<figure><img src="image_22.png" /></figure>

**Fig. 21.** Weathering features within the Argile à Meulières profile. (a) Macromorphological organisation of the Argile à Meulières profiles. The meulières develop from the silicified limestone by dissolution of the residual limestone domains to form the highly porous ‘cellular’ facies. Modified from Thiry (1999). (b) Lower massive meulière with secondary silica coating (vitreous-waxy quartzose lustre) on a fracture through micronodules of silicified limestone parent; Bouchy-St-Genest (Marne). (c) Upper cellular meulière facies showing: (1) primary concretionary silica lining voids of silicified limestone to form (2) thin contoured walls, and (3) porous and powdery infilling of hollows resulting from the dissolution of discontinuously silicified limestone matrix; Brie Plateau, St-Cyr-sur-Morin (Seine-et-Marne).

deposition, paleoclimate and age, all silicified limestones are remarkably similar in terms of form and appearance in the field, facies and fabric. Only after linking the formation of quartzite pans and lenses in the Sable de Fontainebleau to groundwater silicification during glacial periods, as in our model, has it been possible to consider this hypothesis for silicifications in other outcropping formations in the Paris Basin, including the limestones.

# 6 Meulières: weathered silicified limestones

Meulières (millstones) is the name given to a particular facies of cavernous siliceous rocks that formed as a result of weathering of silicified lacustrine limestones in the Paris Basin. The most intriguing feature of the meulières is their cellular aspect. The typical meulières consist of a framework of thin (less than 1 mm) siliceous plates that surround empty centimetre-sized cells and result in a rock having a very low density. Despite the size of the cells, and more than 50% porosity, meulières have a low permeability because most of the cells are sealed or are linked only to a few of their neighbours. Meulières are generally embedded in variegated clay and the formation as a whole is called ‘Argile à Meulières’. The Argile à Meulières is generally considered to be a Plio-Pleistocene weathering product of silicified lacustrine limestone. The most recent review of this facies was by Ménillet (1987) and we refer to much of his work here.

## 6.1 Field relationships

### 6.1.1 Geological setting

The Argile à Meulières Formation marks old plateau surfaces in the southern Paris Basin (Figs. 1, 2 and 4): (1) the Plateau de Beauce, armoured by Calcaire de Beauce (Miocene); and (2) the Plateau de Brie, where the Argile à Meulières rests on the Calcaire de Brie (early Rupelian) and cuts eastwards across the underlying Argile Verte and then the Calcaire de Champigny (Priabonian). The Beauce Plateau, together with the outliers on its northern extension, form the primordial surface of the Paris Basin. The Brie Plateau is a former marine abrasion surface (Sable de Fontainebleau, Rupelian) that has only relatively recently been exhumed from its sedimentary cover (Lutaud, 1948). West of the Seine, at the foot of the Beauce Plateau escarpment, the exhumation is younger and continues today.

On the Plateau de Brie, the Argile à Meulières is discontinuous and missing in areas where the Calcaire de Brie is at its maximum thickness (Fig. 4). On the other hand, it is well developed where it rests on underlying clayey facies (Argile Verte and marls of the Calcaire de St-Ouen). There are generally thicker profiles and more mature facies of the Argile à Meulières on outliers of the Beauce Plateau which has a longer period of regolith evolution than the more recently exhumed Brie Plateau (Ménillet, 1987).

On the outliers of the Plateau de Beauce in the northwest, the meulières locally include sand grains of the Late Pliocene
<figure><img src="image_22.png" /></figure>

**Fig. 21.** Weathering features within the Argile à Meulières profile. (a) Macromorphological organisation of the Argile à Meulières profiles. The meulières develop from the silicified limestone by dissolution of the residual limestone domains to form the highly porous ‘cellular’ facies. Modified from Thiry (1999). (b) Lower massive meulière with secondary silica coating (vitreous-waxy quartzose lustre) on a fracture through micronodules of silicified limestone parent; Bouchy-St-Genest (Marne). (c) Upper cellular meulière facies showing: (1) primary concretionary silica lining voids of silicified limestone to form (2) thin contoured walls, and (3) porous and powdery infilling of hollows resulting from the dissolution of discontinuously silicified limestone matrix; Brie Plateau, St-Cyr-sur-Morin (Seine-et-Marne).

deposition, paleoclimate and age, all silicified limestones are remarkably similar in terms of form and appearance in the field, facies and fabric. Only after linking the formation of quartzite pans and lenses in the Sable de Fontainebleau to groundwater silicification during glacial periods, as in our model, has it been possible to consider this hypothesis for silicifications in other outcropping formations in the Paris Basin, including the limestones.

# 6 Meulières: weathered silicified limestones

Meulières (millstones) is the name given to a particular facies of cavernous siliceous rocks that formed as a result of weathering of silicified lacustrine limestones in the Paris Basin. The most intriguing feature of the meulières is their cellular aspect. The typical meulières consist of a framework of thin (less than 1 mm) siliceous plates that surround empty centimetre-sized cells and result in a rock having a very low density. Despite the size of the cells, and more than 50% porosity, meulières have a low permeability because most of the cells are sealed or are linked only to a few of their neighbours. Meulières are generally embedded in variegated clay and the formation as a whole is called ‘Argile à Meulières’. The Argile à Meulières is generally considered to be a Plio-Pleistocene weathering product of silicified lacustrine limestone. The most recent review of this facies was by Ménillet (1987) and we refer to much of his work here.

## 6.1 Field relationships

### 6.1.1 Geological setting

The Argile à Meulières Formation marks old plateau surfaces in the southern Paris Basin (Figs. 1, 2 and 4): (1) the Plateau de Beauce, armoured by Calcaire de Beauce (Miocene); and (2) the Plateau de Brie, where the Argile à Meulières rests on the Calcaire de Brie (early Rupelian) and cuts eastwards across the underlying Argile Verte and then the Calcaire de Champigny (Priabonian). The Beauce Plateau, together with the outliers on its northern extension, form the primordial surface of the Paris Basin. The Brie Plateau is a former marine abrasion surface (Sable de Fontainebleau, Rupelian) that has only relatively recently been exhumed from its sedimentary cover (Lutaud, 1948). West of the Seine, at the foot of the Beauce Plateau escarpment, the exhumation is younger and continues today.

On the Plateau de Brie, the Argile à Meulières is discontinuous and missing in areas where the Calcaire de Brie is at its maximum thickness (Fig. 4). On the other hand, it is well developed where it rests on underlying clayey facies (Argile Verte and marls of the Calcaire de St-Ouen). There are generally thicker profiles and more mature facies of the Argile à Meulières on outliers of the Beauce Plateau which has a longer period of regolith evolution than the more recently exhumed Brie Plateau (Ménillet, 1987).

On the outliers of the Plateau de Beauce in the northwest, the meulières locally include sand grains of the Late Pliocene
<figure><img src="image_23.png" /></figure>

**Fig. 22.** Schematic showing development of the meulière facies. Dissolution of residual limestone patches (1) generated at first a cellular facies (2). There are two subsequent evolution paths. In the upper part of the profile (3), the silica framework inherited from the silicified limestone was progressively dissolved, voids enlarged, and illuviated clay infiltrated some hollows. In the lower part of the profile (4), secondary euhedral quartz was precipitated in the voids. Adapted from Thiry (1999).

Sables de Lozère (Ménillet, 1987) and thus post-date the deposition of the Sable de Lozère. On the Brie Plateau, the Argile à Meulières Formation is consistently missing beneath the Sable de Fontainebleau indicating that it post-dates exhumation of the plateau (Cholley, 1960; Grisoni, 1979; Turland, 1974; Ménillet, 1987). The Argile à Meulières Formation on the residual buttes of Sable de Fontainebleau in the centre (Paris) and northern edge of the Paris Basin is related to the Beauce Plateau meulières (Fig. 4).

The Argile à Meulières is a heterogeneous formation, rather discontinuous and from 2 to 10 m thick. The meulières occur as siliceous blocks from decimetre to several tens of metres in diameter, irregularly shaped, within a clay or sand matrix that is variegated red, ochre or grey in colour. The blocks often have cell-like hollows infilled with brown sandy clay (see Supplementary File#4). The precursors of all Argile à Meulières facies are the silicified lacustrine limestones of the Paris Basin. Weathering and karst development within these limestones has exposed the meulières. As the limestones generally have very little insoluble residue, the host brown sandy clay has been either derived from the overlying loess and sand or inherited from the underlying clay and marl formations.

### 6.1.2 Profile description

In most localities, the Argile à Meulières overlies a lacustrine limestone which contains numerous microkarst dissolution features. Elsewhere, it can overlie clay formations, such as the Argile Verte, or even sand formations like the Sable de Fontainebleau, where all of the parent limestone has been removed by dissolution. A systematic vertical arrangement of macro-morphological features can be distinguished in profiles (Fig. 21a).

* At the base there is generally a clay horizon with residual limestone boulders and silicified limestone masses. Metre-size collapse structures relating to karst dissolution features in the underlying limestone are common.

* The lower part of the siliceous horizon (massive meulières) is made up of compact silica-rich masses in brown clay: they are of irregular shape and vary from 0.5 to several metres in diameter. They generally have a dull lustre but can be slightly translucent and are light in colour (white, yellowish or even greenish). A scoria-like rim surrounds the siliceous masses and also occurs along joints (Fig. 21b). The brown clay displays numerous illuviation features.

* The upper part of the siliceous horizon (cellular meulières) consists of porous or cellular siliceous masses (pale yellow to ochre in colour) within variegated illuvial clays (Fig. 21c). The siliceous masses are horizontally elongated slabs, 0.5–1 m thick at the base of the horizon but smaller (0.1–0.5 m in diameter) and irregularly shaped towards the top.

* The meulières do not usually crop out at the landsurface but are covered by a blanket of Quaternary loess and soil, or even an organic-rich and iron-stained hardpan (grisons) containing weathered silica-leached clasts of meulières.

