Chloé Franca Margot Marcilly

• Domeier, Mathew Michael; Gallo, Leandro C.; Marcilly, Chloé M. & Torsvik, Trond H. (2026). Quadrupolar sea level fluctuations reveal episodes of rapid polar wander. Science. ISSN 0036-8075. 394(6819), p. 87–90. doi: 10.1126/science.aec8423. Full text in Research Archive Show summary

  True polar wander (TPW) is presently occurring at a rate of ~10 centimeters per year, exceeding the mean rate of differential plate motion. Whether this rate is transient and negligible on geological timescales or whether Earth has experienced rapid TPW lasting millions of years is unclear. Paleomagnetic evidence has been used to propose fast episodes of TPW, but limitations of the paleomagnetic record have precluded definitive results. Rapid TPW will induce global sea level fluctuations associated with relative changes in centrifugal potential, offering an independent test. We evaluated this prediction using continental flooding reconstructions and identified multiple robust quadrupolar patterns since 320 million years ago, confirming that protracted rapid TPW has occurred on Earth and that couplings among Earth’s rotational dynamics, mantle processes, and surface environments can be strongly episodic.

• Marcilly, Chloe M. & Torsvik, Trond H. (2026). Palaeogeography and palaeoelevation through time: controls on weatherability and long-term CO2 evolution. Geological Society Special Publication. ISSN 0305-8719. 565(1). doi: 10.1144/gslspecpub2025-135. Full text in Research Archive Show summary

  Palaeogeography plays a fundamental control on Earth's long-term climate by regulating the efficiency of silicate weathering, the primary negative feedback stabilizing atmospheric CO 2 over geological timescales. Accurate reconstructions of past land distribution, topography and shelf geometry are therefore essential for quantifying weatherability and modelling deep-time climate–carbon cycle interactions. In this study, we present a new Paleozoic palaeogeographic and palaeoelevation model that can be extended for the whole Phanerozoic. Using updated plate tectonic models, fossil-constrained land–sea boundaries, climatically sensitive lithologies and physically informed elevation classes derived from modern Earth statistics, we produce global 10 Myr-interval maps that include seven topographic layers from deep shelves (−200 m) to high mountains (>4 km). Our approach improves estimates of exposed land area, shallow and deep continental shelves, and regions of high weatherability. We show that differences in land distribution within ±10° of the equator and within climatically defined high-weatherability zones, strongly affect CO 2 predictions in carbon-cycle models, particularly during the Early Paleozoic and the Devonian. The new reconstructions refine Paleozoic sea-level estimates and reveal how evolving continental elevations modulated silicate weathering intensity and contributed to transitions between greenhouse and icehouse states, including the initiation and termination of the Late Paleozoic Ice Age.

• Torsvik, Trond Helge; Cocks, L. Robin M.; Domeier, Mathew Michael; Marcilly, Chloe M. & Dowding, Elizabeth M. (2025). Devonian palaeogeography and environmental change: an incomplete chronicle. Zeitschrift der Deutschen Gesellschaft fur Geowissenschaften. ISSN 1860-1804. 176(2), p. 193–214. doi: 10.1127/zdgg/2025/0454. Full text in Research Archive Show summary

  Abstract: The 60-million-year-long Devonian Period witnessed a host of major environmental changes, encompassing the rise and global expansion of large land plants, the occurrence of several major biological turnovers (including the third largest mass-extinction), and significant fluctuations in atmospheric CO2 that may have, enigmatically, been decoupled from coeval trends in global temperature. Despite their importance, the origins and impacts of these environmental changes remain poorly understood. Palaeogeography undoubtedly played a key role in instigating and influencing these changes, but it too remains ill-resolved in Devonian time. Here we seek to both illuminate and promote the further consideration of the interplay between the evolving palaeogeography of the Devonian and its environmental transitions. We present a detailed dissection of the changing geography, palaeobiology and environment of the Devonian at the regional and global scale, together with a series of new palaeogeographic and palaeoenvironmental reconstructions. We also compare our new reconstructions with other widely used reconstructions from this time and discuss some key outstanding uncertainties whose resolution will be essential to further unravel the

