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Abstract : In sedimentary basins, source rocks may generate aqueous and hydrocarbon fluids during burial and diagenesis. This fluid production in very-low permeability sediments is responsible for the development of fluid overpressure, and in some cases leads to hydrofracturing processes. Such processes are evidenced by the occurrence of mineralized fibrous veins distributed parallel to black shale layering in many mature basins, known as “beef” or “bedded parallel fibrous calcite veins”. A link between the beef formation and the total organic carbon (TOC) has been suggested since overpressure and hydrofracturing is most likely to be triggered by a phase transition (solid-liquid) during chemical compaction and thermal maturation of kerogene. In parallel, the organic matter preservation and TOC evolution in marine sediments are highly influenced by eustatic and climatic fluctuations. At short to medium timescales (< 1.106 yr), these fluctuations are cyclic and influenced by Milankovitch cycles, thus illustrating an orbital control on the stratigraphical evolution of the organic matter content. Considering a presumed relationship between mechanisms of beef generation and the TOC as well as a control of orbital parameters on the TOC evolution, we address the following question: is there an orbital control on the beef distribution in source rock? Hereby, we present the preliminary results of a field mission aiming to answer this question and performed in the Neuquén Basin (Argentina) during March 2017. We conducted fieldwork in the Loconpué area where the Late Jurassic Vaca Muerta Formation offers exceptional exposures composed of organic matterrich black shales interbedded with numerous calcite beef of reliable lateral continuity (100’s meters) and thickness (0.2 to 7 cm). We performed a detailed 100 m thick outcrop logging focusing on the beef stratigraphical position, thickness and continuity. In parallel, we carried out a 10 cm interval shale sampling in order to investigate magnetic susceptibility trends in the stratigraphical record. Knowing that the magnetic susceptibility of sediments is a good indicator of the detrital fraction, we aim to decipher a possible climatic and orbital signal in this Late Jurassic sedimentary record. Using these datasets, we later performed spectral analyses on the beef stratigraphical distribution, the beef thickness and the magnetic susceptibility signal to evidence a possible control of orbital parameters on beef distribution.
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Contributor : Isabelle Dubigeon <>
Submitted on : Tuesday, February 27, 2018 - 10:49:02 AM
Last modification on : Wednesday, October 14, 2020 - 4:16:53 AM


  • HAL Id : insu-01718136, version 1


Edouard Ravier, Mathieu Martinez, Alain Zanella, Salomé Larmier. AN ORBITAL CONTROL ON BEEF DISTRIBUTION IN MATURE SOURCE ROCK ? (VACA MUERTA FORMATION, NEUQUÉN BASIN, ARGENTINA). International Meeting of Sedimentology 2017, Oct 2017, Toulouse, France. pp.745. ⟨insu-01718136⟩



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