## 6.2 Successive weathering steps

Petrographic data from Thiry (1999) indicates that the first stage of weathering produced karst features in the silicified limestone. The residual silicified domains, enclosing some remnant limestone, became surrounded by sands and clays infilling the karst voids. The resulting complex constitutes the Argile à Meulières Formation. Ongoing alteration has expression at various scales from top to bottom of the profiles as well as from the outer fringes of the silicified masses towards their inner cores (Fig. 22; see Supplementary File#4).

* In the first instance, in the upper parts of the profiles, there was progressive decalcification of remnant limestone within the silicified domains leaving numerous irregularly shaped secondary voids and thus very porous siliceous masses (Fig. 22, 2).

* In the upper parts of the profile there was also some dissolution of the primary silica matrix. It started with the least well crystallised silica phases (opal and micro-cryptocrystalline quartz) and resulted in the formation of micropores. Progressively, weathering dissolved almost all the silica matrix leaving only palisadic quartz lining primary voids (Fig. 22, 3). This produced a very porous siliceous mass of cellular appearance. Further dissolution led to breakage and collapse of the primary silica framework and available voids were infiltrated with sand.

* In the lower parts of the profile, the inherited silicified limestone structures have been further modified by new deposits of secondary silica (most obviously euhedral quartz crystals and sometimes chalcedony) in the secondary voids (Fig. 22, 4). There is no evidence of precipitation of secondary quartz in primary voids which are lined with palisadic quartz that form a sealed siliceous shell.
<figure><img src="image_23.png" /></figure>

**Fig. 22.** Schematic showing development of the meulière facies. Dissolution of residual limestone patches (1) generated at first a cellular facies (2). There are two subsequent evolution paths. In the upper part of the profile (3), the silica framework inherited from the silicified limestone was progressively dissolved, voids enlarged, and illuviated clay infiltrated some hollows. In the lower part of the profile (4), secondary euhedral quartz was precipitated in the voids. Adapted from Thiry (1999).

Sables de Lozère (Ménillet, 1987) and thus post-date the deposition of the Sable de Lozère. On the Brie Plateau, the Argile à Meulières Formation is consistently missing beneath the Sable de Fontainebleau indicating that it post-dates exhumation of the plateau (Cholley, 1960; Grisoni, 1979; Turland, 1974; Ménillet, 1987). The Argile à Meulières Formation on the residual buttes of Sable de Fontainebleau in the centre (Paris) and northern edge of the Paris Basin is related to the Beauce Plateau meulières (Fig. 4).

The Argile à Meulières is a heterogeneous formation, rather discontinuous and from 2 to 10 m thick. The meulières occur as siliceous blocks from decimetre to several tens of metres in diameter, irregularly shaped, within a clay or sand matrix that is variegated red, ochre or grey in colour. The blocks often have cell-like hollows infilled with brown sandy clay (see Supplementary File#4). The precursors of all Argile à Meulières facies are the silicified lacustrine limestones of the Paris Basin. Weathering and karst development within these limestones has exposed the meulières. As the limestones generally have very little insoluble residue, the host brown sandy clay has been either derived from the overlying loess and sand or inherited from the underlying clay and marl formations.

### 6.1.2 Profile description

In most localities, the Argile à Meulières overlies a lacustrine limestone which contains numerous microkarst dissolution features. Elsewhere, it can overlie clay formations, such as the Argile Verte, or even sand formations like the Sable de Fontainebleau, where all of the parent limestone has been removed by dissolution. A systematic vertical arrangement of macro-morphological features can be distinguished in profiles (Fig. 21a).

* At the base there is generally a clay horizon with residual limestone boulders and silicified limestone masses. Metre-size collapse structures relating to karst dissolution features in the underlying limestone are common.

* The lower part of the siliceous horizon (massive meulières) is made up of compact silica-rich masses in brown clay: they are of irregular shape and vary from 0.5 to several metres in diameter. They generally have a dull lustre but can be slightly translucent and are light in colour (white, yellowish or even greenish). A scoria-like rim surrounds the siliceous masses and also occurs along joints (Fig. 21b). The brown clay displays numerous illuviation features.

* The upper part of the siliceous horizon (cellular meulières) consists of porous or cellular siliceous masses (pale yellow to ochre in colour) within variegated illuvial clays (Fig. 21c). The siliceous masses are horizontally elongated slabs, 0.5–1 m thick at the base of the horizon but smaller (0.1–0.5 m in diameter) and irregularly shaped towards the top.

* The meulières do not usually crop out at the landsurface but are covered by a blanket of Quaternary loess and soil, or even an organic-rich and iron-stained hardpan (grisons) containing weathered silica-leached clasts of meulières.

## 6.2 Successive weathering steps

Petrographic data from Thiry (1999) indicates that the first stage of weathering produced karst features in the silicified limestone. The residual silicified domains, enclosing some remnant limestone, became surrounded by sands and clays infilling the karst voids. The resulting complex constitutes the Argile à Meulières Formation. Ongoing alteration has expression at various scales from top to bottom of the profiles as well as from the outer fringes of the silicified masses towards their inner cores (Fig. 22; see Supplementary File#4).

* In the first instance, in the upper parts of the profiles, there was progressive decalcification of remnant limestone within the silicified domains leaving numerous irregularly shaped secondary voids and thus very porous siliceous masses (Fig. 22, 2).

* In the upper parts of the profile there was also some dissolution of the primary silica matrix. It started with the least well crystallised silica phases (opal and micro-cryptocrystalline quartz) and resulted in the formation of micropores. Progressively, weathering dissolved almost all the silica matrix leaving only palisadic quartz lining primary voids (Fig. 22, 3). This produced a very porous siliceous mass of cellular appearance. Further dissolution led to breakage and collapse of the primary silica framework and available voids were infiltrated with sand.

* In the lower parts of the profile, the inherited silicified limestone structures have been further modified by new deposits of secondary silica (most obviously euhedral quartz crystals and sometimes chalcedony) in the secondary voids (Fig. 22, 4). There is no evidence of precipitation of secondary quartz in primary voids which are lined with palisadic quartz that form a sealed siliceous shell.
<figure><img src="image_24.png" /><figcaption>**Fig. 23.** Conceptual model of hydrological and thermal conditions within the Argile à Meulières during Quaternary glacial stages. The interface between a warmer near-surface zone and permafrost at depth could account for precipitation of silica. Concomitant limestone dissolution in the saturated zone could be related to acidity enhanced by bogs and podzols of the tundra environment.</figcaption></figure>

Microcrystalline silica is likely to have precipitated in the matrix of the siliceous masses but we have not observed this.

* Clays were illuviated into hollows in the outer fringes of the resulting meulières blocks and setts forming distinctive laminar deposits. Initially, clays were illuviated into primary voids rimmed with palisadic quartz but later infiltrated large dissolution hollows where clay laminae covered and sealed residual deposits of sand grains in the base (Fig. 22, 3).

## 6.3 Geomorphological context and environmental conditions

It is well established that the Argile à Meulières Formation on morpho-structural plateaux in the Paris Basin is of post-Pliocene age (Cholley, 1943; Lutaud, 1948; Ménillet, 1987). However, the mechanism for precipitating the silica has never been adequately identified. Post-Pliocene paleoclimatic conditions as well as field observations negate a mechanism of silica concentration by evaporation. A concept of releasing silica by weathering of illite and smectite into kaolinite has also been proposed (Prost, 1961) but is not convincing because the mass balance between weathered clays and secondary silicification in the lower horizon of the Argile à Meulières Formation is not satisfied. It has also been proposed that a redistribution of silica between silica leaching in the upper part of the profile and re-silicification in the lower part could be a likely mechanism (Ménillet 1987) but the trigger for precipitating silica was not addressed. If silica redistribution is a response to lower and higher degrees of saturation of groundwaters, proximity to a cold front could be the trigger for silica precipitation.

The hydrology of the Argile à Meulières formation exhibits a combination of features typical of both vadose and phreatic environments. The upper part of the profile contains illuviated clay deposits which indicate downward percolation of infiltrating waters through a non-saturated, vadose realm. On the other hand, palisadic quartz cutans lining dissolution voids in the lower part of the profile are

characteristic of a water saturated phreatic groundwater environment. This combination of features could correspond to the arrangement of an active zone composed of a non-saturated zone, with summer infiltrations, and a deeper frozen zone (therefore a permanent aquitard at a relatively regular level) likely to cut across the lithological units (Walvoord and Kurylyk, 2016).

Silica redistribution, specifically dissolution in the upper parts of the profile and precipitation near the base, could have been a response to infiltration in the upper unsaturated parts of the profile and precipitation below induced by proximity to the cold front bound to permafrost (Fig. 23).

The masses of silicified limestone at the base of the meulières profiles in areas that have been exploited for the manufacture of grinding wheels are commonly very large and up to 2-4 m thick and contrast with the relatively disparate silicified masses in limestone in quarries. This is conceivable if the top of the limestone formation was part of the active zone of permafrost and was silicified supra-permafrost by groundwater flow. Such masses would thus have the same characteristics as groundwater silicified limestones below the permafrost.

These hydrological conditions and related weathering phases may have repeated and their effects accumulated over successive glacial periods. The thicker profiles on the NW of the Plateau de Beauce and the NE of the Plateau de Brie plateau occur on the oldest exposed surfaces.

## 6.4 Structural and hydrological arrangement

A geological section equivalent to that of Figure 4 but extended to the western and eastern edges of the Paris Basin allows us to delineate the extension of the Argile à Meulière surfaces and to discuss their evolution and their hydrological behaviour (Fig. 24). The current geomorphology was formed after deposition of the Sables de Lozère during the Pleistocene, at least in the southern part of the basin (Larue and Etienne 2002, Cojan et al., 2007). It is possible that in the north the basin had experienced earlier erosion.
<figure><img src="image_24.png" /><figcaption>**Fig. 23.** Conceptual model of hydrological and thermal conditions within the Argile à Meulières during Quaternary glacial stages. The interface between a warmer near-surface zone and permafrost at depth could account for precipitation of silica. Concomitant limestone dissolution in the saturated zone could be related to acidity enhanced by bogs and podzols of the tundra environment.</figcaption></figure>

Microcrystalline silica is likely to have precipitated in the matrix of the siliceous masses but we have not observed this.

