Comment on Ossa Ossa et al. (2018) paper published in EPSL

Alain Préat , Francis Weber (1)

1 LHyGeS - Laboratoire d'Hydrologie et de Géochimie de Strasbourg

Ossa Ossa et al. (2018) presented a fairly comprehensive geochemical study of the FB and FC formations of the Francevillian (Gabon), consisting of five formations (FA to FE, Weber, 1968). Unfortunately, if the samples from the FB formation were taken from the so-called Franceville basin where the stratigraphic succession was defined (Donot and Weber, 1968), the FC formation was sampled at the edge of the basin, in the dolomitic formation of Lastoursville, considered by Ossa Ossa et al. (2018) as belonging, as a whole, to the FC. Donot and Weber (1968) and Weber (1968) considered the Lastoursville dolomitic formation as a condensed series corresponding to the FB and FC formations of the Franceville basin. Ossa Ossa et al. (2018) did not even discuss the stratigraphic position of the Lastoursville dolomitic formation, they simply, without any comment, assimilated in totality their studied series to the FC Formation of the Franceville basin. We think that this attribution is erroneous and part of their conclusion is therefore questionable. There isn't two-step deoxygenation at the end of the Lomagundi Event, but only one step. The first step of deoxygenation proposed by Ossa Ossa et al. (2018) concerns the FB1c unit in the Franceville basin, the second one corresponds to the same unit in the dolomitic formation of Lastoursville.

Domaines: Planète et Univers [physics]; Sciences de la Terre

Alain Préat, Francis Weber. Comment on Ossa Ossa et al. (2018) paper published in EPSL. Earth and Planetary Science Letters, 2019, 511, pp.256-258. ⟨10.1016/j.epsl.2019.01.017⟩. ⟨insu-03708525⟩