EGU22-12195, updated on 28 Mar 2022
EGU General Assembly 2022
© Author(s) 2022. This work is distributed under
the Creative Commons Attribution 4.0 License.

Extraterrestrial 3He shows that Mesozoic marl-limestone alternations are mainly driven by CaCO3 variations at the astronomical timescale

Pierre-Henri Blard1,2, Baptiste Suchéras-Marx3, Guillaume Suan4, and Taous Mezine3
Pierre-Henri Blard et al.
  • 1CRPG, CNRS, Université de Lorraine, Nancy, France
  • 2Laboratoire de Glaciologie, DGES-IGEOS, Université Libre de Bruxelles, Brussels, Belgium
  • 3Aix Marseille Université, CNRS, IRD, INRAE, Collège de France, CEREGE, Aix-en-Provence, France
  • 4LGLTPE, UMR CNRS 5276, Université de Lyon 1, Lyon, France


Marl-limestone alternations are well known rhythmical inter-bedded deposits that commonly occur in many hemipelagic to pelagic deposits of the Phanerozoic. It is quite well established that the origin of these lithological variations are astronomically-driven climatic variations (22, 41, 100 and 405 ka being the main periods) e.g. [1]. However, the exact sedimentological control is not clear: several models attribute these alternations to cyclic changes in the carbonate flux, whereas the terrigenous silicoclastic flux remained relatively constant. On the opposite, some models suggest that the carbonate flux was constant while the silicoclastic flux changed cyclically.

Material and methods

To disentangle these different scenarios, we collected marlstone and limestone samples from two sedimentary successions of Bajocian, Middle Jurassic (3 marl-limestone- couplets over 3.5 m) and Valanginian, Lower Cretaceous (1 marl-limestone couplet over 1 m) age from the Southern French Alps (Barles). We measured their carbonate contents, the nannofossil proportion, as well as their extraterrestrial 3He (3HeET) concentrations in ~200 mg decarbonated aliquots.

Results and discussion

The carbonate content ranges from 45% in marls to 86% in limestones. Importantly, for all samples, measured 3HeET concentrations are constant in the silicoclastic fractions, within uncertainties. Hence, our results indicate that sedimentation rates at the astronomical timescale in the examined examples were mainly controlled by large changes in the CaCO3 net fluxes, leading to variable dilution of the terrigenous and 3HeET fractions. Nannofossil counting shows that pelagic CaCO3 fluxes of coccolithophores are inversely correlated to the total CaCO3 along the marl-limestone alternations and represent less than 4% of the total carbonate content. Hence, in this setting, these marl-limestone alternations were more probably driven by variations in the CaCO3 supply from the nearby carbonate platform. Finally, assuming a constant 3HeET flux of 0.1 pcc/cm2/ka [2], and the whole thickness of Bajocian and Valanginian strata in this region, the measured 3HeET concentrations imply sedimentation rates that are broadly compatible with current duration estimates of these two stages.



[1] Eldrett J. S. et al. (2015) Earth. Plan. Sci. Let., 423, 98-113.

[2] Farley K.A. et al. (2012) GCA, 84, 314-328.

How to cite: Blard, P.-H., Suchéras-Marx, B., Suan, G., and Mezine, T.: Extraterrestrial 3He shows that Mesozoic marl-limestone alternations are mainly driven by CaCO3 variations at the astronomical timescale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12195,, 2022.


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