* Clays were illuviated into hollows in the outer fringes of the resulting meulières blocks and setts forming distinctive laminar deposits. Initially, clays were illuviated into primary voids rimmed with palisadic quartz but later infiltrated large dissolution hollows where clay laminae covered and sealed residual deposits of sand grains in the base (Fig. 22, 3).

## 6.3 Geomorphological context and environmental conditions

It is well established that the Argile à Meulières Formation on morpho-structural plateaux in the Paris Basin is of post-Pliocene age (Cholley, 1943; Lutaud, 1948; Ménillet, 1987). However, the mechanism for precipitating the silica has never been adequately identified. Post-Pliocene paleoclimatic conditions as well as field observations negate a mechanism of silica concentration by evaporation. A concept of releasing silica by weathering of illite and smectite into kaolinite has also been proposed (Prost, 1961) but is not convincing because the mass balance between weathered clays and secondary silicification in the lower horizon of the Argile à Meulières Formation is not satisfied. It has also been proposed that a redistribution of silica between silica leaching in the upper part of the profile and re-silicification in the lower part could be a likely mechanism (Ménillet 1987) but the trigger for precipitating silica was not addressed. If silica redistribution is a response to lower and higher degrees of saturation of groundwaters, proximity to a cold front could be the trigger for silica precipitation.

The hydrology of the Argile à Meulières formation exhibits a combination of features typical of both vadose and phreatic environments. The upper part of the profile contains illuviated clay deposits which indicate downward percolation of infiltrating waters through a non-saturated, vadose realm. On the other hand, palisadic quartz cutans lining dissolution voids in the lower part of the profile are

characteristic of a water saturated phreatic groundwater environment. This combination of features could correspond to the arrangement of an active zone composed of a non-saturated zone, with summer infiltrations, and a deeper frozen zone (therefore a permanent aquitard at a relatively regular level) likely to cut across the lithological units (Walvoord and Kurylyk, 2016).

Silica redistribution, specifically dissolution in the upper parts of the profile and precipitation near the base, could have been a response to infiltration in the upper unsaturated parts of the profile and precipitation below induced by proximity to the cold front bound to permafrost (Fig. 23).

The masses of silicified limestone at the base of the meulières profiles in areas that have been exploited for the manufacture of grinding wheels are commonly very large and up to 2-4 m thick and contrast with the relatively disparate silicified masses in limestone in quarries. This is conceivable if the top of the limestone formation was part of the active zone of permafrost and was silicified supra-permafrost by groundwater flow. Such masses would thus have the same characteristics as groundwater silicified limestones below the permafrost.

These hydrological conditions and related weathering phases may have repeated and their effects accumulated over successive glacial periods. The thicker profiles on the NW of the Plateau de Beauce and the NE of the Plateau de Brie plateau occur on the oldest exposed surfaces.

## 6.4 Structural and hydrological arrangement

A geological section equivalent to that of Figure 4 but extended to the western and eastern edges of the Paris Basin allows us to delineate the extension of the Argile à Meulière surfaces and to discuss their evolution and their hydrological behaviour (Fig. 24). The current geomorphology was formed after deposition of the Sables de Lozère during the Pleistocene, at least in the southern part of the basin (Larue and Etienne 2002, Cojan et al., 2007). It is possible that in the north the basin had experienced earlier erosion.
<figure><img src="image_25.png" /><figcaption>**Fig. 24.** Geological section through southern edge of the Paris Basin to western and eastern borders (extension of section Fig. 4) showing the hydrological characteristics of the Tertiary formations and the extent of the geomorphological surfaces related to the Meulière units. Data sources: InfoTerre (2023); Allouc (2016).</figcaption></figure>

The thickness of the Argile à Meulière is directly related to the uplifted edges of the basin. The Argile à Meulière de Beauce disappears with distance southward from the northern edge of the Beauce Plateau and reaches its maximum thickness (more than 8 m at Trappes) on the NW edge of the plateau, that is to say on the piedmont of the Bray anticline (Fig. 24). Similarly, the Argile à Meulière de Brie is the thickest on the eastern edge of the basin (La Ferté-sous-Jouare), near the raised edge of the basin, and decreases in distal parts against the escarpment of the Beauce Plateau. The Argile à Meulière is discontinuous and thinner in this area but also younger, according to the timing of exhumation of the Brie Plateau (Fig. 24). There is likely to be an impact of hydrological flow dynamics induced by recharge from the raised regions of the plateau edges. In other words, we suggest that the thickness of the Meulières profiles is related to the mass balance of the nourishing groundwater, probably starting with the formation of the silicified limestones and their later secondary silicification within the Argile à Meulières.

It should also be noted that both the upper and lower level Argile à Meulières seem to record opposite hydrological characteristics: pervious Sable de Fontainebleau for the upper Meulière de Beauce and impervious Argile Verte for the lower Meulière de Brie. In fact, placed in a periglacial context, both Argile à Meulières levels could have surmounted a frozen horizon that acted as an impervious layer.

# 7 Summary

In the first instance we confirm that all silicifications within the Tertiary formations of the Paris Basin that are the subject of this study were formed as a result of absolute accumulation of silica manifested by deposition and crystal growth in pores and voids. This required a continuous flow of solution containing silica, part of which precipitated cumulatively over a relatively long period of time, depending on the flow rate and the amount of precipitated silica per unit volume. The links we identify between silicification of sands, gypseous formations and

Quaternary geomorphology, as well as the links between Meulière and extensive post-Miocene plateaux, promote a mechanism related to cooling of groundwaters in regolith environments. This causes an exponential decrease in the solubility of silica and is a very efficient mechanism for triggering its precipitation. In this context, water flowing from a warmer to a cooler aquifer could continuously deposit silica against the cold front.

## 7.1 The various kinds of silicification

Figure 4 shows the distribution of the various types of silicification in a geological section through the southern edge of the Paris Basin. Our studies originated from work on the tightly cemented quartzite pans within uncemented Sables de Fontainebleau. A relationship between the quartzites and landscape morphology indicates a Plio-Quaternary age. This is supported by studies of Fontainebleau sand calcite crystals, some of which are locally encased within the quartzite pans and therefore predate the silicification (Thiry et al., 2021). Coherence of our data on the Sables de Fontainebleau and observations made in different sand formations elsewhere in the Paris Basin reinforced our arguments for silicification by groundwater flows during well-documented Pleistocene cold periods. Several particular and peculiar structures (convoluted and spindle-like quartzite masses) have previously been difficult to explain but we now consider that the silicification responsible could be linked to constrained groundwater flows beneath permafrost. Other unusual forms (gogottes and silica deposits on fractures) appear to be due to precipitation of silica from percolating water in vadose environments, possibly in periodically thawed active zones above permafrost.

Our model for silicification of sands can be applied to the silicification of gypsum in that it could account for the spatial distribution of silicified gypseous formations and be related to glacial periods. It could also explain the paragenesis of dissolution of limestone formations and concurrent precipitation of calcite together with silica and is reinforced by the association with calcite of inverse rhombohedron habit ('cold calcite'; Ezikova, 1958).
<figure><img src="image_25.png" /><figcaption>**Fig. 24.** Geological section through southern edge of the Paris Basin to western and eastern borders (extension of section Fig. 4) showing the hydrological characteristics of the Tertiary formations and the extent of the geomorphological surfaces related to the Meulière units. Data sources: InfoTerre (2023); Allouc (2016).</figcaption></figure>

The thickness of the Argile à Meulière is directly related to the uplifted edges of the basin. The Argile à Meulière de Beauce disappears with distance southward from the northern edge of the Beauce Plateau and reaches its maximum thickness (more than 8 m at Trappes) on the NW edge of the plateau, that is to say on the piedmont of the Bray anticline (Fig. 24). Similarly, the Argile à Meulière de Brie is the thickest on the eastern edge of the basin (La Ferté-sous-Jouare), near the raised edge of the basin, and decreases in distal parts against the escarpment of the Beauce Plateau. The Argile à Meulière is discontinuous and thinner in this area but also younger, according to the timing of exhumation of the Brie Plateau (Fig. 24). There is likely to be an impact of hydrological flow dynamics induced by recharge from the raised regions of the plateau edges. In other words, we suggest that the thickness of the Meulières profiles is related to the mass balance of the nourishing groundwater, probably starting with the formation of the silicified limestones and their later secondary silicification within the Argile à Meulières.

It should also be noted that both the upper and lower level Argile à Meulières seem to record opposite hydrological characteristics: pervious Sable de Fontainebleau for the upper Meulière de Beauce and impervious Argile Verte for the lower Meulière de Brie. In fact, placed in a periglacial context, both Argile à Meulières levels could have surmounted a frozen horizon that acted as an impervious layer.

# 7 Summary

In the first instance we confirm that all silicifications within the Tertiary formations of the Paris Basin that are the subject of this study were formed as a result of absolute accumulation of silica manifested by deposition and crystal growth in pores and voids. This required a continuous flow of solution containing silica, part of which precipitated cumulatively over a relatively long period of time, depending on the flow rate and the amount of precipitated silica per unit volume. The links we identify between silicification of sands, gypseous formations and

Quaternary geomorphology, as well as the links between Meulière and extensive post-Miocene plateaux, promote a mechanism related to cooling of groundwaters in regolith environments. This causes an exponential decrease in the solubility of silica and is a very efficient mechanism for triggering its precipitation. In this context, water flowing from a warmer to a cooler aquifer could continuously deposit silica against the cold front.

## 7.1 The various kinds of silicification

Figure 4 shows the distribution of the various types of silicification in a geological section through the southern edge of the Paris Basin. Our studies originated from work on the tightly cemented quartzite pans within uncemented Sables de Fontainebleau. A relationship between the quartzites and landscape morphology indicates a Plio-Quaternary age. This is supported by studies of Fontainebleau sand calcite crystals, some of which are locally encased within the quartzite pans and therefore predate the silicification (Thiry et al., 2021). Coherence of our data on the Sables de Fontainebleau and observations made in different sand formations elsewhere in the Paris Basin reinforced our arguments for silicification by groundwater flows during well-documented Pleistocene cold periods. Several particular and peculiar structures (convoluted and spindle-like quartzite masses) have previously been difficult to explain but we now consider that the silicification responsible could be linked to constrained groundwater flows beneath permafrost. Other unusual forms (gogottes and silica deposits on fractures) appear to be due to precipitation of silica from percolating water in vadose environments, possibly in periodically thawed active zones above permafrost.

