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

J.-B. Regnet, Cédric Bailly, Sylvie Bourquin, P. Robion, Marc Poujol, X. Sengelen, Olivier Serrano, B. Ledésert

<figure><img src="image_1.png" /></figure>

## To cite this version:

J.-B. Regnet, Cédric Bailly, Sylvie Bourquin, P. Robion, Marc Poujol, et al., Paleosol-induced early dolomitization with U Pb age constraints and its implications for fluid pathways in ancient sandstone aquifers. Sedimentary Geology, 2024, 470, pp.106719. 10.1016/j.sedgeo.2024.106719. insu-04650793v2

HAL Id: insu-04650793

https://insu.hal.science/insu-04650793v2

Submitted on 5 Aug 2024

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

<figure><img src="image_2.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# Paleosol-induced early dolomitization with U—Pb age constraints and its implications for fluid pathways in ancient sandstone aquifers

<figure><img src="image_3.png" /></figure>

Check for
updates

J.-B. Regnet<sup>a,*</sup>, C. Bailly<sup>b</sup>, S. Bourquin<sup>c</sup>, P. Robion<sup>a</sup>, M. Poujol<sup>c</sup>, X. Sengelen<sup>a</sup>, O. Serrano<sup>d</sup>, B. Ledésert<sup>a</sup>

## ARTICLE INFO

**Article history:**

Received 23 April 2024

Received in revised form 4 July 2024

Accepted 8 July 2024

Available online 14 July 2024

Editor: Dr. Basilici Giorgio

**Keywords:**

Dolomitization

Sandstone aquifer

Fluid flow

Paleosol

Geochronology

## ABSTRACT

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) meticulous, high-resolution measurements of porosity and permeability coupled with well-log data from an outcrop and two boreholes; (2) investigation of petrographic features of diagenetic minerals and their ages using the U-Pb geochronology system; and (3) an integration of these methodologies to grasp rock properties and fluid flow at a broader scale. 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.

© 2024 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

## 1. Introduction

Understanding the behavior of groundwater reservoirs and the factors governing their characteristics is crucial for sustainable resource management, especially given the increasing depletion of surface water and rising overall water consumption (Boretti and Rosa, 2019). To achieve this objective, it is essential to appreciate the hydrological system in which groundwater flow occurs, including the presence and extent of aquifers and semi-permeable layers characterized by various properties such as thickness, permeability, porosity, mechanical strength, and elastic storage coefficients. Since the 1990s, there has been a growing interest in modeling fluid flow within sedimentary units (Jessop and Majorowicz, 1994; Bjørlykke and Høeg, 1997; Eaton, 2006; Bense and Person, 2006; Huuse et al., 2010; Kampman et al., 2014), with much of the research focusing on numerical simulations (Doré et al., 1993; Raffensperger, 1996; Bjørlykke and Høeg, 1997;

Mádl-sznyi and Tóth, 2015; Santos et al., 2020). Although such modeling has improved our understanding of the processes involved, our ability to predict fluid flow within specific units or aquifers remains limited due to the poorly constrained petrophysical properties of rocks, particularly permeability (Bjørlykke, 1993). Sedimentary rocks exhibit significant heterogeneity, with permeability ranging from several Darcy in sandstones and limestones to less than one nanodarcy in tight shales (Zinszner and Pellerin, 2007). For instance, modeling of compaction-driven flow indicates that this process is slow and relatively independent of permeability, as fluid supply rather than permeability primarily controls flow velocities (Bethke, 1985; Bjørlykke, 1997). Regional simulation of fluid pathways in basins using models requires input parameters from geological formations, the properties of which vary spatially, often comprising sequences of layers with contrasted hydraulic values. The properties of sedimentary rocks, influenced by initial mineral composition and depositional environments, change continuously during burial due to diagenesis and tectonic deformation. Various models have been proposed to explain the role of mineral dissolution and precipitation in controlling porosity and permeability (Wilson and

<footnote><sup>a</sup> Cergy Paris Université, Laboratoire Géosciences & Env., 95000 Neuville sur Oise, France</footnote>

<footnote><sup>b</sup> Université Paris-Saclay, CNRS, GEOPS, 91045 Orsay, France</footnote>

<footnote><sup>c</sup> Univ. Rennes, CNRS, Géosciences Rennes - UMR 6118, F-35000 Rennes, France</footnote>

<footnote><sup>d</sup> BRGM (French Geological Survey), Orléans, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: jean-baptiste.regnet@cyu.fr (J.-B. Regnet).</footnote>
Stanton, 1994), with dolomite being a particularly favored topic due to its association with porous and permeable levels in carbonate rocks (Warren, 2000; Ehrenberg et al., 2006; Voorn et al., 2015). Dolomite's formation and its impact on fluid flow properties involve complex interactions between petrophysical properties and crystal textures (Wardlaw and Taylor, 1976; Ghosh and Friedman, 1989; Kopaska-Merkel and Friedman, 1989; Choquette et al., 1992; Warren, 2000; Ehrenberg et al., 2006; Voorn et al., 2015; Weber et al., 2021). Early models suggested that dolomitization increased porosity by replacing limestone with dolomite, but subsequent diagenetic modifications such as recrystallization and cementation can significantly alter porosity (Gregg et al., 2015; Warren, 2000; Ehrenberg et al., 2006). Dolomitization can either enhance, maintain, or diminish porosity depending on various factors, including the original nature of the rocks and the volume of fluids involved (Lucia and Major, 1994). Dolomite has been observed not only in marine sequences but also in continental settings, where its formation mechanisms and controls have been studied (Wright and Tucker, 2009; Colson and Cojan, 1996; Martín Pérez et al., 2012; Casado et al., 2014). Since dolomite can be formed in a great variety of geological environments as both a primary and secondary mineral phase, it can incorporate uranium during its crystallization, making this mineral a potentially suitable chronometer for U—Pb and U—Th geochronology. During the past few years, several studies have been successfully applied to the dating of dolomite in various environment (Barale et al., 2021; Elisha et al., 2021; Gao et al., 2022; Su et al., 2022; Gasparrini et al., 2023; Zheng et al., 2023; Zhang et al., 2023; Ben-Israel et al., 2024; McCormick et al., 2024). Therefore, dolomite geochronology has the potential to provide direct timing constraints on both dolomitization phases and associated fluid circulation. The high spatial resolution of LA-ICP-MS U—Pb carbonate geochronology is beneficial over traditional Isotope Dilution methods, particularly for diagenetic and hydrothermal dolomite, because uranium and lead are heterogeneously distributed on the sub-mm scale. Understanding fluid flow patterns and their evolution during time in such settings is crucial, given their significance for climate change mitigation and water resource management (Regnet et al., 2019a). Flow patterns in fractured strata are particularly important for understanding porosity and permeability connectivity at regional scales. The challenge lies in identifying patterns within geological formations to forecast the distribution of fluid pathways and permeability walls (Montañez, 1997; Hendry, 2002; Regnet et al., 2019b), emphasizing the importance of understanding the

palaeohydrological system and its evolution. This study aims to address two significant research questions related to fluid flow: (1) the impact of paleosol-induced dolomitization on flow properties, and (2) its implications for fluid flow pattern distribution in continental sedimentary units. These objectives will be achieved by conducting continuous high-resolution porosity-permeability measurements and well-log data analysis, coupled with petrographic analysis of diagenetic minerals and their ages using the U—Pb geochronology system. Given the focus on the impact of dolomitization on fluid flow properties, this paper briefly touches on the mechanisms responsible for the formation of different dolomite types, while emphasizing the importance of aquifer heterogeneities related to sedimentary facies and structural deformation.

## 2. Geological settings

The Mesozoic succession of the Ardèche region is exposed along a NE-SW trend at the southeastern edge of the Hercynian basement of the French Massif Central (Fig. 1). The Triassic and Jurassic successions represent the western palaeomargin of the Subalpine Basin, which is directly related to the opening of the Ligurian Tethys to the east. An extensional tectonic regime initiated at the beginning of the Late Triassic gave rise to an east-west distal-proximal polarity in the terrigenous and evaporitic sedimentary systems (Courel et al., 1998), and the development of rifting during the Early and Middle Jurassic, i.e. Lias and Dogger, led to the formation of a passive margin. This area consisted of sub-basins separated by permanent or temporary highs and structured by a mosaic of faulted blocks delimited by primary NNE-SSW and secondary NW SE faults. During the Triassic, the western part of the paleomargin corresponds to the proximal domain. It is well known from outcrop observations (Courel et al., 1998; Elmi, 1990) as well as from subsurface data acquired during mining operations at the Largentière Pb—Zn deposit and during the 1990’s GPF (Géologie Profonde de la France) program led in the nineties through drilled wells and seismic profiles (Razin et al., 1996; Bonijoly et al., 1996). From geophysical data, Bonijoly et al. (1996) show that the Mesozoic is deformed by a series of kilometer-size blocks downthrown to the east by retrogressive NNE SSW listric normal faults that flatten in depth along an inferred detachment fault within the Carboniferous layers. Landwards, to the west, this decollement cuts upward through the sedimentary succession and emerges along the synsedimentary Uzer Fault (Fig. 1) which is clearly fossilized by late Bathonian deposits (Bonijoly et al., 1996).

<figure><img src="image_4.png" /><figcaption>**Fig. 1.** Simplified geological map of the Ardèche margin (France), and location of studied outcrop (CHA – Chassagnes) and boreholes (MM1 – Morte-mérie & BA1 – Balazuc). BUF: Bariolée d’Ucel Formation (Fm). Modified from Bonijoly et al. (1996).</figcaption></figure>
This study is carried out along an E-W transect perpendicular to the Ardèche margin, from outcrop in the Chassagnes area to subsurface data from two wells (Morte-Mérie 1 – MM1 and Balazuc - BA1, Fig. 1). The investigated stratigraphic intervals are the continental deposits of the Bariolée d'Ucel Formation (Fm) (Fig. 1) attributed to the Late Triassic (i.e. late Carnian to Norian; Spy, 1980; Razin et al., 1996). The thickness of this formation increases from west to east from the proximal deposits of the borehole south of the Argentière (S53.49.7, Fig. 1) to the more distal deposits of BA1 (148 m). In MM1, the thickness is about 115 m. This proximal to distal thickness variation is partly due to the Uzer Fault and the other normal small-scale faults created during the margin extension (Razin et al., 1996; Poli, 1997).