• Marcilly, Chloé Franca Margot; Torsvik, Trond Helge & Jones, Morgan Thomas (2025). Late Paleozoic climate transition from a long-term carbon cycle modeling perspective. Global and Planetary Change. ISSN 0921-8181. 253. doi: 10.1016/j.gloplacha.2025.104984. Full text in Research Archive Show summary

  The Late Paleozoic ice age (LPIA) is the longest-lived Phanerozoic icehouse climate and the only recorded greenhouse–icehouse–greenhouse cycle on a vegetated Earth. Sedimentary archives partially detail the glaciation events, but the reasons and timing of the LPIA's onset (∼330 Ma) and end (∼260 Ma) remain debated. In many models, the shift to icehouse conditions is linked to enhanced CO2 uptake through silicate weathering, but the causes of this increased carbon sink are unclear. Most carbon cycle models are limited by their non-dimensional nature, and spatially resolved models rely heavily on variables such as topography and bathymetry, which are difficult to constrain over time. This study investigates the influence of weatherability reconstructions in non-dimensional versus spatially resolved models in the context of the LPIA's onset and ending. We review constraints on simulated silicate weathering fluxes and test forcings affecting its rate. Our paleogeographic forcing review uses newly developed land-maps and reconstructed climatic belts to constrain weathering based on fossil paleo-indicators. Our findings suggest that increased land availability in the high weatherability zones (HWZ) led to enhanced weathering processes, likely contributing to the glaciation onset. However, when a high solid Earth degassing factor is included, the likelihood of an extensive glaciation diminishes, indicating the need for an intensified CO2 sink driven by higher erosion rates and associated chemical weathering tied to topographic elevation to instigate widespread glaciation. A reduction in available land for weathering in the HWZ appears to have a determining role in the LPIA's termination.

• McGairy, Anna; Nguyen, Phong Duc; Williams, Mark; Stocker, Christopher P.; Harvey, Thomas H. P. & Komatsu, Toshifumi [Show all 10 contributors for this article] (2025). An Ordovician Assemblage of Cool Water-Adapted Paleotropical Ostracods Suggests an Early Psychrosphere. Island Arc. ISSN 1038-4871. 34(1). doi: 10.1111/iar.70001. Full text in Research Archive Show summary

  An ostracod assemblage from the Late Ordovician (Katian) Phu Ngu Formation of northern Vietnam, South China paleoplate, yields typical Baltic and Laurentian-affinity genera together with some endemic forms. Detailed paleontological and sedimentary analysis of the Phu Ngu Formation suggests it was deposited in a deeper marine forearc setting, below storm wave base, but with (at least intermittently) oxygenated sea-bottom conditions. Taphonomic assessment of the ostracod assemblage suggests it is in situ. The occurrence of globally widespread ostracod genera, including those from paleocontinents that were geographically remote from South China, is difficult to reconcile with the assumed limited dispersal capability of ostracods in shallow-shelf settings—a characteristic that has often been used to refine Ordovician paleogeographical reconstructions. Here, we present the novel approach of using paleoclimate reconstructions to assess the environmental distributions of Paleozoic ostracod genera. We show that the deep-marine depositional setting of our documented assemblage, together with general circulation model simulations of Ordovician ocean-temperatures, suggests an early radiation of benthic ostracods into the deeper, colder, and thermally uniform ocean below the thermocline. The presence of a globally-distributed psychrospheric (cool and deep marine) ostracod fauna would imply that our understanding of Ordovician ostracod dispersal is incomplete, and future paleobiogeographical studies should try to decouple the signal of shallow-shelf benthic taxa, often endemic and probably limited by sea temperature, from those that are more cosmopolitan and tolerant of cooler, deeper waters.

• Torsvik, Trond Helge; Royer, Dana L.; Marcilly, Chloe M. & Werner, Stephanie C. (2024). User-friendly carbon-cycle modelling and aspects of Phanerozoic climate change. Applied Computing and Geosciences. 23. doi: 10.1016/j.acags.2024.100180. Full text in Research Archive Show summary

  Carbon-cycle modelling is essential for testing the main carbon sources and sinks as climate forcings, and we introduce and describe GEOCARB_NET, a graphical user interface for the geologic carbon and sulfur cycle model GEOCARBSULFvolc. The software system is menu-driven, user-friendly, and the user is never far removed from the basic input parameters from which atmospheric CO2 and O2 concentrations can be derived. GEOCARB_NET is supplied with several published models and the user can easily test and refine these models with different parametrizations. GEOCARB_NET also contains libraries of models and proxy data, which easily can be compared with each other. Our examples focus on how to use GEOCARB_NET in the context of Phanerozoic climate change and highlights how certain key input parameters can seriously affect reconstructed CO2 levels.