Our model for silicification of sands can be applied to the silicification of gypsum in that it could account for the spatial distribution of silicified gypseous formations and be related to glacial periods. It could also explain the paragenesis of dissolution of limestone formations and concurrent precipitation of calcite together with silica and is reinforced by the association with calcite of inverse rhombohedron habit ('cold calcite'; Ezikova, 1958).
<figure><img src="image_26.png" /><figcaption>**Fig. 25.** Conceptual model of hydrological and thermal arrangements within Paris Basin plateaux during Pleistocene glacial periods. (a) At the beginning of the cold period the chilled grounds remained relatively thin and approached the water table level only in its shallowest areas, near springs. (b) With the cold period ongoing, permafrost developed, and the upper parts of the aquifers froze, resulting in overpressures causing ‘forced’ flows along the undulating base of the permafrost and through cracks and taliks. (c) With climate warming the permafrost thawed at its base and at its top. The active layer thickened. A superficial groundwater formed above the permafrost and flowed towards the lowland area. Note that the gradient of the water table and thickness of the permafrost appear reduced on plateau edges due to an extended vertical scale vs horizontal scale.</figcaption></figure>

In terms of the lacustrine limestones, the large volume of silica crystallized in voids demonstrates that significant amounts of water containing silica in solution must have flowed through them. The omnipresence of isotropic cutans around voids points to phreatic environments. We suggest that these conditions could only be fulfilled after the limestones were uplifted and incised to create the necessary hydraulic gradient for groundwater flows. As in the case of quartzites formed by silicification of sands, the absence of an appropriate trigger mechanism to induce silica precipitation in the limestones led us to propose a model in which there was significant cooling of groundwater solutions close to a cold front during glacial periods. It is thus possible to conceive of the dissolution of limestone during silicification and to explain how the ‘compactness’ of the cherts was achieved. We suggest that the groundwaters may at times, or in certain locations, have been confined by impervious permafrost.

For Meulières, the question of the origin and mode of precipitation of silica remained open. From our perspective, these forms of silicification occurred in glacial environments and, more particularly, in the active layer above a permafrost. The dissolution of the silica at the top of the profiles and its

precipitation at the base is simply explained by cooling of meteoric water in contact with the underlying permafrost. As well, groundwater silicification above impervious permafrost possibly explains the exceptionally large monoliths that have been exploited: they are actually overprints of the cherts (prior silicification of the parent limestones) inherited from beneath the permafrost. In addition, groundwater flow over permafrost would have resulted in ‘planar’ decalcification that explains the systematic absence of vertical collapse, except in late and local circumstances.

## 7.2 Dynamics of the periglacial model for silicification

A schematic NE-SW section through the Brie and Beauce Plateaux (Fig. 25) is a synthesis of our model of the spatial-temporal relationships between geomorphology, hydrology and the various forms of silicification in periglacial environments. It could represent conditions during the last ice age when the geomorphology of the Paris basin was not fundamentally different from that of today. Three stages in the evolution of cold regolith are envisaged: (a) an initial stage in which the thickness of the cold ground is limited to 10–30 m;
<figure><img src="image_26.png" /><figcaption>**Fig. 25.** Conceptual model of hydrological and thermal arrangements within Paris Basin plateaux during Pleistocene glacial periods. (a) At the beginning of the cold period the chilled grounds remained relatively thin and approached the water table level only in its shallowest areas, near springs. (b) With the cold period ongoing, permafrost developed, and the upper parts of the aquifers froze, resulting in overpressures causing ‘forced’ flows along the undulating base of the permafrost and through cracks and taliks. (c) With climate warming the permafrost thawed at its base and at its top. The active layer thickened. A superficial groundwater formed above the permafrost and flowed towards the lowland area. Note that the gradient of the water table and thickness of the permafrost appear reduced on plateau edges due to an extended vertical scale vs horizontal scale.</figcaption></figure>

In terms of the lacustrine limestones, the large volume of silica crystallized in voids demonstrates that significant amounts of water containing silica in solution must have flowed through them. The omnipresence of isotropic cutans around voids points to phreatic environments. We suggest that these conditions could only be fulfilled after the limestones were uplifted and incised to create the necessary hydraulic gradient for groundwater flows. As in the case of quartzites formed by silicification of sands, the absence of an appropriate trigger mechanism to induce silica precipitation in the limestones led us to propose a model in which there was significant cooling of groundwater solutions close to a cold front during glacial periods. It is thus possible to conceive of the dissolution of limestone during silicification and to explain how the ‘compactness’ of the cherts was achieved. We suggest that the groundwaters may at times, or in certain locations, have been confined by impervious permafrost.

For Meulières, the question of the origin and mode of precipitation of silica remained open. From our perspective, these forms of silicification occurred in glacial environments and, more particularly, in the active layer above a permafrost. The dissolution of the silica at the top of the profiles and its

precipitation at the base is simply explained by cooling of meteoric water in contact with the underlying permafrost. As well, groundwater silicification above impervious permafrost possibly explains the exceptionally large monoliths that have been exploited: they are actually overprints of the cherts (prior silicification of the parent limestones) inherited from beneath the permafrost. In addition, groundwater flow over permafrost would have resulted in ‘planar’ decalcification that explains the systematic absence of vertical collapse, except in late and local circumstances.

## 7.2 Dynamics of the periglacial model for silicification

A schematic NE-SW section through the Brie and Beauce Plateaux (Fig. 25) is a synthesis of our model of the spatial-temporal relationships between geomorphology, hydrology and the various forms of silicification in periglacial environments. It could represent conditions during the last ice age when the geomorphology of the Paris basin was not fundamentally different from that of today. Three stages in the evolution of cold regolith are envisaged: (a) an initial stage in which the thickness of the cold ground is limited to 10–30 m;
(b) a period of maximum cooling when permafrost may have reached 50 m or more in thickness; and (c) a period of warming. We suggest that the latter would have involved thawing of the upper part of the permafrost accompanied by an increase in the thickness of the active zone and a concomitant thawing of the base of the permafrost. The genetic axiom is that silicification occurred in zones of groundwater flow to satisfy the mass balance and in response to contact between groundwater and cold ground that cooled it and triggered precipitation of silica.

* Under peri-glacial conditions, before permafrost developed, we suggest that groundwater continued to flow through the spring lines at the base of the valleys (Fig. 25a) and silica precipitated at the contact of the water table with the cold ground. This configuration is considered to be the origin of the regular and flat quartzite pans in the sand formations. Superposed levels of quartzite could reflect fluctuations of the base of the cold ground in the regolith and/or the water table. However, in limestones, groundwater flow paths were complex and heterogeneous, linked to karst structures, and silicification was sporadic and discontinuous.

* The development of permafrost led to important hydrological changes, in particular: more or less complete occlusion of groundwater outflows due to permafrost sinking below valley bottoms, and a concomitant increase in pressure within the aquifer due to volume expansion by groundwater freezing. Pressurized water flows could have occurred beneath the undulating basal surface of the permafrost, and upward through pipes and hydraulically-fractured frozen zones (Fig. 25b). These pressurized flows would explain some of the complex quartzite morphologies, particularly fusiform, spindle-shaped and tortuous quartzite walls. We suggest that these morphologies are indicative of deep permafrost below the water table. Such forms are never observed in limestones because concomitant karst drained groundwater flows.

* Climate warming and melting of the permafrost led to hydrological conditions comparable to those at the time of initiation of the glacial period in terms of groundwater outflow and silicification of horizontal quartzite slabs. But conditions would have been significantly different at the landsurface (Fig. 25c). With time and an increasing in air temperature after the glacial maximum, the thawed layer would have progressively thickened at the expense of the uppermost permafrost while substantial groundwater bodies could have existed above the underlying impervious permafrost. Significant silica deposition and limestone dissolution probably occurred along outflow zones at this time. Such supra-permafrost reactive zones are considered to have been responsible for the development of thick Meulière layers, together with the concomitant dissolution of the limestone substrate along regular horizontal surfaces.

On the basis of our studies, the disposition and evolution of permafrost in the landscape could explain most of the morphological characteristics and spatial arrangements of the diverse silicifications in the Paris Basin. All of the silicifications of the Tertiary formations in the Paris Basin can be integrated into a single coherent scheme taking into account their geochemical and geomorphological aspects and their distribution. They are

linked to the hydrology of the superimposed limestone plateaux landscapes and the associated confined or free aquifers.

The robustness of our model is yet to be established but there are many opportunities to test it on other examples of Late Cenozoic to modern continental silicifications for which there is published information on relationships and characteristics. The viability of the model will need to withstand geochemical and isotopic analysis data obtained by increasingly refined new techniques that can investigate, with increasing accuracy, ages of silicification and their links to cold environments.