The Bariolée d'Ucel Fm is considered to be a distal alluvial fan that evolved downstream to a braided river in a flood-plain environment with periodic sheet flood, subaerial erosion and pedogenesis (Spy, 1980; Razin et al., 1996). It is composed of fining-upward sequences of one to several meters in thickness. Every sequence begins with a microconglomerate to sandstone interval showing an erosional base that evolved vertically to clay and then to dolomite beds (Razin et al., 1996). These dolomitic beds are attributed to dolocrete associated with pedogenetic feature (Spy, 1980). Root marks (pil-lars) and dolomitic nodules are observed in clay and sandstones re-sulting from pedogenesis (Spy, 1980; Vinchon et al., 1996). For these authors, the coarse-grained facies are seen in thin section to be dominantly quartz and feldspar with a small quantity of terrige-nous illite matrix sealed by later silicification. The feldspars are highly weathered with pores and clay minerals. This alteration is likely to have started before deposition (Vinchon et al., 1996). The coarse-grained facies also contain scarce barite grains that have been reworked by pedogenesis and which could be of detrital origin (Vinchon et al., 1996).

Correlations realized along a transect on the western margin of Ardèche (Razin et al., 1996; Poli, 1997; Courel et al., 1998) allow to defined stratigraphic cycles within the whole Triassic sedimentary succession. For these authors, the Bariolée d'Ucel Fm marks the end of a major progradational cycle with paleosol developments. Two minor stratigraphic cycles can be observed within this formation with a maximum flooding surface considered as a reference level (MFS8) that splits the cycle 8 from cycle 9 (Figs. III.9, III.17 in the work of Poli, 1997).

The Bariolée d'Ucel Fm was also thoroughly described in terms of diagenesis and mineralization (Spy, 1980; Cros et al., 1993; Vinchon et al., 1996). According to these authors, the paragenesis is composed of an early dolomitization stage, originating from a dolocrete development throughout the formation, in association with pedogenesis. Dolomites are sometimes associated with silica overgrowth on some detrital grains, carbonate cement and amorphous silica precipitation in pores. For Vinchon et al. (1996), this dolomitization comes on top of a previous alteration of the initial sandstone fabric and grow (1) in the matrix as a dolomicrite or (2) in pores as larger dolomite crystals (i.e. dolosparite), where some of them are displaying saddle dolomite characteristics.

### 3. Approach and analytic methods

Samples and in-situ measurements realized in this study were retrieved from an outcrop located below the Chassagne village (44°24' 47.4"N 4°09'28.5"E) and from the MM1 and BA1 wells (Fig. 1). After a sedimentological description of The Bariolée d'Ucel Fm, the laboratory measurements were performed on 38 one-inch (2.54 mm) plugs drilled and oriented horizontally with respect to the bedding (for Chassagne); and directly on the field from the BRGM core repository (160 measurements on MM1 and 105 measurements on BA1). All plugs were thus cut to an average length of 5 cm and part of each was used to make a thin section, optical observations, and U—Pb geochronology.

#### 3.1. Detailed petrography

Thin sections were impregnated with blue-died and pink-died epoxy to visualize the pore space. Petrographic analyses (texture, composition) were conducted on both macroscopic and microscopic scales. Microfacies were analyzed on 56 thin sections using an Olympus optical microscope with Zeiss lenses. Sphericity and roundness were defined visually following the chart by Flügel and Munnecke (2010). The intensity of compaction was described for each sample. Grain size was measured along the maximum length of 50 grains within a square window on the 56 samples, to cross-check macroscopic descriptions of clast size. These measurements were made using a MATLAB script and Jmicrovision software. Mean grain size was then calculated following the method of Boggs (2009).

The facies codes are largely based on the widely used Miall's classification for fluvial deposits (Miall, 2013). The grain size is indicated by a capital letter (F for fine-grained lithologies, i.e., clay or silt, S for sand, G for conglomerate, D for dolomite), followed by lowercase letters indicating the sedimentary characteristics (m for massive, h for horizontal, v for vertical, t for through cross-stratifications, i.e., 3D megaripples). Sedimentary facies were determined and represented in Fig. 3, each facies corresponds to a depositional process. Then, facies associations were ascribed to depositional environments described in the text (Section 4.1).

Optical cathodoluminescence (OPEA cathodyne (14–18 kV and 200–250 mA) coupled to an Olympus microscope and a digital camera) was used for the recognition and chronology of the diagenetic phases. The paragenetic sequences of the dolomite phases were established on the basis of superposition and cross cutting relationships from thin sections and fresh broken surface observations.

#### 3.2. U—Pb dating

U—Pb geochronology was conducted by in-situ laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) at the GeOHeLiS analytical platform (Univ. Rennes) using an ESI NWR193UC excimer laser coupled to a quadripole Agilent 7700x ICP-MS equipped with a dual pumping system to enhance sensitivity (Paquette et al., 2014). The instrumental conditions are reported in the Supplementary Table. The ablated material is carried into helium, and then mixed with nitrogen and argon, before injection into the plasma source. The alignment of the instrument and mass calibration was performed before each analytical session using the NIST SRM 612 reference glass, by inspecting the ²³⁸U signal and by minimizing the ThO+/Th+ ratio (<0.5 %). During the course of an analysis, the signals of ⁴³Ca, ²⁰⁴(Pb + Hg), ²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb and ²³⁸U masses are acquired. The ²³⁵U signal is calculated from ²³⁸U on the basis of the ratio ²³⁸U/²³⁵U = 137.818 (Hiess et al., 2012).

Single analyses performed in-context within polished thick-sections mounted in epoxy pucks, consisted of 20 s of background integration followed by 30 s integration with the laser firing and then a 10 s delay to wash out the previous sample. Ablation spot diameters of 100 µm with repetition rates of 10 Hz were used for all the analyses. Data were corrected for U—Pb fractionation and for mass bias by the repeated measurements of the WC-1 calcite standard (254.4 ± 6.4 Ma; Roberts et al., 2017). In addition, the standard WC-1 was analyzed as an unknown (quality control) and yielded an age of 254 ± 2 Ma (N = 45; MSWD = 1.4). Data reduction was carried out with the Iolite 4 software (Paton et al., 2010) and the data reduction scheme VizualAge_UcomPbine (Chew et al., 2014). This data reduction scheme performs a common Pb correction using the ²⁰⁷Pb method for the initial Pb isotope composition specified in the standard reference value file for the WC-1 standard. More information about the analytical protocol can be found in Bouat et al. (2023) and in Supplementary Table 1. Data treatment and age calculation have been done using the IsoplotR software (Vermeesch, 2018). Data are reported in the Supplementary Table.
### 3.3. Physical properties

Laboratory porosity data were obtained by the triple weight method using water, which gives only access to the volume of connected pores in the samples. Each sample was oven dried at 60 °C for 12 h and then saturated with distilled water. If we take into account the error on the mass measurements, the standard error is in the range 0.5 %. The laboratory gas permeability measurements (Vinci Technologies) on plugs were performed with a Hassler cell using nitrogen and the steady state method (lower limit of $10^{-2}$ mD) at a confining pressure of 3 MPa. During the measurements the flow was laminar. Permeability is calculated from the gas flow rate through the sample using Darcy's equation. The measurements are reproducible and the data have been systematically corrected of the Klinkenberg slip effect. Permeability measurements on the cores MM1 and BA1 were performed using the TinyPerm instrument (by New England Research Inc., NER). The instrument is a hand-held air permeameter that can measure permeability on both outcrop surface and sample laboratory (Brown and Smith, 2013). The permeability can be measured within a range of 1 mD to 10 D. This is a syringe device type that provides a recording of how the air volume pressure in the syringe is returning to the ambient pressure at rate controlled by outcrop surface permeability (or sample surface). The device consists of a soft circular rubber nozzle connected to air chamber containing an absolute air pressure transducer. The operator, after pressing the rubber nozzle against the surface rocks, operates a piston to withdraw air from it. Since the physical interpretation of the representative volume measurement is not straightforward (Molz III et al., 2003), Brown and Smith (2013) proposed that the investigation depth of TinyPerm would be of the order of two times the probe inner radii (0.8 cm). Heidsiek et al. (2020) proposed smaller value, about one order of magnitude. If we assume a depth of investigation around one order of magnitude, then the equivalent hemispherical volume of investigation would be around $2 cm^3$ (Heidsiek et al., 2020). Cross-checking on the consistency of the obtained values from the two instruments (Lab vs TinyPerm) was completed on the outcrop samples and shows a very good conformity (Fig. 2). All reported data are well within the 95 % confidence interval.

<figure><img src="image_5.png" /><figcaption>**Fig. 2.** Laboratory permeability (steady state) vs TinyPerm permeability. The dispersion domain (in blue) is the equivalent of a one order magnitude variability.</figcaption></figure>

### 3.4. Boreholes

BA1 and MM1 wells are located near the Uzer Fault (Fig. 1). The wells were cored through Triassic and Early Jurassic. The Triassic is lying in fault contact (Uzer Fault) on upper Carboniferous rocks. These two wells have well-log data such as neutron (NPhi), density (RhoB), Sonic and Gamma-Ray (GR) tools. Well-log analysis is used to define electrofacies associated with sedimentary facies deduced from core analysis, and to infer electrofacies associations and diagenetic features directly from well-logs. It is essential to use complete sets of log data to identify facies associations and associated features, especially in continental environments, since sandstones containing large amounts of radioactive minerals (potassium-rich feldspar, heavy minerals, etc.) may produce high GR values similar to those measured in clays. All logging tools used here are standard Schlumberger-issued instruments. The density data are captured by the LDT instrument, porosity is extracted from the CNL logging instrument, the Sonic is the DSI tool and the Gamma Ray is based on the NGS instrument. Data acquisition was done every 15 cm, making the logs mid-resolution data.