• Ontiveros, Daniel Eliahou; Beaugrand, Gregory; Lefebvre, Bertrand; Marcilly, Chloe M.; Servais, Thomas & Pohl, Alexandre (2023). Impact of global climate cooling on Ordovician marine biodiversity. Nature Communications. 14. doi: 10.1038/s41467-023-41685-w. Full text in Research Archive Show summary

  Abstract Global cooling has been proposed as a driver of the Great Ordovician Biodiversification Event, the largest radiation of Phanerozoic marine animal Life. Yet, mechanistic understanding of the underlying pathways is lacking and other possible causes are debated. Here we couple a global climate model with a macroecological model to reconstruct global biodiversity patterns during the Ordovician. In our simulations, an inverted latitudinal biodiversity gradient characterizes the late Cambrian and Early Ordovician when climate was much warmer than today. During the Mid-Late Ordovician, climate cooling simultaneously permits the development of a modern latitudinal biodiversity gradient and an increase in global biodiversity. This increase is a consequence of the ecophysiological limitations to marine Life and is robust to uncertainties in both proxy-derived temperature reconstructions and organism physiology. First-order model-data agreement suggests that the most conspicuous rise in biodiversity over Earth’s history – the Great Ordovician Biodiversification Event – was primarily driven by global cooling.

• Marcilly, Chloe M.; Torsvik, Trond Helge & Conrad, Clinton Phillips (2022). Global Phanerozoic sea levels from paleogeographic flooding maps. Gondwana Research. ISSN 1342-937X. 110, p. 128–142. doi: 10.1016/j.gr.2022.05.011. Full text in Research Archive Show summary

  The validity of sea level estimates based on stratigraphic correlations has been debated since the 1990 s as relative sea level curves differ between sites due to local tectonics, different deposition rates and changes in dynamic topography. Here, we offer a new eustatic (global) sea level curve for the past 520 million years (Myrs) based on observations of global flooding. We use paleogeographic reconstructions to measure the area of today’s exposed land that was flooded in the past (modern-land flooding). We then apply the modern global hypsometric slope to reconstruct the sea level history. We find minimum sea levels (comparable to today’s level) towards the end of Pangea (210 Ma) and peak levels (∼280 m higher than today) at 80 Ma when Pangea was widely dispersed. A first-order “supercontinent” cycle of 250 million years (Myrs) is recognized but we also document a second-order cycle of 37 Myrs that was previously thought to be undetectable using the hypsometric method. The hypsometric slope is critical for reconstructing past sea levels, and steepening the hypsometric slope during Pangea assembly implies dramatically larger sea level fluctuations. Our new sea level curve shares strong similarities with stratigraphic constraints and correlates with seafloor production proxies throughout the Phanerozoic. Measurements of global flooding represent averages across great continental extents, making them less sensitive than stratigraphic analyses to regional-scale vertical land motion, such as from dynamic topography and hence more reliable for estimating eustatic sea level. This method can also help to identify local deviations caused by regional uplift or subsidence and serves to constrain geodynamic mechanisms for sea level change. Our new sea level reconstruction usefully tracks global variations in Phanerozoic eustatic sea level, but also opens opportunities to estimate such variations in deeper time.

• Marcilly, Chloe M.; Maffre, Pierre; Hir, Guillaume Le; Pohl, Alexandre; Fluteau, Frédéric & Godderis, Yves [Show all 9 contributors for this article] (2022). Understanding the early Paleozoic carbon cycle balance and climate change from modelling. Earth and Planetary Science Letters. ISSN 0012-821X. 594. doi: 10.1016/j.epsl.2022.117717. Full text in Research Archive Show summary