## Acknowledgments

This research is part of Collaborative Research Projects (PCR) – Réseau de lithothèques en région Centre-Val de Loire, coordinated by Vincent Delvigne, Raphaël Angevin, Paul Fernandes and Harold Lethrosne, supported by the Direction Régionale des Affaires Culturelles de Centre-Val-de-Loire (France) (decree N° 20/CV/NJ889 – 03.06.2020) and – Matières premières du Bassin parisien : les silex cénozoïques d’Ile de France, coordinated by Pierre Allard, Vincent Delvigne and Françoise Bostyn supported by the Direction Régionale des Affaires Culturelles d’Ile de France (decree N° 20/11034 – 01.03.2020). Joël Billiotte from Geosciences Mines-ParisTech is thanked for his discussions on gypsum geochemical behaviour and Jean-Marc Fourcault from Museum d’Histoire Naturelle de Paris for its availability when searching for reference samples of silica pseudomorphs of gypsum crystals. Authors are particularly grateful to Irene Cantarero from University of Barcelona (Spain) and Augustin Deconinck from Université Libre de Bruxelles (Belgium) who reviewed this paper and whose comments and suggestions strengthened the initial submitted version. MT highlights:

* the invaluable input to this review of the open geological data bank “Banque du Sous-Sol (BSS)” organized and managed by the BRGM; all the geologists of the BRGM, the University, the Research Institutes and the Oil Companies who, for decades, transmitted accurate and neat data to safeguard their experiences for the future;

* the geologists encountered in the field who firstly demonstrated the primary importance of sections and sample descriptions then shared their personal geological knowledge and perceptions: Marie Pierre Aubry, Claude Cavelier, Isabelle Cojan, Georges Kuntz, François Ménillet, Jean-Michel Schmitt, Michel Turland, and many others;

* pedologist Folkert van Oort, who taught me to look and describe a top-down profile;

* geomorphologist Régine-Simon-Coinçon, for demonstrating the importance of reading landscapes; and

* ‘masters’ Georges Millot and Norbert Trauth, who led me to the silicification path, shown me that geochemistry starts in the field in front of a section or a landscape, and emphasized that a collaboration is only fruitful if it is generous.

## Supplementary material

**Supplementary File#1:** Occurrences and morphologies of sand silicifications in Tertiary deposits, Paris Basin.

**Supplementary File#2:** History of the discovery of silica pseudomorphs of gypsum in the Paris region and studies of museum samples described at that time.
(b) a period of maximum cooling when permafrost may have reached 50 m or more in thickness; and (c) a period of warming. We suggest that the latter would have involved thawing of the upper part of the permafrost accompanied by an increase in the thickness of the active zone and a concomitant thawing of the base of the permafrost. The genetic axiom is that silicification occurred in zones of groundwater flow to satisfy the mass balance and in response to contact between groundwater and cold ground that cooled it and triggered precipitation of silica.

* Under peri-glacial conditions, before permafrost developed, we suggest that groundwater continued to flow through the spring lines at the base of the valleys (Fig. 25a) and silica precipitated at the contact of the water table with the cold ground. This configuration is considered to be the origin of the regular and flat quartzite pans in the sand formations. Superposed levels of quartzite could reflect fluctuations of the base of the cold ground in the regolith and/or the water table. However, in limestones, groundwater flow paths were complex and heterogeneous, linked to karst structures, and silicification was sporadic and discontinuous.

* The development of permafrost led to important hydrological changes, in particular: more or less complete occlusion of groundwater outflows due to permafrost sinking below valley bottoms, and a concomitant increase in pressure within the aquifer due to volume expansion by groundwater freezing. Pressurized water flows could have occurred beneath the undulating basal surface of the permafrost, and upward through pipes and hydraulically-fractured frozen zones (Fig. 25b). These pressurized flows would explain some of the complex quartzite morphologies, particularly fusiform, spindle-shaped and tortuous quartzite walls. We suggest that these morphologies are indicative of deep permafrost below the water table. Such forms are never observed in limestones because concomitant karst drained groundwater flows.

* Climate warming and melting of the permafrost led to hydrological conditions comparable to those at the time of initiation of the glacial period in terms of groundwater outflow and silicification of horizontal quartzite slabs. But conditions would have been significantly different at the landsurface (Fig. 25c). With time and an increasing in air temperature after the glacial maximum, the thawed layer would have progressively thickened at the expense of the uppermost permafrost while substantial groundwater bodies could have existed above the underlying impervious permafrost. Significant silica deposition and limestone dissolution probably occurred along outflow zones at this time. Such supra-permafrost reactive zones are considered to have been responsible for the development of thick Meulière layers, together with the concomitant dissolution of the limestone substrate along regular horizontal surfaces.

On the basis of our studies, the disposition and evolution of permafrost in the landscape could explain most of the morphological characteristics and spatial arrangements of the diverse silicifications in the Paris Basin. All of the silicifications of the Tertiary formations in the Paris Basin can be integrated into a single coherent scheme taking into account their geochemical and geomorphological aspects and their distribution. They are

linked to the hydrology of the superimposed limestone plateaux landscapes and the associated confined or free aquifers.

The robustness of our model is yet to be established but there are many opportunities to test it on other examples of Late Cenozoic to modern continental silicifications for which there is published information on relationships and characteristics. The viability of the model will need to withstand geochemical and isotopic analysis data obtained by increasingly refined new techniques that can investigate, with increasing accuracy, ages of silicification and their links to cold environments.

## Acknowledgments

This research is part of Collaborative Research Projects (PCR) – Réseau de lithothèques en région Centre-Val de Loire, coordinated by Vincent Delvigne, Raphaël Angevin, Paul Fernandes and Harold Lethrosne, supported by the Direction Régionale des Affaires Culturelles de Centre-Val-de-Loire (France) (decree N° 20/CV/NJ889 – 03.06.2020) and – Matières premières du Bassin parisien : les silex cénozoïques d’Ile de France, coordinated by Pierre Allard, Vincent Delvigne and Françoise Bostyn supported by the Direction Régionale des Affaires Culturelles d’Ile de France (decree N° 20/11034 – 01.03.2020). Joël Billiotte from Geosciences Mines-ParisTech is thanked for his discussions on gypsum geochemical behaviour and Jean-Marc Fourcault from Museum d’Histoire Naturelle de Paris for its availability when searching for reference samples of silica pseudomorphs of gypsum crystals. Authors are particularly grateful to Irene Cantarero from University of Barcelona (Spain) and Augustin Deconinck from Université Libre de Bruxelles (Belgium) who reviewed this paper and whose comments and suggestions strengthened the initial submitted version. MT highlights:

* the invaluable input to this review of the open geological data bank “Banque du Sous-Sol (BSS)” organized and managed by the BRGM; all the geologists of the BRGM, the University, the Research Institutes and the Oil Companies who, for decades, transmitted accurate and neat data to safeguard their experiences for the future;

* the geologists encountered in the field who firstly demonstrated the primary importance of sections and sample descriptions then shared their personal geological knowledge and perceptions: Marie Pierre Aubry, Claude Cavelier, Isabelle Cojan, Georges Kuntz, François Ménillet, Jean-Michel Schmitt, Michel Turland, and many others;

* pedologist Folkert van Oort, who taught me to look and describe a top-down profile;

* geomorphologist Régine-Simon-Coinçon, for demonstrating the importance of reading landscapes; and

* ‘masters’ Georges Millot and Norbert Trauth, who led me to the silicification path, shown me that geochemistry starts in the field in front of a section or a landscape, and emphasized that a collaboration is only fruitful if it is generous.

## Supplementary material

**Supplementary File#1:** Occurrences and morphologies of sand silicifications in Tertiary deposits, Paris Basin.

**Supplementary File#2:** History of the discovery of silica pseudomorphs of gypsum in the Paris region and studies of museum samples described at that time.
**Supplementary File#3:** Configuration and composition of silicified limestones ('cherts') in Tertiary deposits, Paris Basin.

**Supplementary File#4:** Meulières: weathering and secondary silicification of silicified limestone.

The Supplementary Material is available at https://www.bsgf.fr/10.1051/bsgf/2024008/olm.

## References

Alimen H. 1936. Etude sur le Stampien du Bassin de Paris. *Mém Soc géol Fr* 31: 309.

Allouc J. 2016. Argiles à meulières sur une paléosurface de cote 200 à encroûtements crayeux en Champagne sèche nord-orientale. Vestiges probables de l'"Argile à meulières". *Conséquences paléogéographiques. Bull Inf Géol Bass Paris* 53: 12-26.

Andersen DT, Pollard WH, McKay CP, Heldmann J. 2002. Cold springs in permafrost on Earth and Mars. *J Geophys Res* 107: 4-1-4-7.

Andrieux E, Bertran P, Saito K. 2016. Spatial analysis of the French Pleistocene permafrost by a GIS database. *Permafrost and Periglacial Processes* 27: 17-30.

Arakel AV, Jacobson G, Salehi M, Hill CM. 1989. Silicification of calcrete in palaeodrainage basins of the Australian arid zone. *J Geolog Soc Aust* 36: 73-89.

Aubert J, Lorain JM. 1977. Les calcaires lacustres de la Région Parisienne. *Bull Liaison LPC* 4: 101-120.

Auzel M, Cailleux A. 1949. Silicifications nord-sahariennes. *Bull Soc géol Fr* 5: 553-559.

Banks NG. 1970. Nature and origin of early and late cherts in the Leadville Limestone, Colorado. *Geolog Soc Am Bull* 81: 3033-3048.

Bariteau A, Thiry M. 2001. Analyse et simulation des transferts géochimiques au sein d'un aquifère : la nappe de Beauce et l'altération des Sables de Fontainebleau. *Bull Soc géol Fr* 17: 367-381.

Bertran P., Stadelmaier KH, Ludwig P. 2022. Last Glacial Maximum active layer thickness in Western Europe, and the issue of 'tundra gleys' in loess sequences. *J Quat Sci* 37(7): 1222-1228.

Boike J, Roth, K, Overduin, PP. 1998. Thermal and hydrologic dynamics of the active layer at a continuous permafrost site (Taymyr Peninsula, Siberia). *Water Resour Res* 34: 355-363.

Bustillo MA, Arribas ME, Bustillo M. 2002. Dolomitization and silicification in low-energy lacustrine carbonates (Paleogene, Madrid Basin, Spain). *Sediment Geol* 151: 107-126.

Cantarero I, Parcerisa D, Plata MA, et al. 2020. Fracturing and near-surface diagenesis of a silicified Miocene deltaic sequence: the Montjuïc Hill (Barcelona). *Minerals* 10: 135, 22 p.

Cayeux L. 1929. Les roches sédimentaires de la France. Roches siliceuses. *Mém. servir expl. Carte Géol. détaillée de la France*, 774 p.

Cholley A. 1960. Remarques sur la structure et l'évolution morphologique du Bassin de Paris. *Bull l'Assoc Géograph Français* 7: 2-26.