## 4. Results

### 4.1. Depositional environment and diagenesis

#### 4.1.1. Depositional environment

The facies association (Fig. 3), recognized in the Bariolée d'Ucel Fm along the Chassagnes outcrop and the two boreholes MM1 and BA1 (Fig. 3), is mainly characterized by sandstones (S) and conglomerates (G) interbedded with red-green fine-grained facies (F) and massive dolomite (D). The sandstones are essentially composed of massive fine- to coarse-grained sandstones well- to poorly-sorted (Fig. 4A & B) with occasional pebble clasts (Sm facies) attributed to subaerial hyper concentrated flow (Postma, 1990) or subaqueous high-density turbidity currents (Lowe, 1982; Mulder and Alexander, 2001). Rarely, trough cross-bedded medium- to coarse-grained well- to poorly-sorted sandstones (St facies) attributed to 3D megaripple migration (Miall, 2014) is observed. The conglomerates, poorly sorted, clast-supported with erosional base (Gm facies) are attributed to lag deposited or debris flow (Miall, 2014; Postma, 1990). The fine-grained facies (F) are composed of red or marmorized (green-red) clay and silty clay that characterized deposition from suspension of floodplain or lake deposits. Sometimes vertical root traces (R, Fig. 4C & D) overprinted by vertical pedogenic feature typical of paleosol development with glaebule are underlined by vertical dolomitic nodule Dv (Fig. 4E; e.g., Retallack et al., 1988). The facies association, with sequences characterized by Gm, Sm and St facies is dominated by sandy sheetflood deposits (Sm and Gm facies) and represents terminal alluvial fan deposits (e.g. Bourquin et al., 1998) which grade into floodplain or lake deposits (F) and end by soil with root traces (Dv) and homogeneous massive dolomite development (Dh). This massive dolomite represents dolomite development (Fig. 4F, G & H) and pedogenic carbonates at the top of the vadose setting (Alonso-Zarza, 2003; Alonso-Zarza and Wright, 2010) and attests to semi-arid climate condition (e.g. Hasiotis, 2007; i.e. a climate characterized by a succession of arid and humid episodes). Within this depositional environment, the F facies can be dolomitized (dolomite clay, Fig. 3) and the feldspars are also heavily altered (Fig. 4F). In addition, aligned dolomitic nodules (Dn) are observed within the S or G facies attesting to the fluctuation of the groundwater table and characterizing groundwater dolomite (e.g. Wright and Tucker, 2009; Kraus and Aslan, 1993; Fig. 5).

#### 4.1.2. Cements & pores

Three types of cement occur in the Bariolée d'Ucel Fm: dolomite, calcite and silica. Dolomite consists in three distinct generations, formed during the first stage of burial. The earliest, D0, is microcrystalline (dolomicrite) and associated with pedogenetic structures (Figs. 4E, 7A).
<figure><img src="image_6.png" /><figcaption>**Fig. 3.** Sedimentological logs of the Chassagnes outcrop and the two boreholes MM1 & BA1, Late Triassic. Permeability data (K, blue dots) displayed for the Chassagnes outcrop are from laboratory measurements. The ones for MM1 & BA1 are from on core measurements (TinyPerm apparatus). Laboratory porosity (Φ, green dots) is from laboratory measurements for Chassagnes, and from NPHI logging for MM1 and BA1. Vertical scale is different on each log.</figcaption></figure>

Dolomite D1 and Dolomite D2 appear after D0 (Figs. 6A & B, 7A) are part of the same crystals, displaying a dark core (D1) and a clear outer crystal (D2) (Fig. 7A & B). D1 and D2 are embedded in the rock matrix and usually grow around altered feldspars or along the dissolution-induced pore after the feldspar alteration (Fig. 6C & D). Finally, D3 appears as a crack or

fracture-filling phase (Figs. 6A & B, 7C, D, E & F), associated with a blocky calcite generation (Fig. 7B). D1 and D2 are rather non-luminescent in the Chassagnes outcrop, and display a warm yellow to orange luminescence in the MM1 borehole (Fig. 7A, B & D). Silica is the latest diagenetic phase in the Bariolée d'Ucel Fm and consists of amorphous silica that
<figure><img src="image_7.png" /><figcaption>**Fig. 4.** Petrographic character of different facies from the Formation Bariolée d'Ucel, Ardèche, Late Triassic. (A & B) Sm & Gm facies. Feldspar (Fe), quartz (Q) and a few dolomites (D1 and D2). Clast-supported, ungraded, well- to poorly-sorted composition. Morte-Mérie borehole. (C & D) Well-developed dolomite-filled root system (Dv) within conglomerates, sandstones and fine facies, that is associated with pedogenic dolomitization over thick sections (several meters). R = root trace. Chassagnes outcrop. (E) Pedogenic feature (*Glaebule*) within Dv facies, three dolomite generations (D0, D1 and D2). Note the presence of D0 in the *Glaebule*. Chassagnes outcrop. (F) Altered detrital grains (feldspar) with dolomite crack-filling growth. Dolocrete level. Morte-Mérie borehole. (G & H) Dolocrete development Dh with a microcrystalline dolomite matrix (D0), larger dolomite crystal (dolomites D1 & D2), microcalcitic cement (µspar), muscovite (msc). Dh facies. Morte-Mérie borehole.</figcaption></figure>

fills cracks, fractures and pores. It comes after the dolomite phase (Fig. 6E, F, G & H) and is only visible in the BA1 well. It is absent from the MM1 well and Chassagnes outcrop.

All the sections are essentially characterized by intercrystalline macroporosity in the sandstones and conglomerate deposits, open cracks, or fractures. Macropores are essentially inherited from the dissolution of feldspars (Figs. 4F, 6C & D and G & H). Microporosity is poorly developed and limited to the dolomiticrite associated with pedogenetic structures (Fig. 4E).

## 4.2. Well logs and electrofacies

Well-log analysis is used to calibrate electrofacies with sedimentary facies and diagenetic features, and to infer electrofacies associations and associated diagenesis directly from well-logs. This electrofacies-based classification involves identifying clusters in the well-log response that reflect “similar” minerals and lithofacies within the logged interval (Bourquin et al., 1998; Perez et al., 2005). On the density (RhoB) and neutron logs, 0 % of NPhi corresponds to 2.70 g/cm³ of RhoB (Fig. 8).
CHASSAGNES - BOTTOM SECTION

<figure><img src="image_8.png" /><figcaption>**Fig. 5.** Bottom section of the Chassagnes outcrop (A) and its interpreted structure (B). Purple patches within the sandstone and conglomerate beds are the nodular dolomites. (C, D, E & F) Dolomitic nodules in horizontal position, aligned within the F, S or G facies attesting groundwater table fluctuation.</figcaption></figure>

Both curves are evolving in opposition: the density curve from left to right while increasing, and the neutron porosity curve from right to left. Negative polarity (NPhi to the right of the RhoB), positive polarity (NPhi to the left of the RhoB) zero polarity when curves are merged and RhoB-NPhi spacing were defined in this way (Fig. 8, Table 1). From the study of classical well-logs (GR, RhoB, NPhi), four electrofacies are defined, characterizing the main sedimentary facies and diagenetic features of Bariolée d'Ucel Fm (Fig. 8, Table 1).

The electrofacies 1 can be easily recognized from well-logs and corresponds to sandstone (St, Sm) and conglomerate (Gm) facies (Figs. 8, 9). Electrofacies 2 corresponds to dolomitic nodules within the S or G facies and attests to groundwater dolocrete (Dn) (Figs. 8, 9). Paleosols with root traces and dolocretes (respectively Dv, Dh facies) are grouped in electrofacies 3 (Figs. 8, 9). The electrofacies 2 and 3 can be mistaken if dolomitic nodules are abundant in the S and G facies (Fig. 4). Clay (F facies) corresponds to the electrofacies 4 (Figs. 8, 9). All these electrofacies can be recognized if the thickness of the associated facies is larger than the vertical resolution of the well-logs (Fig. 9). Sedimentary environment variations can be observed in each well: vertical transitions from (1) lag deposits/subaerial hyper concentrated flow and megaripple (electrofacies 1, Sm, St and Gm) to (2) clay deposits from suspension (electrofacies 4, F) and (3) paleosol development (electrofacies 3, Dv and Dh) that induced water table dolomitization in underlying facies (electrofacies 2, Dn) (Fig. 9).

### 4.3. U—Pb geochronology

Eight samples from MM1 well and Chassagnes outcrop were selected for U—Pb geochronology (Fig. 10). For the Chassagnes section, five samples were analyzed (see orange stars on Fig. 3 for locations). One sample concerns the D0 dolomite, two the D1/D2 and two the D3 dolomite. For the D0 dolomite (sample CHA-25), 42 analyses were performed (Supp Table 1). They are all highly discordant demonstrating that the amount of common Pb is high. They yield a lower intercept date of 213 ± 31 Ma (Fig. 10A; MSWD = 0.52; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.839 ± 0.016). Regarding D1 and D2, because of their small size, we could not analyze them separately. Forty-two analyses were performed

for each sample (CHA-13 and CHA-21; Supp Table 1). Again, the data demonstrate the presence of a high content of common Pb (Fig. 10B & C). They yield lower intercept dates of 199 ± 28 Ma (MSWD = 1.4; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.840 ± 0.004) and 195 ± 26 Ma respectively (MSWD = 0.52; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.840 ± 0.009). Forty-two analyses for the D3 dolomite in sample CHA-19 and 36 analyses for dolomite D3 in sample CHA-08 were realized (Supp Table 1). In both cases, the data are highly discordant because of the presence of a non-negligible amount of common Pb (Fig. 10D & E). They yield lower intercept dates of 166 ± 16 Ma (MSWD = 1; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.819 ± 0.011) and 183 ± 7 Ma (MSWD = 1; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.830 ± 0.003).

In MM1, we analyzed one sample for each generation of dolomite. Forty-one analyses were realized on the sample MM1-19 (Dolomite D0). Data show the presence of a high amount of common Pb (Supp Table 1 and Fig. 10F) and yield a lower intercept date of 203.2 ± 31 Ma (MSWD = 1.7; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.848 ± 0.010). Regarding dolomites D1 & D2 (sample MM1-19), 42 analyses were acquired (Supp Table 1). They are highly discordant due to the high proportion of common Pb (Fig. 10G). They yield a poorly constrained lower intercept date of 212.6 ± 12.9 Ma (MSWD = 3.3; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.840 ± 0.004). Finally, 49 analyses were performed on dolomite D3 (Sample MM1-17; Supp Table 1). Again, data demonstrate the presence of a high amount of common Pb (Fig. 10H) and yield a lower intercept date of 195 ± 18 Ma (MSWD = 1.4; ($^{207}$Pb/$^{206}$Pb)$_0$ = 0.850 ± 0.001).