  The Ordovician global cooling trend observed by several temperature proxies, which coincides with one of the most significant evolutionary diversifications on Earth, is yet to be fully understood. This study presents new simulations of pCO2 and surface temperatures using a spatially resolved climate-carbon cycle Earth system model fed with refined continental reconstructions and new estimates of solid Earth degassing. First, in order to quantify the respective roles of paleogeography and degassing, the impact of continental drift alone is investigated. This is done by calculating its imprint on continental weathering rates throughout the Ordovician under a constant pCO2, and by testing different topography inputs. Secondly, the sensitivity of the Earth's climate to paleogeography and carbon degassing changes is investigated by coupling the climate and carbon cycles in the GEOCLIM model. Based on our experiments we show that, although Early Ordovician high temperatures can be replicated within error margins, our new constraints cannot explain the intense cooling over the Mid to Late Ordovician, even if a progressive enhancement in Earth surface weatherability is taken into account. By using GEOCLIM in an inverse modelling approach, we calculate that the theoretical degassing necessary to reach proxy-derived temperatures for the Early Ordovician is three-to-five times higher compared to modern values. Further, in order to simulate the following Ordovician cooling trend, the solid Earth degassing must be reduced to modern-day values in only 30 Myrs. We conclude that, if accepting the veracity of the high Early Ordovician temperatures, alternative sources but also sinks of carbon must be considered to explain the climatic shift over the period.

• Marcilly, Chloe M.; Torsvik, Trond Helge; Domeier, Mathew Michael & Royer, Dana L. (2021). New paleogeographic and degassing parameters for long-term carbon cycle models. Gondwana Research. ISSN 1342-937X. 97, p. 176–203. doi: 10.1016/j.gr.2021.05.016. Full text in Research Archive Show summary

  Long-term carbon cycle models are critical for understanding the levels and underlying controls of atmospheric CO2 over geological time-scales. We have refined the implementation of two important boundary conditions in carbon cycle models, namely consumption by silicate weathering and carbon degassing. Through the construction of continental flooding maps for the past 520 million years (Myrs), we have estimated exposed land area relative to the present-day (fA), and the fraction of exposed land area undergoing silicate weathering (fAW-fA). The latter is based on the amount of exposed land within the tropics (±10°) plus the northern/southern wet belts (40-50°N/S) relative to today, which are the prime regions for silicate weathering. We also evaluated climate gradients and potential weatherability by examining the distribution of climate-sensitive indicators. This is particularly important during and after Pangea formation, when we reduce fAW-fA during times when arid equatorial regions were present. We also estimated carbon degassing for the past 410 Myrs using subduction flux from full-plate models as a proxy. We then, for the first time, used the subduction flux to scale and normalize the arc-related zircon age distribution (arc-activity), which allows us to estimate carbon degassing in much deeper time. The effect of these refined modelling parameters for weathering and degassing was then tested in the GEOCARBSULF model, and the results are compared to other climate models and CO2 proxies. The use of arc-activity as a proxy for carbon degassing brings Mesozoic model estimates closer to CO2 proxy values but our models are highly sensitive to the definition of fAW-fA. Considering the land availability to weathering to only variations in tropical latitudes (corrected for arid regions) combined with our new degassing estimates leads to notably higher CO2 levels in the Mesozoic and a better fit with the CO2 proxies.

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• Marcilly, Chloe M.; Torsvik, Trond Helge & Conrad, Clinton Phillips (2024). Corrigendum to “Global Phanerozoic sea levels from paleogeographic flooding maps” [Gondwana Res. 110 (2022) 128–142, (S1342937X22001563), (10.1016/j.gr.2022.05.011)]. Gondwana Research. ISSN 1342-937X. 129, p. 367–368. doi: 10.1016/j.gr.2024.01.006. Full text in Research Archive
• Marcilly, Chloe M. (2022). Understanding the early Paleozoic carbon cycle balance and climate change from modelling. Full text in Research Archive
• Marcilly, Chloe M.; Torsvik, Trond Helge; Domeier, Mathew Michael & Royer, Dana L. (2021). Refining key parameters for long-term carbon cycle models. Full text in Research Archive
• Marcilly, Chloe M.; Torsvik, Trond Helge; Domeier, Mathew Michael & Royer, Dana L. (2021). Revising key parameters for long-term carbon cycle models. Full text in Research Archive
• Marcilly, Chloe Franca Margot & Torsvik, Trond H. (2020). The impact of paleogeography on long-term CO2 models. Full text in Research Archive
• Marcilly, Chloe Franca Margot & Torsvik, Trond H. (2020). Improving long-term CO2 models for the Phanerozoic: What can be done? Full text in Research Archive

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