Clark ID, Lauriol B, Harwood L, Marschner M. 2001. Groundwater contributions to discharge in a permafrost setting, Big Fish River, N.W.T., Canada. *Arctic, Antarctic and Alpine Res* 33: 62-69.

Cojan I, Brulhet J, Corbonnois J, et al. 2007. Morphologic evolution of eastern Paris Basin: "ancient surfaces" and Quaternary incisions. *Mém Soc géol Fr* 178: 135-155.

Conrad G. 1969. L'évolution continentale post hercynienne du Sahara algérien (Saoura, Erg Chech-Tnezrouft, Ahnet-Mouydir). Centre National de la Recherche Scientifique, Paris, Centre de Reherches sur les Zones Arides, Géologie, 10, 527 p.

Cooper MR, Evans J, Flint SS, Hogg JC, Hunter RH. 2000. Quantification of detrital, authigenic and porosity components of the Fontainebleau Sandstone: a comparison of conventional optical and combined scanning electron microscope-based methods of modal analyses. *In: Worden RH, Morad S, Eds., Quartz cementation in sandstones, Spec. Publs Int. Ass. Sediment.* 29: 89-101.

Daley B. 1989. Silica pseudomorphs from the Bembridge limestone (upper Eocene) of the Isle of Wight, southern England and their palaeoclimatic significance. Palaeogeogr Palaeoclimatol Palaeoecol 69: 233-240.

Delmas AB, Garcia-Hernandez JE, Pedro G. 1982. Discussion sur les conditions et les mécanismes de la formation du quartz à 25°C en milieu ouvert. Analyse réactionelle par voie cinétique. *Sci Géolog Bull* 35: 81-91.

Dewers T, Ortoleva P. 1990. Force of crystallization during the growth of siliceous concretions. *Geology* 18: 204-207.

Dobiński W. 2012. Permafrost. The Contemporary Meaning of the Term and its Consequences. *Bull Geogr Phys Geogr Ser* 5: 29-42.

Dobiński W. 2020. Permafrost active layer. *Earth-Sci Rev* 208: 103301.

Evzikova NZ. 1958. On a question on changing the habit of mineral crystals in the process of their growth. *Zapiski Vsesoyuz Miner Obsh* 6: 647-656.

Fournier RO. 1985. The behavior of silica in hydrothermal solutions. *Rev Econ Geol* 2: 45-61.

Garrels RM, Christ CL. 1965. Solutions, Minerals and Equilibria. New York: Harper et Row, 450 p.

Grisoni JC. 1979. Argiles à Meulières et Calcaire de Beauce en Hurepoix. Synthèse géologique. *Rapport de Recherche du LPC* 87: 2-75.

Haddad SC, Worden RH, Prior DJ, Smalley, PC. 2006. Quartz cement in the Fontainebleau Sandstone, Paris Basin, France: crystallography and implications for mechanisms of cement growth. *J Sediment Res* 76: 244-256.

Hatrival JN, Chertier B, Morfaux P. 1988. Notice explicative, carte géologique France au 1/50 000, feuille Montmort (187). Orléans: Edition BRGM, 38 p.

Hemmerle H., Bayer P. 2020. Climate change yields groundwater warming in Bavaria, Germany. *Front Earth Sci* 523.

Herdianita HR, Browne PRL, Rodgers KA, Campbell KA. 2000. Mineralogical and textural changes accompanying ageing of silica sinter: *Mineralium Deposita* 5: 48-62.

Hesse R. 1987. Selective and reversible carbonate-silica replacements in Lower Cretaceous carbonate-bearing turbidites of the Eastern Alps; *Sedimentology* 34: 1055-1077.

InfoTerre 2023. http://infoterre.brgm.fr/gives access to 1:50 000 geological maps and to the BSS (Banque du Sous-Sol), a database of boreholes, quarries, hydrological information. InfoTerre does not presently provide access to explanatory notes for 1:50 000 geological maps. Query: explicative de la carte géologique à 1/50 000 + name of sheet.

Imbeaux M, Affolter J, Martineau R. 2018. Diffusion du silex crétacé des minières de Saint-Gond (Marne, France) au Néolithique récent et final. *Bull Soc Préhistorique Française* 115: 733-767.
**Supplementary File#3:** Configuration and composition of silicified limestones ('cherts') in Tertiary deposits, Paris Basin.

**Supplementary File#4:** Meulières: weathering and secondary silicification of silicified limestone.

The Supplementary Material is available at https://www.bsgf.fr/10.1051/bsgf/2024008/olm.

## References

Alimen H. 1936. Etude sur le Stampien du Bassin de Paris. *Mém Soc géol Fr* 31: 309.

Allouc J. 2016. Argiles à meulières sur une paléosurface de cote 200 à encroûtements crayeux en Champagne sèche nord-orientale. Vestiges probables de l'"Argile à meulières". *Conséquences paléogéographiques. Bull Inf Géol Bass Paris* 53: 12-26.

Andersen DT, Pollard WH, McKay CP, Heldmann J. 2002. Cold springs in permafrost on Earth and Mars. *J Geophys Res* 107: 4-1-4-7.

Andrieux E, Bertran P, Saito K. 2016. Spatial analysis of the French Pleistocene permafrost by a GIS database. *Permafrost and Periglacial Processes* 27: 17-30.

Arakel AV, Jacobson G, Salehi M, Hill CM. 1989. Silicification of calcrete in palaeodrainage basins of the Australian arid zone. *J Geolog Soc Aust* 36: 73-89.

Aubert J, Lorain JM. 1977. Les calcaires lacustres de la Région Parisienne. *Bull Liaison LPC* 4: 101-120.

Auzel M, Cailleux A. 1949. Silicifications nord-sahariennes. *Bull Soc géol Fr* 5: 553-559.

Banks NG. 1970. Nature and origin of early and late cherts in the Leadville Limestone, Colorado. *Geolog Soc Am Bull* 81: 3033-3048.

Bariteau A, Thiry M. 2001. Analyse et simulation des transferts géochimiques au sein d'un aquifère : la nappe de Beauce et l'altération des Sables de Fontainebleau. *Bull Soc géol Fr* 17: 367-381.

Bertran P., Stadelmaier KH, Ludwig P. 2022. Last Glacial Maximum active layer thickness in Western Europe, and the issue of 'tundra gleys' in loess sequences. *J Quat Sci* 37(7): 1222-1228.

Boike J, Roth, K, Overduin, PP. 1998. Thermal and hydrologic dynamics of the active layer at a continuous permafrost site (Taymyr Peninsula, Siberia). *Water Resour Res* 34: 355-363.

Bustillo MA, Arribas ME, Bustillo M. 2002. Dolomitization and silicification in low-energy lacustrine carbonates (Paleogene, Madrid Basin, Spain). *Sediment Geol* 151: 107-126.

Cantarero I, Parcerisa D, Plata MA, et al. 2020. Fracturing and near-surface diagenesis of a silicified Miocene deltaic sequence: the Montjuïc Hill (Barcelona). *Minerals* 10: 135, 22 p.

Cayeux L. 1929. Les roches sédimentaires de la France. Roches siliceuses. *Mém. servir expl. Carte Géol. détaillée de la France*, 774 p.

Cholley A. 1960. Remarques sur la structure et l'évolution morphologique du Bassin de Paris. *Bull l'Assoc Géograph Français* 7: 2-26.

Clark ID, Lauriol B, Harwood L, Marschner M. 2001. Groundwater contributions to discharge in a permafrost setting, Big Fish River, N.W.T., Canada. *Arctic, Antarctic and Alpine Res* 33: 62-69.

Cojan I, Brulhet J, Corbonnois J, et al. 2007. Morphologic evolution of eastern Paris Basin: "ancient surfaces" and Quaternary incisions. *Mém Soc géol Fr* 178: 135-155.

Conrad G. 1969. L'évolution continentale post hercynienne du Sahara algérien (Saoura, Erg Chech-Tnezrouft, Ahnet-Mouydir). Centre National de la Recherche Scientifique, Paris, Centre de Reherches sur les Zones Arides, Géologie, 10, 527 p.

Cooper MR, Evans J, Flint SS, Hogg JC, Hunter RH. 2000. Quantification of detrital, authigenic and porosity components of the Fontainebleau Sandstone: a comparison of conventional optical and combined scanning electron microscope-based methods of modal analyses. *In: Worden RH, Morad S, Eds., Quartz cementation in sandstones, Spec. Publs Int. Ass. Sediment.* 29: 89-101.

Daley B. 1989. Silica pseudomorphs from the Bembridge limestone (upper Eocene) of the Isle of Wight, southern England and their palaeoclimatic significance. Palaeogeogr Palaeoclimatol Palaeoecol 69: 233-240.

Delmas AB, Garcia-Hernandez JE, Pedro G. 1982. Discussion sur les conditions et les mécanismes de la formation du quartz à 25°C en milieu ouvert. Analyse réactionelle par voie cinétique. *Sci Géolog Bull* 35: 81-91.

Dewers T, Ortoleva P. 1990. Force of crystallization during the growth of siliceous concretions. *Geology* 18: 204-207.

Dobiński W. 2012. Permafrost. The Contemporary Meaning of the Term and its Consequences. *Bull Geogr Phys Geogr Ser* 5: 29-42.

Dobiński W. 2020. Permafrost active layer. *Earth-Sci Rev* 208: 103301.

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Khalaf FI. 1988. Petrography and diagenesis of silcrete from Kuwait, Arabian Gulf. J Sediment Res 58: 1014–1022.

Khalaf FI, Thiry M, Milnes AR, Alnaqi R. 2020. Characterization of chert in the Dammam Formation (Eocene), Kuwait: Clues to groundwater silicification processes. *J Sediment Res* 90: 297–312.

Lacroix A. 1901. Minéralogie de la France et de ses colonies. vol. 3. Paris, Beranger, 815 p.

Lamplugh GW. 1907. The geology of the Zambezi Basin around the Batoka Gorge (Rhodesia). *Quat. J. Geol. Soc. London* 63: 162–216.

Larue J-P., Etienne R. 2002. Les Sables de Lozère et les Sables de Sologne : nouvelles interprétations de deux décharges détritiques du Miocène inférieur, issues de la paléo-Loire (Bassin parisien, France). *Bull Soc Géol Fr* 173: 185–192.