The earliest dolomitization stage D0 in Chassagnes is pointing toward the Late Triassic times, but Early Jurassic in MM1 (Fig. 11). D1 and D2 are Late Triassic–Early Jurassic in both Chassagnes and MM1. D3 is clearly Early Jurassic in Chassagnes, but Late Triassic to Early Jurassic in MM1 (Fig. 11). When considering outcrop data, there is a good agreement in the relative chronology from D0 to D3 in dolomite stages and stratigraphy. This information is somehow lost in the MM1 well.

### 4.4. Fluid flow properties

The vertical permeability evolution mostly follows the porosity trend, especially on the Chassagnes outcrop and MM1 borehole, and rises around or below identified or presumed paleosol levels (Fig. 3).
<figure><img src="image_9.png" /><figcaption>**Fig. 6.** Petrographic character of different facies from the Formation Bariolée d'Ucel, Ardèche, Late Triassic. (A & B) Crack-filling with dolomites D1 and D2, with microspar and a third generation of dolomite D3, and occasional calcitic cement. Balazuc borehole. (C & D) Altered detrital grains (feldspar, Fe) with dolomite growth (dolomitic D0, and scarce D1 and D2 and microspar, white arrows) in the residual porosity (P, pinkish color). Mortemérie section. (E & F) Amorphous silica-filled fractures (Si, white arrows) with embedded dolomite crystals (D1 and D2). Balazuc section. (G & H) Amorphous silica in residual porosity (Si, black arrows). Comes as a pore-filling phase, after feldspar dissolution and subsequent dolomite precipitation D1 and D2 with microspar. Porosity P in pinkish color. Balazuc section.</figcaption></figure>

In BA1, permeability evolution through depth essentially displays a flat pattern, with the exception of the interval located between 1387 m and 1397 m, which is marked by higher and rather constant permeability values centered on 1 mD (Fig. 3).

Porosity across the two boreholes and outcrop displays a wide range of values from 2.1 % to 28.5 % (Fig. 12A). Individually, the BA1 borehole displays the lowest porosities from 2.1 % to a maximum of 6.23 %, the MM1 borehole encompasses the wider range of porosity variation from 3.8 % to 28.5 %, while for Chassagnes the porosity value varies

from 4 % to 15.5 % (Fig. 12A). The vertical porosity evolution is marked by several different trends along the section (Fig. 3). The porosity is very stable along the BA1 section but shows peculiar variations in the MM1 and Chassagnes sections: it increases around or below identified or presumed paleosol levels (Fig. 3). This observation is not always true as porosity is rather constant in MM1 between 230 and 250 m for example, where several paleosol levels have been observed (Fig. 3). Permeability across the two boreholes and outcrop displays a wide range of values from $10^{-2}$ mD to $10^4$ mD (Fig. 12A). Individually, the BA1
<figure><img src="image_10.png" /><figcaption>**Fig. 7.** Petrographic character of dolomite phases under cathodoluminescence (CL) from the Formation Bariolée d'Ucel, Ardèche, Late Triassic. (A & B) Dolomites D0, D1 and D2, and a third generation of dolomite D3 with occasional blocky calcite cement. Note the yellow to orange CL hue of D0, D1 and D2. Mortemérie borehole. (C & D) Fracture-filling dolomite cement D3 with non-luminescent D1 and D2 phases. Crack-porosity developed in D1 and D2 cements (blue, P). Chassagnes Outcrop. (E & F) Dolomite crystal D3. Crystal zoning is present as well as sporadic dissolution gulfs (white arrow, P). Chassagnes Outcrop.</figcaption></figure>

<figure><img src="image_11.png" /><figcaption>**Fig. 8.** Well-log characterization of the main sedimentary features based on real core and log data. Four electrofacies are defined: 1 = Sandstone (S facies) and Conglomerate (G facies); 2 = Water table induced dolomitization (Dolomitic Nodules Dn); 3 = Paleosols (Dh, Dv facies); 4 = Clay (F facies). See Table 1 for electrofacies characterization.</figcaption></figure>

borehole displays a skewed permeability distribution toward the lowest values, as 80% of the samples have a permeability smaller than $10^{-1}$ mD (Fig. 12B). The permeability values in the MM1 borehole almost follow a normal low distribution centered on 1 mD, with no permeability below $10^{-2}$ mD (Fig. 12C). 60% of the MM1 permeabilities are >1 mD. Measures carried out of the Chassagnes outcrop samples show in-between values from $10^{-2}$ mD to $10^2$ mD (Fig. 12A).

Overall, the positive correlation between porosity and permeability is confirmed on Fig. 12A, although a scattering is observed as a wide permeability range exists for the same porosity value. This positive trend is less obvious for the BA1 borehole, where data do not display any clear distribution pattern (Fig. 12A).

When data points are discriminated with the presence of dolomite in the sample, two different porosity-permeability (phi-k) trends appear (Fig. 13A). Dolomitized samples in BA1 do not display a clear trend, as 99% of them are contained in a rather narrow phi-k space (Fig. 13A) ranging from 0 to 6.5% porosity and $10^{-2}$ to 1 mD. Furthermore, Fig. 13B shows that even the dolomitized samples from BA1 fall into the non-dolomitized samples range when looking at permeability values, except for one value displaying 70.3 mD (Fig. 13A). On the other hand, MM1 and Chassagnes samples systematically display the higher phi-k trend (Fig. 13A). On the other hand, in MM1 specifically, dolomitized samples display a normal-law distribution centered on values between 10 and 100 mD (Fig. 13C).
<table><caption>**Table 1**
The four electrofacies characterizing the main sedimentary facies and diagenetic features of the Fm ascertained from well-log data and matched with cores.</caption><thead><tr><th>Electro-facies</th><th>Polarity</th><th>RHOB-NPHI spacing</th><th>Gamma ray</th><th>Sedimentary facies & diagenetic features</th></tr></thead><tbody><tr><td>1</td><td>Negative</td><td>Medium to coincided (Function of dol cement)</td><td>Low to high (If radioactive sand)</td><td>Sandstone (St, Sm) facies</td></tr><tr><td>2</td><td>Positive or zero</td><td>Coincided to wide (If dolomitic sandstone or large amount of nodules)</td><td>Low to high (If radioactive)</td><td>Dolomitic nodules Dn in F, S & G facies</td></tr><tr><td>3</td><td>Positive</td><td>Wide</td><td>Low to medium (Function of clay content)</td><td>Paleosol (Dh, Dv) facies</td></tr><tr><td>4</td><td>Positive</td><td>Wide</td><td>High</td><td>Clay (F) facies</td></tr></tbody></table>

# 5. Discussion

## 5.1. Dolomitization timing & origin

The depositional setting of the Bariolée d'Ucel Formation was not indicative of braided river deposits, as noted by Spy (1980), but rather assembled a terminal alluvial fan environment transitioning eastward into a playa-lake setting with evaporite formation, as described by Poli (1997). Earlier investigations in the region have identified the paleosols and their associated characteristics as ancient dolocretes, as documented by Spy (1980) and Poli (1997). Dolomitization occurred early in the system, as shown by the presence of dolomite crystals in pedogenic structures (D0 in glaebules, sensu Brewer and Sleeman, 1964) and the U/Pb geochronology data pointing toward Late Triassic (D0, D1 & D2) to Early Jurassic (D3) ages (Fig. 11). The low uranium content as well as the high common Pb contents yields large uncertainties, as high as 31 Ma for D0 (Fig. 11). Nevertheless, there is a good chronology between each dolomitic phase, D0 being the oldest (~217 ± 21 Ma), then D1 & D2 (~208 ± 11 Ma) and D3 the youngest (~182 ± 6 Ma). When considering outcrop data, there is a good agreement in the relative chronology from D0 to D3 in dolomite stages and stratigraphy: these first ages provide a rather-well constrained absolute timing of dolomite precipitation and fluid flow in the considered section, confirming the early formation of dolomites for D0, D1, D2 and a relatively younger age for D3. This information is somehow lost in the MM1 well where dolomite stages and their deposition age overlap. This could be the result of progressive dolomite recrystallization during burial, as shown by the CL luminescence (Fig. 7) and in good agreement with fluid-inclusion data published by Pagel et al. (1998) on the same dolomites. This finding also relates to a broader discussion concerning dolomite and the impact of recrystallization on dolomitic sequences (Gasparrini et al., 2023). Recrystallization affects the accuracy of models explaining the origin of dolomitization and the ability to predict the distribution of porosity and permeability within dolomitic reservoirs. Recrystallization may initiate shortly after dolomitization or occur later during diagenesis due to interactions with fluids of marine, meteoric, or basinal origin (Gregg et al., 1992; Montanez and Read, 1992; Kaczmarek and Sibley, 2014; Ryan et al., 2022; Gasparrini et al., 2023; Mueller et al., 2024). This process can unfold over an extended period, as demonstrated by a combined Δ⁴⁷/U-Pb thermochronometry approach applied to dolomite from the Upper Jurassic Arab Formation in the United Arab Emirates (Gasparrini et al., 2023). Despite deep burial conditions, early dolomites may retain their original characteristics (Al-Aasm and Packard, 2000; Mueller et al., 2020; Immenhauser, 2022; Gasparrini et al., 2023).

Since dolomitization is very early in our system, accumulation of calcium and magnesium could have been produced by soil roots through direct calcification/dolomitization of their cells and by microbial activity (Hinsinger et al., 2006; Alonso-Zarza, 2018). Within the soil surrounding roots exists a symbiotic relationship between plant roots and a diverse microbial community known as the rhizosphere (Hinsinger et al., 2006). This association in the rhizosphere actively participates in both the formation and degradation of minerals in soils (Uroz et al., 2009). For instance, microorganisms play a role in precipitating new minerals and contributing to carbonate production (Petrash et al.,

2017), as well as in mineral weathering, a process of significant environmental importance as it influences the availability of chemical elements crucial for sustaining life (Uroz et al., 2009). Silicate weathering, in particular, affects the availability of essential chemical elements like K, Mg, Ca, and Fe, which are vital for plant nutrition, especially in soils deficient in nutrients (Calvaruso et al., 2006). Microbial-driven mineral weathering is a widely observed phenomenon (Uroz et al., 2009), with evidence suggesting that plant-induced chemical weathering of silicates may have contributed to accelerated terrestrial carbonate production since the Devonian period (Brasier, 2011). In certain environments, the weathering of magnesium silicates releases free Ca and Mg ions, which can combine with bicarbonate ions and lead to the precipitation of dolomite. Laboratory experiments have shown that structures resembling those found in ancient and recent calcretes, such as calcified roots, coated grains, needle fiber calcite, and micro-rods, can form within days (Burford et al., 2006; Masaphy et al., 2009; Bindschedler et al., 2014), highlighting the rapidity of these mineralization processes (Alonso-Zarza, 2018). In our considered interval, dolomitization is also occurring in the sandstone and conglomerate levels below the soil development horizon. In those beds, dolomite precipitation is strongly linked to the alteration of feldspar in terms of spatial development, by forming into the secondary and residual porosity left by the feldspar's progressive dissolution (Figs. 4F, 6E & F).

