depending on the width of the bandpass filters. And this is only including ‘internal’ errors inherent to the interpretation of the signal, not including e.g. uncertainties in the exact duration of precession. Don’t get me wrong, including an error estimate at all is great, and a step forward from many cyclostratigraphic studies – but if the authors are going to include it, they may as well do it carefully.
Figure 4, 5, etc: Again, I would like to see the actual bandwidths of the bandpass filters in the figures for transparency.
Figure 6c: The difference between dotted and dashed diagonals is very hard to see.
Lines 439-450: While I agree that changes in detrital influx are the most likely underlying process here, considering the hyperpycnite interpretation, changes in the amount of detrital content could also be the result of changes in carbonate influx (i.e. productivity cycles) – do you see any evidence for that in this core based on the lithology?
Lines 456-457: I don’t completely understand phase relationship that is meant by ‘high γ- and χ-values are interpreted to reflect periods of strong climatic precession’. Do you link high GR and MS values to either precession minima or maxima (how do you arrive at that phase relationship?), or do you mean that extreme (either low or high) GR and MS values are linked to precession extrema? Or something else?
Figure 9b: Please add a unit to the y-axis.
Lines 684-693: I do not understand the point behind this exercise and this paragraph if no conclusions are drawn from it; it could be removed in my opinion.
Lines 760-762: This is mostly a (potentially ill-informed) question arising from my limited experience with half-precession cycles, but are they not fundamentally restricted to the intertropical belt, specifically the region between max ~24° N and ~24° S where the sun can be directly overhead twice a year during both equinoxes? If so, would it not have to be a teleconnection mechanism (either through ocean circulation in the tropics, or potentially even continental precipitation dynamics in the tropics, depending on the size of the catchment system that ultimately drains into the Appalachian Basin)? But the use of ‘amplify’ here seems to suggest to me that you can also have ‘in-situ’ half-precession forcing at higher latitudes, which I don’t really understand.
Technical comments:
Line 69: First instance in the main text of ‘late Givetian’, I suggest adding ‘(“Middle Devonian”) to orient readers who may not be familiar with Devonian stratigraphic terminology.
Line 95: Add ‘groups’ after ‘…the Genessee, Tully and Hamilton…’?
Line 288: Remove ‘~1 m’ (you mention three key components in this sentence and then list four; the fourth 1 m component is already discussed separately in the next sentence).
Line 403: ‘do’ rather than ‘does’?
Line 418: Fig. 8 is referenced here before Fig. 7.
Line 481: ‘….unfolds on the decreasing limb..’, rather than ‘…unfolds of the decreasing limb…’?
Line 709: ‘Fig. 7a’ instead of ‘Fig. 7A’ for consistency.
Line 793-796: This is very much a stylistic preference so feel free to ignore, but the repetition of ‘exerted considerable control’, ‘exerted strong control’ and ‘underscoring the strong and complex influence’ reads somewhat excessive.
Line 827, references in general: There are some inconsistencies with DOIs being added or not; I suggest adding them for all references that have one available.
Line 914: This reference is missing a title.