Lebret P, Dupas A, Clet M, Coutard J-P., Lautridou J-P., Courbouleix S, Gaercin M, Levy M, Vliet-Lanoë BV. 1994. Modelling of permafrost thickness during the late glacial stage in France: preliminary results. *Can J Earth Sci* 31: 959–968.

Lemieux JM, Sudicky EA, Peltier WR, Tarasov L. 2008. Dynamics of groundwater recharge and seepage over the Canadian landscape during the Wisconsinan glaciation. *J Geophys Res: Earth Surface* 113(F1).

Lutaud L. 1948. L'évolution morphologique du Bassin tertiaire parisien et le site de Paris. *Bull Soc Roy Belge de Géogr* 72: 149–187.

Maliva RG, Siever R. 1988. Diagenetic replacement controlled by force of crystallization. *Geology* 16: 688–691.

Ménillet F. 1980. Les lithofaciès des calcaires de Beauce (Stampien supérieur et Aquitanien) du bassin de Paris (France). *Bull. B.R.G. M.* (2), sect. 4, n°4.; 15–55.

Ménillet F. 1987. Les meulières du Bassin de Paris (France) et les faciès associés. Rôle des altérations supergènes néogènes à quaternaire ancien dans leur genèse. Thèse Sciences, Univ. Louis Pasteur, Strasbourg, 536 p.

Ménillet F. 1988. Les accidents siliceux des calcaires continentaux à lacustre du Tertiaire du Bassin de Paris. *Bull Inf Géol Bass Paris* 25: 57–70.

Millot G, Radier H, Muller-Feuga R, Defossez M, Wey R. 1959. Sur la géochimie de la silice et les silicifications sahariennes. *Bull Serv Carte Géol Als Lor* 12: 3–15.

Munier-Chalmas E. 1890. I. Sur les formations gypseuses du Bassin de Paris. II. Sur les dépôts siliceux qui ont remplacé le gypse. *C R Acad Sci Paris* 110: 663–666.

Netterberg F. 1982. Calcretes and their decalcification around Rundu, Okavangoland, South West Africa. South Africa Society of Quaternary Research, 6th Biennale Conference, Pretoria, May 1981. Proceedings; in Palaeoecology of Africa and Surrounding Islands, Rotterdam, 15: 159–169.

Peterson MNA, Von der Borch CC. 1965. Chert: modern inorganic deposition in a carbonate-precipitating locality. *Science* 149: 1501–1503.

Pittman Jr JS. 1959. Silica in Edwards Limestone, Travis County, Texas. In: Ireland H.A. (ed), Silica in sediments, Society of Economic Paleontologists and Mineralogists, Special Publication 7: 121–134.

Pomerol C, Feugueur L. 1968. Bassin de Paris. Ile de France. Guides géologiques régionaux. Paris, Masson, 174 p.

Prost A. 1961. Nouvelles données sur le marno-calcaire de Brie et sur l'origine de la meuliérisation de cette formation. *C R Acad Sci Paris* 253: 1977–1979.

Rimstid JD. 1997. Quartz solubility at low temperatures: *Geochim Cosmochim Acta* 61: 2553–2558.

Smale D. 1973. Silcretes and associated silica diagenesis in southern Africa and Australia. *J Sediment Res* 43: 1077–1089.

Storz M. 1928. Zur petrogenesis des Sekundären Kieselgesteine in der Südlichen Namib. *In: Kaiser E, Ed., Die Diamantenwüste Südwest-Afrikas. Dietrich Reimer, Berlin, pp. 254–282.*

Thiry M. 1981. Sédimentation continentale et altérations associées : calcitisations, ferruginisations et silicifications. Les Argiles Plastiques du Sparnacien du Bassin de Paris. *Sciences Géologiques Mém* 64: 2–173.

Thiry M. 1999. Diversity of continental silicifications features: examples from the Cenozoïc deposits in the Paris Basin and neighbouring basement. *Spec Publs Int Ass Sediment* 27: 87–127.

Thiry M, Ben Brahim M. 1997. Silicifications de nappe dans les formations carbonatées tertiaires du piedmont atlasique (Hamada du Guir, Maroc). *Geodinamica Acta* 10: 12–29.

Thiry M, Maréchal B. 2001. Development of tightly cemented sandstone lenses within uncemented sand: Example of the Fontainebleau Sand (Oligocene) in the Paris Basin. *J Sediment Res* 71: 473–483.

Thiry M, Millot G. 1987. Mineralogical forms of silica and their sequence of formation in silcretes. *J Sediment Petrol* 57: 343–352.

Thiry M, Milnes AR. 1991. Pedogenic and groundwater silcretes at Stuart Creek Opal Field, South Australia. *J Sediment Petrol* 61: 111–127.

Thiry M, Milnes AR. 2017. Silcretes: Insights into the occurrences and formation of materials sourced for stone tool making. *J Archaeolog Sci: Rep* 15: 500–513.

Thiry M, Ribet I. 1999. Groundwater silicification in Paris Basin limestones: fabrics, mechanisms, and modeling. *J Sedimentary Res* 69: 171–183.

Thiry M, Bertrand-Ayrault M, Grisoni JC. 1988a. Ground-water silicification and leaching in sands: Example of the Fontainebleau Sand (Oligocene) in the Paris Basin. *Geol Soc Am Bull* 100: 1283–1290.

Thiry M, Bertrand-Ayrault M, Grisoni JC, Ménillet F, Schmitt JM. 1988b. Les grés de Fontainebleau : silicification de nappes liées à l'évolution géomorphologique du bassin de Paris durant le Pliо-Quaternaire. *Bull Soc géol Fr* 8: 419–430.

Thiry M, Schmitt J-M., Innocent C, Cojan I. 2013. Sables et Grès de Fontainebleau : que reste-t-il des faciès sédimentaires initiaux ? 14ème Congrès Français de Sédimentologie, Paris 2013, Trois excursions géologiques en région parisienne, Livre d'excursions, *Publication ASF* 74: p. 37–90. Available: https://hal-mines-paristech.archives-ouvertes.fr/hal-00906717/document (last consult: 2021/12/07).

Thiry M, Fernandes P, Milnes AR, Raynal J-P. 2014. Driving forces for the weathering and alteration of silica in the regolith: implications for studies of prehistoric flint tools. *Earth Sci Rev* 136: 141–154.

Thiry M, Milnes AR, Ben Brahim M. 2015. Pleistocene cold climate groundwater silicification, Jbel Ghassoul region, Missour Basin, Morocco. *J Geol Soc* 172: 125–137.

Thiry M, Innocent C, Girard J-P., Milnes AR, Franke C, Guillon S. 2021. Sand calcites as a key to Pleistocene periglacial landscapes. *Quatern Res* 101: 225–244.

Thiry M, Milnes AR. 2024. Paléohydrologies à l'origine des grès de Fontainebleau : restitution à partir de la morphologie des grès. Bull. Ass. Natur. Vallée Loing 102: 2–13.
Jiraková H, Huneau F, Celle-Jeanton H, Hrkal Z, Le Coustumer P. 2011. Insights into palaeorecharge conditions for European deep aquifers. Hydrol J 19: 1545–1562.

Khalaf FI. 1988. Petrography and diagenesis of silcrete from Kuwait, Arabian Gulf. J Sediment Res 58: 1014–1022.

Khalaf FI, Thiry M, Milnes AR, Alnaqi R. 2020. Characterization of chert in the Dammam Formation (Eocene), Kuwait: Clues to groundwater silicification processes. *J Sediment Res* 90: 297–312.

Lacroix A. 1901. Minéralogie de la France et de ses colonies. vol. 3. Paris, Beranger, 815 p.

Lamplugh GW. 1907. The geology of the Zambezi Basin around the Batoka Gorge (Rhodesia). *Quat. J. Geol. Soc. London* 63: 162–216.

Larue J-P., Etienne R. 2002. Les Sables de Lozère et les Sables de Sologne : nouvelles interprétations de deux décharges détritiques du Miocène inférieur, issues de la paléo-Loire (Bassin parisien, France). *Bull Soc Géol Fr* 173: 185–192.

Lebret P, Dupas A, Clet M, Coutard J-P., Lautridou J-P., Courbouleix S, Gaercin M, Levy M, Vliet-Lanoë BV. 1994. Modelling of permafrost thickness during the late glacial stage in France: preliminary results. *Can J Earth Sci* 31: 959–968.

Lemieux JM, Sudicky EA, Peltier WR, Tarasov L. 2008. Dynamics of groundwater recharge and seepage over the Canadian landscape during the Wisconsinian glaciation. *J Geophys Res: Earth Surface* 113(F1).

Lutaud L. 1948. L'évolution morphologique du Bassin tertiaire parisien et le site de Paris. *Bull Soc Roy Belge de Géogr* 72: 149–187.

Maliva RG, Siever R. 1988. Diagenetic replacement controlled by force of crystallization. *Geology* 16: 688–691.

Ménillet F. 1980. Les lithofaciès des calcaires de Beauce (Stampien supérieur et Aquitanien) du bassin de Paris (France). *Bull. B.R.G. M.* (2), sect. 4, n°4.; 15–55.

Ménillet F. 1987. Les meulières du Bassin de Paris (France) et les faciès associés. Rôle des altérations supergènes néogènes à quaternaire ancien dans leur genèse. Thèse Sciences, Univ. Louis Pasteur, Strasbourg, 536 p.

Ménillet F. 1988. Les accidents siliceux des calcaires continentaux à lacustre du Tertiaire du Bassin de Paris. *Bull Inf Géol Bass Paris* 25: 57–70.

Millot G, Radier H, Muller-Feuga R, Defossez M, Wey R. 1959. Sur la géochimie de la silice et les silicifications sahariennes. *Bull Serv Carte Géol Als Lor* 12: 3–15.

Munier-Chalmas E. 1890. I. Sur les formations gypseuses du Bassin de Paris. II. Sur les dépôts siliceux qui ont remplacé le gypse. *C R Acad Sci Paris* 110: 663–666.