Dolocretes are not limited to soil profiles (known as pedogenic dolocretes) but can also manifest in other environments, such as within the vadose zone, or at the capillary fringe and below the water table, forming groundwater dolocrete (Wright and Tucker, 2009). They can take on various forms, ranging from powdery to nodular to highly compacted. Dolocrete formation occurs through the cementation process and the introduction of calcium carbonate and magnesium, either by displacive or replacement means, into soil profiles, bedrock, and sediments. This phenomenon typically happens in regions where vadose and shallow phreatic groundwaters become saturated with respect to dolomite (Wright and Tucker, 2009). Here, the thickness of the Bariolée d'Ucel Fm increases from the proximal deposits of Chassagnes (38 m) to the more distal deposits of Balazuc (148 m). The variation in thickness from proximal to distal regions is attributed in part to the presence of the Uzer Fault and other small-scale normal faults resulting from margin extension. These faults generated deeper topographic depressions, providing additional space for sediment deposition. The cumulative paleosol thickness in the Chassagnes outcrop accounts for 56 % of the total thickness of the considered interval. This share of paleosol thickness in total thickness is falling to 31 % in MM1 and only 23 % in BA1 (Fig. 3). At the top of the section, the paleosols are displaying a stacking up sequence making them rather continuous both vertically and laterally (Fig. 3). Dolomite precipitation is affecting the paleosol beds as well as the underlying sandstone (per descensum) and the dolomitization perimeter is very visible within the sandstones, resulting in vertical and horizontal dolomite nodules (Fig. 5). In continental systems, dolomitization can have two main origins: a (i) classic soil-induced dolomitization (sensu Casado et al., 2014; Petrash et al., 2017), where dolomite occurs as dolomiticrite primarily precipitated and/or replacing clays, or resulting from soil microorganisms' activity after the decaying of roots and/or mineral alteration, and (ii) a groundwater dolomitization (sensu Wright and Tucker, 2009). In the latter, three major processes
<figure><img src="image_12.png" /><figcaption>**Fig. 9.** Sedimentological logs of the Chassagnes outcrop and the two boreholes MM1 & BA1, Late Triassic. Permeability data (K, blue dots) displayed for the Chassagnes outcrop are from laboratory measurements. The ones for MM1 & BA1 are from on core measurements (TinyPerm apparatus). Laboratory porosity (Φ, green dots) is from laboratory measurements for Chassagnes, and from NPHI for MM1 and BA1. Vertical scale is different on each log.</figcaption></figure>

occur: CO₂, degassing; evaporation and evapotranspiration of mobile, shallow groundwaters; and a common-ion effect. This model predicts dolomite formation to the down-dip evolution of the groundwaters, i.e. an increase if the Mg/Ca ratio toward the center of the basin, following the hydraulic gradient. In such a model, the final product is a ribbon-

shaped dolomite, which is preceded by calcrete, and passes downflow into gypcrete. Here, this lateral distribution along the regional flow is not observed, as dolomite is ubiquitous, from the most proximal (Chassagnes) to distal domain (Balazuc), pointing toward a coupled dolomitization system between pedogenic and groundwater fluctuations.
<figure><img src="image_13.png" /></figure>

Sample CHA-25

Dolomite - D0

Lower Intercept = 213 ± 31 Ma

MSWD=0.52 (n=42)

(207Pb/206Pb)₀ = 0.839 ± 0.016

<figure><img src="image_14.png" /></figure>

Sample CHA-13

Dolomite - D1/D2

Lower Intercept = 199 ± 28 Ma

MSWD=1.4 (n=42)

(207Pb/206Pb)₀ = 0.840 ± 0.004

<figure><img src="image_15.png" /></figure>

Sample CHA-21

Dolomite - D1/D2

Lower Intercept = 195 ± 26 Ma

MSWD=0.52 (n=42)

(207Pb/206Pb)₀ = 0.840 ± 0.009

<figure><img src="image_16.png" /></figure>

Sample CHA-19

Dolomite - D3

Lower Intercept = 166 ± 16 Ma

MSWD=1 (n=42)

(207Pb/206Pb)₀ = 0.819 ± 0.011

<figure><img src="image_17.png" /></figure>

Sample CHA-08

Dolomite - D3

Lower Intercept = 183 ± 7 Ma

MSWD=1 (n=36)

(207Pb/206Pb)₀ = 0.830 ± 0.003

<figure><img src="image_18.png" /></figure>

Sample MM1-19

Dolomite - D0

Lower Intercept = 203.2 ± 31 Ma

MSWD=1.7 (n=41)

(207Pb/206Pb)₀ = 0.848 ± 0.010

<figure><img src="image_19.png" /></figure>

Sample MM1-19

Dolomite - D1/D2

Lower Intercept = 212.6 ± 12.9 Ma

MSWD=3.3 (n=33)

(207Pb/206Pb)₀ = 0.840 ± 0.004

<figure><img src="image_20.png" /></figure>

Sample MM1-17

Dolomite - D3

Lower Intercept = 195 ± 18 Ma

MSWD=1.4 (n=49)

(207Pb/206Pb)₀ = 0.850 ± 0.001
Fig. 14 embodies a conceptual model of such a mixed groundwater-pedogenic mechanism. The work of Poli (1997) proposed stratigraphic correlation between the BA1 and MM1 boreholes (Fig. 9), with a large surface extension of floodplain or lacustrine facies that marking a maximum flooding surface (MFS8) considered as a reference level, thus dividing the Bariolée d'Ucel Fm into two stratigraphic cycles. The first one is characterized by a retrogradational trend marked by a decrease in sandstone facies up to a maximum extension of floodplain or lacustrine levels (MFS8, Fig. 9) and the second one by a progradational trend with well-developed paleosols. By way of comparison, we propose that the Chassagne outcrop corresponds to the highest part of the Bariolée d'Ucel Fm, i.e. the progradational trend above the MFS8 surface. Since the Balazuc section is heavily dolomitized although the proportion of its total paleosol thickness is reduced compared to the more proximal domains (from 56% to 23% of total thickness from Chassagnes to Balazuc, if preservation is optimal in Chassagnes). The highly stacked number of paleosol levels (probably due to a drastic decrease in sedimentary input at the end of Triassic times) in Chassagnes, the most proximal domain during Triassic times played the role of a source for calcium and magnesium. These ions would be later distributed to more distal domains through a process of coupled water table fluctuations and hydrologic gradient slowly drifting to the southeast of the margin, toward the basin. The Middle Triassic and Lower Jurassic marls probably played a huge role in containing the fluid flow in the Bariolée d'Ucel Fm during burial. Such a model is also backed up by geochemical data performed on the dolomite cements and bearing the signature of meteoric water composition (Aquilina et al., 1996).

That being said, another relevant possibility for D3 origin could be a
basinal fluid flow event, which is also backed by the fluid inclusion data
(Pagel et al., 1998) and by the saddle-like shape of the dolomites as well.
This event would likely be linked to the vast amount of fluid
mobolization during North Atlantic opening in the same time interval
(Mueller et al., 2020 and 2024). Specifically, the latter of those papers
has shown that dolomite phases can precipitate from mixed basinal/hy-
drothermal - meteoric origin. Mueller et al. (2020) documented a most
extreme case example about well-developed dolomite fabric and proxy
preservation despite extreme multi-stage overprint. The U-Pb ages of
their study are similar to the ages obtained here (partially of D1-2 and
certainly of D3). They interpreted the Jurassic ages as driven by the
opening of the North Atlantic Ocean at that time. In a very recent
study (Mueller et al., 2024), they also found Jurassic dolomites precipi-
tated by the same event in the Rhenish Massif.

## 5.2. Paleosol induced dolomitization and fluid flow properties

The vertical and lateral distribution of paleosols appears to be a key
factor in understanding the petrophysical property distribution of an-
cient sandstone aquifers in continental sedimentary units, as well as
the distribution of microfacies. The shift between well-developed aqui-
fer layers and impervious levels can be explained by early dolomite pre-
cipitation thanks to the development of soils. Dolomite precipitation is
affecting the paleosol beds (Dv, Dh) as well as the underlying sand-
stones (per descensum; Dn) and the dolomitization perimeter is very
visible within the sandstones, resulting in vertical and horizontal dolo-
mite nodules (Fig. 5); thanks to the interplay of water-table fluctuations
and groundwater flow. Dolomitization exerts a strong control on fluid
flow properties, as shown in Section 4.4 (Fig. 13). To go further,
Fig. 15A shows the dolomitization vertical extension and its influence
on permeability, taking the closest paleosol top bed as a reference
point in the two boreholes. The Morte-Mérie section reveals peculiar re-
lationship between the permeability of samples and their position to the
closest paleosol (Fig. 15B). Most of the dolomite permeability data
shows an increase by two orders of magnitude until around 7 m

