# Paleosol-induced early dolomitization constrained by U-Pb age and its implications for fluid pathways in ancient sandstone aquifers

J.B. Regnet, Cédric Bailly, Sylvie Bourquin, Philippe Robion, Béatrice Ledésert, Marc Poujol, Xavier Sengelen

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J.B. Regnet, Cédric Bailly, Sylvie Bourquin, Philippe Robion, Béatrice Ledésert, et al., Paleosol-induced early dolomitization constrained by U-Pb age and its implications for fluid pathways in ancient sandstone aquifers. 29ème Réunion des Sciences de la Terre 2025, Société Géologique de France (SGF), Oct 2025, Montpellier, France. pp.666433. insu-05350607

HAL Id: insu-05350607

https://insu.hal.science/insu-05350607v1

Submitted on 6 Nov 2025

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# Paleosol-induced early dolomitization constrained by U-Pb age and its implications for fluid pathways in ancient sandstone aquifers

Jb Regnet*<fnref n="1" />, Cédric Bailly<fnref n="2" />, Sylvie Bourquin<fnref n="3" />, Philippe Robion, Béatrice Ledésert, Marc Poujol<fnref n="4" />, and Xavier Sengelen

## Résumé

In hydrogeology, a key challenge involves identifying patterns within ancient formations to forecast the distribution of fluid pathways and barriers to permeability, as well as comprehending the palaeohydrological system and its changes over time. This study addresses two main research inquiries concerning fluid flow: firstly, the influence of dolomitization induced by paleosols on flow characteristics, and secondly, the implications for fluid flow pattern distribution in continental sedimentary units. The objectives are pursued through: (1) investigation of petrographic features of diagenetic minerals and their ages using the U-Pb geochronology system; (2) meticulous, high-resolution measurements of porosity and permeability coupled with well-log data from an outcrop and two boreholes. Findings suggest that early dolomitization in continental sequences significantly affects fluid flow properties across the basin. The development of paleosols triggered early dolomitization, supported by U-Pb geochronology evidence. Subsequent groundwater migration along hydraulic gradients, influenced by fluctuations in the local aquifer's water table, facilitated the vertical distribution of dolomitization. Dolomitization occurred in residual pores resulting from initial mineral alteration, early lithifying the sediment and preventing mechanical compaction, thus preserving porosity. During migration events, fluids moved vertically along local faults and horizontally through the dolomitized layers of the formation, which likely remained porous at the time, leading to substantial silica mineralization.

**Mots-Clés:** U, Pb geochronology, dolomite, paleosols, aquifers

<footnote n="1">¹Institut des Sciences de la Terre de Paris – Institut National des Sciences de l'Univers, Sorbonne Université, Centre National de la Recherche Scientifique, CY Cergy Paris Université – France</footnote>

<footnote n="2">²Géosciences Paris Saclay – Institut National des Sciences de l'Univers, Université Paris-Saclay, Centre National de la Recherche Scientifique, Centre National de la Recherche Scientifique : UMR8148,</footnote>

<footnote>Université Paris-Saclay : UMR8148, Institut National des Sciences de l'Univers : UMR8148 – France</footnote>

<footnote n="3">³Géosciences Rennes – Université de Rennes, Institut National des Sciences de l'Univers, Centre National de la Recherche Scientifique – France</footnote>

<footnote n="4">⁴Géosciences – Université de Rennes I – Rennes, France</footnote>

<footnote>*Intervenant</footnote>