Netterberg F. 1982. Calcretes and their decalcification around Rundu, Okavangoland, South West Africa. South Africa Society of Quaternary Research, 6th Biennale Conference, Pretoria, May 1981. Proceedings; in Palaeoecology of Africa and Surrounding Islands, Rotterdam, 15: 159–169.

Peterson MNA, Von der Borch CC. 1965. Chert: modern inorganic deposition in a carbonate-precipitating locality. *Science* 149: 1501–1503.

Pittman Jr JS. 1959. Silica in Edwards Limestone, Travis County, Texas. In: Ireland H.A. (ed), Silica in sediments, Society of Economic Paleontologists and Mineralogists, Special Publication 7: 121–134.

Pomerol C, Feugueur L. 1968. Bassin de Paris. Ile de France. Guides géologiques régionaux. Paris, Masson, 174 p.

Prost A. 1961. Nouvelles données sur le marno-calcaire de Brie et sur l'origine de la meuliérisation de cette formation. *C R Acad Sci Paris* 253: 1977–1979.

Rimstidt JD. 1997. Quartz solubility at low temperatures: *Geochim Cosmochim Acta* 61: 2553–2558.

Smale D. 1973. Silcretes and associated silica diagenesis in southern Africa and Australia. *J Sediment Res* 43: 1077–1089.

Storz M. 1928. Zur petrogenesis des Sekundären Kieselgesteine in der Südlichen Namib. *In: Kaiser E, Ed., Die Diamantenwüste Südwest-Afrikas. Dietrich Reimer, Berlin, pp. 254–282.*

Thiry M. 1981. Sédimentation continentale et altérations associées : calcitisations, ferruginisations et silicifications. Les Argiles Plastiques du Sparnacien du Bassin de Paris. *Sciences Géologiques Mém* 64: 2–173.

Thiry M. 1999. Diversity of continental silicifications features: examples from the Cenozoïc deposits in the Paris Basin and neighbouring basement. *Spec Publs Int Ass Sediment* 27: 87–127.

Thiry M, Ben Brahim M. 1997. Silicifications de nappe dans les formations carbonatées tertiaires du piedmont atlasique (Hamada du Guir, Maroc). *Geodinamica Acta* 10: 12–29.

Thiry M, Maréchal B. 2001. Development of tightly cemented sandstone lenses within uncemented sand: Example of the Fontainebleau Sand (Oligocene) in the Paris Basin. *J Sediment Res* 71: 473–483.

Thiry M, Millot G. 1987. Mineralogical forms of silica and their sequence of formation in silcretes. *J Sediment Petrol* 57: 343–352.

Thiry M, Milnes AR. 1991. Pedogenic and groundwater silcretes at Stuart Creek Opal Field, South Australia. *J Sediment Petrol* 61: 111–127.

Thiry M, Milnes AR. 2017. Silcretes: Insights into the occurrences and formation of materials sourced for stone tool making. *J Archaeolog Sci: Rep* 15: 500–513.

Thiry M, Ribet I. 1999. Groundwater silicification in Paris Basin limestones: fabrics, mechanisms, and modeling. *J Sedimentary Res* 69: 171–183.

Thiry M, Bertrand-Ayrault M, Grisoni JC. 1988a. Ground-water silicification and leaching in sands: Example of the Fontainebleau Sand (Oligocene) in the Paris Basin. *Geol Soc Am Bull* 100: 1283–1290.

Thiry M, Bertrand-Ayrault M, Grisoni JC, Ménillet F, Schmitt JM. 1988b. Les grés de Fontainebleau : silicification de nappes liées à l'évolution géomorphologique du bassin de Paris durant le Pliо-Quaternaire. *Bull Soc géol Fr* 8: 419–430.

Thiry M, Schmitt J-M., Innocent C, Cojan I. 2013. Sables et Grès de Fontainebleau : que reste-t-il des faciès sédimentaires initiaux ? 14ème Congrès Français de Sédimentologie, Paris 2013, Trois excursions géologiques en région parisienne, Livre d'excursions, *Publication ASF* 74: p. 37–90. Available: https://hal-mines-paristech.archives-ouvertes.fr/hal-00906717/document (last consult: 2021/12/07).

Thiry M, Fernandes P, Milnes AR, Raynal J-P. 2014. Driving forces for the weathering and alteration of silica in the regolith: implications for studies of prehistoric flint tools. *Earth Sci Rev* 136: 141–154.

Thiry M, Milnes AR, Ben Brahim M. 2015. Pleistocene cold climate groundwater silicification, Jbel Ghassoul region, Missour Basin, Morocco. *J Geol Soc* 172: 125–137.

Thiry M, Innocent C, Girard J-P., Milnes AR, Franke C, Guillon S. 2021. Sand calcites as a key to Pleistocene periglacial landscapes. *Quatern Res* 101: 225–244.

Thiry M, Milnes AR. 2024. Paléohydrologies à l'origine des grès de Fontainebleau : restitution à partir de la morphologie des grès. Bull. Ass. Natur. Vallée Loing 102: 2–13.
Toulemont M. 1982. Les épigénies siliceuses du gypse lutétien du bassin de Paris. *Sci Géolog Bull.* 35: 3-16.

Turland M. 1974. Géologie des terrains tertiaires de la région de Montereau (Seine-et-Marne). D.E.S. Univ. Paris VI, 115 p.

Ullyott JS, Nash DJ, Shaw PA. 1998. Recent advances in silcrete research and their implications for the origin and palaeoenvironmental significance of sarsens. Proc Geolog Assoc 109: 255-270.

Van Der Lee J, De Windt L, Lagneau V, Goblet P. 2003. Module-oriented modeling of reactive transport with HYTEC. *Comput Geosci* 29: 265-275.

Van Vliet-Lanoë B, Lisitsyna O. 2001. Permafrost extent at the Last Glacial Maximum and at the Holocene Optimum. The Climex Map. In: Paepe R. et al., Eds. Permafrost Response on Economic Development, Environmental Security and Natural Resources, Springer, Dordrecht, pp. 215-225.

Walther JV, Helgeson HC. 1977. Calculation of the thermodynamic properties of aqueous silica and the solubility of quartz and its polymorphs at high pressures and temperatures. *Am J Sci(United States)* 277 (10).

Walvoord MA, Kuryly BL. 2016. Hydrologic impacts of thawing permafrost - a review. *Vadose Zone J* 15: vzj2016-01.

Webb JA Nash DJ. 2020. Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts. *Earth Surface Process Landforms* 45: 3396-3413.

Wheeler WH, Textoris DA. 1978. Triassic limestone and chert of playa origin in North Carolina. J Sediment Petrol 48: 765-776.

White DE, Hem JD, Waring GA. 1963. Chemical composition of subsurface waters. In: Fleischer M, Ed. Data of Geochemistry 6th ed. *US Geol. Surv. Prof. Pap.440-F*.

Williams LA. Crerar DA. 1985 ) Silica diagenesis; II, General mechanisms. J Sediment Res 55: 312-321.

Woolnough WG. 1927. The duricrust of Australia. *J Proc Roy Soc New South Wales* 61: 24-53.

Yoshikawa K, Kane DL. 2021. Permafrost Features and Talik Geometry in Hydrologic System. Arctic Hydrol Permafrost Ecosyst 409-440.

**Cite this article as:** Thiry M, Milnes A. 2024. Quaternary periglacial silicifications in the Paris Basin-Silicifications périglaciaires quaternaires du Bassin de Paris, *BSGF - Earth Sciences Bulletin* 195: 11.
Toulemont M. 1982. Les épigénies siliceuses du gypse lutétien du bassin de Paris. *Sci Géolog Bull.* 35: 3-16.

Turland M. 1974. Géologie des terrains tertiaires de la région de Montereau (Seine-et-Marne). D.E.S. Univ. Paris VI, 115 p.

Ullyott JS, Nash DJ, Shaw PA. 1998. Recent advances in silcrete research and their implications for the origin and palaeoenvironmental significance of sarsens. Proc Geolog Assoc 109: 255-270.

Van Der Lee J, De Windt L, Lagneau V, Goblet P. 2003. Module-oriented modeling of reactive transport with HYTEC. *Comput Geosci* 29: 265-275.

Van Vliet-Lanoë B, Lisitsyna O. 2001. Permafrost extent at the Last Glacial Maximum and at the Holocene Optimum. The Climex Map. In: Paepe R. et al., Eds. Permafrost Response on Economic Development, Environmental Security and Natural Resources, Springer, Dordrecht, pp. 215-225.

Walther JV, Helgeson HC. 1977. Calculation of the thermodynamic properties of aqueous silica and the solubility of quartz and its polymorphs at high pressures and temperatures. *Am J Sci(United States)* 277 (10).

Walvoord MA, Kuryly BL. 2016. Hydrologic impacts of thawing permafrost - a review. *Vadose Zone J* 15: vzj2016-01.

Webb JA Nash DJ. 2020. Reassessing southern African silcrete geochemistry: implications for silcrete origin and sourcing of silcrete artefacts. *Earth Surface Process Landforms* 45: 3396-3413.

Wheeler WH, Textoris DA. 1978. Triassic limestone and chert of playa origin in North Carolina. J Sediment Petrol 48: 765-776.

White DE, Hem JD, Waring GA. 1963. Chemical composition of subsurface waters. In: Fleischer M, Ed. Data of Geochemistry 6th ed. *US Geol. Surv. Prof. Pap.440-F*.

Williams LA. Crerar DA. 1985) Silica diagenesis; II, General mechanisms. J Sediment Res 55: 312-321.

Woolnough WG. 1927. The duricrust of Australia. *J Proc Roy Soc New South Wales* 61: 24-53.

Yoshikawa K, Kane DL. 2021. Permafrost Features and Talik Geometry in Hydrologic System. Arctic Hydrol Permafrost Ecosyst 409-440.

**Cite this article as:** Thiry M, Milnes A. 2024. Quaternary periglacial silicifications in the Paris Basin-Silicifications périglaciaires quaternaires du Bassin de Paris, *BSGF - Earth Sciences Bulletin* 195: 11.