<figure><img src="image_21.png" /><figcaption>**Fig. 11.** Age synthesis from U–Pb geochronology data on dolomite in Chassagnes and Morte-Mérie. The earliest dolomitization stage D0 in Chassagnes is pointing toward Late Triassic times, but Early Jurassic in MM1. D1 and D2 are Late Triassic–Early Jurassic in both Chassagnes and MM1. D3 is clearly Early Jurassic in Chassagnes, but Late Triassic to Early Jurassic in MM1.</figcaption></figure>

below a paleosol bed top, although two of them display high permeabil-
ities at 2 m below a paleosol bed. Moreover, there is a clear clustering of
the data appearing between dolomitized (green circles) and non-
dolomitized samples (yellow circles). Dolomitized samples display
higher permeabilities at a given vertical position. This is confirmed by
the Probability Density Function (PDF, Fig. 15B), representing the prob-
ability of having a data point in a given area by fitting a normal law on X
and Y variables and calculating its intersecting probability. Seventy per-
cent of the dolomite samples are centered around 10² mD and 4 m,
whereas 70 % of non-dolomite samples are centered on 8.10⁻¹ mD
and 2.5 m. Such observation is very much in agreement with a water-
table fluctuation type of dolomitization as mentioned in the previous
paragraph. The Balazuc section, however, (Fig. 15C) does not display
any correlation or particular behavior, confirming that most of the sec-
tion is characterized by a very low permeability despite the dolomitiza-
tion. Its poorly-developed fluid flow properties are the result of two
things: (1) the dolomitization dynamic is less paleosol-oriented in the
section because of its distal position along the margin, and much more
groundwater dominated resulting in a less widespread vertical distribu-
tion of dolomite; and (2) an intense silicification episode is affecting
most of the dolomitized samples. This amorphous silica cement, visible
in thin sections (Section 4.1.2, Fig. 6), is precipitating in the residual po-
rosity left by the dolomite crystallization after the initial mineral disso-
lution. In BA1, the fluid inclusions in dolomite D3 (reequilibrated during
burial) indicate a trapping temperature of 130–145 °C at 1600 m and a
temperature decrease toward the surface (Pagel et al., 1998). This value
is in good agreement with the maximum paleotemperature obtained
with the burial method on organic matter, indicating a maximum burial
temperature of 130 °C at the same depth (Pagel et al., 1998). This means
that most of the dolomitized section stayed porous during burial for the
fluid to be free to migrate laterally and for the section to be heavily silic-
ified. This porosity preservation is typical of early cementation of the
sediment where the sediment framework is lithified very quickly. In
<figure><img src="image_22.png" /><figcaption>**Fig. 12.** Porosity and permeability data from the investigated sections. A – Porosity-permeability relationship from logging tools (NPHI, BA1 and MM1 sections) and laboratory measurements (water porosity, Chassagnes). B – Permeability distribution in the Balazuc borehole. Note the skewed distribution to lower permeabilities. C – Permeability distribution in the Mortemérie borehole. Distribution displays almost normal-law behavior.</figcaption></figure>

this context, the early dolomitization occurring within pores and grain interfaces partially restrains mechanical compaction during burial, thereby promoting porosity preservation. These microstructures may also act as partial inhibitors of stylolitization under burial conditions, as few instances have been observed. Similar observations have been documented in carbonate sequences (Heydari, 2003; Brigaud et al., 2010; Regnet et al., 2015) and could be relevant in the context of kontinental sequences during periods of active paleosol development.

Regarding silicification events, two distinct phases of fluid migration were identified in the Balazuc section: the first associated with the late Liassic rifting extension of the margin, and the second occurring during the Early Cretaceous, related to fluids expelled from the basin during the primary Mesozoic compaction phase (Cros et al., 1993). The absence of silicification in the Morte-Mérie section can be attributed to the presence of the Uzer Fault, which exclusively funneled fluids into the Balazuc section (Fig. 16). It is likely that fluid circulation along the fault was hindered or sealed off by the presence of Liassic marls, acting as a cap rock in the region (Vinchon et al., 1996).

## 6. Conclusion

The primary challenge in modeling fluid flow within sedimentary basins lies in accurately describing rock properties such as porosity,

permeability, compressibility, or thermal conductivity, given the constraints of the models and the availability of data to constrain these values. When permeability is uniform in all directions, pore water flow can be determined solely from the groundwater table elevation and fluid densities. However, sedimentary rocks typically exhibit significant heterogeneity, where variations in permeability due to clay layers, sand, or gravel beds overwhelmingly influence water flow. In such scenarios, mathematical modeling is of limited utility without accurate characterization of the sedimentary sequences' stratigraphy, sedimentology, and structural deformation. This study demonstrates the substantial impact of early dolomitization in continental successions on basin-scale fluid flow properties. The presence of paleosols facilitated the concentration of calcium and magnesium ions around root systems, leading to early dolomitization. This timing is supported by U–Pb geochronology. Subsequent groundwater migration along hydraulic gradients, influenced by fluctuations in the local aquifer's water table, enabled vertical distribution of dolomitization. Dolomitization occurred in residual pores left by initial mineral alterations, early stiffening the sediment, thereby impeding mechanical compaction and favoring porosity preservation. Along the Ardèche margin, the distal section of Balazuc underwent silicification during a Jurassic/Cretaceous fluid migration event, facilitated by the nearby Uzer Fault system. Vertical fluid migration along the fault and horizontal percolation through

<figure><img src="image_23.png" /><figcaption>**Fig. 13.** Porosity and permeability data from the investigated sections. A – Porosity-permeability relationship from logging tools (NPHI, BA1 and MM1 sections) and laboratory measurements (water porosity, Chassagnes). Data are discriminated with their dolomitization attribute and localization. Note the cloudy distribution in 99 % of Balazuc dataset. B – Permeability distribution in the Balazuc borehole. Note the skewed distribution to lower permeabilities and the low contribution to fluid flow of dolomitization. C – Permeability distribution in the Morte-mérie borehole. Distribution displays almost normal-law behavior. High dolomitization contribution to permeability.</figcaption></figure>
<figure><img src="image_24.png" /><figcaption>**Fig. 14.** Conceptual model of a mixed groundwater-pedogenic dolomitization, Late Triassic times, Ardèche Margin, France. The proximal domain played the role of a source for calcium and magnesium. These ions are later distributed to distal domains through a process of coupled water table fluctuations and hydrologic flow slowly drifting toward the basin.</figcaption></figure>

still-porous dolomitized layers of the formation occurred. This study highlights the significant role of paleosol-induced early dolomitization in shaping fluid pathways and their resultant patterns in fluid-flow properties within ancient sandstone aquifers and continental sedimentary units.

Supplementary data to this article can be found online at https://doi.org/10.1016/j.sedgeo.2024.106719.

**CRediT authorship contribution statement**

**J.-B. Regnet:** Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation, Conceptualization.
**C. Bailly:** Writing – review & editing, Methodology, Investigation, Formal analysis, Conceptualization.
**S. Bourquin:** Writing – original draft, Validation, Investigation, Formal analysis, Conceptualization.

**P. Robion:** Writing – review & editing, Supervision, Resources,

**Methodology.** **M. Poujol:** Writing – review & editing, Writing – original draft, Validation, Methodology, Formal analysis, Data curation.
**X. Sengelen:** Supervision, Project administration, Investigation.
**O. Serrano:** Writing – review & editing, Resources.
**B. Ledésert:** Writing – review & editing, Supervision, Project administration, Funding acquisition.

**Data availability**

Data set can be found here: https://entrepot.recherche.data.gouv.fr/dataverse/cyu.

**Declaration of competing interest**

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

<figure><img src="image_25.png" /><figcaption>**Fig. 15.** Vertical extension of dolomitization and its contribution to fluid flow. The "distance from top paleosol" represents the vertical distance between a sample and the closest paleosol top bed. Mortemérie shows that the highest permeabilities are reached around 7 m. The Probability Density Function (PDF) shows that 70% on the dolomitized samples falls into the 0.05–0.12 green-outlined areas. There is no contribution of the dolomitization vertical extension to fluid flow in Balazuc, probably because the dolomitization dynamic is less paleosol-oriented, and much more groundwater dominated.</figcaption></figure>
<figure><img src="image_26.png" /><figcaption>**Fig. 16.** Cross section of the Ardèche margin along the Mortemérie borehole (MM1) and Balazuc borehole (BA1), adapted and modified from Bonijoly et al. (1996) & Razin et al. (1996). Mineralization fluids circulated along the Uzer Fault and horizontally percolated through sedimentary layers that stayed porous and permeable during burial thanks to the early dolomitization. The fluids never reached the Mortemérie section due to the Early Jurassic marls acting as a cap rock.</figcaption></figure>

## Acknowledgments

This work was supported by the European Union's Horizon 2020 research and innovation program (Grant agreement No. 792037-MEET Project). We are very grateful to the BRGM (French Geological Survey) for giving us access to their core repository in Orléans, France. We thank Didier Bonijoly for the fruitful discussions about the Ardèche region and ideas developed in the manuscript.

We would like to thank the three reviewers (two anonymous, and Matthias Mueller) for their constructive remarks that enhanced the quality of the manuscript, and added fruitful discussions about the origin of dolomite and their associated fluid flow properties.

## References

* Al-Aasm, I.S., Packard, J.J., 2000. Stabilization of early-formed dolomite: a tale of divergence from two Mississippian dolomites. Sedimentary Geology 131 (3-4), 97-108.

* Alonso-Zarza, A.M., 2003. Palaeoenvironmental significance of palustrine carbonates and calcretes in the geological record. Earth-Science Reviews 60 (3-4), 261-298.

* Alonso-Zarza, A.M., 2018. Study of a modern calcrete forming in Guadalajara, Central Spain: an analogue for ancient root calcretes. Sedimentary Geology 373, 180-190.

* Alonso-Zarza, A.M., Wright, V.P., 2010. Calcretes. Developments in Sedimentology 61, 225-267.

* Aquilina, L., Scheerens, S., Dromart, G., Vinchon, C., Le Strat, P., GPF research team, 1996. Cored section of the Balazuc well (Southeastern Basin of France): geologic and geochemical approach (Deep Geology of France Programme). Marine and Petroleum Geology 13 (6), 725-735.

* Barale, L., Bertok, C., d'Atri, A., Piana, F., Bernasconi, S., Czuppon, G., Palcsu, L., Gerdes, A., Birgel, D., Martire, L., 2021. U-Pb dating and geochemical constraints to Early Cretaceous hydrothermal dolomitization in the provençal domain (Maritim Alps, NW Italy - SE France). Ofioliti 46 (2). https://doi.org/10.4454/ofioliti.v46i2.543.

* Ben-Israel, M., Holder, R.M., Nelson, L.L., Smith, E.F., Kylander-Clark, A.R.C., Ryb, U., 2024. Late Paleozoic oxygenation of marine environments supported by dolomite U-Pb dating. Nature Communications 15 (1), 2892. https://doi.org/10.1038/s41467-024-46660-7.

* Bense, V.F., Person, M.A., 2006. Faults as conduit-barrier systems to fluid flow in siliceous sedimentary aquifers. Water Resources Research 42 (5).

* Bethke, C.M., 1985. A numerical model of compaction-driven groundwater flow and heat transfer and its application to the paleohydrology of intracratonic sedimentary basins. Journal of Geophysical Research: Solid Earth 90 (B8), 6817-6828.

