An outstanding paper published in 2020 in the BSGF (Bulletin de la Société Géologique de France – Earth Sciences Bulletin).
Abstract:
The giant Jurassic-aged pockmark field of Beauvoisin developed in a 800m wide depression for over 3.4 Ma during the Oxfordian; it formed below about 600m water depth. It is composed of sub-sites organized in clusters and forming vertically stacked carbonate lenses encased in marls . This fine-scale study is focused on a detailed analysis of petrographical organization and geochemical signatures of crystals that grew up in early to late fractures of carbonate lenses, surrounding nodules, and tubes that fed them. The isotopic signature (C, O and Sr) shows that at least three different episodes of fluid migration participated to the mineralization processes. Most of the carbonates precipitated when biogenic seepage was active in the shallow subsurface during the Oxfordian. The second phase occurred relatively soon after burial during early Cretaceous and thermogenic fluids came probably from underlying Pliensbachian, Late Toarcian or Bajocian levels. The third phase is a bitumen-rich fluid probably related to these levels reaching the oil window during Mio-Pliocene. The fluids migrated through faults induced by the emplacement of Triassic salt diapir of Propiac during the Late Jurassic and that remained polyphased drain structures over time.
“This paper is based on 15 years of field work, meaning that research needs time to get outcomes”
The detailed petrographic analyses of all mineralogical phases identified in a tube, in nodules and in the carbonate lenses have led to the conclusion that the evolution of a seep site is entirely recorded from its birth to its death and long after its burial.
https://www.bsgf.fr/articles/bsgf/full_html/2020/01/bsgf200003/bsgf200003.html
https://doi.org/10.1051/bsgf/2020036
Thanks to Thibault Cavailhes for scale.