the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 21 Jul 2026
Carbon Cycle Perturbance During the Carnian Pluvial Episode (Larne Basin, Northern Ireland)
Abstract. The Late Triassic Carnian Pluvial Episode (CPE, ~232 Ma) marks a major global climatic transition characterized by intensification of humid conditions following a prolonged period of aridity through much of the Triassic. This episode triggered profound environmental and biotic change that ushered in modern environments and ecosystems. Here, we present a new high-resolution integrated geochemical and sedimentological record from the Knocksoghey Formation, Mercia Mudstone Group, in the Larne Basin, Northern Ireland. The high-resolution organic carbon isotopes document a ~4 ‰ negative excursion, whose onset coincides with a small, reproducible rise in Hg concentrations from background levels, thought to be associated with the emplacement of the Wrangellia Large Igneous Province (LIP). The geochemical anomalies stratigraphically closely precede a pulse of coarse siliciclastics, indicative of intensified weathering driven by enhanced rainfall, and are followed by a return to arid, restricted conditions, marked by deposition of stacked anhydrite nodules and beds. The CPE was previously suggested to be characterized by a succession of negative carbon isotope excursions (NCIEs) in sedimentary archives. However, our new data demonstrates a more protracted stepped carbon cycle perturbance, as reflected by a single, stratigraphically prolonged carbon isotope excursion, comparable in nature to NCIEs observed during other LIP-driven climatic perturbations, such as the Toarcian Oceanic Anoxic Event.
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Status: open (until 15 Sep 2026)
- RC1: 'Comment on egusphere-2026-2964', Anonymous Referee #1, 24 Jul 2026 reply
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- 1
Publisher’s note: a supplement was added to this comment on 27 July 2026.
This study examines the record of the Carnian Pluvial Event (CPE) in a drillcore through continental facies in northern Ireland. The main goal is to evaluate the relationship of the CPE to volcanic activity (proxied by Hg concentrations), which is assumed to be associated with the Wrangellia LIP.
Summary: There are many problems, both large and small, with this study that preclude publication in its present form. It can either be rejected or assigned “major revision followed by re-review”, depending on the editor’s preference.
Weathering proxy calculations: In looking at Figure 3, I realized that the calculated CIA values are completely in error. CIA values begin around 40-50 for fresh (unweathered) igneous rocks and go to 100 for highly weathered sediments. All of the values here are <25, which probably means that carbonate CaO has not been subtracted out. CIA is a proxy for silicate weathering intensity, so CaO associated with carbonates and phosphates must first be removed, yielding a silicate CaO value (designated CaO*). The authors seem completely unaware of this (while the first two authors may be students, why didn’t any of the more senior authors further down the authorship list catch such a serious problem??). The same thing applies to the CIW values.
Significance of volcanic proxy evidence: The authors document modest increases in Hg concentrations in the study core, but the significance of these data is uncertain. Rather than volcanic inputs, higher Hg concentrations might have resulted from redox changes (e.g., a shift to more reducing conditions, e.g., Shen et al. 2019) or decreased sedimentation rates (e.g., Liu and Algeo, 2020). Demonstrating that the increased Hg concentrations were due to enhanced volcanic Hg fluxes generally requires paired Hg isotope data, with a shift to near-zero values of D199Hg reflecting volcanic inputs.
Shen, J., Algeo, T.J., Chen, J., Planavsky, N.J., Feng, Q., Yu, J. and Liu, J., 2019. Mercury in marine Ordovician/Silurian boundary sections of South China is sulfide-hosted and non-volcanic in origin. Earth and Planetary Science Letters, 511, pp.130-140.
Liu, J. and Algeo, T.J., 2020. Beyond redox: Control of trace-metal enrichment in anoxic marine facies by watermass chemistry and sedimentation rate. Geochimica et Cosmochimica Acta, 287, pp.296-317.
Also, even if the increased Hg concentrations represent volcanic inputs, there is no evidence showing that the volcanic Hg came from the Wrangellia LIP—this is merely a speculation. Speculation is okay but it must be acknowledged as such in the text.
The Introduction is full of factual misstatements—I identified four errors on lines 34-42.
Project goals--What are the study goals? They need to be articulated in the final paragraph of the Introduction. The text is just stating what the authors did, not what the project goals were.
Figure 1—the Wrangellia LIP is shown as a huge feature, far larger than any modern continent. The actual size might have been ~20% of what is shown here.
Other figures—nearly all of the figures need various improvements per the comments that I have added to them.
Language—there are numerous errors in verb tense, subject-verb agreement, word choice, grammar and other issues. I have pointed some of them out with comments, but one of the native-English-speaking coauthors needs to go over the manuscript carefully and correct all of the language errors.