* Bindschedler, S., Cailleau, G., Braissant, O., Millière, L., Job, D., Verrecchia, E.P., 2014. Unravelling the enigmatic origin of calcitic nanofibres in soils and caves: purely physicochemical or biogenic processes? Biogeosciences 11 (10), 2809-2825.

* Bjørlykke, K., 1993. Fluid flow in sedimentary basins. Sedimentary Geology 86 (1-2), 137-158.

* Bjørlykke, K., 1997. Lithological control on fluid flow in sedimentary basins. Fluid Flow and Transport in Rocks: Mechanisms and Effects. Springer Netherlands, Dordrecht, pp. 15-34.

* Bjørlykke, K., Hæg, K., 1997. Effects of burial diagenesis on stresses, compaction and fluid flow in sedimentary basins. Marine and Petroleum Geology 14 (3), 267-276.

* Bøggs Jr., S., 2009. Petrology of Sedimentary Rocks. Cambridge University Press.

* Bonijoly, D., Perrin, J., Roure, F., Bergerat, F., Courel, L., Elmi, S., Mignot, A., 1996. The Ardèche palaeomargin of the South-East Basin of France: Mesozoic evolution of a part of the Tethyan continental margin (Géologie Profonde de la France programme). Marine and Petroleum Geology 13 (6), 607-623.

* Boretti, A., Rosa, L., 2019. Reassessing the projections of the World Water Development Report. npj Clean Water 2 (15). https://doi.org/10.1038/s41545-019-0039-9.

* Bouat, L., Strzerzynski, P., Mourgues, R., Branquet, Y., Cogné, N., Barré, G., Gardien, V., 2023. Early, farfield and diffuse tectonics records in the North Aquitaine Basin (France). Bulletin de la Société Géologique de France, Earth Sciences Bulletin. https://doi.org/10.1051/bsgf/2023014.

* Bourquin, S., Rigollet, C., Bourges, P., 1998. High-resolution sequence stratigraphy of an alluvial fan-fan delta environment: stratigraphic and geodynamic implications—an example from the Keuper Chaunoy Sandstones, Paris Basin. Sedimentary Geology 121 (3-4), 207-237.

* Brasier, A.T., 2011. Searching for travertines, calcretes and speleothems in deep time: processes, appearances, predictions and the impact of plants. Earth-Science Reviews 104 (4), 213-239.

* Brewer, R., Sleeman, J.R., 1964. Glaebules: their definition, classification and interpretation. Journal of Soil Science 15 (1), 66-78.

* Brigaud, B., Vincent, B., Durlet, C., Deconinck, J.F., Blanc, P., Trouiller, A., 2010. Acoustic properties of ancient shallow-marine carbonates: effects of depositional environments and diagenetic processes (Middle Jurassic, Paris Basin, France). Journal of Sedimentary Research 80 (9), 791-807.

* Brown, S., Smith, M., 2013. A transient-flow syringe air permeameter. Geophysics 78 (5), D307-D313.

* Burford, E.P., Hillier, S., Gadd, G.M., 2006. Biomineralization of fungal hyphae with calcite (CaCO₃) and calcium oxalate mono- and dihydrate in carboniferous limestone microcosms. Geomicrobiology Journal 23 (8), 599-611.

* Calvaruso, C., Turpault, M.P., Frey-Klett, P., 2006. Root-associated bacteria contribute to mineral weathering and to mineral nutrition in trees: a budgeting analysis. Applied and Environmental Microbiology 72 (2), 1258-1266.

* Casado, A.I., Alonso-Zarza, A.M., La Iglesia, Å., 2014. Morphology and origin of dolomite in paleosols and lacustrine sequences. Examples from the Miocene of the Madrid Basin. Sedimentary Geology 312, 50-62.

* Chew, D.M., Petrus, J.A., Kamber, B.S., 2014. U-Pb LA-ICPMS dating using accessory mineral standards with variable common Pb. Chemical Geology 363, 185-199.

* Choquette, P.W., Cox, A., Meyers, W.J., 1992. Characteristics, distribution and origin of porosity in shelf dolostones; Burlington-Keokuk Formation (Mississippian), US Mid-Continent. Journal of Sedimentary Research 62 (2), 167-189.
Colson, J., Cojan, I., 1996. Groundwater dolocretes in a lake-marginal environment: an alternative model for dolocrete formation in continental settings (Danian of the Provence Basin, France). Sedimentology 43 (1), 175-188.

Courel, L., Poli, E., Vannier, F., Le Strat, P., Baud, A., Jacquin, T., 1998. Sequence Stratigraphy Along a Triassic Transect on the Western Peritethyan Margin in Ardèche (SE France Basin): Correlations With Subalpine and Germanic Realms.

Cros, P., Lanau, P., Vinchon, C., Bonhomme, M.G., Boulegue, J., Cula, P., ... Giot, D., 1993. Diagenese des gres et histoire de la porosite d'un reservoir potentiel traisique (region de Privas, Ardeche). Bulletin de la Société Géologique de France 164 (5), 631-647.

Doré, A.G., Augustson, J.H., Hermanrad, C., Stewart, D.J., Sylta, Ø., 1993. Basin Modelling: Advances and Applications.

Eaton, T.T., 2006. On the importance of geological heterogeneity for flow simulation. Sedimentary Geology 184 (3-4), 187-201.

Ehrenberg, S.N., Eberli, G.P., Keramati, M., Moallemi, S.A., 2006. Porosity-permeability relationships in interlayered limestone-dolostone reservoirs. AAPG Bulletin 90 (1), 91-114.

Elisha, B., Nuriel, P., Kylander-Clark, A., Weinberger, R., 2021. Towards in situ U-Pb dating of dolomite. Geochronology 3, 337-349. https://doi.org/10.5194/gchron-3-337-2021.

Elmi, S., 1990. Les applications géodynamiques de la stratigraphie: l'histoire triasico-jurassique de la marge vivaro-cévénole (France, Sud-Est). Travaux et Documents des Laboratoires de Géologie de Lyon 9 (1), 93-123.

Flügel, E., Munnecke, A., 2010. Microfacies of Carbonate Rocks: Analysis, Interpretation and Application. Vol. 976. Springer, Berlin, p. 200.

Gao, Y.-X., Jiang, G.-P., Qu, Y., Zhang, R.-Q., Tang, Y.-W., Zhu, R., Yao, S.-J., 2022. Syn-technical dolomite U-Pb geochronology constraining intracontinental deformation: a case study from the Gouloung Gold Deposit in the Qinling Orogen, China. Minerals 12, 1045. https://doi.org/10.3390/min12081045.

Gasparrini, M., Morad, D., Mangenot, X., Bonifacie, M., Morad, S., Nader, F.H., Gerdes, A., 2023. Dolomite recrystallization revealed by $\Delta\sigma/47$U-Pb thermochronometry in the Upper Jurassic Arab Formation, United Arab Emirates. Geology 51 (5), 471-475.

Ghosh, S.K., Friedman, G.M., 1989. Petrophysics of a dolostone reservoir: San Andres Formation (Permian), West Texas. Carbonates and Evaporites 4, 45-119.

Gregg, J.M., Howard, S.A., Mazzullo, S.J., 1992. Early diagenetic recrystallization of Holo-cene (<3000 years old) peritidal dolomites, Ambergris Cay, Belize. Sedimentology 39 (1), 143-160.

Gregg, J.M., Bish, D.L., Kaczmarek, S.E., Machel, H.G., 2015. Mineralogy, nucleation and growth of dolomite in the laboratory and sedimentary environment: a review. Sedimentology 62 (6), 1749-1769.

Hasiotis, S.T., 2007. Continental ichnology: fundamental processes and controls on trace fossil distribution. Trace Fossils. Elsevier, pp. 268-284.

Heidsiek, M., Butscher, C., Blum, P., Fischer, C., 2020. Small-scale diagenetic facies heterogeneity controls porosity and permeability pattern in reservoir sandstones. Environmental Earth Sciences 79, 1-14.

Hendry, J.P., 2002. Geochemical trends and palaeohydrological significance of shallow burial calcite and ankerite cements in middle Jurassic strata on the East Midlands Shelf (onshore UK). Sedimentary Geology 151 (1-2), 149-176.

Heydari, E., 2003. Metoric versus burial control on porosity evolution of the Smackover Formation. AAPG Bulletin 87 (11), 1779-1797.

Hiess, J., Condon, D.J., McLean, N., Noble, S.R., 2012. $^{238}$U/$^{235}$U systematics in terrestrial uranium-bearing minerals. Science 335, 1610-1614.

Hinsinger, P., Plassard, C., Jaillard, B., 2006. Rhizosphere: a new frontier for soil biogeochemistry. Journal of Geochemical Exploration 88 (1-3), 210-213.

Huuse, M., Jackson, C.A.L., Van Rensbergen, P., Davies, R.J., Flemings, P.B., Dixon, R.J., 2010. Subsurface sediment remobilization and fluid flow in sedimentary basins: an overview. Basin Research 22 (4), 342-360.

Immenhauser, A., 2022. On the delimitation of the carbonate burial realm. The Depositional Record 8 (2), 524-574.

Jessop, A.M., Majorowicz, J.A., 1994. Fluid flow and heat transfer in sedimentary basins. In: Parnell, J. (Ed.), Geofluids: Origin, Migration and Evolution of Fluids in Sedimentary Basins. 78. Geological Society, London, Special Publications, pp. 43-54.

Kaczmarek, S.E., Sibley, D.F., 2014. Direct physical evidence of dolomite recrystallization. Sedimentology 61 (6), 1862-1882.

Kampman, N., Bickle, M., Wigley, M., Dubacq, B., 2014. Fluid flow and CO₂-fluid-mineral interactions during CO₂-storage in sedimentary basins. Chemical Geology 369, 22-50.

Kopaska-Merkel, D.C., Friedman, G.M., 1989. Petrofacies analysis of carbonate rocks: example from lower Paleozoic Hunton Group of Oklahoma and Texas. AAPG Bulletin 73 (11), 1289-1306.

Kraus, M.J., Aslan, A., 1993. Eocene hydromorphic Paleosols; significance for interpreting ancient floodplain processes. Journal of Sedimentary Research 63 (3), 453-463.

Lowe, D.R., 1982. Sediment gravity flows; II, depositional models with special reference to the deposits of high-density turbidity currents. Journal of Sedimentary Research 52 (1), 279-297.

Lucia, F.J., Major, R.P., 1994. Porosity evolution through hypersaline reflux dolomitization. Dolomites: A Volume in Honour of Dolomieu, pp. 325-341.

Mádl-sznyi, J., Tóth, Á., 2015. Basin-scale conceptual groundwater flow model for an un-confined and confined thick carbonate region. Hydrogeology Journal 23 (7), 1359.

Martín Pérez, A., Martín García, R., Alonso-Zarza, A.M., 2012. Diagenesis of a Drapery Speleothem From Castañar Cave: From Dissolution to Dolomitization.

Masaphy, S., Zabari, L., Pastrana, J., Dultz, S., 2009. Role of fungal mycelium in the formation of carbonate concretions in growing media—an investigation by SEM and synchrotron-based X-ray tomographic microscopy. Geomicrobiology Journal 22 (7), 442-450.

McCormick, C.A., Corlett, J., Roberts, N.M.W., Johnston, P.A., Collom, C.J., Stacey, J., ... Hollis, C., 2024. U-Pb geochronology reveals that hydrothermal dolomitization was coeval to the deposition of the Burgess Shale lagerstätte. Communications Earth & Environment 5 (1), 318. https://doi.org/10.1038/s43247-024-01429-0.

Miall, A.D., 2013. The Geology of Fluvial Deposits: Sedimentary Facies, Basin Analysis, and Petroleum Geology. Springer.

Miall, A.D., 2014. Fluvial Depositional Systems. Vol. 14. Springer International Publishing, Cham, p. 316.

Molz III, F.J., Dinwidde, C.L., Wilson, J.L., 2003. A physical basis for calculating instrument spatial weighting functions in homogeneous systems. Water Resources Research 39 (4).

Montañez, I.P., 1997. Secondary Porosity and Late Diagenetic Cements of the Upper Knox Group, Central Tennessee Region: A Temporal and Spatial History of Fluid Flow Conduct Development Within the Knox Regional Aquifer.

Montanez, I.P., Read, J.F., 1992. Fluid-rock interaction history during stabilization of early dolomites, Upper Knox Group (Lower Ordovician), US Appalachians. Journal of Sedimentary Research 62 (5), 753-778.

Mueller, M., Igbokwe, O.A., Walter, B., Pederson, C.L., Riechelmann, S., Richter, D.K., ... Immenhauser, A., 2020. Testing the preservation potential of early diagenetic dolomites as geochemical archives. Sedimentology 67 (2), 849-881.

Mueller, M., Walter, B.F., Giebel, R.J., Beranoaguirre, A., Swart, P.K., Lu, C., ... Immenhauser, A., 2024. Towards a better understanding of the geochemical proxy record of complex carbonate archives. Geochimica et Cosmochimica Acta 376, 68-99.

Mulder, T., Alexander, J., 2001. The physical character of subaqueous sedimentary density flows and their deposits. Sedimentology 48 (2), 269-299.

Pagel, M., Clauer, N., Disnar, J.R., Mossmann, J.R., Sureau, J.F., Steinberg, M., Vinchon, C., 1998. Thermal history and timing of fluid flow at the Ardèche palaeomargin, France. Geological Society, London, Special Publications 144 (1), 145-151.

Paquette, J.-L., Piro, J.L., Devidal, J.L., Bosse, V., Didier, A., Sanac, S., Abdelnour, Y., 2014. Sensitivity enhancement in LA-ICP-MS by N2 addition to carrier gas: application to radiometric dating of U-Th-bearing minerals. Agilent ICP-MS Journal 58, 4-5.

Paton, C., Woodhead, J.D., Hellstrom, J.C., Hergt, J.M., Greig, A., Maas, R., 2010. Improved laser ablation U-Pb zircon geochronology through robust downhole fractionation correction. Geochimistry, Geophysics, Geosystems 11 (3). https://doi.org/10.1029/2009GC002618.

Perez, H.H., Datta-Gupta, A., Mishra, S., 2005. The role of electrofacies, lithofacies, and hydraulic flow units in permeability prediction from well logs: a comparative analysis using classification trees. SPE Reservoir Evaluation & Engineering 8 (02), 143-155.

Petrash, D.A., Bialik, O.M., Bontognali, T.R., Vasconcelos, C., Roberts, J.A., McKenzie, J.A., Konhauser, K.O., 2017. Microbially catalyzed dolomite formation: from near-surface to burial. Earth-Science Reviews 171, 558-582.

Povl, E., 1997. Stratigraphie séquentielle haute-résolution, modèles de dépôt et géométrie 2D-3D des séquences triasiques de la marge téthysienne ardéchoise (Doctoral dissertation, Dijon).

Postma, G., 1990. An analysis of the variation in delta architecture. Terra Nova 2 (2), 124-130.

Raffensperger, J.P., 1996. Numerical simulation of sedimentary basin-scale hydrochemical processes. Advances in porous media 3, 185-305.

Razin, P., Bonijoly, D., Le Strat, P., Courel, L., Poli, E., Dromart, G., Elmi, S., 1996. Stratigraphic record of the structural evolution of the western extensional margin of the Subalpine Basin during the Triassic and Jurassic, Ardèche, France. Marine and Petroleum Geology 13 (6), 625-652.

Regnet, J.B., Robion, P., David, C., Fortin, J., Brigaud, B., Yven, B., 2015. Acoustic and reservoir properties of microporous carbonate rocks: implication of micrite particle size and morphology. Journal of Geophysical Research: Solid Earth 120 (2), 790-811.

Regnet, J.B., David, C., Robion, P., Menéndez, B., 2019a. Microstructures and physical properties in carbonate rocks: a comprehensive review. Marine and Petroleum Geology 103, 366-376.

Regnet, J.B., Fortin, J., Nicolas, A., Pellerin, M., Guéguen, Y., 2019b. Elastic properties of continental carbonates: from controlling factors to an applicable model for acoustic-velocity predictions. Geophysics 84 (1), MR45-MR59.

Retallack, G.J., Reinhardt, J., Sigleo, W.R., 1988. Field recognition of paleosols. Geological Society of America Special Paper 216, 1-20.

Roberts, N.M.W., Ransbury, E.T., Parrish, R.R., Smith, C.J., Horstwood, M.S.A., Condon, D.J., 2017. A calcite reference material for LA-ICP-MS U-Pb geochronology. Geochemistry, Geophysics, Geosystems 18 (7), 2807-2814.

Ryan, B.H., Kaczmarek, S.E., Rivers, J.M., Manche, C.J., 2022. Extensive recrystallization of Cenozoic dolomite during shallow burial: a case study from the Palaeocene-Eocene Umm er Radhuma formation and a global meta-analysis. Sedimentology 69 (5), 2053-2079.

Santos, J.E., Xu, D., Jo, H., Landry, C.J., Prodanović, M., Pyrcz, M.J., 2020. PoreFlow-Net: a 3D convolutional neural network to predict fluid flow through porous media. Advances in Water Resources 138, 103539.

Spy, A., 1980. Dolocretes and nodules dolomitiques. Resultats de la dolomitisation directe, en milieu continental, de sediments terrigènes de la "formation barolleuse superieure" (Keuper) de la region des Vans (Ardeche, sud-est de la France).

Su, A., Chen, H., Feng, Y.-x., Zhao, J.-x., Wang, Z., Hu, M., ... Duc Nguyen, A., 2022. In situ U-Pb dating and geochemical characterization of multi-stage dolomite cementation in the Ediacaran Dengying Formation, Central Sichuan Basin, China: constraints on diagenetic, hydrothermal and paleo-oil filling events. Precambrian Research 368, 106481. https://doi.org/10.1016/j.precamres.2021.106481.

Uroz, S., Calvaruso, C., Turpault, M.P., Frey-Klett, P., 2009. Mineral weathering by bacteria: ecology, actors and mechanisms. Trends in Microbiology 17 (8), 378-387.

Vermeesch, P., 2018. IsoplotR: a free and open toolbox for geochronology. Geoscience Frontiers 9, 1479-1493 doi: 10.

Vinchon, C., Giot, D., Orsag-Sperber, F., Arbey, F., Thibieroz, J., Cros, P., ... Sizun, J.P., 1996. Changes in reservoir quality determined from the diagenetic evolution of Triassic and Lower Lias sedimentary successions (Balazuc borehole, Ardèche, France). Marine and Petroleum Geology 13 (6), 685-694.

Vonm, M., Exner, U., Barnhoorn, A., Baud, P., Reuschlé, T., 2015. Porosity, permeability and 3D fracture network characterisation of dolomite reservoir rock samples. Journal of Petroleum Science and Engineering 127, 270-285.
Wardlaw, N.C., Taylor, R.P., 1976. Mercury capillary pressure curves and the interpretation of pore structure and capillary behaviour in reservoir rocks. Bulletin of Canadian Petroleum Geology 24 (2), 225-262.

Warren, J., 2000. Dolomite: occurrence, evolution and economically important associations. Earth-Science Reviews 52 (1-3), 1-81.

Weber, J., Cheshire, M.C., Bleuel, M., Mildner, D., Chang, Y.J., levley, A., ... Anovitz, L.M., 2021. Influence of microstructure on replacement and porosity generation during experimental dolomitization of limestones. Geochimica et Cosmochimica Acta 303, 137-158.

Wilson, M.D., Stanton, P.T., 1994. Diagenetic Mechanisms of Porosity and Permeability Reduction and Enhancement.

Wright, V.P., Tucker, M.E. (Eds.), 2009. Calcretes. John Wiley & Sons.

Zhang, J., Wang, J., Zheng, B., Sheng, Q., Wei, H., Shen, L., ... Mansour, A., 2023. Age assignment of dolomite in palaeo-reservoirs of the Qiangtang Basin: new evidence from palaeontology and carbonate in situ U-Pb dating. Marine and Petroleum Geology 158, 106545. https://doi.org/10.1016/j.marpetgeo.2023.106545.

Zheng, J., Wen, L., Ge, Y., Zhou, G., Zhang, Y., Yan, W., Jiang, H., Zhang, Z., Xi, A., 2023. U-Pb dating of fibrous dolomite in the hydrothermal dolostone of the Dengying Formation, Central Sichuan Basin, and its response to supercontinent breakup. Minerals 13, 1353. https://doi.org/10.3390/min13101353.

Zinszner, B., Pellerin, F.M., 2007. A geoscientist's Guide to Petrophysics. Editions Technip.